Patent Application
20120316733
1. Field of the Invention
The present invention relates to a vehicle turning control device that controls the turning of a vehicle by using braking.
Priority is claimed on Japanese Patent Application Nos. 2010-047835, 2010-047836, 2010-047837, and 2010-047838, filed Mar. 4, 2010, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Among this type of turning control device, a turning control device is known that achieves a stabilization of vehicle behavior by performing braking control on specific wheels in a direction in which the deviation between the lateral acceleration (i.e., acceleration in the vehicle transverse direction) standard yaw rate, which is calculated based on the lateral acceleration of the vehicle and on the vehicle speed, and the vehicle's actual yaw rate approaches zero.
Another turning control device is known in which, when braking is performed by this device, it assists the yaw moment by performing control in accordance with the turning state (for example, the steering angle of the steering wheel and the rate of change in this steering angle) of the vehicle so as to vary the braking force between the left and right front wheels, and so as to also vary the braking force between the left and right rear wheels, so that an improvement in the turning performance of the vehicle can be achieved(see, for example, Japanese Patent No. 2572860 (Patent document 1)).
Moreover, a device is also known that achieves an improvement in the turning performance of the vehicle by calculating a corrected yaw moment by adding together a first yaw moment, which is calculated based on the steering angle speed or on the steering angle acceleration, and a second yaw moment, which is calculated based on the steering angle, the vehicle speed, and the yaw rate, and by then performing control so as to vary the braking force between the left and right front wheels, and so as to also vary the braking force between the left and right rear wheels, such that this corrected yaw moment is generated (see, for example, Japanese Unexamined Patent Application No. 2005-153716 (Patent document 2)).
However, in the turning control device described in Patent document 1, when the device is performing braking at the same time as the vehicle is turning, because the yaw moment is constantly assisted, it is possible that the yaw moment will become excessively large and that the stability of the vehicle will deteriorate, so that this turning control device is not realistically useable.
Furthermore, in the turning control device described in Patent document 2, when the vehicle turns suddenly (i.e., when there are a large steering angle speed and a large steering angle acceleration), the first yaw moment is reflected hugely. Although there is an improvement in the turning performance of the vehicle at such times, during normal turning, there is no effective improvement in the turning performance of the vehicle. Because of this, a turning control device that is able to achieve an improvement in the turning performance even when a vehicle is making a normal turn is strongly desired.
The present invention provides a vehicle turning control device that is also able to achieve an improvement in the turning performance when a vehicle is making a normal turn.
In the vehicle turning control device according to this invention, the following means are employed in order to solve the above-described problem.
According to the vehicle turning control device described above in (1), a first standard yaw rate which is calculated based on lateral acceleration and vehicle speed is corrected in a direction in which it increases so as to derive a second standard yaw rate, and a yaw moment can be generated by controlling the braking force such that the yaw rate deviation between this second standard yaw rate and the actual yaw rate is canceled out. As a result, the vehicle turning performance is improved even when the vehicle is making a normal turn, and the responsiveness of the steering is improved. Furthermore, the yaw rate convergence is improved by the correcting section in accordance with the state of the vehicle body and the state of the road surface, so that even when the vehicle is traveling at low speed, the ability of the vehicle to follow the steering is improved, and the stability of the vehicle behavior can be controlled.
Hereinafter, embodiments of the vehicle turning control device according to this invention will be described with reference made to
Firstly, the vehicle turning control device according to a first embodiment of this invention will be described with reference made to
A vehicle turning control device 1A (1) of the present embodiment is provided with a braking control section 2, and a braking device (i.e., a braking control device) 10.
The braking control section 2 decides the amounts of braking force control to be applied to the front and rear, left and right wheels of a vehicle in accordance with the running state of the vehicle. The braking device 10 controls the braking force of each wheel based on the amounts of braking force control for each wheel decided by the braking control section 2.
Detection signals that correspond to detection values obtained from various sensors are input into the braking control section 2. The various sensors include a steering angle sensor (i.e., a steering amount detecting device) 3 that detects the steering angle (i.e., the amount of steering) of the vehicle steering wheel, a vehicle speed sensor (i.e., a vehicle speed detecting device) 4 that detects the speed of the vehicle, a lateral acceleration sensor (i.e., a lateral acceleration detecting device: shortened below to a lateral G sensor) 5 that detects the acceleration in the left-right direction of the vehicle (i.e., the transverse direction of the vehicle), namely, that detects the lateral acceleration (shortened below to the lateral G), a yaw rate sensor (i.e., a yaw rate detecting device) 6 that detects the yaw rate of the vehicle, and an accelerator opening angle sensor (i.e., a required torque detecting device) 7 that detects the accelerator opening angle in the vehicle. In addition, a μ calculating section (i.e., a road surface friction estimating section) 8 calculates the coefficient of friction between the vehicle wheels and the road surface, and outputs electrical signals that correspond to the calculated coefficients of friction to the braking control section 2.
The braking control section 2 is provided with a steering angle standard yaw rate operating section 11, a steady-state standard yaw rate operating section 12, a lateral G standard yaw rate operating section (i.e., a control amount operating section) 14, a correcting section 15, a limit yaw rate deviation operating section 16, and a first braking force control operating section (i.e., a feedback control amount operating section: shortened below to an FB control amount operating section) 19.
The steering angle standard yaw rate operating section 11 calculates a steering angle standard yaw rate based on the steering angle of the steering wheel which is detected by the steering angle sensor 3, and on the vehicle speed which is detected by the vehicle speed sensor 4. When the driver wants the vehicle to make a genuine turn, the driver enlarges the steering angle of the steering wheel, so that the steering angle standard yaw rate is enlarged. Namely, when the steering angle standard yaw rate calculated on the basis of the steering angle is large, it is assumed that the driver who wishes the vehicle to turn has a genuine intention to steer the vehicle.
The steady-state standard yaw rate operating section 12 calculates a steady-state standard yaw rate gain Kv which corresponds to the vehicle speed by referring to a steady-state standard yaw rate gain table 21, and then multiplies the steady-state standard yaw rate gain Kv by the steering angle standard yaw rate, so as to obtain a steady-state standard yaw rate ω_high. In the steady-state standard yaw rate gain table 21 of the present embodiment, the horizontal axis shows the vehicle speed, while the vertical axis shows the steady-state standard yaw rate gain Kv. The steady-state standard yaw rate gain table 21 is set such that the greater the vehicle speed, the closer the steady-state standard yaw rate gain Kv converges to 1, while the lower the vehicle speed, the greater the steady-state standard yaw rate gain Kv becomes.
The lateral G standard yaw rate operating section 14 calculates a lateral G standard yaw rate (i.e., a first standard yaw rate) ω_low based on the lateral G detected by the lateral G sensor 5, and on the vehicle speed detected by the vehicle speed sensor 4. The lateral G standard yaw rate ω_low is the yaw rate that can be generated by the current lateral G, and is expressed, for example, by ω_low=Gy/V. Here, Gy is a lateral acceleration detection value detected by the lateral G sensor 5, and V is the vehicle speed detected by the vehicle speed sensor 4.
The correcting section 15 calculates a limit standard yaw rate (i.e. a second standard yaw rate) ω_TAR based on the steady-state standard yaw rate ω_high and the lateral G standard yaw rate ω_low. The method used to calculate the limit standard yaw rate ω_TAR in the correcting section 15 is described below in detail.
The limit yaw rate deviation operating section 16 subtracts the yaw rate detected by the yaw rate sensor 6 (i.e., the actual yaw rate) from the limit standard yaw rate ω_TAR so as to obtain a limit yaw rate deviation Δωfb.
The FB control amount operating section 19 calculates a feedback control amount (i.e., a braking force control amount: shortened below to FB control amount) based on the limit yaw rate deviation Δωfb, and outputs it to the braking device 10 as a command value.
Next, a method of calculating the limit standard yaw rate ω_TAR in the correcting section 15 will be described with reference made to the drawings in
As shown in
In the correcting section 15, a reference limit standard yaw rate ω_t1 is calculated in the reference limit standard yaw rate operating section 32 based on the distribution coefficient HB1 which was calculated by the distribution coefficient HB1 operating section 31, on the steady-state standard yaw rate high, and on the lateral G standard yaw rate ω_low. Furthermore, the correction coefficient HS1 calculated by the correction coefficient HS1 operating section 33 and the correction coefficient HS2 calculated by the correction coefficient HS2 operating section 34 are multiplied by the reference limit standard yaw rate ω_t1, and the correction coefficient HS3 calculated by the correction coefficient HS3 operating section 35 is then added to the value thereby obtained. As a result, the limit standard yaw rate ω_TAR is obtained (see Formula (1) below). Note that the correction amount by which the lateral G standard yaw rate ω_low is corrected in the direction in which it increases is decided by the distribution coefficient HB1, the correction coefficient HS1, the correction coefficient HS2, and the correction coefficient HS3.
ω_TAR=ω—t1×HS1×HS2+HS3 (1)
This limit standard yaw rate ω_TAR forms a yaw rate target value for the feedback control.
More specifically, the reference limit standard yaw rate operating section 32 corrects, in the direction of increase, the lateral G standard yaw rate ω_low, which was set as the target value in the feedback control in the conventional steering assist braking control in association with the steady-state standard yaw rate ω_high, which was calculated based on the steering angle, and thus obtains the reference limit standard yaw rate ω_t1. By doing this, it is possible to achieve both control that stabilizes the yaw moment generated in the vehicle body, and control that improves the steering responsiveness.
The increase correction of the lateral G standard yaw rate will now be described with reference to
In the present embodiment, this concept is developed still further. For the method used to correct the lateral G standard yaw rate by increasing it, the lateral G standard yaw rate is corrected such that it approaches the steady-state standard yaw rate ω_high which was calculated based on the steering angle standard yaw rate.
More specifically, in the present embodiment, the reference limit standard yaw rate ω_t1 is calculated from the following Formula (2) based on the distribution coefficient HB1 which is calculated by the distribution coefficient HB1 operating section 31, the lateral G standard yaw rate ω_low, and the steady-state standard yaw rate ω_high.
t1=HB1ω_high+(1−HB1)×ω_low (2)
Here, the distribution coefficient HB1 is a numerical value from 0 to 1. When HB1=0, the reference limit standard yaw rate ω_t1 corresponds to the lateral G standard yaw rate ω_low. On the other hand, when HB1 equals 1, the reference limit standard yaw rate ω_t1 corresponds to the steady-state standard yaw rate ω_high.
Next, the distribution coefficient HB1 calculated in the distribution coefficient HB1 operating section 31 will be described with reference made to
The distribution coefficient HB1 is calculated by multiplying together a distribution coefficient HB1a which is calculated in accordance with the vehicle speed, a distribution coefficient HB1b which is calculated in accordance with the rate of change in the yaw rate, a distribution coefficient HB1c which is calculated in accordance with the yaw rate deviation integral, and a distribution coefficient HB1d which is calculated in accordance with the steering wheel turning speed (see Formula (3) below).
HB1=HB1a×HB1b×HB1c×HB1d (3)
Each of the distribution coefficients HB1a, HB1b, HB1c, and HB1d are calculated by referring to the respective distribution coefficient tables 40, 41, 42, and 43 shown in
In the distribution coefficient table 40 which is used to calculate the distribution coefficient HB1a, the horizontal axis shows the vehicle speed, while the vertical axis shows the distribution coefficient HB1a. In this distribution coefficient table 40, in a low vehicle speed region, HB1a is fixed as HB1a=1. When the vehicle speed exceeds a predetermined value, then as the vehicle speed increases, the distribution coefficient HB1a becomes gradually smaller, and in a high vehicle speed region, HB1a is fixed as HB1a=0. As a consequence of this, when the vehicle speed is low, the limit standard yaw rate ω_TAR, which is the target value in the FB control amount operating section 19, becomes larger, so that the turning performance and the ability of the vehicle to follow a line are improved. In contrast, when the vehicle speed is high, the limit standard yaw rate ω_TAR, which is the target value in the FB control amount operating section 19, does not increase, so that the stability of the vehicle behavior is ensured.
In the distribution coefficient table 41 which is used to calculate the distribution coefficient HB1b, the horizontal axis shows the rate of change in the yaw rate, while the vertical axis shows the distribution coefficient HB1b. In this distribution coefficient table 41, in the region where the rate of change in the yaw rate is small, HB1b is fixed as HB1b=1. When the rate of change in the yaw rate exceeds a predetermined value, then as the rate of change in the yaw rate increases, the distribution coefficient HB1b becomes gradually smaller, and in the region where the rate of change in the yaw rate is large, HB1b is fixed as HB1b =0. Here, the rate of change in the yaw rate refers to temporal changes in the actual yaw rate which are detected by the yaw rate sensor 6, and can be calculated by creating a time derivative of the actual yaw rate. For example, when the vehicle is making a violent slalom maneuver, or when the vehicle behavior is unstable, a large rate of change in the yaw rate is evident.
At times such as this, because it is undesirable for the limit standard yaw rate ω_TAR which is the target value in the FB control amount operating section 19 to increase, when the rate of change in the yaw rate is large, the distribution coefficient HB1b is set to a small value so that the limit standard yaw rate ω_TAR does not increase.
In the distribution coefficient table 42 which is used to calculate the distribution coefficient HB1c, the horizontal axis shows the yaw rate deviation integral value, while the vertical axis shows the distribution coefficient HB1c. In this distribution coefficient table 42, in the region where the yaw rate deviation integral value is small, HB1c is fixed as HB1c=1. When the yaw rate deviation integral value exceeds a predetermined value, then as the yaw rate deviation integral value increases, the distribution coefficient HB1c becomes gradually smaller, and in the region where the yaw rate deviation integral value is large, HB1c is fixed as HB1c=0. Here, the yaw rate deviation integral value is a value obtained by accumulating the deviation between the limit standard yaw rate and the actual yaw rate detected by the yaw rate sensor 6, namely, the limit yaw rate deviation Δωfb from the time when the turning of the steering wheel was first started. For example, even if the limit yaw rate deviation Δωfb is small, if that state continues for a prolonged period, the yaw rate deviation integral value increases to a large value. At times such as this, there is a gradually increasing possibility, albeit one that only increases slowly, that the vehicle will spin out. Therefore, it is undesirable for the limit standard yaw rate ω_TAR, which is the target value in the FB control amount operating section 19, to increase. For this reason, when the yaw rate deviation integral value is large, the distribution coefficient HB1c is set to a small value so that the limit standard yaw rate ω_TAR does not increase.
In the distribution coefficient table 43 which is used to calculate the distribution coefficient HB1d, the horizontal axis shows the steering wheel turning speed, while the vertical axis shows the distribution coefficient HB1d. This distribution coefficient table 43 is set such that the greater the steering wheel turning speed, the larger the distribution coefficient HB1d becomes, and when the steering wheel turning speed is positive, the distribution coefficient HB1d is larger than when the steering wheel turning speed is negative. Here, the steering wheel turning speed is a value that is decided based on the amount of change over time in the steering angle of the steering wheel and on the steering angle which are detected by the steering angle sensor 3, and can be calculated by creating a time derivative of the steering angle and then comparing this with the steering angle. The steering wheel turning speed is positive when, in a state in which the steering wheel is rotated in a direction away from a neutral position (i.e., a position in which the vehicle travels in a straight line), an amount of change over time is generated in that same direction, and also when, in a state in which the steering wheel is rotated towards the neutral position (i.e., the position in which the vehicle travels in a straight line), an amount of change over time is generated in that same direction. In contrast, the steering wheel turning speed is negative when, in a state in which the steering wheel is rotated in a direction away from a neutral position (i.e., a position in which the vehicle travels in a straight line), an amount of change over time is generated in a direction facing the neutral position, and also when, in a state in which the steering wheel is rotated in a direction in which it returns to the neutral position, an amount of change over time is generated in a direction moving away from the neutral position.
When the steering wheel turning speed is positive, because it is assumed that the driver has a genuine desire to make the vehicle make a sizable turn, the value of the distribution coefficient HB1d is increased proportionally as the steering wheel turning speed is increased (with the maximum value of HB1d fixed as HB1d=1), so that the limit standard yaw rate ω_TAR is increased to a large value. As a result of this, the responsiveness of the vehicle to the steering is improved. On the other hand, when the steering wheel turning speed is negative, because it is assumed that the driver is about to conclude the turning operation, the value of the distribution coefficient HB1d is decreased proportionally as the absolute value of the steering wheel turning speed is increased (with the minimum value of HB1d fixed as HB1d=0), so that the limit standard yaw rate ω_TAR does not increase.
As a result of this, the responsiveness of the vehicle to the steering when avoiding an object in front of it, or when making a lane change or the like is improved.
In other case, it is also possible for the distribution coefficient HB1d to be calculated based on the steering wheel turning angle (i.e., the amount of steering wheel turning) instead of the steering wheel turning speed. This is because the greater the steering wheel turning angle, the more it can be assumed that the driver has a strong intention to genuinely turn the vehicle. In this case, the steering wheel turning angle has the same definition as the steering angle.
Next, the correction coefficient HS1 which is calculated in the correction coefficient HS1 operating section (i.e., a second correction regulating section) 33 will be described with reference made to
This correction coefficient HS1 is the correction coefficient employed under a supposition that the driver has loaded the front of a vehicle, and is performing an operation to turn the vehicle by turning the steering wheel.
As shown in
HS1=HS1a×HS1b (4)
The vehicle front load refers to the amount of load movement towards the front of the vehicle, and can be estimated based, for example, on a longitudinal acceleration sensor (not shown) which detects the acceleration in the longitudinal direction of the vehicle. In this case, the longitudinal acceleration sensor can be called a load movement estimating device that estimates the amount of load movement in the longitudinal direction.
Each of the correction coefficients HS1a and HS1b are calculated by referring to the correction coefficient tables 44 and 45 shown in
In the correction coefficient table 44 which is used to calculate the correction coefficient HS1a, the horizontal axis shows the steering speed, while the vertical axis shows the correction coefficient HS1a. In this correction coefficient HS1a table 44, in the region where the steering speed is low, HS1a is fixed as HS1a=1. When the steering speed exceeds a predetermined value, then as the steering speed increases, the correction coefficient HS1a becomes gradually smaller, and in the region where the steering speed is large, HS1a is fixed as HS1a=0.
In the correction coefficient table 45 which is used to calculate the correction coefficient HS1b, the horizontal axis shows the front load (i.e., the amount of load movement towards the front of the vehicle), while the vertical axis shows the correction coefficient HS1b. In this correction coefficient HS1b table 45, in the region where the front load is small, HS1b is fixed as HS1b=1. When the front load exceeds a predetermined value, then as the front load increases, the correction coefficient HS1b becomes gradually smaller, and in the region where the front load is large, HS1b is fixed as HS1b=0.
As described above, if the vehicle is in a front load state and the steering wheel is turned, then it is easy to turn the vehicle, however, as the front load increases, the vehicle behavior more easily becomes unstable. Moreover, the greater the steering speed, the easier it is for the vehicle behavior to become unstable. The correction coefficient HS1 is a correction coefficient that is intended to adjust the limit standard yaw rate ω_TAR during this type of steering.
As a result of the correction coefficient HS1 being calculated in this manner, because the correction coefficient HS1 is 1 both in the region where the steering speed is low, and in the region where the front load is small, it is possible to increase the limit standard yaw rate ω_TAR, and to improve the turning performance of the vehicle. In contrast to this, because the correction coefficient HS1 becomes smaller than 1 proportionally as the steering speed and the front load increase, the limit standard yaw rate ω_TAR can be reduced, and the stability of the vehicle behavior can be ensured.
Next, the correction coefficient HS2 which is calculated in the correction coefficient HS2 operating section (i.e., a third correction regulating section) 34 will be described.
This correction coefficient HS2 is a correction coefficient for a case in which a lane change (i.e., an operation in which, by turning the steering wheel, the direction of travel of a vehicle is immediately restored to the original direction of travel) on a road surface having a high coefficient of friction (abbreviated below to μ) (abbreviated below to a high μ road) between the vehicle wheels and the road surface is hypothesized.
The correction coefficient HS2 is a gain that is formed such that, with 1 being set as the maximum value, if the following conditions are satisfied, a predetermined decrease count value is subtracted from an initial value, while if any one of the following conditions are not satisfied, a predetermined increase count value is added to the initial value so that it approaches 1. The predetermined decrease count value is subtracted in accordance with the following conditions, namely: (a) when it is determined that the coefficient of friction μ is high (or when an acceleration in the longitudinal or transverse directions corresponding to traveling on a road surface having a high coefficient of friction is detected); (b) when it is determined that there is a large steering angle; (c) when it is determined that there is a large rate of decrease in the lateral G; (d) when it is determined that there is a large rate of decrease in the yaw rate. In other case, the aforementioned conditions may be either one of, or an arbitrary combination of a plurality of (a) through (d). In particular, if the convergence of the vehicle behavior at a time of a high coefficient of friction is considered, then it is preferable for a combination of the above-described (a) as well as any one of (b) through (d) to be used.
The coefficient of friction μ is calculated by the μ calculating section 8. The rate of decrease in the lateral G is the diminution rate of the lateral G, and is calculated based on the lateral G detected by the lateral G sensor 5. The rate of decrease in the yaw rate is the diminution rate of the actual yaw rate, and is detected by the yaw rate sensor 6.
An example of the processing to decide the correction coefficient HS2 will now be described in accordance with the flowchart shown in
Firstly, in step S01, a determination is made as to whether or not the coefficient of frictionμ is greater than a threshold value μth.
If the result of the determination in step S01 is [YES] (i.e., if μ>μth), the routine moves to step S02, and a determination is made as to whether or not at least one of the following conditions is satisfied: namely, whether the steering angle δ is greater than a threshold angle δth (i.e., whether δ>δth), or whether the rate of decrease in the lateral G ΔG is greater than a threshold value ΔGth (i.e., whether ΔG>ΔGth), or whether a rate of decrease in the yaw rate γ is greater than a threshold value γth (i.e., whether γ>γth).
The result of the determination in step S02 is [YES], the routine proceeds to step S03, and the correction coefficient HS2 is decided by subtraction processing. The processing of this routine is then temporarily ended. In this subtraction processing, a predetermined decrease count value is continually subtracted from an initial value for the correction coefficient HS2, so that the correction coefficient HS2 converges on 0.
In contrast, if the result of the determination in step S01 is [NO] (i.e., if μth), and if the result of the determination in step S02 is [NO], the routine proceeds to step S04, and the correction coefficient HS2 is decided by addition processing. The processing of this routine is then temporarily ended. In this addition processing, a predetermined increase count value is continually added so that the correction coefficient HS2 converges on 1.
The initial value for the correction coefficient HS2 is a predetermined value between 0 and 1.
When a lane change has been performed on a high μ road surface, if there is a sudden decrease in the yaw rate and the lateral G, then there are cases in which a sizable yaw rate is generated by the steering in the opposite direction from the direction in which the driver wishes to proceed. At such times, if the limit standard yaw rate ω_TAR is increased, there is a possibility that the ability of the vehicle to follow the steering will deteriorate. The correction coefficient HS2 is intended to suppress this occurrence. Namely, when the coefficient of friction the steering angle, the rate of decrease in the lateral GE, and the rate of decrease in the yaw rate are large, by setting the correction coefficient HS2 to a small value, the limit standard yaw rate ω_TAR is prevented from increasing, which results in the convergence of the yaw rate after the lane change being improved.
Next, the correction coefficient HS3 which is calculated in the correction coefficient HS3 operating section (i.e., a fourth correction regulating section) 35 will be described with reference made to
This correction coefficient HS3 is a correction coefficient for a case in which it is hypothesized that a driver has made a tack-in. A tack-in is a phenomenon that occurs when the driver suddenly takes their foot off the accelerator pedal during a turn causing the vehicle to become front-loaded, and veer towards the inside of the turn direction. In some cases, however, this phenomenon is intentionally used by the driver in order to perform a turning operation. However, if a turning operation utilizing this tack-in is performed, then if the accelerator is released while a large amount of torque is still required from the vehicle (in other words, while the accelerator opening angle is still large), or while the vehicle speed is still too great, it is easy for the vehicle behavior to become unstable. The correction coefficient HS3 is a correction coefficient that is intended to adjust the limit standard yaw rate ω_TAR during a tack-in.
As shown in
HS3=HS3a×HS3b (6)
The amount of torque required from the vehicle can be calculated from the accelerator opening angle detected by the accelerator opening angle sensor 7, and the amount of required torque increases as the accelerator opening angle increases.
Each of the correction coefficients HS3a and HS3b are calculated by referring to the correction coefficient tables 51 and 52 shown in
In the correction coefficient table 51 which is used to calculate the correction coefficient HS3a, the horizontal axis shows the vehicle speed, while the vertical axis shows the correction coefficient HS3a. In this correction coefficient HS3a table 51, in the region where the vehicle speed is less than a predetermined value, HS3a is a positive fixed value. When the vehicle speed exceeds the predetermined value, then as the vehicle speed increases, the correction coefficient HS3a becomes gradually smaller, and when it exceeds a predetermined speed V0, it changes to a negative value. In the region where the vehicle speed is extremely high, HS3a is a negative fixed value.
In the correction coefficient table 52 which is used to calculate the correction coefficient HS3b, the horizontal axis shows the amount of torque required from the vehicle, while the vertical axis shows the correction coefficient HS3b. In this correction coefficient HS3b table 52, in the region where the required torque is less than a predetermined value T0, HS3b is a positive value, while in the region where the required torque is greater than the predetermined value T0, the correction coefficient HS3b=0. Here, the predetermined value T0 is an extremely small value and is set, for example, to the required torque that corresponds to when the accelerator opening angle is close to zero.
By setting the correction coefficient tables 51 and 52 in this manner, when the required torque is greater than the predetermined value T0 (namely, when it is determined that the vehicle is not in a tack-in state), then irrespective of the vehicle speed, the correction coefficient HS3 is 0, and it is possible to avoid having to correct the limit standard yaw rate ω_TAR.
Moreover, when the required torque is less than the predetermined value T0 (namely, when it is determined that the vehicle is in a tack-in state), and the vehicle speed is also less than V0, then because the correction coefficient HS3 becomes a positive value, the limit standard yaw rate ω_TAR can be increased to a large value. In contrast, when the required torque is less than the predetermined value T0, and the vehicle speed is greater than V0, then because the correction coefficient HS3 becomes a negative value, the limit standard yaw rate ω_TAR can be reduced to a small value. Furthermore, when the vehicle speed is less than V0, and the required torque is the same, then the correction coefficient HS3 can be increased to a large positive value proportionally as the vehicle speed lessens, so that the limit standard yaw rate ω— TAR can be increased to a large value. By employing this method, the turning performance of the vehicle during tack-in at a low or medium speed can be improved. In particular, the lower the vehicle speed, the greater the improvement in the turning performance of the vehicle during tack-in. In contrast, when the vehicle speed is greater than V0, and the required torque is the same, then the correction coefficient HS3 can be increased to a large negative value proportionally as the vehicle speed increases, so that the limit standard yaw rate ω_TAR can be reduced to a small value. By employing this method, when the vehicle is speed high, it is possible to prevent an excessive yaw moment being generated and causing the vehicle to oversteer. Consequently, it is possible to prevent the vehicle behavior from becoming unstable.
Next, the calculation of the braking control amount executed by the FB control amount operating section 19 (referred to below as the FB control amount) will be described with reference made to
In the FB control amount operating section 19, based on the limit yaw rate deviation Δωfb calculated by the limit yaw rate deviation operating section 16, an FB pressure increase amount ΔP1fb for an FR inside wheel during a turn, an FB pressure increase amount ΔP3fb for an outside wheel on the front wheel side during a turn (hereinafter, abbreviated to the FR outside wheel during a turn), an FB pressure increase amount ΔP2fb for an RR inside wheel during a turn, and an FB pressure increase amount ΔP4fb for an outside wheel on the rear wheel side during a turn (hereinafter, abbreviated to the RR outside wheel during a turn) are calculated. ΔP1fb, ΔP2fb, ΔP3fb, and ΔP4fb are first control amounts for braking control. An example is described of a case in which, for subsequent turning directions, the symbols of deviation Δωfb are positive, and both the standard yaw rate and the actual yaw rate are positive.
The FB pressure increase amount ΔP1fb for the FR inside wheel during a turn is calculated by referring to a pressure increase amount table 80 based on the limit yaw rate deviation Δωfb. In the pressure increase amount table 80, the horizontal axis is the limit yaw rate deviation Δωfb, while the vertical axis is the FB pressure increase amount ΔP1fb. In the present embodiment, when the limit yaw rate deviation Δωfb is less than 0, the FB pressure increase amount ΔP1fb is 0, and when the limit yaw rate deviation Δωfb is more than 0, the FB pressure increase amount ΔP1fb increases proportionally as the limit yaw rate deviation Δωfb increases.
The FB pressure increase amount ΔP2fb for the RR inside wheel during a turn is calculated by referring to a pressure increase amount table 81 based on the limit yaw rate deviation Δωfb. In the pressure increase amount table 81, the horizontal axis is the limit yaw rate deviation Δωfb, while the vertical axis is the FB pressure increase amount ΔP2fb. In the present embodiment, when the limit yaw rate deviation Δωfb is less than 0, the FB pressure increase amount ΔP2fb is 0, and when the limit yaw rate deviation Δωfb is more than 0, the FB pressure increase amount ΔP2fb increases proportionally as the limit yaw rate deviation Δωfb increases.
The FB pressure increase amount ΔP3fb for the FR outside wheel during a turn is calculated by referring to a pressure increase amount table 82 based on the limit yaw rate deviation Δωfb. In the pressure increase amount table 82, the horizontal axis is the limit yaw rate deviation Δωfb, while the vertical axis is the FB pressure increase amount ΔP3fb. In the present embodiment, when the limit yaw rate deviation Δωfb is more than 0, the FB pressure increase amount ΔP3fb is 0, and when the limit yaw rate deviation Δωfb is less than 0, the FB pressure increase amount ΔP3fb increases proportionally as the absolute value of the limit yaw rate deviation Δωfb increases.
The FB pressure increase amount ΔP4fb for the RR outside wheel during a turn is calculated by referring to a pressure increase amount table 83 based on the limit yaw rate deviation Δωfb. In the pressure increase amount table 83, the horizontal axis is the limit yaw rate deviation Δωfb, while the vertical axis is the FB pressure increase amount ΔP4fb. In the present embodiment, when the limit yaw rate deviation Δωfb is more than 0, the FB pressure increase amount ΔP4fb is 0, and when the limit yaw rate deviation Δωfb is less than 0, the FB pressure increase amount ΔP4fb increases proportionally as the absolute value of the limit yaw rate deviation Δωfb increases.
Namely, in the FB control amount operating section 19, when the limit yaw rate deviation Δωfb is more than 0, because the actual yaw rate is smaller than the limit standard yaw rate, the FB control amount for each wheel is set in a direction in which the yaw rate increases (in other words, in a direction in which the limit yaw rate deviation Δωfb is canceled out). Specifically, the FB pressure increase amount is set in a direction in which the brake hydraulic pressure on the FR inside wheel during the turn and on the RR inside wheel during the turn increases, and the FB pressure increase amount is also set such that the brake hydraulic pressure on the FR outside wheel during the turn and on the RR outside wheel during the turn does not increase.
In contrast, when the limit yaw rate deviation Δωfb is less than 0, because the actual yaw rate is larger than the limit standard yaw rate, the FB control amount for each wheel is set in a direction in which the yaw rate decreases (in other words, in a direction in which the limit yaw rate deviation Δωfb is canceled out). Specifically, the FB pressure increase amount is set in a direction in which the brake hydraulic pressure on the FR outside wheel during the turn and on the RR outside wheel during the turn increases, and the FB pressure increase amount is also set such that the brake hydraulic pressure on the FR inside wheel during the turn and on the RR inside wheel during the turn does not increase.
In addition, the FB control amount operating section 19 outputs to the braking device 10 the FB pressure increase amount ΔP1fb for the FR inside wheel during a turn, the FB pressure increase amount ΔP2fb for the RR inside wheel during a turn, the FB pressure increase amount ΔP3fb for the FR outside wheel during a turn, and the FB pressure increase amount ΔP4fb for the RR outside wheel during a turn. The braking device 10 controls the brake pressure of each wheel in accordance with the control amounts for each wheel that are input.
According to the vehicle turning control device of the present embodiment, because the lateral G standard yaw rate ω_low is corrected by the correcting section 15 in a direction of increase, in association with the steady-state standard yaw rate ω_high which is calculated based on the steering angle, so that the limit standard yaw rate ω_TAR is calculated, it is possible to achieve both control that stabilizes the yaw moment generated in the vehicle body, and control that improves the steering responsiveness. As a result, the turning intention of a driver is reflected with an accurate response, and the steering feel is improved.
Moreover, because the lateral G standard yaw rate ω_low is corrected in a direction of increase so as to form the limit standard yaw rate ω_TAR, it is possible to increase the target value in the FB control amount operating section 19, and thereby improve the turning performance of the vehicle. As a result, it becomes possible to make a vehicle turn around a driving course, and the ability of the vehicle to follow the road (i.e., the traceability) is improved.
Furthermore, because the distribution coefficient HB1 operating section 31, the correction coefficient HS1 operating section 33, the correction coefficient HS2 operating section 34, and the correction coefficient HS3 operating section 35 are provided in the correcting section 15, the convergence and the like of the yaw rate are improved in accordance with the state of the vehicle and the state of the road surface and the like (for example, after a lane change on a high μ road surface and the like), and even if the vehicle is traveling at low speed, the ability of the vehicle to follow the steering is improved.
Next, a second embodiment of the vehicle turning control device according to this invention will be described with reference made to the drawings shown in
The vehicle turning control device according to the second embodiment is described below, however, because the feedback control system shown in the control block diagram in
The vehicle turning control device 1B (1) according to the second embodiment is provided, additionally to the structure of the vehicle turning control device 1A of the first embodiment, with a feed-forward control system that is formed by a steady-state yaw rate deviation operating section 13, and a feed-forward control amount operating section (i.e., a second braking force control operating section, abbreviated below to an ‘FF control amount operating section’) 18. A braking force control amount operating section 17 is formed by the FF control amount operating section 18 and the FB control amount operating section 19 of the first embodiment.
The steady-state yaw rate deviation operating section 13 receives inputs of steering angle standard yaw rates from which the noise has been removed by performing temporal change smoothing processing or peak hold processing or the like on the steering angle standard yaw rate calculated by the steering angle standard yaw rate operating section 11. In addition, the steady-state yaw rate deviation operating section 13 subtracts the steering angle standard yaw rate after the noise has been removed therefrom from the steady-state standard yaw rate ω_high, so as to obtain a steady-state yaw rate deviation Δωff.
The braking force control amount operating section 17 calculates a feed-forward control amount based on the steady-state yaw rate deviation Δωff in the FF control amount operating section 18, and calculates a feedback control amount (i.e., an FB control amount) based on the limit yaw rate deviation Δωfb in the FB control amount operating section 19, and then adds together the FF control amount and the FB control amount, so as to obtain an overall control amount. This overall control amount is then output as a command value to the braking device 10.
Next, the braking control amount operation which is executed by the braking force control amount operating section 17 will be described with reference made to
The calculation of the FF control amount in the FF control amount operating section 18 will now be described.
Firstly, based on the steering angle which has been detected by the steering angle sensor 3, a pressure increase distribution is decided for the front inside wheel during a turn (abbreviated below to FR inside wheel during a turn) and a rear inside wheel during a turn (abbreviated below to RR inside wheel during a turn). Next, based on this pressure increase distribution, a pressure increase coefficient K1fr for the FR inside wheel during a turn and a pressure increase coefficient K1rr for the RR inside wheel during a turn are calculated. Here, it is possible for the settings to be made such that, if a large load movement is generated by the steering, the pressure increase coefficient K1fr for the FR inside wheel during the turn increases in accordance with the steering angle.
The calculation of the FF pressure increase amount ΔP1ff for the FR inside wheel during the turn and the calculation of the FF pressure increase amount ΔP2ff for the RR inside wheel during the turn are executed in parallel based on the pressure increase coefficient K1fr for the FR inside wheel during the turn and the pressure increase coefficient K1rr for the RR inside wheel during the turn. The ΔP1ff and the ΔP2ff are second braking force control amounts.
Firstly, the FF pressure increase amount ΔP1ff for the FR inside wheel during the turn will be described. The pressure increase coefficient K1fr is multiplied by the steady-state yaw rate deviation Δωff which was calculated by the steady-state yaw rate deviation operating section 13, so that a steady-state yaw rate deviation Δω1ff for the FR inside wheel during a turn is obtained.
Next, a brake hydraulic pressure increase amount ΔP1ffk for the FR inside wheel during the turn is calculated in accordance with the steady-state yaw rate deviation Δω1ff for the FR inside wheel during the turn by referring to a first pressure increase table 60. In the first pressure increase table 60, the horizontal axis is the steady-state yaw rate deviation Δω1ff, while the vertical axis is the brake hydraulic pressure increase amount ΔP1ffk. In the present embodiment, when the steady-state yaw rate deviation Δω1ff for the FR inside wheel during the turn is less than 0, the brake hydraulic pressure increase amount ΔP1ffk is 0, while when the steady-state yaw rate deviation Δω1ff for the FR inside wheel during the turn is more than 0, the brake hydraulic pressure increase amount ΔP1ffk increases proportionally as the steady-state yaw rate deviation Δω1ff increases.
Next, in a first limit processing section 61, limit processing is performed such that the brake hydraulic pressure increase amount ΔP1ffk for the FR inside wheel during the turn does not exceed an upper limit value. The upper limit value is an arbitrary value calculated by a first upper limit value calculating section 62, and by making the settings such that this value is not exceeded, any sudden variations in the brake hydraulic pressure increase amount ΔP1ffk are restricted.
Next, a gain that corresponds to the vehicle speed is multiplied by the brake hydraulic pressure increase amount ΔP1ffk for the FR inside wheel during the turn that has undergone the limit processing, resulting in an FF pressure increase amount ΔP1ff for the FR inside wheel during the turn being obtained. The gain that corresponds to the vehicle speed is calculated based on a first gain table 63. In this first gain table 63, the horizontal axis shows the vehicle speed, while the vertical axis shows the gain. In the region where the vehicle speed is low, the gain is fixed so as to =1. When the vehicle speed exceeds a predetermined value, then as the vehicle speed increases, the gain becomes gradually smaller, and in a high vehicle speed region, the gain is fixed so as to =0.
As a result of multiplying a gain that corresponds to the vehicle speed by the brake hydraulic pressure increase amount ΔP1ffk for the FR inside wheel during the turn, when the vehicle speed is high, the FF pressure increase amount ΔP1ff for the FR inside wheel during the turn becomes 0. In other words, when the vehicle is moving at high speed, the FF pressure increase amount ΔP1ff for the FR inside wheel during the turn is disabled. By doing this, it is possible to prevent the vehicle behavior becoming unstable because of turning assist braking at high vehicle speeds. In the present embodiment, the gain table 63 forms a disabled structure. In other case, instead of multiplying a gain that corresponds to the vehicle speed, it is also possible to supply an arbitrary limit value which decreases as the vehicle speed increases, and to apply settings that prevent ΔP1ff from exceeding this limit value.
The calculation of the FF pressure increase amount ΔP2ff for the RR inside wheel during a turn is the same as the calculation of the FF pressure increase amount ΔPfr1 for the FR inside wheel during a turn, therefore, the description thereof will be simplified.
The pressure increase coefficient K1rr for the RR inside wheel during a turn is multiplied by the steady-state yaw rate deviation Δωff which was calculated by the steady-state yaw rate deviation operating section 13, so that a steady-state yaw rate deviation Δω2ff for the RR inside wheel during a turn is obtained.
Next, a brake hydraulic pressure increase amount ΔP2ffk for the RR inside wheel during the turn is calculated in accordance with the steady-state yaw rate deviation Δω2ff for the RR inside wheel during the turn by referring to a second pressure increase table 64. The second pressure increase table 64 is the same as the first pressure increase table 60, therefore, no description thereof is provided here.
Next, in a second limit processing section 65, limit processing is performed such that the brake hydraulic pressure increase amount ΔP2ffk for the RR inside wheel during the turn does not exceed an upper limit value. The upper limit value is calculated by a second upper limit value calculating section 66. The second upper limit value calculating section 66 is the same as the first upper limit value calculating section 62.
Next, a gain that is calculated using a second gain table 67 is multiplied by the brake hydraulic pressure increase amount ΔP2ffk for the RR inside wheel during the turn that has undergone the limit processing, resulting an FF pressure increase amount ΔP2ff for the RR inside wheel during the turn being obtained. The second gain table 67 is the same as the first gain table 63, therefore, no description thereof will be provided here. In the present embodiment, the second gain table 67 forms a disabled structure.
Moreover, the FF control amount operating section 18 is provided with an inside wheel pressure decrease amount calculating section 70. The purpose of the inside wheel pressure decrease amount calculating section 70 is to place preset limits on the brake hydraulic pressure of the inside wheels during a turn under the assumption that the vehicle behavior will become unstable if braking is applied at high speed and under high lateral G conditions.
In the inside wheel pressure decrease amount calculating section 70, a rate of pressure decrease that corresponds to the vehicle speed is calculated by referring to a first pressure decrease rate table 71, and a rate of pressure decrease that corresponds to the lateral G is calculated by referring to a second pressure decrease rate table 72. These pressure decrease rates are then multiplied together to give an overall rate of pressure decrease.
In the first pressure decrease rate table 71, the horizontal axis is the vehicle speed, while the vertical axis is the rate of pressure decrease. In the region where the vehicle speed is low, the rate of pressure decrease is fixed so as to =0. When the vehicle speed exceeds a predetermined value, then as the vehicle speed increases, the rate of pressure decrease becomes gradually larger, and in a high vehicle speed region, the rate of pressure decrease is fixed so as to =1.
In the second pressure decrease rate table 72, the horizontal axis is the lateral G, while the vertical axis is the rate of pressure decrease. In the region where the lateral G is small, the rate of pressure decrease is fixed so as to =0. When the lateral G exceeds a predetermined value, then as the lateral G increases, the rate of pressure decrease becomes gradually larger, and in a high lateral G region, the rate of pressure decrease is fixed so as to =1.
By employing this type of structure, the overall rate of pressure decrease is set to a value between 0 and 1 in accordance with the vehicle speed and the lateral G while the vehicle is traveling.
By then multiplying the master cylinder pressure in the braking device 10 by the overall rate of pressure decrease which has been determined in this manner, and by then further multiplying the result thereby obtained by negative 1, an inside wheel pressure decrease rate ΔPd is obtained.
The calculation of the FB control amount performed in the FB control amount operating section 19 is the same as in the first embodiment, therefore, no description thereof will be given here.
In the braking force control amount operating section 17, a value obtained by adding together the FF pressure increase amount ΔP1ff of the FR inside wheel during a turn, the FB pressure increase amount ΔP1fb of the FR inside wheel during a turn, and the inside wheel pressure decrease rate ΔPd is taken as the overall control amount for the FR inside wheel during a turn. In addition, a value obtained by adding together the FF pressure increase amount ΔP2ff of the RR inside wheel during a turn, the FB pressure increase amount ΔP2fb of the RR inside wheel during a turn, and the inside wheel pressure decrease rate ΔPd is taken as the overall control amount for the RR inside wheel during a turn. Moreover, the FB pressure increase amount ΔP3fb for the FR outside wheel during a turn is taken as the overall control amount for the FR outside wheel during a turn, and the FB pressure increase amount ΔP4fb for the RR outside wheel during a turn is taken as the overall control amount for the RR outside wheel during a turn. These four control amounts are output to the braking device 10.
The braking device 10 controls the braking pressure of each wheel in accordance with the control amounts for the respective wheels that have been input.
According to the vehicle turning control device of the present embodiment, in the same way as in the first embodiment, the lateral G standard yaw rate ω_low is corrected by the correcting section 15 in a direction in which its value increases, in association with the steady-state standard yaw rate ω_high which is calculated based on the steering angle, so that the limit standard yaw rate ω_TAR is obtained. Because of this, it is possible to achieve both control that stabilizes the yaw moment generated in the vehicle body, and control that improves the steering response. As a result, the turning intention of a driver is reflected with an accurate response, and the steering feel is improved.
Moreover, because the lateral G standard yaw rate ω_low is corrected in a direction of increase so as to form the limit standard yaw rate ω_TAR, it is possible to increase the target value in the FB control amount operating section 19, and thereby improve the turning performance of the vehicle. As a result, it becomes possible to make a vehicle turn around the course being driven, and the ability of the vehicle to follow the road (i.e., the traceability) is improved.
Furthermore, because the distribution coefficient HB1 operating section 31, the correction coefficient HS1 operating section 33, the correction coefficient HS2 operating section 34, and the correction coefficient HS3 operating section 35 are provided in the correcting section 15, the convergence of the yaw rate is improved in accordance with the state of the vehicle and the state of the road surface and the like (for example, after a lane change on a high μ road surface and the like), and even if the vehicle is traveling at low speed, the ability of the vehicle to follow the steering is improved.
Moreover, according to the vehicle turning control device of the present embodiment, because the braking pressure is controlled based on an overall control amount that is obtained by adding an FF control amount, which is calculated based on the steering input, to an FB control amount, which is calculated based on the vehicle behavior, it is possible to improve the steering responsiveness and followability, while maintaining the stability of the vehicle behavior. For example, as in a steady-state circular turn or the like, in the step of holding the steering after having made the initial steering input, variations in the control amount are suppressed, and the ability of the vehicle to follow the road is improved.
Next, a third embodiment of the vehicle turning control device according to this invention will be described with reference made to the drawings shown in
When determining whether or not a vehicle is in a tack-in state based on the return speed, as shown in
The correction coefficient HS3c is calculated by referring to a correction coefficient table 53 shown in
By employing this type of method, when the speed at which the accelerator pedal or the accelerator opening angle is returned is slower than the predetermined value, the vehicle is determined not to be in a tack-in state, and the correction coefficient HS3c is set to 0. As a result, the correction of the limit standard yaw rate ω_TAR using the correction coefficient HS3 is not performed. In contrast, when the speed at which the accelerator pedal or the accelerator opening angle is returned is faster than the predetermined value, the vehicle is determined to be in a tack-in state, and a correction coefficient HS3c that corresponds to the vehicle speed is obtained, and the limit standard yaw rate ω_TAR is corrected using the correction coefficient HS3.
When a determination as to whether or not the vehicle is in a tack-in state is made based on both the required torque and the return speed, as shown in
In this manner, in both cases when a determination as to whether or not the vehicle is in a tack-in state is made based on the return speed of the accelerator pedal or the accelerator opening angle, and cases when a determination as to whether or not the vehicle is in a tack-in state is made based on both the required torque and the return speed, it is possible to calculate the correction coefficient HS3, and obtain the same type of effects as those obtained in the first embodiment or the second embodiment.
A fourth embodiment of the vehicle turning control device of this invention will now be described with reference made to
A vehicle turning control device 1C (1) of the present embodiment is provided with a braking control section 2, and a braking device (i.e., a braking control device) 10.
The braking control section 2 decides the amounts of braking force control to be applied to the front and rear, left and right wheels of a vehicle in accordance with the running state of the vehicle. The braking device 10 controls the braking force of each wheel based on the amounts of braking force control for each wheel decided by the braking control section 2.
Detection signals that correspond to detection values obtained from a variety of sensors are input into the braking control section 2. The variety of sensors include a steering angle sensor (i.e., a steering amount detecting device) 3 that detects the steering angle (i.e., the amount of steering) of the vehicle steering wheel, a vehicle speed sensor (i.e., a vehicle speed detecting device) 4 that detects the speed of the vehicle, a lateral acceleration sensor (i.e., a lateral acceleration detecting device: shortened below to a lateral G sensor) 5 that detects the acceleration in the left-right direction of the vehicle (i.e., the transverse direction of the vehicle), namely, that detects the lateral acceleration (shortened below to the lateral G), and a yaw rate sensor (i.e., a yaw rate detecting device) 6 that detects the yaw rate of the vehicle.
The braking control section 2 is provided with an assist amount operating section (i.e., an assist amount setting device) 23, a lateral G standard yaw rate operating section (i.e., a control amount operating section) 14, a yaw rate deviation operating section 16, and a braking force control amount operating section 17. The braking force control amount operating section 17 is provided with a second braking force control operating section (i.e., a feed-forward control amount operating section: shortened below to an FF control amount operating section) 18, and a first braking force control operating section (i.e., a feedback control amount operating section: shortened below to an FB control amount operating section) 19.
The assist amount operating section 23 calculates an amount of assist As that is supplied by the brakes in order to assist the turning of the vehicle (i.e., a turning assist amount) based on the steering angle detected by the steering angle sensor 3, and on the vehicle speed detected by the vehicle speed sensor 4. More specifically, the assist amount operating section 23 calculates a gain Ks that corresponds to the steering angle by referring to a steering angle gain table 24, and also calculates a gain Kv that corresponds to the vehicle speed by referring to a vehicle speed gain table 25, and by then setting the product obtained by multiplying these gains Ks and Kv together as the assist amount As (i.e., As=Ks×Kv).
In the steering angle gain table 24 of the present embodiment, the horizontal axis shows the steering angle, while the vertical axis shows the steering angle gain Ks. The steering angle is a positive steering angle when the steering wheel is rotated clockwise from a neutral position (i.e., a position in which the vehicle travels in a straight line), and is a negative steering angle when the steering wheel is rotated anticlockwise from a neutral position. In this steering angle gain table 24, in the region where an absolute value of the steering angle is less than a predetermined value, the steering angle gain Ks is fixed as Ks=0. When the absolute value of the steering angle reaches the predetermined value, the steering angle gain Ks abruptly increases to a positive fixed value, and when the absolute value of the steering angle exceeds the predetermined value, then as the absolute value of the steering angle becomes larger, the steering angle gain Ks is set so as to become gradually greater.
On the other hand, in the vehicle speed gain table 25 of the present embodiment, the horizontal axis shows the vehicle speed, while the vertical axis shows the vehicle speed gain Kv. As the vehicle speed increases, the vehicle speed gain Kv becomes smaller and converges on 1. The vehicle speed gain Kv is set so as to become proportionally larger as the vehicle speed decreases.
Because the steering angle gain table 24 and the vehicle speed gain table 25 are set in this manner, when an absolute value of the steering angle is less than a predetermined value, then irrespective of the size of the vehicle speed, the assist amount As is 0. In contrast, when the absolute value of the steering angle exceeds the predetermined value, then as the absolute value of the steering angle increases, the assist amount As increases. In addition, as the vehicle speed decreases, the assist amount As increases, and as the vehicle speed increases, the assist amount As decreases.
The lateral G standard yaw rate operating section 14 calculates a lateral G standard yaw rate ω_low based on the lateral G detected by the lateral G sensor 5, and on the vehicle speed detected by the vehicle speed sensor 4. The lateral G standard yaw rate low is the yaw rate than can be generated by the current lateral G, and is expressed, for example, by ω_low=Gy/V. Here, Gy is a lateral acceleration detection value detected by the lateral G sensor 5, and V is the vehicle speed detected by the vehicle speed sensor 4.
The yaw rate deviation operating section 16 subtracts the yaw rate detected by the yaw rate sensor 6 (i.e., the actual yaw rate) from the lateral G standard yaw rate ω_low so as to obtain a yaw rate deviation Δωfb.
The braking force control amount operating section 17 calculates a feed-forward control amount (abbreviated below to ‘FF control amount’) based on the assist amount As in the FF control amount operating section 18, and calculates a feedback control amount (abbreviated below to ‘FR control amount’) based on the yaw rate deviation Δωfb in the FB control amount operating section 19, and then adds together the FF control amount and the FB control amount, so as to obtain an overall control amount for each wheel. The value obtained by this addition is then output as a command value to the braking device 10. In the present embodiment, the braking force control amount operating section 17 forms the braking force control amount operating section.
Next, the braking control amount operation which is executed by the braking force control amount operating section 17 will be described with reference made to
The calculation of the FF control amount in the FF control amount operating section 18 will now be described.
Firstly, based on the steering angle of the steering wheel which has been detected by the steering angle sensor 3, a pressure increase distribution is decided for the front inside wheel of a vehicle during a turn (abbreviated below to FR inside wheel during a turn) and a rear inside wheel during a turn (abbreviated below to RR inside wheel during a turn). Next, based on this pressure increase distribution, a pressure increase coefficient K1fr for the FR inside wheel during a turn and a pressure increase coefficient K1rr for the RR inside wheel during a turn are calculated. Here, it is possible for the settings to be made such that, if a large load movement is generated by the steering, the pressure increase coefficient K1fr for the FR inside wheel during the turn increases in accordance with the steering angle.
The calculation of the FF pressure increase amount ΔP1ff for the FR inside wheel during the turn and the calculation of the FF pressure increase amount ΔP2ff for the RR inside wheel during the turn are executed in parallel based on the pressure increase coefficient K1fr for the FR inside wheel during the turn and the pressure increase coefficient K1rr for the RR inside wheel during the turn.
Firstly, the FF pressure increase amount ΔP1ff for the FR inside wheel during the turn will be described. The pressure increase coefficient K1fr is multiplied by the assist amount As which was calculated by the assist amount operating section 23, so that an assist amount As1 for the FR inside wheel during a turn is obtained.
Next, a brake hydraulic pressure increase amount ΔP1ffk for the FR inside wheel during the turn is calculated in accordance with the assist amount As1 for the FR inside wheel during the turn by referring to a first pressure increase table 68. In the first pressure increase table 68, the horizontal axis is the assist amount As1, while the vertical axis is the brake hydraulic pressure increase amount ΔP1ffk.
In the present embodiment, when the assist amount As1 for the FR inside wheel during the turn is less than 0, the brake hydraulic pressure increase amount ΔP1ffk is 0. In contrast, when the assist amount AFAs1 for the FR inside wheel during the turn is more than 0, then as the assist amount As1 increases, the brake hydraulic pressure increase amount ΔP1ffk increases proportionally.
Next, in the first limit processing section 61, limit processing is performed such that the brake hydraulic pressure increase amount ΔP1ffk for the FR inside wheel during the turn does not exceed an upper limit value. The upper limit value is an arbitrary value calculated by a first upper limit value calculating section 62, and by creating settings that do not allow this value to be exceeded, any sudden variations in the brake hydraulic pressure increase amount ΔP1ffk are restricted.
Next, a gain that corresponds to the vehicle speed is multiplied by the brake hydraulic pressure increase amount ΔP1ffk for the FR inside wheel during the turn that has undergone the limit processing, resulting in an FF pressure increase amount ΔP1ff for the FR inside wheel during the turn being obtained. The gain that corresponds to the vehicle speed is calculated based on a first gain table 63. In this first gain table 63, the horizontal axis is the vehicle speed, while the vertical axis is the gain. In the region where the vehicle speed is low, the gain is fixed so as to =1. When the vehicle speed exceeds a predetermined value, then as the vehicle speed increases, the gain becomes gradually smaller, and in a high vehicle speed region, the gain is fixed so as to =0.
As a result of multiplying a gain that corresponds to the vehicle speed, when the vehicle speed is high, the FF pressure increase amount ΔP1ff for the FR inside wheel during the turn becomes 0. In other words, when the vehicle is moving at high speed, the FF pressure increase amount ΔP1ff for the FR inside wheel during the turn is disabled. By doing this, it is possible to prevent the vehicle behavior becoming unstable due to turning assist braking at high vehicle speeds. In the present embodiment, the first gain table 63 forms a disabled structure. In other case, instead of multiplying a gain that corresponds to the vehicle speed, it is also possible to supply an arbitrary limit value which decreases as the vehicle speed increases, and to apply settings that prevent ΔP1ff from exceeding this limit value.
The calculation of the FF pressure increase amount ΔP2ff for the RR inside wheel during a turn is the same as the calculation of the FF pressure increase amount ΔPfr1 for the FR inside wheel during a turn, therefore, the description thereof is simplified.
The pressure increase coefficient K1rr for the RR inside wheel during a turn is multiplied by the assist amount As which was calculated by the assist amount operating section 23, so that an assist amount As2 for the RR inside wheel during a turn is obtained.
Next, a brake hydraulic pressure increase amount ΔP2ffk for the RR inside wheel during the turn is calculated in accordance with the assist amount As2 for the RR inside wheel during the turn by referring to a second pressure increase table 69. The second pressure increase table 69 is the same as the first pressure increase table 68, therefore, no description thereof is provided here.
Next, in the second limit processing section 65, limit processing is performed such that the brake hydraulic pressure increase amount ΔP2ffk for the RR inside wheel during the turn does not exceed an upper limit value. The upper limit value is calculated by the second upper limit value calculating section 66. The second upper limit value calculating section 66 is the same as the first upper limit value calculating section 62.
Next, a gain that is calculated using the second gain table 67 is multiplied by the brake hydraulic pressure increase amount ΔP2ffk for the RR inside wheel during the turn that has undergone the limit processing, resulting an FF pressure increase amount ΔP2ff for the RR inside wheel during the turn being obtained. The second gain table 67 is the same as the first gain table 63, therefore, no description thereof will be provided here. In the present embodiment, the second gain table 67 forms a disabled structure.
Moreover, the FF control amount operating section 18 is provided with an inside wheel pressure decrease amount calculating section 70. The purpose of the inside wheel pressure decrease amount calculating section 70 is to place preset limits on the brake hydraulic pressure of the inside wheels during a turn under the assumption that the vehicle behavior will become unstable if braking is applied when the vehicle is travelling at high speed and when a high lateral G is acting on the vehicle.
In the inside wheel pressure decrease amount calculating section 70, a rate of pressure decrease that corresponds to the vehicle speed is calculated by referring to the first pressure decrease rate table 71, and a rate of pressure decrease that corresponds to the lateral G is calculated by referring to the second pressure decrease rate table 72. These pressure decrease rates are then multiplied together to give an overall rate of pressure decrease.
In the first pressure decrease rate table 71, the horizontal axis is the vehicle speed, while the vertical axis is the rate of pressure decrease. In the region where the vehicle speed is low, the rate of pressure decrease is fixed so as to =0. When the vehicle speed exceeds a predetermined value, then as the vehicle speed increases, the rate of pressure decrease becomes gradually larger, and in a high vehicle speed region, the rate of pressure decrease is fixed so as to =1.
In the second pressure decrease rate table 72, the horizontal axis is the lateral G, while the vertical axis is the rate of pressure decrease. In the region where the lateral G is small, the rate of pressure decrease is fixed so as to =0. When the lateral G exceeds a predetermined value, then as the lateral G increases, the rate of pressure decrease becomes gradually larger, and in a high lateral G region, the rate of pressure decrease is fixed so as to =1.
By employing this type of structure, the overall rate of pressure decrease is set to a value between 0 and 1 in accordance with the vehicle speed and the lateral G while the vehicle is running.
By then multiplying the master cylinder pressure in the braking device 10 by the overall rate of pressure decrease which has been set in this manner, and by then further multiplying the result thereby obtained by negative 1, an inside wheel pressure decrease rate ΔPd is obtained.
Next, the calculation of the FB control amount performed in the FB control amount operating section will be described.
In the FB control amount operating section 19, based on the yaw rate deviation Δωfb calculated by the yaw rate deviation operating section 16, an FB pressure increase amount ΔP1fb for an FR inside wheel during a turn, an FB pressure increase amount ΔP3Fb for an outside wheel on the front wheel side during a turn (hereinafter, abbreviated to the FR outside wheel during a turn), an FB pressure increase amount ΔP2fb for an RR inside wheel during a turn, and an FB pressure increase amount ΔP4fb for an outside wheel on the rear wheel side during a turn (hereinafter, abbreviated to the RR outside wheel during a turn) are obtained. An example is described of a case in which, for subsequent turning directions, the symbol of the deviation Δωfb is positive, and both the standard yaw rate and the actual yaw rate are positive.
The FB pressure increase amount ΔP1fb for the FR inside wheel during a turn is calculated by referring to the first pressure increase amount table 80 based on the yaw rate deviation Δωfb. In the first pressure increase amount table 80, the horizontal axis is the yaw rate deviation Δωfb, while the vertical axis is the FB pressure increase amount ΔP1fb. In the present embodiment, when the yaw rate deviation Δωfb is less than 0, the FB pressure increase amount ΔP1fb is 0, and when the yaw rate deviation Δωfb is more than 0, the FB pressure increase amount ΔP1fb increases proportionally as the yaw rate deviation Δωfb increases.
The FB pressure increase amount ΔP2fb for the RR inside wheel during a turn is calculated by referring to a second pressure increase amount table 81 based on the yaw rate deviation Δωfb. In the second pressure increase amount table 81, the horizontal axis is the yaw rate deviation Δωfb, while the vertical axis is the FB pressure increase amount ΔP2fb. In the present embodiment, when the yaw rate deviation Δωfb is less than 0, the FB pressure increase amount ΔP2fb is 0, and when the yaw rate deviation Δωfb is more than 0, the FB pressure increase amount ΔP2fb increases proportionally as the yaw rate deviation Δωfb increases.
The FB pressure increase amount ΔP3fb for the FR outside wheel during a turn is calculated by referring to a third pressure increase amount table 82 based on the yaw rate deviation Δωfb. In the third pressure increase amount table 82, the horizontal axis is the yaw rate deviation Δωfb, while the vertical axis is the FB pressure increase amount ΔP3fb. In the present embodiment, when the yaw rate deviation Δωfb is more than 0, the FB pressure increase amount ΔP3fb is 0, and when the yaw rate deviation Δωfb is less than 0, the FB pressure increase amount ΔP3fb increases proportionally as absolute value of the yaw rate deviation Δωfb increases.
The FB pressure increase amount ΔP4fb for the RR outside wheel during a turn is calculated by referring to a fourth pressure increase amount table 83 based on the yaw rate deviation Δωfb. In the fourth pressure increase amount table 83, the horizontal axis is the yaw rate deviation Δωfb, while the vertical axis is the FB pressure increase amount ΔP4fb. In the present embodiment, when the yaw rate deviation Δωfb is more than 0, the FB pressure increase amount ΔP4fb is 0, and when the yaw rate deviation Δωfb is less than 0, the FB pressure increase amount ΔP4fb increases proportionally as absolute value of the yaw rate deviation Δωfb increases.
Namely, in the FB control amount operating section 19, when the yaw rate deviation Δωfb is more than 0, because the actual yaw rate is smaller than the lateral G standard yaw rate ω_low, the FB control amount for each wheel is set in a direction in which the yaw rate increases (in other words, in a direction in which the yaw rate deviation Δωfb is canceled out). Specifically, the FB pressure increase amount is set in a direction in which the brake hydraulic pressure on the FR inside wheel during the turn and on the RR inside wheel during the turn increases, and the FB pressure increase amount is also set such that the brake hydraulic pressure on the FR outside wheel during the turn and on the RR outside wheel during the turn does not increase.
In contrast, when the yaw rate deviation Δωfb is less than 0, because the actual yaw rate is larger than the lateral G standard yaw rate ω_low, the FB control amount for each wheel is set in a direction in which the yaw rate decreases (in other words, in a direction in which the yaw rate deviation Δωfb is canceled out). Specifically, the FB pressure increase amount is set in a direction in which the brake hydraulic pressure on the FR outside wheel during the turn and on the RR outside wheel during the turn increases, and the FB pressure increase amount is also set such that the brake hydraulic pressure on the FR inside wheel during the turn and on the RR inside wheel during the turn does not increase.
In the braking force control amount operating section 17, a value obtained by adding together the FF pressure increase amount ΔP1ff of the FR inside wheel during a turn, the FB pressure increase amount ΔP1fb of the FR inside wheel during a turn, and the inside wheel pressure decrease rate ΔPd is taken as the overall control amount for the FR inside wheel during a turn. In addition, a value obtained by adding together the FF pressure increase amount ΔP2ff of the RR inside wheel during a turn, the FB pressure increase amount ΔP2fb of the RR inside wheel during a turn, and the inside wheel pressure decrease rate ΔPd is taken as the overall control amount for the RR inside wheel during a turn. Moreover, the FB pressure increase amount ΔP3fb for the FR outside wheel during a turn is taken as the overall control amount for the FR outside wheel during a turn, and the FB pressure increase amount ΔP4fb for the RR outside wheel during a turn is taken as the overall control amount for the RR outside wheel during a turn. These four values are output to the braking device 10.
The braking device 10 controls the braking pressure of each wheel in accordance with the control amounts for the respective wheels that have been input.
According to the vehicle turning control device of the present embodiment, when a vehicle is being steered through a turn, in addition to the yaw moment that is generated in response to the steering angle, because it is also possible to generate yaw moment by controlling the braking pressure based on the FF control amount which is calculated based on the steering input (i.e., the steering angle), the amount of yaw moment during normal steering can be increased and the vehicle steering can be assisted, so that the turning performance and responsiveness of the vehicle are improved. Moreover, because the amount of assist As is decided such that the gain is increased as the vehicle speed becomes slower, the lower the vehicle speed region, the more the turning performance and responsiveness of the vehicle are improved. In contrast, because the amount of assist As decreases as the vehicle speed increases, it is possible to suppress the braking force when the vehicle is traveling at high speed from becoming excessive and reducing the stability of the vehicle.
According to the vehicle turning control device of the present embodiment, because the brake pressure is controlled based on an overall control amount that is obtained by adding the FB control amount, which is calculated based on the vehicle behavior (i.e., the lateral G and the yaw rate), to the FF control amount, which is calculated based on the steering input (i.e., the steering angle), the intervention timing for the turning assist braking control is brought forward, and it is possible, while also improving the responsiveness of the steering, to improve the stability of the vehicle and the followability of the steering when the vehicle is making a turn. For example, in a step in which a steering input is made and that steering input is then held, such as when a vehicle is making a steady-state circular turn or the like, variations in the amount of control are restricted and the ability of the vehicle to follow the road is improved.
In the present embodiment, the brake pressure is controlled based on an overall control amount that is obtained by adding the FB control amount, which is calculated based on the vehicle behavior (i.e., the lateral G and the yaw rate), to the FF control amount, which is calculated based on the steering input (i.e., the steering angle), however, it is also possible for a turn to be assisted by controlling the brake pressure based solely on the FF control amount, which is calculated based on the steering input (i.e., the steering angle) without the FB control amount, which is calculated based on the vehicle behavior (i.e., the lateral G and the yaw rate) being added thereto. This invention is still applicable in this type of structure as well.
In other case, this invention is not limited to the above described embodiments. For example, in the above-described embodiment 2, an overall control amount is calculated by adding together the FF control amount and the FB control amount, however, it is also possible to calculate an overall control amount by multiplying the FF control amount by the FB control amount.
Moreover, instead of the detection values from a vehicle speed sensor, it is also possible to use an estimated vehicle speed that is estimated based on detection values from a wheel speed sensor.
Moreover, in the above-described embodiment 2, by disabling the FF pressure increase amount ΔP1ff for the FR inside wheel during a turn and the FF pressure increase amount ΔP2ff for the RR inside wheel during a turn when the vehicle is moving at high speed, the vehicle behavior is prevented from becoming unstable because of steering (i.e., turning) assist braking at high vehicle speeds, however, it is possible for the FF pressure increase amount for the inside wheels during a turn to also be disabled when the steering speed is extremely large or when ABS is in operation.
According to the vehicle turning control device of the present invention, it is possible to achieve both control that stabilizes the yaw moment generated in a vehicle body, and control that improves the steering response. As a result, the turning intention of a driver is reflected with an highly accurate response, and the steering feel is improved even when the vehicle is travelling at low speed. Moreover, the turning performance of the vehicle is improved, and the ability of the vehicle to follow the road is improved.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-047835 | Mar 2010 | JP | national |
| 2010-047836 | Mar 2010 | JP | national |
| 2010-047837 | Mar 2010 | JP | national |
| 2010-047838 | Mar 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/054702 | 3/2/2011 | WO | 00 | 8/23/2012 |
