Patent Application
20250196657
This application claims the priority benefits of Japanese application no. 2023-212132, filed on Dec. 15, 2023. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.
The disclosure relates to a driving force control apparatus for a four-wheel drive vehicle.
Conventionally, a driving force control apparatus for a four-wheel drive vehicle is known, which monitors longitudinal acceleration using an in-vehicle accelerometer, calculates the dynamic loads applied to the front wheels and rear wheels in consideration of the pitching direction moment caused by this longitudinal acceleration, and distributes the front and rear driving forces (controls the front and rear dynamic load distribution) so that the ratio of driving force for the dynamic loads on the front wheels and rear wheels does not exceed the traction limit of the tires (Japanese Patent Application Laid-Open No. 2012-187984).
There is also a driving force control apparatus that further monitors lateral acceleration during turning, calculates the dynamic load applied to each of the left wheels and right wheels in consideration of the rolling direction moment generated by this lateral acceleration, and distributes the front and rear driving forces (controls the inner wheel dynamic load ratio distribution) so that the ratio of the larger driving force to this dynamic load (the inner wheel side during turning) does not exceed the traction limit of the tires (Japanese Patent No. 7310703).
Furthermore, a technique is known which calculates the yaw rate based on the value of a G sensor and feedback-controls the front and rear driving force distribution ratio, but feedback control based on the yaw rate has the drawback of slow response in control.
The best front and rear wheel driving force distribution for traction, that is, the front and rear wheel driving force distribution for favorable off-road capability on low-u roads such as snow, is said to be approximately half front and half rear. As this driving force distribution becomes more biased to the front or rear, the traction performance on low-u roads decreases.
On the other hand, from the viewpoint of handling performance, FF vehicles (100% front wheel drive distribution) have a tendency to understeer (US), while FR vehicles (100% rear wheel drive distribution) have a tendency to oversteer (OS). With the best front and rear wheel driving force distribution for traction, that is, approximately half front and half rear, the steering characteristics are intermediate between US and OS, but since the linearity of the turning radius relative to acceleration (steering characteristics) is not constant, it is necessary to make fine correction to the accelerator and steering when cornering. The steering characteristics are constant in a region where the rear wheel drive distribution is slightly higher (best handling region), and when driving in this region, there is no need to make fine correction to the accelerator and steering when cornering.
Because the best front and rear wheel drive distribution for traction differs from the best front and rear wheel drive distribution for handling, the conventional driving force control apparatus has the problem that it cannot always achieve both excellent traction performance and excellent handling performance.
The disclosure provides a driving force control apparatus which is capable of obtaining excellent handling performance while maintaining excellent traction performance.
A driving force control apparatus (1) according to the disclosure is configured to determine a front and rear wheel drive distribution which is a ratio of driving force between front wheels (21) and rear wheels (22) in a four-wheel drive vehicle, and configured to calculate positive or negative standard driving acceleration (XG) obtained based on an input amount from a driving force instruction device (42) of the vehicle and a vehicle speed, and based on the standard driving acceleration (XG), switch between and perform dynamic load ratio distribution control that determines the front and rear wheel drive distribution in accordance with a dynamic load ratio distribution curve (L1) which is a curve of a dynamic load ratio applied to the front wheels and the rear wheels with respect to the standard driving acceleration (XG), and rear wheel-biased distribution control that determines the front and rear wheel drive distribution in accordance with a rear wheel-biased distribution curve (L2) which increases a rear wheel drive distribution compared to the dynamic load ratio distribution curve.
A driving force control apparatus (1) according to the disclosure is configured to determine a front and rear wheel drive distribution which is a ratio of driving force between front wheels (21) and rear wheels (22) in a four-wheel drive vehicle, and configured to calculate positive or negative standard driving acceleration (XG) obtained based on an input amount from a driving force instruction device (42) of the vehicle and a vehicle speed, and based on the standard driving acceleration (XG), switch between and perform dynamic load ratio distribution control that determines the front and rear wheel drive distribution in accordance with a dynamic load ratio distribution curve (L1) which is a curve of a dynamic load ratio applied to the front wheels and the rear wheels with respect to the standard driving acceleration (XG), and rear wheel-biased distribution control that determines the front and rear wheel drive distribution in accordance with a rear wheel-biased distribution curve (L2) which increases a rear wheel drive distribution compared to the dynamic load ratio distribution curve.
While dynamic load ratio distribution control with favorable traction performance is the basis, the vehicle has good traveling stability when the acceleration/deceleration of the vehicle is small, so this configuration can switch to rear wheel-biased distribution control with favorable handling performance to stabilize characteristics such as over-steer and under-steer. In addition, since the standard driving acceleration (XG) (target value of acceleration) is calculated from the instruction amount of the driving force instruction device (accelerator, brake, or the like) and the control is performed based on this, responsiveness is improved compared to feedback based only on actual acceleration or the like.
It is preferable that the dynamic load ratio distribution curve (L1) and the rear wheel-biased distribution curve (L2) are curves in which the rear wheel drive distribution increases as the standard driving acceleration (XG) increases, except for a transition curve (L3, L4) therebetween.
According to this configuration, the dynamic load ratio distribution curve reduces the ratio of driving force to the dynamic load applied to the front wheels and rear wheels in consideration of the pitching direction moment caused by the longitudinal acceleration, thereby increasing the margin relative to the tire traction limit. In addition, the rear wheel-biased distribution curve also provides a relatively large margin relative to the tire traction limit even under conditions of a high rear wheel drive distribution.
It is preferable that the driving force control apparatus (1) performs the rear wheel-biased distribution control in response to the standard driving acceleration (XG) being equal to or smaller than a first input amount (XG1), and it is preferable that this first input amount (XG1) is standard driving acceleration (XG) that provides acceleration at a limit at which drive wheels do not slip on a road surface in a predetermined condition (dry, wet, snowy).
Further, it is preferable that the driving force control apparatus (1) performs the rear wheel-biased distribution control in response to the standard driving acceleration (XG) being equal to or larger than a second input amount (XG2), and it is preferable that this second input amount (XG2) is standard driving acceleration (XG) that provides deceleration at a limit at which drive wheels do not slip on a road surface in a predetermined condition (dry, wet, snowy).
According to this configuration, when there is no sudden acceleration or deceleration and the acceleration or deceleration is within the traction limit in the predetermined road surface conditions, the rear wheel-biased distribution control is performed, thereby making it possible to improve handling performance.
It is preferable that the driving force control apparatus (1) is configured so that a value of the first input amount (XG1) is changeable by a mode switching operation of a driver, and it is also preferable that a value of the second input amount (XG2) is changeable by a mode switching operation of a driver.
This configuration provides the Sport mode which assumes only dry and wet road surfaces and expands the acceleration/deceleration range in which rear wheel-biased distribution control is performed, and the Normal mode which assumes snowy road surfaces in addition to dry and wet road surfaces and narrows the acceleration/deceleration range in which rear wheel-biased distribution control is performed, and can ensure a wide region of high handling performance in the Sport mode when the road surface is known to be not slippery as well as ensure stability in the Normal mode when the road surface is known to be slippery.
It is preferable that the driving force control apparatus (1) does not perform the rear wheel-biased distribution control in response to standard lateral acceleration (YG) calculated based on a steering amount of a steering device of the vehicle and the vehicle speed being equal to or larger than a third input amount (YG3), and it is preferable that the third input amount (YG3) is standard lateral acceleration (YG) at a limit at which drive wheels do not slip on a road surface in a predetermined condition.
According to this configuration, when lateral acceleration occurs due to sudden steering, rear wheel-biased distribution control is not performed, thereby making it possible to ensure traveling stability. Furthermore, since the control is based on the standard lateral acceleration (YG) (target value of acceleration) calculated based on the amount instructed by the driver such as the steering angle of the steering wheel, responsiveness is improved compared to feedback based only on actual acceleration or the like.
It is preferable that the driving force control apparatus (1) does not perform the rear wheel-biased distribution control in response to the vehicle speed (V) of the vehicle being lower than a first predetermined speed (V1), and it is preferable that the rear wheel-biased distribution control is not performed in response to the vehicle speed (V) being higher than a second predetermined speed (V2).
According to this configuration, when the vehicle travels at a low speed immediately after starting and immediately before stopping which requires traction, or when the vehicle travels at a high speed which requires traveling stability, rear wheel-biased distribution control is not performed regardless of the front/rear and left/right acceleration/deceleration. Therefore, traction and traveling stability can be ensured in these cases.
It is preferable that a drive source for the front wheels of the vehicle to which the driving force control apparatus (1) is applied is a drive source including an electric motor, it is preferable that a drive source for the rear wheels of the vehicle is a drive source including an electric motor, and it is preferable that a drive source for the front wheels and rear wheels of the vehicle is a drive source including an electric motor.
It is preferable that the driving force control apparatus (1) has a map in which the vehicle speed (V), standard lateral acceleration (YG) calculated based on a steering amount of a steering device, standard driving acceleration (XG) calculated based on the input amount from the driving force instruction device, and the front and rear wheel drive distribution (Rr) are recorded, and the front and rear wheel drive distribution (Rr) is determined based on the map.
According to this configuration, the rear wheel drive distribution can be determined more quickly compared to calculation based on computation, thereby increasing the speed of controlling the driving forces for the front and rear wheels.
It is preferable that the driving force instruction device (42, 44) is at least one of an accelerator pedal (accelerator operator) and a brake pedal (brake operator), and the input amount from the driving force instruction device is at least one of the depression amount (operation amount) of the accelerator pedal and the depression amount (operation amount) of the brake pedal.
According to these configurations, the standard driving acceleration (XG) (target value of acceleration) is calculated from the instruction amount of the driver such as accelerator operation amount and brake operation amount, and the control is performed based on this, so responsiveness is improved compared to feedback based only on actual acceleration or the like.
The driving force control apparatus according to the disclosure switches between best traction control, which determines the rear wheel drive distribution in accordance with the optimal traction curve, and rear wheel-biased distribution control, which determines the rear wheel drive distribution in accordance with the rear wheel-biased distribution curve, based on the standard driving acceleration (target value of acceleration). Therefore, the traction performance during traveling can be maintained when traction is required, such as during high acceleration/deceleration, and excellent handling performance can also be obtained when there is sufficient traction, such as during low acceleration/deceleration.
Hereinafter, embodiments of the disclosure will be described in detail with reference to the accompanying drawings.
The vehicle 100 further includes, as operating devices, a steering wheel (steering device) 40, a steering angle sensor 41 that detects the steering amount of the steering wheel, an accelerator pedal (accelerator operator) 42, an accelerator depression amount sensor 43 that detects the depression amount (operation amount) of the accelerator pedal 42, a brake pedal (brake operator) 44, a brake depression amount sensor 45 that detects the depression amount (operation amount) of the brake pedal 44, and a vehicle speed sensor 46.
The vehicle 100 further includes a battery 60, a front wheel drive circuit 61, and a rear wheel drive circuit 62 as a drive system, and an electronic control unit (ECU) 50 as a control system. The electronic control unit 50 is a unit including a CPU (not shown) for operational control, a memory (not shown) for storing operational programs, a memory (not shown) for saving data, etc., and is configured as, for example, a microcomputer. The electronic control unit 50 is configured to control the front wheel drive circuit 61 and the rear wheel drive circuit 62, and to control the power supplied from the battery 60 to the front wheel drive motor 31 and the rear wheel drive motor 32, thereby controlling the driving forces thereof.
The driving force control apparatus 1 of this embodiment is an apparatus that determines the front and rear wheel drive distribution, and in this embodiment, the electronic control unit 50 is configured with a program that enables the CPU (not shown) to operate. The driving force control apparatus 1 includes a driving acceleration calculation part 2, a lateral acceleration calculation part 3, maps 4a and 4b, a drive distribution determination part 5, and an output part 6.
The driving acceleration calculation part 2 calculates the positive or negative standard driving acceleration XG (target value of acceleration) based on the depression amount of the accelerator pedal 42 detected by the accelerator depression amount sensor 43 and the current vehicle speed V detected by the vehicle speed sensor 46, and inputs the same to the drive distribution determination part 5. This is because the actual driving acceleration of the vehicle is considered to be determined by the difference between the driving force determined by the depression amount of the accelerator pedal 42 and the air resistance and regenerative resistance determined by the current vehicle speed V.
The driving acceleration calculation part 2 further calculates the negative standard driving acceleration XG (target value of acceleration) based on the depression amount of the brake pedal 44 detected by the brake depression amount sensor 45 and the current vehicle speed V detected by the vehicle speed sensor 46, and inputs the same to the drive distribution determination part 5. This is because the actual driving acceleration of the vehicle is considered to be determined by the sum of the braking force determined by the depression amount of the brake pedal 44 and the air resistance and regenerative resistance determined by the current vehicle speed V.
The lateral acceleration calculation part 3 calculates the positive or negative standard lateral acceleration YG (target value of acceleration) based on the steering angle of the steering wheel (steering device) 40 detected by the steering angle sensor 41 and the current vehicle speed V detected by the vehicle speed sensor 46, and inputs the same to the drive distribution determination part 5. Since the control is based on the amounts instructed by the driver such as accelerator depression amount and brake operation amount, responsiveness is improved compared to feedback control based only on actual acceleration or the like.
The maps 4a and 4b are data in which the vehicle speed V, standard lateral acceleration YG, standard driving acceleration XG, and optimal rear wheel drive distribution (rear wheel distribution ratio Rr) are recorded in advance, and are saved in the memory (not shown) that saves data of the electronic control unit (ECU) 50 for the drive distribution determination part 5 to refer to. Details will be described later.
The drive distribution determination part 5 is a program that determines the front and rear wheel drive distribution based on the standard driving acceleration XG input from the driving acceleration calculation part 2, the standard lateral acceleration YG input from the lateral acceleration calculation part 3, and the vehicle speed V input from the vehicle speed sensor 46. The detailed operation will be described later.
The output part 6 is a program that controls the front wheel drive circuit 61 and the rear wheel drive circuit 62 in accordance with the front and rear wheel drive distribution determined by the drive distribution determination part 5, and controls the power supplied from the battery 60 to the front wheel drive motor 31 and the rear wheel drive motor 32 to control the driving forces thereof.
Next, the control of the front and rear wheel drive distribution performed by the driving force control apparatus 1 configured as above will be described for each condition.
(1) Dynamic Load Ratio Distribution Control (Best Traction Control) when Traveling Straight in the Normal Mode
The dynamic load ratio distribution curve L1 is a curve of the dynamic load ratio (horizontal axis) applied to the front wheels 21 and the rear wheels 22 with respect to the standard driving acceleration XG (vertical axis). This dynamic load ratio is the ratio of the loads Wf and Wr applied to the front wheels 21 and the rear wheels 22 shown in
In the dynamic load ratio distribution control that determines the front and rear wheel drive distribution in accordance with this dynamic load ratio distribution curve L1, the ratios of driving force to dynamic load at the front wheels 21 and the rear wheels 22 (Ff/Wf and Fr/Wr in
However, since slippage is generally likely to occur during deceleration, a safety factor is applied in design to reduce the absolute acceleration value of each traction limit line (not shown).
(2) Rear Wheel-Biased Distribution Control (Best Handling Control) when Traveling Straight in the Normal Mode
In the Normal mode, when the standard driving acceleration XG is small, specifically, in a standard driving acceleration XG range inside the traction limit line Ls of “SNOW” (see
As shown in
The switching between the dynamic load ratio distribution control and the rear wheel-biased distribution control is performed along a transition curve L3 along the lower side of the upper traction limit line Ls of “SNOW” (see
(3) Front and Rear Wheel Drive Distribution Control when Turning in the Normal Mode
The drive distribution determination part 5 performs the dynamic load ratio distribution control and the rear wheel-biased distribution control when turning as well as when traveling straight. However, considering the rolling direction moment generated by the lateral acceleration ay when the vehicle turns as shown in
The reason for this is that, for example, when the vehicle turns to the right, as shown in
Further, when the vehicle turns to the left, particularly, when the vehicle is accelerating, for the same reason, the load on the left front wheel 21a decreases the most, making it more likely to slip.
Therefore, from the viewpoint of preventing slippage, the dynamic load ratio distribution curve L1a and the rear wheel-biased distribution curve L2a for turning are set to have a higher rear wheel drive distribution than the dynamic load ratio distribution curve L1 and the rear wheel-biased distribution curve L2a when traveling straight, in order to further reduce the driving force distribution to the right front wheel 21b and the left front wheel 21a.
In the Sport mode, when the standard driving acceleration XG is inside the traction limit line Lw of “WET” (see
However, unlike the Normal mode, the first input amount XG1, which is the upper limit standard driving acceleration XG (positive value) of the range in which rear wheel-biased distribution control is performed, and the second input amount XG2, which is the lower limit standard driving acceleration XG (negative value), are set close to the traction limit line Lw of “WET” shown in
The switching between the Normal mode and the Sport mode can be performed by a mode switching operation of the driver. As described above, in the Normal mode and the Sport mode, the first input amount XG1, which is the upper limit of the standard driving acceleration XG range in which rear wheel-biased distribution control is performed, and the second input amount XG2, which is the lower limit, are different, and these values can be changed by the mode switching operation of the driver.
This configuration provides the Sport mode which assumes only dry and wet road surfaces and expands the acceleration/deceleration range in which rear wheel-biased distribution control is performed, and the Normal mode which assumes snowy road surfaces in addition to dry and wet road surfaces and narrows the acceleration/deceleration range in which rear wheel-biased distribution control is performed, and can ensure a wide region of high handling performance in the Sport mode when the road surface is known to be not slippery as well as ensure stability in the Normal mode when the road surface is known to be slippery.
The drive distribution determination part 5 is configured not to perform rear wheel-biased distribution control when the standard lateral acceleration YG calculated based on the steering amount of the steering wheel (steering device) 40 and the vehicle speed V and input from the lateral acceleration calculation part 3 is equal to or larger than the third input amount YG3, even if the standard driving acceleration XG is small. Here, the third input amount YG3 refers to the standard lateral acceleration YG at the limit at which the drive wheels do not slip on the road surface in a predetermined condition. This “standard lateral acceleration YG at the limit at which the drive wheels do not slip on the road surface in a predetermined condition” is, for example, standard lateral acceleration YG that does not exceed the traction limit in a predetermined road surface condition as shown in
As shown in
On the other hand, in the region where the standard lateral acceleration YG to the right of the third input amount YG3 is high, rear wheel-biased distribution control is not performed regardless of the standard driving acceleration XG.
According to this configuration, when lateral acceleration occurs due to sudden steering, rear wheel-biased distribution control is not performed, thereby making it possible to ensure traveling stability. Furthermore, since the control is based on the amount instructed by the driver such as the steering angle of the steering wheel 40, responsiveness is improved compared to feedback based only on actual acceleration or the like.
The drive distribution determination part 5 is configured not to perform rear wheel-biased distribution control when the vehicle speed V detected by the vehicle speed sensor 46 shown in
As shown in
According to this configuration, when the vehicle travels at a low speed immediately after starting and immediately before stopping which requires traction, or when the vehicle travels at a high speed which requires traveling stability, rear wheel-biased distribution control (best handling control) is not performed regardless of the front/rear and left/right acceleration/deceleration, and dynamic load ratio control (best traction control) is performed. Therefore, traction and traveling stability can be ensured in these cases.
Furthermore, with preparation of such maps 4a and 4b, the corresponding front and rear wheel drive distribution can be immediately obtained when the drive distribution determination part 5 specifies the vehicle speed V and the standard driving acceleration XG. Therefore, the rear wheel drive distribution can be determined more quickly compared to calculation based on computation, thereby increasing the speed of controlling the driving forces for the front and rear wheels.
Although embodiments of the disclosure have been described above, the disclosure is not limited to the above embodiments, and various modifications are possible within the scope of the claims and the scope of the technical ideas described in the specification and drawings. For example, the above embodiment illustrates an example of application of the driving force control apparatus 1 to the vehicle 100 with a front and rear twin-motor configuration that includes the front wheel drive motor 31 and the rear wheel drive motor 32. However, the disclosure is not limited thereto, and can also be applied to a vehicle with a four-motor configuration that has a drive motor for each of the four wheels, a single-motor configuration that distributes the driving force of one drive motor to the four wheels, and even a vehicle with a configuration that replaces each of these motors with a gasoline engine.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-212132 | Dec 2023 | JP | national |
