Patent Application
20200139782
The present invention relates to a control system for a variable damping force damper for controlling the roll attitude based on a motion state quantity.
In recent years, various types of variable damping force dampers, which can vary the damping force in steps or continuously, have been developed for use in suspensions of automobiles. Known mechanisms for varying the damping force include a mechanical type in which the area of an orifice provided in the piston of the damper is varied by a rotary valve and an magnet-rheological fluid (MRF) type in which MRF is used as hydraulic oil and the viscosity of the MRF is controlled by a magnetic fluid valve provided in the piston. In a vehicle equipped with such variable damping force dampers (may be simply referred to as dampers), by variably controlling the damping force of each damper depending on the running state of the vehicle, it is possible to improve the steering stability and the ride comfort.
One known technique to improve the ride comfort is roll control, in which the rolling of the vehicle body is suppressed to optimize the attitude of the vehicle body. In the roll control, in order to suppress the rolling of the vehicle body or sprung mass, the damping force of each damper is controlled such that the larger the roll angular speed (roll rate), lateral acceleration, front-wheel steering angle, etc. of the vehicle body become, the larger the damping force becomes (see JP2015-047906A, for example).
On the other hand, there is known a vehicle control system that performs skyhook control by controlling the braking/driving force produced by electric motors provided for the respective four wheels, without using variable damping force dampers (see JP2016-104605A, for example). The dampers (shock absorbers) used in the control system disclosed in JP2016-104605A have a constant damping coefficient, and thus, the damping force generated by each damper for a given stroke speed is not variable. Each electric motor is controlled to generate a target torque that is a sum of a target driving torque for driving and a target torque for damping vibration. The target torque for damping vibration is determined based on a target vertical force for damping the vibration of the vehicle, which is obtained as a sum of a first vertical force computed by multiplying a vertical speed of the vehicle body by a first control constant and a second vertical force computed by multiplying a stroke speed of the damper by a second control constant, where the second control constant is set to a negative value such that the second vertical force is proportional to the roll stroke speed and has a direction opposite to an actual damping force produced by the damper. Thus, the vertical force generated by the electric motor includes a force having a direction opposite to an actual damping force produced by the damper, and therefore, an apparent damping force generated by the damper is reduced even though the damper has a constant damping coefficient, whereby the ride comfort is improved in a high frequency region. In an embodiment disclosed in JP2016-104605A, the stroke speed includes a roll stroke speed computed by subtracting a sprung mass roll angular speed from an unsprung mass roll angular speed.
Incidentally, in the roll control using the variable damping force dampers, when the damping force (or the damping coefficient) of the dampers is increased, a roll damping ratio, which is determined in dependence on the damping coefficient, is increased. A roll damping ratio of 1 (one) means critical damping. If the roll damping ratio becomes one or higher, a further increase in the roll damping force is not effective in suppressing the roll vibration. On the other hand, even in a region where the roll damping ratio is one or higher, an increase in the roll damping force reduces a transient roll response, but since it also slows the roll response, the roll damping force was conventionally controlled to keep the roll damping ratio below one.
However, when a vehicle is turning, not only the sprung mass rolls, but also the unsprung mass rolls due to deflection of the tires, and therefore, when the roll of the unsprung mass is taken into consideration, there is room for further improvement in the roll attitude control of the vehicle in a period from start of steering to a steady turning state.
In view of such background, a primary object of the present invention is to provide a control system for a variable damping force damper that can suppress the rolling of the vehicle body more effectively.
To achieve the above object, one embodiment of the present invention provides a control system (20) for a variable damping force damper (6), comprising: a motion state quantity sensors (11-16) configured to detect motion state quantities (V, δf) of a vehicle (1); a roll damping force base value setting unit (22) configured to set a roll damping force base value (DFb) based on the motion state quantities, the roll damping force base value being used to compute a target damping force (DFr) of the variable damping force damper (6) for controlling a roll attitude of the vehicle; a roll rate computation unit (23) configured to compute a sprung mass roll rate (ωs) and an unsprung mass roll rate (ωu) of the vehicle based on the motion state quantities (V, δf); and a roll damping force correction unit (24) configured to correct the roll damping force base value (DFb) based on a roll rate difference (Δω) that is a difference between the sprung mass roll rate (ωs) and the unsprung mass roll rate (ωu) and to output the corrected roll damping force base value as the target damping force (DFr).
Thus, by correcting the roll damping force base value based on the roll rate difference and using the corrected roll damping force base value as the target damping force of the variable damping force damper, the rolling of the vehicle body can be suppressed more effectively than when such correction is not made.
Preferably, the roll damping force correction unit (24) is configured to normalize the unsprung mass roll rate (ωu) and the sprung mass roll rate (ωs) relative to each other based on an unsprung mass roll stiffness and a sprung mass roll stiffness and to compute the roll rate difference (Δω) based on absolute values of the normalized unsprung mass roll rate (ωu) and sprung mass roll rate (ωs).
Thereby, the roll rate difference between the sprung mass roll rate and the unsprung mass roll rate can be computed properly.
Preferably, the roll damping force correction unit (24) is configured to correct the roll damping force base value (DFb) to be larger in absolute value than before correction when the unsprung mass roll rate (ωu) is larger in absolute value than the sprung mass roll rate (ωs) after normalization and to correct the roll damping force base value (DFb) to be smaller in absolute value than before correction when the normalized unsprung mass roll rate (ωu) is smaller in absolute value than the sprung mass roll rate (ωs) after normalization.
Thereby, in a situation where the absolute value of the unsprung mass roll rate is large, a damping force exceeding (in absolute value) the damping force corresponding to the critical damping of the sprung mass is generated to advance the phase of the unsprung mass roll rate so that the ground contact load distribution between the left and right wheels (tires) is changed quickly. In addition, in a situation where the absolute value of the unsprung mass roll rate is small, a damping force smaller in absolute value than the damping force corresponding to the critical damping of the sprung mass is generated to advance the phase of the sprung mass roll rate so that the phase difference between the sprung mass roll rate and the unsprung mass roll rate is reduced, which suppresses an increase in the delay of the roll response.
According to another aspect of the present invention, there is provided a control system (20) for a variable damping force damper (6), comprising: motion state quantity sensors (11-16) configured to detect motion state quantities (V, δf) of a vehicle (1); a roll damping force base value setting unit (22) configured to set a roll damping force base value (DFb) based on the motion state quantities, the roll damping force base value being used to compute a target damping force (DFr) of the variable damping force damper (6) for controlling a roll attitude of the vehicle; a roll rate computation unit (23) configured to compute a sprung mass roll rate (ωs) and an unsprung mass roll rate (ωu) of the vehicle based on the motion state quantities (V, δf); and a roll damping force correction unit (24) configured to correct the roll damping force base value (DFb) based on the sprung mass roll rate (ωs) and the unsprung mass roll rate (ωu) and to output the corrected roll damping force base value as the target damping force (DFr), wherein the roll damping force correction unit (24) is configured to correct the roll damping force base value (DFb) so as to be larger in absolute value than before correction when the sprung mass roll rate (ωs) and the unsprung mass roll rate (ωu) are both positive and are increasing in absolute value with time, to correct the roll damping force base value (DFb) so as to be smaller in absolute value than before correction when the sprung mass roll rate (ωs) and the unsprung mass roll rate (ωu) are both positive and decrease in absolute value with time, to correct the roll damping force base value (DFb) so as to be larger in absolute value than before correction when the sprung mass roll rate (ωs) and the unsprung mass roll rate (ωu) are both negative and are increasing in absolute value with time, and to correct the roll damping force base value (DFb) so as to be smaller in absolute value than before correction when the sprung mass roll rate (ωs) and the unsprung mass roll rate (ωu) are both negative and are decreasing in absolute value with time.
This arrangement also can suppress the rolling of the vehicle body more effectively than a conventional arrangement that is not equipped with the above-mentioned roll damping force correction unit.
Thus, according to an embodiment of the present invention, it is possible to provide a control system for a variable damping force damper that can suppress the rolling of the vehicle body more effectively.
In the following, an embodiment of the present invention will be described in detail with reference to the drawings.
The vehicle 1 includes an Electronic Control Unit (ECU) 8 and various sensors, such as vehicle speed sensors 11, a steering angle sensor 12, a roll rate sensor 13, a pitch rate sensor 14, a lateral acceleration sensor 15, a longitudinal (fore-and-aft) acceleration sensor 16, stroke sensors 17, and the like. The ECU 8 is utilized for various control. The vehicle speed sensors 11 are provided for the respective wheels 3 and output pulse signals generated in accordance with the wheel speeds of the respective wheels 3 to the ECU 8. The steering angle sensor 12 provides the ECU 8 with a signal generated in accordance with a steering wheel angle, which corresponds to a steering angle δf of the front wheels 3F. The roll rate sensor 13 provides the ECU 8 with a signal representing the roll rate ω of the vehicle 1, and the pitch rate sensor 14 provides the ECU 8 with a signal representing the pitch rate ωx of the vehicle 1. The lateral acceleration sensor 15 and the longitudinal acceleration sensor 16 provide the ECU 8 with signals representing the lateral acceleration Gy and the longitudinal (fore-and-aft) acceleration Gx of the vehicle 1, respectively. Each stroke sensor 17 is positioned near the wheelhouse of the corresponding wheel 3 and outputs a signal corresponding to the damper stroke Sd (stroke of the corresponding suspension 7) to the ECU 8. These sensors 11-17 serve as motion state quantity detectors configured to detect motion state quantities of the vehicle 1.
The ECU 8 is constituted of a microcomputer, a ROM, a RAM, peripheral circuits, an input/output interface, various drivers, and the like, and is connected to the dampers 6 of the respective wheels 3 and the sensors 11-17 via a communication line such as a Controller Area Network (CAN). The control system 20 is constituted of the ECU 8, the sensors 11-17, and the like.
The ECU 8 obtains the wheel speeds of the respective wheels 3 based on the signals from the vehicle speed sensors 11 and obtains a vehicle speed V by averaging the wheel speeds. The ECU 8 also obtains the steering angle δf, which is a steering angle of the front wheels 3F, based on the signal from the steering angle sensor 12. Further, the ECU 8 obtains the roll rate ω, the pitch rate ωx, the lateral acceleration Gy, the longitudinal acceleration Gx, and the damper strokes Sd generated in the vehicle 1, based on the signals from the roll rate sensor 13, the pitch rate sensor 14, the lateral acceleration sensor 15, the longitudinal acceleration sensor 16, and the stroke sensors 17.
Each damper 6 includes a cylinder and a piston rod received in the cylinder. A lower end of the cylinder is connected to an upper surface of the suspension arm 4, which may be considered as a wheel-side member. An upper end of the piston rod is connected to a damper base (an upper part of the wheelhouse), which may be considered as a vehicle body-side member. Each damper 6 may have any known structure including a coil for increasing and decreasing the damping force (or damping coefficient), such as an MLV coil or an electromagnetic coil, and increases and decreases the damping force (or damping coefficient) in accordance with the electric current supplied from the ECU 8 to the coil.
In the present disclosure, expressions such as “the damping force becomes larger” or “the damping force is made large” mean that the damping force becomes large or is made greater in absolute value unless otherwise mentioned. Conversely, an expression “the damping force becomes smaller” means that the damping force becomes smaller in absolute value unless otherwise mentioned. On the other hand, expressions such as “the damping force is high” or “the damping force is low” mean that the damping force is large or small in algebraic value. Therefore, for example, when the damping force has a negative value and is made lower, the damping force is made larger (or increased) in absolute value.
Besides the roll attitude control unit 21 shown in
Further, the ECU 8 includes an electric current control unit that computes or selects a damping force to be generated for each wheel 3 based on the damping forces computed by the above control units, sets an electric current corresponding to the damping force, and supplies the damper 6 of each wheel 3 with the set electric current. When setting the electric current, the electric current control unit of the ECU 8 may refer to an electric current setting map shown in
These functional units may be conventional ones, and a detailed description thereof is omitted here.
As shown in
Also, the roll attitude control unit 21 includes a vehicle model 23. The vehicle model 23 functions as a roll rate computation unit that computes the sprung mass roll rate ωs and the unsprung mass roll rate ωu of the vehicle 1 based on the motion state quantities of the vehicle 1, such as the steering angle δf of the front wheels 3F and the vehicle speed V.
The roll attitude control unit 21 further includes a roll damping force correction unit 24 that corrects the roll damping force base value DFb based on a roll rate difference Δω, which is a difference between the sprung mass roll rate ωs and the unsprung mass roll rate ωu.
The roll damping force correction unit 24 will be described in the following, but before that, the purpose of the correction will be described with reference to
As a result of the above-described roll behavior of the vehicle 1, the unsprung mass roll rate ωu is advanced relative to the sprung mass roll rate ωs by a prescribed phase difference, as shown in
However, in a period (1) in
These will be explained concretely below with reference to
In this model, as shown in (A) of
Therefore, by correcting the conventional target damping force of the dampers 6 indicated by the imaginary line in
Likewise, as shown in (3)
The corrected target damping force described above may be obtained by using a virtual roll rate ωh for damping force computation shown by an imaginary line in
To put it in a different way, the correction quantity is added to the target damping force (or corrects the target damping force) to make the target damping force larger in absolute value in a region where the sprung mass roll rate ωs and the unsprung mass roll rate ωu are both positive and are increasing in absolute value with time or a region where the sprung mass roll rate ωs and the unsprung mass roll rate ωu are both negative and are decreasing in absolute value with time, and to make the target damping force smaller in absolute value in a region where the sprung mass roll rate ωs and the unsprung mass roll rate ωu are both positive and are decreasing in absolute value with time or a region where the sprung mass roll rate ωs and the unsprung mass roll rate ωu are both negative and are decreasing in absolute value with time.
Based on the above idea, the roll damping force correction unit 24 shown in
Thus, in the roll attitude control unit 21 of the present embodiment, instead of computing the target damping force by using the virtual roll rate ωh as shown in
In another embodiment, the roll attitude control unit 21 may compute the virtual roll rate ωh and compute the target damping force based on the virtual roll rate ωh, which is essentially the same process as correcting the roll damping force base value DFb.
In the following, a concrete process performed by the roll damping force correction unit 24 shown in
The unsprung mass roll rate ωu is normalized by a normalization unit 25. Specifically, the normalization unit 25 normalizes the unsprung mass roll rate ωu by multiplying the unsprung mass roll rate ωu by the ratio of the unsprung mass roll stiffness to the sprung mass roll stiffness. This is because the unsprung mass roll rate ωu has a larger amplitude than the sprung mass roll rate ωs owing to the difference in the roll stiffness as mentioned above, and hence, it is necessary to correct the unsprung mass roll rate ωu to have an amplitude comparable to that of the sprung mass roll rate ωs.
The sprung mass roll rate ωs is converted to an absolute value by a first absolute value computation unit 26, and the normalized unsprung mass roll rate ωu is converted to an absolute value by a second absolute value computation unit 27. The absolute value of the sprung mass roll rate ωs and the absolute value of the unsprung mass roll rate ωu are used in the arithmetic processing performed by a difference computation unit 28. The difference computation unit 28 computes the roll rate difference Δω by subtracting the absolute value of the sprung mass roll rate ωs from the absolute value of the unsprung mass roll rate ωu.
Because the unsprung mass roll rate ωu is normalized based on the ratio of the unsprung mass roll stiffness to the sprung mass roll stiffness as described above, it is possible to properly compute the roll rate difference Δω.
The roll rate difference Δω is used in the processing performed by a damping force correction quantity computation unit 29 and a first switching unit 30. The damping force correction quantity computation unit 29 refers to a map (“POSI” in
The first switching unit 30 switches the output thereof between the two damping force correction quantity absolute values |DFc| computed by the damping force correction quantity computation unit 29, based on the sign (positive or negative) of the roll rate difference Δω such that the damping force correction quantity absolute value |DFc| corresponding to the sign of the roll rate difference Δω is output.
The sprung mass roll rate ωs computed by the vehicle model 23 and the unsprung mass roll rate ωu normalized by the normalization unit 25 are used in the processing performed by a maximum value selection unit 31 and a minimum value selection unit 32. The maximum value selection unit 31 selects a maximum roll rate ωmax, which is the maximum value (in algebraic value) of the sprung mass roll rate ωs and the normalized unsprung mass roll rate ωu, while the minimum value selection unit 32 selects a minimum roll rate ωmin, which is the minimum value (in algebraic value) of the sprung mass roll rate ωs and the normalized unsprung mass roll rate ωu. The maximum roll rate ωmax and the minimum roll rate ωmin are converted to absolute values by a third absolute value computation unit 33 and a fourth absolute value computation unit 34, respectively, and the obtained absolute values are compared by a comparing unit 35 to determine which is larger. The result of comparison by the comparing unit 35, the maximum roll rate ωmax, and the minimum roll rate ωmin are used in the processing performed by a second switching unit 36. The second switching unit 36 outputs one of the maximum roll rate ωmax and the minimum roll rate ωmin that has a larger absolute value to a sign setting unit 37, in accordance with the comparison result.
The sign setting unit 37 sets a sign (namely, “+1” or “−1”) according to the sign of the one of the maximum roll rate ωmax and the minimum roll rate ωmin selected by the second switching unit 36.
The damping force correction quantity absolute value |DFc| from the first switching unit 30 and the sign from the sign setting unit 37 are multiplied by each other at a multiplication unit 38, and the result of the multiplication is output to a correction unit 39 as the damping force correction quantity DFc. The correction unit 39 is an adder and adds the damping force correction quantity DFc to the roll damping force base value DFb from the roll damping force base value setting unit 22 to correct the roll damping force base value DFb, whereby the roll damping force DFr is computed as the corrected roll damping force base value DFb. The roll damping force DFr is substantially identical with the corrected target damping force in
As described above, the roll damping force correction unit 24 corrects the roll damping force base value DFb by using the roll rate difference Δω that is a difference between the sprung mass roll rate ωs and the unsprung mass roll rate ωu. Thereby, the rolling of the vehicle body 2 can be suppressed more effectively.
As shown in (A) and (B) of
Because the roll damping force correction unit 24 computes the damping force correction quantity DFc based on the roll rate difference Δω as described above, when the roll rate difference Δω has a positive value, the damping force correction quantity DFc is computed to have a sign for increasing the target damping force in absolute value. On the other hand, when the roll rate difference Δω has a negative value, the damping force correction quantity DFc is computed to have a sign for decreasing the target damping force in absolute value. And, the damping force correction quantity DFc becomes large when the absolute value of the roll rate difference Δω becomes large. Also, for example, when the roll rate difference Δω has a positive value and the unsprung mass roll rate ωu is higher (larger in algebraic value) than the sprung mass roll rate ωs ((1) in
Owing to the above features, as shown in
A concrete embodiment of the present invention has been described in the foregoing, but the present invention should not be limited by the foregoing embodiment and various modifications and alterations are possible within the scope of the present invention. The concrete structure, arrangement, number, processing details, etc. of the component parts/units of the embodiment may be appropriately changed within the scope of the present invention. On the other hand, not all of the component parts/units shown in the foregoing embodiments are necessarily indispensable, and they may be selectively used as appropriate.
In the foregoing embodiment, the unsprung mass roll rate ωu was normalized by being multiplied with the ratio of the unsprung mass roll stiffness to the sprung mass roll stiffness. However, it may be also possible to normalize the sprung mass roll rate ωs by multiplying the sprung mass roll rate ωs by the ratio of the sprung mass roll stiffness to the unsprung mass roll stiffness. Namely, the unsprung mass roll rate ωu and the sprung mass roll rate ωs may be preferably normalized relative to each other.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018208691 | Nov 2018 | JP | national |
