JPH04197812A - Method for controlling active suspension for vehicle - Google Patents

Abstract

PURPOSE:To ease a feeling of stiffness mainly on deceleration of a vehicle by providing a reference car height changing circuit which lowers reference car height as the absolute value of longitudinal (g) or longitudinal (g) on deceleration increases. CONSTITUTION:A longitudinal acceleration signal detected by a longitudinal (g) sensor 14 is converted by hysterisis 17 and a dead zone circuit 18 into such a signal that does not react with the normal fluctuation of longitudinal (g) during normal running of a car but with large pitching of the car body as when an accelerator is fully released or when the car is braked by more than a middle level, and the signal is then input to a longitudinal load transfer calculating circuit 19 and a reference car height changing circuit 28. The reference car height changing circuit 28 changes and sets reference car height proportionately to the absolute value of longitudinal (g) in response to the signal input. An actual suspension stroke change signal based on a suspension stroke sensor 13 and a vehicle height adjusting switch 16 is corrected by a reference car height variable signal so that the higher the absoulte value the lower the desired value of car height regarding all of the four wheels.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for controlling an active suspension for a motor vehicle.

Conventional technology At least the vertical relative displacement of the sprung and unsprung parts of each suspension is detected, and the injection and discharge of fluid such as liquid or gas is controlled independently for each suspension so as to maintain the suspension at the standard vehicle height. In the active suspension for automobiles, two front and rear sensors and two lateral sensors are installed to detect the longitudinal acceleration (2 longitudinal) and lateral acceleration (51 lateral) of the vehicle body, and the sensor detects the longitudinal acceleration (2 longitudinal) and the lateral acceleration (51 lateral) of the vehicle body. Predict the pitch and roll of the vehicle body from information on 2 and lateral 2.

A system in which fluid injection and discharge control is performed by calculating the amount of fluid injection and discharge necessary for suppressing pitching and keeling for each suspension is disclosed in Japanese Patent Application Laid-Open No. 2-95.
It is published in Publication No. 911.

Problems to be Solved by the Invention As mentioned above, in an active suspension, the so-called feed/vine control, which detects the amount of vertical relative displacement between the sprung and unsprung portions of the suspension and controls the suspension to maintain the reference vehicle height, has the following problems: Front and back 2 during acceleration/deceleration and turning
Combining so-called feedforward control, which detects lateral and lateral 2 and suppresses predicted pitching and roll of the vehicle body, can bring about the effect that the vehicle body posture can be maintained at the target posture without delay. Since the sinking of the front wheels during braking of the vehicle is reduced to zero, a problem arises in that it gives the driver an unnatural feeling of stiffness, especially during sudden braking.

The main object of the present invention is to alleviate such a stiff feeling when the vehicle is decelerated.

Means for Solving the Problems As described above, the present invention detects at least the vertical relative displacement of the sprung and unsprung portions of each suspension, and injects and discharges fluid for each suspension to maintain each suspension at a reference vehicle height. It has a feedback control system that controls the vehicle body, and a feedforward control system that detects at least the longitudinal acceleration of the vehicle body and controls fluid injection and discharge for each suspension so as to suppress pitching of the vehicle body that is predicted during acceleration and deceleration. In an active suspension for an automobile, a reference vehicle height change circuit is provided that lowers the reference vehicle height as the absolute value of the longitudinal acceleration or the acceleration during deceleration increases, thereby suppressing pitching of the vehicle body during acceleration and deceleration. The present invention is characterized in that the vehicle height of the entire vehicle body is controlled to be lowered as the absolute value of the longitudinal acceleration or the acceleration during deceleration increases.

As a result of the above, the greater the acceleration during acceleration or deceleration, the deeper the entire vehicle sinks, which almost eliminates the unnatural feeling of stiffness felt by passengers including the driver, and reduces the acceleration during deceleration. During sudden braking, the vehicle body becomes lower, which lowers the height of the vehicle's center of gravity and reduces the amount of load transfer in the longitudinal direction.The amount of change in tire ground reaction force becomes smaller than before, resulting in braking ability (during braking). A vehicle with a high limit 2) can be obtained.

Example Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a system diagram showing an example of an active suspension control system to which the present invention is applied;
In the figure, 1 and 12 are the suspensions for the left and right front wheels, and 13 and 14 are the suspensions for the left and right rear wheels. Each suspension is a gas spring section in which an oil chamber A and a sealed gas chamber B are separated by a diaphragm C. The oil chamber A and the oil chamber F of the oil cylinder E are communicated via an orifice G, and one end of the oil cylinder E (for example, the bottom surface of the cylinder) is connected to a wheel side member such as a suspension arm, and the other end (for example, The piston rods are connected to the vehicle body side members, and oil flows between the oil cylinder and the oil chambers F and A of the gas spring part through the orifice G to generate an appropriate damping force against vertical loads. , shows an example employing a conventionally known hydro-pneumatic suspension in which a spring action is obtained by the volumetric elasticity of gas sealed in a gas chamber B via a diaphragm C.

21.22, 23.24 supply oil to the oil chamber F (and oil chamber A of the gas spring part) of the oil cylinder E of each suspension, and discharge oil from the oil chamber F (and A). a control valve, each of these control valves 2 l
+ 22 and 23 + 2 s are independently controlled by valve drive signals from the controller 3, which will be described later.

4 is an oil tank, and 5 is an oil pump. The oil pump 5 is rotationally driven by the engine 6, but in the illustrated embodiment, the oil pump 5' for power steering and the oil pump 5 are in tandem, and the oil pump 5 is driven by the engine 6. An example is shown in which the re-extraction pumps 5 and 5' are driven to rotate at the same time.

The oil discharged from the oil pump 5 passes through the check valve 7 and is accumulated in the high-pressure accumulator 8, and when one or more of the control valves is switched to the resident side, the oil is discharged from the control valve switched to the injection side. High pressure oil is supplied to the oil chamber of one or more suspensions, and when one or more of the control valves is switched to the discharge side, one of the control valves switched to the discharge side Alternatively, the oil in the oil chambers of two or more suspensions is drained and flows into the oil tank 4 through the oil cooler 9. 81 is a pressure sensor that detects the internal pressure of the high pressure accumulator 8.

10 is a relief valve, 11 is a load/unload valve, and the load/unload valve 11 receives an instruction from the controller 3 at the time of starting the engine, sets it to the unload state shown in the figure, reduces the engine start load, and completes the engine start. Then it will switch to load state.

Each suspension l 1, 12, 13.14 above has the following:
Two upper and lower sensors 12 for detecting the vertical acceleration on the spring and a suspension stroke sensor 13 for detecting the vertical relative displacement between the sprung mass and the unsprung mass, that is, changes in the expansion and contraction stroke of the suspension, are provided respectively. Detection signals are input to the controller 3, respectively, and the two front and rear sensors 14. detect the longitudinal acceleration (front and rear 2) of the vehicle body. Lateral 2 sensor 15 that detects the lateral acceleration (lateral 2) of the vehicle body (a device that calculates lateral 2 by calculation from the vehicle speed and steering angle detected by the vehicle speed sensor and steering angle sensor, or a steering torque, steering assist force, etc.) These detection signals are also input to the controller 3, and based on these signal inputs, the controller 3 performs the control described below.

Next, a first embodiment of the control logic of the controller 3 will be described with reference to FIG.

In Fig. 2, the part surrounded by a chain line is one of the front, rear, left, and right suspensions, for example, the left front wheel suspension 11.
Although not shown in FIG. 2, four sets of the same control logic are provided, and each suspension is controlled independently.

When the vertical acceleration and the suspension stroke change are detected by the respective sensors 12 and 13 in each suspension part, the vertical acceleration signal is passed through a low-pass filter LPF to reduce high frequency components.
The signal in the setting range near zero is removed through the gain G
Multiply by 1 to obtain a control instruction amount Q1 that matches the characteristics of the control valve.

The suspension stroke change signal is divided into two types: one that passes through the differentiation circuit DC and one that remains as is.The signal that passes through the differentiation circuit DC becomes a suspension stroke change speed signal that passes through the dead band circuit 2 and becomes a signal in the setting range near zero. is removed and further multiplied by gain G2 to obtain a control instruction amount Q2 that matches the control valve characteristics, and the suspension stroke change signal is generated by the reference vehicle height signal generation circuit H that reads the state of the vehicle height adjustment switch 16 and outputs the reference vehicle command. The difference from the high signal is taken to obtain an actual suspension stroke change signal, which is passed through a dead band circuit 3 to remove signals in the setting range near zero, and multiplied by a gain G3 to become a control instruction amount Q3 matching the control valve characteristics.

Control instruction amount Q+ in accordance with the control valve characteristics described above.

Q2. What is Q3? 1 For example, if the control valve is a flow control valve, consider the valve opening/closing characteristics and replace the amount of oil to be injected or discharged with the valve opening instruction time or valve opening degree on the injection side or discharge side of the control valve. It means that.

The above three control instruction amounts Ql, Q2. Q3 is added and converted through the control amount correction circuit R into a correction instruction amount Q that takes into account environmental conditions such as temperature and pressure loss due to differences in pipe length, and a control valve opening/closing signal is issued through the valve drive signal generation circuit W, and the control valve 21 is switched to the injection side or the discharge side, and the specified amount of oil is injected or discharged into the suspension 11.

In the above control, in the control based on vertical acceleration, the oil in the suspension 11 is drained in response to upward acceleration, and the oil is injected into the suspension 11 in response to downward acceleration. The suspension has a soft and highly damped suspension characteristic against forces from below, such as thrusting up, and maintains the vehicle height at the standard vehicle height against forces from above (i.e. the vehicle body), and controls the oil discharge. It works in conjunction with the stroke change speed and suspension stroke change control to create apparently stiff suspension characteristics to maintain the vehicle height, and also allows vertical acceleration signals to pass through a low-pass filter LPF to reduce unsprung resonance. The control specification prioritizes bouncing and a low-consumption ride that does not react much to vibrations in the high frequency range, and concentrates control on vibrations in the low frequency range near sprung mass resonance, consuming energy.

The vehicle height adjustment switch 16 is, for example, a switch for switching from normal vehicle height to high vehicle height, and when the normal vehicle height is selected, the reference vehicle height signal generation circuit H generates a low reference vehicle height signal. When the vehicle height adjustment switch 16 is switched to the high vehicle height side, the reference vehicle height signal generation circuit H generates a high reference vehicle height signal, and the control based on the suspension stroke change signal is a control that attempts to maintain the vehicle height at the reference vehicle height. When the standard vehicle height is switched from the low standard vehicle height to the high standard vehicle height, the oil injection control instruction amount Q3 is issued according to the deviation from the target standard vehicle height, and oil is injected into the suspension 1 to control the vehicle. If you raise the vehicle height to a height equal to the high standard vehicle height and return the vehicle height adjustment switch 16 to the normal vehicle height side, the oil discharge control instruction amount Q3 is issued according to the deviation from the target standard vehicle height, and the suspension 11 It works to drain the oil inside and lower the vehicle height to the normal standard vehicle height. The oil is put in and taken out of all the suspensions at the same time by changing the vehicle height adjustment switch 16.

With the vehicle height adjustment switch 16, the vehicle height can be adjusted in multiple stages of three or more stages or steplessly.

In addition to the control in normal driving conditions described in L, 4. Accurate vehicle posture control without delay when large accelerations are applied suddenly in the longitudinal or lateral direction, such as during sudden braking, sudden acceleration, and sharp turns. 14. 2 sensors front and rear to carry out. A control logic based on detection signals from the two lateral sensors 15 is provided.

That is, as shown in FIG. 2, the longitudinal acceleration signal detected by the two front and rear sensors 14 is converted into a hysteresis 17. The dead band circuit 18 converts the signal so that it does not respond to normal two-way changes in the front and back during normal driving, but acts when the vehicle body pitches significantly, such as during full acceleration or moderate or higher braking. It is input to the load movement amount calculation circuit 19 and the reference vehicle height change circuit 28.

Based on the input signal, the reference vehicle height changing circuit 28 adjusts the absolute value of the front and rear heights to 1x1, for example, as shown in FIG.
(+ 2 forward when accelerating.

The reference vehicle height is changed and set according to the direction of the front and rear (the backward direction 2 during deceleration is expressed as -, and the reference vehicle height is indicated by a + or - sign depending on the direction of the front and rear 2), and the reference vehicle height change amount signal is used to adjust the suspension An actual suspension stroke change signal based on a stroke sensor 13 and a vehicle height adjustment switch 16 is corrected, and vehicle height target values for all four wheels are lowered more as IXI increases.

The longitudinal load movement calculation circuit 19 calculates the input signal, vehicle specifications stored in advance, and the vehicle height adjustment switch 16.
The amount of load movement in the longitudinal direction is calculated from the ground 1-height information of the center of gravity of the vehicle obtained from the reference vehicle height change data corresponding to the front and back 2, and the calculation result is output to the suspension reaction force increase calculation circuit 20. . The suspension reaction force increase calculation circuit 20 calculates the amount of load movement in the longitudinal direction from the input information, the type of each suspension, the drive type (front wheel drive type, rear wheel drive type, four wheel drive type, etc.), etc. , the suspension reaction that would occur due to the amount of load movement mentioned above at each suspension position, taking into consideration the driving force and braking force applied to the tires, and taking into account the change in suspension geometry due to the change in the reference vehicle height corresponding to the front and rear. Calculate the force increase/decrease for each suspension.

The longitudinal acceleration No. 1 detected by the two lateral sensors 15 is also processed by the hysteresis circuit 21 as in the case of the two longitudinal sensors 14 described above. Through the dead zone circuit 22, the vehicle is made not to react to slight lateral fluctuations during normal running, and only signals exceeding a predetermined value are input to the roll moment calculation circuit 23. The roll moment calculation circuit 23 calculates the generated roll moment based on the vehicle specifications stored in advance from the input lateral 2 signal, the vehicle height adjustment fee, and the information on the ground clearance of the center of gravity obtained from 16. Furthermore, the generated roll moment is distributed between the moments of the front and rear wheels according to the target front and rear load transfer ratio, and the left and right load transfer of the front and rear wheels is calculated based on the height of the vehicle's center of gravity and the front and rear wheel tread information. The load movement amount distribution circuit 24 calculates the amount and outputs it to the suspension reaction force increase calculation circuit 25. In the suspension reaction force increase calculation circuit 25,
Calculate the suspension reaction force increase/decrease by taking into consideration the amount of load movement at each wheel, tire lateral force, vehicle height, suspension ring type, etc.

The control amount calculation circuit 26 calculates the suspension reaction force increase/decrease based on the front and rear 2 occurrences and the suspension reaction force increase/decrease based on the lateral 2 occurrence calculated by the two suspension reaction force increase calculation circuits 20 and 25, respectively.
In this step, the two suspension reaction force increases and decreases are added for each suspension to obtain the total suspension reaction force increase and decrease for each suspension, and the suspension show' internal pressure corresponding to the total suspension reaction force increase and decrease ( The amount of control for oil injection and discharge to maintain the internal pressure of the suspension's gas chamber is calculated for each suspension. Then, the control amount is determined by the control amount conversion circuit 27 for each suspension according to the valve specifications. (means changing to the valve opening instruction time), and the vertical acceleration on the spring.

Control instruction amount Ql, Q2 for each suspension based on the vertical relative displacement speed and vertical relative displacement amount of the sprung mass and unsprung mass
．． These Q1. Q2
, Q 3 , and Q a are passed through the control amount correction circuit R as described above and set as the correction instruction amount Q, and the valve drive signal generation circuit W issues a control valve opening/closing signal to perform oil injection or injection for each suspension. Control emissions.

When the front and rear 2 or lateral 2 acts on the vehicle body, the front and rear 2 or lateral 2
Based on this, load shifts in the longitudinal or lateral direction, resulting in changes in vehicle body posture in the pitching direction or in the roll direction, such as nose dive or swivel.゜If only feedback control is used to control the normal posture using the signal from the suspension stroke sensor that detects changes in the stroke of the suspension that are a result of lateral 2, the control will be delayed, especially for relatively large front and rear 2. Or, if the lateral 2 is applied suddenly and only for a very short time, there is a risk that the control will not be done in time and the vehicle body attitude will have to change once and then return to its normal attitude. , front and rear 2. which is the cause of changes in vehicle body posture as mentioned above. Detects the lateral position 2, calculates the amount of load movement of the vehicle body based on this, and also calculates the amount of load movement on the front, rear, left, and right suspensions, taking into account the braking force, driving force, or lateral force applied to the tires from the suspension type, drive type, etc. By adding feedforward control to the feedback control that calculates the increase or decrease in suspension reaction force that will occur for each suspension, and independently controls oil injection and discharge for each suspension based on the calculation result, Control delay can be significantly reduced and accurate vehicle body attitude control can be achieved.

However, simply reducing the control delay significantly by adding feedforward control during vehicle acceleration or deceleration will hardly cause the rear wheels or front wheels to sink when the vehicle accelerates or decelerates. A problem arises in that it gives an unnatural feeling of stiffness to the occupants including the occupants.

Therefore, in the present invention, as described above, control is added to lower the overall vehicle height by changing the reference vehicle height according to the absolute value of the two front and rear sensors 14 detected by the two front and rear sensors 14 during vehicle acceleration and deceleration. By controlling the car so that the larger the absolute value is, the more the car body sinks as a whole, the car body remains almost horizontal when the vehicle accelerates or decelerates, but when the front and back 2 are large, the car body sinks relatively largely overall. , the amount of sinking of the entire vehicle body changes depending on the size of the front and rear 2, such that when the front and rear 2 are small, the car body sinks less, and thereby the unnatural feeling of stiffness can be eliminated.

Furthermore, by lowering the vehicle height as the front and rear 2 become larger, the larger the front and rear 2, the lower the height of the vehicle's center of gravity and the lower the amount of load movement in the front and back direction, and the amount of change in tire ground reaction force becomes smaller than the conventional one. Tire slippage during acceleration and deceleration is reduced on all road surfaces including roads with a low coefficient of friction (low friction roads), and a vehicle with high acceleration and braking capabilities (limit 2 during acceleration and deceleration) can be obtained.

The above embodiment shows an example in which the vehicle height of the entire vehicle body is controlled to be lowered as the absolute value IXI of the front and rear 2 becomes larger. It is possible to eliminate the feeling of burr, reduce tire slippage during acceleration and deceleration, and obtain a vehicle with high acceleration and deceleration capabilities. With conventional active suspensions that suppress changes in attitude without delay, the stiffness felt by the driver is mainly experienced during sudden braking, and tire slippage becomes a problem mainly during braking. , the vehicle height may be lowered depending on the magnitude of occurrence 2 only during braking.

That is, the reference vehicle height changing circuit 28 is connected to the front and rear two sensors 1.
Based on the signal input from 4, as shown in FIG.
A control characteristic in which the reference vehicle height is changed and set lower as the absolute value increases only for the rearward direction, that is, the 2 of one sign among the front and rear 2, and the reference vehicle height is not changed for the forward direction, that is, the 2 of the tens sign. Then, the longitudinal load movement amount calculation circuit 19 and the suspension reaction force increase calculation circuit 2o also calculate the longitudinal load movement amount and the suspension reaction force increase/decrease in anticipation of the change in the standard vehicle height based on the reference vehicle height change data shown in FIG. By setting the calculation to be performed, control may be performed so that the entire vehicle sinks more as the backward direction increases only during braking.

The embodiment shown in Fig. 1 shows an example in which the present invention is applied to an active suspension using a hydropneumatic suspension, but the present invention also uses air or other gas as a spring (such as an auxiliary damper with low damping force). have)
The present invention can also be applied to an active suspension in which the vibration damping of the vehicle body is improved and the posture of the vehicle body is controlled by injecting or discharging the air or other gas.

Effects of the Invention As described above, according to the present invention, at least the vertical relative displacement of the sprung mass and unsprung mass is detected for each suspension, and fluid is injected independently for each suspension so as to maintain the suspension at the reference vehicle height. , has a feedback control system that controls the discharge, detects at least the front and back 2 that occurs on the vehicle body, and injects and discharges fluid for each suspension.
In the active suspension of a car that has a feedforward control system that controls pitching of the vehicle body during acceleration and deceleration, the above reference vehicle height increases as the absolute value of the two front and back or two of the two front and rear during deceleration increases. A reference vehicle height change circuit is installed to lower the vehicle height, suppressing beeching of the vehicle body during acceleration and deceleration, and lowering the vehicle height of the entire vehicle body as the absolute value of front and rear 2 or 2 during deceleration increases. As a result, the overall car body sinks more during sudden acceleration or sudden braking, eliminating the unnatural feeling of stiffness, and as 2 increases during deceleration, the overall Since the vehicle height is lower, tire slippage during braking is reduced on all road surfaces including low-P roads, making it possible to obtain a vehicle with high braking ability (braking limit 2), which has a great practical effect. It is something that can be brought about.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a fluid injection and discharge system showing an embodiment of the present invention, Fig. 2 is a block diagram showing an embodiment of the control logic of the present invention, and Figs. 3 and 4 are for the front and rear two. FIG. 6 is a diagram showing first and second examples of change characteristics of the reference vehicle height, respectively. 11.12,13,1 a...Suspension, 21
゜22.23.24...Control valve, 3...Controller, 12...Vertical acceleration sensor, 13...Suspension stroke sensor, 14...2 front and rear sensors, 15...2 lateral sensors, 16... Vehicle height adjustment switch, 19... Front-rear load movement amount calculation circuit, 20... Suspension reaction force increase calculation circuit, 26... Controlled amount calculation circuit, 27... Controlled amount conversion circuit, 28 ...Reference vehicle height change circuit. that's all

Claims (2)

[Claims] (1) A feedback control system that detects at least the vertical relative displacement of the sprung and unsprung parts of each suspension, and controls fluid injection and discharge independently for each suspension to maintain the suspension at the reference vehicle height. The system detects at least the longitudinal acceleration generated in the vehicle body, and uses this to inject and discharge fluid independently for each suspension.
In an active suspension of an automobile having a feedforward control system that controls pitching of the vehicle body during acceleration and deceleration, the reference vehicle height is lowered as the acceleration during deceleration increases among the longitudinal accelerations. An active vehicle for an automobile, which is equipped with a standard vehicle height change circuit, suppresses pitching of the vehicle body during acceleration and deceleration, and controls the vehicle height of the entire vehicle body to be lowered as the acceleration during deceleration increases. How to control the suspension. (2) In the active suspension for a vehicle according to claim (1), a reference vehicle height change circuit is provided that lowers the reference vehicle height as the absolute value of longitudinal acceleration increases, and In addition to suppressing pitching,
A control method for an active suspension for an automobile, characterized in that the vehicle height of the entire vehicle body is controlled to be lowered as the absolute value of longitudinal acceleration increases.