JP4546323B2 - Variable damping force damper - Google Patents

Description

  The present invention relates to a variable damping force damper that variably controls a damping force of a damper provided in a suspension device of a vehicle according to a motion state of the vehicle by a control means.

  As the viscous fluid of the variable damping force damper for the suspension device, a magnetic viscous fluid (MRF: Magneto-Rheological Fluids) whose viscosity is changed by the action of a magnetic field is adopted, and the fluid is applied to the piston that is slidably fitted into the cylinder. Patent Document 1 below discloses a coil provided with a coil for applying a magnetic field to a magnetorheological fluid in a passage. According to this variable damping force damper, the damping force of the damper can be arbitrarily controlled by changing the viscosity of the magnetorheological fluid in the fluid passage by a magnetic field generated by energizing the coil.

Also, when the vehicle decelerates and stops, the wheels try to stop by braking, but the vehicle body keeps moving forward due to inertia, so there is a posture change (nose dive) where the front part of the vehicle body goes down and the rear part of the vehicle body goes up On the contrary, when the vehicle accelerates, the vehicle body tends to be left behind due to inertia, so that a posture change (nose lift) occurs in which the rear portion of the vehicle body is lowered and the front portion of the vehicle body is raised. In order to suppress the change in the attitude in the pitch direction due to the longitudinal acceleration of the vehicle and improve the steering stability performance, it is generated in the variable damping force damper using the longitudinal acceleration with low-pass filter and the longitudinal acceleration without low-pass filter. A method for determining the control amount of the damping force to be performed is known from Patent Document 2 below.
JP-A-60-113711 JP 9-309314 A

  By the way, if the damping force of the variable damping force damper is controlled based on the longitudinal acceleration of the vehicle, a response delay may occur. Therefore, it is variable using the differential value of the longitudinal acceleration in which the pitching phase change appears earlier than the longitudinal acceleration It is conceivable to control the damping force of the damping force damper. In this way, it is possible to suddenly raise the damping force at the initial stage of sudden acceleration or sudden deceleration and to obtain a stable damping force that does not depend on the stroke of the variable damping force damper.

  However, in general, the magnitude of deceleration generated by sudden braking of the vehicle is larger than the magnitude of acceleration generated by sudden acceleration of the vehicle, and the time when deceleration occurs is shorter than the time when acceleration occurs. If the same differential filter is used for the longitudinal acceleration during deceleration and acceleration, there is a possibility that the optimal control time and control amount that effectively suppress the change in the pitch attitude of the vehicle may not be obtained.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to effectively suppress a change in the pitch posture of the vehicle both when the vehicle is decelerating and when accelerating, thereby improving the steering stability performance.

In order to achieve the above object, according to the first aspect of the present invention, a variable damping force that variably controls the damping force of a damper provided in the suspension device of the vehicle according to the motion state of the vehicle by the control means. The damper is a variable damping force damper that controls the damping force of the damper based on a differential value of the longitudinal acceleration obtained by differentiating the longitudinal acceleration of the vehicle detected by the longitudinal acceleration sensor with a differential filter . A variable damping force damper is proposed in which the characteristic of the differential filter is changed between when the vehicle is accelerated and when the vehicle is decelerated so that the gain during deceleration is greater than the gain during acceleration .

According to the invention described in claim 2, in addition to the configuration of claim 1, the characteristic of the differential filter is that the gain at the time of deceleration is higher than the gain at the time of acceleration in a region where the frequency is 0.1 Hz or more. A variable damping force damper characterized by being set to be large is proposed.

  The electronic control unit U of the embodiment corresponds to the control means of the present invention, and the acceleration differential filter 32 and the deceleration differential filter 33 correspond to the differential filter of the present invention.

According to the configuration of the first aspect, the control means for variably controlling the damping force of the damper provided in the vehicle suspension device according to the motion state of the vehicle is based on the differential value of the longitudinal acceleration of the vehicle. Therefore, compared with the case where the damping force of the damper is controlled based on the longitudinal acceleration itself of the vehicle, the control delay can be prevented and the responsiveness can be improved. In addition, the characteristic of the differential filter that differentiates the longitudinal acceleration of the vehicle is changed between when the vehicle is accelerated and when the vehicle is decelerated so that the gain when the vehicle is decelerated is larger than the gain when the vehicle is accelerated. By varying the damper control time and control amount during acceleration when the acceleration occurs for a long time and deceleration when the relatively large deceleration occurs for a short time, the vehicle pitching is effective both during acceleration and deceleration. Can be suppressed.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on examples of the present invention shown in the accompanying drawings.

  1 to 7 show an embodiment of the present invention. FIG. 1 is a front view of a vehicle suspension device, FIG. 2 is an enlarged sectional view of a variable damping force damper, and FIG. 3 is a control law of pitch control by the damper. FIG. 4 is a graph showing the characteristics of the low-pass filter, FIG. 5 is a graph showing the characteristics of the differential filter, FIG. 6 is a flowchart of a target current calculation routine of the damper, and FIG. It is a map to search for.

  As shown in FIG. 1, a suspension device S that suspends a wheel W of a four-wheeled vehicle has a suspension arm 13 that supports a knuckle 12 in a vertically movable manner on a vehicle body 11, and a variable damping that connects the suspension arm 13 and the vehicle body 11. A force damper 14 and a coil spring 15 connecting the suspension arm 13 and the vehicle body 11 are provided. The electronic control unit U that controls the damping force of the damper 14 includes a signal from the sprung acceleration sensor Sa that detects the sprung acceleration, a signal from the damper displacement sensor Sb that detects the displacement (stroke) of the damper 14, and A signal from the steering angle sensor Sc that detects the steering angle of the vehicle, a signal from the lateral acceleration sensor Sd that detects the lateral acceleration of the vehicle, a signal from the longitudinal acceleration sensor Se that detects the longitudinal acceleration of the vehicle, and the vehicle speed A signal from the vehicle speed sensor Sf to be detected is input.

  As shown in FIG. 2, the damper 14 includes a cylinder 21 whose lower end is connected to the suspension arm 13, a piston 22 that is slidably fitted into the cylinder 21, and an upper wall of the cylinder 21 that extends upward from the piston 22. And a free piston 24 that is slidably fitted to the lower part of the cylinder, and is partitioned by the piston 22 inside the cylinder 21. An upper first fluid chamber 25 and a lower second fluid chamber 26 are partitioned, and a gas chamber 27 in which a compressed gas is sealed in a lower portion of the free piston 24 is partitioned.

  A plurality of fluid passages 22a are formed in the piston 22 so that the upper and lower surfaces thereof communicate with each other, and the first and second fluid chambers 25 and 26 communicate with each other through these fluid passages 22a. The magnetorheological fluid sealed in the first and second fluid chambers 25 and 26 and the fluid passages 22a is a dispersion of magnetic fine particles such as iron powder in a viscous fluid such as oil. By aligning the magnetic fine particles along the magnetic field lines, it is difficult for the viscous fluid to flow, and the apparent viscosity increases. A coil 28 is provided inside the piston 22, and energization of the coil 28 is controlled by the electronic control unit U. When the coil 28 is energized, a magnetic flux is generated as indicated by an arrow, and the viscosity of the magnetorheological fluid changes due to the magnetic flux passing through the fluid passages 22a.

  When the damper 14 contracts and the piston 22 moves downward with respect to the cylinder 21, the volume of the first fluid chamber 25 increases and the volume of the second fluid chamber 26 decreases. Passes through the fluid passage 22a of the piston 22 and flows into the first fluid chamber 25. Conversely, when the damper 14 extends and the piston 22 moves upward relative to the cylinder 21, the volume of the second fluid chamber 26 increases. Since the volume of the first fluid chamber 25 decreases, the magnetorheological fluid in the first fluid chamber 25 passes through the fluid passage 22a ... of the piston 22 and flows into the second fluid chamber 26, and at that time, the fluid passage 22a The damper 14 generates a damping force due to the viscous resistance of the magnetorheological fluid passing through.

  At this time, if the coil 28 is energized to generate a magnetic field, the apparent viscosity of the magnetorheological fluid existing in the fluid passage 22a of the piston 22 increases and it becomes difficult to pass through the fluid passage 22a. Damping force increases. The increase amount of the damping force can be arbitrarily controlled by the magnitude of the current supplied to the coil 28.

  When a shocking compressive load is applied to the damper 14 to reduce the volume of the second fluid chamber 26, the free piston 24 descends while the gas chamber 27 is contracted to absorb the impact. Further, when a shocking tensile load is applied to the damper 14 to increase the volume of the second fluid chamber 26, the impact is absorbed by the free piston 24 rising while the gas chamber 27 is expanded. Further, when the piston 22 descends and the volume of the piston rod 23 accommodated in the cylinder 21 increases, the free piston 24 descends so as to absorb the increase in the volume.

  Thus, the electronic control unit U detects the sprung acceleration detected by the sprung acceleration sensor Sa, the damper displacement detected by the damper displacement sensor Sb, the steering angle detected by the steering angle sensor Sc, and the lateral acceleration detected by the lateral acceleration sensor Sd. Based on the longitudinal acceleration detected by the longitudinal acceleration sensor Se and the vehicle speed detected by the vehicle speed sensor Sf, the damping force of each of the four dampers 14 of each wheel W is individually controlled, so that the unevenness of the road surface is reduced. Ride comfort control such as skyhook control that suppresses vehicle shake when overcoming and enhances ride comfort, and steering stability control that suppresses rolling during turning of the vehicle and pitching during sudden acceleration and deceleration of the vehicle, It is selectively executed according to the driving state of the vehicle.

As shown in FIG. 3, the longitudinal acceleration XG of the vehicle detected by the longitudinal acceleration sensor Se passes through the low-pass filter 31 having the characteristics shown in FIG. 4, and the vehicle is traveling normally without being depressed by the accelerator pedal or the brake pedal. High frequency longitudinal acceleration is blocked. Longitudinal passed through the low pass filter 31 acceleration XG is Ru are passed to the time derivative of the acceleration-time derivative filter 32 or decelerated during a derivative filter 33. FIG. 5 shows the characteristics of the acceleration differential filter 32 and the deceleration differential filter 33. In the frequency range of 0.1 Hz or more, the gain during deceleration is set to be larger than the gain during acceleration. Yes. The differential filter 32 for acceleration and the differential filter 33 for deceleration are selectively used when the vehicle longitudinal acceleration XG detected by the longitudinal acceleration sensor Se is positive (acceleration), and the acceleration differential filter 32 is used and is negative (deceleration). In this case, the differential filter 32 for deceleration may be used.

  The longitudinal acceleration differential value dXG / dt output from the acceleration differential filter 32 or the deceleration differential filter 33 is multiplied by the gain searched by the map 34 based on the vehicle speed V detected by the vehicle speed sensor Sf. A target damping force Ft is calculated.

  FIG. 6 shows a flowchart for explaining the operation of the steering stability control that suppresses pitching by increasing the damping force of the dampers 14 at the time of acceleration / deceleration of the vehicle.

  First, the longitudinal acceleration XG detected by the longitudinal acceleration sensor Se in step S1 is time-differentiated to calculate a longitudinal acceleration differential value dXG / dt, and the longitudinal acceleration differential value dXG / dt is multiplied by a gain Gain set according to the vehicle speed V. Thus, the target damping force Ft to be generated by the damper 14 is calculated. In the subsequent step S2, the damper speed Vp is calculated by differentiating the damper displacement detected by the damper displacement sensor Sb with respect to time. In the following step S3, the target current It is searched by applying the target damping force Ft and the damper speed Vp to the map of FIG. In step S4, the target current It is supplied to the coil of the damper 14 to generate the target damping force Ft, thereby suppressing the pitching of the vehicle and improving the steering stability performance.

  FIG. 7 is a map for searching the target current It from the target damping force Ft and the damper speed Vp. When the damper speed Vp is constant, the target current It increases as the target damping force Ft increases. When the force Ft is constant, the target current It decreases as the damper speed Vp increases. For example, when the target damping force Ft is Ft1 and the damper speed Vp is Vpt, the target current is It5. However, when the damper speed Vp increases to Vpt1, the target current decreases to It4 and the damper speed Vp decreases to Vpt2. Then, the target current increases to It6.

Thus, when the longitudinal acceleration XG at the time of acceleration and deceleration of the vehicle is detected, the damper 14 is controlled based on the differential value dXG / dt of the longitudinal acceleration XG in order to suppress the nose lift accompanying the acceleration and the nose dive accompanying the deceleration. Therefore, compared to the case where the damping force of the damper 14 is set based on the longitudinal acceleration XG itself of the vehicle, the control delay can be prevented and the responsiveness can be improved. The characteristics of the differential filter for differentiating the longitudinal acceleration XG of the vehicle, as the gain during deceleration of the vehicle becomes larger than the gain in acceleration, Mochikaeru between acceleration for differentiating filter 32 and the deceleration-time derivative filter 33 Therefore, the control time and the control amount of the damper 14 are made different between acceleration when a relatively small acceleration occurs for a long time and deceleration when a relatively large deceleration occurs for a short time, and both during acceleration and deceleration. Therefore, it is possible to effectively suppress the pitching of the vehicle and improve the steering stability performance.

  Although the embodiments of the present invention have been described above, various design changes can be made without departing from the scope of the present invention.

  For example, in the embodiment, the acceleration and deceleration of the vehicle are determined by the sign of the longitudinal acceleration XG output by the longitudinal acceleration sensor Se, but may be determined by the sign of the output of the acceleration differential filter 22 having a large time constant. .

Front view of vehicle suspension system Expanded sectional view of variable damping force damper Block diagram of control law of pitch control by damper Graph showing characteristics of low-pass filter Graph showing characteristics of differential filter Damper target current calculation routine flowchart Map to search for target current from damper speed and target damping force

14 Damper 32 Acceleration differential filter (filter)
33 Differential filter for deceleration (filter)
dXG / dt Longitudinal acceleration differential value S Suspension device Se Longitudinal acceleration sensor U Electronic control unit (control means)
XG Vehicle longitudinal acceleration

Claims (2)

A variable damping force damper that variably controls the damping force of the damper (14) provided in the suspension device (S) of the vehicle according to the motion state of the vehicle by the control means (U),
The control means (U) is a damper based on the differential value (dXG / dt) of the longitudinal acceleration obtained by differentiating the longitudinal acceleration (XG) of the vehicle detected by the longitudinal acceleration sensor (Se) with the differential filter (32, 33). In the variable damping force damper that controls the damping force of (14),
A variable damping force damper characterized in that the characteristic of the differential filter (32, 33) is changed between when the vehicle is accelerated and when the vehicle is decelerated so that the gain when the vehicle is decelerated is larger than the gain when the vehicle is accelerated. The characteristic of the differential filter (32, 33) is set so that the gain at the time of deceleration becomes larger than the gain at the time of acceleration in a region where the frequency is 0.1 Hz or more. Variable damping force damper.

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