JP2007313951A - Vehicle suspension device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a driver's burden by optimizing phase different of motion in which roll motion and pitch motion are combined. <P>SOLUTION: When roll is generated, such that phase difference of a period of roll and a period of pitch becomes a value within 1/4 period, attenuation characteristic of a front wheel side absorber arranged between a front wheel side member and a vehicle body side member and set with the attenuation characteristic such that attenuation force at a stretching side becomes larger than attenuation force at a contraction side and attenuation characteristic of a rear wheel side absorber arranged between a rear wheel side member and the vehicle body side member and set with the attenuation characteristic such that attenuation force at the stretching side becomes larger than attenuation force at the contraction side are set. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a vehicle suspension device, and in particular, a vehicle suspension in which roll feeling (roll) and pitch motion (pitch) are combined to optimize a roll feeling and vehicle behavior recognizability. Relates to the device.

In a conventional vehicle suspension device (suspension device), when a turning motion of the vehicle is detected, the instantaneous center of rotation of the front wheel carrier is moved backward or upward, or the instantaneous center of rotation of the rear wheel carrier is moved forward. Alternatively, a technique is known in which the pitch moment lever due to cornering resistance during turning is shortened by moving upward to suppress and prevent vehicle body pitch movement during turning (Patent Document 1). This technique aims to prevent a change in the posture of the vehicle by suppressing and preventing the vehicle body pitch motion.
JP 2005-53356 A

  As the vehicle motion, a turning motion is started by a steering input, a roll motion is generated in the vehicle, and a pitch moment is generated by a force pushing up the front and rear axles by expansion and contraction of the suspension by the roll motion, and the pitch motion is generated by this pitch moment. For this reason, the recognizability of a roll feeling and a vehicle behavior improves by optimizing the exercise | movement which combined roll exercise | movement and pitch exercise | movement.

  However, the conventional technology described above does not optimize the motion combining the roll motion and the pitch motion, but prevents the suppression of the vehicle body pitch motion, thereby improving the recognition of the roll feeling and the vehicle behavior. There is a problem that it is difficult to reduce the driving burden on the driver.

  The present invention has been made to solve the above-described problems, and provides a vehicle suspension apparatus that reduces the driving burden on the driver by optimizing the phase of the motion that combines the roll motion and the pitch motion. The purpose is to provide.

  In order to achieve the above object, the vehicle suspension device of the present invention is disposed between the front wheel side member and the vehicle body side member, and has a damping characteristic such that the damping force on the expansion side is larger than the damping force on the contraction side. The front wheel side absorber that has been set, and the rear wheel side that is disposed between the rear wheel side member and the vehicle body side member, and has a damping characteristic set so that the damping force on the expansion side is greater than the damping force on the contraction side A suspension device for a vehicle having an absorber, wherein when a roll is generated, the front wheel side absorber and the rear wheel are configured such that a phase difference between a roll cycle and a pitch cycle is within a quarter cycle. The damping characteristics of the side absorber are set.

  Since the driver always recognizes the behavior of the vehicle and is driving, it is desirable for the driver to be able to recognize and recognize the vehicle behavior with respect to the steering without any sense of incongruity in order to reduce the driving load. When turning, damping force is generated according to the displacement speed of the absorber (front wheel side absorber and rear wheel side absorber) due to roll motion, and the axle is adjusted according to the difference between the damping force on the expansion side and the damping force on the contraction side. A pressing force is generated. In addition, since a pitch moment is generated due to a difference in damping force between the front and rear wheels, a motion in which a roll motion and a pitch motion are combined is generated in the vehicle when turning. By appropriately setting these left and right and front and rear damping force differences, the pitch angle gain characteristic with respect to the roll angle can be set, and by appropriately setting the roll rate and the absorber displacement speed, the roll angle relative to the roll angle can be set. The phase difference of the pitch angle can be set, and by optimally setting or controlling the phase of these motions, the roll feeling can be improved and the vehicle behavior can be easily recognized.

  According to the present invention, since the damping characteristics of the front wheel side absorber and the rear wheel side absorber are set so that the phase difference between the roll cycle and the pitch cycle is a value within ¼ cycle, roll motion and pitch motion The phase of the motion that combines the above is optimized, and the vehicle behavior with a sense of unity between the roll motion and the pitch motion in the transitional motion can be realized, and the driving burden on the driver can be reduced.

  In order to optimize the phase of the motion that combines roll motion and pitch motion, when roll is generated, the difference between the damping force on the expansion side of the front wheel side absorber and the damping force on the contraction side is the difference between the damping force on the rear wheel side absorber. You may make it set so that it may become larger than the difference of the damping force of an expansion | extension side, and the damping force of a contraction side.

  In the present invention, by setting the allowable range of the damping characteristic based on the swinging sensation characteristic, it is possible to realize a characteristic that can be easily accepted by a general user without feeling uncomfortable.

  Further, in the present invention, the motion area in which the comfort related to the roll during steering is important, for example, the lateral acceleration is within a predetermined range including 0.2 G (where G represents gravitational acceleration) or 0.2 G. In the motion region, the damping coefficient of the front wheel side absorber and rear wheel side absorber with respect to the suspension stroke speed is increased linearly from the contraction side to the expansion side, or increased by a characteristic that approximates the linear characteristics stepwise. This is effective.

  As described above, according to the present invention, it is possible to optimize the phase of the motion that combines the roll motion and the pitch motion, so that the roll feeling is improved, the vehicle behavior is easily recognized, and the driving burden on the driver is increased. Can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  In general, absorbers for vehicle suspension devices (front wheel side absorbers and rear wheel side absorbers), that is, shock absorbers that provide damping force characteristics, are compatible with both ride comfort and vibration damping when a vehicle rides on a step or the like. As shown in FIG. 1, the extension side and the contraction side have different damping force characteristics, and the extension side damping force is set to be larger than the compression side damping force for the same suspension stroke speed. ing. For this reason, when roll angular velocity is generated during steering, the damping force of the extension wheel out of the left and right wheels becomes larger than the damping force of the contraction side wheel. As a result, the force that pushes down the axle against the axle as shown in FIG. Acts. When the force that pushes down the axle is different between the front and rear axes, that is, when an absorber having different damping force characteristics is used on the front and rear axes, pitch motion occurs due to the unbalance of the force that pushes down the front and rear axes.

Here, the difference between the damping force on the expansion side and the damping force on the contraction side, that is, the force that pushes down the axle is expressed as f _f (p) and f _r (p) as a function of the roll angular velocity p. In the case of an absorber having a typical damping force characteristic, it can be described by the following equations (1) and (2).

However, accompanied woo of f, r is axis before each represents the rear axle, c _f, c _r, respectively, represent the difference between the attenuation coefficient for the roll angular velocity of the extension side and the contraction side of the front and rear wheels.

  Further, the pitch motion when the roll motion is generated can be approximated by the following equation of motion (3).

Where q: pitch angular velocity, θ: pitch angle, I _θ : pitch moment of inertia, k: pitch stiffness, c: pitch damping coefficient, l _f : distance from front axis to center of gravity, l _r : from rear axis to center of gravity Distance.

  By the way, the characteristic of the pitch angle at the time of sign steering assuming a lane change is that the pitch angle is maximum when the roll angular velocity is maximum when the roll angular velocity is zero (the forward tilt direction is normal) in order for the vehicle behavior to steering to occur without a sense of incongruity. It is desirable that On the contrary, this indicates that it is desired that the pitch angle is minimized when the roll angular velocity is maximum, that is, when the roll angle is zero. In addition, the pitch moment (angular acceleration) and the pitch angle at the time of synchronous input have the property of being in opposite phases, so in order to minimize the pitch angle, the following corresponding to the pitch moment This indicates that it is desired that the input term of the above equation (3) represented by the equation (4) is maximized (positive maximum value).

Considering that both f _f (p) and f _r (p) in the above expression (4) are positive, the following expression (5) is established.

Usually, the distance l _f from the front axis to the center of gravity and the distance l _r from the rear axis to the center of gravity are substantially the same, so from the above equation (5), Of the absorber so that the difference (the force that pushes down the axle of the front wheel) is larger than the difference between the damping force on the extension side of the rear wheel and the damping force on the contraction side (force that pushes down the axle of the rear wheel) If the attenuation characteristic is set, it can be understood that the attenuation characteristic that maximizes the pitch angle can be obtained when the roll angle is maximum.

  For example, this characteristic is that when rolls are generated during steering, the front-rear wheel expansion side damping force is the same, and the front wheel contraction side damping force is smaller than the rear wheel contraction side damping force. This can be realized by setting. Also, when rolls are generated during steering, etc., the damping force on the contraction side of the front and rear wheels will be the same, and the expansion damping force on the front wheels will be larger than the expansion damping force on the rear wheels This can also be realized. Even in this case, the general damping force characteristics shown in FIG. 1 are provided.

  Next, consider a state in which the roll angular velocity p is generated as shown in the following equation (6) by sine steering.

  However, a and b are constants and t is time. At this time, in the suspension having a general damping force characteristic as shown in FIG. 1, the force for pushing down the shaft is expressed by the following equation (7), and the roll angular velocity becomes maximum and minimum as shown in FIG. The maximum value is obtained when the roll angle is 0).

  The force that pushes down this axis is approximately ½ period of roll motion, but if strict ½ period characteristics as shown by the broken line can be realized by setting the damping force characteristics, the pitch motion also has hysteresis. It can be brought close to the characteristics of the 1/2 cycle of the roll motion without being generated, and a clean roll feeling (sensory evaluation of the motion of the body such as a roll generated during steering) can be realized. The predetermined shaft pressing force characteristic indicated by the broken line in FIG. 3 can be described by the following equation (8).

  This shaft pressing force characteristic can be realized by correcting the general damping coefficient characteristic with respect to the roll angular velocity shown in FIG. 4A to the damping coefficient characteristic with respect to the roll angular velocity shown in FIG. 4B. In the characteristic of FIG. 4B, the absorber damping coefficient with respect to the suspension stroke speed is linearly increased from the contraction side to the expansion side.

  In FIG. 4B, “a” is the maximum of the motion region in which the comfort related to the steering roll is important, that is, the maximum motion region in which the lateral acceleration of about 0.2 G, which is important in the roll feeling evaluation, is performed. Although it is desired to set the roll angular velocity to a larger value, even if the roll angular velocity is set to a value smaller than the maximum roll angular velocity, an effect of improving the roll feeling can be expected as compared with the general damping coefficient characteristics shown in FIG. . Further, as shown in FIG. 4C, the linear characteristic shown in FIG. 4B may be approximately realized by a characteristic that changes in multiple steps step by step.

  4B can be expressed as a damping force characteristic as shown in FIG. That is, in the stretch side region where the roll angular velocity is -a or less, the slope is represented by a line segment where the slope is the stretch side attenuation coefficient, and in the shrink side region where the roll angular velocity is a or more, the slope is represented by a line segment. At the same time, in the section where the roll angular velocity is from -a to a, the characteristic is described by an upward convex quadratic function that touches at the end point of each line segment. That is, by setting the damping coefficient of the damping force characteristic on the expansion side and the damping coefficient of the damping force characteristic on the contraction side to values that are linearly interpolated, it is possible to set the combined motion of the roll and the pitch.

  By the way, as described above, in order to make the difference between the damping force on the expansion side of the front wheel and the damping force on the contraction side larger than the difference between the damping force on the expansion side of the rear wheel and the damping force on the contraction side, For example, as shown in FIG. 5A, it can be realized by setting in advance such that the contraction-side damping force of the rear wheels is larger than the contraction-side damping force of the front wheels. Here, the roll angular velocity is described on the horizontal axis, but the same characteristics can be obtained by using the suspension stroke speed generated according to the roll angular velocity instead of the roll angular velocity.

  The absorber is attached to the vehicle body side member through an elastic body such as a rubber bush, and the operating speed of the absorber is delayed with respect to the roll angular speed due to friction in the absorber. This delay can be equivalently expressed by a first-order lag characteristic, for example, as indicated by Gf and Gr in the following formulas (9) and (10). Is added, and a phase delay of the pitch angle with respect to the roll angle as shown in the Lissajous waveform of FIG. 6 occurs.

  Due to the increase in the phase difference as shown in FIG. 6, the occupant feels the roll feeling deteriorated because the correspondence between the maximum value of the roll angle and the maximum value of the pitch angle is shifted. When the phase difference is 0, a good roll feeling can be obtained because the roll angle and the pitch angle are matched. On the other hand, the phase difference π / b is bad.

  The occupant recognizes and discriminates these phase differences from the roll motion and the pitch motion by visual and bodily sensations. FIG. 7 shows the fluctuation sensation characteristics related to the actually measured phase difference. In the example shown in the figure, the evaluator recognizes that the phase difference is 0 to π / (2b), that is, the case where the phase difference is 0 to ¼ period, as the phase difference is 0 by visual perception or bodily sensation. From this measurement result, it can be understood that when rolls are generated, the phase difference between the roll period and the pitch period may be set to a value within ¼ period. Therefore, the characteristics of the axle pressing force that falls within this region are set so that the time constants of Gf and Gr can be obtained, or a damping force variable shock absorber is attached between the vehicle body side member and the wheel side member. The desired roll feeling can be obtained by actively controlling the damping force.

  To set the axle push-down force in advance, for example, appropriately set at least one of the elastic modulus and viscosity characteristics of an elastic body such as a rubber bush at the shock absorber mounting portion, and the friction force characteristics inside the shock absorber. To do. By this setting, a setting equivalent to the time constants of the first-order lag characteristics Gf and Gr can be performed.

  The above-mentioned Gf and Gr have a first-order lag characteristic. However, by adding a leading element, the pitch angle in the case where the desired front-rear damping force characteristic distribution shown in the expressions (4) and (5) cannot be set. Compensation is also possible.

  Based on the above, the phase difference between the roll period and the pitch period is based on the state where no phase lag is generated, and the range of 1/4 cycle delay of the pitch period to 1/4 cycle delay of the pitch period. The damping force may be set so that

  In addition, in the suspension that can actively control the damping force, the roll feeling can be improved by adding such control characteristics.

  An embodiment of the present invention based on the above principle will be described. First, a first embodiment of the present invention in which the axle pressing force is preset will be described with reference to FIG. As shown in the figure, shocks that constitute suspension devices are respectively provided between the left and right front wheels FL and FR side members and the vehicle body 10 side, and between the left and right rear wheels RL and RR side members and the vehicle body 10 side. Absorbers 12FL, 12FR, 12RL, and 12RR are attached via an elastic body such as a rubber bush. In the drawing, the right front wheel FR and the right rear wheel RR are not shown.

  As described above, the characteristics of the elastic coefficient and viscosity of the rubber bush at the mounting portion of the shock absorber 12FL, 12FR, 12RL, 12RR are the difference between the damping force on the expansion side of the rear wheel and the damping force on the contraction side. The difference between the damping force on the extension side and the damping force on the contraction side of the front wheel is larger, and the phase difference between the cycle of the roll motion and the cycle of the pitch motion is set to a value within ¼ cycle. Yes. It should be noted that the frictional force characteristics inside the shock absorber, or the elastic bushing's elastic coefficient and viscosity characteristics and the frictional force characteristics inside the shock absorber are set appropriately, and the equivalent time constant of Gf and Gr is You may make it obtain.

  Next, a second embodiment of the present invention for actively controlling the axle pressing force will be described with reference to FIG. In the present embodiment, the damping force is actively controlled so that the characteristic shown in FIG. 5 is realized only at the time of steering where a roll feeling is required, that is, only when a roll is generated. In this case, since the characteristics shown in FIG. 5 are realized only during steering where a roll feeling is required, a high roll feeling can be realized without impairing riding comfort and vibration attenuation.

  In this embodiment, in place of the shock absorber of the above embodiment, damping force variable shock absorbers 14FL, 14FR, 14RL, 14RR with variable damping force are attached.

  As the damping force variable shock absorber of the present embodiment, a conventionally known one is used. Briefly explaining the structure, this damping force variable shock absorber is composed of a twin tube type gas-filled strud type absorber having a cylinder tube composed of an outer cylinder and an inner cylinder, and is slidably stored in the inner cylinder. The inner cylinder is partitioned into an upper pressure chamber and a lower pressure chamber by the formed piston. The piston has an extension side oil passage and a contraction side oil passage. The compression side oil passage is rotated relative to the piston by a stepping motor, and each orifice formed between the piston and the piston is formed. A valve body for adjusting the opening is provided. According to this damping force variable shock absorber, the damping force characteristic can be set by adjusting the opening area of each orifice formed between the valve element and the piston by rotating the stepping motor.

  Stepping motors provided in the damping force variable shock absorbers 14FL, 14FR, 14RL, and 14RR are connected to a control circuit 16 constituted by a microcomputer or the like. A vehicle speed sensor 18 for detecting the vehicle speed is connected to the control circuit 16.

  The control circuit 16 stores in advance a rotation angle data of the step motor for obtaining the damping force characteristic described above and a control routine program for setting the damping force characteristic. In the control circuit, when the vehicle speed greater than the angle at which the roll is generated is detected in accordance with a pre-stored control routine, the pre-stored stepping motor rotation angle data is fetched to obtain the damping characteristic described above. Control the stepper motor to

  Instead of detecting the vehicle speed, the displacement speed of the suspension may be detected, and the stepping motor may be controlled so that the above-described damping characteristics can be obtained when the speed exceeds a predetermined value. .

It is a diagram which shows the general damping force characteristic of a shock absorber. It is the schematic which shows the motion of the axle shaft at the time of roll angular velocity generation | occurrence | production of the vehicle provided with the shock absorber of the general damping force characteristic. It is a diagram which shows the relationship between roll angular velocity and axle pressing force. It is a figure for demonstrating the setting of the attenuation coefficient for improving an axle | axis axle pushing down characteristic, (a) is a diagram which shows a general attenuation coefficient, (b) is a diagram which shows the improved attenuation coefficient. (A) is a diagram showing the damping force characteristics of the front wheels, (b) is a diagram showing the damping force characteristics of the rear wheels. It is a diagram which shows the change of the phase characteristic of the pitch angle with respect to a roll angle. It is a diagram which shows the fluctuation sensation characteristic regarding the phase difference of the pitch angle with respect to a roll angle. 1 is a schematic diagram of a vehicle to which a first embodiment of the present invention is applied. It is a block diagram of the 2nd Embodiment of this invention.

Explanation of symbols

12FL-12RR Shock absorber 14FL-14RR Shock absorber 16 Control circuit 18 Vehicle speed sensor

Claims (7)

A front wheel side absorber disposed between the front wheel side member and the vehicle body side member, and having a damping characteristic set such that the expansion side damping force is larger than the contraction side damping force, and the rear wheel side member and the vehicle body side A vehicle suspension apparatus including a rear wheel side absorber disposed between a member and a damping characteristic set such that an extension side damping force is larger than a contraction side damping force;
A suspension device for a vehicle in which damping characteristics of the front wheel side absorber and the rear wheel side absorber are set so that a phase difference between a roll cycle and a pitch cycle is a value within a quarter cycle when a roll is generated. . A front wheel side absorber disposed between the front wheel side member and the vehicle body side member, and having a damping characteristic set such that the expansion side damping force is larger than the contraction side damping force, and the rear wheel side member and the vehicle body side A vehicle suspension apparatus including a rear wheel side absorber disposed between a member and a damping characteristic set such that an extension side damping force is larger than a contraction side damping force;
When a roll is generated, the difference between the extension side damping force and the contraction side damping force of the front wheel side absorber is larger than the difference between the extension side damping force and the contraction side damping force of the rear wheel side absorber. A suspension device for a vehicle set to be   3. The vehicle suspension apparatus according to claim 2, wherein a contraction side damping force of the rear wheel side absorber is set to be larger than a contraction side damping force of the front wheel side absorber.   4. The vehicle according to claim 2, wherein the combined motion of the roll and the pitch is set by setting the damping coefficient of the damping force characteristic on the expansion side and the damping coefficient of the damping force characteristic on the contraction side to values that are linearly interpolated. Suspension device.   The phase difference between the roll cycle and the pitch cycle is attenuated so that the phase difference is within a range from 1/4 cycle advance of the pitch cycle to 1/4 cycle delay of the pitch cycle with reference to a state where no phase delay occurs. The vehicle suspension device according to any one of claims 1 to 4, wherein a force is set.   The front wheel is set so that the phase difference between the roll cycle and the pitch cycle is in a range from 1/4 cycle advance of the pitch cycle to 1/4 cycle delay of the pitch cycle with reference to a state where no phase delay occurs. The vehicle suspension device according to claim 1, wherein at least one of rigidity of a mounting bush for attaching the side absorber and the rear wheel side absorber and a frictional force of the front wheel side absorber and the rear wheel side absorber is set.   In the motion region where the comfort related to the roll during steering is important, the damping coefficient of the front wheel side absorber and the rear wheel side absorber with respect to the suspension stroke speed is increased linearly from the contraction side to the extension side, or the linear The suspension device according to any one of claims 1 to 6, wherein the characteristic is increased by a characteristic approximated stepwise.