JP3081041B2 - Vehicle suspension device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a suspension device for a vehicle, and more particularly to an improvement in a device having a variable damping coefficient shock absorber between a sprung portion and a unsprung portion, the damping coefficient of which can be changed in a plurality of stages. Get involved.

[0002]

2. Description of the Related Art Generally, a vehicle suspension system is provided with a shock absorber between a sprung portion on the vehicle body side and a unsprung portion on the wheel side to attenuate vertical vibration of the wheel. As the shock absorber, there are various types of variable damping coefficients, such as a variable damping coefficient that can be changed in two stages, a large one or a continuously variable one.

[0003] Such a method of controlling a shock absorber with a variable damping coefficient is basically based on the so-called skyhook that the damping force actually generated by the shock absorber does not change vertically. This is to change and control the damping coefficient of the shock absorber so that the damping force is obtained. As a specific control method, for example, Japanese Unexamined Patent Publication No. 60-248419 discloses a sign of a relative displacement between a sprung portion and a unsprung portion and a sign of a relative speed between a sprung portion and an unsprung portion which is a differential value thereof. Is checked to see if they match, and when they match, the damping coefficient of the shock absorber is increased by increasing the damping coefficient of the shock absorber, and when they do not match, the damping coefficient of the shock absorber is reduced to generate It is disclosed to reduce the damping force generated.

In such control, a dead zone is generally provided to prevent the damping coefficient of the shock absorber from being frequently switched with respect to a displacement near the neutral position. For example, Japanese Utility Model Laid-Open 63-40
No. 213 discloses that the damping coefficient is changed and controlled based on whether the sign of the relative displacement between the sprung unsprung and the sign of the relative speed between the sprung unsprung is changed. In the dead zone, the damping coefficient of the shock absorber is always kept small in the dead zone, and when the sprung input such as the steering angle and the steering angular velocity is large, the width of the dead zone is reduced. It is disclosed that rolling can be suppressed.

[0005]

By the way, in the control of a shock absorber in which the damping coefficient can be changed in a plurality of stages, when the above-mentioned dead zone is provided, from the viewpoint of facilitating the control, the damping coefficient is usually smaller or smaller. Regardless of the difference, it is conceivable to provide the same dead zone in any of the switching stages. However, especially when a large external force acts suddenly, such as when the wheel gets over a protrusion on the road while the vehicle is running, the change of the damping coefficient to the hard side causes a control delay due to the provision of the dead zone. However, there is a problem that insufficient generation of damping force occurs.

The present invention has been made in view of the above point, and an object of the present invention is to provide a dead zone in the control of a shock absorber in which the damping coefficient can be changed to a plurality of stages as described above. It is necessary to provide a vehicle suspension device capable of appropriately changing the dead zone according to the size and minimizing a control delay in the control for changing the damping coefficient to improve driving stability and riding comfort at a high level. Is what you do.

[0007]

According to a first aspect of the present invention, there is provided a shock absorber which is disposed between a sprung portion and a unsprung portion and whose damping coefficient can be changed to a plurality of stages. The vehicle suspension apparatus further comprising: control means for changing and controlling the damping coefficient of the shock absorber so that the damping force actually generated by the shock absorber becomes a target damping force in which the sprung mass does not change vertically. Prohibiting means for prohibiting change control of the control means when a difference between the actual damping force of the shock absorber and the target damping force is within a predetermined range; and a magnitude of a currently selected damping coefficient of the shock absorber. And an upper threshold changing means for changing the upper threshold of the predetermined range accordingly.

The invention according to claim 2 is dependent on the invention according to claim 1, wherein the upper limit threshold value changing means is set to a predetermined range as the currently selected damping coefficient of the shock absorber is larger. The configuration is such that the upper threshold is set to be small.

[0009]

According to the above-mentioned structure, according to the first aspect of the present invention,
In the control in which the damping coefficient of the shock absorber is changed by the control means so that the damping force actually generated by the shock absorber becomes a target damping force in which the sprung does not change vertically, the actual damping force of the shock absorber is different from the actual damping force of the shock absorber. When the difference from the target damping force is within a predetermined range, the change control of the control means is prohibited by the prohibition means. This allows
Frequent change of the damping coefficient of the shock absorber can be prevented. In addition, the upper threshold of the predetermined range (that is, the dead zone) is changed by the upper threshold changing means according to the magnitude of the currently selected damping coefficient of the shock absorber. In particular, claim 2
In the shock absorber of the present invention, as the currently selected damping coefficient of the shock absorber becomes larger, the upper limit threshold value becomes smaller. When a large external force is suddenly applied, the change of the damping coefficient to the hard side is caused by the above-mentioned dead zone. Is performed quickly with almost no influence of the presence of, and a sufficient damping force is generated.

[0010]

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

FIG. 1 shows a component layout of a vehicle equipped with a suspension device according to an embodiment of the present invention.

In FIG. 1, reference numerals 1, 2, 3 and 4 denote four left and right front wheels 5 (only the left front wheel is shown) and four rear wheels 6 (only the left rear wheel is shown). A shock absorber that attenuates the vertical movement of each wheel. Each of the shock absorbers 1 to 4 is provided so that the damping coefficient can be changed to ten different stages by a built-in actuator (see FIGS. 2 and 3), and the magnitude of the damping force actually generated is provided. Pressure sensor (not shown) for detecting the pressure. Reference numeral 7 denotes a coil spring disposed on the upper outer periphery of each of the shock absorbers 1 to 4, and 8 denotes a control unit which outputs a control signal to an actuator in each of the shock absorbers 1 to 4 to change and control its damping coefficient. Each of the shock absorbers 1 is directed toward the control unit 8.
The detection signals are output from the pressure sensors in.

Reference numerals 11, 12, 13 and 14 denote four acceleration sensors for detecting vertical acceleration on a spring of each wheel, and reference numeral 15 denotes a vehicle speed detecting means for detecting a vehicle speed from a rotational speed of a front wheel 5 as a driven wheel. A vehicle speed sensor 16; a steering angle sensor 16 for detecting a steering angle of the front wheels 5 from rotation of a steering shaft;
4 is a mode selection switch for switching the attenuation coefficient to any one of a hard mode, a soft mode, and a control mode.
When the hard mode is selected, a large damping coefficient is selected, and the damping force becomes hard. Also, when the soft mode is selected, a small damping coefficient is selected,
The damping force becomes soft. Further, when the control mode is selected, the control unit 8
The control for changing the damping coefficients of the shock absorbers 1 to 4 is performed based on a map or a table stored in the memory. This change control will be described later in detail.

FIG. 2 shows the structure of the shock absorbers 1-4. However, in this figure, shock absorbers 1 to
The pressure sensor built in 4 is omitted for convenience.

In FIG. 2, reference numeral 21 denotes a cylinder,
A piston unit 22 formed by integrally molding a piston and a piston rod is slidably fitted in the cylinder 21. The cylinder 21 and the piston unit 22 are connected to the unsprung part and the sprung part via a separately provided connecting structure.

The piston unit 22 has two orifices 23 and 24 formed therein. One of the orifices 23 is always open, and the other orifice 24 has a passage area (restriction) of the actuator 25.
Are provided so as to be changeable in ten steps. As shown in FIG. 3, the actuator 25 includes a sleeve 26 fixed in the piston unit 22, a shaft 27 penetrating through the sleeve 26 and rotatably provided, and a shaft 27. A first motor having a step motor 28 for rotating at predetermined angles and a first orifice having nine circular holes 29, 29,... Attached to the plate 30 and the lower end of the sleeve 26,
A second orifice plate 32 having a long hole 31 formed in an arc shape along the circumferential direction. And
When the step motor 28 is operated and the first orifice plate 30 is rotated, the circular hole 29 of the first orifice plate 30 does not face the long hole 31 of the second orifice plate 32 or not. The number of the opposed circular holes 29 is also sequentially changed from zero to nine.

The upper chamber 33 and the lower chamber 34 in the cylinder 21
And a piston unit 22 communicating with the two chambers 33, 34.
The interior cavity is filled with a fluid having a moderate viscosity. The fluid moves between the upper chamber 33 and the lower chamber 34 through one of the orifices 23 and 24.

FIG. 4 shows a vibration model of the suspension device, where ms is the sprung mass, mu is the unsprung mass, zs is the sprung displacement, zu is the unsprung displacement, ks is the spring constant of the coil spring 7, and kt is the tire. And Dk is the damping coefficient of the shock absorbers 1-4.

FIG. 5 is a diagram showing the damping coefficients of the shock absorbers 1 to 4, and D1 to D10 indicate the damping coefficients of the shock absorbers 1 to 4, respectively. In FIG. 5, the vertical axis represents the damping force generated by the shock absorbers 1-4, and the horizontal axis represents the difference between the displacement speed Xs (dzs / dt) above the spring and the displacement speed Xu (dzu / dt) below the spring. , The relative displacement speed between the sprung and unsprung (Xs-Xu
). The damping coefficients D1 to D10 can be changed in ten steps in each of the shock absorbers 1 to 4, where D1 indicates a damping coefficient for generating the softest damping force, and D10 indicates a hardest damping force. Indicates the attenuation coefficient. Here, the damping coefficient Dk (k = 1 to 10) corresponds to nine circular holes 2 formed in the first orifice plate 30.
Among 9, 29,..., (10−k) circular holes 29 are
It is selected by communicating with the long hole 31 formed in the second orifice plate 32. Accordingly, the damping coefficient D1 is such that all nine circular holes 29, 29,... Of the first orifice plate 30
Is selected by communicating with the long hole 31 and the damping coefficient D10
Are nine circular holes 29 in the first orifice plate 30,
.. Are selected because they do not communicate with the long holes 31 of the second orifice plate 32.

FIGS. 6 and 7 show the structure of the step motor 28. FIG. That is, the step motor 28 has a tubular body 40, a rotor 41 and a stator 42 housed in the tubular body 40, and a lid 43 attached to the tubular body 40. A plurality of rectangular teeth 41a, 41a,... Are formed on an outer peripheral portion of the rotor 41, and a plurality of rectangular teeth 42a, 42a are correspondingly formed on an inner peripheral portion of the stator 42. , And a solenoid 44 is wound around the stator 42. Two stopper pins 45 and 46 are formed on the rotor 41. On the other hand, as shown in FIG. 8, two grooves 47 and 48 are formed on the rear surface of the lid 43 at positions corresponding to the stopper pins 45 and 46 in the circumferential direction. The groove 47 engages with the stopper pin 45 to limit the movable range of the step motor 28, while the groove 48 engages with the stopper pin 46. Then, the stopper pins 45 and 46 are respectively inserted into the grooves 47 and
By engaging with 48, the center of gravity of the rotor 41 coincides with the center of rotation when the cover 43 is put on. Accordingly, the circumferential angle when viewing both ends of the grooves 47 and 48 from the center of the lid 43 is set to be larger in the groove 48 than in the groove 47, and the movable range of the step motor 28 is determined exclusively by the groove 47. It has become so. When the rotor 41 rotates clockwise in FIG. 7, the damping coefficients Dk of the shock absorbers 1 to 4 become larger and the damping force becomes harder. On the other hand, when the rotor 41 rotates counterclockwise, the damping coefficient Dk becomes larger. It becomes smaller and the damping force becomes softer, and furthermore, when the rectangular teeth 41a of the rotor 41 are moved to positions facing the adjacent rectangular teeth 42a of the stator 42, When the step motor 28 rotates one step, the damping coefficient Dk changes by one. Therefore, the stopper pin 45
Is located at the first reference position, which is the left end of the groove 47 in FIG. 8, the damping coefficient Dk becomes D10, and the shock absorbers 1-4 generate the hardest damping force, while the stopper pin 45 When it is located at the second reference position, which is the right end of the groove 47 in FIG. 8, the damping coefficient Dk becomes D1, and the shock absorbers 1-4 generate the softest damping force.

FIG. 9 shows a block configuration of a control system of the suspension device. In FIG. 9, the first pressure sensor 51, the acceleration sensor 11, and the actuator 25a are provided on the left front wheel 5 of the vehicle, the second pressure sensor 52, the acceleration sensor 12, and the actuator 25b are provided on the front wheel 5 on the right side of the vehicle. Sensor 53, acceleration sensor 13, and actuator 2
5c is provided on the rear wheel 6 on the left side of the vehicle body, and the fourth pressure sensor 54, the acceleration sensor 14, and the actuator 25d are provided on the rear wheel 6 on the right side of the vehicle body. still,
The actuators 25a to 25d are the same as the actuator 25 in FIG.
It is built in each of the shock absorbers 1-4.

Reference numerals 15, 16, and 17 denote the above-described vehicle speed sensor, steering angle sensor, and mode selection switch, respectively.
Reference numeral 55 denotes a road surface μ sensor for detecting a friction coefficient (μ) of a running road surface of the vehicle. The road surface μ sensor 55 detects a friction coefficient from a conventionally known method, for example, a vehicle speed and a vehicle acceleration which is a differential value thereof. It is supposed to. These sensors
All the detection signals of the switches are input to the control unit 8, and the control signals are sent from the control unit 8 to the first to fourth actuators 25a to 25a, respectively.
The damping coefficient Dki of each of the shock absorbers 1 to 4 is changed and controlled by operating the actuators 25a to 25d based on the control signal. The subscript k on the front side of the damping coefficient Dki indicates a switching stage,
Take the value of 10. The subscript i on the rear side indicates the actuator 25
a to 25d or shock absorber 1 incorporating it
Means numbers from 4 to 4, and takes a value from 1 to 4.

Next, control for changing the damping coefficient Dki of the shock absorbers 1-4 by the control unit 8 will be described. This change control is performed according to flowcharts shown in FIGS. 10 and 11, respectively. FIG. 10 is a flowchart of a damping coefficient limiting routine for changing the damping coefficient Dki of the shock absorbers 1 to 4 among a plurality of steps in a limited range among the ten steps. FIG. 9 is a flowchart of a basic routine of control for changing the damping coefficient Dki executed when the control mode is selected by the switch 16.

In FIG. 10, after starting, first, the vehicle speed V detected by the vehicle speed sensor 15 in step S1 and the vertical acceleration ai on the spring detected by the first to fourth acceleration sensors 11 to 14 in step S1. Input each signal.

Subsequently, in step S2, it is determined whether or not the vehicle speed V is equal to or higher than a first predetermined vehicle speed V1 (for example, 3 km / h) which is an extremely low vehicle speed value. If the determination is NO, step S3 is performed. The vehicle speed V is extremely low, so to prevent Scott and braking dives, the shock absorber 1
So that the damping coefficient Dki of ~ 4 becomes hard
Fix ki to D8i. In this case, the damping coefficient Dki is fixed at D8i, so that the basic routine of the damping coefficient change control shown in FIG. 11 is not performed.

On the other hand, when the vehicle speed V exceeds the first predetermined vehicle speed V1 (YES), the process proceeds to step S4, and the vehicle is traveling on a rough road where the absolute value of the vertical acceleration ai on the spring is equal to or higher than the predetermined value ai0. It is determined whether or not. If the determination is YES, the vehicle is traveling on a rough road, and the process proceeds to step S5 to determine whether the vehicle speed V is equal to or higher than a third predetermined vehicle speed V3 (for example, 50 km / h).

When the determination in step S5 is YES, in step S6, the damping coefficient Dki is controlled to be changed within a relatively hard range with emphasis on the improvement of the running stability.
The attenuation coefficient Dki is set in the range of D5i to D7i. As a result, in the basic routine of the change control of the damping coefficient shown in FIG. 11, the damping coefficient Dki has a lower limit value of D5i. D5i, while D7i is at the upper limit, and even if the condition to change more hardly holds,
The damping coefficient Dki will be held at D7i.

On the other hand, if the determination in step S5 is NO, the process proceeds to step S7, where it is necessary to achieve both running stability and ride comfort, so that the damping coefficients of the shock absorbers 1-4 are required. The damping coefficient Dki is set in the range of D3i to D7i in order to make it possible to control the change of Dki from a relatively soft state to a hard state. Therefore, in the basic routine of the damping coefficient change control shown in FIG. 11, the damping coefficient Dki has a lower limit value of D3i, and even if the condition to be changed softly is satisfied, the damping coefficient Dki becomes D3i. Held, while D
7i becomes the upper limit, and the damping coefficient Dki is held at D7i even if the condition to change more hardly holds.

On the other hand, when the determination in step S4 is NO, that is, when it is considered that the vehicle is not traveling on a rough road but on a normal road, the vehicle speed V is further increased in step S8.
Is less than or equal to a second predetermined vehicle speed V2 (for example, 30 km / h). When this determination is YES, in step S9, in order to emphasize the improvement of the riding comfort, the damping coefficient Dki of the shock absorbers 1-4 is controlled so as to be changed and controlled within a relatively soft range. D
Set in the range of 1i to D3i. Accordingly, in the basic routine of the change control of the damping coefficient shown in FIG. 11, when the damping coefficient Dki is D1i, the damping coefficient Dki is held at D1i even if the condition to be further softened is satisfied. , D3i becomes the upper limit value, and the damping coefficient Dki is held at D3i even if the condition to be changed more hardly holds.

If the determination in step S8 is NO, the vehicle speed V is further reduced to a fourth predetermined vehicle speed V4 in step S10.
(For example, 60 km / h) or less. If the determination is YES, the process proceeds to step S11, where it is necessary to achieve both of the two requirements of improving the running stability and the riding comfort. Therefore, the damping coefficients Dki of the shock absorbers 1-4 are relatively soft. The damping coefficient Dki is set in the range of D2i to D6i so that the change control can be performed within the range from the state to the hard state. Therefore, FIG.
In the basic routine of the damping coefficient change control shown in FIG. 1, the damping coefficient Dki has a lower limit of D2i. Even if the condition to be changed more softly is satisfied, the damping coefficient Dki remains at D2i.
On the other hand, D6i becomes the upper limit value, and even if the condition to be changed more hardly holds, the damping coefficient Dki is
6i.

On the other hand, if the determination in step S10 is NO, the process proceeds to step S12, and it is further determined whether the vehicle speed V is equal to or less than a fifth predetermined vehicle speed V5 (for example, 80 km / h). If this determination is YES, the process proceeds to step S13, and the control is performed to slightly change the damping coefficients Dki of the shock absorbers 1-4 while achieving the two requirements of running stability and ride comfort at the same time. The attenuation coefficient Dki is set in a range from D4i to D8i. Therefore, in the basic routine of the damping coefficient change control shown in FIG. 11, the damping coefficient Dki has D4i as the lower limit value, and even if the condition to be changed softly is satisfied, the damping coefficient Dki is held at D4i. On the other hand, D8i becomes the upper limit value, and even if the condition to be changed more hardly holds, the damping coefficient D
ki will be held in D8i.

When the determination in step S12 is NO, ie, when the vehicle is in the high-speed running state, the process proceeds to step S14, in which the damping coefficient Dki of the shock absorbers 1-4 is controlled within a hard range, with emphasis placed on improving running stability. , The damping coefficient Dki is set in the range of D7i to D10i. Therefore,
In the basic routine of the control for changing the damping coefficient shown in FIG. 11, the damping coefficient Dki has a lower limit of D7i.
Is held at D7i, while the damping coefficient Dki is held at D10i even if the conditions to be changed more hardly hold.

According to the above routine, the upper and lower limits of the damping coefficient Dki of the shock absorbers 1-4 selected in the basic routine of the damping coefficient changing control shown in FIG. A limiting means 61 is provided to limit the range of the damping coefficient Dki of the selected shock absorbers 1-4 by setting.

On the other hand, in the basic routine of the control for changing the damping coefficient shown in FIG. 11, after starting, first, in step S21, the currently selected damping coefficient Dki of the shock absorbers 1-4 is recognized. . Subsequently, in step S22, an upper threshold value α corresponding to the above-mentioned attenuation coefficient Dki is read from a map stored in advance as shown in FIG. In the map shown in FIG. 12, the upper limit threshold value α is set to 1 or more, and is set so as to decrease stepwise as the damping coefficient Dki increases every third.

Subsequently, in step S23, the above-mentioned attenuation coefficient D is obtained from a map stored in advance as shown in FIG.
Read the lower threshold value β corresponding to ki. In the map shown in FIG. 13, the lower limit threshold value β is set in a range between 0 and 1, and is set so as to increase stepwise as the damping coefficient Dki increases every third.

Thereafter, in step S24, the signals of the vertical acceleration ai on the spring and the damping force Fsi actually generated by the shock absorbers 1-4 detected by the first to fourth pressure sensors 51 to 54 are input. I do. Subsequently, in step S25, the acceleration ai is integrated to calculate a vertical displacement speed Xsi (= Σai) on the spring. In step S26, the displacement speed Xsi is multiplied by a predetermined constant K (K <0). The skyhook damper force Fai, which is the ideal damping force, is calculated.

Subsequently, in step S27, hαi is calculated according to the following equation: hαi = Fsi · (Fai−α · Fsi).

Thereafter, in step S28, it is determined whether or not hαi is positive. If YES is determined that hαi is positive, in step S33, the shock absorbers 1-4 are determined.
Control signals are output to the actuators 25a to 25d, and the step motor 28 of the actuators 25a to 25d is rotated clockwise in FIG.
ki is set to D (K + 1) i, which is one step larger than the previous attenuation coefficient Dki,
In other words, change to be harder. On the other hand, hαi
If NO is not positive, the process proceeds to step S29, and hβi = Fsi · (Fai−β · Fsi)... Hβi is calculated according to the following equation.

Thereafter, it is determined in step S30 whether hβi is negative. If YES is determined that hβi is negative,
In step S32, control signals are output to the actuators 25a to 25d of the shock absorbers 1 to 4 in which hβi is negative, and the step motor 28 of each of the actuators 25a to 25d is rotated by one step in the counterclockwise direction in FIG. The coefficient Dki is changed so that it becomes D (k-1) i one step smaller than the previous attenuation coefficient Dki, that is, becomes softer. On the other hand, when hβi is not negative and NO, in step S31, the stepping motor 28 is not rotated, that is, the damping coefficient Dki is changed to the previous damping coefficient Dki.
The next cycle is maintained without any change.

Here, α and β are thresholds for preventing the attenuation coefficient Dki from being changed too frequently, and as shown in FIGS. 12 and 13, α> 1, 0 <
β <1 is set.

That is, when Fsi and Fai have the same sign, (Fai−α · Fsi) in the above equation is α> 1, so that Fsi is not multiplied by α. Since the sign of Fsi tends to be different from that of Fsi, and as a result, hαi tends to be negative, it is difficult to change the attenuation coefficient Dki to the hard side. (Fai−β · Fsi) in the above equation is 0 <β <
Since it is 1, it is easy to have the same sign as Fsi as compared to the case where Fsi is not multiplied by β, and as a result, hβi is likely to be positive. Therefore, the attenuation coefficient Dki is also changed to the soft side. It becomes difficult. Furthermore, as the upper threshold value α decreases toward 1, the change of the damping coefficient Dki to the hard side becomes easier, and as the lower threshold value β decreases toward 0, the damping coefficient Dki decreases. Changes to the Dki software side are more difficult to make.

On the other hand, when Fsi and Fai have different signs, it is impossible to match the actual damping force Fsi with the skyhook damper force Fai which is an ideal damping force, It is desirable to set the coefficient Dki to a value close to zero, that is, to change the coefficient Dki to be softer in order to make Fsi closer to Fai. Therefore, in this embodiment, when Fsi and Fai have different signs, hαi and hβ
i are both negative values, so that the control unit 8 sets the damping coefficient Dki to D (k-1) i, which is one step smaller than the previous damping coefficient Dki, that is,. It is possible to satisfy such a request because it is changed to a shift.

In the basic routine of the damping coefficient change control shown in FIG. 11, in steps S24 to S33, the damping force Fsi actually generated by the shock absorbers 1 to 4 is changed to the skyhook in which the sprung does not change up and down. Control means 62 for changing and controlling the damping coefficients Dki of the shock absorbers 1 to 4 so as to obtain the damper force Fai is configured.
According to 28 to S31, when the difference between the actual damping force Fsi of the shock absorbers 1 to 4 and the skyhook damper force Fai is within a predetermined range (a so-called dead zone region), the control means 62 is controlled.
On the other hand, a prohibiting means 63 is configured to prohibit the change of the damping coefficient Dki of the shock absorbers 1-4. Further, the shock absorbers 1 to 4 are determined in steps S21 and S22.
The upper limit threshold changing means 64 is configured to decrease the upper limit threshold α of the predetermined range so as to approach 1 as the currently selected attenuation coefficient Dki increases.

Accordingly, in such damping coefficient change control, the shock absorbers F1 to F4 are generated so that the damping force Fsi actually generated becomes the skyhook damper force Fai whose sprung does not change up and down. Since the damping coefficients Dki of 1 to 4 are controlled to be changed, the vertical change on the sprung can be suppressed as much as possible, and the running stability can be enhanced.

In addition, when the difference between the actual damping force Fsi of the shock absorbers 1-4 and the skyhook damper force Fai is within a predetermined range, the change control is prohibited,
The upper limit and the lower limit of the selected damping coefficient Dki of the shock absorbers 1 to 4 are set in accordance with the running state of the vehicle such as the vehicle speed, and the damping coefficient Dki of the shock absorbers 1 to 4 is set within this limited range. Since it is changed, it is possible to prevent the generation of loud switching noise and vibration due to a large change in the damping coefficient of the shock absorber while achieving both running stability and riding comfort according to the running state of the vehicle.

Further, the above-mentioned predetermined range of the change prohibition, that is, the upper threshold value α of the dead zone is set to
4 is smaller as the damping coefficient Dki is larger, and when a large external force is suddenly applied, such as when the wheel gets over a bump on the road while the vehicle is running, the change of the damping coefficient Dki to the hard side is caused by the dead zone. Performed quickly with little effect of the presence of the region. For this reason, shock absorbers 1
No. 4 generates a damping force close to the skyhook damper force Fai and exerts a sufficient damping effect, so that the riding comfort and running stability can be improved at a high level.

[0047]

As described above, according to the vehicle suspension device of the present invention, when the difference between the actual damping force of the shock absorber and the target damping force is within a predetermined range, the damping coefficient of the shock absorber is reduced. In addition to prohibiting the change control, the upper limit threshold of the predetermined range is changed according to the currently selected damping coefficient of the shock absorber, thereby minimizing the control delay in the damping coefficient changing control. The driving stability and riding comfort can be improved at a high level.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a component layout of a vehicle including a suspension device according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view showing a main part of the shock absorber.

FIG. 3 is an exploded perspective view of the actuator.

FIG. 4 is a schematic view showing a vibration model of the suspension device.

FIG. 5 is a diagram showing a damping coefficient of a shock absorber.

FIG. 6 is a perspective view of a step motor.

FIG. 7 is a plan view of a rotor and a stator of the step motor.

FIG. 8 is a bottom view of the lid of the step motor.

FIG. 9 is a block diagram of a control system of the suspension device.

FIG. 10 is a flowchart illustrating a routine for limiting an attenuation coefficient.

FIG. 11 is a flowchart illustrating a basic routine of change control of a damping coefficient.

FIG. 12 is a map diagram for setting an upper threshold value α.

FIG. 13 is a map diagram for setting a lower threshold value β.

[Explanation of symbols]

 1, 2, 3, 4 Shock absorber 62 Control means 63 Prohibition means 64 Upper threshold change means

Continuation of front page (56) References JP-A-2-74411 (JP, A) JP-A-2-303913 (JP, A) JP-A-61-184113 (JP, A) JP-A-61-268508 (JP) JP-A-61-75007 (JP, A) JP-A-60-244610 (JP, A) JP-A-62-153108 (JP, U) JP-A-5-13806 (JP, U) (58) Field surveyed (Int.Cl. ⁷ , DB name) B60G 17/015 B60G 17/08

Claims (2)

(57) [Claims] 1. A shock absorber which is disposed between a sprung portion and a unsprung portion and whose damping coefficient can be changed in a plurality of stages, and wherein the damping force actually generated by the shock absorber does not change vertically. Control means for changing and controlling the damping coefficient of the shock absorber so as to attain the target damping force, wherein the difference between the actual damping force of the shock absorber and the target damping force is within a predetermined range. A prohibition means for prohibiting the change control of the control means; and an upper threshold change means for changing the upper threshold of the predetermined range according to the magnitude of the currently selected damping coefficient of the shock absorber. And a suspension device for a vehicle. 2. The vehicle according to claim 1, wherein said upper limit threshold value changing means is configured to decrease the upper limit threshold value of a predetermined range as the currently selected damping coefficient of the shock absorber increases. Suspension device.