JP3139579B2 - Control device for vehicle suspension - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control system for a vehicle suspension.

[0002]

2. Description of the Related Art Research has been made to change the damping force of a damper in real time according to the vibration state of a vehicle to further improve the riding comfort.
It is disclosed in Japanese Patent Publication No. 1-163011.

In this prior art, a damping force variable damper (shock absorber) capable of switching between a hard damping force characteristic on both the extension side and the compression side, and a soft damping force characteristic on both the extension side and the compression side. A vertical displacement speed on a sprung (ie, vehicle body) and a vertical relative displacement speed (suspension stroke speed) between a sprung portion and a unsprung portion are detected, and they are upward (for example, +) or downward (for example,-). The damping force characteristic of the damper is switched to a hard characteristic when both are upward or downward, and to a soft characteristic when one is upward and the other is downward. It was made.

[0004]

The above is based on the theory of a skyhook damper (a virtual model in which a one-wheel suspension is regarded as one degree of freedom and damping is applied to an absolute space). It is approximated by a damping force variable damper mounted at the position, and has the effect of improving the ride comfort by optimizing the vehicle vibration near the vehicle body natural frequency (1-2 Hz). On the other hand, in the conventional control described above, the damper characteristic is switched even by a high-frequency, small-amplitude vibration input centered on the unsprung resonance frequency band, and the control for such high-frequency, small-amplitude vibration is performed. However, there is a problem that it is difficult to mechanically follow the vehicle, leading to a deterioration in riding comfort due to a delay in following the vehicle, and a problem that the durability is reduced due to an increase in the number of switching operations.

For the purpose of solving the above problems, the present applicant previously set a threshold δ for the vertical displacement speed on the spring, and when the vertical displacement speed on the spring is less than the threshold δ, the vertical displacement on the spring has been set. High-frequency, small-amplitude vibration is maintained by maintaining soft or slightly soft damping force characteristics on both the extension side and the compression side regardless of whether the speed direction and the suspension stroke speed direction are the same or opposite. A control method and a control device for improving the vibration isolation against input and reducing the frequency of switching the damper to improve the durability have been developed. 13
Patent pending as 5433.

As described above, in the method in which the threshold value δ is fixedly set to a certain value for the sprung vertical displacement speed, the threshold value δ is set to a relatively large value when emphasis is placed on the improvement of riding comfort when traveling straight. If δ is set relatively large in this way, there is a problem that vibration control for the vehicle body roll during turning of the vehicle tends to be delayed, and a countermeasure is required. That is, when the vehicle turns, the outer wheel side sinks and the inner wheel side lifts, and a vertical displacement speed occurs in each wheel, but the value does not easily exceed the threshold value δ set to a relatively large value as described above, and the roll starts. This causes a problem that a time lag occurs until the vertical displacement speed exceeds the threshold value δ and the vibration suppression control is delayed.

SUMMARY OF THE INVENTION It is an object of the present invention to address the above-described problems of a suspension control device in which a threshold value is set for the vertical displacement speed on a spring.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a vehicle suspension control device equipped with a damping force variable damper which can be switched between two stages of high damping force characteristics and low damping force characteristics. When is smaller than the threshold value, the characteristic of the damper is the low damping force characteristic, and when the vertical displacement speed on the sprung is larger than the threshold value, the direction of the vertical relative displacement speed between the sprung and unsprung is the same as the vertical displacement speed. A controller is provided to switch and control the damping force characteristics of the above damper to high damping force characteristics if low and low damping force characteristics if different.
And changes in lateral acceleration caused by turning the vehicle.
Predict the rate and check if the predicted value is greater than or equal to the set value
Threshold change that changes the above threshold depending on whether it is less than
It is characterized by comprising control means .

[0009]

In the above description, the threshold value of the vertical displacement speed on the sprung is set to a relatively large value during straight running or near normal running, whereby a high-frequency, small-amplitude vibration input near the unsprung resonance frequency band is obtained. In the case of a turn in which a body roll occurs, the threshold is changed and set to a small value, so that a spring generated with the actual body roll is provided. The upper vertical displacement speed easily exceeds the threshold, that is, the area of the dead zone, and as a result, the vibration suppression control for the vehicle body roll is accurately performed without delay.

[0010]

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

FIGS. 1 and 2 show a first embodiment of the present invention, and show an example in which the present invention is applied to the invention of Japanese Patent Application No. 3-135433 mentioned above as a prior patent. That is, in the first embodiment, as shown in FIG. 1A, the damper of each suspension of four wheels in the front, rear, right and left directions of the vehicle has a characteristic a (shown by a solid line) of high damping force on both the extension side and the compression side and the extension side. , The compression side has two damping force characteristics of a low damping force characteristic b (shown by a dotted line), and these two characteristics can be switched by an electric signal. Is shown.

FIG. 1B is a model diagram in which a controller 5 for controlling the one-wheel model of the suspension having the above-described variable damping force damper is combined with a variable damper force damper (hereinafter simply referred to as a damper). 2) a suspension spring, 3 a vertical acceleration sensor for detecting the vertical acceleration on the spring, and 4 a suspension stroke sensor for detecting the vertical relative displacement between the sprung and unsprung, that is, the suspension stroke. Each sensor 3, 4 is mounted for each suspension. Also, in FIG. 1B, M1 and K
1 represents the unsprung mass, that is, the mass of the tire and the spring constant.
M2 is the sprung mass of the vehicle body, K2 is the spring constant of the suspension spring 2, C is the damping coefficient of the damper 1, X0
Is the vertical displacement of the road surface, X1 is the unsprung vertical displacement, and X2 is the unsprung vertical displacement.

Reference numeral 8 denotes a threshold change control means for changing and controlling a threshold δ of a vertical displacement speed, which will be described later. The threshold change control means 8 includes a vehicle speed sensor 6 for detecting a vehicle speed and a steering angular speed sensor 7 for detecting a steering angular speed. Based on each detection signal, the driver's driving operation is detected, and the lateral acceleration change rate (substantially proportional to the roll speed) that occurs thereafter is predicted. When the predicted value exceeds a certain set value, the threshold δ is changed to a small value. Set,
If the predicted value is less than the set value, δ is set to a large value. As the vehicle speed sensor 6 and the steering angular velocity sensor 7, any conventionally known ones can be adopted.

The controller 5 includes an integrating circuit 51 for obtaining the vertical displacement speed on the spring from the detection signal of the vertical acceleration sensor 3 and the vertical relative displacement speed between the sprung and unsprung components based on the detection signal of the suspension stroke sensor 4. A differential circuit 52 for determining a suspension stroke speed;
The absolute value of the vertical displacement speed on the spring obtained by 1 (the direction of the vertical displacement speed is assumed to be indicated by a sign of + in the upward direction and-in the downward direction) is the threshold value δ selected and set by the threshold value change control means 8. It is determined whether or not it is within the range. If it is not less than δ, the direction of the suspension stroke speed obtained by the differentiating circuit 52 (upward is represented by +, downward is represented by the sign of −) and the vertical displacement Judge whether the direction of the speed is the same or different, if high, select the high damping force characteristic a,
If they are different, the low damping force characteristic b is selected, and a signal for switching the damping force characteristic of the damper 1 according to the selection is issued. If the vertical displacement speed is less than the threshold value δ, a signal to make the damper 1 have a low damping force characteristic is generated by selecting the low damping force characteristic b.

As described above, the threshold value δ for determining the dead zone of the damping force characteristic switching control of the damper 1 is set to the threshold value changing control means 8.
When the predicted value of the lateral acceleration change rate at the time of steering is equal to or larger than a set value, the value is set to be small, and when the predicted value is smaller than the set value, the value is variably controlled so that the vehicle is traveling straight ahead or close to normal driving. With a large threshold δ (large dead zone region of sprung vertical displacement speed), vibration control with high vibration isolation and good ride comfort is performed for high frequency, small amplitude vibration input.
Also, when turning the vehicle, the threshold δ is set small, and the sprung vertical displacement speed generated with the actual body roll makes it easy to come out of the dead zone, thereby accurately changing the vehicle posture change (body roll) due to the turn. Vibration suppression control is performed.

The above control is represented by a flowchart.
As shown in FIG.

FIGS. 3 and 4 show a second embodiment of the present invention, in which the present invention is applied to the invention of Japanese Patent Application No. 3-135432 described above as a prior patent. That is, in this example, as shown in FIG. 3A, the damper 1 mounted on the front, rear, left and right four-wheel suspension has a soft (low damping force) on the extension side and a hard (high damping force) on the compression side. One mode a '(shown by a solid line) and a second mode b' (shown by a dotted line) in which the extension side is hard (high damping force) and the compression side is soft (low damping force).
Slightly soft (slightly low damping force) on both the extension and compression sides
And the third mode c ′ (shown by a dashed line)
The detection signal of the vertical acceleration sensor 3 for detecting the vertical acceleration on the spring is integrated by the integration circuit 51 of the controller 5 using a damping force variable damper which switches these modes by an electric signal. It is determined whether or not the obtained absolute value of the vertical displacement speed on the spring (the direction of the vertical displacement speed is represented by a + sign in the upward direction and a minus sign in the downward direction) is less than the threshold value δ. The third mode c 'is selected. If it is not less than δ, it is determined whether the direction of the vertical displacement speed is upward or downward. If it is upward, the second mode b' is selected. The mode a 'is selected, and a signal for switching the mode of the damping force variable damper 1 according to the selection is issued. Therefore, in this embodiment, there is an advantage that the suspension stroke sensor 4 and the differentiating circuit 52 can be omitted and the switching frequency of the damper 1 is further reduced as compared with the first embodiment shown in FIG.

In such a suspension control device, the threshold value δ is variably controlled by the threshold value changing control means 8 in the same manner as in the first embodiment, so that the vehicle travels straight or when the vehicle is running normally. By increasing the threshold value δ, the vibration isolation for high-frequency, small-amplitude vibration input near the unsprung resonance frequency band is improved to control the ride comfort, and when turning with a relatively large body roll, By making the threshold value δ small, the vertical displacement speed on the spring easily exceeds the dead zone region. As a result, the damper on the turning outer wheel side moves to the first mode a ′ (compression side hard) due to the roll generation,
The damper on the turning inner wheel side is the second mode b '(extension side hard)
In this case, the damping force characteristics are switched and controlled, and the vibration control for the vehicle body roll is accurately performed without delay.

It should be noted that the reference numerals in FIG.
The same reference numerals denote the same components.

FIG. 4 is a flowchart showing the control mode of the second embodiment.

Next, a specific example of the method of setting the threshold value δ by the threshold value change control means 8 in FIGS. 1B and 3B will be described with reference to FIG.

The threshold value selection setting of the threshold value change control means 8 uses a data map as shown in FIG. 5A, for example, and determines the vehicle speed and the steering angular speed based on the input of each detection signal of the vehicle speed sensor 6 and the steering angular speed sensor 7. A search is made as to whether or not the condition of the shaded area of the data map is satisfied. If the condition of the shaded area is not satisfied, a threshold δ having a large value is selected and set so as to be optimal for the vibration suppression control during straight running, and the shaded area is set. If the condition (1) is satisfied, it is determined that the vibration suppression control for the vehicle body roll is necessary, and threshold change control is performed to change and set the threshold to a smaller value δ.

Although the above description shows an example in which the threshold value δ is changed and set to two levels, as shown in Table 1 below, the estimated roll rate is divided into three levels of large, medium and small, and FIG. )
The threshold value change control means 8 may change the threshold value δ from the data map to three levels of large, medium, and small, or finely set the threshold value to a plurality of levels of four levels or more. Change control may be performed.

[0024]

[Table 1]

The method of changing and setting the threshold value δ is described in FIG.
The method is not limited to the method using the data maps of (A) and (B), but if the body roll is predicted, for example, the change rate of the lateral acceleration is predicted from the slope of the detection signal of the conventionally known lateral g sensor, and δ is reduced. Any method that can achieve the purpose described above can be adopted.

[0026]

As described above, according to the present invention, in a vehicle suspension control device equipped with a damping force variable damper capable of switching between two stages of high damping force characteristics and low damping force characteristics, When the displacement speed is smaller than the threshold value, the characteristic of the damper is a low damping force characteristic, and when the vertical displacement speed on the sprung is larger than the threshold value, the direction of the vertical relative displacement speed between the sprung and unsprung is equal to the vertical displacement speed. if they are the same in the high damping force characteristic, as well as to the low damping force characteristic switching the damping force characteristic of the damper control different, during turning of the vehicle
Predict the rate of change in lateral acceleration that will occur, and set the predicted value
The above threshold is changed and controlled depending on whether it is greater than or less than the set value.
With the arrangements as that normally travel at high frequency around the unsprung resonance frequency band, with the damping control of the comfort ride improves the vibration insulating preference for the vibration input of small amplitude is performed, body roll when the vehicle is turning Can be accurately performed without delay, and can bring a great effect in practical use.

[Brief description of the drawings]

1A and 1B show a first embodiment of the present invention, in which FIG. 1A shows a damping force characteristic of a damping force variable damper, and FIG. 1B shows a one-wheel model of a suspension combined with a controller for controlling the suspension. FIG.

FIG. 2 is a flowchart showing a control mode of the apparatus shown in FIG.

3A and 3B show a second embodiment of the present invention, in which FIG. 3A shows a damping force characteristic of a damping force variable damper, and FIG. 3B shows a one-wheel model of a suspension combined with a controller for controlling the same. FIG.

FIG. 4 is a flowchart showing a control mode of the apparatus shown in FIG.

FIGS. 5A and 5B are diagrams respectively showing examples of data maps used for threshold change setting of a threshold change controller.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 damping force variable damper 2 suspension spring 3 vertical acceleration sensor 4 suspension stroke sensor 5 controller 6 vehicle speed sensor 7 steering angular velocity sensor 8 threshold value change control means 51 integration circuit 52 differentiation circuit

Claims (2)

(57) [Claims] 1. A control device for a vehicle suspension equipped with a damping force variable damper switchable between two stages of a high damping force characteristic and a low damping force characteristic. When the vertical displacement speed on the sprung is larger than the threshold value, the characteristic of the vertical relative displacement speed between the unsprung and unsprung is the same as the vertical displacement speed. A controller for switching the damping force characteristic of the damper to a low damping force characteristic if different , and
The rate of change in lateral acceleration that occurs, and the predicted value
Above depending on whether it is greater than or equal to the set value
A suspension control device for a vehicle, comprising: a threshold change control unit configured to change and control a threshold . 2. A first mode having a characteristic of low damping force on the extension side and a high damping force on the compression side, a second mode having a characteristic of high damping force on the extension side and a low damping force on the compression side, A control device for a vehicle suspension equipped with a damping force variable damper having a third mode having substantially the same damping force characteristics on the compression side and the compression side, When the vertical displacement speed is smaller than the threshold, the third mode is selected. When the vertical displacement speed on the spring is larger than the threshold, the first mode is selected when the vertical displacement speed is downward, and the second mode is selected when the vertical displacement speed is upward. A controller for selecting and controlling switching of the damping force characteristic of the damper; and a threshold change control unit for variably setting the threshold in accordance with a roll state of the vehicle. Vehicle suspension The control device.