JPH08183318A - Electronic control suspension of vehicle - Google Patents

Abstract

PURPOSE: To reduce roll and improve yaw characteristics in simple constitution by delaying a front wheel side for a specified time and taking measures to change suspension characteristics over to hard when lateral acceleration exceeds a specified value. CONSTITUTION: A changeover by two stages or more is made in at least either a spring constant or damping force as suspension characteristics by an actuator (a) for each of front and rear wheels of a vehicle. Additionally, lateral acceleration of the vehicle is detected by a means (b), and when this detected value exceeds a specified value, a control signal to change suspension characteristics over to hard by way of delaying the front wheel side by specified time is output by a means (c). Furthermore, when the lateral acceleration becomes the specified value or less, a control signal to change the suspension characteristic over to soft by way of delaying the front wheel side for the specified time is output by a means (d). Thereafter, the actuator (a) is driven by a means (e) in accordance with these output signals. Consequently, reduction of roll and improvement of yaw characteristics are realized in simple constitution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a vehicle electronically controlled suspension.

[0002]

2. Description of the Related Art In order to achieve a high level of ride comfort and maneuverability of a vehicle, the spring constant of the air spring and the damping force of the shock absorber are normally kept in a soft state while the maneuverability during turning is improved. An electronically controlled suspension is known, which is designed to be switched to a hard one in a driving situation where importance is attached to (Mitsubishi Motors Technical Review 199
3 NO.5 “Development of electronically controlled suspension for large buses”
reference). During this so-called semi-active suspension control, there is a technique of reducing the roll angle of the vehicle body by switching the air spring and the shock absorber to hard.

By the way, when the roll rigidity of the front wheel side and the rear wheel side is changed, the load transfer between the left and right wheels is changed, and the grip balance (that is, the steer characteristic) between the front wheel side and the rear wheel side is changed. When the roll rigidity distribution of is increased, there is an understeer tendency, and when the roll rigidity distribution to the rear wheels is increased, there is an oversteer tendency. Therefore, in order to improve the yaw characteristics of the vehicle in the active suspension, the distribution on the rear wheel side is large in the driving situation where the turning performance of the vehicle is required, and the distribution to the front wheel side is performed in the driving situation where the convergence of the vehicle is required. It is known that the motor is controlled to a large degree (see MotorFan magazine No. 89/12, "Stair characteristic control of Nissan active suspension").

[0004]

However, in the former case (semi-active suspension), control of the yaw characteristic is not taken into consideration, and in the latter case (active suspension), a complicated mechanism is required, resulting in an expensive system. There was a problem that became.

An object of the present invention is to reduce rolls and improve yaw characteristics with a simple structure in a semi-active suspension.

[0006]

According to the present invention, as shown in FIG. 6, an actuator a for switching at least two steps of at least one of a spring constant and a damping force as a suspension characteristic for each front and rear wheels of a vehicle, The means b for detecting the lateral acceleration of the vehicle and the means c for outputting a control signal for delaying the front wheel side by a predetermined time to switch the suspension characteristics to the hard side when the lateral acceleration exceeds a predetermined value based on the detection signal are also used. When the acceleration becomes equal to or lower than a predetermined value, a means d for delaying the front wheel side for a predetermined time to output a control signal for softly changing the suspension characteristic, and a means e for driving an actuator according to these output signals are provided.

[0007]

When the lateral acceleration exceeds a predetermined value when the vehicle is turning or when changing lanes, only the suspension characteristics of the rear wheels are switched to hard at first, so the roll rigidity of the rear wheels is lower than that of the front wheels. As the yaw characteristic increases, the yaw characteristic tends to oversteer, which improves the turning performance of the vehicle. When a predetermined time elapses in this state, the suspension characteristics on the front wheel side are also switched to hard after the rear wheel side. Therefore, it is possible to efficiently suppress the roll due to lateral acceleration exceeding a predetermined value. After that, when the lateral acceleration becomes a predetermined value or less, the front wheel side is delayed by a predetermined time and the suspension characteristics are softly switched, so that the yaw characteristics tend to be understeer this time and the convergence of the vehicle is improved.

[0008]

1 and 2, 20 is a vehicle body as a sprung system of a vehicle, 1a to 1d are tires as unsprung systems of the vehicle, and air springs 2a to 2f and shock absorbers 7a to 7f are attached to them. Intervened. Although not shown, the shock absorbers 7a to 7f are provided with a damping force variable mechanism (including an actuator) that is switched between two stages, hard and soft, by opening and closing the orifice of the piston.

The air springs 2a to 2f are connected to the air reservoir 3 via leveling valves 4a to 4c for controlling air supply and exhaust so as to maintain desired vehicle heights. Since there is one leveling valve 4c on the rear wheel side, the air springs 2c, 2e at the rear left and right are in communication with 2d, 2f. Therefore, from the standpoint of increasing roll rigidity during turning, etc., each pipe has an on-off valve 8a, 8b is provided.

The sub-tanks 5a to 5d are connected to the air springs 2a to 2f via the switching valves 6a to 6f, respectively. When the opening / closing of the valves 6a to 6f is controlled, the substantial air volume changes, so that the air spring 2a. The spring constant of ~ 2f is switched between two levels (hard and soft). FIG. 1 is an overall system configuration diagram, and FIG. 2 is a configuration diagram on a front wheel side representing a suspension for one wheel.

The vehicle speed sensor 17 for detecting the traveling speed of the vehicle, the lateral acceleration sensor 14 for detecting the lateral acceleration of the vehicle body, and the vertical direction of the vehicle body are provided as the detection means necessary for performing various controls according to the traveling condition of the vehicle. A vertical acceleration sensor 15 for detecting acceleration, a steering angle sensor 11 for detecting a steering angle of a steering wheel, a foot brake switch 12, a back lamp switch 16, and a side brake switch 13 for detecting a braking state of a vehicle, manual control and automatic control. A mode selector switch 10 for selecting control is provided.

The controller 9 controls rolls of the vehicle body, brake dives, pitching and bouncing, etc. based on input signals from these sensors and switches.
The functional block configuration for performing the roll control is shown in FIG. 3, where the lateral acceleration sensor 14 and the vehicle speed sensor 17 are used.
Means 31 for input-processing the detection signals of the above, a means 32 for determining necessity of roll control from these processed signals (lateral acceleration and vehicle speed), and means for determining a drive pattern of roll control according to elapsed time. 33, and means 34 and 35 for outputting drive signals to the switching valves 6a to 6f of the air springs 2a to 2d and the damping force varying mechanism of the shock absorbers 7a to 7f based on these results.

FIG. 4 is a flow chart for explaining the roll control in the automatic mode, which is repeatedly executed at a predetermined control cycle. First, after initialization, the detection signal Gy of the lateral acceleration sensor and the detection signal V of the vehicle speed sensor are read (steps 1 and 2). When the vehicle speed signal V is zero (stopped state), the switching valves 6a and 6b of all the air springs 2a to 2f are "opened",
The damping force varying mechanism of all the shock absorbers 7a to 7f is switched to the "soft" state (step 3 → step 21 to step 22).

If the vehicle speed signal is not zero, the lateral acceleration threshold value Gt corresponding to the vehicle speed signal V at that time is read from the data map as shown in FIG. 5 (step 4). This threshold Gt
And the absolute value of the lateral acceleration signal Gy are compared, and | Gy |> Gt
At that time, it is determined that the roll control is necessary, and the timer is turned on from that point and the flag is set to 1 (steps 5 and 6).

Until the timer counts the elapse of the predetermined time T ₁ , the switching valves 6a and 6b of the front wheel side air springs 2a and 2b are "opened" and the rear wheel side air spring 2c.
The switching valves 6c to 6f of 2 to 2f are closed, the damping force variable mechanism of the front wheel side shock absorbers 7a and 7b is switched to "soft", and the damping force variable mechanism of the rear wheel side shock absorbers 7c to 7f is switched to "hard" ( Step 7 to Step 1
1).

When the timer counts the lapse of the predetermined time T ₁ , the switching valves 6a to 6f of all the air springs 2a to 2f.
Is closed, and the damping force varying mechanism of all shock absorbers 7a to 7f is switched to "hard" (steps 12 and 13).

When the absolute value | Gy | of the lateral acceleration is less than the threshold value Gt, the state of the flag is confirmed (step 5 → step 14). When the flag is 0, it is determined that the roll control is not required in normal time, and the switching valves 6a to 6f of all the air springs 2a to 2f are "opened", and all the shock absorbers 7a to 7f.
The variable damping force mechanism is maintained in the "soft" state (step 14 → step 21, step 22).

[0018] If not flag = 0, the timer until counts a lapse of a predetermined period of time T _2, the front-wheel-side air springs 2a, selector valve 6a of 2b, 6b to "closed", the rear-wheel-side air springs 2c~2f The switching valves 6c to 6f are opened, the damping force varying mechanism of the front wheel side shock absorbers 7a and 7b is switched to "hard", and the damping varying mechanism of the rear wheel side shock absorbers 7c to 7f is switched to "soft" (step 15). ~ Step 19). When the timer counts the elapse of the predetermined time T ₂ , the timer is turned off and the flag is set to 0.
To clear (step 15 → step 20). Then, the switching valves 6a to 6f of all the air springs 2a to 2f are "opened", and the damping force varying mechanisms of all the shock absorbers 7a to 7f are switched to "soft" (steps 21 and 22).

With such a configuration, the air springs 2a to 2f and all the shock absorbers 7a to 7f of the front and rear wheels are kept in a "soft" state during normal times including when the vehicle is stopped, which is peculiar to the air suspension. Good ride comfort can be obtained.

When turning or changing lanes, when the absolute value of lateral acceleration | Gy | exceeds a threshold value Gt, initially only the suspension characteristics on the rear wheel side are switched to hard.
Since the roll rigidity of the rear wheels is higher than that of the front wheels,
The yaw characteristic tends to oversteer, which improves the turning performance of the vehicle.

[0021] While continues until this condition is the predetermined time T ₁ is elapsed the predetermined time T ₁ is passed, because the suspension characteristic of the front wheel side behind the rear wheel side switched to hard, the lateral acceleration exceeds a predetermined value The accompanying roll can be efficiently suppressed.

After that, when the lateral acceleration becomes a predetermined value or less,
Only the suspension characteristic on the rear wheel side is softly switched until the predetermined time T ₂ elapses prior to the front wheel side, so that the yaw characteristic tends to understeer this time and the convergence (stability) of the vehicle is improved.

In this case, since the spring constants and damping forces of the front and rear wheels are controlled according to the elapsed time, the program can be simple. In addition, it does not require a complicated mechanism like the active suspension, and the on / off type that ensures the control of the suspension characteristics can reduce rolls and improve the yaw characteristics at low cost. The steering angle or the steering angular velocity may be used as a parameter for roll control instead of the lateral acceleration.

[0024]

According to the present invention, an actuator for switching at least one of a spring constant and a damping force as suspension characteristics in two or more stages for each of front and rear wheels of a vehicle, and means for detecting a lateral acceleration of the vehicle. Based on this detection signal, when the lateral acceleration exceeds a predetermined value, a means for outputting a control signal for delaying the front wheel side for a predetermined time to switch the suspension characteristics to hardware, and when the lateral acceleration becomes equal to or less than the predetermined value, Since a means for outputting a control signal for softly switching the suspension characteristics after delaying for a predetermined time and a means for driving the actuator in response to these output signals are provided, it is possible to prevent turning at the initial stage when turning or changing lanes. While improving the convergence at the end stage, it is possible to efficiently suppress the rolling of the vehicle body that continues during that time. Further, the control is simple and a complicated mechanism is not required, which is advantageous in terms of cost.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an entire system showing an embodiment of the present invention.

FIG. 2 is a configuration diagram showing a suspension for one wheel.

FIG. 3 is a block diagram of a roll control system.

FIG. 4 is a flowchart illustrating roll control.

FIG. 5 is a threshold map of lateral acceleration used for roll control.

FIG. 6 is a diagram corresponding to the claims of the present invention.

[Explanation of symbols]

 1a-1d Tire 2a-2f Air spring 4a-4c Leveling valve 5a-5d Sub-tank 6a-6f Switching valve 7a-7f Shock absorber 9 Control unit 14 Lateral acceleration sensor 17 Vehicle speed sensor

Claims (1)

[Claims] 1. At least one of a spring constant as a suspension characteristic and a damping force for each of the front and rear wheels of a vehicle is 2
An actuator that performs switching in steps or more, a means that detects the lateral acceleration of the vehicle, and a control signal that delays the front wheel side for a predetermined time when the lateral acceleration exceeds a predetermined value based on this detection signal to switch the suspension characteristics to hardware. A means for outputting, a means for outputting a control signal for delaying the front wheel side for a predetermined time to softly change the suspension characteristics when the lateral acceleration becomes equal to or less than a predetermined value, and a means for driving an actuator according to these output signals A vehicle suspension device characterized by the above.