JPH01172070A - Auxiliary steering device for car - Google Patents

Abstract

PURPOSE:To enhance the safety in braking a car equipped with an anti-skid system by steering the rear wheels in a minute angle when control is made on a crossover road with different coefficients of friction of the left and right grounding wheels with the road surface. CONSTITUTION:The left and right wheel speeds at the front and rear of a car are sensed by sensors S1-S4. The brake pressure applied to each wheel is controlled by a solenoid valve A1. When brakes are applied, this solenoid valve A1 is controlled by a brake pressure control means U1 on the basis of detection signals given by the sensors S1-S4. On the other hand, the brake pressure presumed values on the left and right wheels are calculated by a presuming means U2 on the basis of signals controlling the solenoid valve A1. The correctional steering angle is calculated by a steering angle calculating means U3 on the basis of the difference between the brake pressure presumed values on the left and light wheels. According to the correctional steering angle the rear wheels are steered by a rear wheel steering means A2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an auxiliary steering device for correcting a vehicle course during braking in a vehicle equipped with an anti-skid system.

[Conventional technology]

Conventionally, as shown in Japanese Patent Application Laid-Open No. 58-164460, vehicles equipped with an anti-skid system detect the rotational speed of each left and right wheel and control the brake pressure of the left and right wheels to prevent skidding. During anti-skid control such as during braking, the coefficient of friction μ of the road surface that the left and right wheels touch is
Due to this difference, the brake pressure applied to the left and right wheels will be different. This is because the wheels on the side with a low road surface μ (low μ road) tend to lock, so the brake pressure is lowered to allow the wheels to roll and prevent them from locking. Conversely, wheels on the side of the road with a high μ (high μ road) are less likely to lock up than those on the low μ road.
It is controlled with higher brake pressure than the roadside wheels.

[Problem that the invention seeks to solve]

As a result, in conventional anti-skid systems, the left and right wheels contact the road surface with different μ (so-called straddling roads, etc.).
When braking suddenly, there is a difference in braking force between the left and right wheels, creating a yaw moment that tends to cause the vehicle's course to deviate toward a high-μ road.

Therefore, the present invention aims to provide a safe system that does not deviate the course of the vehicle even when a vehicle equipped with an anti-skid system brakes suddenly on a road surface (straddle road, etc.) where the road surfaces on which the left and right wheels contact differ in μ. The purpose of this is to enable braking.

[Means for solving problems]

In order to achieve the above object, the present invention provides wheel speed sensors S1 to S1 for detecting the left and right wheel speeds of a vehicle as shown in FIG.
S4, a solenoid valve AI that controls the brake pressure applied to the wheels, and a brake pressure control means U1 that controls the solenoid valve A1 to prevent skidding based on the detection signals of the wheel speed sensors S1 to S4 when braking the vehicle. , an estimating means U2 that calculates estimated brake pressure values for the left and right wheels based on a signal that controls the solenoid valve AI; and a steering angle that calculates a corrected steering angle for the rear wheels from the difference between the estimated brake pressure values for the left and right wheels. Calculation means U3 and rear wheel steering means A2 that steers the rear wheels according to the corrected steering angle
Adopt technical means to provide

[Effect]

When suddenly braking on a straddling road, the present invention estimates the brake pressure of the left and right wheels from the control signal of the solenoid valve for brake pressure control, and determines that the road is a straddle road from the difference in the estimated brake pressure values of the left and right wheels. Based on this, the rear wheels are steered by a small angle. As a result, the yaw moment caused by the difference between the left and right wheels is canceled out, and the vehicle is braked safely without being deflected.

〔Example〕

The present invention will be explained below with reference to embodiments shown in the drawings.

Figure 2 shows the electronic control circuit E for the 4-wheel anti-skid system.
The configuration of the CUI and rear wheel steering system electronic control circuit ECU2 is shown.

Circuits ECU 1 and ECU 2 are microcomputer systems, each including a CPU, RoM, RAM, and l1.
Equipped with 0 (input/output) units. ECUI I10
Connected to the unit are wheel speed sensors S1 to S4 which generate pulse signals with a frequency proportional to the wheel rotation speed of the vehicle. Here, sensor S1 is for the left front wheel, and sensor S2 is for the left front wheel.
is for the right front wheel, sensor S3 is for the left rear wheel, and sensor S4 is for the right rear wheel.

The I10 unit of the ECU1 has four 2-position (open/close) solenoid valves 11 to 1 that control the brake pressure applied to each wheel.
A solenoid valve unit consisting of 4) Al is connected. The valve 11 is for the left front wheel, the valve 12 is for the right front wheel, the valve 13 is for the left rear wheel, and the valve 14 is for the right rear wheel.

These constitute an anti-skid system, and the EC
Ul outputs a pulse signal with a desired duty ratio to the two-position solenoid valves 11-14. Each electromagnetic valve assumes an open position or a closed position according to this pulse signal. In this way, the brake pressure of the wheels is controlled by these two-position electromagnetic valves, and the slip rate during braking is set to an optimal value, thereby preventing skids.
Since it is well known as shown in No. 3, detailed explanation will be omitted.

The I10 unit of the ECU 2 includes a voltage sensor S5. S6, rear wheel steering angle sensor 37 that detects the steering angle of the rear wheels. S8 and a front wheel steering angle sensor S9 that detects the turning angle of a steering wheel that steers the front wheels are connected.

The I10 unit of the ECU2 is connected to the solenoid valve voltage sensor S5. S6 signal, rear wheel steering angle sensor 37. A/D which inputs the signal of S8 and the signal of front wheel steering angle sensor S9 via an analog buffer (not shown) and converts it from analog to digital.
A converter (not shown) is provided.

In addition, the I10 unit of ECU2 has 3 positions for rear wheel steering (
(Open/Hold/Close) solenoid valves 15 to 18 are connected, and the solenoid valves 15 to 18 perform steering by controlling the hydraulic pressure of the rear wheel steering mechanism. In addition, solenoid valves 15 and 16 are for the right rear wheel, and solenoid valves 17 and 16 are for the right rear wheel.
．． IE (is for the left rear wheel.

Next, FIG. 3 schematically shows the configuration of the rear wheel steering device, taking the right rear wheel as an example. This device includes an accumulator 34 that accumulates high pressure generated by a hydraulic pump 32 driven by a motor 31, and the high pressure oil in the accumulator 34 is controlled by two 3-point, 3-position solenoid valves (solenoid valves for rear wheel steering control). 15
．． 16 and 7) to the two cylinders of the rear wheel steering actuator 35. The piston 36 of the actuator 35 is slid or held left and right in the state of the two solenoid valves 15 and 16. The piston 36 is connected to a knuckle arm 37, and the linear movement of the piston 36 causes the wheels 38 to rotate left and right. S7 is a steering angle sensor that detects the position of the piston 36 of the actuator and detects the steering angle of the rear wheels.

Note that 51g3 and 4 are signals that drive the excitation coils of the solenoid valves 15 and 16, and are output from the electronic control circuit ECU2.
Further, 51g5 is a signal indicating the steering angle of the rear wheels, and is input to the ECU 2. Note that the left rear wheel is also steered with a similar configuration.

Next, according to the flowchart shown in Fig. 4, the ECU 2
The rear wheel steering control will be explained below.

Steps 501 to 509 shown in the flowchart are performed at regular intervals, for example, every 8 ms. Hereinafter, the processing operations for one cycle will be explained in order. First, in step 501, the voltage sensor S5 of the solenoid valve. The brake is being controlled by the signal from S6 (
4-wheel anti-skid control). If brake control is in progress, the process advances to step 503; otherwise, the process proceeds to step 5 (12). In step 502, the rear wheel steering angle command value is set to O and the process proceeds to step 506. On the other hand, in step 503, the front wheel steering angle sensor is The absolute value 1θF1 of the signal, that is, the turning angle θ of the front wheels, is a constant K.

Determine whether it is smaller than K is a constant value stored in advance in the ROM, and is set so that when 1θF1 is smaller than this value, it is determined that the front wheels are not being steered. In step 503, 1θFl<Kl
If so, the process proceeds to step 504; otherwise, the process proceeds to step 502.

This step 504 will be explained in detail with reference to FIG. In step 601, the solenoid valve 1 for brake pressure control of the left and right front wheels is
1.12 voltage signal is taken in, and the solenoid valve 11 is set based on the voltage value.
, 1.2 is determined, and the opening time t of the solenoid valve 11.12 is determined.
c, find tR. Next, in step 602, the estimated value PF1.1PFR of the left and right brake pressures is determined as follows. That is, in the anti-skid system, as shown in European Patent Publication No. 231113, a two-position solenoid valve is opened and closed so that the calculated target oil pressure and the current oil pressure match. This situation will be shown in Part 6 using the left front wheel as an example. The pressure increase and decrease characteristics of the brake hydraulic pressure are expressed by the following equations (1) and (2), respectively.

P” P o +a-t ・・・・・・・・・
...(1) Pressure increase F=P, e-'°1...
(2) Pressure reduction (a', b are constants, L is time) Therefore, if one cycle of increase/decrease in oil pressure is T, then the initial value P
,. The oil pressure after - period is pL, -(Pto+a Htt) He-bn-tH
・,,,',・It is obtained by (3). Therefore, if the opening time tL of the solenoid valve is determined for each period, the estimated brake pressure value PL at any time can be obtained by successively calculating equation (3).

In step 603, the estimated value P of the left and right front wheel brake oil pressure is
FL+ P Estimated brake pressure value 1ΔP1 from FR
=IPFRPFLI is calculated, and in step 604 this 1
A basic rear wheel steering angle θR5II is calculated using ΔP1 as a parameter. FIG. 7 shows an example of the relationship between IΔP1 and θR51l. In this example, as the brake pressure lΔPI increases, the basic rear wheel steering angle θ□8 increases monotonically.

However, to prevent θR5B from becoming unnecessarily large, θ□SB
Guard is applied with +. Further, in a portion where 1ΔP1 is extremely small, a dead zone ΔP is set in consideration of noise and the like. ``This relationship may be stored as a calculation formula, or may be calculated by interpolation by storing values at several points as a memory map.

In step 605, a vehicle speed correction coefficient Kv is calculated in order to correct θR3B based on the vehicle speed. Here, for example, as shown in FIG. 8, the smaller the vehicle speed, the larger the value of Kv (the value that approaches I). It is set to have. In step 606, the final rear wheel steering angle command value θNS is set to θR.
Calculate as s=KyXθ□SB. The wheels are steered so that the vehicle moves toward the wheel with lower brake pressure. This is because the brake pressure is controlled independently for each wheel by the brake control described above, and the road surface on which the tire with the lower brake pressure is in contact has a lower coefficient of friction μ, and the yaw moment that tries to turn the vehicle toward the side of the road with a higher μ is generated. This is done to cancel out this yaw moment. In other words, if the rear wheels are not steered, the course of the vehicle will be changed to the side of a high-μ road, but if the rear wheels are steered using the procedure described above, the vehicle will be diverted to a low-μ road.
A yaw moment that the vehicle tries to imitate on the road side is generated, and the yaw moment that the vehicle tries to imitate on the high μ road side is canceled out, allowing the vehicle to move straight.

Returning to FIG. 4, in step 506, rear wheel steering angle sensor S7. In step S8, the actual steering angles of the left and right rear wheels are calculated, and in step 507, the rear wheel steering angle command value obtained in step 504 is compared with each actual steering angle, and in step 508, the rear wheels are steered in a direction that reduces the error. The current value to be passed through the control solenoid valves 15 to 1 is calculated, and a signal is output to the output circuit of the 110 unit (step 509).

In this way, by positioning the rear wheels independently according to the difference in brake pressure between the left and right front wheels, changes in the vehicle's dynamic characteristics due to the difference in the friction coefficient μ of the road surface that the left and right wheels contact can be minimized. , the vehicle can be controlled stably.

(Other Examples) In the above example, the opening time of the solenoid valve for brake pressure control is
Brake pressure was estimated assuming that the increase in oil pressure is linear and the decrease is exponential. However, even if the increase/decrease characteristics of oil pressure are different from this, if the characteristics are clear theoretically or experimentally, Since brake pressure can be estimated, control can be performed using it.

〔Effect of the invention〕

As described above, the present invention has the advantage that even when sudden braking is performed on a cross road where the friction coefficient μ of the road surface on which the left and right wheels contact differs, the course of the vehicle will not be deflected and braking can be performed safely. It has a good effect.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of an electronic control circuit, FIG. 3 is a schematic diagram showing the configuration of a steering control device, and FIGS. The figure is a flowchart showing a processing procedure for rear wheel steering control, and FIGS. 6, 7, and 8 are characteristic diagrams for explaining the rear wheel steering control. 81-S4... Wheel speed sensor, 11-G4... Brake pressure solenoid valve, 15-18... Steering solenoid valve, 35
...Steering actuator, ECUI, ECU2...
・Electronic control circuit. Representative Patent Attorney Takashi Okabe Figure 1 Figure 2 Figure 8

Claims (2)

[Claims] (1) A wheel speed sensor that detects the left and right wheel speeds of the vehicle, a solenoid valve that controls brake pressure applied to the wheels, and a solenoid valve that controls the solenoid valve based on the detection signal of the wheel speed sensor when the vehicle is braked. , a brake pressure control means for preventing skidding; an estimating means for calculating an estimated brake pressure value for the left and right wheels based on a signal for controlling the solenoid valve; 1. An auxiliary steering device for a vehicle, comprising: a steering angle calculation means for calculating a corrected steering angle; and a rear wheel steering means for steering a rear wheel according to the corrected steering angle. (2) Calculate the opening time of the solenoid valve, and calculate the amount of change in brake pressure during brake control by the brake pressure control means,
An auxiliary steering system for a vehicle, characterized in that the estimated brake pressure value is calculated sequentially from the opening time.