JPS63192667A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To improve substantially rear wheel steering controllability in yaw rate feedback control by applying a response delay suitable for a running condition to a target yaw rate operated depending upon the running condition. CONSTITUTION:A control unit 6 is constituted with a waveform shaping circuit 61 for shaping a speed signal outputted from a vehicle speed sensor 1a and reading the shaped signal into a micro computer 60, a rear wheel steering angle sensor 2, a front wheel steering angle sensor 1b, an analogue buffer 63 for reading in a signal from a yaw rate sensor 1c, and a drive circuit 180 for supplying a servo motor 5 with an electric current corresponding to a signal from the micro computer 60 Target yaw rate gain characteristics corresponding to a vehicle speed are obtained and a front wheel steering angle is thereby multiplied for computing a target yaw rate before delay and saving the rate in a memory. A target yaw rate after delay corresponding to a running condition is computed and then a delay extent corresponding to the running condition is computed. According to the delay extent, a steering angle command position for rear wheels is computed and the servo motor 5 is thereby controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rear wheel steering device for a front and rear wheel steering axle that serves for steering the front wheels of a vehicle and also steers the rear wheels.

[Prior Art] Conventionally, various rear wheel steering devices have been proposed for improving the steering performance and stability of a vehicle. For example, by steering the rear wheels at a predetermined front and rear wheel steering ratio using the vehicle speed as a parameter, the sideslip angle of the vehicle can be reduced, and the increase in yaw rate gain at high speeds can be suppressed to improve vehicle maneuverability and stability. This aims to achieve both, and this means that the steady yaw rate gain characteristic of the vehicle with respect to the front wheel steering angle input is changed to the yaw rate gain characteristic a of the front two-wheel steered vehicle, for example, as shown in FIG. The objective is to obtain yaw rate gain characteristics by front and rear wheel steering. Here, the yaw rate gain is the ratio of the yaw rate to the front wheel steering angle, and the yaw rate is the rotational angular velocity (yaw angular velocity) around the center of gravity of the vehicle as seen from above the axle, which is generated by steering. However, when the rear wheels are steered using the aforementioned predetermined front and rear wheel steering ratios, when the vehicle weight changes or the road surface friction coefficient changes, the target yaw rate gain characteristics as shown in Figure 5 cannot be obtained, and the initially desired yaw rate gain characteristics cannot be obtained. There was a problem that the steering stability could not be achieved. On the other hand, JP-A-60-124572
In the publication, the target yaw rate ψ is calculated directly from the steering wheel and vehicle speed, and 1. A rear wheel steering device using so-called yaw rate feedback control has been proposed, which steers the rear wheels so that the target yaw rate always matches the actual yaw rate ψ. In this device, when the actual yaw rate ψ with respect to the target yaw rate ψ6 is φ7>ψ, the rear wheels are steered in the opposite direction to the steering direction of the front wheels (reverse phase steering) so as to increase the actual yaw rate ψ. In this case, the target yaw rate is obtained by steering the rear wheels in the same direction as the front wheels (in-phase steering) so as to reduce the actual yaw rate ψ.

[Problem that the invention seeks to solve]

However, after the front wheels are steered, a sideslip angle occurs in the wheels and cornering power is generated, and as a result there is a slight time delay before the vehicle actually starts turning and the yaw rate occurs, and the yaw rate sensor itself also detects this. There is a response delay. Therefore, when the front wheels are steered in a steady running state, the target yaw rate ψ8 is set accordingly, but since the actual yaw rate signal detected from the yaw rate sensor has the above-mentioned time delay,
During this period, ψ8>ψ, and the rear wheels are always steered in the opposite phase. As mentioned above, the rear wheels are generally steered in phase to suppress the increase in yaw rate gain at high speeds, but
In this case, after unnecessary anti-phase steering is performed, in-phase steering is performed, and there is a problem in that the originally intended steering stability of the vehicle cannot be obtained.

In view of the above-mentioned problems, the present invention avoids the above-mentioned unnecessary reverse phase steering at high speeds and obtains the desired steering stability.
The object of the present invention is to provide a rear wheel steering device for a vehicle that enables rear wheel steering control according to the driving condition of the vehicle even at low and medium speeds, thereby achieving superior vehicle steering stability. .

[Means for solving problems]

In order to achieve the above object, the present invention includes a rear wheel steering mechanism M7 that adjusts the rear wheel steering angle of the vehicle in response to an electrical command value as shown in FIG. At least a vehicle speed sensor 1a that detects the vehicle speed, a front wheel steering angle sensor 1b that detects the steering angle of the front wheels, and a yaw rate sensor I that detects the yaw rate.
A driving state detecting means Ml comprising: C; a target yaw rate calculating means M2 for calculating a target yaw rate according to the driving state detected by the driving state detecting means M1; and a traveling state detected by the driving state detecting means M1. a delay means M3 that calculates a delay degree N according to the state and provides a response delay corresponding to the delay degree N when the target yaw rate calculated by the target yaw rate calculation means M2 is output; The means M3 calculates the steering angle command position of the rear wheels so as to reduce the error between the delayed target yaw rate having a response delay and the actual yaw rate detected from the yaw rate sensor IC in the driving state detecting means M1. It is characterized by comprising: a rear wheel steering angle calculation means M45; and a rear wheel positioning control means 6 that generates an electrical command value to the steering mechanism M7 so as to steer and position the rear wheels to the rear wheel steering angle command position. do.

[Effect]

According to the above configuration of the present invention, the target yaw rate is output with a response delay that changes depending on the driving state of the vehicle.

For example, when the front wheel steering angle is relatively small during in-phase steering at high speeds, the target yaw rate is output with a response delay commensurate with the detection delay of the actual yaw rate described above. It is possible to avoid reverse phase steering. Further, when the steering angle of the front wheels becomes large or, for example, when the front wheel steering angular velocity is large, by reducing the time delay, it is possible to reduce the phase delay in the yaw rate gain frequency characteristic of the vehicle. Furthermore, by setting the response delay to a small value (minimum at medium speed) during reverse phase steering at low and medium speeds, reverse phase steering with good responsiveness can be obtained as the front wheels are steered.

〔Example〕

Embodiments of the present invention will be described based on the drawings.

In FIG. 2, a DC servo motor 5 installed in a rear wheel steering mechanism 3 rotates in forward and reverse directions in response to an electrical command value signal from an electrical control device 6, and is passed through a reduction gear 4 to a rack with hydraulic power assist. - It is connected to the input shaft (torsion bar, not shown) of the and pinion mechanism 3, that is, the steering mechanism.

A pinion gear 3b is attached to the other end of the torsion bar, and meshes with a rack 3c formed at one end of the power piston 3a. That is, one end of the torsion bar is rotated by the motor 5, the torsion bar is twisted, the throttle area of the hydraulic valve 4a is changed, and hydraulic pressure is supplied in a direction to correct the twist of the torsion bar to move the power piston 3a. ing. power piston 3a
Both ends of are connected to knuckle arms 3c via tie rods 3b, respectively. The rear wheel 8 is supported by a knuckle arm 3c so as to be swingable in the left-right direction.

Therefore, by moving the power piston 3a in the direction of the arrow in the figure, the rear wheels 8 are steered left and right.

When the torsion bar is no longer twisted, the throttle area of the hydraulic valve 4a becomes 0, and the oil pressure that moves the power piston becomes 0.
The power piston stops.

Here, the rear wheel steering angle sensor 2 detects the position of the power piston 3a and outputs a signal. Based on this signal, the electric control device 6 determines the rear wheel shaft steering angle from the relationship between the position of the power piston 3a and the rear wheel actual steering angle, and also calculates the steering angular velocity from the rate of change of the rear wheel actual steering angle. demand. The steering mechanism 3 including the servo motor 5 and the control device 6 constitute a positioning servo system that positions and controls the rear wheels so that the actual rear wheel steering angle matches the rear wheel steering angle command position. Furthermore, 7a
7b indicates a hydraulic pump that supplies hydraulic pressure to the power piston 3a via a hydraulic valve 4a, and an oil tank.

la~IC is a sensor serving as a state detection means for detecting the driving and running state of the vehicle, and outputs a detection signal to the electrical control device 6. lb is a front wheel steering angle sensor that detects the rotation of the steering wheel IO and outputs a front wheel steering angle signal according to the steering angle θ of the front wheels 9; 1a detects the rotational speed of the axle or wheel and outputs a front wheel steering angle signal according to the steering angle θ of the front wheels 9; The vehicle speed sensor 1c outputs a vehicle speed signal, and is a yaw rate sensor composed of a gyro or the like and outputs a yaw rate signal corresponding to the rotational angular velocity (yaw rate ψ) of the vehicle around the center of gravity of the vehicle.

The control device 6 will be explained based on the block diagram of FIG.

The control device 6 includes a waveform shaping circuit 61 for waveform-shaping the vehicle speed signal from the vehicle speed sensor 1a and inputting it into the microcomputer 60, and each signal from the rear wheel steering angle sensor 2, front wheel steering angle sensor lb, and yaw rate sensor IC. an analog buffer 63 for taking in the current command value signal 1. The drive circuit 180 supplies the DC servo motor 5 with a current corresponding to the current.

Next, the processing procedure of the control device 6 and the microcomputer 60 will be explained according to the flowchart shown in FIG.

First, after being initialized in step S1, in step S2, the cycle is determined from the vehicle speed signal from the vehicle speed sensor la, and the vehicle speed ■ is calculated. Next, in step S3, a predetermined period T
Various A/D conversion data are taken every s. Then, in step S4, the front wheel steering angle θ1 is determined based on these A/D conversion data.
, actual yaw rate ψ, rear wheel actual steering angle θ1, front wheel steering angular speed δ
1. Calculate the rear wheel steering angular velocity θ. Here, the front wheel steering angular velocity θ and the rear wheel steering angular velocity θ are calculated by dividing the amount of change in the A/D conversion data for each multiplication period k T s of the A/D conversion period T3 by the period 'l's. It is calculated by

In step S5, the target yaw rate gain characteristic according to the vehicle speed V shown in FIG. Once stored in the memory of the microcomputer in sequence. Step S6 and Step S
In step 7, the target yaw rate toner after the delay according to the running condition is calculated and output. First, in step S6, a delay degree N according to the driving state is calculated. First of all, this can be seen in Figure 6 (
The degree of delay Nv according to the vehicle speed V is calculated based on the map shown in a). This delay degree N is set to provide a time delay commensurate with the detection delay of the actual yaw rate mentioned above at high speeds, and to reduce the delay (minimum in the medium speed range) at medium and constant speeds. It is something. Next, based on a map as shown in FIG. 6(b), a delay degree Nθ corresponding to the front wheel steering angle 1θ, 1 (absolute value) is calculated. This delay degree N is set such that the delay is large in a range where the front wheel steering angle is small, and the delay becomes gradually smaller as the front wheel steering angle becomes larger (such as when the vehicle turns suddenly). Moreover, the steering angular velocity 1 of the front wheels as shown in FIG. 6(C)
A delay degree N6 according to θf 1 is calculated. This delay N
e is set so that the degree of delay sharply decreases when the steering angular velocity exceeds a predetermined value (during sudden steering operation). Then, by calculating the final delay N, for example, as the minimum value, N=min, (Nv, NB, NM), it is possible to lower the delay with priority during sudden steering operations, etc. .

Next, in step S7, according to the delay degree N calculated in step S6, out of the target yaw rate ψ□ before delay calculated in step S5 and stored in the memory,
The pre-delay target yaw rate ψMIIN) N cycles before is extracted and this ψH1fN) is output as the target yaw rate signal. As a result, the change in the target yaw rate φ due to the change in the front wheel steering angle θ shown in FIG. With respect to the target yaw rate shown (which is equal to the latest pre-delay target yaw rate ψM+ +01), the output is delayed by a time TcN obtained by multiplying the calculation period Tc by N.

In step S8, the error ΔE between the target yaw rate ψ and the actual yaw rate ψ is calculated, and in step S9 this error ΔE
By so-called PID control calculation, the rear wheel steering angle command position θ is reduced. Calculate.

In step SIO, the rear wheel steering angle command position θ is determined.

From the rear wheel actual steering angle θ calculated in step S4, and the steering speed δ, a speed feedback positioning servo (M'jl) using a generally known DC servo motor is performed.
A current command value I to the servo motor is calculated so that the error between θ0 and θ1 and the steering speed θ1 both converge to O, and is output to the drive circuit 180 in step Sll.

In the above embodiment, only the vehicle speed sensor, front wheel steering angle sensor, and yaw rate sensor were used as the driving state detection means, but the acceleration/deceleration state of the axle can be detected by adding sensors such as an accelerator sensor and a placket inch. death,
It is easily possible to provide a response delay for the target yaw rate depending on the acceleration/deceleration state. In addition, the response delay of the target yaw rate according to the delay degree N is determined by calculating the final target yaw rate by calculating the moving average from the latest pre-delay target yaw rate to the N times previous pre-delay target yaw rate. It is also possible to set it as a delay.

Furthermore, although an example of a rear wheel steering mechanism equipped with a DC servo motor has been shown, a rear wheel steering mechanism equipped with a pulse motor may also be used.

〔Effect of the invention〕

As explained in detail above, the present invention significantly improves the rear wheel steering controllability of yaw rate feedback control by giving the target yaw rate calculated according to the driving condition of the vehicle a response delay corresponding to the driving condition. and
Therefore, it is possible to always stably obtain desired axle yaw rate gain characteristics. Furthermore, it not only stabilizes the steady yaw rate gain characteristics, but also enables transient rear wheel steering in response to changes in driving conditions, resulting in more fine-grained axle steering stability than ever before. An object of the present invention is to provide a rear wheel steering device for an axle that can obtain the following characteristics.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of the present invention, Fig. 2 is a schematic block diagram showing an embodiment of the present invention, Fig. 3 is an electric circuit block diagram showing an electrical control device (6), and Fig. 4 is a block diagram showing the configuration of the present invention. 5 is a flowchart showing the procedure of the microcomputer (60), FIG. 5 is a target yaw rate gain characteristic diagram with respect to vehicle speed (V), and FIGS. 6(a) and (b). (C) are vehicle speed ■, front wheel steering angular velocity δ2, respectively. FIG. 7 is a characteristic diagram showing the delay degrees Nv, Nf, Ne' with respect to the front wheel steering angular velocity θ, and is a diagram illustrating the target yaw rate and its time delay associated with front wheel steering. 1a...Vehicle speed sensor, lb...Front wheel steering angle sensor. 1c... Yaw rate sensor, 2... Rear wheel steering angle sensor. 4... Reduction gear, 5... DC servo motor, 6...
・Electrical control device, 8... Rear wheel, 9... Front wheel, Ml
... State detection means, M2 ... Target yaw rate calculation means, M3 ... Delay means 1M45 ... Rear wheel steering angle calculation means, M6 ... Rear wheel positioning control means, M7 ... Rear wheel steering mechanism. □ m) Figure 7

Claims (6)

[Claims] (1) A rear wheel steering mechanism that adjusts the rear wheel steering angle of the vehicle in response to an electrical command value, a vehicle speed sensor that detects the running state of the vehicle and at least the vehicle speed, and a front wheel steering that detects the front wheel steering angle. A driving state detection means comprising an angle sensor and a yaw rate sensor that detects a yaw rate (yaw angular velocity) generated in the vehicle; and a target yaw rate calculation that calculates a target yaw rate according to the driving state detected by the driving state detection means. means, rear wheel steering angle calculating means for calculating a rear wheel steering angle command position so as to reduce an error between the target yaw rate and the actual yaw rate detected by the yaw rate sensor; and rear wheel positioning control means for generating an electrical command value to the rear wheel steering mechanism so as to steer and position the wheels, wherein the degree of delay is determined according to the running state of the vehicle detected by the running state detecting means. A rear wheel steering system for a vehicle, comprising a delay means for calculating the target yaw rate calculated by the target yaw rate calculation means and providing a response delay corresponding to the delay degree N when outputting the target yaw rate calculated by the target yaw rate calculation means. (2) The vehicle according to claim 1, wherein the delay degree N calculated by the delay means is a delay degree N_v calculated according to the vehicle speed detected by the vehicle speed sensor. rear wheel steering device. (3) The degree of delay N calculated by the delay means is the degree of delay N_e calculated according to the front wheel steering angle detected by the front wheel steering angle sensor. The rear wheel steering device for a vehicle as described in 2. (4) The delay degree N calculated by the delay means is the delay degree N calculated according to the temporal change rate of the front wheel steering angle detected by the front wheel steering angle sensor, that is, the front wheel steering angular velocity.
The rear wheel steering device for a vehicle according to claim 1, characterized in that: _■. (5) The degree of delay N calculated by the delay means is the differential of the degree of delay N_v calculated according to the vehicle speed, the degree of delay N_θ calculated according to the front wheel steering angle, and the front wheel steering angle. The rear wheel steering system for a vehicle according to claim 1, wherein the delay is the minimum value of the delay degrees N_■ calculated according to the values. (6) A rear wheel for a vehicle according to claim 1, wherein the response delay according to the delay degree N in the delay means is a predetermined time or phase delay proportional to the delay degree N. Steering device.