JPH0580391B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a vehicle steering control device, and more particularly to a vehicle rear wheel steering control device suitable for controlling the steering angle of the rear wheels of a vehicle.

[Prior art]

Conventionally, in this type of vehicle rear wheel steering control device, for example, as disclosed in Japanese Patent Application Laid-Open No. 59-81269, there has been a change from a fixed mode that is unrelated to the running speed of the vehicle to a fixed mode that is independent of the running speed of the vehicle. The rear wheel steering control mode is switched to the automatic mode when the traveling speed of the vehicle exceeds a set traveling speed.

[Problem that the invention seeks to solve]

However, in such a configuration, if the steering wheel of the vehicle is operated, the steering angle of the rear wheels is instantaneously controlled in a direction contrary to the driver's intention when switching from fixed mode to automatic mode. There is a risk of impairing vehicle handling stability. In contrast, as disclosed in Japanese Patent Application Laid-open No. 59-81270, the fixed mode is switched to the automatic mode when the steering wheel is in the neutral position.
Alternatively, as disclosed in Japanese Patent Application Laid-Open No. 59-81271, the fixed mode is switched to the automatic mode when the vehicle speed exceeds the set speed and the steering wheel is in the neutral position. However, in either case, if the fixed mode is switched to the automatic mode during a steering operation of the steering wheel, the same problem as described above will occur.

In order to cope with this problem, the present invention provides a rear wheel steering system for a vehicle in which switching between two steering control modes for the rear wheels of the vehicle is performed when target steering angle ratios in each steering control mode match. It is intended to provide a control device.

[Means for solving problems]

In order to solve this problem, the structural features of the present invention are as illustrated in FIG. ), and the first target steering angle ratio of the first and second target steering angle ratios of the rear wheels with respect to the front wheels becomes negative in a low traveling speed region and changes continuously according to changes in the traveling speed. A first steering angle ratio pattern is determined to be positive in the high traveling speed region, and a second target steering angle ratio is set to be larger than the first target steering angle ratio at least on the low speed side of the low traveling speed region. and a second steering angle ratio pattern determined to match the first target steering angle ratio at a predetermined running speed. target steering angle ratio determining means 3 (steps in the embodiment) for determining the first and second target steering angle ratios based on the first and second steering angle ratio patterns in relation to the value of the travel speed detection signal 161 and 162), an operating means 4 (corresponding to the operating switch 60 of the embodiment) that is operated to generate an operating signal when selecting the determined second target steering angle ratio, and a normal first state. a holding means 5 (corresponding to the flip-flop 80 of the embodiment) which holds the flip-flop and is switched to a second state and held in the second state in response to the operation signal, and the holding means 5 is held in the second state. a return means 6 (corresponding to the comparator 100 and the AND gate 110 of the embodiment) for returning the holding means 5 to the first state when the determined first and second target steering angle ratios match in the state where the steering angle ratio is the same; When the means 5 is set to the first state, it outputs a control signal representing the determined first target steering angle, and when the holding means 5 is set to the second state, it outputs the determined second target steering angle. An output means 7 (corresponding to the analog switches 120, 140 in the embodiment) outputs a control signal representing the angle ratio, and a steering angle ratio of the rear wheels to the front wheels is displayed by the control signal in response to the output control signal. The steering control means 8 (corresponding to the drive circuit 150, displacement sensor 50, and actuator 31 of the embodiment) is provided to control the steering of the rear wheels so as to achieve the first or second target steering angle ratio.

[Effect]

In the present invention constructed as described above, when the operation signal is generated from the operation means 4, when the operation signal is generated from the operation means 4, the first The holding means 5 set in the state is switched to the second state. Therefore, the output means 7 uses the target steering angle ratio determining means 3 to determine the value of the steering angle ratio based on the first and second steering angle ratio patterns in the setting means 2 in relation to the value of the traveling speed detection signal from the traveling speed detecting means 1. Outputting a control signal representing a second target steering angle ratio of the determined first and second target steering angle ratios to the steering control means 8;
The steering control means 8 controls the steering of the rear wheels so that the steering angle ratio of the rear wheels to the front wheels becomes the second target steering angle ratio represented by the control signal. On the other hand, when the first and second target steering angle ratios determined by the target steering angle ratio determining means 3 match due to an increase in the traveling speed of the vehicle, the return control means 6 returns the holding means 5 to the first state. Therefore, the output means 7 outputs a control signal representing the determined first target steering angle ratio to the steering control means 8.
The steering control means 8 then controls the steering of the rear wheels so that the steering angle ratio of the rear wheels to the front wheels becomes the first target steering angle ratio represented by the control signal. Therefore, the rear wheel steering angle changes smoothly when switching from the second target steering angle ratio to the first target steering angle ratio without being affected by the operation of the vehicle's steering wheel, thereby improving vehicle steering stability. becomes good.

[Embodiment] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 2 shows an example in which the rear wheel steering control device according to the present invention is applied to a four-wheeled vehicle. This rear wheel steering control device has a rear wheel steering mechanism 30, and this rear wheel steering mechanism 30 is configured by an actuator 31 fixed to a part of the vehicle body and a longitudinal rotating member 32. It is configured. The actuator 31 includes a rod 31a extending displaceably.
The rod 31a is connected at its tip to a rotation fulcrum 32a of a rotation member 32.

The rotation member 32 is connected to the tie rod 10a of the left front wheel 10 via a link rod 33 at its rotation fulcrum 32b, and the rotation point 32c of this rotation member 32 is connected to the left rear wheel 20 via a link rod 34. The tie rod 20a is connected to the tie rod 20a. Therefore, in the rear wheel steering mechanism 30, the rotating member 3
2 rotates about the rotation fulcrum 32a in accordance with the amount of displacement of the rod 31a of the actuator 31 in relation to the steering angle of both the front wheels 10, 10.
Controls the steering angle of 0. In such a case, the rotating member 3
The distance between the rotation fulcrum 32a and the rotation point 32b and the distance between the rotation fulcrum 32a and the rotation point 32c of No. 2 are (steering angle of the rear wheel 20)/(steering angle of the front wheel 10), that is, the steering angle ratio. K to the rod 31a of the actuator 31.
It is set to uniquely correspond to the amount of displacement. In addition, in Fig. 2, the code 10A indicates both front wheels 1.
2 shows a front wheel steering mechanism for controlling a steering angle of 0,10.

Further, the rear wheel steering control device includes a speed sensor 40
, a displacement sensor 50, an operation switch 60, a waveform shaper 70 connected to the speed sensor 40, and a slip slot 80 connected to the operation switch 60, and the speed sensor 40 detects the running speed u of the vehicle. A series of velocity pulses is generated at a frequency proportional to this. The displacement sensor 50 detects the actual amount of displacement of the rod of the actuator 31 corresponding to the actual amount of rotation of the rotating member 32, and generates a displacement detection signal. In such a case, the actual rotation amount of the rotation member 32 corresponds to the actual steering angle ratio K.

The operating switch 60 is a self-returning normally open type, and when it is temporarily closed, it generates the power supply voltage +Vb from the DC power source as an operating signal. Waveform shaper 7
0 sequentially shapes the waveform of each speed pulse from the speed sensor 40 and generates it as a shaped pulse. Flip-flop 80 is set in response to an operation signal from operation switch 60, and generates a low level signal from its output terminal Q and a high level signal from its output terminal. The flip-flop 80 is reset in response to a high level signal from an AND gate 110, which will be described later, and generates a high level signal from its output terminal Q and a low level signal from its output terminal.

The microcomputer 90 has a data bus 91
A central processing unit 92 (hereinafter referred to as CPU92), a read-only memory 93 (hereinafter referred to as ROM93), a random access memory 94 (hereinafter referred to as RAM94), which are connected to each other via
Each input port 95, 96 and each output port 97,
98 and 99, and the CPU 92 has a ROM 9
The computer program stored in advance in No. 3 is transferred to No. 4.
In accordance with the flowchart shown in the figure, the operation is repeatedly executed in cooperation with the waveform shaper 70 and the flip-flop 80, and during the repetition of the execution, the comparator 100 and both analog switches 120, 140 are
performs various calculation processes necessary for control. Note that the input port 95 is connected to the waveform shaper 70, and the input port 96 is connected to the output terminal Q of the flip-flop 80.
It is connected to the.

Comparator 100 has both output ports 98, 9
The first and second, which arise from 9 as described below, respectively.
A low level signal is generated when the level of the first output signal is lower than the level of the second output signal, and a high level signal is generated when the levels of both output signals match. AND gate 110 generates a high level signal in response to each high level signal from the output terminal of comparator 100 and flip-flop 80, and generates a low level signal in response to a low level signal from at least one of the output terminals of comparator 100 and flip-flop 80. Generates a level signal.

The analog switch 120 is closed (or opened) in response to a high level signal (or low level signal) from the output terminal Q of the flip-flop 80, and a drive circuit 150 for a first output signal generated from the output port 97 as described below. (or
Cut off. The analog switch 140 is closed (or opened) in response to the inverting action of the inverter 130 in response to a low level signal (or high level signal) from the output terminal Q of the flip-flop 80, and the output port 99 is connected to the drive circuit 150. The drive circuit 150, which allows (or blocks) the provision of the second output signal, is configured to control the level of the first output signal from the analog switch 120 (or the level of the second output signal from the analog switch 140) and the displacement sensor. The actuator 31 generates a drive signal that reduces the difference in level from the displacement detection signal from the actuator 50.
granted to.

In this embodiment configured as described above, if the vehicle is running at low speed without operating the operating switch 60, the CPU 92 executes the step 160 while executing the computer program according to the flowchart of FIG. In cooperation with the vehicle speed sensor 40, each shaped pulse generated from the waveform shaper 70 is received through the input port 95 and the data bus 91, and the running speed u of the vehicle is calculated based on the number of the shaped pulses. Next, in step 161, the CPU 92 determines the traveling speed u of the target steering angle ratio K1.
The target steering angle ratio K1 is determined according to the calculated travel speed u from the steering angle ratio pattern A (see Figure 3) representing the relationship between
In step 162, the target steering angle ratio is calculated.
A target steering angle ratio K2 is calculated according to the calculated running speed u from a steering angle ratio pattern B (see FIG. 3) representing the relationship between K2 and the running speed u.

In such a case, each steering angle ratio pattern A, B is
This is stored in the ROM 94 in advance, and in steering angle ratio pattern A, the target steering angle ratio K1 becomes negative when traveling speed u<predetermined traveling speed uo, and u
It is set to be zero at =uo and positive at u>uo. Also, steering angle ratio pattern B
In , the target steering angle ratio K2 is determined to be zero when u≦uo. However, each target steering angle ratio K1, K2 corresponds to (target steering angle of the rear wheels 20)/(target steering angle of the front wheels 10), and the steering angle ratio pattern A (or B) is Selected based on operation (or operations).

After that, since the operation switch 60 is not operated at this stage, the CPU 92 at step 163
A high level signal from the output terminal Q of the flip-flop 80 is received through the input port 96 and the data bus 91, and it is determined as "NO", and in step 164, the calculated target steering angle ratio K1 is sent to the output port 97 as the first output signal. arises from. Then, the analog switch 120 applies the first output signal from the output port 97 to the drive circuit 150 in a closed state based on the high level signal from the output terminal Q of the flip-flop 80. Next, the drive circuit 150 generates a drive signal that reduces the difference between the level of the displacement detection signal from the displacement sensor 50 and the level of the first output signal from the analog switch 120, and in response to this, the actuator 31 moves to the rod. The rotating member 32 is rotated so that the actual displacement amount of the rotation member 31a matches the value of the drive signal. Thereby, the actual steering angle of the rear wheels 20 is controlled to match the target steering angle. Note that at this stage, since u<uo,
K1<0.

In such a state, for example, the rear wheel 20 is replaced by the front wheel 10.
In order to turn the vehicle without significantly steering the vehicle in the opposite phase (without significantly protruding the rear part of the vehicle on the outside of the turn), turn the operating switch 6.
0 to generate an operating signal by its temporary closing, the flip-flop 80 generates a low level signal from its output terminal Q and a high level signal from its output terminal, and the CPU 92
At step 163, the low level signal from the output terminal Q of the flip-flop 80 is input to the input port 96.
and the data bus 91, and it is determined as “YES”, and in step 165, the calculation target steering angle ratio is determined.
K1 is used as the first output signal to be generated from the output port 98, and in step 166, the calculated target steering angle ratio is
K2 is generated from output port 99 as a second output signal.

Analog switch 140 is then closed by the inverting action of inverter 130 in response to the low level signal from output terminal Q of flip-flop 80, providing a second output signal from output port 99 to drive circuit 150. At this time, K1<K2=0
Therefore, the output of the comparator 100 is a low level signal, and the analog switch 120 is open. Thus, the drive circuit 150 generates a drive signal that reduces the difference between the level of the displacement detection signal from the displacement sensor 50 and the level of the second output signal from the analog switch 140, and in response, the actuator 31 By rotating the rotating member 31 in the same manner as described above, the actual steering angle of the rear wheels 20 is changed to the target steering angle (that is, corresponding to K1=0).
match. This allows the vehicle to turn smoothly.

After that, due to an increase in the traveling speed u of the vehicle,
When the calculated target steering angle ratio K1 in step 161 matches the calculated target steering angle ratio K2 in step 162, the comparator 100 generates a high level signal, the AND gate 110 generates a high level signal, and the flip-flop 80 is reset. A high level signal and a low level signal are generated from each output terminal Q. Then, in the same manner as described above, the analog switch 140 is opened and at the same time the analog switch 120 is closed, allowing the first output signal to be applied from the output port 97 to the drive circuit 150.

In other words, when the calculated target steering angle ratio K1 matches the calculated target steering angle ratio K2 at u=uo, the application of the second output signal from the output port 99 to the drive circuit 150 is interrupted by opening the analog switch 140. Since the first output signal is allowed to be applied from the output port 97 to the drive circuit 150 by closing the analog switch 120, the drive circuit 15
The value of the drive signal from 0 changes smoothly without becoming discontinuous, and the control of the steering angle of the rear wheels 20 by the rear wheel steering mechanism 30 to the target value is achieved by the steering mechanism 10A.
It is carried out smoothly regardless of continuous operation. This means that the steering angle ratio pattern B of the rear wheels 20
This means that the steering control at the time of switching from the steering angle ratio pattern A to the steering angle ratio pattern A is always performed smoothly without impairing the steering stability of the vehicle.

In addition, in the above embodiment, an example was explained in which the steering angle ratio pattern B was set such that K2=0 when u≦uo, but the invention is not limited to this, for example,
As shown by the broken line in FIG. 5, the steering angle ratio pattern C may be adopted in place of the steering angle ratio pattern B. In such a case, steering angle ratio pattern C
, target steering angle ratio K3 (target steering angle ratio K2
) becomes positive in the ultra-low speed range of the vehicle (i.e., the area below the ultra-low speed u1 (<uo)), becomes zero at u=u1, and becomes negative immediately after u>u1 is established. Therefore, it is made to match K1.
Therefore, when switching from steering angle ratio pattern C to steering angle ratio pattern A, it goes without saying that the rear wheel steering control is performed smoothly as in the above embodiment.
Even when there is an obstacle near the rear wheel 20, when u<u1, the rear wheel 20 is prevented from overhanging the obstacle according to K3>0 under the operation of the operating switch 30. As a result, the vehicle can be smoothly run at an extremely low speed while preventing the rear wheels 20 from coming into contact with the obstacle.

Further, in the embodiment described above, the steering angle ratio pattern B is stored in advance in the microcomputer 90, but instead of this, a potentiometer is employed to determine the target steering angle ratio of the steering angle ratio pattern B.
K1 is not limited to zero, and may be arbitrarily changed and set using the potentiometer according to preference.

Furthermore, in carrying out the present invention, the steering angle ratio pattern A is not limited to a single pattern, but is composed of a plurality of steering angle ratio patterns that are partially or entirely parallel to each other, Each of these steering angle ratio patterns may be selected according to preference using an appropriate selection switch.

Further, in the embodiment, in controlling the steering of the rear wheels 20, the rear wheel steering mechanism 30, the displacement sensor 5
0 and the drive circuit 50, but instead of this, a hydraulic cylinder provided on the axle between the rear wheels 20, 20, an electro-hydraulic servo mechanism connected to this hydraulic cylinder, and an electro-hydraulic A differential amplifier, a front wheel steering angle sensor and a rear wheel steering angle sensor are connected to the servo mechanism, and step 164
(or 165), the target rear wheel steering angle of the rear wheels 20 is determined by multiplying the target steering angle ratio K1 by the detection result of the front wheel steering angle sensor for the steering angle of the front wheels 10, and a first target rear wheel steering angle signal is obtained. occurs as step 1
At step 66, the target rear wheel steering angle of the rear wheels 20 is determined by multiplying the target steering angle ratio K2 by the detection result of the front wheel steering angle sensor in the same manner as described above, and is generated as a second target rear wheel steering angle signal, and the difference is calculated. A dynamic amplifier differentially amplifies the difference between the value of the first (or second) target rear wheel steering angle signal and the detection result for the steering angle of the rear wheel 20 by the rear wheel steering angle sensor, and - Even if the hydraulic servomechanism hydraulically drives the hydraulic cylinder according to the differential amplification result to control the steering angles of both rear wheels 20, 20 to the target values, it is substantially the same as in the embodiment described above. can achieve the following effects. The electro-hydraulic servo mechanism includes a torque motor that rotates according to the differential amplification result of the differential amplifier, a conversion mechanism that converts the rotation of the torque motor into linear motion, and a linear momentum of the conversion mechanism. and a switching valve that selectively switches between three positions depending on the switching position of the switching valve, and applying pressure oil from a hydraulic source to one (or the other) of both chambers of the hydraulic cylinder according to the switching position of the switching valve, or The system is designed to shut off the hydraulic cylinder.

[Brief explanation of drawings]

FIG. 1 is a diagram corresponding to the configuration of the invention described in the claims, FIG. 2 is an overall configuration diagram showing one embodiment of the present invention, and FIG. 3 is the relationship between the target steering angle ratio and the vehicle running speed. 4 is a flowchart showing the operation of the microcomputer shown in FIG. 2, and FIG. 5 is a pattern diagram showing a modification of the pattern shown in FIG. 3. Explanation of symbols 10...Front wheel, 20...Rear wheel, 30...
Rear wheel steering mechanism, 40... Vehicle speed sensor, 50... Displacement sensor, 60... Operation switch, 80... Flip-flop, 90... Microcomputer, 100... Comparator, 110... AND gate, 120, 1
40...Analog switch, 130...Inverter.

Claims (1)

[Scope of Claims] 1. Traveling speed detection means that detects the traveling speed of the vehicle and generates a traveling speed detection signal, and the first target steering angle ratio of the first and second target steering angle ratios of the rear wheels with respect to the front wheels. a first steering angle ratio pattern in which the ratio is negative in the region where the traveling speed is low, changes continuously according to changes in the traveling speed, and becomes positive in the region where the traveling speed is high; A second target steering angle ratio is set to be larger than the first target steering angle ratio at least on the low speed side of the low traveling speed region and to match the first target steering angle ratio at a predetermined traveling speed. a setting means configured to set a second steering angle ratio pattern; and a setting means configured to set a second steering angle ratio pattern;
and target steering angle ratio determining means for determining the first and second target steering angle ratios based on a second steering angle ratio pattern, respectively; and an operation signal that is operated when selecting the determined second target steering angle ratio. operating means for causing a change in temperature; holding means for normally holding a first state and switching to a second state and holding the second state in response to the operating signal; and holding means for holding the second state in the second state. a return means for returning the holding means to the first state when the determined first and second target steering angle ratios match in the state where the holding means is set to the first state; output means for outputting a control signal representing the determined first target steering angle ratio and outputting a control signal representing the determined second target steering angle ratio when the holding means is set to a second state; Steering control means for controlling the steering of the rear wheels in response to the output control signal so that the steering angle ratio of the rear wheels to the front wheels becomes a first or second target steering angle ratio represented by the control signal. A rear wheel steering control device for a vehicle characterized by comprising: