JP2532113B2 - Steering control device for front and rear wheel steering vehicles - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a steering control device for a front and rear wheel steering vehicle, and more specifically, a rear wheel according to a deviation between a target steering angle and an actual steering angle by an actuator such as an electric motor. The present invention relates to a steering control device for a front / rear wheel steering vehicle, which steers with a steering force and imparts steering speed dependence to the steering characteristics of the rear wheels in relation to steering resistance.

(Prior Art) In a front and rear wheel steering vehicle that steers both front and rear wheels, steering performance is generally improved by controlling the steering phase and the steering angle ratio of the front and rear wheels according to the vehicle speed. . In such a front-rear wheel steering vehicle, the rear wheel is steered in the opposite direction (opposite phase) to the front wheel in the low vehicle speed range to reduce the turning radius, and in the high vehicle speed range, the rear wheel is in the same direction as the front wheel. Steer to the same phase to improve stability.

Conventionally, a front and rear wheel steering vehicle of this type has been disclosed in JP-A-60-67272.
Japanese Patent Application Laid-Open Publication No. H10-202,009 is known. The steering control device disclosed in Japanese Patent Laid-Open No. 60-67272 outputs a pulse signal having a step angle corresponding to the steering speed to a pulse motor to drive the rear wheels by the pulse motor, and the rear wheels to the steering speed. The motor is made to respond with the corresponding characteristics to improve the followability of the motor.

(Problems to be solved by the present invention) However, in the above-mentioned steering control device of Japanese Patent Laid-Open No. 60-67272, the motor is always following and the turning performance at a high steering speed is taken into consideration. However, since the step angle of the pulse motor is changed according to the steering speed, the control becomes complicated in terms of method, and the steering speed is calculated by differentiating the output signal of the steering angle sensor that detects the steering angle of the steering wheel. There is a problem in that a calculation circuit for calculating or a detector for directly detecting the steering speed of the steering wheel is indispensable and the structure becomes complicated.

The present invention has been made in view of the above problems, and provides a steering control device that can improve the motion characteristics by imparting a steering speed dependent characteristic to the steering characteristics of the rear wheels by a simple control method, at low cost and with a simple structure. The objective is to achieve with a simple configuration.

(Means for Solving Problems) A steering control device for a front and rear wheel steering vehicle according to the present invention is
As shown in FIG. 1, in a front and rear wheel steering vehicle that steers the rear wheels together with the front wheels in response to steering of the steering wheel, a target rudder angle determining means for deciding a target rudder angle of the rear wheels and a rear wheel actual rudder angle. Steering angle detection means, deviation calculation means for calculating the deviation between the target steering angle and the actual rear wheel steering angle, and the rear wheel steering force is increased and then decreased in response to the increase in the calculated deviation. And a drive for steering the rear wheels with the rear wheel steering force determined by the steering force determination means to steer the rear wheels to the target steering angle determined by the target steering angle determination means. The gist is to have means.

(Operation) According to the steering control device for a front and rear wheel steering vehicle according to the present invention, the rear wheels are steered by the steering force corresponding to the deviation between the target steering angle and the detected actual steering angle. The rate of change of the angle changes according to the applied steering force and the steering reaction force. If the steering reaction force is constant, the deviation is large when the steering speed is high, and is small when the steering speed is low. Therefore, the steering speed can be estimated by calculating the deviation. That is, the driver's intention can be reflected in the turning behavior of the vehicle only by applying the steering force according to the deviation, and the control system can be simplified. The rate of change of the actual steering angle depends on the steering resistance, and the steering resistance depends on the road surface reaction force determined by the friction coefficient of the road surface, etc., so that the road surface reaction force dependence can be added to the steering characteristics of the rear wheels. On a road having a low road surface friction coefficient such as a snowy road, the followability of the motor is enhanced, and the in-phase steering amount in the transition period is larger than that on the normal road surface, and the stability can be further improved.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

2 to 4 show a steering control device for a front and rear wheel steering vehicle according to an embodiment of the present invention. FIG. 2 is an overall schematic diagram, FIG. 3 is a block diagram, and FIG. 4 is a flow chart.

In FIG. 2, reference numeral 11 denotes a lateral handle, and the steering handle 11 is connected to a rack and pinion type steering gear mechanism 13 via a steering shaft 12. The steering shaft 12 is provided with a steering angle sensor 14 that detects the rotation angle of the steering shaft 12. The steering angle sensor 14 is composed of an encoder or the like, is connected to a controller 16 described later, and outputs a detection signal indicating the steering angle to the controller 16.

As is well known, the steering gear mechanism 13 includes a pinion gear 13a that rotates integrally with the steering shaft 12 and a rack 13b that meshes with the pinion gear 13a and extends in the vehicle width direction. Knuckle arms 19FL, 19FR for left and right front wheels 18FL, 18FR and tie rods 17
They are connected via a steering linkage composed of FL, 17FR, etc. These front wheels 18FL, 18FR are provided with vehicle speed sensors 20FL, 20FR, respectively.
FR is connected to the controller 16 and outputs a symbol indicating the vehicle speed. Further, as will be described later, vehicle speed sensors 20RL, 20RR are also provided on the rear wheels 18RL, 18RR, respectively, and these vehicle speed sensors 20RL, 20RR are also connected to the controller 16 to output a symbol representing the vehicle speed. Needless to say, the aforementioned steering angle sensor 14 can be replaced by a sensor that detects the moving distance of the rack 13b of the steering gear mechanism 13 or the steering angle of the front wheels 18FL and 18FR.

Reference numeral 21 is an electric motor that is connected to the controller 16 and is fed with electric power from the controller 16. The output shaft of the electric motor 21 is connected to a rack and pinion type steering gear mechanism 23 via a bevel gear mechanism 22. The bevel gear mechanism 22 is an electric motor.
It has a bevel gear 22b fixed to the output shaft of 21 and a bevel gear 22a that rotates integrally with the pinion gear 23a of the steering gear mechanism 23. The steering gear mechanism 23 has a pinion gear 23a and a rack 23b similarly to the above-mentioned steering mechanism 13, the pinion gear 23a is connected to the electric motor 21 via a bevel gear mechanism 22, and both ends of the rack 23b are left and right rear wheels. It is connected to the knuckle arms 19RL and 19RR of the 18RL and 18RR via a steering linkage including tie rods 17RL and 17RR. Rack of steering gear mechanism 23
23b is provided with a rear wheel steering angle sensor 24 for detecting a moving distance of the rack 23b in the axial direction. The rear wheel steering angle sensor 24 is
It is composed of a differential transformer or the like and is connected to the controller 16, and detects the steering angle of the rear wheels 18RL and 18RR with respect to the moving distance of the rack 23b and outputs a signal representing the steering angle to the controller 16. This rear wheel steering angle sensor 24 is, as is well known, a controller 16
AC pulse signal is input to the primary coil from the rack 23b.
In both cases, the core is displaced and the differential signal is output from the secondary coil. In this embodiment, the electric motor 21 is provided only for steering the rear wheels 18RL, 18RR, but the output of the electric motor 21 is set to the front wheels 18FL, 18RR.
Needless to say, the present invention can be achieved by distributing the 8FR together with the rear wheels 18RL and 18RR and adding a steering angle function generating mechanism or the like to the transmission system of the steering force to the rear wheels 18RL and 18RR.

The controller 16 has a control circuit 25 and a drive circuit 26 as shown in FIG.
A current sensor 28 of a drive circuit 26, which will be described later, is connected together with 4, 20, 24, and the above-mentioned electric motor 21 is connected to the drive circuit 26.

The control circuit 25 includes a constant voltage circuit 30, a microcomputer circuit 31, input interface circuits 32, 34, 35, 37 and the like. The constant voltage circuit 30 is connected to the battery via a fuse or the like, and supplies a constant voltage power to each circuit.
The input interface circuits 32, 34, 35, 37 are connected to the above-mentioned respective sensors 14, 20, 24, 28 to which they correspond respectively, and are also connected to the microcomputer circuit 31 via a data bus. The input interface circuit 32 connected to the steering angle sensor 14 processes the output signal of the steering angle sensor 14 and outputs a signal representing the steering angle and direction of the front wheels 18FL, 18FR to the microcomputer circuit 31. The interface circuit 35 connected to the rear wheel steering angle sensor 24 is composed of an oscillating circuit, a rectifying circuit, a low-pass filter, etc., outputs an AC pulse signal to the primary coil of the rear wheel steering angle sensor 24, and outputs it from the secondary coil. The signal is shaped and output to the microcomputer circuit 31. The interface circuit 34 connected to the vehicle speed sensor 20 includes a waveform shaping circuit, an arithmetic circuit, and the like, and outputs a signal representing the vehicle speed to the microcomputer circuit 31 based on the output signal of each vehicle speed sensor 20. The interface circuit 37 connected to the current sensor 28 includes an amplifier circuit and an A / D converter, and converts the output signal of the current sensor 28 into a digital signal and outputs the digital signal to the microcomputer circuit 31.

The microcomputer circuit 31 includes a CPU, a ROM, a RAM, a clock, and the like, constitutes deviation calculating means and steering force determining means, and operates in accordance with a program stored in the ROM through the interface circuits 32, 34, 35, 37, and the sensors. The signal input from is processed to determine the duty factor of the current flowing to the electric motor 21, and the pulse width modulation signal (PWM signal) g, h, i, j representing this duty factor is output to the drive circuit 26.

The drive circuit 26 includes a booster circuit 38, a gate drive circuit 39,
The current sensor 28, the relay circuit 41, the switch circuit 40, and the like are provided, the gate drive circuit 39 is connected to the battery, and the switch circuit 40 is connected to the battery via the relay circuit 41. The switch circuit 40 is formed by connecting four field effect transistors (FETs) Q1, Q2, Q3, Q4 in a bridge shape, and the gates of these FETs Q1, Q2, Q3, Q4 are connected to a gate drive circuit 39. . The drains of the FETs Q1 and Q2 are connected to the battery via the relay circuit 41 and the sources thereof are connected to the drains of the FETs Q3 and Q4, respectively, and the sources of the FETs Q3 and Q4 are grounded via the current sensor 28 (one terminal of the battery). )
The electric motor 21 is connected between the source / drain connection parts of the FETs Q1 and Q3 and the source / drain connection parts of the FETs Q2 and Q4. The booster circuit 38 boosts the voltage of the battery and outputs the boosted voltage to the gate drive circuit 39, and the gate drive circuit 39 uses the PWM signals g, h, i, j input from the microcomputer circuit 31 for each FET Q1 of the switch circuit 40. The drive signal is output to the gates of Q2, Q3 and Q4. The current sensor 28 detects the current supplied to the electric motor 21 and outputs a detection signal of this current to the above-mentioned interface circuit 37. The switch circuit 40 is
The drive signal of the duty factor corresponding to the PWM signal g is input to the gate of FETQ1, and similarly, the PWM signal h is input to the gate of FETQ2, the PWM signal i is input to the gate of FETQ3, and the duty factor of the PWM signal j is input to the gate of FETQ4. Input signals respectively.

Next, the operation of this embodiment will be described with reference to FIG.

The steering control device of the front and rear wheel steering device controls the electric motor 21 by executing a series of processes shown in the flowchart of FIG.

First, when the ignition key is operated and the key switch is turned on, the microcomputer circuit 31
And the like, and the microcomputer circuit 31 operates. Then, in step P1, the microcomputer circuit 31 is initialized (initialized), and the stored data in the internal register and the like are erased and the address is designated. Then, in step P2, initial failure diagnosis is performed according to another defined subroutine, and the following processing is performed only when all functions normally.

In step P3, the vehicle speed V is read from the output signal of each vehicle speed sensor 20, and in subsequent step P4, the vehicle speed V
Is used as an address, a map search is performed for the steering angle ratio k from the data table 1 shown in FIG. As is apparent from FIG. 5, the steering angle ratio k is a negative value (representing an opposite phase) in a low vehicle speed range lower than the predetermined vehicle speed V1, and a positive value (representing the same phase) in a high vehicle speed range higher than the predetermined vehicle speed V1. ) Has.

Next, in step P5, the output signal θF 'of the steering angle sensor 14 is read, and in step P6 the steering angle sensor 14
The steering angle from the neutral position θF (θ
F = θF′−θM) is calculated. This steering angle θF represents the steering angle of the front wheels 18FL, 18FR because the rotation angle of the steering shaft 12 corresponds to the steering angle of the front wheels 18FL, 18FR (hereinafter referred to as the front wheel steering angle). Subsequently, in step P7, whether the front wheel steering angle θF is positive or negative, that is, the direction is determined. If the front wheel steering angle θF is positive, the flag F1 is set to 0 in step P8, and the front wheel steering angle θF is set.
If F is negative, the front wheel steering angle θF is set to a positive value (absolute value) in step P9, and then the flag F1 is set to 1 in step P10. Then, in the next step P11, the front wheel steering angle θF
Is multiplied by a steering angle ratio k to calculate a target steering angle (rear wheel target steering angle) θRT of the rear wheels 18RL and 18RR.

Next, in step P12, the vehicle speed V becomes the predetermined vehicle speed V _0.
It is determined whether it exceeds the vehicle speed V is performs steps P13, P14, P15 if beyond a predetermined vehicle speed V _0, also,
If the vehicle speed V is less than or equal to the predetermined vehicle speed V ₀ , steps P16, P17, P18
Process. In step P13, the value of the flag F1 is determined, and if the flag F1 is 1, the flag F3 is set to 1 in step P14.
If the flag F1 is 0, the flag F3 is set to 0 in step P15. Similarly, in step P16,
The value of the flag F1 is determined, and if the flag F1 is I, step
The flag F3 is set to 0 in P17, and if the flag F1 is 0, the flag F3 is set to 1 in step P18.

In the following step P19, the output signals θR1 and θR2 of the rear wheel steering angle sensor 24 are read, and failure diagnosis of the rear wheel steering angle sensor 24 is performed in accordance with a subroutine defined elsewhere in step P20. In this step P20, the following processing is executed only when it is determined that the rear wheel steering angle sensor 24 is functioning normally. Then, in step P21, the rear wheel steering angle θR is calculated by subtracting the output signals θR1 and θR2 of the rear wheel steering angle sensor 24. Subsequently, in step 22, whether the rear wheel steering angle θR is positive or negative is determined. If the rear wheel steering angle θR is positive, the flag F2 is set to 0 in step P23, and the rear wheel steering angle θR is set.
If is negative, the rear wheel steering angle θR is set to a positive value (absolute value) in step P24, and then the flag F2 is set to 1 in step P25. In the next step P26, flag F2 and flag F3
Is determined, and if the values of the flags F2 and F3 are different, step P
27. If the flags F2 and F3 have the same value, the process from step P28 to step P33 is performed. Step
At P27, the deviation ΔθR is calculated by adding the rear wheel target steering angle θRT and the rear wheel steering angle θR. In step P28, the deviation ΔθR is calculated by subtracting the rear wheel steering angle θR from the rear wheel target steering angle θRT, and thereafter, in step P29, the sign of the deviation ΔθR is determined. In this step P29, if it is determined that the deviation ΔθR is negative, the deviation ΔθR is made positive in step P30, and then the value of the flag F3 is replaced in steps P31, P32, and P33.
That is, the value of the flag F3 is determined in step P31. If the flag F3 is 0, the flag F3 is replaced with 1 in step P32. If the flag F3 is 1, the flag F3 is changed in step P33.
Replace 3 with 0.

Next, in step P34, the rear wheel steering force D is set from the data table 2 shown in FIG. 6 using the deviation ΔθR as an address.
Search the map. The rear wheel steering force D represents a duty factor of the current supplied to the electric motor 21, that is, a current value. It has a dead zone of 0 in a low deviation range close to 0, increases as the deviation increases, and then decreases in a high deviation range. It converges to a constant value with a value slightly larger than the steering force DR required for steering on a normal road surface.

Subsequently, in Step P35, it is determined whether or not the rear wheel steering force D is 0, and if the rear wheel steering force D is 0, Step P36
Set 0,0,1,1 to PWM signal g, h, i, j respectively, and
If the rear wheel driving force D is not 0, the value of the flag F3 is determined in step P37. If it is determined in step P37 that the flag F3 is 0, in step P38 the PWM signals g, h, i, j are set to 1,0,0, D, respectively, and it is determined that the flag F3 is 1. Then, in step P39, the PWM signals g, h, i, j are set to 0, 1, D, 0 respectively.
Set. Then, in step P40, the PWM signals g, h, i, j are output. Therefore, the electric motor 21 is energized with a current having a duty factor D according to the turning direction of the rear wheels 18RL, 18RR to steer the rear wheels 18RL, 18RR to the target steering angle, and the windings are short-circuited when not energized. Electric braking is performed to maintain the rear wheel steering angle at the target steering angle. Thereafter, in step P41, a failure diagnosis of the drive system such as the electric motor 21 and the switch circuit 40 is performed in accordance with another defined subroutine, and the series of processes from step P2 is repeated again.

As described above, in the steering control device of the present embodiment, the electric motor according to the deviation ΔθR between the actual steering angle θR of the rear wheels 18RL, 18RR and the target steering angle θRT determined according to the vehicle speed, etc.
The power is supplied to the motor 21 and the rear wheels 18RL and 18RR are steered by the electric motor 21 to reduce the deviation.

For normal steering, the deviation will be within the range of b
When θR is large, the steering wheel is steered with a relatively large steering force, and when the deviation ΔθR is small, the steering wheel is steered with a relatively small steering force, and the rear wheels are steered to the target steering angle promptly. Further, the dead zone in the area a prevents motor hunting. When the steering speed is high, the deviation is in the region of c or d, the driving force of the motor is reduced, and the steering of the rear wheels becomes gentle. Therefore, during high-speed turning where the rear wheels 18RL, 18RR are steered in the same phase as the front wheels 18FL, 18FR, normal steering is swiftly steered to the target steering angle, and the rear wheel steering angle is hunted to the target steering angle θRT. If the steering speed is high, the steering force is small and the steering angle ratio k is transiently small. It is possible to obtain quick turning behavior (good turning ability) by suppressing the turning. And
The rear wheels 18RL and 18RR are affected by the steering force and the steering reaction force on which the change rate of the actual steering angle θR acts, and when the steering reaction force is small, the change rate of the actual steering angle θR becomes large. Therefore, as described above, the followability is improved as compared with a normal road surface, the same effect can be obtained by increasing the steering angle ratio k, and the vehicle can be stabilized on a low friction coefficient road surface such as a snowy road. .

FIG. 7 shows a data table of a steering control device for a front and rear wheel steering vehicle according to another embodiment of the present invention.

In this embodiment, the rear wheel steering force D, that is, the duty factor of the current supplied to the electric motor 21 is determined based on the deviation ΔθR from the data table shown in FIG. 7 (step P34 in the flowchart of FIG. 4). Other configurations and operations are the same as those of the above-described embodiment, and the description thereof will be omitted.

In each of the above-described embodiments, the electric motor 21 controls the rear wheel 18.
Although the RL and 18RR are steered, it goes without saying that the present invention can also be achieved by a hydraulic actuator or the like.

(Effects of the Invention) As described above, according to the steering control device for a front-rear wheel steering vehicle according to the present invention, the deviation between the target steering angle and the actual rear wheel steering angle is calculated, and this deviation is dealt with to increase. The steering force is increased by increasing the steering force on the rear wheels and then reduced to steer the rear wheels.
A characteristic that depends on the steering speed and the road surface reaction force can be added to the steering characteristics of the rear wheels without complicating the control system, and a good steering feeling can be obtained.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a steering control device according to the present invention. Second
1 to 6 show a steering control device according to an embodiment of the present invention, FIG. 2 is an overall schematic diagram, FIG. 3 is a block diagram,
FIG. 4 is a flowchart, and FIGS. 5 and 6 are data tables used for control processing. FIG. 7 is a data table of the steering control device according to another embodiment of the present invention. 11 …… Steering wheel 14 …… Steering angle sensor 16 …… Controller 18FL, 18FR …… Front wheel 18RL, 18RR …… Rear wheel 20 …… Vehicle speed sensor 21 …… Motor 24 …… Rear wheel steering angle sensor 25 …… Control Circuit 26 …… Drive circuit 31 …… Microcomputer circuit

Claims (2)

(57) [Claims] 1. A front-rear wheel steering vehicle that steers rear wheels together with front wheels in response to steering of a steering wheel, wherein a target rudder angle determining means for deciding a target rudder angle of the rear wheels and a rear wheel actual rudder angle are set. Rudder angle detection means for detecting, deviation calculation means for calculating the deviation between the target rudder angle and the actual rear wheel steering angle, and to increase and decrease the rear wheel steering force in response to the increase in the calculated deviation. The steering force determining means for determining the steering angle, and the rear wheel steering force determined by the steering force determining means to drive the rear wheels to steer the rear wheels to the target steering angle determined by the target steering angle determining means. A steering control device for a front-rear wheel steering vehicle, comprising: 2. The driving means includes an electric motor for generating a rear wheel steering force, and a drive circuit for supplying a current according to the target steering force to the electric motor. A steering control device for a front and rear wheel steering vehicle as described above.