JPH0773999B2 - Rear wheel control system for front and rear wheel steering vehicles - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to an improvement of a rear wheel control device for a front and rear wheel steering vehicle.

[Prior art]

Conventionally, as a rear wheel control device for a front and rear wheel steering vehicle, for example, as disclosed in JP-A-57-60974, acceleration / deceleration during vehicle turning is detected, and the rear wheels are steered accordingly. Thus, it has been proposed that the turning radius can be prevented from changing even if the vehicle is accelerated or decelerated during turning. Further, as another rear wheel control device for a front and rear wheel steering vehicle, for example,
As disclosed in Japanese Unexamined Patent Publication No. 57-11173, a proposal is made to control the rear wheels by setting the rear wheel steering angle to a constant k times the front wheel steering angle so that the sideslip angle of the vehicle becomes small. Has been done. Further, as a vehicle steering device, as disclosed in Japanese Patent Publication No. 52-11485, the steering angle given by the driver and the vehicle body yaw rate are compared, and the front wheel steering angle is corrected based on the comparison result. Something that has been done is proposed.

[Problems to be Solved by the Invention]

However, the above-mentioned conventional device does not consider the moment about the vertical axis of the vehicle body center of gravity caused by the difference between the driving force or the braking force of the left and right wheels of the vehicle. The moment about the vertical axis of the vehicle body weight is referred to as a so-called yawing moment (unit: m · Kg, etc.). For various acting forces acting on the vehicle body, such as the moment about the vertical axis of the body weight of the vehicle, refer to, for example, "New Edition Automotive Engineering Handbook <Second Edition>" (published on November 26, 1982, first edition.
The issue is described on pages 1-37, etc. of the Japan Society of Automotive Engineers (the moment about the vertical axis of the body weight of the vehicle is shown as the moment Mz about the z axis). Conventionally, since the moment around the vertical axis of the vehicle body weight is not taken into consideration, there are the following problems. First, there is a case where a limited slip differential gear (hereinafter referred to as LSD) is used in the differential gear to increase the driving force in the related art, but for a vehicle in which such an LSD is used, Has a problem that it becomes difficult to turn due to generation of differential torque. That is, as shown in FIG. 7, when an FF (front engine front drive) vehicle 8 equipped with an LSD7 turns around a turning center O, a differential as shown in FIG. Torque Td is generated, which causes left and right front wheels
9A, the driving force of 9B F _1, F ₃ is _{F 1 = Tq / 2 + Td} , changes as _{F 3 = Tq / 2-Td} , the driving force of the inner wheels as compared to the driving force F ₃ of the outer wheel in turning There is a problem that F ₁ increases and a moment about the vertical axis of the vehicle body center in the direction opposite to the vehicle turning direction is generated, which makes it difficult to turn, that is, there is a tendency of so-called understeer or torque steer. Note that FIG. 8 shows the ring gear torque Tq and the differential torque Td of the differential gear as the engine output torque.
And a solid line P in the figure shows a normal differential gear, and a broken line Q shows an LSD. Also, the seventh
Reference numeral 7A in the figure indicates an engine. The tendency of understeer and torque steer as described above is not limited to LSD, and even in a normal differential gear, when accelerating and decelerating turning with a large torque, FF vehicles and FR (front engine rear drive) vehicles are concerned. May occur without any action. Secondly, when the braking force of the left and right wheels is imbalanced during braking or when the friction coefficient μ of the ground contact road surface of the left and right wheels is different, a difference occurs in the braking force or the driving force of the left and right wheels. As a result, a moment is generated in the vehicle about the vertical axis of the weight of the vehicle, which causes the vehicle body to be deflected or spun.

[Object of the Invention]

The present invention has been made to solve the above-mentioned conventional problems, and front and rear wheels capable of preventing a vehicle body deflection during traveling or a vehicle rolling-in phenomenon caused by a difference in driving force or braking force between left and right wheels of a vehicle. An object of the present invention is to provide a rear wheel control device for a steered vehicle.

[Means for solving problems]

The present invention relates to a rear wheel control device for a front and rear wheel steering vehicle, comprising:
As shown in the figure, the right wheel / driving / braking force detection means for detecting the driving / braking force of the right wheel and the driving / braking force of the left wheel are detected.
The left wheel / driving / braking force detecting means for detecting the braking force, the front wheel steering angle detecting means for detecting the front wheel steering angle, the detected right wheel / driving / braking force and the detected left wheel / driving / braking force Based on the difference and the detected steering angle of the front wheels, a vehicle body moment calculating means 3 for calculating a moment around the vertical axis of the vehicle body weight caused by a difference between the driving force or the braking force of the left and right wheels of the vehicle, and a vehicle speed detecting means 4 for detecting the vehicle speed. A rear wheel steering angle calculating means 5 for calculating a rear wheel steering angle so as to cancel the detected vehicle body moment according to the calculated vehicle body moment and the detected vehicle speed; and a rear wheel steering wheel based on the calculated rear wheel steering angle. The above object is achieved by including the rear wheel steering mechanism 6 for steering.

[Action]

In the present invention, first, the driving / braking force of the right wheel is detected. At the same time, the driving / braking force of the left wheel is detected.
Further, the moment about the vertical axis of the vehicle body weight is calculated from the difference between the detected right wheel / driving / braking force and the detected left wheel / driving / braking force and the front wheel steering angle. That is, the moment around the vertical axis of the vehicle body weight center generated by the difference between the driving force or the braking force of the left and right wheels of the vehicle is calculated, the vehicle speed is detected, and the calculated vehicle body rotation according to the calculated vehicle body moment and the detected vehicle speed. The rear wheel steering angle that cancels the moment is calculated, and the rear wheels are steered based on the calculated rear wheel steering angle. Therefore, vehicle deflection and spin that occur due to the difference in driving force and braking force between the left and right wheels are prevented,
The vehicle maneuverability that faithfully follows the steering operation of the driver can be obtained. That is, it is possible to prevent the deflection during braking (one-sided effect) and the deflection during driving (torque steer).

【Example】

An embodiment of a rear wheel control device for a front and rear wheel steering vehicle to which the present invention is applied will be described in detail with reference to the drawings. FIG. 2 shows a front wheel steering mechanism A, a rear wheel steering mechanism B, and an electric control device C for the rear wheel steering mechanism B of a vehicle to which the present invention is applied. The front wheel steering mechanism A includes a pinion and rack mechanism 11 and a pair of left and right relay rods 12a and 12b connected to the rack portion of the mechanism 11. The pinion and rack mechanism 11 is connected to a steering handle 14 via a steering shaft 13 at its pinion portion, and converts the rotational movement of the steering handle 14 into the reciprocating movement of the relay rods 12a, 12b. The left and right relay rods 12a and 12b are connected to the left and right front wheels 16 via left and right tie rods and left and right knuckle arms 15a and 15b (not shown).
The left and right relay rods 12 are connected to a and 16b respectively.
The left and right front wheels 16a and 16b are steered by a and 12b. The rear wheel steering device B includes a hydraulic pump 20 driven by an engine, and a hydraulic cylinder that steers both rear wheels 22a and 22b by applying oil discharged from the hydraulic pump 20 via a servo valve 21.
It has 23 and. The hydraulic pump 20 is connected at its inflow port to the reservoir 24 via the conduit P _1, and at its discharge port to the servo valve 21 via the conduit P ₂ . The servo valve 21 closes the conduit P ₃ connected to the right chamber 23b of the hydraulic cylinder 23 at its neutral position, and
The conduit P ₄ connected to the left chamber 23a of 3 is closed. Also, servo valve
21 connects the conduit P ₂ to the conduit P ₃ and the conduit P ₄ to the reservoir 24 via the conduit P ₅ when switched to the first position which is displaced downwards in FIG. Also, when switched to the second position displaced upward in FIG. 2, the conduit P ₂ is connected to the conduit P ₄ , and the conduit P ₃ is connected to the reservoir 24 via the conduit P ₅ . The switching operation of the servo valve 21 is effected by the operation of the torque motor 21a provided in the servo valve 21, and the operation of the torque motor 21a is effected by the control signal given from the electric control device C. Be done. The hydraulic cylinder 23 is configured by connecting a pair of left and right piston rods 26a and 26b to a piston 25 housed inside. The left piston rod 26a is connected to the rear wheel 22a via a tie rod 27a and a knuckle arm 28a.
The right piston rod 26b is connected to the rear wheel 22b via a tie rod 27b and a knuckle arm 28b. The electric control unit C picks up the rotation of the vehicle speed detecting gear 16c provided on the right front wheel and generates a pick up signal having a frequency corresponding to the vehicle speed, and a vehicle speed sensor 30 and wheels 16a, 16b, 22a of the vehicle, Torque sensor mounted on 22b
31a, 31b, 32a, 32b and front wheels attached to the steering shaft 13
A front wheel steering angle sensor that detects the front wheel steering angle of 16a, 16b and generates an analog signal indicating a voltage value corresponding to the front wheel steering angle
34, a rear wheel steering angle sensor 36 for measuring the actual steering angle with respect to the target rear wheel steering angle and performing steering angle feedback control to the target steering angle, and these sensors 30, 31a, 31b, 32
The microcomputer 38 that outputs a target steering angle control signal for the rear wheels by executing a program described below based on the signals given from a, 32b, 34, and 36, the control signal of the microcomputer 38, and the rear wheels. A comparator 40 that outputs a difference signal from the actual steering angle signal from the steering angle sensor 36 and a servo amplifier 41 that amplifies the output signal from the comparator 40 and drives the servo valve 21 are provided. The microcomputer 38 constitutes the vehicle body moment calculating means 3, the vehicle speed detecting means 4, and the rear wheel steering angle calculating means 5 in FIG. 1, and is a program corresponding to the flow chart shown in FIG. A read-only memory (ROM) 38a for storing parameters for calculating the rear wheel steering coefficient C (v) (see FIG. 5), a central processing unit (CPU) 38b for executing this program, and this program A writable memory (RAM) 38c for temporarily storing necessary variables and flags is connected to the vehicle speed sensor 32 via a waveform shaper (not shown), and torque sensors 31a-b, 32a-b, front wheel rudder. The angle sensor 34 and the rear wheel steering angle sensor 36 are connected to each other via an analog / digital converter (A / D converter) not shown, and the comparator 40 has a digital / analog converter (D / A converter) not shown. An input / output interface circuit (I / O) 38d connected via a switch and a bus 38e for commonly connecting the ROM 38a, the CPU 38b, the RAM 38c, and the I / O 38d. The operation of the vehicle rear wheel steering control device configured as described above will be described with reference to the flow chart of FIG. When the ignition switch (not shown) is closed to start the vehicle, the CPU 38b starts executing the program in step 100, and in step 102, the left front wheel drive / braking torque F is detected by the torque sensor 31a of the left front wheel 16a. Read ₁ Next, in step 104, the right front wheel drive / braking torque F ₃ is read by the torque sensor 31b of the right front wheel 16b. Next, at step 106, the left rear wheel torque sensor 3
The driving / braking torque F ₂ of the left rear wheel 22a is read by 2a. Next, at step 108, the torque sensor 32b of the right rear wheel 22b is
Read the right rear wheel drive / braking torque F ₄ . Next, in step 110, it is determined whether the absolute value of the difference between the left front wheel drive / braking torque F ₁ and the right front wheel drive / braking torque F ₃ detected in the preceding steps 102 and 104 is greater than a predetermined value ΔFf. To do. If it is determined to be no in this step 110, that is, if the absolute value of the difference between the left front wheel drive / braking torque F ₁ and the right front wheel drive / braking torque F ₃ is determined to be the predetermined value ΔFf or less, the step 112 is performed. move on. In step 112, it is determined whether or not the absolute value of the difference between the left rear wheel drive / braking torque F ₂ and the right rear wheel / drive braking torque F ₄ is larger than a predetermined value ΔFr. This step 112
If it is determined to be positive, that is, if the absolute value of the difference between the driving and braking torques of the left and right rear wheels is greater than the predetermined value ΔFr, the process proceeds to step 114. In step 114, the front wheel steering angle θf is read from the front wheel steering angle sensor 34. Next, in step 116, based on the drive / braking torques F _{1 to} F ₄ and the front wheel steering angle θf obtained in the above-mentioned steps, the moment Mg about the vertical axis of the vehicle body weight center (hereinafter, simply , The vehicle body moment Mg) is calculated. _{Mg = (F 1 -F 3)} (rcosθf-lfsinθf) + (F 2 -F 4)
r (1) As shown in FIG. 4, the above equation (1) divides the driving / braking torques F _{1 to} F ₄ of the wheels into a vehicle front-rear direction component force and a vehicle width direction component force. Is multiplied by the distance r from each wheel to the center of gravity of the vehicle and lf, and then added to obtain the vehicle body moment Mg. Next, in step 118, it is determined whether or not the absolute value of the vehicle body moment Mg calculated in step 116 is larger than a predetermined value ΔM. If it is determined positive in step 118, that is, if the vehicle body moment Mog is determined to be larger than the predetermined value ΔM, the vehicle body moment
If it is determined that the rear wheels need to be steered to cancel Mg, the process proceeds to step 120. In step 120, the vehicle speed V is read by the vehicle speed sensor 30. Next, in step 122, the rear wheel steering coefficient C (v) is calculated from the map data of the vehicle speed V and the rear wheel steering coefficient C (v) as shown in FIG. The rear wheel steering coefficient C (v) is set so that its value gradually decreases as the vehicle speed V increases. Next, the routine proceeds to step 124, where the vehicle body moment Mg obtained in the preceding step 116 and the rear wheel steering coefficient C (v) obtained in the preceding step 122 are multiplied to obtain the rear wheel steering angle θr (= Mg・ C
(V)) is calculated. Next, the routine proceeds to step 126, where the rear wheel steering control is performed on the basis of the rear wheel steering angle θr obtained in the preceding step 124, and then the routine returns to the preceding step 102. Control the snake. Also, in the above-mentioned step 110, when it is determined to be positive,
That is, the absolute value of the difference between the driving and braking torques of the left and right front wheels | F ₁ −
When it is judged that F ₃ | is larger than the predetermined value ΔFf,
Go to step 114 above. Further, when it is determined to be no in the above steps 112 and 118, that is, the absolute value of the difference between the driving and braking torques of the left and right rear wheels |
When F ₂ −F ₄ | and the absolute value | Mg | of the vehicle body moment Mg are less than or equal to the predetermined values ΔFr and ΔM, the rear wheel steering that cancels the moment around the vertical axis of the vehicle body weight is used. If it is determined that there is no need to do so, the process returns to the above step 102. As can be understood from the above description of the operation, according to the present embodiment, the driving / braking torques F _{1 to} F ₄ of the wheels are detected from the torque sensors 31a, 31b, 32a, 32b, and the detected values and the front wheel steering are detected. A vehicle body moment Mg is calculated based on the angle θf, and it is determined whether or not the rear wheels need to be steered so as to cancel the vehicle body moment Mg based on the vehicle body moment Mg. When it is necessary to adjust the vehicle body moment Mg to the rear wheel steering coefficient C
(V) is multiplied to determine the rear wheel steering angle θr, and the rear wheels are steered based on the rear wheel steering angle θr. Therefore, it is possible to cancel the vehicle body moment Mo generated by the difference between the driving force and the braking force of the left and right wheels, and prevent the vehicle from deflecting or spinning during traveling. Particularly, in the present embodiment, when determining the rear wheel steering angle θr, the vehicle deflection correction is performed by using the rear wheel steering coefficient C (v) whose value gradually decreases as the vehicle speed V increases. Can be done accurately according to It should be noted that, in the above embodiment, step 110 and step 1
At 12, the absolute value of the difference between the driving and braking torques of the left and right wheels is obtained, and based on the absolute value of the difference, whether or not rear wheel steering is necessary is determined in advance to simplify the control. But,
The present invention is not limited to this, for example, omitting the above-mentioned steps 110 and 112, directly calculating the vehicle body moment Mg from the driving / braking torques F _{1 to} F _{4 of} each wheel, and the vehicle body moment It is also possible to determine whether or not rear wheel steering is necessary only from Mg. Further, in the above-mentioned embodiment, the detection of the driving / braking torque of each wheel is performed by the torque sensor, but the present invention is not limited to this, and the driving / braking force of each wheel is not limited to this. You may make it detect. For example, instead of the torque sensor, a front / rear force sensor that detects the suspension front / rear force of each wheel may be used to detect the driving / braking force of the wheel. Further, in the above embodiment, not only the driving force but also the braking force is detected by using the torque sensor mounted on the wheel side, and the vehicle deflection and the spin are prevented based on the driving force and the braking force. However, the present invention is not limited to this, and the present invention may be applied to improve the vehicle deflection phenomenon only during driving. In this case, a torque sensor may be attached between the differential gear such as a drive shaft and the wheel to detect the driving force. Further, instead of the torque sensor mounted on the wheel side, the torque generated by the engine is obtained, for example, by detecting the ring gear torque Tq. From this ring gear torque Tq, the characteristic diagram of the differential gear shown in FIG. The differential torque Td may be calculated based on the differential torque Td, and the difference between the driving forces of the left and right wheels may be obtained from the differential torque Td, and the rear wheels may be steered based on the difference in the driving forces. Further, in order to prevent a phenomenon such as vehicle deflection or spin caused by a difference in friction coefficient of the road surface contacting the left and right wheels, when the present invention is applied, the friction coefficient M of the road surface is detected instead of the torque sensor. Is provided, and the product of the friction coefficient μ detected by this μ sensor and the ground load W is
The driving force F (= Wμ) may be obtained, the vehicle body moment Mg may be calculated based on the driving force F, and the rear wheels may be steering-controlled. Instead of using the μ sensor, the slip rate S is calculated from the ground speed v of the vehicle body, the rotation speed ω of the wheel, and the ground contact load W (S = (rω−v / rω), and the slip rate S is calculated based on the slip rate S. The road surface friction coefficient μ is obtained from the relationship between the slip ratio S and the road surface friction coefficient μ shown in FIG. 6, and the friction force μ is multiplied by the ground load W to obtain the driving force F. From this driving force F, the vehicle body moment Mg May be calculated to control the steering of the rear wheels.

As described above, according to the present invention, driving of the left and right wheels
This has an excellent effect that the moment around the vertical axis of the vehicle body weight caused by the difference in braking force is canceled by the rear wheel steering to prevent the occurrence of vehicle deflection, spin, etc., and improve the vehicle steering stability.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a rear wheel control system for a front and rear wheel steering vehicle according to the present invention, and FIG. 2 is a front wheel in an embodiment of a rear wheel control system for a front and rear wheel steering vehicle according to the present invention. FIG. 3 is a plan view showing a steering mechanism, a rear wheel steering mechanism, and an electric control device, including a partial block diagram and a conduit diagram; FIG. 3 is a flow chart showing the operation of the microcomputer in the embodiment;
FIG. 5 is a plan view showing various parameters for calculating the vehicle body moment, FIG. 5 is a diagram showing the relationship between vehicle speed and rear wheel steering coefficient in the same embodiment, and FIG. 6 is another embodiment. Fig. 7 is a diagram showing the relationship between the slip ratio and the road surface friction coefficient, Fig. 7 is a plan view showing the driving force when the conventional FF vehicle is turning, and Fig. 8 is a relationship between the operating torque and the ring gear torque. FIG. 7 is a diagram showing the characteristics of a differential gear. A ... Front wheel steering mechanism, B ... Rear wheel steering mechanism, C ... Electric control device, 11 ... Pinion and rack mechanism, 16a, 16b ... Front wheels,
21 ... Servo valve, 22a, 22b ... Rear wheel, 23 ... Hydraulic cylinder, 30
... Vehicle speed sensor, 31a, 31b, 32a, 32b ... Torque sensor, 34
… Front wheel steering angle sensor, 36… Rear wheel meandering angle sensor, 38… Micro computer, 40… Comparator, 41… Servo amplifier.

Claims (1)

[Claims] 1. A right wheel for detecting driving / braking force of the right wheel.
Driving / braking force detecting means, left wheel / driving / braking force detecting means for detecting driving / braking force of the left wheel, front wheel steering angle detecting means for detecting front wheel steering angle, and the detected right wheel / driving / braking force Based on the difference between power and the detected left wheel / driving / braking force, and the detected front wheel steering angle, the moment around the vehicle body that calculates the moment around the vertical axis of the vehicle body weight caused by the difference between the driving force or braking force of the left and right wheels of the vehicle Calculating means, vehicle speed detecting means for detecting a vehicle speed, and rear wheel steering angle calculating means for calculating a rear wheel steering angle so as to cancel the detected vehicle body moment according to the calculated vehicle body moment and the detected vehicle speed, A rear-wheel steering system comprising: a rear-wheel steering mechanism for steering the rear wheels based on the calculated rear-wheel steering angle.