JPS63184576A - Rear wheel steering device for automobile - Google Patents

Abstract

PURPOSE:To improve accuracy and stability of steering, by detecting shaft loads of right and left rear wheels upon rotary operation of a steering wheel, and controlling steering angles of right and left rear wheels individually according to a difference between said shaft loads. CONSTITUTION:Upon rotary operation of a steering wheel 1, a control circuit 4 determines steering direction and angle of rear wheel based on a steering angle of front wheel detected through a steering angle sensor 2 and a vehicle speed detected through a vehicle speed sensor 3 so as to control a rear wheel steering mechanism. In such device, the rear wheel steering mechanism is constructed with independent steering mechanisms L, R for steering right and left rear wheels 14R, 14L individually. Respective steering mechanisms L, R are constructed such that a tie rod 12 is displaced axially by means of a motor 5 through gear rows 6-9. Difference between right and left shaft loads is calculated based on outputs from respective rear wheel shaft load sensors 15, and the motor 5 is controlled based on the calculated result such that the steering angle of inner wheel with respect to the steering angle of outer wheel increases as the difference of shaft load increases.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a rear wheel steering device for an automobile.

Conventional technology In automobiles, various vehicles have been developed in which the rear wheels are simultaneously steered when the front wheels are steered by turning the steering wheel. It has already been published in etc.

Problems to be Solved by the Invention In the conventional rear wheel steering device as described above, the left and right rear wheels are connected, and the left and right rear wheels are controlled based on the steering angle (or steering force) of the front wheels and the vehicle speed at that time. Normally, a method is adopted in which both wheels are steered together.

However, when a running vehicle turns, the load shifts between the left and right wheels depending on the extent of the turn, and while the ground contact load on the outer turning wheel increases, the ground contact load on the inner turning wheel decreases, resulting in a decrease in cornering force. Therefore, the tire performance of the left and right rear wheels (
In other words, in order to maximize the steering angle of the rear wheels (resistance against side-to-side ratio), it is necessary to determine the steering angle of the rear wheels according to the load.However, in the conventional device described above, the left and right rear wheels are connected and the steering angle is adjusted to the maximum. Since it has a steered structure, it has to be steered as an average of the loads on the left and right rear wheels, which poses the problem of not being able to maximize the tire characteristics.

The main purpose of the present invention is to address the problems of the conventional rear wheel steering device as described above.

Means for Solving the Problems The present invention provides a left rear wheel steering mechanism and a right rear wheel steering mechanism, each of which is independently provided, and in which the left and right rear wheels are independently steered by an output signal from a control circuit. In addition to configuring it so that
Left and right axle load sensors are provided that detect the respective axle loads of the left and right rear wheels and input the axle load signals to the control circuit, and when the front wheels are steered, the control circuit detects the axle load signals of the left and right axles, which also receive input from the axle load sensors. The left and right axle load difference is calculated from the heavy signal, and the steering angle at which the left and right rear wheels should be steered is determined based on the axle load difference. The present invention is characterized in that it is configured such that the output signal is separately determined for the left and right rear wheel steering mechanisms so as to be large, and output signals are issued separately to the left and right rear wheel steering mechanisms.

Effect As described above, front wheel steering causes the left and right rear wheels to be steered in the same direction as the front wheels. At this time, if a difference in axle load between the left and right rear wheels occurs due to the load shift caused by the degree of turning, the axle load difference will be The larger the angle, the more the inner wheel in the turn is steered than the outer wheel in the turn, and the reduction in the cornering force on the inner wheel in the turn due to the decrease in the ground contact load on the inner wheel in the turn due to load transfer is due to the increase in cornering force due to the increase in the steering angle. compensated,
This allows both the inner and outer rear wheels to maximize tire performance and improve steering stability.

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

In FIG. 1, reference numeral 1 denotes a steering handle, and by rotating the steering handle l to the right or left, a known front wheel steering device (not shown), such as a rack-and-binion steering device, is actuated to turn the front wheels to the right or left. It is now possible to operate the steering.

2 is a front wheel steering angle sensor that detects the front wheel steering angle due to the steering operation of the steering wheel l and generates a front wheel steering angle signal; 3 is a vehicle speed sensor that generates a vehicle speed signal; Based on the vehicle speed signal from the vehicle speed sensor 3, the control circuit 4 determines whether or not the vehicle is turning. When it determines that the vehicle is turning, the control circuit 4 receives a signal from the left and right rear wheel axle load sensors 15, which will be described later. Based on the input, the steering angle (including the steering direction) at which the rear wheels should be steered is determined and an output signal is generated.

The left and right rear wheels 14L and 14R are configured to be steered separately by independent steering mechanisms and R, respectively.

The steering mechanisms R and R each include an actuator such as an electric motor 5 controlled by an output signal from a control circuit 4, a cylindrical worm 6 fixed to the output shaft of the electric motor 5, and a worm wheel meshing with the cylindrical worm 6. 7, and a pinion gear 8 that rotates integrally with the worm wheel 7.
, a rack shaft 9 that meshes with the pinion gear 8, and a gear box 11 that houses these, and each rack shaft 9 is connected to left and right rear wheels 14L and 14R via tie rods 12 and knuckle arms 13, respectively. As the electric motor 5 rotates, the rack shaft 9 is actuated in the axial direction, so that the rear wheels 14L and 141 can be steered separately.

The steering mechanisms R and R are provided with a rear wheel steering angle sensor 10 that detects the actual steering angle of each rear wheel and issues actual steering angle signals for the left and right rear wheels to the control circuit 4.

Reference numeral 15 denotes left and right axle load sensors that respectively detect vertical loads, that is, axle loads acting on the respective axes of the left and right rear wheels 14L and 14H, and input axle load signals to the control circuit 4 separately. In a car equipped with this, a pressure sensor that detects the air pressure of the air suspension of each of the left and right rear wheels can be used as the axle load sensor 15.

The relationship between the difference in axle loads between the left and right rear wheels and the respective optimum steering angles of the left and right rear wheels is preset in the control circuit 4 as a map, and the relationship between the difference in the axle loads of the left and right rear wheels and the respective optimum steering angles of the left and right rear wheels is preset as a map. The left and right axle load difference is calculated from the axle load information, and the steering angle of the left and right rear wheels is adjusted based on the above map according to the change in the left and right axle load difference, and when the left and right axle load difference is small, the left and right rear wheels are adjusted. are almost the same steering angle, and when the difference in left and right axle loads becomes large, the steering angle on the inner turning wheel of the left and right rear wheels is made larger than the steering angle on the outer turning wheel side, and the difference in the steering angle between the left and right rear wheels is equal to the left and right axle load. The larger the difference is, the larger the difference is determined, and output signals are sent to the left and right rear wheel steering mechanisms and the electric motors 5 and 5 of H, respectively, and the left and right rear wheels 14L and 14R are respectively steered. left and right rear wheel steering angle sensors 10. The left and right rear wheels are individually steered according to the steering angle determined by the control circuit 4 under feedback control based on the rear wheel actual steering angle signal input from the to.

In the above, the steering direction of the left and right rear wheels is the same as the steering direction of the front wheels.

Generally, when a vehicle turns, a load shifts between the left and right wheels depending on the degree of the turn, and the axle load on the inner wheel side tends to decrease, resulting in a decrease in drag against side-to-side rotation, that is, cornering force.

On the other hand, the cornering force of the tires increases as the turning angle in the turning direction increases.

Therefore, as mentioned above, the steering angle in the same direction as the front wheel steering direction of the rear wheels is set so that the inner turning wheel side is larger than the turning outer wheel side, and the larger the difference in left and right axle loads, the larger the difference in the steering angle between the inner and outer turning wheels. By controlling the cornering force so that This makes it possible to maximize steering performance and significantly improve steering stability.

In the above embodiment, each optimum steering angle of the left and right rear wheels is determined by the axle load sensor 15.
, 15 is shown in which the determination is made based on a preset map from the left and right axle load information input from the front wheel steering angle sensor 2. Based on the front wheel steering angle information obtained and the vehicle speed information obtained from the vehicle speed sensor 3, the average steering angle of the left and right rear wheels is determined as before, and then the control circuit 4 determines the axle load obtained from the axle load sensors 15, 15. From the difference information, for example, based on the characteristics of the difference in steering angle between the inner and outer wheels relative to the difference in axle load between the inner and outer wheels (this is set in advance in the control circuit 4) as shown in FIG. It may be configured such that the respective steering angles of the inner and outer wheels are determined to appropriate values such that the inner wheel side takes a larger steering angle than the outer wheel side by correcting the steering angles of the inner and outer wheels, and an output signal is generated.

In this case, the method of determining the average rear wheel steering angle from the front wheel steering angle and vehicle speed is, for example, in a low speed range, the rear wheels are slightly steered in the opposite direction to the front wheel steering direction (reverse phase steering). A conventional average rear wheel steering angle determination method that sets the rear wheel steering direction in the same direction as the front wheel steering direction (in-phase steering) from medium to high speed ranges, and increases the rear wheel steering angle as the vehicle speed increases. Alternatively, an average rear wheel steering angle determination method may be adopted in which all rear wheels are steered in the same phase from a low speed range to a high speed range, and the rear wheel steering angle is gradually increased as the vehicle speed increases. Also good.

If one of the above methods is adopted, in which the rear wheels are steered in reverse phase in the low speed range, and in the same phase in the high speed range, the left and right axes will be steered in the low speed range, which is reverse phase steering. The load difference is almost zero, and control with a difference in the steering angle between the inner and outer wheels based on the difference in left and right axle loads is performed during high-speed steering while in-phase steering, so this is the same as in the previous embodiment. By compensating for the decrease in the axle load of the inner turning wheel by increasing the cornering force based on the increase in the steering angle of the inner turning wheel in the same phase direction, it is possible to maximize tire performance and improve steering stability.

In the illustrated embodiment, an electric motor is used as a seven-wheel drive unit for rear wheel steering, and the rotation of the electric motor drives a reduction gear mechanism and a pinion gear.

Although a structure in which the rear wheels are steered through a rack shaft or the like is shown, the rear wheel steering actuator and the mechanism for transmitting the steering force from the actuator to the rear wheels are other than those in the above-illustrated embodiment. For example, any configuration may be adopted, such as a mechanism that steers the rear wheels using the hydraulic pressure of a hydraulic actuator.

Effects of the Invention As described above, according to the present invention, when steering by rotating the steering wheel, the axle loads of the left and right rear wheels are detected, and the axle loads are adjusted according to the difference in the axle loads of the left and right rear wheels. By controlling the steering angle of the left and right rear wheels separately so that the larger the difference, the larger the steering angle is given to the inner turning wheel relative to the outer turning wheel, the ground load on the inner turning wheel of the left and right rear wheels is reduced. The decrease in cornering force caused by the decrease in cornering force can be compensated for by increasing the steering angle of the inner wheel in the turn, making it possible to maximize the performance of the tire and significantly improving the accuracy and stability of maneuverability. This can bring about great effects.

[Brief explanation of the drawing]

FIG. 1 is an explanatory plan view showing an embodiment of the present invention, and FIG. 2 is a diagram showing control characteristics of the difference in steering angle between the inner and outer wheels relative to the difference in axle load between the inner and outer wheels. DESCRIPTION OF SYMBOLS 1... Steering handle, 2... Front wheel steering angle sensor, 3... Vehicle 1st speed sensor, 4... Control circuit, L. R... Rear wheel steering mechanism, 10... Rear wheel steering angle sensor, 1
4L, 14R...Rear wheel, 15...Axle load sensor. that's all

Claims (2)

[Claims] (1) As the front wheels are steered by rotating the steering wheel, the control circuit determines the direction and steering angle in which the rear wheels should be steered, issues an output signal, and operates the rear wheel steering mechanism to steer the rear wheels. In a rear wheel steering system of an automobile, a left rear wheel steering mechanism and a right rear wheel steering mechanism are provided independently to steer the left and right rear wheels separately, and a left rear wheel steering mechanism and a right rear wheel steering mechanism are provided independently. Left and right axle load sensors are provided to detect the respective axle loads of the wheels and input axle load signals to the above-mentioned control circuit, and when the front wheels are steered, the control circuit receives axle load signals input from the above-mentioned left and right axle load sensors, respectively. The difference in the left and right axle loads is calculated based on the axle load difference, and the steering angle at which the left and right rear wheels should be steered is determined based on the axle load difference. A rear wheel steering device for an automobile, characterized in that the rear wheel steering device for an automobile is configured to separately determine the left and right rear wheel steering mechanisms so as to cause the left and right rear wheel steering mechanisms to operate separately. (2) The rear wheel steering device for an automobile according to claim 1, wherein the rear wheel steering direction determined by the control circuit is the same direction as the front wheel steering direction.