JPH0537906Y2 - - Google Patents

Description

[Detailed explanation of the idea] [Industrial application field]

The present invention relates to a rear wheel steering device for a front and rear wheel steered vehicle, and more particularly to a rear wheel steering device for a front and rear wheel steered vehicle, which is suitable for use in a front and rear wheel steered vehicle equipped with an electronic control device.

[Conventional technology]

Conventionally, two-wheel steering vehicles (so-called 2WS vehicles), which turn only the front wheels of the vehicle, have been common in vehicles such as passenger cars.
However, the above two-wheel steering vehicle has not been able to achieve a dramatic improvement in the ability to turn around at low speeds and the steering stability at high speeds. Therefore, today, front and rear wheel steered vehicles (so-called 4WS vehicles) have been developed that actively give a steering angle to the rear wheels of the vehicle, aiming to actively improve the above-mentioned tight turning performance and maneuverability. It has reached the point where Regarding such front and rear wheel steered vehicles, various techniques have been devised for controlling the steering of the rear wheels (Japanese Patent Application Laid-open No. 60-161262, No. 61-50878, etc.). Among these technologies, at low speeds, the rear wheels are steered in the opposite phase to the front wheels to improve maneuverability, and at high speeds, the rear wheels are steered in the same phase as the front wheels to improve steering performance. There is a technology to
50078). In addition, there is a front and rear wheel steered vehicle in which the rear wheels are steered by a servo actuator based on electric signals (Japanese Patent Application Laid-Open No. 1987-
44568), and a high-speed steering angle regulating device to prevent unintentional large-angle steering of the rear wheels when a failure occurs during high-speed driving (Japanese Patent Laid-Open No. 60-150164, Japanese Patent Laid-Open No. 60-60-
150165) etc.

[Problem that the invention attempts to solve]

However, in the conventional rear wheel steering system, if the electronic control system or actuator system malfunctions, the rear wheels cannot be steered, resulting in both improved steering stability at high speeds and small turning ability at low speeds may be lost at the same time. Furthermore, in order to eliminate such fears, when trying to increase the reliability of electronic control systems, conventionally, a redundant system such as a triple system was required for detection sensors and electronic control devices, etc.
The device configuration was expensive and difficult to install. In addition, although the above-mentioned high-speed steering angle regulation device can achieve steering angle regulation at high speeds, the effect of this steering angle regulation cannot be obtained in front and rear wheel steered vehicles that aim to achieve small turning ability at low speeds. Ta.

[Purpose of invention]

The present invention has been made to solve the above-mentioned conventional problems, and even if a part of the rear wheel steering device of a front and rear wheel steering vehicle breaks down, at least some of its functions can be maintained, for example at low speeds. The rear wheels of a front-rear wheel steered vehicle can perform at least some functions, such as the ability to steer the rear wheels in the opposite phase to the front wheels at times, or the ability to steer the rear wheels in the same phase as the front wheels at high speeds. The purpose is to provide a steering device.

[Means to solve the problem]

The present invention includes a first rear wheel steering angle setting section that outputs a rear wheel steering angle according to a predetermined first rear wheel steering characteristic based on at least a steering angle of a steering wheel;
The steering angle is detected without interfering with the operation of the first rear wheel steering angle setting section, which is provided separately from the first rear wheel steering angle setting section, and at least the detected steering angle is a second rear wheel steering angle setting section that outputs a rear wheel steering angle according to a predetermined second rear wheel steering characteristic different from the first rear wheel steering characteristic; and a differential section for synthesizing each rear wheel steering angle inputted from the second rear wheel steering angle setting section and controlling steering of the rear wheels based on the synthesized steering angle. has been achieved.

[Effect]

In a front and rear wheel steering vehicle equipped with a rear wheel steering device,
If some kind of failure occurs in the rear wheel steering device, the rear wheels will not be able to be steered, but the same steering and steering as in conventional front wheel steering vehicles will be ensured, so there will be no safety issues. It is not. however,
Many of the conveniences of a front and rear wheel steered vehicle equipped with a rear wheel steering device are lost. For example, large steering becomes inconvenient when a small turn is required, such as when parking a vehicle in a garage. The present invention focuses on this point in particular, and even if a part of the rear wheel steering device malfunctions,
This was done based on the fact that it is very effective to maintain at least some of the functions. In addition, the present invention has discovered a more excellent configuration for this purpose. As mentioned above, it is conceivable to use a triple control system for the rear wheel steering system, but in this case, it would be expensive and difficult to mount. In the configuration of the present invention, the control section that determines the rear wheel steering angle based on the steering angle of the steering wheel is divided into a first rear wheel steering angle setting section and a second rear wheel steering angle setting section, and these sections are operated in parallel. I am trying to get it to work. The first rear wheel steering angle setting section and the second rear wheel steering angle setting section each have predetermined rear wheel steering characteristics that are different from each other, for example, characteristics of the rear wheel steering angle determined based on at least the steering angle of the steering wheel. ing. Moreover, these first rear wheel steering angle setting section and the second rear wheel steering angle setting section
The rear wheel steering angle setting sections operate independently without interfering with each other. In particular, the detection of the steering angle of the steering wheel is also independent and non-interfering with each other, so that a malfunction in one will not hinder the operation of the other. For example, in the embodiment described later, an anti-phase steering section 14 is provided as a first rear wheel steering angle setting section, and an in-phase steering section 37 is provided as a second rear wheel steering angle setting section. The anti-phase steering section 14 uses a predetermined first rear wheel steering characteristic as shown in the graph of FIG. 3 when obtaining the rear wheel steering angle based on at least the steering angle of the steering wheel. On the other hand, at least when determining the rear wheel steering angle based on the steering angle of the steering wheel, the in-phase steering section 37
A second rear wheel steering characteristic as shown in equation (1), which will be described later, is used. Also in this embodiment, the opposite phase steering section 14 corresponding to the first rear wheel steering angle setting section and the same phase steering section 37 corresponding to the second rear wheel steering angle setting section are separate from each other. are provided so that they can operate without interfering with each other. Furthermore, in the embodiment described later, since the in-phase steering section 37 detects the steering angle of the steering wheel using the steering wheel angle sensor 26, the operation based on the steering wheel steering angle of the anti-phase steering section 14 is performed. be independent and non-interfering with
Further, although the rear wheel steering angle output from the anti-phase steering section 14 and the rear wheel steering angle output from the same phase steering section 37 are combined by the differential device 24, these rear wheel steering angles are Changes in the steering angle are independent and non-interfering with each other, and the operation of the anti-phase steering section 14 and the operation of the same-phase steering section 37 do not interfere with each other. Therefore, in this embodiment, even if a failure occurs in the anti-phase steering section 14, the function of the in-phase steering section 37 to steer the rear wheels to the same phase as the front wheels at high speeds is maintained. can be secured. On the other hand, even if a failure occurs in the in-phase steering section 37, the function of the anti-phase steering section 14 to steer the rear wheels in a phase opposite to that of the front wheels at low speeds can be ensured.

【Example】

Hereinafter, embodiments of the present invention will be described in detail. FIG. 1 is a block diagram showing the configuration of a rear wheel steering system according to this embodiment. As shown in the figure, when the steering wheel 10 is steered, the front wheels 12 are steered via the steering gear box 11, and the reverse phase steering section 14 is also activated. This anti-phase steering unit 14 includes a connecting shaft 18 for transmitting the steering amount of the steering wheel 10 via the pinion 16, and a connecting shaft 18 for transmitting the steering amount of the steering wheel 10 through the pinion 16, and a connecting shaft 18 for transmitting the steering amount of the steering wheel 10 to a rear wheel steering angle of a phase opposite to that of the front wheels 12. A reverse phase steering conversion device 20 for conversion is provided.
The rear wheel steering angle output from this anti-phase steering conversion device 20 is transmitted to the differential gear 24 as a first rear wheel steering input via the coupling shaft 22. This differential device 24 is configured to steer a rear wheel 34 via connection shafts 38 and 40, which will be described later. Therefore, the anti-phase steering section 14 is
The front wheel 12 and the rear wheel 34 are mechanically connected. Further, near the steering wheel 10,
A steering wheel angle sensor 26 is installed to detect the steering angle of the steering wheel 10, and the output of the steering wheel angle sensor 26 is input to an electronic control unit (ECU) 28. Various quantities detected by a vehicle speed sensor 30 and a yaw rate sensor 32 are also input to this ECU 28 . The ECU 28 calculates a rear wheel steering angle output for steering the rear wheels 34 in the same phase as the front wheels 12 from these input signals. The calculated rear wheel steering angle output is input to the servo actuator 36, and the differential gear 2 is output via the servo actuator 36.
4 as the second rear wheel steering input. Each of the above sensors 26, 30, 32, ECU 28,
A same-phase steering section 37 is configured by the servo actuator 36 and the like. Note that an electric servo motor or the like can be used as the servo actuator 36. The differential device 24 combines the first and second rear wheel steering inputs as a rear wheel steering amount, and connects a connecting shaft 38, so that the rear wheels are steered according to the combined rear wheel steering amount. The rear wheels 34 are steered via a rack-and-pinion gear 40 and a rack-and-pinion gear 42 for the rear wheels. In addition, in order to provide auxiliary steering force to the rear wheel steering rod 44 in accordance with the rotation of the connection shaft 38 for the purpose of assisting the steering force of the rear wheels 34, hydraulic pressure is applied in accordance with the rotation of the connection shaft 38. A hydraulic pressure control valve 46 for switching and a hydraulic cylinder 48 for operating the rear wheel steering rod 44 with the switched hydraulic pressure are provided. In addition, in the figure, the reference numeral 50 is an engine, and 52
A hydraulic pump converts the output of the engine 50 into hydraulic pressure, and 54 is a hydraulic line for transmitting the hydraulic pressure from the hydraulic pump 52 to the hydraulic control valve 46. Here, a configuration example of the anti-phase steering conversion device 20 and the differential device 24 will be described. First, a first configuration example in which a planetary gear mechanism is used for the differential device 24 will be explained based on FIG. 2. In this first configuration example, the anti-phase steering conversion device 20 uses the rotation angle of the coupling shaft 18 as an input angle, the rotation angle of the coupling shaft 22 on the output side as an output angle, and the input angle and the output angle are It has a function of outputting an output angle so that the relationship as shown in FIG. 3 is established. Therefore, the reverse phase steering conversion device 20 includes the connection shaft 18.
A ball screw 56 connected or formed at the end of the
and a groove 6 for converting the rotational motion of the ball screw 56 into a back and forth motion in the axial direction and converting the back and forth motion into a motion perpendicular to the axial direction via a pin 58.
a ball nut 62 with 0 formed on its surface;
A rack gear 64A and a pinion gear 64B are provided for converting the back and forth movement of the pin 58 into rotational movement of the connection shaft 22. The shape of the groove of this ball nut 62 is such that the relationship between the input angle and the output angle shown in FIG. 3 can be obtained. In addition, the third
In the relationship shown in the figure, there is a dead zone in the vicinity of neutrality in which the rear wheels are not steered with respect to the input angle, that is, the steering wheel angle. Therefore, when the steering wheel is steered and the steering wheel angle reaches a predetermined value or more, the rear wheels 34 are steered in a reverse phase. Further, the differential device 24 is connected to the connecting shaft 2.
2, a planetary gear 68 that meshes with the sun gear 66, and a ring gear 70 that meshes with the planetary gear 68. In this differential device 24, the rotation angle of the connecting shaft 22 is inputted to the differential device 24 as a first rear wheel steering input.
The rotation angle 2 is the rotation angle of the sun gear 66. or,
In order to input the rotation angle of the servo actuator 36 controlled by the ECU 28 to the differential device 24 as a second rear wheel steering input, a worm 72 and a worm foil 7 formed on the circumferential surface of the ring gear are used.
4, the rotation angle of the servo actuator 36 becomes the rotation angle of the ring gear 70. The planetary gear 68 is connected to the output side connecting shaft 38 so as to output the revolution angle. Thereby, the revolution angle of the planetary gear 68 caused by the relative rotational movement of the sun gear 66 rotated by the first rear wheel steering input and the ring gear 70 rotated by the second rear wheel steering input is the composite input of each of the rear wheel steering inputs. This combined input can be output to the connecting shaft 38 to control the steering of the rear wheels. Note that the rotation angle of the servo actuator 36 is expressed as a rotation angle θr ₂ corresponding to the rear wheel steering angle θr, as shown in the following equation (1), based on the steering wheel angle θf, vehicle speed v, and vehicle yaw rate r. , is input to the differential device 24 as a second rear wheel steering input. θr ₂ = K ₁ (v)・θf+K ₂ (v)・r ...(1) The constants K ₁ (v) and K ₂ (v) in the formula are determined by the vehicle speed v as shown in Fig. 4. It has changing characteristics. Therefore, when the vehicle is in an extremely low speed range, K ₁ (v)=
Since K ₂ (v)=0 and the rotation angle θr ₂ =0, the servo actuator 36 is fixed at the neutral position. In this case, since the output of the differential device 24 is determined only by the first rear wheel steering input inputted as the rotation angle of the connecting shaft 22, The steering wheel will be steered in the opposite phase depending on the input angle from the steering wheel operation, which will improve the ability to turn around in the extremely low speed range. In addition, in the medium to high vehicle speed range, the amount of steering wheel operation by the driver generally becomes small and becomes near the neutral position of the relationship shown in Figure 3, so in most cases, the first rear wheel steering input is almost zero. Become. For this reason(1)
According to the relationship shown in the equation, the rear wheels are steered in the same phase by substantially only the second rear wheel steering input, and it is possible to improve the steering performance in the medium and high speed range. Note that there is a step 7 on the outer circumference of the ring gear 70.
5 is provided, and a protrusion 76 is provided within the housing of the differential device 24. Therefore, when the ring gear 70 attempts to rotate beyond a predetermined angle, the step 75 comes into contact with the protrusion 76 and cannot rotate, and the ring gear 70 is restricted from rotating beyond a predetermined angle. This restriction is a mechanical restriction in which the range of the rotation angle θr ₂ is the operating range of the small steering angle of |θr ₂ |=0.5. Therefore, each sensor 26, 30, 32, ECU2
8. Even in the unlikely event that a failure occurs in the electronic control system such as the servo actuator 36, the above regulation prevents the rear wheels 34 from being steered at a large steering angle against the driver's will, and driving The reliability of the inside rear wheel steering system is ensured. Furthermore, when the ECU 28 detects a failure in the electronic control system, it stops controlling the servo actuator 36, thereby effectively keeping the rear wheels 34 in a fixed state in the medium and high speed range as described above, thereby improving steering stability. Although the performance improvement function is eliminated, 2WS driving by steering only the front wheels 12 is guaranteed, and a small turning function is ensured in the low vehicle speed range due to the relationship shown in FIG. 3. or,
Since the amount of steering angle of the rear wheels that occurs against the driver's will is always regulated within a certain steering angle range, there is no need to change this regulation value depending on the vehicle speed; This eliminates the need for other mechanisms and control devices, improving system reliability. Next, a second configuration example of the differential device 24 will be described, which differs from the planetary gear mechanism of the first configuration example and has a mechanism consisting of a rack gear and a pinion gear. The differential device 24 in this second configuration example includes two rack gears 78, as shown in FIG.
A, 78B and their rack gears 78A, 78B
It has a pinion gear 80 that meshes with. One rack gear 78A operates according to the ball screw 56, ball nut 62, and pin 58 similarly to the rack gear 64A of the first configuration example.
Further, the other rack gear 78B is provided with a gear 82 for converting the rotational motion of the servo actuator 36 into linear motion of the rack gear 78B. The operating range of the rack gear 78B is between the housing abutting portion 83 of the differential device 24 and the rack gear 78B.
The gap between the 8B ends is δ. This results in
Since the rack gear 78B cannot move beyond this gap δ, the maximum steering amount of the second rear wheel steering input input from the servo actuator 36 is restricted. Therefore, even if the electronic control system should fail, the same effects as in the first configuration example can be obtained. Note that the other configurations and operations are the same as those in the first configuration example, and similar parts are denoted by the same reference numerals and description thereof will be omitted. In the above embodiment, the second rear wheel steering input is determined from the steering wheel angle, vehicle speed, and yaw rate, but the second rear wheel steering input is determined based on at least one of these vehicles or by taking other factors into consideration. A rear wheel steering input signal can be obtained. Further, in the above embodiments, a differential device constituted by a planetary gear mechanism as shown in FIG. 2 and a rack gear and a pinion gear as shown in FIG. 5 was illustrated, but the differential device according to the present invention is not limited to what is shown in the figure, and the present invention can be applied to any other device as long as it is a device that combines the first and second rear wheel steering inputs and steers the rear wheels based on the combined input. can.

[Effect of the idea]

As explained above, according to the present invention, even if a part of the rear wheel steering device of a front and rear wheel steering vehicle breaks down, at least part of its functions can be maintained, for example, by moving the rear wheels in the opposite phase to the front wheels at low speeds. At least some functions can be exerted, such as a steering function and a function of steering the rear wheels in the same phase as the front wheels at high speed.
For this reason, for example, in the case of the above-mentioned embodiment, even if the in-phase steering section fails, excellent effects such as being able to ensure tight turning performance at low vehicle speeds can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of a front and rear wheel steered vehicle in which the present invention is implemented, and FIG. 2 is a first configuration example in which the differential device of the front and rear wheel steered vehicle is configured with a planetary gear mechanism. FIG. 3 is a diagram showing an example of the relationship between the input angle and the output angle of the first rear wheel steering input in the front and rear wheel steering vehicle, and FIG. A diagram showing an example of the relationship between a constant that determines the second rear wheel turning input in a steered vehicle and the vehicle speed, and FIG. 5 is a plan view showing a second configuration example in which the differential device 24 is configured with a rack gear and a pinion gear. It is a diagram. 10... Steering wheel, 12... Front wheel, 18, 22, 38, 40... Connection shaft,
20... Anti-phase steering conversion device, 24... Differential device, 26... Steering wheel angle sensor, 28... Electronic control unit (ECU), 30... Vehicle speed sensor, 32
...Yaw rate sensor, 34...Rear wheel, 36...
Servo actuator, 50...Engine (E/
G), 56...ball screw, 58...pin,
60...Groove, 62...Ball nut, 64A...
Rack gear, 64B...Pinion gear, 66...
Sun gear, 68... Planetary gear, 70... Ring gear, 72... Worm gear, 74... Worm wheel, 78A, 78B... Rack gear,
80...pinion gear, 82...gear.

Claims (1)

[Claims for Utility Model Registration] A first rear wheel steering angle setting unit that outputs a rear wheel steering angle according to a predetermined first rear wheel steering characteristic based on at least a steering angle of a steering wheel; and the first rear wheel. The steering angle is detected without interfering with the operation of the first rear wheel steering angle setting section, which is provided separately from the steering angle setting section, and the first rear wheel steering angle is detected based on at least the detected steering angle. a second rear wheel steering angle setting section that outputs a rear wheel steering angle according to a predetermined second rear wheel steering characteristic different from the rear wheel steering characteristic; the first rear wheel steering angle setting section and the second rear wheel A front and rear wheel steered vehicle comprising: a differential section for synthesizing each rear wheel steering angle inputted from a steering angle setting section and controlling steering of the rear wheels based on the synthesized steering angle; Rear wheel steering device.