JP2004090784A - Steering system for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering system for a vehicle capable of attaining excellent steering even at the occurrence of a sensor failure in a steer-by-wire system. <P>SOLUTION: In this steering system for the vehicle, a reaction actuator 20 usually applies operation reaction to a steering member 2 through a planetary gear mechanism 6. When abnormality occurs to either one of a steering angle sensor 24 and a steering torque sensor 25, a steering actuator 12 is made free, while the reaction actuator 20 is stopped and locked to restrict the rotation of a ring gear 18. The rotation of a steering member 2 is transmitted to a pinion 14 by a transmission ratio between a sun gear 15 and a carrier 16 for holding a planetary gear 17, to allow manual steering. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a vehicle steering device that steers steered wheels based on an operation of a steering member.
[0002]
[Prior art]
2. Description of the Related Art In recent years, a so-called steer-by-wire system (also referred to simply as SBW) in which a mechanical connection between a steering member such as a steering wheel and a steered wheel is released and a part of a steering transmission system is configured by an electric path. ) Is provided for a vehicle steering system.
In this type of vehicle steering apparatus, a reaction motor for applying a steering reaction force to a steering member is used in addition to a steering motor for turning a steered wheel.
[0003]
Further, a steering angle sensor for detecting a steering angle of the steering member and a steering torque sensor for detecting a steering torque applied to the steering member are provided, and the detected steering angle and / or the steering angle detected by the steering angle detection sensor are provided. The driving of the steering motor and / or the reaction motor is controlled based on the detected steering torque detected by the torque detecting means.
[0004]
[Problems to be solved by the invention]
In this type of steer-by-wire system, it is important to take fail-safe measures when an abnormality occurs in the steering angle sensor or the steering torque sensor.
The present invention has been made in view of the above problems, and has as its object to provide a vehicle steering apparatus that can achieve good steering even when a sensor failure occurs in a so-called steer-by-wire system. .
[0005]
Means for Solving the Problems and Effects of the Invention
In order to achieve the above object, the invention according to claim 1 provides a steering element, a first element connected to the steering element, a second element connected to the steered wheels, and a third element that associates the first and second elements. , A steering actuator for turning a steered wheel, and a reaction force coupled to a third element of the differential transmission mechanism so as to be able to transmit a drive, and for applying a steering reaction force to the steering member. An actuator, a steering angle detecting means for detecting a steering angle of the steering member, a steering torque detecting means for detecting a torque applied to the steering member, and a detected steering angle and / or steering torque detected by the steering angle detecting means A control unit for driving and controlling the steering actuator and / or the reaction force actuator based on the detected steering torque detected by the detection unit; and the steering torque detection unit and / or the steering angle detection. Abnormality detecting means for detecting the occurrence of an abnormality in the step, wherein the control unit includes a reaction force actuator when an abnormality in the steering torque detecting means and / or the steering angle detecting means is detected by the abnormality detecting means. The rotation of the third element is restricted.
[0006]
In the present invention, an appropriate steering reaction force is applied to the steering member via the differential transmission mechanism by generating an appropriate torque in the reaction force actuator during normal times. Further, when an abnormality occurs in the steering torque detecting means or the steering angle detecting means, the third element of the differential transmission mechanism is restrained from rotating by the reaction force actuator, so that the remaining two of the differential transmission mechanism are not rotated. Manual steering with a transmission ratio by the elements can be achieved. In addition, the third element of the differential transmission mechanism is non-rotatably constrained by the reaction force actuator and the steering actuator is driven, whereby the vehicle steering apparatus can function as an electric power steering apparatus.
[0007]
Further, the invention according to claim 2 is characterized in that the abnormality occurrence detecting means is based on a comparison between a detected steering torque and a detected steering angle detected during traveling and a detected steering torque and a detected steering angle detected last time during traveling. It is characterized by detecting an abnormality. According to the present invention, it is easy to detect abnormality of the steering torque detecting means or the steering angle detecting means.
The invention according to claim 3 is characterized in that the abnormality occurrence detecting means detects an abnormality when at least one of the detection signals of the steering torque detecting means and the steering angle detecting means is not detected. According to the present invention, it is possible to more easily detect the abnormality of the steering torque detecting means or the steering angle detecting means.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of a vehicle steering system according to an embodiment of the present invention. Referring to FIG. 1, a vehicle steering system 1 is provided with a first steering shaft 3 that is integrally rotatably connected to a steering member 2 such as a steering wheel, and is provided coaxially with the first steering shaft 3. A second steering shaft 5 connected to a steering mechanism 4 such as a rack and pinion mechanism, and a planetary transmission mechanism constituting a differential transmission mechanism for allowing a differential rotation between the first and second steering shafts 3 and 5. And a planetary gear mechanism 6.
[0009]
The steering mechanism 4 includes a steering shaft 7 that extends in the left-right direction of the vehicle, and a knuckle arm 10 that is coupled to both ends of the steering shaft 7 via tie rods 8 and supports a steered wheel 9. The steered shaft 7 is supported by a housing 11 and is slidable in the axial direction. A steering actuator 12 composed of an electric motor is coaxially installed in the middle of the steered shaft 7. The drive rotation of the steering actuator 12 is converted into sliding of the steered shaft 7 by a motion conversion mechanism such as a ball screw mechanism, and the steered wheels 9 are steered by the sliding of the steered shaft 7.
[0010]
A rack 7a is formed on a part of the steering shaft 7, and a pinion 14 provided at an end of the second steering shaft 5 and integrally rotating with the second steering shaft 5 meshes with the rack 7a. ing. As will be described later, when the steering actuator 12 is out of order, when the second steering shaft 5 is rotationally driven in accordance with the operation of the steering member 2, the rotation of the second steering shaft 5 is rotated by the pinion 14 and the rack 7a. This is converted into sliding of the rudder shaft 7, and the steered wheels 9 are steered.
[0011]
The planetary gear mechanism 6 is rotatable by a sun gear 15 as a first element (sun member) on the input side, which is integrally rotatably connected to an end of the first steering shaft 3, and a carrier 16 on the output side. It includes a plurality of planetary gears 17 that are held and mesh with the sun gear 15 as a second element (planetary member), and a ring gear 18 as a ring member having an inner tooth 18a that meshes with each planetary gear 17 on its inner periphery.
The ring gear 18 forms, for example, a worm wheel by forming the external teeth 18b. The external teeth 18b are drivingly connected to a reaction force actuator 20 for applying an operation reaction force to the steering member 2 via a drive transmission gear 19 made of, for example, a worm. The reaction force actuator 20 is composed of, for example, an electric motor, and its casing is fixed to an appropriate position on the vehicle body.
[0012]
The steering actuator 12 and the reaction force actuator 20 are controlled by a control unit C including a CPU 31, a ROM 32 storing a control program and the like, a PROM 33 for storing previous running data described later, a RAM 34 used as a work area for calculation and the like, and the like. It is controlled.
The first steering shaft 3 has a steering angle sensor 24 as a steering angle detecting means for detecting a steering angle of the steering member 2, and a steering torque detecting means for detecting a steering torque inputted from the steering member 2. A torque sensor 25 is provided. Detection signals from the steering angle sensor 24 and the torque sensor 25 are input to the control unit C.
[0013]
Further, the steered shaft 7 is provided with a steered position sensor 26 for detecting a steered position in relation to the axial position of the steered shaft 7, and also controls a detection signal from the steered position sensor 26. The data is input to the unit C. Further, a detection signal from a vehicle speed sensor 27 for detecting a vehicle speed is input to the control unit C.
The control unit C outputs a control signal to drive circuits 28 and 29 as drive units for driving the steering actuator 12 and the reaction force actuator 20 based on the input signals from the sensors.
[0014]
FIG. 2 is a flowchart for explaining a steering control process performed by the control unit C. Referring to FIG. 2, control unit C monitors whether steering angle sensor 24 and torque sensor 25 are operating normally (step S1).
If no abnormality has occurred in the steering actuator 12 (NO in step S1), the control unit C uses the reaction force actuator 20 to apply an operation reaction force corresponding to, for example, a road surface reaction force to the steering member 2. A torque is generated (Step S2).
[0015]
Further, for example, the ratio (transmission ratio, gear ratio) between the rotation amount of the steering member 2 and the steering amount of the steered wheels 9 is set in accordance with the traveling state of the vehicle (VGR function), and the set transmission ratio and steering are set. A voltage command value of the steering actuator 12 is set based on the operation amount of the member 2 and the like, and a control signal corresponding to the voltage command value is given to the drive circuit 28 to drive and control the steering actuator 12 (step S3). ).
As a result, a torque for sliding the turning shaft 7 in a direction corresponding to the operation direction of the steering member 2 is output from the steering actuator 12, and the torque is good according to the running condition of the vehicle and the operation mode of the steering member 2. Steering is achieved. Note that it is not always necessary to set the VGR function.
[0016]
In this way, if an abnormality occurs in at least one of the steering angle sensor 24 and the torque sensor 25 while controlling the driving of the steering actuator 12 (YES in step S1), the control unit C outputs a control signal to the drive circuit 28. Then, the operation of the steering actuator 12 is made free (freely rotatable) (step S4), and a control signal is output to the drive circuit 29 to control the reaction force actuator 20 to a stop state, thereby rotating the ring gear 18. Is constrained (step S5).
[0017]
This achieves mechanical coupling between the steering member 2 and the steering mechanism 4 via the planetary gear mechanism 6, and can function as a manual steering having a gear ratio between the sun gear 15 and the carrier 16. At this time, as described above, by allowing the steering actuator 12 to freely rotate, it is possible for the driver to easily perform manual steering. As a result, good steering can be achieved even when the steering angle sensor 24 and the torque sensor 25 are abnormal.
[0018]
In step S4, the vehicle steering apparatus 1 functions as a normal electric power steering apparatus by controlling the drive of the steering actuator 12 (steering assist control) without making the steering actuator 12 freely rotatable. You may make it do.
Next, details of the abnormality detection in step S1 of FIG. 2 will be described based on the flowchart of FIG.
[0019]
First, the detected operation angle data and the detected operation torque data during the previous run, which are stored in the nonvolatile PROM 33 during the previous run, are read (step T1).
Next, it is determined whether there is a signal input from both the steering angle sensor 24 and the torque sensor 25, and if a signal is not input from at least one of the sensors 24 or 25 (NO in step T2), the sensor 24 Alternatively, it is determined that an abnormality has occurred in 25 (step T3), and the process proceeds to step S4 in the flowchart of FIG.
[0020]
Next, when there is a signal input from both the steering angle sensor 24 and the torque sensor 25 (YES in step T2), a detected steering angle and a detected steering torque during traveling are obtained based on those signals (step T4). ).
The difference between the obtained detected steering angle and the read detected steering angle data during the previous run is obtained, and the difference between the obtained detected steering torque and the read detected steering angle torque data during the previous run is obtained. Is obtained (step T5).
[0021]
On the other hand, when both of the obtained differences are equal to or smaller than the corresponding specified values (YES in step T6), since both the steering angle sensor 24 and the torque sensor 25 are normal, the process proceeds to step S2 in the flowchart of FIG. Then, normal reaction force control and steering control are performed.
On the other hand, when at least one of the obtained differences exceeds the corresponding specified value (NO in step T6), it is determined that abnormality has occurred in at least one of the steering angle sensor 24 and the torque sensor 25 (step T7). The process proceeds to step S4 in the flowchart of FIG. 2 and can function as a manual steering or an electric power steering device.
[0022]
The data to be stored in the PROM 33 includes, for example, the maximum value of the detected steering angles detected during the period from the turning on to the off of the ignition key and the maximum value of the detected steering torque detected during the same period. It may be only.
The present invention is not limited to the above-described embodiment. For example, when the reaction force actuator 20 is formed of an electric motor that can be stopped and locked, the reaction force actuator 20 is used in step S5 of the flowchart of FIG. The rotation of the ring gear 18 may be restricted by stopping and locking the rotation of the ring gear 18.
[0023]
In addition, various changes can be made within the scope of the claims of the present invention.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a schematic configuration of a vehicle steering system according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a flow of steering control of the vehicle steering system of FIG. 1;
FIG. 3 is a flowchart showing details of steps of abnormality detection in the flowchart of FIG. 2;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Vehicle steering device 2 Steering member 3 First steering shaft 4 Steering mechanism 5 Second steering shaft 6 Planetary gear mechanism (differential transmission mechanism)
7 Steering shaft 7a Rack 9 Steered wheels 12 Steering actuator 14 Pinion 15 Sun gear (first element)
16 Career (2nd element)
17 planetary gear (second element)
18 Ring gear (third element)
18a Internal teeth 18b External teeth 19 Drive transmission gear 20 Reaction force actuator C Control unit (abnormality detection means)
24 Steering angle sensor (steering angle detecting means)
25 Torque sensor (steering torque detecting means)
26 Steering position sensor 27 Vehicle speed sensor 28, 29 Drive circuit 31 CPU
32 PROM

Claims (3)

A steering member;
A differential transmission mechanism including a first element connected to the steering member, a second element connected to the steered wheels, and a third element that associates the first and second elements;
A steering actuator for turning the steered wheels,
A reaction force actuator coupled to the third element of the differential transmission mechanism so as to be able to transmit drive, and for applying a steering reaction force to the steering member;
Steering angle detection means for detecting the steering angle of the steering member,
Steering torque detecting means for detecting torque applied to the steering member;
A control unit that drives and controls the steering actuator and / or the reaction force actuator based on the detected steering angle detected by the steering angle detection unit and / or the detected steering torque detected by the steering torque detection unit;
Abnormality occurrence detection means for detecting abnormality occurrence of the steering torque detection means and / or the steering angle detection means,
The control unit restricts the rotation of the third element by a reaction force actuator when an abnormality of the steering torque detection unit and / or the steering angle detection unit is detected by the abnormality occurrence detection unit. Steering device. 2. The method according to claim 1, wherein the abnormality occurrence detecting means detects an abnormality based on a comparison between a detected steering torque and a detected steering angle detected during traveling and a previously detected steering torque and detected steering angle during traveling. A vehicle steering system characterized by the above-mentioned. 2. A vehicle steering system according to claim 1, wherein said abnormality occurrence detecting means detects an abnormality when at least one of a steering torque detecting means and a steering angle detecting means does not detect a detection signal.

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