JP4226169B2 - Vehicle steering system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle steering apparatus, and more particularly to a vehicle steering apparatus configured to generate an additional turning force with respect to a manual turning force with an electric motor.
[0002]
[Prior art]
As a so-called power steering device for reducing the steering force of the driver, the motor is used to assist the manual steering force applied to the steering wheel, and the amplification degree of the detection signal of the steering torque applied by the driver to the steering wheel It is known that the output of the motor is increased or decreased so that the optimum steering torque can always be obtained by changing the vehicle speed according to the vehicle speed or road conditions (see Japanese Patent Publication No. 50-33584). .
[0003]
This conventional power steering apparatus is configured such that the electric motor generates the auxiliary steering torque only after the driver steers. Therefore, this power steering device can be used for turning due to disturbances such as when the vehicle is subjected to strong crosswinds or traveling on a narrow road and the actual travel line of the vehicle deviates from the target travel line. The electric motor does not generate drive torque. In addition, the conventional power steering apparatus generally reduces the auxiliary steering torque against a temporary increase in the lateral acceleration and yaw rate of the vehicle. Therefore, in order to suppress the deflection of the vehicle due to disturbance, the driver himself has to operate the steering wheel. However, the greater the deflection, the greater the manual steering torque required for correction. .
[0004]
Therefore, for example, in JP-A-5-105100, a reaction force torque value is determined based on a detected value of a vehicle behavior such as a yaw rate and a lateral acceleration, and an auxiliary torque value is determined based on a manual steering torque value. There has been proposed an apparatus in which the driving torque of the electric motor is controlled based on the reaction force torque value and the auxiliary torque value.
[0005]
According to this configuration, it is possible to improve the vehicle running stability by improving the deflection suppression performance when a disturbance caused by a cross wind or road surface is applied to the vehicle, and also between the tire and the road surface such as a snowy road. The steering force of the steering wheel can be optimized even when traveling on a road surface having a low friction coefficient or traveling at a low speed.
[0006]
[Problems to be solved by the invention]
However, the vehicle behavior such as the yaw rate and the lateral acceleration is detected, and the above described based on the reaction torque value determined based on the detected value and the auxiliary torque value determined based on the detected value such as the manual steering torque. In the case of controlling the drive torque of the motor, if the detected value of the vehicle behavior is wrong due to a sensor failure or the like, the reaction torque value may be erroneously determined, and accordingly the drive torque of the motor may be an incorrect value. Obtained. In other words, the above-described conventional configuration has a disadvantage that the driver may feel a sense of incongruity in steering if a sensor for detecting vehicle behavior fails.
[0007]
The present invention has been devised to solve such problems of the prior art, and its main purpose is to provide a driver with a sense of discomfort in steering even when a sensor for detecting vehicle behavior fails. It is an object of the present invention to provide an improved vehicle steering apparatus that does not need to be applied to the vehicle.
[0008]
[Means for Solving the Problems]
In order to achieve such an object, in the present invention, manual steering means (steering wheel 1) for applying a manual turning force to the steering wheel (6) of the vehicle, and manual steering torque detecting means (12). And an electric motor (9) for applying an additional turning force to the steered wheel, and an auxiliary torque determining means (21) for determining an auxiliary torque component included in the additional turning force based on a detected value of the steering torque. A reaction force torque determining means (22) for determining a reaction force torque component included in the additional turning force based on the detection values of the vehicle behavior detecting means (steering angular velocity sensor 11, yaw rate sensor 15); in a steering apparatus for a vehicle and a control means for controlling the electric motor with a combined value in the form of the drive torque target value of the torque value and the reaction force torque (steering control unit 17), the steering torque detection means The comparison means (31) for comparing the output value with the drive torque target value to be given to the motor for a predetermined time, and the input to the control means of the reaction force torque value determined by the reaction force torque determination means is compared by the comparison means. And prohibiting means (40) for prohibiting based on the result.
[0009]
According to this, the direction of the detected value of the steering torque detecting means and the direction of the drive torque target value are compared. If they are different from each other for a predetermined time, for example, it is determined that the vehicle behavior detecting means has failed, and the auxiliary torque determining means The electric motor is controlled only by the auxiliary torque value determined by. Therefore, the operation force of the steering wheel does not increase unnecessarily.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
[0011]
FIG. 1 shows a schematic configuration of a vehicle steering apparatus to which the present invention is applied. The steering device is connected to a steering shaft 2 integrally coupled to the steering wheel 1 via a connecting shaft 3 having a universal joint, and meshes with the pinion 4 to which manual steering force is applied via the steering wheel 1 and the pinion 4. A rack-and-pinion mechanism having a rack shaft 8 having both ends connected to knuckle arms 7 of left and right front wheels 6 as steering wheels via tie rods 5 and reciprocating in the vehicle width direction; In order to apply an auxiliary steering force as a power steering device to the rack shaft 8, an electric motor 9 is provided coaxially in the middle of the rack shaft 8.
[0012]
Near the pinion 4 of the rack and pinion mechanism, a steering angular velocity sensor 11 for detecting the rotational angular velocity of the steering wheel 1 and a steering torque sensor 12 for detecting the manual steering torque acting on the pinion 4 are provided. Is provided. The signal output of these two sensors 11 and 12 is a yaw rate sensor 15 for outputting a signal corresponding to the yaw rate (yaw angular velocity) of the vehicle, and a vehicle speed sensor 16 for outputting a signal corresponding to the traveling speed of the vehicle. Are output to the steering control unit 17 for controlling the output of the electric motor 9.
[0013]
As shown in FIG. 2, in the steering control unit 17, an auxiliary torque determining means 21 for calculating a normal auxiliary torque component as an electric power steering device and the vehicle behavior against disturbance input are stabilized. Accordingly, the reaction force torque determining means 22 for calculating the reaction force torque component applied to the rack shaft 8 of the rack and pinion mechanism and the torque values output from the auxiliary torque determining means 21 and the reaction force torque determining means 22 are calculated. Accordingly, target current determining means 23 for setting a target current to be supplied to the electric motor 9 and output current control means 24 for controlling a current flowing through the electric motor 9 according to the target current are provided.
[0014]
Detection signals from the steering angular velocity sensor 11, the torque sensor 12, and the vehicle speed sensor 16 are input to the auxiliary torque determining means 21, and the target auxiliary torque AT is determined according to these detection signals. The reaction force torque determining means 22 receives detection signals of the steering angular velocity sensor 11, the yaw rate sensor 15, and the vehicle speed sensor 16 as vehicle behavior detecting means, and the target reaction force torque CT is determined in accordance with these detection signals. Is done. Then, a current control signal from the output current control means 24 is input to a drive circuit 25 provided between the steering control unit 17 and the electric motor 9, and a drive current is supplied from the drive circuit 25 to the electric motor 9, and Feedback control of the output current is performed between the drive circuit 25 and the output current control means 24.
[0015]
Next, the means 31 for comparing the steering torque input to the steering wheel 1 and the drive torque generated by the electric motor 9 will be described.
[0016]
In this comparison means 31, the steering torque value TS from the steering torque sensor 12 and the steering torque reference value TSR set by the reference steering torque setting means 32 are compared by the steering torque comparison means 33, and the comparison result is logically calculated. It outputs to the means 34. At the same time, the drive torque target value TM from the output current control means 24 and the drive torque reference value TMR set by the reference drive torque setting means 35 are compared by the drive torque comparison means 36, and the comparison result is ANDed. 34. Then, it is determined whether or not the relationship between the steering torque TS and the drive torque target value TM is in the sensor failure determination region indicated by the mesh line in FIG. The direction determination signal D is output to the time measuring means 37.
[0017]
The time measuring means 37 outputs a time measuring signal T1 obtained by measuring the duration of the logical level 1 (existence) of the logical product calculating means 34 to the time comparing means 38. At the same time, the reference time setting means 39 outputs a predetermined (for example, 15 msec) reference time signal T2 to the time comparison means 38. Then, the time comparison means 38 compares the time measurement signal T1 with the reference time signal T2, and if the time measurement signal T1 continues for more than the reference time signal T2 (T1 ≧ T2), the time comparison means 38 is a switch that constitutes a prohibition means. 40, a time comparison signal of logic level 1 is output as a reaction force control inhibition signal, and the normally closed switch 40 is opened. Thereby, it is prohibited to add a reaction torque component to the target drive torque of the electric motor 9.
[0018]
In this manner, in the vehicle steering apparatus according to the present invention, by providing the comparison means 31 and the switch 40 (prohibition means) in the steering control unit 17, the direction of the drive torque by the electric motor 9 applied to the rack shaft 8, When the direction of the steering torque applied to the pinion 4 is different from each other for a predetermined time (for example, 15 msec), the reaction force torque component applied to the rack shaft 8 by the electric motor 9 can be made zero. It should be noted that an analog circuit may be used instead of the logical product calculation means 34 as described above to generate a signal for prohibiting the input of reaction torque. Further, by changing the reference time signal T2 of the reference time setting means 39 according to the steering torque TS and the drive torque target value TM in the sensor failure determination area (see FIG. 3), the characteristics of the electric motor 9, the vehicle weight and the vehicle It is possible to optimally control the time until the output of the reaction force torque component stops according to the transient characteristics of the.
[0019]
【The invention's effect】
As described above, according to the present invention, when a sensor for detecting vehicle behavior such as yaw rate or lateral acceleration fails, the reaction force torque component generated by the motor is prohibited from being applied to the steering wheel. It is not necessary to produce a change in the steering force that gives a strange feeling to the user. Further, the reaction force torque input prohibition means according to the present invention does not prohibit addition of the reaction force torque component by the electric motor when the predetermined time is not reached, so that manual steering is performed against an instantaneous handle removal in a crosswind or a narrow road. Torque in a direction opposite to the direction of torque can be generated. Therefore, according to the present invention, a great effect can be obtained in further improving the handling stability and the safety at the time of sensor failure at a higher level.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a vehicle steering system to which the present invention is applied. FIG. 2 is a block diagram of a control system according to the present invention.
DESCRIPTION OF SYMBOLS 1 Steering wheel 6 Front wheel 9 Electric motor 11 Steering angular velocity sensor 12 Steering torque sensor 15 Yaw rate sensor 17 Steering control unit 21 Auxiliary torque determination means 22 Reaction force torque determination means 31 Comparison means 40 Switch (prohibition means)

Claims (1)

Manual steering means for applying a manual steering force to the steering wheel of the vehicle, steering torque detection means for detecting a steering torque applied to the manual steering means, and additional steering force to the steering wheel An electric motor for applying, auxiliary torque determining means for determining an auxiliary torque component included in the additional turning force based on a detection value of the steering torque detecting means, and detecting behavior of the vehicle including yaw rate Vehicle behavior detection means, reaction force torque determination means for determining a reaction force torque component included in the additional turning force based on a detection value of the vehicle behavior detection means, the auxiliary torque value and the reaction force In a vehicle steering apparatus having a control means for controlling the electric motor with a drive torque target value that is a combined value with a torque value ,
A comparison means for comparing a detection value of the steering torque detection means with a drive torque target value applied to the electric motor for a predetermined time;
A vehicle steering apparatus comprising: prohibiting means for prohibiting input of the reaction force torque value determined by the reaction force torque determining means to the control means based on a comparison result of the comparing means.

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