JP2009166674A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device enabling the turning operation by a driver even when the force applied to a steering wheel by the driver is not mechanically transmitted to a steering mechanism by an accident that a steering shaft is broken without using any special device. <P>SOLUTION: In a microcomputer 10 in an ECU 100 of the electric power steering device, a target current setting unit 12, a subtractor 1 14 and an FB control computation unit 16 are functioned as a motor control unit for the auxiliary steering during the steerable state. Since the stroke detection value L is not changed irrespective of the change of the steering angle detection value θ, the turning operation by a driver can be performed by displacing a rack shaft by a motor 6 according to the steering angle detection value θ by a target stroke setting unit 52 and a motor control computation unit 53 if a steering impossibility determination unit 51 determines the steering is impossible. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that applies a steering assist force to a steering mechanism of a vehicle by an electric motor, and more particularly to a technique for operating a steering mechanism even when a steering operation is impossible.

  2. Description of the Related Art Conventionally, an electric power steering apparatus that applies a steering assist force to a steering mechanism by driving an electric motor in accordance with a steering torque applied to a steering wheel (steering wheel) by a driver has been used.

  Since such an electric power steering device is premised on assisting the driver with the force applied to the steering wheel, the force applied by the driver to the steering wheel due to an accident such as a broken steering shaft or disconnection of the connecting portion is applied to the steering wheel. If it is not mechanically transmitted to the mechanism, it will hardly function.

On the other hand, a steering device using a so-called steer-by-wire technique based on the premise that the force applied to the steering wheel is not mechanically transmitted to the steering mechanism has been proposed (for example, see Patent Document 1). According to this device, since the steering wheel and the steering mechanism are not mechanically connected, it is not necessary for the driver to apply a force to the steering wheel in order to move the steering mechanism. Also, with this configuration, accidents such as breaking of the steering shaft do not occur in the first place.
JP-A-9-142330

  However, a steering device using the so-called steer-by-wire technique requires an actuator and a precise control mechanism for generating a reaction torque for giving the driver a good steering feeling, and thus requires a high manufacturing cost.

  If this device is to be used in combination with an electric power steering device, a special control mechanism (for example, steering) for switching between the case where the force applied to the steering wheel is mechanically transmitted to the steering mechanism and the case where the force is not transmitted to the steering mechanism is used. A mechanism for connecting and disconnecting the shaft is required, which further increases manufacturing costs.

  Therefore, the present invention enables a steering operation by the driver even when the force applied to the steering wheel by the driver is not mechanically transmitted to the steering mechanism due to an accident such as a broken steering shaft without using a special device. An object is to provide an electric power steering apparatus.

A first invention is an electric power steering device that applies a steering assist force to a steering mechanism that steers the wheels of a vehicle by driving an electric motor in accordance with an operation by an operation means for vehicle steering.
Steering angle detection means for detecting a steering angle indicating the amount of operation by the operation means;
Steering inability determination means for determining whether mechanical torque transmission from the operation means to the steering mechanism is possible or not;
Steering assisting means for applying the steering assisting force by driving the electric motor when it is determined by the steering impossibility determining means that torque transmission is possible;
Control means for controlling the steering mechanism by driving the electric motor in accordance with a steering angle detected by the steering angle detection means when torque transmission is determined to be impossible by the steering impossible determination means; It is characterized by providing.

According to a second invention, in the first invention,
A steering side detection means for detecting a turning angle of the wheel by the steering mechanism or a mechanically changing amount corresponding to the turning angle;
The steering impossibility determining means cannot transmit the torque when the amount detected by the steered side detecting means does not change even though the steering angle detected by the steering angle detecting means is changing. It is determined that it is.

According to a third invention, in the second invention,
The steered side detecting means is rack stroke detecting means for detecting a stroke amount that is a displacement amount of a rack shaft that is included in the steering mechanism and steers the wheel,
The control means calculates a stroke amount to be targeted according to the steering angle detected by the steering angle detection means, and calculates the stroke amount to be targeted and the stroke amount detected by the rack stroke detection means. The electric motor is driven based on the above.

  According to the first aspect of the invention, when it is determined that the torque transmission is possible by the steering impossible determination means, the steering auxiliary force is given by the steering auxiliary means, and when the torque transmission determination is impossible by the steering impossible determination means, the steering is performed. Since the steering mechanism is controlled by driving the electric motor in accordance with the steering angle detected by the angle detection means, the driver operates the operation means due to an accident such as a broken steering shaft or a disconnected part. Even when the force applied to the vehicle is not mechanically transmitted to the steering mechanism, the driver can perform the turning operation without providing a special device.

  According to the second invention, when the steering angle detected by the steering angle detecting means is changed by the steering impossibility determining means but the amount detected by the steered side detecting means is not changed, the machine It can be easily determined that the torque transmission is impossible.

  According to the third aspect, the stroke amount detected by the rack stroke detection means can be used for the steering impossibility determination.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
<1. Overall configuration>
FIG. 1 is a schematic diagram showing a configuration of an electric power steering apparatus according to an embodiment of the present invention, together with a vehicle configuration related thereto. This electric power steering apparatus includes a steering shaft 102 having one end fixed to a handle (steering wheel) 101 as an operation means for steering, a rack and pinion mechanism 104 connected to the other end of the steering shaft 102, a handle Steering angle sensor 2 for detecting a steering angle indicating a rotation angle of 101, torque sensor 3 for detecting a steering torque applied to steering shaft 102 by operation of handle 101, and left and right displacement amounts on the rack shaft of rack and pinion mechanism 104 And an electric motor 6 for generating a steering assist force for reducing a driver's load in a steering operation (steering operation). Although not shown, the steering assist force of the electric motor 6 is provided. The pinion of the rack and pinion mechanism 104 And an electronic control that receives power from an in-vehicle battery via an ignition switch and controls driving of the motor 6 based on sensor signals from the steering angle sensor 2, the torque sensor 3, and a vehicle speed sensor (not shown). Unit (ECU). The components as described above are often provided in a general electric power steering apparatus and are well known.

  When the driver operates the steering wheel 101 in a vehicle equipped with such an electric power steering device, the steering torque by the operation is detected by the torque sensor 3 and the steering angle is detected by the steering angle sensor 2, and the detected steering is detected. The motor 6 is driven by the ECU based on the torque and the steering angle and the vehicle speed detected by the vehicle speed sensor. As a result, the motor 6 generates a steering assist force, and this steering assist force is applied to the pinion shaft via the reduction gear, thereby reducing the driver's load in the steering operation. That is, the sum of the steering torque applied by the steering operation and the torque by the steering assist force generated by the motor 6 is given to the rack and pinion mechanism 104 as an output torque. Thus, when the pinion shaft rotates, the rotation is converted into a reciprocating motion of the rack shaft by the rack and pinion mechanism 104. Both ends of the rack shaft are connected to a wheel 108 via a connecting member 106 composed of a tie rod and a knuckle arm, and the direction of the wheel 108 changes according to the reciprocating motion of the rack shaft.

<2. Configuration of control device>
FIG. 2 is a block diagram showing a functional configuration of the ECU 100 which is a control device in the electric power steering apparatus. The ECU 100 generates a microcomputer (hereinafter abbreviated as “microcomputer”) 10 functioning as a motor control unit and a pulse width modulation signal (PWM signal) having a duty ratio corresponding to a command value D output from the microcomputer 10. The PWM signal generation circuit 18 that performs this operation, the motor drive circuit 20 that applies a voltage corresponding to the duty ratio of the PWM signal to the motor 6, and the current detector 19 that detects the current flowing through the motor 6.

  The microcomputer 10 executes a predetermined program stored in its internal memory, whereby a target current setting unit 12, a subtractor 14, and a feedback control calculation unit (hereinafter abbreviated as "FB control calculation unit") 16 And, it functions as a motor control unit including a steering impossible determination unit 51, a target stroke setting unit 52, and a motor control calculation unit 53.

  More specifically, the target current setting unit 12, the subtractor 14, and the FB control calculation unit 16 of the motor control unit function as a motor control unit for assisting steering when steering is possible, and the target stroke setting unit 52 The motor control calculation unit 53 functions as a motor control unit when steering is impossible, and the steering impossible determination unit 51 switches functions of these motor control units. Each will be described below.

  In such a motor control unit, the target current setting unit 12 detects the steering torque detection value (hereinafter referred to as “steering torque detection value”) T output from the torque sensor 3 and the vehicle speed output from the vehicle speed sensor 4. Based on the value (hereinafter referred to as “vehicle speed detection value”) V, a target value It of current to be supplied to the motor 6, that is, a value of current to be supplied to the motor 6 in order to generate a steering assist force that facilitates steering operation. Generate. Specifically, a map (referred to as an “assist map”) indicating the relationship between the value of the assist current to be supplied to the motor 6 and the value of the steering torque in order to generate an appropriate steering assist force according to the vehicle speed The target current setting unit 12 obtains an assist current value corresponding to the steering torque detection value T and the vehicle speed detection value V with reference to the assist map, and stores this value. The current target value It is output. This assist map is set so that the assist current value increases as the vehicle speed decreases and the steering torque increases. As a result, the steering assist force increases as the handle 101 is heavier, and the handle operation becomes easier.

  Further, the subtractor 14 calculates a deviation (It−Is) between the current target value It and the detected value Is of the motor current output from the current detector 19. The FB control calculation unit 16 generates the command value D for feedback control to be given to the PWM signal generation circuit 18 by a proportional-integral control calculation based on this deviation (It-Is).

  Next, in the motor control unit, the steering impossibility determination unit 51 includes a steering angle detection value (hereinafter referred to as “steering angle detection value”) θ output from the steering angle sensor 2 and a rack shaft output from the stroke sensor 5. Based on the detected value (hereinafter referred to as “stroke detection value”) L, it is determined whether or not the steering is disabled due to the steering shaft being broken or the connection portion in the middle being disconnected. . When the steering is impossible (abnormal state), the target current setting unit 12, the subtractor 14, and the FB control calculation unit 16 are controlled to be stopped by the control signal S1, and the target stroke is set by the control signal S2. Control is performed so that the unit 52 and the motor control calculation unit 53 are activated. When the steering is possible (normal time), the target current setting unit 12, the subtractor 14, and the FB control calculation unit 16 are activated, and the target stroke setting unit 52 and the motor control calculation unit 53 are stopped. Shall. Specific operation of the steering impossibility determination unit 51 as described above will be described later.

  Further, in the motor control unit, the target stroke setting unit 52 is based on the stroke detection value L, the target value Lt of the position change amount (stroke value) to be changed on the rack shaft, that is, the rotation to be generated corresponding to the steering operation. A target value for generating a steering amount (steering angle) is generated. The motor control calculation unit 53 performs a calculation for controlling how much the motor 6 should be moved in order to cause the displacement of the rack shaft to be targeted based on the target value Lt, thereby performing the PWM signal generation circuit 18. The command value D for the control to be given to is generated.

  That is, the motor control calculation unit 53 performs the proportional-integral control calculation based on the deviation (Lt−L) between the target value Lt and the stroke detection value L, thereby performing the above-described feedback control for the feedback control to be given to the PWM signal generation circuit 18. A command value D is generated.

  The PWM signal generation circuit 18 changes the pulse width in accordance with the pulse signal having a duty ratio corresponding to the command value D received from either the FB control calculation unit 16 or the motor control calculation unit 53, that is, the command value D. A PWM signal is generated. The motor drive circuit 20 is configured by using a plurality of power transistors as switching elements. By turning on / off these power transistors using a PWM signal, the motor drive circuit 20 corresponds to the pulse width (duty ratio) of the PWM signal. A voltage is applied to the motor 6. The motor 6 generates a torque having a magnitude and direction corresponding to the current that flows when the voltage is applied. Next, the operation of the steering impossibility determination unit 51 will be described in detail.

<3. Operation of Steering Impossibility Determination Unit>
FIG. 3 is a flowchart showing a procedure of the steering impossible determination process executed by the microcomputer 10 in order to realize the steering impossible determination unit 51 by software. When the ignition switch is turned on, the microcomputer 10 operates as follows according to this procedure.

  First, the steering impossibility determination unit 51 performs necessary initialization processing such as deleting the stored value (step S10). As described above, when steering is possible (normal time), the target current setting unit 12, the subtractor 14, and the FB control calculation unit 16 are activated, and the target stroke setting unit 52 and the motor control calculation unit 53 are Although it is assumed that the vehicle is stopped, the steering impossibility determination unit 51 controls the target current setting unit 12, the subtractor 14, and the FB control calculation unit 16 to be activated by the control signal S1, and by the control signal S2. You may control so that the target stroke setting part 52 and the motor control calculating part 53 may be maintained in a stop state.

  Next, the steering impossibility determining unit 51 acquires the steering angle detection value θ from the steering angle sensor 2 and stores the value (step S12), and acquires the stroke detection value L from the stroke sensor 5 and stores the value. Store (step S14).

  Then, the steering impossibility determination unit 51 calls the steering angle detection value θ stored last time or a predetermined time ago, compares the called value with the value acquired in step S12 this time, and determines the steering angle detection value θ. It is determined whether or not has changed over time (step 16). If the steering angle detection value θ has changed as a result of the determination in step S16 (step S16: Yes), the process proceeds to the determination process in step S18, and if the steering angle detection value θ does not change (step S16: No), the process returns to step S12, and thereafter, steps S12 to S16 are repeatedly executed until the detected steering angle value θ changes. Note that a determination based on a predetermined threshold value may be provided for determining whether or not the steering angle detection value θ has changed over time. In this configuration, it is determined that there is no change when the amount of change is equal to or less than the threshold value.

  Subsequently, the steering impossibility determination unit 51 calls the stroke detection value L stored last time or a predetermined time ago, compares the called value with the value acquired in step S14 this time, and the stroke detection value L is calculated. It is determined whether the time has changed (step 18). If the stroke detection value L has changed as a result of the determination in step S18 (step S18: Yes), the process returns to step S12. Thereafter, the stroke detection value L is changed regardless of the change in the steering angle detection value θ. Steps S12 to S18 are repeated until there is no change. Note that a limit based on a predetermined threshold value may also be provided for determining whether or not the stroke detection value L has changed over time. In this configuration, it is determined that there is no change when the amount of change is equal to or less than the threshold value.

  If the stroke detection value L does not change as a result of the determination in step S18 (step S18: No), the steering impossibility determination unit 51 uses the control signal S1 to set the target current setting unit 12, the subtractor 14, and the FB. The control calculation unit 16 is controlled to stop (step S20), and further, the target stroke setting unit 52 and the motor control calculation unit 53 are controlled to be activated by the control signal S2 (step S22), and the above series of processing ends. .

  As described above, when the detected stroke angle L does not change (step S18: No) even though the detected steering angle value θ has changed (step S16: Yes), a force is applied to the steering wheel 101 by the driver. The rack shaft is not displaced even if the steering angle changes due to the steering angle. This is because the steering shaft, which is a torque transmission means for connecting the handle 101 and the rack shaft, is broken, etc., to the steering mechanism. This means that the torque transmission is impossible. Therefore, in this state, steering by mechanical torque transmission is impossible, and steering assistance does not make sense. Therefore, by rotating the motor 6 according to the detected steering angle value θ and displacing the rack shaft, the steering is performed as if mechanical torque is transmitted from the handle 101 to the steering mechanism.

<4. Effect>
As described above, according to the above-described embodiment, by using the microcomputer 10 to realize the functions of the steering impossibility determination unit 51, the target stroke setting unit 52, and the motor control calculation unit 53 described above without using a special device. Even when the force applied by the driver to the steering wheel is not mechanically transmitted to the steering mechanism due to an accident such as the steering shaft being broken or the connection part being disconnected, the rack shaft is displaced by the motor 6 according to the detected steering angle θ Thus, the steering operation by the driver can be made possible.

<5. Modification>
In the above embodiment, the steering impossibility determining unit 51 determines that mechanical torque transmission is disabled when the stroke detection value L does not change despite the change in the steering angle detection value θ. However, instead of the stroke detection value, the detection value of the turning angle of the wheel 108 may be used. In addition, a detection value of a mechanically changing amount corresponding to the turning angle, such as a detection value of the displacement amount of the pinion shaft, can be widely used. That is, the above-described detection value (which is often used in a general electric power steering apparatus) is provided with a steered side detection means. When the detection value of the steered side detection means does not change, it can be determined easily and without providing a special device that mechanical torque transmission is disabled.

  Further, if the torque is not detected by the torque sensor 3 even though the steering angle detection value θ has changed, the steering impossibility determination unit 51 determines that mechanical torque transmission is disabled. Alternatively, without comparing with the detected steering angle value θ, mechanical torque transmission is disabled when the torque is not detected by the torque sensor 3 for a certain period of time despite the vehicle running. It may be determined that Further, for example, it is determined that mechanical torque transmission from the steering wheel 101 to the steering mechanism is impossible, for example, it is determined that mechanical torque transmission is disabled by pressing a failure determination button or the like. Any configuration can be used.

  In the above-described embodiment, an example of a so-called pinion assist type electric power steering device in which the pinion shaft is driven by the motor 6 is described, but the machine from the handle 101 to the steering mechanism is caused by the steering shaft being bent or the like. Even if the torque transmission is impossible, it is not limited to the pinion assist type as long as the steering mechanism can be moved by driving the motor 6. Further, the present invention can be applied even to a hydraulic power steering device.

It is the schematic which shows the structure of the electric power steering apparatus which concerns on one Embodiment of this invention with the vehicle structure relevant to it. It is a block diagram which shows the functional structure of ECU which is a control apparatus in the electric power steering apparatus which concerns on the said embodiment. It is a flowchart which shows the procedure of the process performed by the microcomputer in order to implement | achieve the steering impossible determination part in the said embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 ... Steering wheel, 102 ... Steering shaft, 104 ... Rack and pinion mechanism, 106 ... Connecting member, 108 ... Wheel, θ ... Steering angle detection value, T ... Torque detection value, V ... Vehicle speed detection value, L ... Stroke detection value, D ... Command value

Claims (3)

An electric power steering device that applies a steering assist force to a steering mechanism that steers the wheels of the vehicle by driving an electric motor in accordance with an operation by an operation means for vehicle steering,
Steering angle detection means for detecting a steering angle indicating the amount of operation by the operation means;
Steering inability determination means for determining whether mechanical torque transmission from the operation means to the steering mechanism is possible or not;
Steering assisting means for applying the steering assisting force by driving the electric motor when it is determined by the steering impossibility determining means that torque transmission is possible;
Control means for controlling the steering mechanism by driving the electric motor in accordance with a steering angle detected by the steering angle detection means when torque transmission is determined to be impossible by the steering impossible determination means; An electric power steering apparatus comprising: A steering side detection means for detecting a turning angle of the wheel by the steering mechanism or a mechanically changing amount corresponding to the turning angle;
The steering impossibility determining means cannot transmit the torque when the amount detected by the steered side detecting means does not change even though the steering angle detected by the steering angle detecting means is changing. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is determined as follows. The steered side detecting means is rack stroke detecting means for detecting a stroke amount that is a displacement amount of a rack shaft that is included in the steering mechanism and steers the wheel,
The control means calculates a stroke amount to be targeted according to the steering angle detected by the steering angle detection means, and calculates the stroke amount to be targeted and the stroke amount detected by the rack stroke detection means. The electric power steering device according to claim 2, wherein the electric motor is driven based on the above.

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