JP2003276634A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device making a steering sense of a driver well by restricting a rapidly varied output value even in the case where a steering torque sensor is damaged. <P>SOLUTION: In the electric power steering device for controlling an auxiliary steering force corresponding to at least a steering torque, two steering torque sensors 51, 52 for detecting the steering torque are provided. In a torque operation means 12A of this electric power steering device, when a variation of the output from these steering torque sensors 51, 52 exceeds a predetermined value, the operation making a varied value at a predetermined slope as an output value is carried out against the respective steering torque sensors 51, 52. When the output values from these steering torque sensors 51, 52 are the same symbol, the output value of a small absolute value is made to a sensor value and when the output values have different symbols, the operation is carried out making zero as the sensor value. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering system for controlling an auxiliary steering force according to steering torque or the like.

[0002]

2. Description of the Related Art As a steering device for a vehicle, a so-called electric power steering device has recently become popular, which reduces the steering force of a driver by adding an auxiliary steering force by an electric motor to a steering system when steering a steering wheel. This type of electric power steering device basically detects a steering torque of a steering system generated by steering of a steering wheel with a steering torque sensor,
The auxiliary steering force by the electric motor is controlled according to the direction and magnitude of the detected torque.

[0003]

By the way, in the conventional structure, if the steering torque sensor fails and its output value changes abruptly, a suitable auxiliary steering force cannot be obtained and the driver's steering feeling is reduced. There was a problem that got worse.

Therefore, an object of the present invention is to provide an electric power steering system capable of improving the driver's steering feeling by limiting the output value that changes rapidly even if the steering torque sensor fails. To provide a device.

[0005]

The invention according to claim 1 of the present invention which has solved the above-mentioned problems is an electric power steering apparatus for controlling an auxiliary steering force at least in accordance with a steering torque. A sensor for detection is provided, and when the change in the output from this sensor is within the predetermined range, the output value is taken as the sensor value, but when the change is outside the predetermined range, the value that changes with a predetermined gradient Is used as a sensor value, and this calculated value is used for control.

According to the invention described in claim 1, for example,
When the sensor malfunctions and its output value changes abruptly, it is determined that the change in the output from the sensor is out of the predetermined range, and calculation is performed using the value changing at a predetermined gradient as the sensor value. Then, the auxiliary steering force is appropriately controlled based on the calculated value.

According to a second aspect of the present invention, in the configuration of the first aspect of the invention, the predetermined slope is smaller when the change is away from zero than when the change is closer to zero. Is characterized by.

Here, "when the change goes away from zero" means that the absolute value of the output value from the sensor suddenly increases, that is, the auxiliary steering force is greater than the value that should be set in accordance with the steering torque. This is the case when it becomes larger than the assisting steering force intended by the driver. In addition, "when the change is close to zero" means that the absolute value of the output value from the sensor suddenly decreases, that is, the auxiliary steering force is greater than the value that should be set according to the steering torque (the driver's intention). It is smaller than the auxiliary steering force).

According to the invention described in claim 2, claim 1
In addition to the effect of the invention described in (1), when the change in the output value from the sensor approaches zero, that is, when the absolute value of the output value from the sensor suddenly decreases, it is regarded as a failure of the sensor etc. The value that changes with is referred to as the sensor value. Then, when the change in the output value from the sensor goes away from zero, that is, when the absolute value of the output value from the sensor suddenly increases, the absolute value of the output value from the sensor is considered to be small and the absolute value of the output value from the sensor is small. A value that changes with a gradient smaller than the gradient in the case of is referred to as a sensor value.

According to a third aspect of the present invention, in the electric power steering apparatus for controlling the auxiliary steering force at least according to the steering torque, two sensors for detecting the steering torque are provided, and the output values from the two sensors are provided. When the sign is the same, the output value with the smaller absolute value is used as the sensor value, and when the sign is different, zero is used as the sensor value, and this calculated value is used for control.

According to the invention of claim 3, for example,
When each sensor deteriorates and there is a difference in each output value, when these output values have the same sign, the output value with the smaller absolute value is taken as the sensor value, and when the output values have different signs, the sensor value is zero. The value is calculated. Then, for example, when one sensor fails and the absolute value of its output value suddenly increases, that output value and the output value of the other non-failed sensor have the same sign. The calculation is performed using the output value of the other sensor whose absolute value is smaller than the output value as the sensor value. Further, when the output value of the one sensor that has failed suddenly becomes small and has a different sign from the output value of the other sensor that has not failed, a calculation with zero as the sensor value is performed.

According to a fourth aspect of the present invention, in the electric power steering apparatus for controlling the auxiliary steering force at least according to the steering torque, two sensors for detecting the steering torque are provided, and a change in the output from the sensor is provided. When the value deviates from the predetermined range, the calculation is performed for each sensor with the value changing with a predetermined gradient as the output value. When the output values from these two sensors have the same sign, the absolute value is It is characterized in that the smaller output value is used as the sensor value, and when the sign is different, zero is used as the sensor value, and this calculated value is used for control.

According to the fourth aspect of the present invention, for example, when one of the sensors fails and its output value changes abruptly, it is determined that the change in the output from this sensor is out of the predetermined range, and the predetermined value is determined. An operation is performed in which the output value is a value that changes with the gradient of. Then, the output value replaced with a value that changes with this predetermined gradient is compared with the output value of the other sensor that has not failed, and if they have the same sign, the output value with the smaller absolute value is selected. The calculation that uses the sensor value is performed. If the sign is different, the calculation is performed with zero as the sensor value.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Details of an electric power steering apparatus according to the present invention will be described below with reference to the drawings. In the drawings to be referred to, FIG. 1 is a configuration diagram showing a configuration of a steering system to which an electric power steering device of the present embodiment is applied, and FIG. 2 is a block configuration diagram of the electric power steering device of the present embodiment.

In describing the electric power steering apparatus of this embodiment, first, the structure of a steering system to which the electric power steering apparatus is applied will be described with reference to FIG. This steering system is a so-called rack and pinion type steering system, and a lower end portion of a steering shaft 2 integrally connected to a steering wheel 1 has a pair of universal joints 4, which are mutually connected via a connecting shaft 3. 4 is connected to the input shaft 5A of the gear box 5. In this gear box 5,
Two steering torque sensors 51 and 52 are arranged.
The output shaft of the gear box 5 is integrally formed with a pinion 6A of the rack and pinion mechanism 6.

The rack and pinion mechanism 6 is a pinion 6A.
A rack shaft 6C having rack teeth 6B meshing with each other is formed. Knuckle arms (not shown) attached to the left and right front wheels 7, 7 of the vehicle are provided at both ends of the rack shaft 6C via tie rods 8, 8. Are linked together. The ball screw mechanism 9 is coaxially mounted on the rack shaft 6C.
Ball screw portion 9A is formed. The ball nut 9B that meshes with the ball screw portion 9A is fixed to the rotor 10A of the electric motor 10, and the electric motor 10 is arranged around the rack shaft 6C in a penetrating state.

As shown in FIGS. 1 and 2, the electric power steering apparatus P for controlling the auxiliary steering force in accordance with at least the steering torque has two means as a means for feedback controlling the drive current flowing through the electric motor 10 to a target value. The electric motor control device 12 that inputs the detection signals of the steering torque sensors 51 and 52 and the vehicle speed sensor 11 described later and outputs the control signal of the electric motor 10, and the electric motor 10 according to the control signal output from the electric motor control device 12 The motor drive circuit 13 is driven by a predetermined drive current. Further, the drive current supplied from the electric motor drive circuit 13 to the electric motor 10 is detected, and the detection signal is sent to the electric motor control device 1.
It is equipped with a current sensor 14 for outputting to 2.

The vehicle speed sensor 11 detects the vehicle speed as the number of pulses per unit time and sends an analog electric signal corresponding to the detected number of pulses to the electric motor control device 12 as a vehicle speed signal VP. The vehicle speed sensor 11 may be a dedicated sensor for the electric power steering device P, or a vehicle speed sensor of another system may be used.

The steering torque sensors 51 and 52 detect the magnitude and direction of the manual steering torque by the driver.
Then, the steering torque sensors 51 and 52 transmit analog electric signals corresponding to the detected steering torque to the electric motor control device 12 as steering torque signals (output values) T1 and T2. The steering torque signals T1 and T2 include information on the steering torque indicating the magnitude and the torque direction indicating the direction of the torque. The torque direction is represented by the plus / minus value of the steering torque, and the plus value indicates the steering torque direction. Is to the right,
A negative value indicates that the steering torque direction is to the left. The relationship between the plus / minus value of the steering torque and the steering torque direction may be reversed.

The current sensor 14 is provided with a resistor or a hall element connected in series with the electric motor 10, and detects the magnitude and direction of the electric motor current IM actually flowing in the electric motor 10. Then, the current sensor 14 determines that the motor current I
The electric motor current signal IMO corresponding to M is supplied to the electric motor control device 1
Feedback to 2 (negative feedback). The electric motor current signal IMO includes information on the electric motor current value indicating the magnitude and information on the electric current direction indicating the direction of the electric motor current (direction of auxiliary assist), and the electric current direction is represented by plus / minus value of the electric motor current value. , A plus value indicates that the assist assist direction is to the right, and a minus value indicates that the assist assist direction is to the left. The relationship between the plus / minus value of the electric motor current value and the auxiliary assist direction may be reversed.

Next, the motor control device 12 and the motor drive circuit 13 will be sequentially described. First, the electric motor control device 12 includes the steering torque sensors 51 and 52 and the vehicle speed sensor 1
1, an input / output interface I / O with the current sensor 14 and the like, and an A / D converter for converting an analog signal input from these sensors into a digital signal, and stores various data and programs. ROM
(Read Only Memory), RAM (Random Access Memory) for temporarily storing various data and the like, CPU (Central Processing Unit) for performing various arithmetic processing, and the like are provided as hardware. Further, the electric motor control device 12 has a basic software configuration for outputting a control signal of the electric motor 10, as shown in FIG.
A target current setting unit 12B, a deviation calculation unit 12C, and a drive control unit 12D are provided.

The torque calculating means 12A has steering torque signals T1, T output from the steering torque sensors 51, 52.
2 is converted into a digital signal and input. Then, the torque calculation means 12A includes steering torque sensors 51, 5
When the change in the output from 2 is within the predetermined range, the output value is used as it is, but when the change is out of the predetermined range, the calculation is performed using the value changing with a predetermined gradient as the output value. Sensor 51, 52 of the above. Also,
When the output values from the two steering torque sensors 51 and 52 have the same sign, the torque calculation means 12A calculates the output value having the smaller absolute value as the sensor value, and when the output values have different signs, zero is used as the sensor value. It is carried out. It should be noted that the predetermined gradient set when the change in the output from the steering torque sensors 51, 52 is out of the predetermined range is smaller when the change goes away from zero than when the change approaches zero. It is supposed to be.

A vehicle speed signal VP output from the vehicle speed sensor 11 is input to the target current setting section 12B together with the calculated torque signal TC output from the torque calculating means 12A. The target current setting unit 12B outputs a target current signal IMS for causing the electric motor 10 to generate an auxiliary steering force having a basic characteristic that increases with an increase in steering torque of the steering system and decreases with an increase in vehicle speed. , Calculated torque signal T
The data area having C and the vehicle speed signal VP as an address is instantly searched, and the searched target current signal IMS is output to the deviation calculator 12C.

The deviation calculator 12C is a target current setting unit 12C.
The target current signal IMS from B and the motor current signal IMO from the current sensor 14 are input, and the deviation signal ΔIM is output to the drive control unit 12D. The deviation calculator 12C subtracts the electric motor current signal IMO from the target current signal IMS to calculate a deviation signal ΔIM (= IMS-IMO).

The drive control unit 12D receives the deviation signal ΔIM from the deviation calculation unit 12C, and outputs a motor control signal VO calculated based on the deviation signal ΔIM to the electric motor drive circuit 13. Therefore, the drive control unit 12D
A PID controller, a PWM signal generator, a logic circuit and the like are provided.

The electric motor drive circuit 13 controls the electric motor control signal V.
The electric motor voltage VM is applied to the electric motor 10 based on O to drive the electric motor 10. The electric motor drive circuit 13 is, for example,
As shown in FIG. 3, four power FETs (Field Effect T
ransistor: field effect transistor) 13a, 13b,
A bridge circuit composed of switching elements 13c and 13d and a power supply voltage (12v) 13e. Each gate G of the power FETs 13a, 13b, 13c, 13d
When the motor control signal VO is input to 1, G2, G3, G4, the motor voltage VM is applied to the motor 10 based on the motor control signal VO. Then, the electric motor current IM having a predetermined magnitude flows in the electric motor 10 in a predetermined direction, and the auxiliary steering force corresponding to the direction and the magnitude of the electric motor current IM is generated from the electric motor 10.

Next, this electric power steering device P
A torque selection method of the torque calculation means 12A in FIG. 4 will be described with reference to FIGS. Torque calculation means 1
In 2A, first, by performing the routine work shown in FIG. 4, the output values T1 from the steering torque sensors 51 and 52 are
It is determined whether T2 is an abnormal value, and if it is an abnormal value, that value is appropriately rewritten to a predetermined value.
This routine work is performed by each steering torque sensor 51, 5
Since the same operation is performed for the second steering wheel, only the routine work for one steering torque sensor 51 will be described below, and the routine work for the other steering torque sensor 52 will be omitted.

When the steering torque sensor 51 outputs a current steering torque signal (hereinafter, referred to as "actually measured current value") T1 to the torque calculation means 12A (see FIG. 2), as shown in FIG. From the current value T1 to the previous output value (hereinafter,
It is called "previous value". ) A value obtained by subtracting LT1 is calculated as the difference value ΔT1 (step S1). Next, the actual measured value T
It is determined whether 1 is greater than 0 (step S
2).

In step S2, the actually measured current value T1 is 0.
When it is determined that the difference is larger (YES), it is determined whether the difference value ΔT1 is larger than the predetermined value α (step S3). If it is determined in step S3 that the difference value ΔT1 is larger than the predetermined value α (YES), the difference value ΔT1 is changing at a predetermined gradient in the direction away from zero (hereinafter, “divergence gradient value”). It is rewritten to β (step S4). Then, the previous value L
The calculated current value (hereinafter, referred to as “calculated current value”) is calculated by performing the calculation in which the difference value ΔT1 is added to T1.
CT1 is calculated (step S5). The calculated current value CT1 calculated in step S5 becomes the previous value LT1 in step S1 in the next routine work.

When it is determined in step S3 that the difference value ΔT1 is less than or equal to the predetermined value α (NO), it is next determined whether or not it is smaller than the predetermined value −α (step S).
6). If it is determined in step S6 that the difference value ΔT1 is smaller than the predetermined value −α (YES), a value that changes with a predetermined gradient in the direction in which the difference value ΔT1 approaches zero (hereinafter, “convergence gradient value”). It is rewritten as -α (step S7). Then, this convergence gradient value −α
The difference value ΔT1 rewritten in step S5 is used for the calculation in step S5. The absolute value of the divergence gradient value β is smaller than the absolute value of the convergence gradient value −α. When it is determined in step S6 that the difference value ΔT1 is greater than or equal to the predetermined value −α (NO), the difference value ΔT1 is used for the calculation in step S5 without changing the value calculated in step S1. .

Here, in other words, the operation of steps S3 to S7 is paraphrased so that the difference value ΔT1 is within a predetermined range (-α≤
When ΔT1 ≦ α), the difference value ΔT1 is used for the calculation in step S5 without changing the value calculated in step S1.
The difference value ΔT1 is within a predetermined range (−α ≦ ΔT
If it deviates in the positive direction from 1 ≦ α), it is rewritten to the divergence gradient value β, and if it deviates in the negative direction, it is rewritten to the convergent gradient value −α.

In step S2, the actually measured current value T1
Is determined to be 0 or less (NO), the difference value Δ
It is determined whether T1 is smaller than the predetermined value -α (step S8). When it is determined in step S8 that the difference value ΔT1 is smaller than the predetermined value −α (YES),
Since the amount of change is large, this difference value ΔT1 is equal to the divergence gradient value −β.
After being rewritten to (step S9), the above step S
It is used for the calculation of 5. When it is determined in step S8 that the difference value ΔT1 is equal to or greater than the predetermined value −α (NO), it is determined whether the difference value ΔT1 is larger than the predetermined value α (step S10). This step S
If it is determined in 10 that the difference value ΔT1 is larger than the predetermined value α (YES), since the amount of change is large, the difference value ΔT1 is rewritten to the convergence gradient value α (step S11), and then the calculation in step S5 is performed. Used for. If it is determined in step S10 that the difference value ΔT1 is less than or equal to the convergence gradient value α (NO), the amount of change is small, and thus the difference value ΔT1 remains the value calculated in step S1 in step S5. Used for calculation.

Here, in other words, the operation of steps S8 to S11 is rephrased so that the difference value ΔT1 is within a predetermined range (−α
≦ ΔT1 ≦ α), the difference value ΔT1 is calculated in step S1.
The value calculated in step S5 is used for the calculation in step S5. The difference value ΔT1 is within a predetermined range (−α ≦
If it deviates in the positive direction from ΔT1 ≦ α), it is rewritten to the convergent gradient value α, and if it deviates in the negative direction, the divergence gradient value −β
Can be rewritten as

Next, in the torque calculating means 12A, the routine work for utilizing the above-mentioned routine work for the respective steering torque sensors 51, 52 as subroutines A, B is performed (see FIG. 5). By performing this routine work, the torque calculation means 12
In A, the calculated torque signal (sensor value) TC to be output to the target current setting unit 12B (see FIG. 2) is selected.

As shown in FIG. 5, torque calculating means 12A
Then, first, by the subroutines A and B, the calculated current value C for each of the two steering torque sensors 51 and 52 is calculated.
T1 and CT2 are calculated. Then, it is determined whether or not both of the calculated current values CT1 and CT2 are 0 or more (step S12).

In step S12, the calculated current value CT
When both 1 and CT2 are 0 or more, that is, both are determined to be positive signs (YES), the next calculation current value CT1 is calculated.
Is greater than the calculated current value CT2 (step S13). If it is determined in step S13 that the calculated current value CT1 is larger than the calculated current value CT2 (YES), these calculated current values CT1, C
The smaller calculated current value CT2 of T2 is the sensor value TC.
Is selected (step S14). If it is determined in step S13 that the calculated current value CT1 is less than or equal to the calculated current value CT2 (NO), the smaller calculated current value CT1 of these calculated current values CT1 and CT2.
Is selected as the sensor value TC (step S15).

If it is determined in step S12 that at least one of the two calculated current values CT1 and CT2 is smaller than 0 (NO), it is then determined whether both calculated current values CT1 and CT2 are smaller than 0. It is determined whether or not (step S16). In this step S16, 2
When it is determined that the two calculation current values CT1 and CT2 are both smaller than 0, that is, both have negative signs (YES)
Determines whether the calculated current value CT1 is larger than the calculated current value CT2 (step S17).

In this step S17, the calculated current value C
When it is determined that T1 is larger than the calculated current value CT2 (YES), the larger calculated current value CT1 (the smaller absolute value) of these calculated current values CT1 and CT2 is selected as the sensor value TC. (Step S18). If it is determined in step S17 that the calculated current value CT1 is less than or equal to the calculated current value CT2 (NO), the larger calculated current value CT2 of these calculated current values CT1 and CT2 is selected as the sensor value TC. (Step S19). Then, in step S16, one of the two calculated current values CT1 and CT2 is greater than or equal to 0 and the other is less than 0, that is, the two calculated current values CT.
When it is determined that 1 and CT2 have different signs (NO)
Is selected as the sensor value TC (step S20).

Next, with reference to FIGS. 6 and 7, the specific operation of the torque calculating means 12A when the output values from the two steering torque sensors 51, 52 differ due to aging of the sensors and the like will be described. explain. As shown in FIG. 6, when the output values of the steering torque sensors 51 and 52 have the same sign, the output value of the steering torque sensors 51 and 52 having the smaller absolute value is referred to as the sensor value TC. It Further, these steering torque sensors 51, 52
If the output values of are different from each other, the value of zero is referred to as the sensor value TC.

When the steering torque sensor 52 fails (P1 in FIG. 6) and its output value suddenly changes in the positive direction, step S3 in the subroutine B is executed.
Then, it is determined that the difference value ΔT2 is larger than the predetermined value α, and is rewritten to the divergence gradient value β in step S4 (see FIG. 4). In this way, the calculated current value CT2 calculated by rewriting the difference value ΔT2 into the divergence gradient value β changes as the output value of the steering torque sensor 52 along the gradient shown by the thin line in FIG. After that, this calculation current value CT
2 and the calculated current value CT1 of the steering torque sensor 51 are compared, and when these values have the same sign, the value whose absolute value is smaller is referred to as the sensor value TC, and when they have different signs, the value is zero. The value is referred to as the sensor value TC. Here, P2 shown in FIG. 6 indicates a branch point at which the output value of the steering torque sensor 51 becomes smaller than the virtual output value (divergence gradient value β) of the steering torque sensor 52, and P3 indicates the outputs of the steering torque sensors 51, 52. The branch points where the values have different signs are shown.

As shown in FIG. 7, when the output value of the steering torque sensor 52 suddenly changes in the negative direction (P11), the difference value ΔT2 is negative in step S2 of the subroutine B. It is determined that the difference value ΔT2 is smaller than the predetermined value −α in step S8, and is rewritten to the divergence gradient value −β in step S9. Then, similarly to the above, the calculated current value CT2 calculated by rewriting the difference value ΔT2 into the divergence gradient value −β is
The output value of the steering torque sensor 52 changes along the gradient shown by the thin line in FIG. 7. After that, the calculated current value CT2 and the calculated current value CT1 of the steering torque sensor 51 are calculated.
Are compared with each other, and when these values have the same sign, the value whose absolute value is smaller is referred to as the sensor value TC,
When the signs are different from each other, a value of zero is referred to as the sensor value TC. Here, P12 shown in FIG. 7 indicates a branch point at which the output value of the steering torque sensor 51 becomes smaller than the virtual output value (divergence gradient value-β) of the steering torque sensor 52, and P3.
Indicates a branch point at which the output values of the steering torque sensors 51, 52 have different signs.

According to the above, the following effects can be obtained in this embodiment. (1) When the steering torque sensor 52 fails and outputs an output value that changes abruptly, a value that changes at a predetermined gradient (previous value LT2 + β as a difference value or previous value LT2 +
Since the difference between -β and the like) is calculated as the current value CT2, the rapidly changing output value can be limited, and the steering feeling of the driver can be improved (2). Since the absolute value of the divergence gradient value β is smaller than the absolute value of the convergent gradient value −α, even if the steering torque sensor 52 fails and the absolute value of its output value suddenly increases, the auxiliary steering force rapidly increases. It does not rise but rises gently along a small slope. Therefore, the steering feeling of the driver can be improved.

(3) Even when the output value of one steering torque sensor 52 changes abruptly, after this output value is replaced with a value that changes with a predetermined gradient, that value and the other steering torque sensor 51 The output values are compared. If they have the same sign, the output value with the smaller absolute value is referred to, and if they have different signs, zero is referred to as the sensor value TC. Without reference as
A good steering feeling can be given to the driver.

As described above, the present invention is not limited to the above embodiment, but can be implemented in various forms. In this embodiment, the two steering torque sensors 51 and 52 are provided, but the present invention is not limited to this, and may be one, for example. Even in this case, when the sensor outputs an output value that changes abruptly, the value that changes with a predetermined gradient is used as the sensor value, so the output value that changes abruptly is limited. It is possible to improve the steering feeling of the driver.

[0045]

According to the first aspect of the present invention, for example, when a sensor malfunctions and outputs an output value that changes abruptly, the value that changes at a predetermined gradient is used as the sensor value. Therefore, the output value that changes abruptly can be limited, and the driver's steering feeling can be improved.

According to the invention of claim 2, claim 1
In addition to the effects of the invention described in (1), even if the sensor malfunctions and the absolute value of its output value suddenly increases, the auxiliary steering force does not increase rapidly but increases gradually along a small gradient. Thus, the driver's steering feeling can be improved.

According to the third aspect of the present invention, for example, even if one of the sensors fails and the change in the output values thereof increases rapidly, if the output values of the two sensors have the same sign, the absolute values are absolute. The output value with the smaller value, or zero when the sign is different is referred to as the sensor value. Therefore, it is possible to give the driver a good steering feeling without referring to the output value that has rapidly increased as a sensor value.

According to the fourth aspect of the present invention, for example, even when the output value of one sensor changes abruptly, this output value is replaced with a value that changes with a predetermined gradient, and then that value and the other value are changed. The output values of the sensors are compared. If they have the same sign, the output value with the smaller absolute value is referred to, and if they have different signs, zero is referred to as the sensor value. Therefore, it is possible to give the driver a good steering feeling without referring to the output value that has rapidly increased as a sensor value.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of a steering system to which an electric power steering device of the present embodiment is applied.

FIG. 2 is a block configuration diagram of an electric power steering device of the present embodiment.

FIG. 3 is a circuit diagram showing a main part of the motor drive circuit of FIG.

FIG. 4 is a flowchart showing a part of a torque selection method.

5 is a flowchart showing an entire torque selection method including a part of the torque selection method shown in FIG.

FIG. 6 is a graph showing a sensor value selected when one of the two steering torque sensors fails and its output value changes in a direction away from zero.

FIG. 7 is a graph showing sensor values selected when one of the two steering torque sensors fails and its output value changes in a direction approaching zero.

[Explanation of symbols]

P Electric power steering device 51,52 Steering torque sensor T1, T2 Steering torque signal (output value) 12 Motor control device 12A torque calculation means

Claims (4)

[Claims] 1. An electric power steering apparatus for controlling an auxiliary steering force according to at least a steering torque, wherein a sensor for detecting the steering torque is provided, and when a change in an output from the sensor is within a predetermined range, an output value thereof is provided. Is used as the sensor value, but when the change is out of the predetermined range, the sensor value is calculated as the value that changes with a predetermined gradient, and the calculated value is used for control. Power steering device. 2. The electric power steering apparatus according to claim 1, wherein the predetermined gradient is smaller when the change is away from zero than when the change is closer to zero. 3. An electric power steering apparatus for controlling an auxiliary steering force according to at least a steering torque, wherein two sensors for detecting the steering torque are provided, and when the output values from the two sensors have the same sign, the absolute value is absolute. An electric power steering apparatus characterized in that an output value having a smaller value is used as a sensor value, and a calculation is performed with zero as a sensor value when the sign is different, and the calculated value is used for control. 4. An electric power steering apparatus for controlling an auxiliary steering force according to at least a steering torque, wherein two sensors for detecting the steering torque are provided, and when a change in an output from the sensor is out of a predetermined range. Calculates the output value of a value that changes with a predetermined gradient for each sensor, and when the output values from these two sensors have the same sign, the one with the smaller absolute value is used as the sensor. An electric power steering device characterized in that a calculation is performed with a sensor value of zero when the value is a different value, and the calculated value is used for control.