JP2014196070A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique which accurately grasps a rack shaft load in a simple and inexpensive manner.SOLUTION: An electric power steering device includes: an electric motor which applies an auxiliary force to the operation of a steering wheel of a vehicle; a rack shaft which moves in response to the operation of the steering wheel and steers front wheels; a rack shaft load estimation part 70 which estimates a lock shaft load F occurring in the rack shaft; and a control device which controls the auxiliary force applied by the electric motor on the basis of the rack shaft load F estimated by the rack shaft load estimation part 70. The rack shaft load estimation part 70 estimates the rack shaft load F on the basis of pressures occurring in the front wheels.

Description

  The present invention relates to an electric power steering apparatus.

2. Description of the Related Art In recent years, in an electric power steering apparatus that includes an electric motor in a steering system of a vehicle and assists the steering force of a driver with the power of the electric motor, the assist force of the electric motor is transmitted to control the assist force by the electric motor. It has been proposed to take into account the load generated on the rack shaft.
For example, the electric power steering device described in Patent Document 1 is configured as follows. That is, the target steering torque calculation processing means for deriving the target steering torque based on the steering angle and the vehicle speed, and the rack thrust for estimating the rack thrust from the difference between the back electromotive force voltage of the assist motor calculated from the steering angle and the voltage between the motor terminals. An estimation means, and road load correction coefficient calculating means for deriving a road load correction coefficient based on rack thrust, steering angle, and vehicle speed, and correcting the target steering torque based on the road load correction coefficient A feedback control amount is calculated based on the difference between the target steering torque and the steering torque, and the assist motor is driven based on the feedback control amount.

JP 2007-8292 A

In an apparatus that controls the assist force by the electric motor in consideration of the rack shaft load that is generated on the rack shaft, it is important how accurately the rack shaft load can be grasped. However, if a sensor for directly detecting the rack shaft load is newly provided, the configuration becomes complicated and the cost becomes high.
An object of the present invention is to provide an electric power steering apparatus that can easily and inexpensively grasp a rack shaft load with high accuracy.

  For this purpose, the present invention provides an electric motor that gives an assisting force to an operation of a steering wheel of a vehicle, a rack shaft that moves according to the operation of the steering wheel and steers rolling wheels, and the rack. An estimation means for estimating a load generated on the shaft; and a motor control means for controlling an auxiliary force by the electric motor based on the load estimated by the estimation means, wherein the estimation means is provided on the rolling wheels. The electric power steering apparatus is characterized in that the load is estimated based on a generated pressure.

Here, the estimation means may estimate the load based on an output value from a sensor that is provided in the vehicle and detects a pressure generated in the rolling wheel.
Further, the estimation means may estimate the load in consideration of a turning direction of the vehicle and a change speed of a rotation angle in the turning direction.
The estimating means may estimate the load in consideration of a moving direction and a moving amount of the rack shaft.
The estimating means may estimate the load in consideration of a rotation angle of the steering wheel.
Further, the motor control means may increase the assisting force by the electric motor when the load estimated by the estimation means is large than when the load is small.

  According to the present invention, the rack shaft load can be grasped with high accuracy simply and inexpensively.

It is a figure showing the schematic structure of the electric power steering device concerning an embodiment. It is a schematic block diagram of a control apparatus. It is a schematic block diagram of a target current calculation part. It is the schematic of the control map which shows a response | compatibility with steering torque, vehicle speed, and base current. It is a figure which illustrates the control map which shows a response | compatibility with a rack shaft load and a rack shaft load compensation current. It is a schematic block diagram of a control part. It is a schematic block diagram of a rack axial load estimation part. It is a figure which illustrates the control map which shows a response | compatibility with the tire pressure difference of a right front wheel and a left front wheel, and a base load. It is a figure which illustrates the control map which shows a response | compatibility with the turning direction of a motor vehicle, the rotation angular velocity to the turning direction, and a yaw rate equivalent correction | amendment load. It is a figure which illustrates the control map which shows a response | compatibility with the moving direction of a rack axis | shaft, its moving amount | distance, and a rack shaft displacement equivalent correction | amendment load. It is a figure which illustrates the control map which shows a response | compatibility with a steering angle and a steering angle equivalent correction load.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating a schematic configuration of an electric power steering apparatus 100 according to an embodiment.
Electric power steering device 100 (hereinafter, also simply referred to as “steering device 100”) is a steering device for arbitrarily changing the traveling direction of a vehicle, and in this embodiment, an automobile as an example of the vehicle. The structure applied to is illustrated.

  The steering apparatus 100 includes a wheel-like steering wheel 101 that is operated by a driver to change the traveling direction of the automobile, and a steering shaft 102 that is provided integrally with the steering wheel 101. . The steering device 100 includes an upper connecting shaft 103 connected to the steering shaft 102 via a universal joint 103a, and a lower connecting shaft 108 connected to the upper connecting shaft 103 via a universal joint 103b. . The lower connecting shaft 108 rotates in conjunction with the rotation of the steering wheel 101.

  Further, the steering device 100 is a rolling wheel that includes a right front wheel 151 that is a front wheel on the right side (left side in FIG. 1) and a left front wheel 152 that is a front wheel on the left side (right side in FIG. 1). A tie rod 104 connected to each of the front wheels 150 and a rack shaft 105 connected to the tie rod 104 are provided. Further, the steering device 100 includes a pinion shaft 106 on which a pinion 106 a that constitutes a rack and pinion mechanism is formed together with rack teeth 105 a formed on the rack shaft 105.

  The steering device 100 also has a steering gear box 107 that houses a part of the pinion shaft 106. The pinion shaft 106 is connected to the lower connection shaft 108 via a torsion bar (not shown) in the steering gear box 107. A torque sensor 109 that detects the steering torque T of the steering wheel 101 based on the relative angle between the lower connecting shaft 108 and the pinion shaft 106 is provided inside the steering gear box 107.

  The steering device 100 includes an electric motor 110 supported by the steering gear box 107, and a speed reducing mechanism 111 that decelerates the driving force of the electric motor 110 and transmits it to the pinion shaft 106. Electric motor 110 according to the present embodiment is a three-phase brushless motor. The reduction mechanism 111 includes, for example, a worm wheel (not shown) fixed to the pinion shaft 106, a worm gear (not shown) connected to the output shaft of the electric motor 110, and the like.

In addition, the steering device 100 includes a steering angle sensor 112 that detects a steering angle that is an angle by which the steering wheel (handle) 101 is rotated by detecting a rotation angle of the steering shaft 102.
The steering device 100 includes a control device 10 as an example of a motor control unit that controls the operation of the electric motor 110. Output signals from the torque sensor 109 and the steering angle sensor 112 described above are input to the control device 10. In addition, the control device 10 includes a vehicle speed sensor 170 that detects a vehicle speed Vc, which is a moving speed of the vehicle, via a network (CAN) that performs communication for sending signals for controlling various devices mounted on the vehicle. Output signals are input from a tire pressure sensor 180 that detects the tire pressure that is the pressure of the front wheel 150, a yaw rate sensor 190 that detects the yaw rate of the automobile (the change speed of the rotation angle in the turning direction), and the like.

  The steering device 100 configured as described above detects the steering torque T applied to the steering wheel 101 by the torque sensor 109, drives the electric motor 110 in accordance with the detected torque, and generates torque generated by the electric motor 110. Is transmitted to the pinion shaft 106. Thereby, the torque generated by the electric motor 110 assists the driver's steering force applied to the steering wheel 101.

Next, the control device 10 will be described.
FIG. 2 is a schematic configuration diagram of the control device 10.
The control device 10 is an arithmetic and logic circuit composed of a CPU, ROM, RAM, backup RAM, and the like.
The control device 10 includes a torque signal Td obtained by converting the steering torque T detected by the torque sensor 109 described above into an output signal, and a vehicle speed signal obtained by converting the vehicle speed Vc detected by the vehicle speed sensor 170 into an output signal. v or the like is input.

  Then, the control device 10 calculates a target auxiliary torque based on the torque signal Td and the vehicle speed signal v, and calculates a target current It necessary for the electric motor 110 to supply the target auxiliary torque. 20 and a control unit 30 that performs feedback control or the like based on the target current It calculated by the target current calculation unit 20. Further, the control device 10 is a rack shaft as an example of an estimation unit that estimates a rack shaft load F that is a force applied to the rack shaft 105 based on the tire pressure detected by the tire pressure sensor 180 (see FIG. 1). A load estimation unit 70 is included.

Next, the target current calculation unit 20 will be described in detail.
FIG. 3 is a schematic configuration diagram of the target current calculation unit 20.
The target current calculation unit 20 includes a base current calculation unit 21 that calculates a base current Ib that serves as a reference for setting the target current, and an inertia compensation current calculation unit 22 that calculates a current for canceling the inertia moment of the electric motor 110. And a damper compensation current calculation unit 23 for calculating a current for limiting the rotation of the motor. In addition, the target current calculation unit 20 includes a rack shaft load compensation current calculation unit 27 that calculates a current corresponding to the rack shaft load F generated in the rack shaft 105. Further, the target current calculation unit 20 calculates the target current It based on the values calculated by the base current calculation unit 21, the inertia compensation current calculation unit 22, the damper compensation current calculation unit 23, and the rack shaft load compensation current calculation unit 27. A target current determination unit 25 for determination is provided. In addition, the target current calculation unit 20 includes a phase compensation unit 26 that compensates for the phase of the steering torque T detected by the torque sensor 109.

  The target current calculation unit 20 includes a torque signal Td, a vehicle speed signal v, a rotation speed signal Nms obtained by converting the rotation speed Nm of the electric motor 110 into an output signal, and a rack shaft load F estimated by the rack shaft load estimation unit 70. Etc. are entered. The rotational speed signal Nms is, for example, a sensor configured to detect a rotational position of a rotor (rotor) of the electric motor 110 that is a three-phase brushless motor (for example, a rotor configured by a resolver, a rotary encoder, or the like that detects the rotational position of the rotor) It can be exemplified that the value obtained by differentiating the rotation angle of the electric motor 110 detected by the position detection circuit) is converted into an output signal.

FIG. 4 is a schematic diagram of a control map showing the correspondence between the steering torque T, the vehicle speed Vc, and the base current Ib.
The base current calculation unit 21 calculates a base current Ib based on the torque signal Ts obtained by phase compensation of the torque signal Td by the phase compensation unit 26 and the vehicle speed signal v from the vehicle speed sensor 170. That is, the base current calculation unit 21 calculates the base current Ib according to the phase-compensated steering torque T and the vehicle speed Vc. The base current calculation unit 21 is, for example, a phase-compensated steering torque T (torque signal Ts), vehicle speed Vc (vehicle speed signal v), and base current that are created in advance based on vehicle characteristics and stored in the ROM. The base current Ib is calculated by substituting the steering torque T (torque signal Ts) and the vehicle speed Vc (vehicle speed signal v) into the control map or calculation formula illustrated in FIG. 4 showing the correspondence with Ib.

  The inertia compensation current calculation unit 22 calculates an inertia compensation current Is for canceling the moment of inertia of the electric motor 110 and the system based on the torque signal Ts and the vehicle speed signal v. That is, the inertia compensation current calculation unit 22 calculates the inertia compensation current Is according to the steering torque T (torque signal Ts) and the vehicle speed Vc (vehicle speed signal v). The inertia compensation current calculation unit 22 generates, for example, the steering torque T (torque signal Ts), the vehicle speed Vc (vehicle speed signal v), and the inertia compensation current Is, which are previously created based on vehicle characteristics and stored in the ROM. The inertia compensation current Is is calculated by substituting the steering torque T (torque signal Ts) and the vehicle speed Vc (vehicle speed signal v) into a control map or a calculation formula indicating the correspondence between the two.

  The damper compensation current calculation unit 23 calculates a damper compensation current Id for limiting the rotation of the electric motor 110 based on the torque signal Ts, the vehicle speed signal v, and the rotation speed signal Nms of the electric motor 110. That is, the damper compensation current calculation unit 23 calculates the damper compensation current Id according to the steering torque T (torque signal Ts), the vehicle speed Vc (vehicle speed signal v), and the rotational speed Nm (rotational speed signal Nms) of the electric motor 110. calculate. The damper compensation current calculation unit 23 is, for example, a steering torque T (torque signal Ts), a vehicle speed Vc (vehicle speed signal v), and a rotation speed Nm (rotation) that are created in advance based on vehicle characteristics and stored in the ROM. The steering torque T (torque signal Ts), the vehicle speed Vc (vehicle speed signal v), and the rotational speed Nm (rotational speed signal Nms) are substituted into a control map or calculation formula indicating the correspondence between the speed signal Nms) and the damper compensation current Id. Thus, the damper compensation current Id is calculated.

  The rack shaft load compensation current calculation unit 27 calculates a rack shaft load compensation current Ir for canceling the rack shaft load F based on the rack shaft load F estimated by the rack shaft load estimation unit 70. That is, the rack shaft load compensation current calculation unit 27 calculates the rack shaft load compensation current Ir according to the rack shaft load F estimated by the rack shaft load estimation unit 70. The rack shaft load compensation current calculation unit 27 is, for example, a control map or calculation indicating the correspondence between the rack shaft load F and the rack shaft load compensation current Ir, which is created in advance based on vehicle characteristics and stored in the ROM. The rack shaft load compensation current Ir is calculated by substituting the rack shaft load F estimated by the rack shaft load estimation unit 70 into the equation.

FIG. 5 is a diagram illustrating a control map showing the correspondence between the rack shaft load F and the rack shaft load compensation current Ir.
Here, when the front wheel 150 is not loaded, when the electric motor 110 rotates in one rotation direction, the pinion shaft 106 moves the rack shaft 105 in the lateral direction as viewed in FIG. Rotates to the right. Hereinafter, the moving direction of the rack shaft 105 when the front wheel 150 rotates in the right direction is referred to as “one direction”. When the electric motor 110 rotates in the other rotation direction, the pinion shaft 106 moves the rack shaft 105 in the horizontal direction, and the front wheel 150 rotates in the left direction. Hereinafter, the moving direction of the rack shaft 105 when the front wheel 150 rotates in the left direction is referred to as “the other direction”. In the following, the rack shaft 105 is moved in one direction, in other words, the direction of the current that rotates the electric motor 110 in one rotation direction is plus, and the rack shaft 105 is moved in the other direction, in other words, the electric motor 110 is moved. The direction of the current to be rotated in the other rotation direction is negative. Further, the direction of the load applied to one direction with respect to the rack shaft 105 is positive, and the direction of the load applied to the other direction is negative.

In FIG. 5, the horizontal axis represents the direction and magnitude of the rack shaft load F, and the vertical axis represents the direction and current amount of the rack shaft load compensation current Ir.
The rack shaft load compensation current calculation unit 27 calculates the rack shaft load compensation current Ir based on the control map shown in FIG. 5, and when a load in one direction is applied to the rack shaft 105, the rack shaft load compensation current Ir When the load compensation current Ir is a negative value and a load in the other direction is applied to the rack shaft 105, the rack shaft load compensation current Ir is a positive value and the load applied to the rack shaft 105 is increased. Thus, the rack shaft load compensation current Ir is calculated so as to increase. The same applies to the case where the rack shaft load compensation current calculation unit 27 calculates based on a predetermined calculation formula.

  The target current determination unit 25 includes the base current Ib calculated by the base current calculation unit 21, the inertia compensation current Is calculated by the inertia compensation current calculation unit 22, and the damper compensation calculated by the damper compensation current calculation unit 23. A target current It is determined based on the current Id and the rack shaft load compensation current Ir calculated by the rack shaft load compensation current calculation unit 27. For example, the target current determination unit 25 adds the inertia compensation current Is to the base current Ib, subtracts the damper compensation current Id, and adds the rack shaft load compensation current Ir as the target current It. decide.

Next, the control unit 30 will be described in detail.
FIG. 6 is a schematic configuration diagram of the control unit 30.
The control unit 30 is an example of a motor drive control unit 31 that controls the operation of the electric motor 110, a motor drive unit 32 that drives the electric motor 110, and a current detection unit that detects the actual current Im that actually flows through the electric motor 110. As a motor current detection unit 33.
The motor drive control unit 31 performs feedback control based on a deviation between the target current It determined by the target current calculation unit 20 and the actual current Im supplied to the electric motor 110 detected by the motor current detection unit 33. A feedback (F / B) control unit 40 that performs the above and a PWM signal generation unit 60 that generates a PWM (pulse width modulation) signal for PWM driving the electric motor 110.

  The feedback control unit 40 includes a deviation calculating unit 41 for obtaining a deviation between the target current It finally determined by the target current calculating unit 20 and the actual current Im detected by the motor current detecting unit 33, and the deviation is A feedback (F / B) processing unit 42 that performs feedback processing so as to be zero.

The feedback (F / B) processing unit 42 performs feedback control so that the target current It and the actual current Im match. For example, the feedback (F / B) processing unit 42 is proportional to the deviation calculated by the deviation calculating unit 41. Is proportionally processed, integrated by an integral element, and these values are added by an addition operation unit.
The PWM signal generation unit 60 generates a PWM signal for driving the electric motor 110 by PWM (pulse width modulation) based on the output value from the feedback control unit 40, and outputs the generated PWM signal.

The motor drive unit 32 is a so-called inverter, and includes, for example, six independent transistors (FETs) as switching elements. Three of the six transistors are a positive line of a power source, an electric coil of each phase, The other three transistors are connected to the electric coil of each phase and the negative side (ground) line of the power source. Then, the driving of the electric motor 110 is controlled by driving the gates of two transistors selected from the six and switching the transistors.
The motor current detection unit 33 detects the value of the actual current Im flowing through the electric motor 110 from the voltage generated at both ends of the shunt resistor connected to the motor drive unit 32.

Next, the rack shaft load estimation unit 70 will be described in detail.
FIG. 7 is a schematic configuration diagram of the rack shaft load estimating unit 70.
The rack shaft load estimation unit 70 is based on the base load calculation unit 71 that calculates the base load F1 that is the base of the rack shaft load F based on the tire pressure detected by the tire pressure sensor 180, and the yaw rate detected by the yaw rate sensor 190. A yaw rate equivalent correction load calculating unit 72 for calculating a yaw rate equivalent correction load F2 which is a correction load for correcting the base load F1. The rack shaft load estimating unit 70 also racks the rack based on the rotation angle of the electric motor 110 detected by a sensor (for example, the rotor position detection circuit) that detects the rotation position of the rotor (rotor) of the electric motor 110. A rack axis displacement equivalent correction load that calculates a rack axis displacement equivalent correction load F3, which is a correction load for correcting the base load F1 based on the calculated displacement amount of the shaft 105 in the axial direction. A calculation unit 73 is provided. In addition, the rack shaft load estimation unit 70 includes a steering angle equivalent correction load calculation unit 74 that calculates a steering angle equivalent correction load F4 that is a correction load for correcting the base load F1 based on the steering angle detected by the steering angle sensor 112. I have. The rack shaft load estimation unit 70 includes a base load F1 calculated by the base load calculation unit 71, a yaw rate equivalent correction load F2 calculated by the yaw rate equivalent correction load calculation unit 72, and a rack axis displacement equivalent correction load calculation unit 73. A rack shaft load determination unit 75 that determines the final rack shaft load F based on the calculated rack shaft displacement equivalent correction load F3 and the steering angle equivalent correction load F4 calculated by the steering angle equivalent correction load calculation unit 74 is provided. ing.

FIG. 8 is a diagram illustrating a control map showing the correspondence between the tire pressure difference between the right front wheel 151 and the left front wheel 152 and the base load F1.
When the tire pressure of the right front wheel 151 increases, it is considered that the load applied to the rack shaft 105 from the right front wheel 151 side in the other direction increases. Further, when the tire pressure of the left front wheel 152 increases, it is considered that the load applied to the rack shaft 105 in one direction from the left front wheel 152 side increases. In view of such matters, the base load calculation unit 71 determines the right front wheel that is the basis of the load applied to the rack shaft 105 in the other direction from the tire pressure of the left front wheel 152 that is the basis of the load applied to the rack shaft 105 in one direction. A tire pressure difference obtained by subtracting the tire pressure 151 is calculated, and a base load F1 is calculated based on the tire pressure difference. For example, the base load calculation unit 71 uses the control map or calculation formula illustrated in FIG. 8 that shows the correspondence between the tire pressure difference and the base load F1 that has been created based on the vehicle characteristics and stored in the ROM in advance. The base load F1 is calculated by substituting the pressure difference.

The yaw rate equivalent correction load calculation unit 72 increases the load applied to the rack shaft 105 in the other direction when the automobile turns right, and increases the load applied to the rack shaft 105 in one direction when the vehicle turns left. In view of the above, the yaw rate equivalent correction load F2 corresponding to the turning direction and the change speed of the rotation angle in the turning direction is calculated.
FIG. 9 is a diagram illustrating a control map showing correspondence between the turning direction of the automobile and the rotational angular velocity in the turning direction and the yaw rate equivalent correction load F2.
The yaw rate equivalent correction load calculation unit 72 indicates, for example, the correspondence between the turning direction of the automobile and the rotational angular velocity in the turning direction and the yaw rate equivalent correction load F2 that are created in advance based on the vehicle characteristics and stored in the ROM. The yaw rate equivalent correction load F2 is calculated by substituting the turning direction of the vehicle and the rotational angular velocity in the turning direction into the control map or calculation formula illustrated in FIG.

The rack shaft displacement equivalent correction load calculation unit 73 increases the load applied to the rack shaft 105 in the other direction when the rack shaft 105 moves in one direction, and applies in one direction when the rack shaft 105 moves in the other direction. In view of the increased load, the rack shaft displacement equivalent correction load F3 corresponding to the moving direction and the moving amount of the rack shaft 105 is calculated.
FIG. 10 is a diagram illustrating a control map showing the correspondence between the movement direction and the movement amount of the rack shaft 105 and the rack shaft displacement equivalent correction load F3.
The rack axis displacement equivalent correction load calculation unit 73, for example, the correspondence between the movement direction and the amount of movement of the rack shaft 105 and the rack axis displacement equivalent correction load F3, which are created based on the vehicle characteristics and stored in the ROM in advance. The rack axis displacement equivalent correction load F3 is calculated by substituting the movement direction and the movement amount of the rack shaft 105 into the control map or the calculation formula illustrated in FIG. Since the output shaft of the electric motor 110 and the rack shaft 105 are mechanically coupled, the rack shaft displacement equivalent correction load calculation unit 73 detects the rotational position of the rotor (rotor) of the electric motor 110. Based on the rotation angle of the electric motor 110 detected by the sensor, the moving direction and the moving amount of the rack shaft 105 can be grasped.

When the steering angle in the right direction increases and the amount of movement of the rack shaft 105 in one direction increases, the load applied to the rack shaft 105 in the other direction increases and the steering angle equivalent correction load calculation unit 74 increases in the left direction. Considering that the load applied to the rack shaft 105 in one direction increases as the steering angle of the rack shaft 105 increases and the amount of movement of the rack shaft 105 in the other direction increases, the steering angle equivalent correction load F4 corresponding to the steering angle is calculated. To do.
FIG. 11 is a diagram illustrating a control map showing the correspondence between the steering angle and the steering angle equivalent correction load F4. In FIG. 11, the steering angle in the right direction is positive and the steering angle in the left direction is negative.
The steering angle equivalent correction load calculation unit 74 is, for example, a control map illustrated in FIG. 11 illustrating the correspondence between the steering angle and the steering angle equivalent correction load F4, which is previously created based on the vehicle characteristics and stored in the ROM. The steering angle equivalent correction load F4 is calculated by substituting the steering angle detected by the steering angle sensor 112 into the calculation formula.

  The rack shaft load determination unit 75 includes, for example, a base load F1 calculated by the base load calculation unit 71, a yaw rate equivalent correction load F2 calculated by the yaw rate equivalent correction load calculation unit 72, and a rack axis displacement equivalent correction load calculation unit 73. A value obtained by adding the calculated rack shaft displacement equivalent correction load F3 and the steering angle equivalent correction load F4 calculated by the steering angle equivalent correction load calculation unit 74 is determined as the rack shaft load F. Alternatively, the rack shaft load determination unit 75 may use the base load F1 calculated by the base load calculation unit 71 as the rack shaft load F. Alternatively, the rack shaft load determination unit 75 performs the yaw rate equivalent correction load F2 calculated by the yaw rate equivalent correction load calculation unit 72, the rack axis displacement equivalent correction load F3 calculated by the rack axis displacement equivalent correction load calculation unit 73, and the steering angle equivalent correction. A value obtained by adding any one of the steering angle equivalent correction loads F4 calculated by the load calculation unit 74 to the base load F1 calculated by the base load calculation unit 71 is used as the rack shaft load F. Also good. Alternatively, the rack shaft load determination unit 75 performs the yaw rate equivalent correction load F2 calculated by the yaw rate equivalent correction load calculation unit 72, the rack axis displacement equivalent correction load F3 calculated by the rack axis displacement equivalent correction load calculation unit 73, and the steering angle equivalent correction. A value obtained by adding any two of the steering angle equivalent correction loads F4 calculated by the load calculation unit 74 to the base load F1 calculated by the base load calculation unit 71 is defined as a rack shaft load F. Also good.

In the rack shaft load estimation unit 70 configured as described above, the rack shaft load F is estimated based on the tire pressure of the front wheel 150 and the like which is highly related to the rack shaft load F. can do. Further, since the rack shaft load estimation unit 70 estimates the rack shaft load F using a tire pressure sensor 180, a yaw rate sensor 190, etc. provided in the automobile, a new sensor that directly detects the rack shaft load F is provided. The structure can be simplified and the cost can be reduced.
In addition, since the target current calculation unit 20 according to the present embodiment sets the target current It taking into account the rack shaft load F estimated by the rack shaft load estimation unit 70, the target current calculation unit 20 has a configuration that does not take into account the rack shaft load F. Since the assist force desired by the driver can be applied, the steering feeling can be improved.

  The motor drive control unit 31 of the control unit 30 of the control device 10 includes a feedforward control unit that performs feedforward control in addition to the feedback control unit 40, and the rack shaft load estimated by the rack shaft load estimation unit 70. The feedforward gain may be adjusted based on F. In such a case, when the direction of the rack shaft load F estimated by the rack shaft load estimation unit 70 is opposite to the direction in which the rack shaft 105 moves in accordance with the direction in which the steering wheel 101 is steered, motor drive is performed. The control unit 31 may perform feedforward control by increasing the feedforward gain. The feed forward gain is preferably increased as the rack shaft load F increases. As a result, the responsiveness of the assist force of the electric motor 110 to the operation of the steering wheel 101 can be improved. As a result, the steering feeling can be improved.

DESCRIPTION OF SYMBOLS 10 ... Control apparatus, 20 ... Target electric current calculation part, 27 ... Rack axial load compensation electric current calculation part, 30 ... Control part, 40 ... Feedback control part, 70 ... Rack axial load estimation part, 100 ... Electric power steering apparatus, 110 ... Electric motor, 180 ... tire pressure sensor

Claims (6)

An electric motor for providing an assisting force to the operation of the steering wheel of the vehicle;
A rack shaft that moves according to the operation of the steering wheel to steer the rolling wheels;
Estimating means for estimating a load generated on the rack shaft;
Motor control means for controlling auxiliary force by the electric motor based on the load estimated by the estimation means;
With
The electric power steering apparatus, wherein the estimating means estimates the load based on a pressure generated in the rolling wheel.   2. The electric power steering apparatus according to claim 1, wherein the estimation unit estimates the load based on an output value from a sensor that is provided in the vehicle and detects a pressure generated in the rolling wheel. .   The electric power steering apparatus according to claim 1, wherein the estimation unit estimates the load in consideration of a turning direction of the vehicle and a change speed of a rotation angle in the turning direction.   The electric power steering apparatus according to any one of claims 1 to 3, wherein the estimation unit estimates the load in consideration of a movement direction and a movement amount of the rack shaft.   5. The electric power steering apparatus according to claim 1, wherein the estimation unit estimates the load in consideration of a rotation angle of the steering wheel.   6. The motor control unit according to claim 1, wherein when the load estimated by the estimation unit is large, the motor control unit increases the assisting force by the electric motor more than when the load is small. The electric power steering device described in 1.

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