Electric Power Steering

Abstract

The present invention provides an electric power steering system. The electric power steering system (1) includes: an electric motor (18), a rotation angle detection unit (23), a current detection circuit (32), a steering torque detection unit (12), a target torque setting unit (41), a current command value setting unit and a current control unit. The target torque setting unit (41) includes: a basic target torque setting unit (42), a first compensation value calculation unit (51), a second compensation value calculation unit (52) and a correction unit (43, 44). The basic target torque setting unit (42) sets the basic target torque of the electric motor (18). The first compensation value calculation unit (51) sets a first compensation value based on the steering torque. The second compensation value calculation unit (52) calculates a second compensation value as an estimated value of an interference torque other than the steering torque. The correction unit corrects the basic target torque.

Description

[0001] Background of the Invention Technical Field

[0002] The invention relates to an electric power steering system. Background Art

[0003] Lane keeping travel control devices are known that generate automatic steering torque for causing a vehicle to travel while maintaining a travel lane by estimating and feeding back a state quantity related to the travel state of the vehicle. The following device is proposed as this type of lane keeping travel control device: the device suppresses the degradation of lane keeping performance due to the disturbance torque by estimating the disturbance torque applied to the steering system and feeding back the disturbance torque as a state quantity related to the travel state of the vehicle. However, if the disturbance torque is fed back, even when the driver intentionally intervenes in the steering, the steering torque applied by the driver is fed back as the disturbance torque to be offset, which makes it difficult for the driver to intervene in the steering.

[0004] In order to solve such a problem, Japanese Patent Application Publication No. 2003-63437 (JP2003-63437A) discloses a lane keeping travel control device, in which a disturbance torque applied to a steering system is divided into a high frequency component and a low frequency component to be estimated by an observer, and the high frequency component and the low frequency component are fed back by a regulator so that the feedback gain of the high frequency component of the disturbance torque is smaller than the feedback gain of the low frequency component. With the lane keeping travel control device according to JP 2003-63437 A, when a driver intervenes in steering during lane keeping travel, since the steering torque increases the estimation result of the high frequency component of the disturbance torque while reducing the feedback component, it is easy for the driver to intervene in steering. Summary of the invention

[0005] The present invention makes it possible to vary the degree of priority given to the system and the driver, and enables cooperation between the driver and the system.

[0006] Aspects of the present invention provide an electric power steering system. The electric power steering system includes: a motor configured to apply a motor torque to a steering system; a rotation angle detection unit configured to detect the rotation angle of the motor; a current detection circuit configured to detect a motor current flowing through the motor; a steering torque detection unit configured to detect or estimate a steering torque applied to the steering system; a target torque setting unit configured to set a target torque of the motor based on an automatic steering angle command value; a current command value setting unit configured to set a current command value corresponding to the target torque; and a current control unit configured to make the motor current follow the current command value. The target torque setting unit includes: a basic target torque setting unit, a first compensation value calculation unit, a second compensation value calculation unit, and a correction unit. The basic target torque setting unit is configured to set a basic target torque of the motor so that the rotation angle of the motor follows the automatic steering angle command value. The first compensation value calculation unit is configured to set a first compensation value based on the steering torque. The second compensation value calculation unit is configured to calculate a second compensation value based on the motor torque, the rotation angle, and the steering torque or the target torque. The second compensation value is an estimated value of a disturbance torque other than the steering torque acting on the steering system. The correction unit is configured to correct the basic target torque using the first compensation value and the second compensation value.

[0007] In the above configuration, an estimated value of the disturbance torque other than the steering torque acting on the steering system is calculated as the second compensation value, and is used as a compensation value for the basic target torque. Therefore, it is possible to suppress the reduction in lane keeping performance due to the disturbance torque during automatic steering. On the other hand, the first compensation value is calculated based on the steering torque applied to the steering system. Therefore, appropriate tactile information can be provided to the driver. For example, if the steering torque is set to the first compensation value as it is, a control that gives priority to the system and ignores the driver's input is achieved, and if a value whose absolute value is less than the steering torque is set to the first compensation value, a control that receives the driver's input is achieved. In this way, the degree of priority given to the system and the driver can be changed by adjusting the first compensation value, which enables collaboration between people (drivers) and the system.

[0008] In the electric power steering system, the first compensation value calculation unit may include a weight setting unit that sets a weight and a multiplication unit that calculates the first compensation value by multiplying the steering torque by the weight. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals represent like elements, and in which:

[0010] Figure 1is a schematic diagram showing a schematic configuration of an electric power steering system according to an embodiment of the present invention;

[0011] Figure 2 is a block diagram showing the electrical configuration of the motor control ECU;

[0012] Figure 3 is the torsion bar torque T tb The target assist torque T is set m,md A graph of an example of

[0013] Figure 4 is a schematic diagram showing an example of the configuration of a physical model of an electric power steering system;

[0014] Figure 5 is a block diagram showing a configuration of a disturbance torque estimation unit; and

[0015] Figure 6 is a block diagram showing the configuration of a torque control unit. DETAILED DESCRIPTION

[0016] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Figure 1 1 is a schematic diagram showing a schematic configuration of an electric power steering system according to an embodiment of the present invention. The electric power steering system 1 includes a steering wheel 2 serving as a steering member for steering a vehicle, a steering mechanism 4 operating in conjunction with the rotation of the steering wheel 2 to steer a steering wheel 3, and a steering assist mechanism 5 assisting a driver in steering. The steering wheel 2 and the steering mechanism 4 are mechanically coupled to each other via a steering shaft 6 and an intermediate shaft 7.

[0017] The steering shaft 6 includes an input shaft 8 coupled to the steering wheel 2 and an output shaft 9 coupled to the intermediate shaft 7. The input shaft 8 and the output shaft 9 are coupled to each other via a torsion bar 10 so as to be relatively rotatable. A torque sensor 12 is provided near the torsion bar 10. The torque sensor 12 detects a torsion bar torque T applied to the torsion bar 10 based on the relative rotational displacement amount between the input shaft 8 and the output shaft 9. tb In this embodiment, for example, when the vehicle turns left, the torsion bar torque T detected by the torque sensor 12 is tb is detected as a positive value, and when the vehicle turns right, the torsion bar torque T tb is detected as a negative value, and as the absolute value of the positive or negative value becomes larger, the torsion bar torque T tb The magnitude of the torsion bar torque T tb is an example of “steering torque applied to the steering system” according to the present invention.

[0018] The steering mechanism 4 is composed of a rack and pinion mechanism including a pinion shaft 13 and a rack shaft 14 serving as a steering shaft. The steering wheel 3 is coupled to the respective ends of the rack shaft 14 via a tie rod 15 and a knuckle arm (not shown). The pinion shaft 13 is coupled to the intermediate shaft 7. The pinion shaft 13 rotates in conjunction with the steering operation of the steering wheel 2. A pinion 16 is coupled to the distal end of the pinion shaft 13.

[0019] The rack shaft 14 extends linearly in the left-right direction of the vehicle. A rack 17 meshing with the pinion 16 is formed at the middle portion of the rack shaft 14 in the axial direction. The pinion 16 and the rack 17 convert the rotation of the pinion shaft 13 into the axial movement of the rack shaft 14. The steering wheel 3 can be steered by moving the rack shaft 14 in the axial direction.

[0020] When the steering wheel 2 is operated (rotated), the rotation of the steering wheel 2 is transmitted to the pinion shaft 13 via the steering shaft 6 and the intermediate shaft 7. Then, the rotation of the pinion shaft 13 is converted into axial movement of the rack shaft 14 through the pinion 16 and the rack 17. As a result, the steering wheel 3 is steered. The steering assist mechanism 5 includes an electric motor 18 that generates a steering assist force (assist torque) and a reducer 19 that amplifies the output torque of the electric motor 18 and transmits it to the steering mechanism 4. The reducer 19 is composed of a worm gear mechanism including a worm gear 20 and a worm wheel 21 meshing with the worm gear 20. The reducer 19 is housed in a gear housing 22 serving as a transmission mechanism housing. In the following, the reduction ratio (gear ratio) of the reducer 19 is sometimes expressed as N. The reduction ratio N is defined as the worm gear angle θ wg That is, the rotation angle of the worm gear 20 and the worm gear angle θ ww That is, the ratio of the rotation angle of the worm wheel 21 (θ wg / θ ww ).

[0021] The worm gear 20 is rotationally driven by the motor 18. In addition, the worm wheel 21 is coupled so as to be able to rotate together with the output shaft 9. When the worm gear 20 is rotationally driven by the motor 18, the worm wheel 21 is rotationally driven, which applies the motor torque to the steering shaft 6 and rotates the steering shaft 6 (output shaft 9). Then, the rotation of the steering shaft 6 is transmitted to the pinion shaft 13 via the intermediate shaft 7. The rotation of the pinion shaft 13 is converted into axial movement of the rack shaft 14. Therefore, the steering wheel 3 is steered. That is, the worm gear 20 is rotationally driven by the motor 18, which enables steering assistance by the motor 18 and the steering wheel 3 is steered. The motor 18 is provided with a rotation angle sensor 23 that detects the rotation angle of the rotor of the motor 18.

[0022] Examples of the torque applied to the output shaft 9 (an example of an object driven by the motor 18) include the motor torque applied by the motor 18 and the disturbance torque T other than the motor torque.lc . Disturbance torque T lc Including torsion bar torque T tb , Road load torque (road reaction torque) T rl , the friction torque T generated in the reducer 19 f etc. Torsion bar torque T tb It is torque applied to the output shaft 9 from the steering wheel 2 side by force applied to the steering wheel 2 by the driver, force generated by steering inertia, and the like.

[0023] Road load torque T rl It is a torque applied to the output shaft 9 from the steering wheel 3 side via the rack shaft 14 by the self-aligning torque generated in the tire, the force generated by the suspension and tire wheel alignment, the friction force of the rack and pinion mechanism, etc. The vehicle includes a charge coupled device (CCD) camera 25 mounted thereon that captures an image of the road ahead of the vehicle in the forward direction, a global positioning system (GPS) 26 that detects the position of the vehicle, a radar 27 that detects the road shape and obstacles, and a map information memory 28 that stores map information.

[0024] The CCD camera 25, GPS 26, radar 27, and map information memory 28 are connected to a superior electronic control unit (ECU) 201 that performs driving assistance control and automatic driving control. The superior ECU 201 performs surrounding environment recognition, vehicle position estimation, route planning, etc. based on information obtained by the CCD camera 25, GPS 26, and radar 27 and map information, and determines control target values ​​of steering and drive actuators.

[0025] In the present embodiment, the host ECU 201 sets a target automatic steering angle θ for automatic steering. c,cmda In the present embodiment, the automatic steering control is a control for making the vehicle travel along a target track, for example. The target automatic steering angle θ c,cmda is the target value of the steering angle for automatically driving the vehicle along the target track. c,cmda The process is well known and therefore will not be described in detail herein.

[0026] The target automatic steering angle θ set by the host ECU 201 c,cmda The torsion bar torque T detected by the torque sensor 12 is provided to the motor control ECU 202 via the vehicle network. tb The output signal from the rotation angle sensor 23 is input to the motor control ECU 202. The motor control ECU 202 controls the electric motor 18 based on such input signals and the information provided from the superior ECU 201.

[0027] Figure 2is a block diagram showing the electrical configuration of the motor control ECU 202. The motor control ECU 202 includes: a microcomputer 40, a drive circuit (converter circuit) 31 controlled by the microcomputer 40 to supply power to the motor 18, and a current detection circuit 32 that detects the current flowing through the motor 18 (hereinafter referred to as "motor current I").

[0028] The microcomputer 40 includes a CPU and a memory (such as a ROM, a RAM, and a nonvolatile memory), and executes a predetermined program to function as a plurality of functional processing units. The plurality of functional processing units include: a target assist torque setting unit 41, a basic target torque setting unit 42, a first correction unit 43, a second correction unit 44, a first reduction ratio division unit 45, an overall torque calculation unit 46, a torque control unit 47, a reduction ratio multiplication unit 48, a rotation angle calculation unit 49, a second reduction ratio division unit 50, a first compensation value calculation unit 51, and a second compensation value calculation unit 52.

[0029] The target assist torque setting unit 41 sets a target assist torque (assist control amount) T t as a target value of the assist torque required for manual steering. m,md The target assist torque setting unit 41 is based on the torsion bar torque T detected by the torque sensor 12. tb To set the target assist torque T m,md . Figure 3 The torsion bar torque T is shown in tb The target assist torque T is set m,md .

[0030] When the torsion bar torque T tb When the target assist torque T m,md is positive, and the motor 18 generates a steering assist force for left steering. tb When the target assist torque T m,md is negative, and the electric motor 18 generates a steering assist force for steering to the right. m,md is set so that its absolute value increases with the torsion bar torque T tb becomes larger as the absolute value of becomes larger.

[0031] The target assist torque setting unit 41 can set the torsion bar torque T tb Multiply by a preset constant to calculate the target assist torque T m,md . Back Figure 2 The rotation angle calculation unit 49 calculates the rotor rotation angle θ of the motor 18 based on the output signal from the rotation angle sensor 23. m The second reduction ratio division unit 50 calculates the rotor rotation angle θ mThe rotor rotation angle θ calculated by the rotation angle calculation unit 49 is divided by the reduction ratio N. m This is converted into the rotation angle θ of the output shaft 9 (actual steering angle).

[0032] The basic target torque setting unit 42 uses the target automatic steering angle θ provided from the host ECU 201. c,cmda The basic target torque T required for automatic steering is set by using the actual steering angle θ 0,ad Specifically, the basic target torque setting unit 42 sets the target automatic steering angle θ c,cmda The deviation Δθ (=θ c,cmda -θ) performs proportional-derivative calculation (PD calculation) to calculate the basic target torque T 0,ad .

[0033] The first correction unit 43 is based on the basic target torque T 0,ad The first compensation value w·T calculated by the first compensation value calculation unit 51 is subtracted from tb The symbol “w” indicates a weight. Therefore, the first basic target torque T can be obtained. 1,ad (torque of the output shaft 9), in the first basic target torque T 1,ad In the disturbance torque T lc Torsion bar torque T tb At least a portion of has been compensated. The first compensation value calculation unit 51 will be discussed later.

[0034] The second correction unit 44 is based on the first basic target torque T 1,ad The second compensation value calculated by the second compensation value calculation unit 52 is subtracted from Therefore, the second basic target torque T can be obtained. 2,ad (torque of the output shaft 9), in the second basic target torque T 2,ad The torsion bar torque T is not included. tb The disturbance torque T lc has been compensated. The second compensation value calculation unit 52 will be discussed later. In the present embodiment, the first correction unit 43 and the second correction unit 44 constitute a "correction unit" according to the present invention.

[0035] The first reduction ratio division unit 45 is formed by dividing the second basic target torque T 2,ad Divide by the reduction ratio N to calculate the target automatic steering torque T m,ad (Target torque of the electric motor 18). The overall torque calculation unit 46 calculates the target automatic steering torque T m,ad and the target assist torque T m,md Add to calculate the target overall torque T m,ma .

[0036] The torque control unit 47 drives the drive circuit 31 so that the motor torque of the electric motor 18 is closer to the target overall torque T m,ma The torque control unit 47 will be discussed in detail later. The reduction ratio multiplication unit 48 calculates the target automatic steering torque T calculated by the first reduction ratio division unit 45 by m,ad Multiply the reduction ratio N and set the target automatic steering torque T m,ad Converted into the target automatic output shaft torque N·T acting on the output shaft 9 (worm gear 21) m,ad .

[0037] The first compensation value calculation unit 51 is composed of a weight setting unit 53 and a weight multiplication unit 54. The weight multiplication unit 54 calculates the torsion bar torque T tb The first compensation value w·T is calculated by multiplying the weight w set by the weight setting unit 53. tb The weight w has a value greater than or equal to 0 and less than or equal to 1. The weight setting unit 53 basically sets the weight w to a relatively large value when the driver is not expected to intervene in the steering, and sets the weight w to a relatively small value when the driver is expected to intervene in the steering. In the present embodiment, for example, when the torsion bar torque T tb When the absolute value of is less than the predetermined value α and the driver has little intention to intervene in the steering, the weight setting unit 53 sets the weight w to 1, and when the torsion bar torque T tb When the absolute value of is equal to or greater than the predetermined value α and the driver has a strong intention to intervene in the steering, the weight w is set to 0.

[0038] The weight setting unit 53 can set the weight w according to whether the driver is gripping the steering wheel 2 or has released the steering wheel 2. Specifically, Figure 2 As indicated by the double-dashed line in FIG, a hand-on / hand-off determination unit 59 is provided for determining whether the driver is gripping the steering wheel 2 or has released the steering wheel 2. Then, the weight setting unit 53 sets the weight to 1 when the driver has released the steering wheel 2 (hands-off), and sets the weight to 0 when the driver is gripping the steering wheel 2 (hand-on).

[0039] The hands-on / hands-off determination unit 59 may determine whether the driver is holding the steering wheel 2 or has released the steering wheel 2 based on an output signal from a touch sensor (not shown) provided to the steering wheel 2, determine whether the driver is holding the steering wheel 2 or has released the steering wheel 2 based on an image captured by a camera (not shown) provided in the vehicle, etc. The hands-on / hands-off determination unit 59 may be configured in a manner different from that discussed previously, as long as the hands-on / hands-off determination unit 59 can determine whether the driver is holding the steering wheel 2 or has released the steering wheel 2.

[0040] In addition, in order not to allow the driver to intervene in the steering in an emergency, the weight setting unit 53 may set the weight w to 1, or in order to enable both automatic steering and manual steering, the weight w may be set to 0.5. The second compensation value calculation unit 52 is composed of a disturbance torque estimation unit 55 and a subtraction unit 56. The disturbance torque estimation unit 55 is based on the target automatic output shaft torque N·T calculated by the reduction ratio multiplication unit 48. m,ad and the actual steering angle θ calculated by the second reduction ratio division unit 50 to estimate the disturbance torque T lc . Disturbance torque T lc The estimated value of The subtraction unit 56 obtains the estimated disturbance torque value by Subtract the torsion bar torque T tb To calculate the second compensation value

[0041] The disturbance torque estimation unit 55 will be described in detail. The disturbance torque estimation unit 55 is constituted by a disturbance observer, which uses, for example, Figure 4 The physical model 101 of the electric power steering system 1 is shown to calculate the estimated disturbance torque value Estimated actual steering angle value and the estimated angular velocity The physical model 101 includes a device (an example of an object to be driven by a motor) 102 including an output shaft 9 and a worm gear 21 fixed to the output shaft 9. A torsion bar torque T , which is a torsional torque of the torsion bar 10, is provided to the device 102. tb and the road load torque T from the steering wheel 3 side rl The target automatic output shaft torque N·T from the motor is also provided to the device 102 via the worm gear 20 m,ad , and provides friction torque T to the device 102 through the friction between the worm wheel 21 and the worm gear 20 f .

[0042] When the inertia of the device 102 is defined as J, the motion equation of the inertia of the physical model 101 is expressed by the following formula (1).

[0043]

[0044] T lc =T tb +T rl +T f

[0045] d 2 θ / dt 2 is the angular acceleration of the device 102. N is the reduction ratio of the reducer 19. T lcIndicates the disturbance torque provided to the device 102. In this embodiment, the disturbance torque T lc Indicated as torsion bar torque T tb , road load torque T rl and friction torque T f However, in reality, the disturbance torque T lc Torques other than such torques are included.

[0046] Figure 4 The state equation of the physical model 101 in is expressed by the following formula (2).

[0047]

[0048] In formula (2), x is a state variable vector, u1 is a known input vector, u2 is an unknown input vector, and y is an output vector. In addition, in formula (2), A is a system matrix, B1 is a first input matrix, B2 is a second input matrix, C is an output matrix, and D is a direct matrix. The above state equation is extended to a system including an unknown input vector u2 as a state. The state equation of the extended system (extended state equation) is expressed by the following formula (3).

[0049]

[0050] In formula (3), x e is a state variable vector of the extended system and is expressed by the following formula (4).

[0051]

[0052] In formula (3), A e is the system matrix of the extended system, B e is the known input matrix of the expanded system, and C e is the output matrix of the extended system. The disturbance observer (extended state observer) represented by the following formula (5) is composed of the extended state equation of formula (3).

[0053]

[0054] In formula (5), Represents x e is an estimate of . L is the observer gain. represents the estimated value of y. It is expressed by the following formula (6).

[0055]

[0056] In formula (6), is an estimate of the actual steering angle θ, is an estimate of the angular velocity dθ / dt, and is the disturbance torque T lc The disturbance torque estimation unit 55 calculates the state variable vector based on the equation of formula (5): Figure 5 is a block diagram showing the configuration of the disturbance torque estimation unit 55 .

[0057] The disturbance torque estimation unit 55 includes an input vector input unit 61, an output matrix multiplication unit 62, a first addition unit 63, a gain multiplication unit 64, an input matrix multiplication unit 65, a system matrix multiplication unit 66, a second addition unit 67, an integration unit 68, and a state variable vector output unit 69. Figure 2 ) Calculated target automatic output shaft torque N·T m,ad The input vector input unit 61 outputs the input vector u1 to the input matrix multiplication unit 65. The target overall torque (target torque) T calculated by the overall torque calculation unit 46 can be used. m,ma Instead of the target automatic output shaft torque N·T m,ad .

[0058] The output from the integration unit 68 is the state variable vector (See formula (6)). When the calculation starts, the state variable vector For example, the state variable vector The initial value of is 0. The system matrix multiplication unit 66 converts the state variable vector Multiply by the system matrix A e The output matrix multiplication unit 62 converts the state variable vector Multiply by the output matrix C e .

[0059] The first adding unit 63 subtracts the output vector y from the output matrix multiplication unit 62 from the output vector y which is the actual steering angle θ. That is, the first adding unit 63 calculates the output vector y and the estimated output vector value The difference between The gain multiplication unit 64 converts the output from the first adding unit 63 into The input matrix multiplication unit 65 multiplies the input vector u1 output from the input vector input unit 61 by the input matrix B e The second adding unit 67 adds the output (B e u1), output from system matrix multiplication unit 66 and the output from the gain multiplication unit 64 Add to calculate the differential value of the state variable vector The integration unit 68 integrates the output from the second adding unit 67. The integration is performed to calculate the state variable vector The state variable vector output unit 69 is based on the state variable vector Calculate the estimated disturbance torque value Estimated actual steering angle value and the estimated angular velocity

[0060] A disturbance observer consisting of an inverse model of the device and a low-pass filter can be used instead of the previously discussed extended state observer. In this case, the motion equation of the device is represented by the previously discussed formula (1). Therefore, the inverse model of the device is indicated by the following formula (7).

[0061]

[0062] The input to the disturbance observer using the inverse model of the plant is J·d 2 θ / dt 2 and N.T. m,ad , and uses the second-order differential value of the actual steering angle θ, and is therefore significantly affected by the noise of the rotation angle sensor 23. In contrast, using the previously discussed extended state observer, the disturbance torque is estimated by integration, so the influence of the noise caused by differentiation can be advantageously reduced. Next, we will describe Figure 2 The torque control unit 47 in.

[0063] Figure 6 4 is a block diagram showing the configuration of the torque control unit 47. The torque control unit 47 includes a target motor current calculation unit 71, a current deviation calculation unit 72, a PI control unit 73, and a pulse width modulation (PWM) control unit 74. The target motor current calculation unit 71 calculates the target motor current by converting the target motor current into the target current. Figure 2 ) Calculate the target overall torque T m,ma The target motor current I is calculated by dividing by the torque constant Kt of the motor 18. cmd .

[0064] The current deviation calculation unit 72 calculates the target motor current I obtained by the target motor current calculation unit 71. cmd The deviation ΔI (=I cmdThe PI control unit 73 performs proportional integral calculation (PI calculation) on the current deviation ΔI calculated by the current deviation calculation unit 72 to generate a current deviation value for making the motor current I flowing through the electric motor 18 closer to the target motor current I cmd The PWM control unit 74 generates a PWM control signal having a duty ratio corresponding to the drive command value, and supplies the generated PWM control signal to the drive circuit 31. Thus, electric power corresponding to the drive command value is supplied to the motor 18.

[0065] In the previously discussed embodiments, the torsion bar torque T tb The disturbance torque T lc The estimated value of is calculated as the second compensation value and is always used as the basic target torque T 0,ad Compensation value (see Figure 2 . Therefore, it is possible to suppress a reduction in lane keeping performance due to disturbance torque during automatic steering.

[0066] On the other hand, for the torsion bar torque T as the steering torque applied to the steering system tb , by converting the torsion bar torque T tb The value obtained by multiplying the weight w is calculated as the first compensation value (w·T tb )(See Figure 2 The first compensation value calculation unit 51 and the first correction unit 43 in FIG. 4 are used. Therefore, appropriate tactile information can be provided to the driver. In other words, a human-machine interface (HMI) function can be implemented.

[0067] For example, in the case where the steering torque is compensated as it is (w=1), control is implemented to give priority to the system and ignore the driver's input, and in the case where the steering torque is not compensated as it is (w<1), control is implemented to receive the driver's input. That is, the degree of priority given to the system and the driver can be changed by adjusting the weight w, which enables cooperation between the person (driver) and the system.

[0068] Although the embodiments of the present invention have been described above, the present invention may be implemented in other embodiments. For example, in the previously discussed embodiment, the torsion bar torque T detected by the torque sensor 12 is tb However, the driver torque applied to the steering wheel 2 may be estimated, and the estimated driver torque may be used as the steering torque.

[0069] In addition, when the estimated steering torque is used, the three calculated values, namely, the actual steering angle θ, the target automatic output shaft torque N·T m,ad and torsion bar torque Ttb can be used as an input, and two compensation values, namely a first compensation value and a second compensation value, can be estimated using one observer. In addition, in the previously discussed embodiment, the present invention is applied to the motor control for a column-type EPS. However, the present invention can also be applied to the motor control of an EPS other than a column-type EPS. In addition, the present invention can also be applied to the control of an electric motor for steering angle control of a wire-controlled steer system.

[0070] Furthermore, the present invention may be subjected to various design changes without departing from the scope of the claims.

Claims

1. An electric power steering system (1), Features include: an electric motor (18) configured to apply motor torque to the steering system; a rotation angle detection unit (23) configured to detect a rotation angle of the motor (18); a current detection circuit (32) configured to detect a motor current flowing through the motor (18); a steering torque detection unit (12) configured to detect or estimate a steering torque applied to the steering system; a target torque setting unit (41) configured to set a target torque of the electric motor based on an automatic steering angle command value; a current command value setting unit configured to set a current command value corresponding to the target torque; as well as a current control unit configured to make the motor current follow the current command value, wherein: The target torque setting unit (41) comprises: a basic target torque setting unit (42), a first compensation value calculation unit (51), a second compensation value calculation unit (52) and a correction unit (43, 44); The basic target torque setting unit (42) is configured to set a basic target torque of the electric motor (18) so that the rotation angle of the electric motor (18) follows the automatic steering angle command value; The first compensation value calculation unit (51) is configured to set a first compensation value based on the steering torque; The second compensation value calculation unit (52) is configured to calculate a second compensation value based on the motor torque, the rotation angle and the steering torque, or based on the target torque, the rotation angle and the steering torque, the second compensation value being an estimated value of a disturbance torque other than the steering torque acting on the steering system; and The correction unit is configured to correct the basic target torque using the first compensation value and the second compensation value.

2. The electric power steering system according to claim 1, Features The first compensation value calculation unit (51) includes a weight setting unit (53) that sets a weight and a multiplication unit (54) that calculates the first compensation value by multiplying the steering torque by the weight.

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