JP2008114612A - Electric power steering device - Google Patents

Abstract

An electric power steering device capable of transmitting a target torque without losing output torque of an electric motor even at high output.
An elastic member provided on a worm shaft is elastically deformed based on an angle relative difference Δθ between an angle θm of a motor angle sensor mounted on the electric motor 12 and an angle θw of an angle sensor disposed on the worm wheel. The amount β is estimated, and a current correction value Ia for correcting the current command value It of the electric motor 12 is calculated based on the elastic deformation amount β. Then, by driving and controlling the electric motor 12 based on the corrected current command value Ir (= It + Ia), the output of the electric motor 12 is corrected to compensate for a decrease in output torque caused by elastic deformation of the elastic member. .
[Selection] Figure 1

Description

  The present invention relates to an electric power steering apparatus that applies a steering assist force to a steering system, and more particularly to an electric power steering apparatus that reduces a collision sound (rattle sound) between tooth surfaces caused by backlash of a reduction gear. Is.

  Conventionally, a steering angle control unit that makes the transmission ratio between the rotation angle of the steering wheel and the rotation angle of the wheel steering shaft variable, and assisting the rotation of the wheel steering shaft by the driving force of the assist motor and operating the steering handle There is known a steering control device including an electric power steering control unit that rotationally controls the motor so that a steering angle corresponding to the angle is obtained (see, for example, Patent Document 1).

  There is also known a control method for an electric power steering apparatus for an automobile that automatically corrects the steering angle in accordance with the traveling speed in a braking state of the vehicle and the rotation state of each wheel (see, for example, Patent Document 2). Here, a cooperative steering angle for coordinating with the braking state is set based on the traveling speed, and a target steering angle for performing the automatic correction is set based on the set emphasis steering angle and the actual steering angle of the steering wheel. It is set so that the actual steering angle follows the target steering angle.

Further, as a conventional electric power steering device, there is known that a correction value set based on steering assist thrust and stored in an EEPROM corrects a target current value corresponding to a driving current value of a motor or a handle operating force. (For example, see Patent Document 3).
JP 2004-330841 A JP 2002-220065 A Japanese Patent No. 3390360

  By the way, in the electric power steering apparatus as described in the above Patent Documents 1 to 3, the rotation output of the electric motor serving as the steering assist torque is decelerated by the gear device and transmitted to the output shaft of the steering mechanism, thereby steering. In general, the steering force applied to the wheel is assisted to steer the wheel. In such an electric power steering apparatus, power is transmitted to the output shaft while reducing the rotation of the electric motor using a power transmission mechanism provided in the housing.

When the worm gear speed reduction mechanism is used as the power transmission mechanism, the teeth of the worm and the worm wheel are changed when the power transmission direction changes according to the steering wheel steering or when a large vibration is transmitted from the wheel to the worm wheel. The backlash existing between the surfaces generates a collision sound between the tooth surfaces (rattle sound), which may give the driver discomfort.
Therefore, a rubber damper or a pressurized damper is installed on the worm shaft on which the worm is formed, and measures are taken to actively reduce the rattle noise.

However, in this case, at the time of high output of the electric motor such as stationary steering, when the rotation output of the electric motor is transmitted through the gear, the damper is elastically deformed and the output torque is lost. A situation occurs in which the target torque cannot be transmitted.
Accordingly, an object of the present invention is to provide an electric power steering device that enables target torque transmission without losing the output torque of the electric motor even at high output.

  In order to solve the above problems, an electric power steering apparatus according to a first aspect of the present invention is directed to an electric motor that applies a steering assist force that reduces a driver's steering burden to a steering system, and a worm that urges the worm against the worm wheel. An electric power steering apparatus having an elastic member for applying pressure and a worm gear reduction mechanism for reducing the rotational output of the electric motor and transmitting it to a steering shaft, and estimating an elastic deformation amount of the elastic member And an output correcting means for correcting the output of the electric motor based on the elastic deformation amount estimated by the elastic deformation amount estimating means.

  According to a second aspect of the present invention, there is provided the electric power steering apparatus according to the first aspect of the present invention, wherein the electric power steering device is disposed on the worm wheel and detects the steering angle by being arranged on the worm wheel and the motor rotation angle detecting means for detecting the motor rotation angle of the electric motor. Rudder angle detecting means, and the elastic deformation amount estimating means is based on an angular difference between a motor rotation angle detected by the motor rotation angle detecting means and a rudder angle detected by the rudder angle detecting means. It is characterized by estimating the amount of deformation.

  Furthermore, the electric power steering apparatus according to claim 3 is the invention according to claim 1 or 2, wherein the steering torque detecting means for detecting the steering torque and the current command value of the electric motor are calculated based on at least the steering torque. A current command value calculating means; and a motor control means for driving and controlling the electric motor based on the current command value. The output correcting means is calculated by the current command value calculating means based on the elastic deformation amount. The output of the electric motor is corrected by correcting the current command value.

According to a fourth aspect of the present invention, in the electric power steering apparatus according to any one of the first to third aspects, the output correction means increases the output of the electric motor as the elastic deformation amount increases. It is characterized by correcting as follows.
Furthermore, the electric power steering apparatus according to a fifth aspect is the invention according to any one of the first to fourth aspects, wherein the output correction means uses at least one of a steering torque, a differential value of the steering torque, and a vehicle speed as a parameter. As described above, the output of the electric motor is corrected.

  According to the electric power steering apparatus of the present invention, the elastic deformation amount of the elastic member provided on the worm shaft is estimated, and the output of the electric motor is corrected based on the elastic deformation amount. The elastic member is elastically deformed to compensate for a decrease in output torque caused by absorbing torque to be transmitted to the steering wheel, and the target steering assist force can be appropriately applied. can get.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram showing an embodiment of an electric power steering apparatus according to the present invention.
In the figure, reference numeral 1 denotes a steering wheel, and a steering force applied to the steering wheel 1 from a driver is transmitted to a steering shaft 2 having an input shaft 2a and an output shaft 2b. The steering shaft 2 has one end of the input shaft 2 a connected to the steering wheel 1 and the other end connected to one end of the output shaft 2 b via the torque sensor 3.

  The steering force transmitted to the output shaft 2 b is transmitted to the lower shaft 5 via the universal joint 4 and further transmitted to the pinion shaft 7 via the universal joint 6. The steering force transmitted to the pinion shaft 7 is transmitted to the tie rod 9 via the steering gear 8 and steers steered wheels (not shown). Here, the steering gear 8 is configured in a rack and pinion type having a pinion 8a connected to the pinion shaft 7 and a rack 8b meshing with the pinion 8a, and the rotational motion transmitted to the pinion 8a is linearly moved by the rack 8b. It has been converted to movement.

A steering assist mechanism 10 for transmitting a steering assist force to the output shaft 2b is connected to the output shaft 2b of the steering shaft 2. The steering assist mechanism 10 includes a reduction gear 11 coupled to the output shaft 2b, and an electric motor 12 coupled to the reduction gear 11 and generating a steering assist force with respect to the steering system.
Here, the reduction gear 11 is a worm gear reduction mechanism that meshes with a worm shaft connected to the drive shaft of the electric motor 12 and a worm formed on the worm shaft, decelerates the rotation of the worm, and outputs the output shaft of the steering shaft 2. And a worm wheel for transmission to 2b.

The worm shaft is also provided with a rubber damper that urges the worm to apply pressure to the worm wheel and an elastic member that acts as a pressure damper. Hereinafter, it is called a rattle sound).
A steering angle sensor 14 composed of an angle sensor or the like is disposed on the worm wheel, and the steering angle detection value θw detected by the steering angle sensor 14 is input to the steering assist control device 20.

  The torque sensor 3 detects a steering torque applied to the steering wheel 1 and transmitted to the input shaft 2a, and a torsional angle displacement of a torsion bar (not shown) in which the steering torque is interposed between the input shaft 2a and the output shaft 2b. The torsional angular displacement is detected by, for example, a potentiometer. The detected torque value T output from the torque sensor 3 is input to the steering assist control device 20.

  In addition to the torque detection value T and the steering angle detection value θw, the steering assist control device 20 also receives a motor rotation angle θm of the electric motor 12 detected by the hall sensor 13 and a vehicle speed detection value V detected by the vehicle speed sensor 16. Is done. Then, the steering assist control device 20 performs steering assist force control for drivingly controlling the electric motor 12 so that a steering assist force corresponding to the input torque detection value T and vehicle speed detection value V is applied to the steering system.

At this time, based on the angle difference between the motor rotation angle θm and the detected steering angle value θw, the elastic deformation amount of the elastic member provided on the worm shaft is estimated, and the electric motor 12 of the electric motor 12 is estimated according to the elastic deformation amount. The output is corrected.
In FIG. 1, a torque sensor 3 corresponds to steering torque detection means, a hall sensor 13 corresponds to motor rotation angle detection means, and a steering angle sensor 14 corresponds to steering angle detection means.

FIG. 2 is a block diagram illustrating a configuration of the steering assist control device 20. As shown in FIG. 2, the steering assist control device 20 includes a current command value calculation unit 21, an adder 22, a current feedback corrector 23, a current control unit 24, a motor drive unit 25, and an elastic deformation amount. An estimator 26 and a current correction value calculator 27 are provided.
The current command value calculation unit 21 refers to the steering assist current command value calculation map shown in FIG. 3 on the basis of the torque detection value T detected by the torque sensor 3 and the vehicle speed detection value V detected by the vehicle speed sensor 16, and the electric motor 12 is calculated and output to the adder 22.

  Here, the steering assist current command value calculation map has a steering torque T on the horizontal axis, a current command value It on the vertical axis, and a characteristic line represented by a parabolic curve with the vehicle speed detection value V as a parameter. The current command value It is maintained at “0” when the steering torque T is “0” to a set value Ts1 in the vicinity thereof. When the steering torque T exceeds the set value Ts1, the current command value is initially set. It increases relatively slowly with respect to the increase in steering torque T, but when the steering torque T further increases, the current command value It is set so as to increase sharply with respect to the increase. The inclination is set to decrease as the vehicle speed increases.

The adder 22 corrects the current command value It by adding a current correction value Ia output from a current correction value calculation unit 27 described later to the current command value It output from the current command value calculation unit 21, The result is output to the current feedback corrector 23 as the current command value Ir.
The current feedback corrector 23 feeds back the motor current Im detected by the motor current detector 15 to the current command value Ir, and corrects the current feedback based on the deviation (= Ir−Im) between the current command value Ir and the motor current Im. The value Iout is calculated and output to the current control unit 24.

The current control unit 24 calculates the duty ratio E of the PWM signal that drives the semiconductor switching element of the motor drive unit 25 based on the current feedback correction value Iout, and outputs it to the motor drive unit 25.
The motor drive unit 25 drives the electric motor 12 by operating an H bridge circuit composed of semiconductor switching elements based on the duty ratio E.

Further, the elastic deformation amount estimation unit 26 is based on the angle relative difference calculation unit 26a that calculates the angle relative difference Δθ (= θm−θw) between the motor rotation angle θm and the steering angle detection value θw, and the angle relative difference Δθ. And an elastic deformation amount output unit 26b that estimates and outputs the elastic deformation amount β of the elastic member.
Here, the elastic deformation amount output unit 26b estimates the elastic deformation amount β with reference to the elastic deformation amount estimation map shown in FIG. This elastic deformation amount estimation map is set such that the horizontal axis indicates the angular relative difference Δθ, the vertical axis indicates the elastic deformation amount β, and the larger the angular relative difference Δθ, the larger the elastic deformation amount β is calculated.

The current correction value calculation unit 27 calculates the current correction value Ia with reference to the current correction value calculation map shown in FIG. 5 based on the elastic deformation amount β that is the output of the elastic deformation amount output unit 26b, and calculates the current correction value Ia. Output to the adder 22.
In the current correction value calculation map, the horizontal axis represents the elastic deformation amount β, the vertical axis represents the current correction value Ia, the elastic deformation amount β ≦ β1 is fixed to Ia = 0, β ≧ β2 is fixed to Ia = Ia _MAX , and β1 < The current correction value Ia is set to increase proportionally from 0 to Ia _{MAX as} β <β2 and the elastic deformation amount β increases.

Here, the elastic deformation threshold β1 is an elastic deformation amount when the angular relative difference Δθ = θ1, and the elastic deformation threshold β2 is an elastic deformation amount when the angular relative difference Δθ = θ2. That is, the current correction value Ia is fixed to Ia = 0 when Δθ ≦ θ1 and is fixed to Ia = Ia _MAX when Δθ ≧ θ2, and is set to Ia = Δθ × Ia ₀ (Ia ₀ is a fixed value) when θ1 <Δθ <θ2. Will be.
As described above, the elastic deformation amount of the elastic member is estimated based on the different angle information, and the output torque corresponding to the elastic deformation amount is compensated by correcting the output (current command value) of the electric motor 12.

In FIG. 2, a current command value calculation unit 21 corresponds to a current command value calculation unit, a current feedback corrector 23, a current control unit 24, and a motor drive unit 25 correspond to a motor control unit, and an elastic deformation amount estimation unit 26 Corresponding to the elastic deformation amount estimating means, the adder 22 and the current correction value calculating section 27 correspond to the output correcting means.
Next, the operation and effect of this embodiment will be described.

  Now, it is assumed that the driver starts operating the steering wheel relatively large. In this case, first, the current command value calculation unit 21 calculates the current command value It from the steering assist current command value calculation map of FIG. 3 based on the torque detection value T and the vehicle speed detection value V. Since the electric motor 12 is not driven at the start of steering and the angle deviation Δθ between the motor rotation angle θm of the electric motor 12 and the detected value θw of the steering angle sensor 14 disposed on the worm wheel is 0, the amount of elastic deformation The estimation unit 26b estimates that the amount of elastic deformation β is “0” based on FIG. Therefore, since the current correction value Ia = 0 is output from the current correction value calculation unit 27, the current command value It is not corrected by the current correction value Ia, and the current command value It becomes the current command value Ir as it is. Then, the electric motor 12 is drive-controlled based on the current command value Ir, and the generated torque of the electric motor 12 is converted into the rotational torque of the steering shaft 2 via the reduction gear 11 to assist the driver's steering force. The

By the way, in the electric power steering device, since the steering assist force is generated via the worm gear reduction mechanism, for example, when the transmission direction of power changes according to the steering of the steering wheel, or when a large impact or vibration is generated from the wheel. When transmitted to the worm wheel, rattle noise is generated due to gear backlash.
In order to reduce the rattle noise, an elastic member that urges the worm to apply pressure to the worm wheel is generally provided on the worm shaft. It is known that the greater the output, the greater the elastic deformation.

  FIG. 6 is a diagram illustrating a change in output characteristics due to elastic deformation of the elastic member. In the figure, a thick line (A) indicates a target output characteristic, and a thin line (B) indicates an actual output characteristic. As shown in FIG. 6, when the input torque is small, the actual output characteristic matches the target output characteristic. However, as the input torque increases, the actual output torque decreases with respect to the target output torque. That is, the output torque loss increases.

  This is because when the electric motor 12 generates rotational torque based on the current command value Ir, the torque acting in the axial direction and rotational direction transmitted to the worm shaft is absorbed by the elastic deformation of the elastic member itself, and the steering shaft This is because the torque to be transmitted to the second output shaft 2b is reduced. This phenomenon appears remarkably in the vicinity of stationary steering, and the column output torque or the rack output thrust becomes lower than the target value, resulting in a situation where the steering force becomes heavy.

As described above, the gain of the system characteristic indicating the relationship between the column output torque and the rack output thrust with respect to the input torque tends to be lower than the setting of the assist characteristic (relation between the input torque and the motor current command value).
Therefore, it is conceivable to compensate the system characteristics by increasing the gain of the torque sensor characteristics instead. However, in this case, increasing the gain of the torque sensor increases the sensitivity of the control system and may cause oscillation.

On the other hand, in the present embodiment, the elastic deformation amount β of the elastic member arranged on the worm shaft is estimated, and the output torque of the elastic deformation is corrected by correcting the output of the electric motor 12 based on the elastic deformation amount β. Is compensated for so that the target output characteristics can be obtained.
The elastic deformation amount β of the elastic member appears as a deviation between the angle of the motor angle sensor mounted on the electric motor 12 itself and the angle sensor disposed on the worm wheel. Accordingly, the angle relative difference calculation unit 26a calculates the angle relative difference Δθ based on the motor rotation angle θm and the steering angle detection value θw, and the elastic deformation amount estimation unit 26b then elastically deforms based on the angle relative difference Δθ. The quantity β is estimated.

Here, assuming that the elastic deformation amount β is estimated to be relatively large, the current correction value calculation unit 27 calculates a relatively large current correction value Ia based on the current correction value calculation map of FIG. A value obtained by adding the current correction value Ia to the current command value It is output as the current command value Ir, and the electric motor 12 is driven and controlled based on the current command value Ir.
Here, as shown in the current correction value calculation map of FIG. 5, the current correction value Ia is calculated to be larger as the elastic deformation amount β is larger. Therefore, the current command value It is corrected to be larger as the elastic deformation amount β is larger. As a result, the output torque of the electric motor 12 increases, and as a result, the output torque loss due to elastic deformation is effectively offset.

Thus, in the above embodiment, the amount of elastic deformation of the elastic member provided on the worm shaft is estimated, and the output torque of the electric motor is corrected based on this amount of elastic deformation. A decrease in output torque caused by elastic deformation of the elastic member can be compensated, and the target steering assist torque can be reliably output.
Further, since the elastic deformation amount of the elastic member is estimated based on the difference between the angle of the motor angle sensor mounted on the electric motor and the angle sensor arranged on the worm wheel, the electric motor is based on the current command value. When the rotational torque generated in this way is transmitted to the worm wheel, it is possible to appropriately estimate the torque absorbed by the elastic member, that is, the loss of the output torque.

Furthermore, by correcting the current command value of the electric motor based on the elastic deformation amount of the elastic member, the output of the electric motor is corrected, so that the control system oscillation is prevented and the stability of the system is ensured. A target output characteristic can be obtained.
Further, since the current command value of the electric motor is corrected in the direction in which the output of the electric motor increases as the elastic deformation amount of the elastic member increases, the loss of the output torque due to the elastic deformation can be appropriately compensated.

  In the above embodiment, the current correction value calculation unit 27 can also calculate the current correction value Ia using the steering torque T, the differential value T ′ of the steering torque, and the vehicle speed detection value V as parameters. In this case, the configuration of the steering assist control device 20 is as shown in FIG. 7, and the steering torque T detected by the torque sensor 3, the steering torque differential value T ′ obtained by differentiating the steering torque T by the differentiation circuit 29, and the vehicle speed sensor 16. Except that the detected vehicle speed detection value V is input to the current correction value calculation unit 27, it has the same configuration as the steering assist control device 20 shown in FIG.

  The current correction value calculation unit 27 calculates parameters K1 to K3 corresponding to the steering torque T, the steering torque differential value T ′, and the vehicle speed detection value V with reference to the parameter determination maps shown in FIGS. To do. Then, the final current correction value Ia is calculated from the current correction value Ia calculated based on the above-described current correction value calculation map of FIG. 5 based on the elastic deformation amount β and the parameters K1 to K3 (for example, Ia = (K1 + K2 + K3) × Ia), which is output to the adder 22. Thus, the current command value It can be corrected more appropriately according to the steering situation by the driver and the running situation of the vehicle.

  In the above embodiment, the motor rotation angle θm is detected using the hall sensor. However, a three-phase brushless motor is applied as the electric motor, and the motor rotation angle θm is detected using a resolver, an encoder, or the like. You can also

1 is a schematic configuration diagram of a vehicle in an embodiment of the present invention. It is a block diagram which shows the structure of the steering assistance control apparatus in this embodiment. It is a steering auxiliary current command value calculation map. It is an elastic deformation amount estimation map. It is an electric current correction value calculation map. It is a figure which shows the change of the output characteristic by the elastic deformation of an elastic member. 4 is a block diagram illustrating another example of the steering assist control device 20. FIG. It is a parameter determination map.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steering wheel, 2 ... Steering shaft, 3 ... Torque sensor, 10 ... Steering assist mechanism, 11 ... Reduction gear, 12 ... Electric motor, 13 ... Hall sensor, 14 ... Steering angle sensor, 16 ... Vehicle speed sensor, 20 ... Steering Auxiliary control device, 21 ... current command value calculation unit, 22 ... adder, 23 ... current feedback corrector, 24 ... current control unit, 25 ... motor drive unit, 26 ... elastic deformation amount estimation unit, 26a ... angular relative difference calculation Part, 26b ... elastic deformation amount output part, 27 ... current correction value calculation part

Claims (5)

An electric motor that applies a steering assisting force that reduces a driver's steering burden to the steering system; and an elastic member that applies a pressure to the worm wheel by energizing the worm, and the rotational output of the electric motor An electric power steering device comprising a worm gear speed reduction mechanism that decelerates and transmits to a steering shaft,
An elastic deformation amount estimating means for estimating an elastic deformation amount of the elastic member, and an output correcting means for correcting the output of the electric motor based on the elastic deformation amount estimated by the elastic deformation amount estimating means. Electric power steering device.   A motor rotation angle detection unit that detects a motor rotation angle of the electric motor; a steering angle detection unit that is disposed on the worm wheel and detects a steering angle; and the elastic deformation amount estimation unit includes the motor rotation angle. 2. The electric power steering apparatus according to claim 1, wherein the elastic deformation amount is estimated based on an angle difference between a motor rotation angle detected by a detection means and a steering angle detected by the steering angle detection means.   Steering torque detection means for detecting steering torque, current command value calculation means for calculating a current command value of the electric motor based on at least the steering torque, and motor control for driving and controlling the electric motor based on the current command value And the output correction unit corrects the output of the electric motor by correcting the current command value calculated by the current command value calculation unit based on the elastic deformation amount. The electric power steering apparatus according to claim 1 or 2.   The electric power steering apparatus according to any one of claims 1 to 3, wherein the output correction unit corrects the output of the electric motor to increase as the elastic deformation amount increases.   5. The output correction unit according to claim 1, wherein the output correction unit corrects the output of the electric motor using at least one of a steering torque, a differential value of the steering torque, and a vehicle speed as a parameter. 6. Electric power steering device.

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