JP2010188882A - Power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power steering device having high efficiency and good steering feeling. <P>SOLUTION: An electric motor 24 for driving a hydraulic pump 22 for generating steering assist force is PWM controlled by an ECU 25. The ECU 25 is equipped with a driving method switching part 38 alternately switching a driving method between an 120-degree energizing method and an 180-degree energizing method. The driving method switching part 38 includes a normal control part 381 switching the driving method according to actual rotation speed ω computed by an actual rotation speed computing part 35, and an optimizing control part 382 switching the driving method according to a target rotation acceleration α computed by a target rotation acceleration computing part 40 regardless of switching by the normal control part 381. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a power steering device that generates a steering assist force by driving a hydraulic pump by an electric motor.

  In a power steering device that assists the operation of a steering wheel by supplying hydraulic oil from a hydraulic pump to a power cylinder connected to a steering mechanism such as a rack and pinion mechanism, as a driving source of the hydraulic pump, for example, three-phase There is a case where an electric motor including a brushless motor is used. In this case, the drive power supplied to the electric motor is controlled so that the electric motor is rotated at a target rotational speed corresponding to the steering speed of the steering wheel.

  It has been proposed to switch the driving method of the electric motor between a 120-degree energization method and a 180-degree energization method (see, for example, Patent Document 1).

Japanese Patent No. 4016835

For example, it is conceivable to switch between the 120-degree energization method and the 180-degree energization method according to the actual rotation speed (actual rotation speed) of the electric motor. That is, in the low rotation speed region, the 120-degree energization method can improve energy saving (high efficiency), and in the high rotation speed region, sufficient torque can be secured as the 180-degree energization method.
However, at 120 degrees energization, the actual rotation speed may not sufficiently follow the target rotation speed, and the steering feeling may be deteriorated or the steering assist force may be insufficient (insufficient assist). More specifically, when the electric motor is driven by the 120-degree energization method, when the high-speed steering is performed and the target rotational speed rapidly increases accordingly, the actual rotational speed is sufficiently higher than the target rotational speed. May not follow. This is due to the hydraulic load from the system. Accordingly, it may take a relatively long time for the actual rotational speed to reach the switching threshold value for the 180-degree energization method, or the switching threshold value may not be reached. As a result, a sufficient steering assist force cannot be ensured during high-speed steering, and a so-called “striking feeling” is produced in the steering feeling, resulting in poor steering feeling.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a power steering device that is highly efficient and excellent in steering feeling.

  In order to solve the above-mentioned problems, the present invention PWMs an electric motor (24) for driving a hydraulic pump (22) that generates a steering assist force and a drive current supplied from the drive circuit (26) to the electric motor. And a motor control device (25) for controlling and rotating the electric motor at a target rotational speed, wherein the motor control device alternatively selects a 120-degree energization method and a 180-degree energization method as the electric motor drive method. Drive method switching means (38) for switching, actual rotation speed calculation means (35) for calculating the actual rotation speed of the electric motor, and target acceleration calculation means (40) for calculating the target rotation acceleration of the electric motor, The drive system switching means (38) includes a normal control section (381) that switches the drive system based on the actual rotation speed calculated by the actual rotation speed calculation means, and the normal control section. Is characterized in that comprises a optimization control unit for switching the driving mode based on the target rotational acceleration calculated by Notwithstanding the target acceleration calculating means exchange (382).

  In the present invention, regardless of switching of the normal control unit based on the actual rotation speed (actual rotation speed of the electric motor) calculated by the actual rotation speed calculation means, based on the target rotation acceleration calculated by the target acceleration calculation means. To optimize the drive system. Therefore, for example, when the target rotational speed increases rapidly, the energization method can be switched without waiting for the actual rotational speed to follow. As a result, even if the target rotational acceleration is large and therefore the load on the electric motor becomes large, it is possible to quickly switch to the 180-degree energization method, so that the actual rotational speed of the electric motor is accurately set to the target rotational speed. The steering feeling can be improved by following the vehicle. Further, for example, when the target rotation speed is suddenly decreased, the 120-degree energization method can be quickly switched without waiting for the actual rotation speed to follow. Thereby, the efficiency of the electric motor can be improved. In this way, a power steering device with high efficiency and excellent steering feeling can be realized by switching the energization method by the normal control unit and the optimization control unit.

  When driving the electric motor in the 120-degree energization method, the optimization control is performed when the target rotational acceleration (α) calculated by the target acceleration calculating means is equal to or greater than the first threshold (α1) (α ≧ α1). It is preferable that the unit switches the drive system to a 180-degree energization system (claim 2). When the target rotational acceleration is large, the load that the electric motor receives from the system increases. Therefore, when the electric motor is driven by the 120-degree energization method, even if the actual rotational speed of the electric motor is low, the optimization control unit switches to the 180-degree energization method if the target rotational acceleration is large. As a result, the electric motor does not run out of torque. As a result, the followability of the actual rotational speed of the electric motor can be improved. In addition, the steering feeling can be improved by suppressing the so-called “striking feeling” in the steering feeling.

  When the target rotational acceleration (α) calculated by the target acceleration calculating means becomes equal to or less than the second threshold (α2) (α ≦ α2) when the electric motor is driven by the 180-degree energization method, On the condition that the actual rotation speed (ω) calculated by the rotation speed calculation means is within the range of rotation speed that can be driven by the 120-degree energization method (ω <ω1), the optimization control unit sets the drive method to 120. It is preferable to switch to a current energization method (claim 3).

  If the target rotational acceleration is small (especially when the target rotational acceleration is negative), the load on the electric motor is small. Therefore, it is more energy efficient to adopt the 120-degree energization method. Therefore, when the target rotational acceleration is small when the electric motor is driven by the 180-degree energization method, the optimization control unit is selected if the actual rotation speed of the electric motor falls within the range of the rotational speed that can be driven by the 120-degree energization method. Immediately switches to the 120-degree energization method. Thereby, energy saving can be aimed at and the efficiency of an electric motor can be improved.

In the above description, the alphanumeric characters in parentheses represent reference numerals of corresponding components in the embodiments described later, but the scope of the claims is not limited by these reference numerals.
The target acceleration calculating means may calculate the target rotational acceleration based on the target rotational speed (for example, by differentiating the target rotational speed with respect to time). The power steering device may further include a steering speed detecting means for detecting a steering speed of an operating member operated by a driver for steering the vehicle. In this case, the target acceleration calculating means may calculate a target rotational acceleration according to the steering speed, or may calculate a target rotational acceleration based on the target rotational speed. . The power steering apparatus may further include target rotation speed setting means for setting the target rotation speed in accordance with the steering speed detected by the steering speed detection means. In this case, if the target rotational acceleration is calculated based on the target rotational speed, the target rotational acceleration has a value corresponding to the steering speed.

It is a mimetic diagram showing a schematic structure of a power steering device concerning one embodiment of the present invention. It is a schematic diagram of an electric motor and ECU. In this Embodiment, it is a timing chart which shows the change of an actual rotational speed, a target rotational speed, a target rotational acceleration, and a drive system. It is a timing chart which shows the change of an actual rotational speed, a target rotational speed, and a drive system in a comparison form. It is the schematic of the electric motor and ECU in another embodiment of this invention.

Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of a power steering apparatus according to an embodiment of the present invention. With reference to FIG. 1, the power steering apparatus 1 is provided in association with a steering mechanism 2 of a vehicle, and is for applying a steering assist force to the steering mechanism 2.
The steering mechanism 2 includes a steering wheel 3 as an operation member operated by a driver for steering the vehicle, a steering shaft 4 connected to the steering wheel 3, and a hydraulic control valve at the tip of the steering shaft 4. 14, a pinion shaft 5 having a pinion gear 6 connected thereto, and a rack shaft 7 having a rack gear portion 7a meshing with the pinion gear 6 and extending in the left-right direction of the vehicle.

Tie rods 8 are connected to both ends of the rack shaft 7, and the tie rods 8 are connected to knuckle arms 11 that support the left and right steered wheels 9 and 10, respectively. The knuckle arm 11 is provided to be rotatable around the kingpin 12.
When the steering wheel 3 is operated and the steering shaft 4 is rotated, this rotation is converted into a linear motion along the axial direction X1 of the rack shaft 7 by the pinion gear 6 and the rack gear portion 7a. This linear motion is converted into rotation around the kingpin 12 of the knuckle arm 11, thereby achieving the turning of the left and right steered wheels 9 and 10.

  The hydraulic control valve 14 is a rotary valve, and connects a sleeve valve body (not shown) connected to the steering shaft 4, a shaft valve body (not shown) connected to the pinion shaft 5, and both valve bodies. And a torsion bar (not shown). The torsion bar twists according to the direction and magnitude of the steering torque applied to the steering wheel 3, and the opening degree of the hydraulic control valve 14 changes according to the twist direction and magnitude of the torsion bar.

  The hydraulic control valve 14 is connected to a power cylinder 15 that applies a steering assist force to the steering mechanism 2. The power cylinder 15 has a piston 16 provided integrally with the rack shaft 7 and a pair of cylinder chambers 17 and 18 defined by the piston 16, and the cylinder chambers 17 and 18 respectively correspond to each other. It is connected to the hydraulic control valve 14 through oil passages 19 and 20.

  The hydraulic control valve 14 is further interposed in the middle of an oil circulation path 23 that passes through a reservoir tank 21 and a hydraulic pump 22 for generating a steering assist force. The hydraulic pump 22 is composed of, for example, a gear pump, is driven by the electric motor 24, draws hydraulic oil stored in the reservoir tank 21, and supplies the hydraulic oil to the hydraulic control valve 14. Excess hydraulic oil is returned from the hydraulic control valve 14 to the reservoir tank 21 via the oil circulation path 23.

The electric motor 24 is driven to rotate in one direction to drive the hydraulic pump 22. Specifically, the output shaft of the electric motor 24 is connected to the input shaft of the hydraulic pump 22, and the output shaft of the electric motor 24 rotates, whereby the input shaft of the hydraulic pump 22 rotates and the hydraulic pump. 22 drives are achieved.
The hydraulic control valve 14 supplies hydraulic oil to one of the cylinder chambers 17 and 18 of the power cylinder 15 via one of the oil passages 19 and 20 when a torsion bar is twisted in one direction. At the same time, the other hydraulic oil is returned to the reservoir tank 21. When a twist in the other direction is applied to the torsion bar, the other of the oil passages 19 and 20 is
While supplying hydraulic oil to the other of the cylinder chambers 17 and 18, one hydraulic oil is returned to the reservoir tank 21.

  When the torsion bar is hardly twisted, the hydraulic control valve 14 is in an equilibrium state, so that the cylinder chambers 17 and 18 of the power cylinder 15 are maintained at the same pressure in the steering neutral state, and the hydraulic oil is supplied to the oil circulation path. 23 is circulated. When both valve bodies of the hydraulic control valve 14 are rotated relative to each other by steering, hydraulic oil is supplied to one of the cylinder chambers 17 and 18 of the power cylinder 15 and the piston 16 moves along the vehicle width direction. As a result, a steering assist force acts on the rack shaft 7.

  The electric motor 24 is a three-phase brushless motor. Driving of the electric motor 24 is controlled by an ECU (electronic control unit) 25 as a motor control device. The ECU 25 includes a drive circuit 26 that generates drive power for the electric motor 24, and a control unit 27 that controls the drive circuit 26. The control unit 27 is composed of a microcomputer including a CPU and a memory storing an operation program for the CPU.

The control unit 27 of the ECU 25 is supplied with an output signal of the steering angle sensor 13 as a steering angle detection means and an output signal of the rotational position sensor 30 that detects the rotational position of the rotor of the electric motor 24. ing.
The steering angle sensor 13 is attached to the steering shaft 4 so as to detect the steering angle of the steering wheel 3, and gives an output signal to the control unit 27. The control unit 27 calculates the rotational speed (actual rotational speed) of the output shaft of the electric motor 24 based on the signal given from the rotational position sensor 30.

Further, the control unit 27 is given an output signal of a vehicle speed sensor 31 as vehicle speed detection means for detecting the speed of the vehicle. The vehicle speed sensor 31 may directly detect the speed of the vehicle, or obtains the speed of the vehicle by calculation based on output pulses of wheel speed sensors provided in association with the steered wheels 9 and 10. It may be a thing.
The ECU 25 controls the driving of the electric motor 24 so that an appropriate steering assist force is applied to the steering mechanism 2 based on signals given from the steering angle sensor 13, the rotational position sensor 30 and the vehicle speed sensor 31.

  FIG. 2 is a schematic diagram showing a configuration of the ECU 25 as a motor control device. The electric motor 24 includes a stator having a U-phase field coil 24U, a V-phase field coil 24V, and a W-phase field coil 24W, and a permanent magnet that receives a repulsive magnetic field from the field coils 24U, 24V, and 24W. And a rotor that has been made. The rotational position of the rotor is detected by the rotational position sensor 30. The rotational position sensor 30 can detect the rotational position of the rotor with a resolution of 30 deg / 360 deg (= 1/12) or higher, and the detection signal is input to the control unit 27.

  The drive circuit 26 is a three-phase bridge inverter circuit, and a series circuit of a pair of field effect transistors UH and UL corresponding to the U phase of the electric motor 24 and a series of a pair of field effect transistors VH and VL corresponding to the V phase. A circuit and a series circuit WH, WL of a pair of field effect transistors corresponding to the W phase are connected in parallel between a DC power supply 32 and a ground 33. The U-phase field coil 24U of the electric motor 24 is connected to a connection point between the field effect transistors UH and UL, and the V-phase field coil 24V is connected to a connection point between the field effect transistors VH and VL. The W-phase field coil 24W is connected to a connection point between the series circuits WH and WL of the field effect transistor.

  The control unit 27 includes a steering speed calculation unit 29 that calculates a steering speed, a target rotation speed setting unit 34 that sets a target rotation speed of the electric motor 24, and a rotational position sensor 30 according to program processing executed by the microcomputer. Based on the detection signal, an actual rotation speed calculation unit 35 that calculates an actual rotation speed (actual rotation speed) ω of the electric motor 24 and a calculation necessary for driving the electric motor 24 by the 120-degree energization method 120. Energization calculating section 36, 180-degree energization calculating section 37 for performing calculations necessary for driving the electric motor 24 by the 180-degree energization method, and 120-degree energization method and 180-degree energization method as the driving method of the electric motor 24. The target rotational speed is achieved based on the calculation results of the drive method switching unit 38 and the 120-degree energization calculation unit 36 or the 180-degree energization calculation unit 37. A drive signal generator 39 for generating a drive signal to be applied to the field effect transistors UH, UL, VH, VL, WH, WL of the drive circuit 26 and a target acceleration calculator 40 for calculating a target rotational acceleration α of the electric motor 24. And realize each function.

The steering speed calculation unit 29 calculates the steering speed of the steering wheel 3 by differentiating the output value of the steering angle sensor 13 with respect to time. Therefore, the steering angle sensor 13 and the steering speed calculation unit 29 constitute a steering speed detection means.
The target rotation speed setting unit 34 sets the target rotation speed of the electric motor 24 based on the steering speed of the steering wheel 3 obtained by the steering speed calculation unit 29 and the vehicle speed detected by the vehicle speed sensor 31. Also good.

The target acceleration calculation unit 40 calculates a target rotational acceleration α of the electric motor 24. Specifically, the target acceleration calculation unit 40 may calculate the target rotation acceleration α of the electric motor 24 by differentiating the target rotation speed set by the target rotation speed setting unit 34 with respect to time.
The drive method switching unit 38 includes a normal control unit 381 that switches the drive method based on the actual rotation speed ω calculated by the actual rotation speed calculation unit 35 and a target acceleration calculation unit 40 regardless of the switching by the normal control unit 381. And an optimization control unit 382 for switching the drive method to the optimum energization method based on the calculated target rotational acceleration α.

The drive signal generation unit 39 gives, for example, a signal that turns on the field effect transistors UH, VH, and WH of the drive circuit 26 in order to turn on only in a period corresponding to 120 degrees or 180 degrees in electrical angle. A drive signal composed of a PWM (Pulse Width Modulation) pulse is applied to the effect transistors UL, VL, WL.
When the electric motor 24 is driven by the 120-degree energization method, the duty of the PWM pulse signal (PWM duty) given from the drive signal generator 39 to the field effect transistors UL, VL, WL is calculated by the 120-degree energization calculation section 36. The That is, the 120-degree energization calculation unit 36 includes a duty setting unit 361 that sets a PWM duty corresponding to the target rotation speed set by the target rotation speed setting unit 34 when the electric motor 24 is driven by the 120-degree energization method. Yes. The duty setting unit 361 performs PI (Proportional-Integral) control calculation based on the deviation between the target rotation speed set by the target rotation speed setting unit 34 and the actual rotation speed ω calculated by the actual rotation speed calculation unit 35. The control voltage value to be applied to the electric motor 24 is obtained, and the PWM duty corresponding to the control voltage value is set.

  Then, the drive signal generation unit 39 generates a drive signal in accordance with the 120-degree energization method based on the PWM duty given from the 120-degree energization calculation section 36 and the rotational position of the rotor detected by the rotational position sensor 30. For the field effect transistors UH, VH, and WH, drive signals that are turned on over a period of 120 degrees in electrical angle are provided with phases shifted by 120 degrees. On the other hand, the PWM pulse signal of the PWM duty set by the 120-degree energization calculation unit 36 is given to the field effect transistors UL, VL, WL. As a result, a drive voltage corresponding to the PWM duty is applied from the drive circuit 26 to the electric motor 24, and the electric motor 24 is driven at the target rotational speed set by the target rotational speed setting unit 34.

  On the other hand, when the electric motor 24 is driven by the 180-degree energization method, the duty of the PWM pulse signal (PWM duty) given from the drive signal generator 39 to the field effect transistors UL, VL, WL is determined by the 180-degree energization calculation section 37. Calculated. That is, the 180-degree energization calculation unit 37 includes a duty setting unit 371 that sets a PWM duty according to the target rotation speed set by the target rotation speed setting unit 34 when the electric motor 24 is driven by the 180-degree energization method. Yes. The duty setting unit 371 performs PI (Proportional-Integral) control calculation based on the deviation between the target rotation speed set by the target rotation speed setting unit 34 and the rotation speed calculated by the actual rotation speed calculation unit 35. Then, a control voltage value to be applied to the electric motor 24 is obtained, and a PWM duty corresponding to the control voltage value is set.

  The drive signal generation unit 39 generates a drive signal according to the 180-degree energization method based on the PWM duty given from the 180-degree energization calculation section 37 and the rotational position of the rotor detected by the rotation position sensor 30. For the field effect transistors UH, VH, and WH, a drive signal that is turned on over a period of 180 degrees in electrical angle is given with a phase shift of 180 degrees. On the other hand, the PWM pulse signal of the PWM duty set by the 180-degree energization calculation unit 37 is given to the field effect transistors UL, VL, WL. As a result, a drive voltage corresponding to the PWM duty is applied from the drive circuit 26 to the electric motor 24, and the electric motor 24 is driven at the target rotational speed set by the target rotational speed setting unit 34.

Next, an operation in which the drive method switching unit 38 switches the drive method to the 120-degree energization method and the 180-degree energization method will be described with reference to FIG.
The normal control unit 381 of the drive method switching unit 38 switches the drive method based on the actual rotation speed ω calculated by the actual rotation speed calculation unit 35. Specifically, the normal control unit 381 executes the following normal control A and normal control B.
(1) Normal control A
When the electric motor 24 is driven by the 120-degree energization method, the normal control unit 381 is in a high speed range (ω1 ≦ ω) where the actual rotation speed ω calculated by the actual rotation speed calculation unit 35 is equal to or greater than the first threshold ω1. (Ie, when the actual rotational speed ω increases and reaches the first threshold value ω1), the drive method is switched to the 180 energization method.
(2) Normal control B
In addition, the normal control unit 381 is configured such that the actual rotation speed ω calculated by the actual rotation speed calculation unit 35 is equal to or lower than the second threshold ω2 that is lower than the first threshold ω1 when the electric motor 24 is driven by the 180-degree energization method. The driving method is switched to the 120-degree energization method at the time when the low speed region (ω ≦ ω2) is reached (that is, when the actual rotational speed ω decreases and reaches the second threshold value ω2).

The region where the actual rotational speed ω is equal to or higher than the first threshold ω1 is a high-speed region, and is a region that cannot be driven unless the 180-degree energization method is used. Further, the region where the actual rotational speed ω is equal to or less than the second threshold ω2 is the low speed region, and is a region that can be sufficiently driven even by the 120-degree energization method.
The region where the actual rotational speed ω exceeds the second threshold value ω2 and is less than the first threshold value ω1 is the medium speed region. The medium speed range is an intermediate region that can be driven only by the 180-degree energization method when the load of the electric motor 24 is large, but can be driven by the 120-degree energization method when the load of the electric motor 24 is small. is there.

The optimization control unit 382 of the drive system switching unit 38 executes the following optimization control A and optimization control B.
(1) Optimization control A
When the electric motor 24 is driven by the 120-degree energization method, the optimization control unit 382 has a rapid acceleration range (the target rotational acceleration α calculated by the target acceleration calculation unit 40 is equal to or greater than the first threshold α1 (> 0) ( When α ≧ α1) (that is, when the target rotational acceleration α increases and reaches the first threshold value α1, which corresponds to timing t1 and timing t3 in the timing chart of FIG. 3A described later) Is forcibly switched to 180 energization.

The switching condition at this time is a condition that is suitable for so-called turning steering, in which steering is performed in a direction in which the steering angle increases. More specifically, this is suitable when the driver rapidly operates the steering wheel 3 to perform the turn steering and the target rotational speed increases rapidly. At this time, the load of the electric motor 24 increases greatly, but it is possible to quickly switch to the 180-degree energization method in response to the increase in load. Therefore, when the steering wheel 3 is quickly turned and steered, the driver does not feel that the steering torque is insufficient. In other words, the shortage of the steering torque can be solved by increasing the ratio of the drive time in the 180-degree energization method that occupies the entire time required for the turning steering.
(2) Optimization control B
In addition, the optimization control unit 382 operates on the condition that the rotational speed ω calculated by the actual rotational speed calculation unit 35 is not in the high speed range (ω <ω1) when the electric motor 24 is driven by the 180-degree energization method. When the target rotational acceleration α calculated by the target acceleration calculating unit 40 is in a sudden deceleration region (α ≦ α2) that is equal to or less than the second threshold value α2 (<0) (that is, the target rotational acceleration α is reduced). When the second threshold value α2 is reached, which corresponds to the timing t7 in the timing chart of FIG. 3A described later), the drive method is switched to the 120-degree energization method.

  The switching condition at this time is a condition suitable for so-called return steering in which steering is performed in a direction in which the steering angle decreases. At the time of return steering, the load of the electric motor 24 is remarkably small. Therefore, during the driving by the 180-degree energization method, the rotation speed ω falls below the first threshold value ω1 and can be driven by the 120-degree energization method ( When it becomes within the range of ω <ω1), it is possible to save energy by immediately switching to the 120-degree energization method. In other words, energy saving can be achieved by reducing the ratio of the drive time in the 180-degree energization method to the entire time required for return steering.

  As shown in Table 1, the actual rotation speed ω calculated by the actual rotation speed calculation unit 35 is in the high speed range (ω1 ≦ ω), the medium speed range (ω2 <ω <ω1), and the low speed range (ω ≦ ω2). Judged on three levels. In addition, the target rotational acceleration α calculated by the target acceleration calculation unit 40 has three levels: a sudden acceleration region (α ≧ α1), a medium acceleration region (α2 <α <α1), and a sudden deceleration region (α ≦ α2). Determined.

When at least one of the actual rotational speed ω is in the high speed range and the target rotational acceleration α is in the rapid acceleration range is satisfied, the drive is performed by the 180-degree energization method. Further, when the target rotational acceleration α is in the rapid deceleration range and the actual rotational speed ω is in the medium speed range or the low speed range, the drive is performed by the 120-degree energization method.
When the target rotational acceleration α calculated by the target acceleration calculating unit 40 is in the middle acceleration range and the actual rotational speed ω calculated by the actual rotational speed calculating unit 35 is in the middle speed range, the target rotational acceleration α is executed until then. Continue the current energization method. This is because the normal control unit 381 has hysteresis in the switching characteristics by changing the thresholds ω1 and ω2 applied to the switching of the driving method depending on whether the actual rotational speed ω is increased or decreased.

When the target rotational acceleration α calculated by the target acceleration calculating unit 40 is in the middle acceleration range and the actual rotational speed ω calculated by the actual rotational speed calculating unit 35 is in the low speed range, the 120-degree energization method is used. The electric motor 24 is driven.
That is, in the middle acceleration range (α2 <α <α1), the energization method switching control by the normal control unit 381 is followed. Then, in the rapid acceleration region where the target rotational speed increases rapidly, the energization method switching control by the optimization control unit 382 is followed. In the rapid deceleration range where the target rotational speed decreases rapidly (when the target rotational acceleration α is a negative value and its absolute value is relatively large), the normal control unit 381 switches the energization method in the high speed range (ω ≧ ω1). According to the control, in the medium speed range (ω2 <ω <ω1) and the low speed range (ω ≦ ω2), the energization method switching control by the optimization control unit 382 is followed.

  FIG. 3A shows the actual rotation speed ω calculated by the actual rotation speed calculation unit 35, the target rotation speed set by the target rotation speed setting unit 34, and the target rotation acceleration calculated by the target acceleration calculation unit 40 in this embodiment. It is a timing chart which shows (alpha) and the change of a drive system. FIG. 3B shows the actual rotational speed ω and the driving system when the target rotational speed changes in the same manner as the target rotational speed of FIG. It is a timing chart which shows change.

  Referring to FIG. 3A, when quick steering is performed when the electric motor 24 is driven by the 120-degree energization method, the target rotational speed increases rapidly from the standby rotational speed, and accordingly, the target rotational acceleration α increases rapidly. . Then, at the timing t1 when the target rotational acceleration α reaches the first threshold value α1, the 180-degree energization method is switched. The optimization control A by the optimization control unit 382 contributes to this switching. At timing t1, the actual rotational speed ω does not reach the first threshold value ω1, and therefore the 120-degree energization method is selected in the normal control (normal control A). Therefore, the optimization control A forcibly corrects the selection of the 120-degree energization method by the normal control, and executes switching to the 180-degree energization method. Thereby, the responsiveness at the time of sudden steering is improved, and so-called catching feeling can be suppressed or prevented.

As shown in FIG. 3B, in the comparison mode, the actual rotational speed ω does not reach the first threshold value ω1, and therefore the 120-degree energization method is maintained according to the normal control A. Therefore, the actual rotational speed ω does not increase sufficiently. As a result, torque shortage occurs, and there is a risk that the steering feeling will be caught.
Next, when the electric motor 24 is driven in the 180-degree energization method, the operation is switched to the 120-degree energization method at a timing t2 when the calculated target rotational acceleration α becomes less than the first threshold value α1. The optimization control A and the normal control A by the optimization control unit 382 contribute to this switching. That is, since the execution condition of the optimization control A is not satisfied and the actual rotational speed ω is less than the first threshold value ω1, the operation is switched to the 120-degree energization method selected by the normal control A.

  Next, when the electric motor 24 is driven by the 120-degree energization method and the target rotational speed increases rapidly due to sudden steering, the target rotational acceleration α increases and reaches the first threshold value α1. At this timing t3, regardless of whether the actual rotational speed ω is in the low speed range (ω ≦ ω2), the 180-degree energization method is switched. The optimization control A by the optimization control unit 382 contributes to this switching. At timing t3, because the actual rotational speed ω does not reach the first threshold ω1 due to a response delay of the actual rotational speed ω, the normal control unit 381 selects the 120-degree energization method according to the normal control A. Therefore, the optimization control unit 382 discards the selection of the 120-degree energization method by the normal control unit 381 and forcibly switches to the 180-degree energization method according to the optimization control A.

The increase in the target rotational speed at the timing t3 is accompanied by quick turning steering. At the time of this turning steering, it is possible to quickly switch to the 180-degree energization method in response to an increase in the load of the electric motor 24. Therefore, the steering feeling can be improved without causing the driver to feel that the torque is insufficient at the time of turning steering.
On the other hand, referring to FIG. 3B which is a comparative form, in the comparative form in which the driving method is switched only by the normal control unit, at timing t4 which is delayed from the timing t3 in FIG. 3A of the present embodiment. Finally, the actual rotational speed ω reaches the first threshold value ω1 and is switched to the 180-degree energization method according to the normal control A. For this reason, in the comparative form, it is not possible to quickly cope with an increase in the load of the electric motor 24 at the time of quick turn steering, so that the driver feels insufficient torque at the time of turn steering, and the steering feeling becomes worse.

  Referring again to FIG. 3A of the present embodiment, at timing t5, when the electric motor 24 is driven by the 180-degree energization method, the target rotational speed is stabilized, and accordingly, the target rotational acceleration α is set to the first threshold value α1. Therefore, the optimization control A condition is not satisfied. However, since the actual rotational speed ω has reached a high speed range equal to or higher than the first threshold value ω1, the execution condition for the normal control A is satisfied before that, and the execution condition for the normal control B is not satisfied. Therefore, the 180-degree energization method is maintained and cannot be switched to the 120-degree energization method.

  Next, when the electric motor 24 is driven by the 180-degree energization method, return steering is performed, and when the target rotational speed decreases rapidly, the target rotational acceleration α becomes a negative value correspondingly and suddenly falls below the second threshold value α1. Enter the deceleration area. However, at this timing t6, the actual rotational speed ω is in the high speed range equal to or higher than the first threshold value ω1, so the execution condition of the optimization control B is not satisfied, and the 180-degree energization method that is the previous energization method is maintained. (See Table 1). At timing t7, when the actual rotational speed ω falls within the rotational speed range that can be driven by the 120-degree energization method (ω <ω1, that is, the middle speed range or the low speed range), the execution condition of the optimization control B is satisfied. , Switched to the 120 degree energization method. In this way, at the time of return steering, when the rotational speed ω falls within the range of rotational speeds that can be driven by the 120-degree energization method, it is possible to quickly switch to the 120-degree energization method, so energy saving can be improved.

  On the other hand, referring to FIG. 3B which is a comparative form, in the comparative form in which the drive system is switched only by the normal control unit, the timing at which the actual rotational speed ω decreases to the second threshold value ω2 and enters the low speed range. At t8, the 120-degree energization method is finally switched. For this reason, in a comparative form, since switching to a 120 electricity supply system becomes late at the time of return steering, it is inferior to energy saving property.

  Thus, according to the present embodiment, the target acceleration is achieved regardless of the switching of the normal control unit 381 based on the actual rotation speed ω (actual rotation speed of the electric motor 24) calculated by the actual rotation speed calculation unit 35. Based on the target rotational acceleration α calculated by the calculation unit 40, the drive method can be optimized. Thus, even when the load on the electric motor 24 increases due to quick turn steering, the actual rotational speed ω of the electric motor 24 can accurately follow the target rotational speed to improve the steering feeling. Further, at the time of return steering, it is possible to switch from the 180 degree energization method to the 120 degree energization method according to the sudden decrease in the target rotation speed without waiting for the actual rotation speed ω to fall to the low speed range. The efficiency of the motor 24 can be improved.

  Further, when the electric motor 24 is driven by the 120-degree energization method, when the target rotational acceleration α calculated by the target acceleration calculating unit 40 is equal to or greater than the first threshold value α1 (α ≧ α1), the actual rotational speed calculating unit 35 is used. Regardless of the magnitude of the actual rotational speed ω calculated by the above, the optimization control unit 382 switches the drive method to the 180-degree energization method as in the switching at the timing t1 and the timing t3 described above. Therefore, there are the following advantages. That is, when the electric motor 24 is driven by the 120-degree energization method, even if the actual rotational speed ω of the electric motor 24 does not immediately follow the rapid increase in the target rotational speed, the optimization control unit 382 is 180 degrees. Since switching to the energization method, the electric motor 24 does not run out of torque. As a result, the followability of the actual rotational speed of the electric motor 24 can be improved. As a result, the steering feeling can be improved without the so-called “striking feeling” in the steering feeling.

  When the target rotational acceleration α calculated by the target acceleration calculation unit 40 becomes equal to or less than the second threshold value α2 (α ≦ α2) during driving of the electric motor 24 in the 180-degree energization method, the actual rotation speed calculation unit 35 is used. On the condition that the actual rotational speed ω calculated by the above is within the range of rotational speeds that can be driven by the 120-degree energization method (ω <ω1), the optimization control unit 382 is switched as described above at the timing t7. Switches the drive method to the 120-degree energization method. Therefore, there are the following advantages. That is, when the electric motor 24 is driven by the 180-degree energization method, the target rotation speed is rapidly reduced. Therefore, when the load of the electric motor 24 is reduced, the actual rotation speed ω of the electric motor 24 is driven by the 120-degree energization method. If it is within the range of possible rotation speeds, the optimization control unit 382 immediately switches to the 120-degree energization method. Thereby, energy saving can be aimed at and the efficiency of the electric motor 24 can be improved.

  Further, when the steered position reaches the vicinity of the stroke end of the rack shaft 7, the steering speed decreases, and the target rotational speed decreases rapidly accordingly. As a result, since the target rotational acceleration α is below the second threshold ω2, if the actual rotational speed of the electric motor 24 falls within the range of rotational speeds that can be driven by the 120-degree energization method, the optimization controller 382 immediately Switch to the current-carrying method. Therefore, even though the rack shaft 7 reaches the stroke end and cannot move any more, the electric motor 24 can be prevented from being wasted by energizing the electric motor 24 by the 180-degree energization method. Thereby, energy saving can be aimed at. In addition, it is not necessary to detect that the steered position is near the stroke end of the rack shaft 7, and it is not necessary to provide special control corresponding to the vicinity of the stroke end.

  Although one embodiment of the present invention has been described above, the present invention can be implemented in other forms. For example, in the above-described embodiment, whether or not the execution condition of the optimization control A is satisfied is determined based on one threshold value α1, but as shown in FIG. 4, two threshold values α11 and α12 (α11> α12 ≧ 0). ) May be used. More specifically, the execution condition of the switching control to 180 degree energization is that the target rotational acceleration α is equal to or higher than the first high threshold value α11 at 120 degrees energization. In addition, when energizing 180 degrees, the target rotational acceleration α is less than the first low threshold α12 as a condition for canceling interference with normal control. Thus, similarly, whether or not the execution condition of the optimization control B is satisfied may be determined using the two threshold values α21 and α22 (α21 <α22 ≦ 0. | Α21 |> | α22 |). More specifically, when 180 degrees energization is performed, the execution condition (required condition) for switching control to 120 degrees energization is that the target rotational acceleration α is equal to or less than the second low threshold value α21. In addition, when 120-degree energization is performed, the target rotational acceleration α exceeds the second high threshold α22 as a condition for canceling interference with normal control. As described above, by introducing the hysteresis characteristic to the drive system switching control based on the target rotational acceleration α, hunting in which the drive system is frequently switched can be suppressed or prevented, so that the steering feeling can be further improved.

  In addition, the present invention is not limited to the above-described embodiments, and various design changes can be made within the scope of matters described in the claims.

  DESCRIPTION OF SYMBOLS 1 ... Power steering apparatus, 2 ... Steering mechanism, 7 ... Rack shaft (steering shaft), 13 ... Steering angle sensor, 22 ... Hydraulic pump, 24 ... Electric motor, 25 ... ECU (motor control device), 26 ... Drive circuit , 27 ... control unit, 29 ... steering speed calculation unit, 30 ... rotational position sensor, 34 ... target rotation speed setting unit, 35 ... actual rotation speed calculation unit, 36 ... 120-degree conduction calculation part, 37 ... 180-degree conduction calculation part 361, 371 ... Duty setting unit, 38 ... Drive system switching unit, 381 ... Normal control unit, 382 ... Optimization control unit, 39 ... Drive signal generation unit, 40 ... Target rotational acceleration calculation unit, α ... Target rotational acceleration, α1, α11: first threshold, α2, α21: second threshold, ω: actual rotational speed, ω1: first threshold, ω2: second threshold

Claims (3)

An electric motor for driving a hydraulic pump that generates a steering assist force;
A PWM control of the drive current supplied from the drive circuit to the electric motor, and a motor control device that rotates the electric motor at a target rotational speed.
The motor control device includes a drive system switching unit that selectively switches the drive system of the electric motor to a 120-degree energization system and a 180-degree energization system;
Actual rotation speed calculating means for calculating the actual rotation speed of the electric motor;
And target acceleration calculation means for calculating a target rotational acceleration of the electric motor,
The drive method switching means is calculated by the normal control unit that switches the drive method based on the actual rotation speed calculated by the actual rotation speed calculation unit, and the target acceleration calculation unit regardless of the switching by the normal control unit. And an optimization control unit that switches a driving method based on the target rotational acceleration.   When the target rotational acceleration calculated by the target acceleration calculation means is equal to or greater than the first threshold during driving of the electric motor in the 120-degree energization method, the optimization control unit switches the drive method to the 180-degree energization method. The power steering apparatus according to claim 1, wherein:   When the target rotational acceleration calculated by the target acceleration calculation becomes equal to or less than the second threshold when the electric motor is driven by the 180-degree energization method, the actual rotational speed calculated by the actual rotational speed calculation means is 120 degrees. The power steering apparatus according to claim 1 or 2, wherein the optimization control unit switches the drive method to a 120-degree energization method on condition that the rotation is within a range of rotation speed that can be driven by the energization method.

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