WO2011025010A1

WO2011025010A1 - Electric power steering device

Info

Publication number: WO2011025010A1
Application number: PCT/JP2010/064743
Authority: WO
Inventors: 輝彦鈴木
Original assignee: いすゞ自動車株式会社
Priority date: 2009-08-31
Filing date: 2010-08-30
Publication date: 2011-03-03
Also published as: JP5440916B2; JP2011051380A

Abstract

Disclosed is an electric power steering device (1) provided with a steering force sensor (3), a steering force computation unit (11), an assist instruction value setting unit (20), a correction instruction value setting unit (30), an output instruction value setting unit (50), a motor (2), an inverter (6), and a battery (7). The assist instruction value setting unit (20) sets an assist current instruction value on the basis of the steering force computed by the steering force computation unit (11). The correction instruction value setting unit (30) takes the second time derivative of the steering force computed by the steering force computation unit (11), and sets a correction current instruction value using the computed second time derivative of the steering force. The output instruction value setting unit (50) sets an output instruction value to the sum of the assist current instruction value and the correction current instruction value. The motor (2) is coupled to a steering wheel. The inverter (6) supplies power from the battery (7) to the motor (2) on the basis of the output instruction value set by the output instruction value setting unit (50).

Description

Electric power steering device

The present invention relates to an electric power steering device for a vehicle.

Japanese Patent Application Laid-Open No. 2002-370662 discloses an electric power steering device that drives an electric motor in accordance with a steering torque applied to a steering shaft by operating a steering wheel to give a steering assist force to the steering shaft.

JP 2002-370662 A

However, in the electric power steering device disclosed in Japanese Patent Application Laid-Open No. 2002-370662, for example, when the driver performs minute steering for the course correction on the steering wheel at the neutral position while the vehicle is traveling straight ahead, the steering wheel is coupled. In order to rotate the electric motor from a stopped state where it is not electrically driven, a high steering torque is required at the start of steering, which may cause a deterioration in steering feeling.

The present invention has been made in view of the above-described problems, and an object thereof is to provide an electric power steering device that improves steering feeling.

In order to achieve the above object, an electric power steering apparatus according to the present invention comprises a steering force detection means, an assist instruction value setting means, a calculation means, a correction instruction value setting means, an output instruction value setting means, a motor, and a power supply means. .

The steering force detection means detects the steering force input to the steering wheel. The assist instruction value setting means sets the assist current instruction value based on the steering force detected by the steering force detection means. The calculating means calculates a second-order time derivative of the steering force detected by the steering force detecting means. The correction instruction value setting means sets the correction current instruction value using the second-order time derivative of the steering force calculated by the calculation means. The output instruction value setting means adds the assist current instruction value set by the assist instruction value setting means and the correction current instruction value set by the correction instruction value setting means, and sets the added value as an output instruction value. The motor is coupled to the steering wheel. The power supply means supplies power to the motor based on the output instruction value set by the output instruction value setting means.

The auxiliary current instruction value increases as the second-order time derivative of the steering force increases. When the output instruction value increases due to an increase in the assist current instruction value or the auxiliary current instruction value, the auxiliary torque for assisting the driver to steer the steering wheel increases.

In the above configuration, when the driver steers the steering wheel, the steering force generated by the steering is detected. Next, an assist current instruction value is set based on the detected steering force. Further, a second-order time derivative of the detected steering force is calculated, and a corrected current instruction value using the second-order time derivative of the steering force is set. Next, the assist current instruction value and the correction current instruction value are added, and this addition value is set as the output instruction value. Next, electric power is supplied to the motor based on the output instruction value. Steering of the steering wheel is assisted by driving of a motor supplied with electric power.

Thus, since electric power is supplied to the motor based on the output instruction value including the corrected current instruction value using the second-order time derivative of the steering force, when the steering force increases in a short time, As the second-order time derivative increases, the power supplied to the motor increases and the auxiliary torque increases. For this reason, for example, the motor connected to the steering wheel is in a stopped state, such as when the driver starts steering the steering wheel while the rudder angle is maintained, and the motor in the stopped state is rotated. When a high steering force is required, the motor is driven by the increased electric power according to the increase of the second-order time derivative of the steering force, and the auxiliary torque is increased. Therefore, it is possible to reduce the steering force necessary to rotate the motor in the stopped state, and to improve the steering feeling. In particular, the assist torque can be increased appropriately at the start of steering when the driver performs minute steering for the course correction on the steering wheel at the neutral position while the vehicle is traveling straight ahead, so that a good steering fee can be obtained. You can get a ring.

In addition, the electric power steering apparatus includes a handle state detection unit that detects whether or not the steering wheel returns to the neutral position from the rotational position at which the steering wheel is steered, and the output instruction value setting unit includes the handle state detection unit. When it is detected that the steering wheel is in the steering wheel return state, the assist current instruction value set by the assist instruction value setting means may be set as the output instruction value.

The steering wheel return state may be detected based on, for example, the rotation direction of the steering wheel and the direction of the steering torque.

The output instruction value setting means sets only the assist current instruction value as the output instruction value, for example, without adding the assist current instruction value and the correction current instruction value when it is detected that the steering wheel is returned. Alternatively, an addition value obtained by adding the correction current instruction value set to zero and the assist current instruction value may be set as the output instruction value.

In the above configuration, in the steering wheel return state, the steering angle is reduced by the self-aligning torque, the steering wheel returns from the rotational position to the neutral position, and the motor is being driven. An appropriate steering feeling can be obtained by the auxiliary torque based on the above. Therefore, if the addition value obtained by adding the correction current instruction value to the assist current instruction value is set as the output instruction value, the steering may be lightened and the steering feeling may be deteriorated. Therefore, the correction current instruction value is changed to the assist current instruction value. The assist current instruction value is set as the output instruction value without adding.

The calculating means may calculate a first-order time derivative of the steering force detected by the steering force detecting means, and the correction instruction value setting means further uses the first-order time derivative of the steering force calculated by the calculating means. A corrected current instruction value may be set.

In the above configuration, the assist current instruction value based on the steering force is set, and the correction current instruction value using the first-order time derivative of the steering force is set. The added value of the correction current instruction value and the assist current instruction value The auxiliary torque is increased by supplying electric power to the motor based on the output instruction value. Accordingly, for example, in a series of processes for setting the assist current instruction value based on the steering force and supplying electric power to the motor based on the output instruction value including the assist current instruction value, the response of the assist torque to the steering force is In the electric power steering apparatus having the characteristic of being delayed, it is possible to reduce the shortage of the auxiliary torque with respect to the steering force.

The electric power steering apparatus may further include an operation speed detection unit that detects a steering speed and a steering speed processing value setting unit that sets a steering speed processing value according to the steering speed detected by the steering speed detection unit. The correction instruction value setting unit may set the correction current instruction value by further using the steering speed processing value set by the steering speed processing value setting means.

In the above configuration, when the steering speed is increased by steering the steering wheel, the auxiliary torque increases. Therefore, for example, when there is a mechanical resistance of the motor connected to the steering wheel, such as when the steering wheel is increased, the auxiliary torque increases with an increase in the steering speed. The steering force required to steer the steering wheel against such resistance can be reduced, and the steering feeling can be improved.

According to the present invention, the steering feeling can be improved.

It is a block block diagram of the electric power steering device which concerns on this embodiment. It is a flowchart which shows the output instruction | indication value setting process of the electric power steering apparatus of FIG. It is a flowchart which shows the assist electric current instruction value setting process of the output instruction value setting process of FIG. It is a flowchart which shows the correction electric current instruction value setting process of the output instruction value setting process of FIG. It is a graph of the experimental result which shows the steering torque at the time of steering in the electric power steering apparatus which does not generate | occur | produce auxiliary torque. 6 is a graph of experimental results showing steering torque when steering is performed in an electric power steering apparatus in which auxiliary torque based on an assist current instruction value is generated. It is a graph of the experimental result which shows the steering torque at the time of steering the electric power steering apparatus of FIG.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.

1 is a block diagram of the electric power steering apparatus according to the present embodiment, FIG. 2 is a flowchart showing an output instruction value setting process of the electric power steering apparatus of FIG. 1, and FIG. 3 is an output instruction value of FIG. 4 is a flowchart showing an assist current instruction value setting process of the setting process, FIG. 4 is a flowchart showing a correction current instruction value setting process of the output instruction value setting process of FIG. 2, and FIG. 5 is an electric power steering in which no assist torque is generated. FIG. 6 is a graph of experimental results showing the steering torque when the steering wheel is steered from the neutral position in the apparatus. FIG. 6 is a graph showing the steering torque from the neutral position in the electric power steering apparatus that generates the assist torque based on the assist current instruction value. FIG. 7 is a graph of experimental results showing the steering torque when steered. Is a graph of experimental results showing the steering torque when the steering the steering wheel of the electric power steering device from the neutral position.

As shown in FIG. 1, the electric power steering apparatus 1 of this embodiment includes a motor 2 and is provided in a vehicle. The motor 2 is connected to the speed reduction mechanism and drives the speed reduction mechanism. The speed reduction mechanism is configured by a combination of a plurality of gears and is coupled to the pinion shaft. The pinion shaft is fixed to the output shaft. The output shaft is fixed to one end of the torsion bar. The other end of the torsion bar is fixed to the other end of the steering shaft. One end of the steering shaft is fixed to the steering wheel. The steering wheel is provided in the cab of the vehicle, and the driver inputs steering. Further, the rack shaft moves left and right along the vehicle width direction in accordance with the operation of the pinion shaft. The tie rods connected to both ends of the rack shaft in the vehicle width direction are connected to the wheels. By these mechanisms, the rack shaft moves in the vehicle width direction in conjunction with the rotation of the steering shaft, and the rack shaft moves along the vehicle width direction by the rotation of the steering shaft by the driver's steering and the rotation of the motor 2. Is displaced in the longitudinal direction. That is, the motor 2 generates an auxiliary torque that displaces the rack shaft along the vehicle width direction by its rotational drive, and assists the driver's steering when turning the wheels.

Further, as shown in FIG. 1, the power steering apparatus 1 of the present embodiment includes a steering force sensor 3. The steering force sensor 3 detects a twist angle between one end side and the other end side of the torsion bar. The vehicle also includes a steering angle sensor 4 and a motor drive current sensor 5. The steering angle sensor 4 detects the rotation angle of the steering shaft. The motor drive current sensor 5 is disposed between the motor 2 and an inverter 6 described later, and detects a current flowing from the inverter 6 to the motor 2.

As shown in FIG. 1, the power steering apparatus 1 of the present embodiment includes a controller 10 that includes a steering force calculation unit 11, an assist instruction value setting unit 20, a correction instruction value setting unit 30, and an output instruction value setting unit 50. Have The controller 10 includes a steering speed calculation unit 12 and a steering wheel state detection unit 13. The controller 10 receives signals from the steering force sensor 3, the steering angle sensor 4, and the motor drive current sensor 5, and executes processing based on the program stored therein based on the input signals.

The steering force sensor 3 and the steering force calculation unit 11 constitute a steering force detection unit, the assist instruction value setting unit 20 constitutes an assist instruction value setting unit, and the correction instruction value setting unit 30 includes a correction instruction value setting unit and a calculation unit. And steering speed processing value setting means, the output instruction value setting unit 50 constitutes output instruction value setting means, and the inverter 6 and the battery 7 constitute power supply means. The handle state detection unit 13 constitutes a handle state detection unit.

Steering force calculation unit 11 calculates a steering force. Specifically, the steering force calculation unit 11 calculates the steering force input to the steering wheel based on the twist angle between the one end side and the other end side of the torsion bar detected by the steering force sensor 3. The steering speed calculation unit 12 calculates a steering speed. Specifically, the steering speed calculation unit 12 calculates the steering speed of the steering wheel by differentiating the rotation angle of the steering shaft detected by the steering angle sensor 3 once with respect to time.

The assist instruction value setting unit 20 sets an assist current instruction value based on the steering force detected by the steering force sensor 3. As shown in FIG. 1, in this embodiment, the assist instruction value setting unit 20 includes an assist map storage unit 21, a target current setting unit 22, a current deviation calculation unit 23, a proportional gain calculation unit 24, and an integral gain calculation unit 25. An assist instruction value adding unit 26.

The assist map storage unit 21 stores in advance the relationship between the steering force and the target current for outputting the assist torque corresponding to the steering force. The target current setting unit 22 reads a target current corresponding to the steering force calculated by the steering force calculation unit 11 based on the relationship between the steering force and the target current stored in the assist map storage unit 21. In the present embodiment, the relationship between the steering force and the target current is stored in advance as a map. However, the present invention is not limited to this, and for example, a calculation formula for calculating the target current with respect to the steering force may be stored. May calculate the target current based on the calculation formula and the steering force calculated by the steering force calculation unit 11. The current deviation calculation unit 23 calculates a deviation between the target current set by the target current setting unit 22 and the current detected by the motor drive current sensor 5. The proportional gain calculation unit 24 calculates a value proportional to the deviation calculated by the current deviation calculation unit 23 as a deviation proportional value. The integral gain calculating unit 25 calculates a value proportional to the integral of the deviation calculated by the current deviation calculating unit 23 as a deviation integral proportional value. The assist instruction value adding unit 26 sets an addition value obtained by adding the deviation proportional value calculated by the proportional gain calculating unit 24 and the deviation integral proportional value calculated by the integral gain calculating unit 25 as an assist current instruction value. The assist instruction value setting unit 20 calculates a deviation proportional value, a deviation integral proportional value, and an assist current instruction value based on absolute values in both cases of steering to the right and steering to the left. Then, it is determined whether the steering is to turn rightward or to the left.

The correction instruction value setting unit 30 sets a correction current instruction value for correcting the assist current instruction value. As shown in FIG. 1, in this embodiment, the correction instruction value setting unit 30 includes a first-order time differentiation process value setting unit 31, a second-order time differentiation process value setting unit 34, a steering speed process value setting unit 37, and a correction instruction. A value adding unit 40, and a value proportional to the first-order time derivative of the steering force, a value proportional to the second-order time derivative of the steering force, and a value proportional to the steering speed are limited within a predetermined upper limit value. A corrected current instruction value obtained by adding the steering speed processing value is set.

The first-order time differentiation processing value setting unit 31 constitutes a calculation means, and includes a first-order time differentiation calculation unit 32 and a gain multiplication unit 33. The first-order time derivative calculating unit 32 calculates the first-order time derivative of the steering force based on the steering force calculated by the steering force calculating unit 22. The gain multiplication unit 33 multiplies the first-order time derivative of the steering force calculated by the first-order time derivative calculation unit 32 by a gain, and sets a value proportional to the first-order time derivative of the steering force as a steering force first-order time derivative proportional value. Calculate.

The second-order time differentiation processing value setting unit 34 constitutes a calculation means, and includes a second-order time differentiation calculation unit 35, a gain multiplication unit, and 36. In the present embodiment, the second-order time differentiation calculation unit 35 calculates the steering force calculation unit 22 by further differentiating the first-order time differentiation of the steering force calculated by the first-order time differentiation calculation unit 32. The second-order time derivative of the steering force is calculated. The gain multiplication unit 36 multiplies the second-order time derivative of the steering force calculated by the second-order time derivative calculation unit 35 by a gain, and sets a value proportional to the second-order time derivative of the steering force as a steering force second-order time derivative proportional value. Calculate. Note that the second-order time differentiation calculation unit 35 directly uses the steering force based on the steering force calculated by the steering force calculation unit 22 without using the first-order time differentiation of the steering force calculated by the first-order time differentiation calculation unit 32. The second-order time derivative may be calculated.

The steering speed process value setting unit 37 constitutes a steering speed process value setting unit, and in this embodiment, includes a gain unit 38 and a limiter unit 39. The gain unit 38 calculates a value proportional to the steering speed based on the steering speed calculated by the steering speed calculation unit 12. The limiter unit 39 calculates a steering speed processing value in which a value proportional to the steering speed is limited to a predetermined upper limit value based on the steering speed calculated by the gain unit 38.

The correction instruction value adding unit 40 is a steering force first-order time differential proportional value calculated by the first-order time differential process value setting unit 31 and a steering force second-order time differential proportional value calculated by the second-order time differential process value setting unit 34. And the steering speed processing value calculated by the steering speed processing value setting unit 37 is added to set the corrected current instruction value. In the correction instruction value setting unit 30, the steering force first-order time differential proportional value and the steering force second-order time differential proportional value are determined by absolute values in both cases of steering to the right and steering to the left. A steering speed processing value and a corrected current instruction value are calculated.

In the present embodiment, the correction instruction value setting unit 40 sets the correction current instruction value using the steering force first-order time differential proportional value, the steering force second-order time differential proportional value, and the steering speed processing value. Not limited to such a configuration, the correction current instruction value may be set using only the steering force first-order time differential proportional value, and the steering force first-order time differential proportional value and the steering force second-order time differential proportional value are used. The corrected current instruction value may be set, or the corrected current instruction value may be set using the steering force first-order time differential proportional value and the steering speed processing value. The corrected current instruction value may be set using other values together with the second-order time differential proportional value and the steering speed processing value.

The steering wheel state detection unit 13 detects whether or not the steering wheel is in a steering wheel return state in which the steering wheel returns to the neutral position from the steering position. In the present embodiment, the steering wheel state detection unit 13 determines whether or not the steering wheel is in the steering wheel return state based on the rotation direction of the steering wheel and the direction of the steering torque. Here, the steering wheel is in a state where the steering wheel moves to a rotational position where the steering wheel is increased, a steering wheel return state where the steering wheel moves in a direction returning from the rotational position to the neutral position, It is divided into the handle stop state that is not moving.

The steering wheel state determination unit 13 determines the rotation direction of the steering wheel based on the rotation angle of the steering shaft detected by the steering angle sensor 4. Specifically, the difference between the rotation angle input during the current process and the rotation angle input during the previous process is calculated to determine whether the steering wheel angle has changed and the rotation direction of the steering wheel changes. If it is, it is determined whether the rotation direction of the steering wheel is the right direction or the left direction. At the start of processing, the neutral position value is used as an initial setting value instead of the rotation angle input during the previous processing.

Further, the handle state determination unit 13 determines the direction of the steering torque based on the twist angle between the one end side and the other end side of the torsion bar detected by the steering force sensor 3. Specifically, the difference between the twist angle input during the current process with respect to the twist angle input during the previous process is calculated to determine whether or not the steering torque direction has changed, and the steering torque direction changes. If it is, it is determined whether the direction of the steering torque is the right direction or the left direction. At the start of processing, the value of steering non-input (neutral position) is used as an initial setting value instead of the twist angle input at the previous processing.

Further, the steering wheel state determination unit 13 is configured such that when the steering wheel rotation direction is the right direction and the steering torque direction is the left direction, and the steering wheel rotation direction is the left direction and the steering torque direction is the right direction. When the direction is the direction, it is determined that the handle is in the return state. When the direction of rotation of the steering wheel coincides with the direction of the steering torque, the steering wheel is in the forward direction, and when there is no change in the direction of rotation of the steering wheel or the direction of the steering torque, the steering wheel is in the stopped state.

In the present embodiment, the steering wheel state determination unit 13 determines the steering wheel return state based on the rotation direction of the steering wheel and the direction of the steering torque. However, even if the steering wheel return state is determined based on other information, Good. For example, the steering wheel state determination unit 13 is configured to determine that the steering wheel return state is established when the steering torque direction and the motor rotation direction do not match based on the steering torque direction and the motor rotation direction. May be.

The output instruction value setting unit 50 determines the assist current instruction value set by the assist instruction value setting unit 20 and the correction current instruction value set by the correction instruction value setting unit 30 when it is determined that the handle state determination unit 13 is not in the steering wheel return state. Is set as an output instruction value, and when the steering wheel state determination unit 13 determines that it is in the steering wheel return state, the assist current instruction value set by the assist instruction value setting unit 20 is set as the output instruction value. . The output instruction value setting unit 50 performs steering to the right or the left to determine the absolute assist current instruction value, the absolute auxiliary current instruction value, and the assist instruction value setting unit 20. And an absolute output instruction value including information indicating the rotation direction of the motor 2 based on the information indicating whether or not the steering operation is performed, and outputting the calculated value to the inverter 6. When the auxiliary current instruction value is added to the assist current instruction value by such processing, the output instruction value increases.

In the present embodiment, the output instruction value setting unit 50 sets the assist current instruction value to the output current instruction value by not adding the correction current instruction value when in the handle return state. However, the present invention is not limited to this. The correction current instruction value is always added during the execution of the process. When the steering wheel is in the return state, the assist current instruction value is substantially increased by adding the correction current instruction value multiplied by zero and the assist current instruction value. May be set as the output instruction value. Further, in this embodiment, the output instruction value setting unit 50 does not calculate the correction current instruction value when in the handle return state, but is not limited thereto, and always calculates the correction current instruction value during the execution of the process. It may be a configuration.

As shown in FIG. 1, the inverter 6 supplies power from the battery 7 to the motor 2 based on the output instruction value set by the output instruction value setting unit 50. Specifically, the inverter 6 sets the DC current of the battery 7 to a three-phase AC current based on the output instruction value based on the output instruction value set by the output instruction value setting unit 50 and outputs it to the motor 2. To do. The inverter 6 rotates the motor 2 in the same direction as the left and right directions steered by the driver based on the information indicating the rotation direction of the motor 2 included in the output instruction value.

Hereinafter, output instruction value setting processing executed by the controller 10 of the electric power steering apparatus 1 of the present embodiment will be described with reference to the flowcharts of FIGS. This process is started by starting the engine and is executed every predetermined time (for example, 10 msec).

First, a description will be given along the flowchart of FIG. In step S1, the controller 10 determines that the torsion angle between one end and the other end of the torsion bar detected by the steering force sensor 3, the rotation angle of the steering shaft detected by the steering angle sensor 4, and the motor drive current sensor 5 The detected value of the current flowing from the inverter 6 to the motor 2 is acquired. Next, in step S2, the steering force calculation unit 11 calculates the steering force input to the steering wheel based on the twist angles between the one end side and the other end side of the torsion bar acquired from the steering force sensor 3 in step S1. Calculate. Next, in step S3, the assist instruction value setting unit 20 executes an assist current instruction value setting process.

The assist current instruction value setting process will be described with reference to the flowchart of FIG. First, in step S21, the target current setting unit 22 sets a target current corresponding to the steering force calculated in step S2, based on the relationship between the steering force and the target current stored in the assist map storage unit 21. Next, in step S22, the current deviation calculation unit 23 calculates a deviation between the value of the current input to the motor 2 acquired from the motor drive current sensor 5 in step S1 and the value of the target current set in step S21. To do. Next, in step S23, the proportional gain calculation unit 24 calculates a value proportional to the deviation as a deviation proportional value based on the deviation calculated in step S22. Next, in step S24, the integral gain calculator 25 calculates a value proportional to the integral of the deviation as a deviation integral proportional value based on the deviation calculated in step S22. Next, in step S25, the assist instruction value adding unit 26 sets an addition value obtained by adding the deviation proportional value calculated in step S23 and the deviation integral proportional value calculated in step S24 as an assist current instruction value. Returning to the processing shown in FIG.

Next, in step S4, the steering wheel state detection unit 13 performs the current time with respect to the rotation angle (or the neutral position value of the initial setting value) input during the previous processing based on the rotation angle of the steering shaft detected in step S1. The difference of the rotation angle input at the time of the process is calculated, and it is determined whether or not the steering wheel angle has changed. If it is determined in step S4 that the angle of the steering wheel has changed, the process proceeds to step S5, and the handle state detection unit 13 twists the one end side and the other end side of the torsion bar detected by the steering force sensor 3. Based on the angle, the difference between the twist angle input during the current process with respect to the twist angle input during the previous process (or the value of the initial setting value without steering input) is calculated, and whether the steering torque direction has changed Determine whether. If it is determined in step S5 that the direction of the steering torque is changing, the process proceeds to step S6, and the handle state detection unit 13 determines whether the direction in which the steering torque is changing is the right direction. . If it is determined in step S6 that the steering torque direction is the right direction, the process proceeds to step S7, and the steering wheel state detector 13 determines that the steering wheel rotation direction determined to have changed in step S4 is the left direction. It is determined whether or not there is. If it is determined in step S6 that the direction in which the steering torque is changing is not the right direction (the left direction), the process proceeds to step S8, and the handle state detection unit 13 is changed in step S4. It is determined whether the rotation direction of the steering wheel determined to be rightward.

If it is determined in step S7 that the rotation direction of the steering wheel is the left direction, and if it is determined in step S8 that the rotation direction of the steering wheel is the right direction, the steering wheel state detection unit 13 returns the steering wheel. It determines with it not being in a state, it transfers to step S9, and correction | amendment electric current instruction value setting processing is performed.

The correction current instruction value setting process will be described with reference to the flowchart of FIG. First, in step S31, the first-order time derivative calculating unit 32 calculates the first-order time derivative of the steering force based on the steering force calculated by the steering force calculating unit 11 in step S2. Next, in step S32, the gain multiplication unit 33 multiplies the first-order time derivative of the steering force calculated by the first-order time derivative calculation unit 32 in step S31 by a gain, and is a value proportional to the first-order time derivative of the steering force. Is calculated as a steering force first-order time differential proportional value. Next, in step S33, the second-order time differentiation calculation unit 35 further differentiates the first-order time derivative of the steering force calculated by the first-order time differentiation calculation unit 32 in step S31, thereby obtaining 2 of the steering force. Calculate the floor time derivative. Next, in step S34, the gain multiplication unit 36 multiplies the second-order time derivative of the steering force calculated by the second-order time derivative calculation unit 35 in step S33 by a gain, and is a value proportional to the second-order time derivative of the steering force. Is calculated as a steering force second-order time differential proportional value. Next, in step S35, the steering speed calculation unit 12 calculates the steering speed by differentiating the first rotation time of the rotation angle based on the rotation angle of the steering shaft acquired from the steering angle sensor 4 in step S1. Next, in step S36, the gain unit 38 of the steering speed processing value setting unit 37 calculates a value proportional to the steering speed based on the steering speed calculated by the steering speed calculation unit 12 in step S35. Next, in step S37, the limiter unit 39 of the steering speed processing value setting unit 37 sets a value proportional to the steering speed to a predetermined upper limit value based on the value proportional to the steering speed calculated by the gain unit 38 in step S36. The steering speed processing value restricted within is calculated. Next, in step S38, the correction instruction value adding unit 40 calculates the steering force first-order time differential proportional value calculated in step S32, the steering force second-order time differential proportional value calculated in step S34, and in step S37. An addition value obtained by adding the calculated steering speed processing value is set as a correction current instruction value, and the processing returns to the processing shown in FIG.

Next, in step S10, the output instruction value setting unit 50 sets an addition value obtained by adding the assist current instruction value set in step S25 and the correction current instruction value set in step S38 as an output instruction value. .

Further, when it is determined in step S4 that the angle of the steering wheel has not changed, when it is determined in step S5 that the direction of the steering torque has not changed, and in step S7, the rotation direction of the steering wheel is not leftward. If it is determined that the steering wheel rotation direction is not rightward in step S8, the steering wheel state detection unit 13 determines that the steering wheel is not returned, and the process proceeds to step S11. In step S11, the output instruction value setting unit 50 sets the assist current instruction value set in step S25 as the output instruction value.

Next, in step S12, the output instruction value setting unit 50 outputs the output instruction value to the inverter 6 and ends this process.

Fig. 5 to Fig. 7 show the results of an operation experiment of the electric power steering device in a no-load state. The vertical axis represents the steering torque (Nm) input to the pinion shaft, and the horizontal axis represents time. FIG. 7 shows the experimental results of the electric power steering apparatus 1 of the present embodiment, and FIGS. 5 and 6 show the experimental results of the power steering apparatus for comparison with the present embodiment.

FIG. 5 shows the steering torque when the steering wheel is steered from the neutral position with no output instruction value set and no auxiliary torque generated. As shown in FIG. 5, it can be seen that the steering torque protrudes in a mountain shape at the start of steering (left end portion), resulting in a large resistance to steering. This mountain shape is stopped when the motor or the speed reduction mechanism connected to the steering wheel is in a stopped state, such as when the driver starts steering the steering wheel while the steering angle is maintained. It is generated by the steering torque necessary to move the motor and the speed reduction mechanism in the state. In particular, a relatively large steering torque is required at the start of steering for a neutral steering wheel. It can also be seen that after the mountain-shaped steering torque at the start of steering (right side), the steering torque frequently changes along the time axis. The shape in which the steering torque frequently changes is generated by a steering torque necessary for steering with respect to a mechanical resistance of a motor or a speed reduction mechanism connected to the steering wheel.

FIG. 6 shows the steering torque when the assist wheel instruction value is set as the output instruction value and the steering wheel is steered from the neutral position in the state where the assist torque is generated based on the assist current instruction value. As shown in FIG. 6, it can be seen that the steering torque required as a whole is smaller than the steering torque of FIG. 5, but there is a steering torque protruding in a mountain shape at the start of steering as in FIG. 5. For this reason, even if the auxiliary torque is generated, the driver is given a sense of resistance that is stuck at the start of steering. Further, after the start of steering, there is a shape in which the steering torque frequently changes along the time axis, as in FIG. For this reason, in the electric power steering apparatus 1 that sets the assist current instruction value as the output instruction value, the steering feeling is not good.

FIG. 7 shows the electric power steering apparatus 1 of the present embodiment, where an addition value obtained by adding the correction current instruction value to the assist current instruction value is set as an output instruction value, and is based on the assist current instruction value and the correction current instruction value. The steering torque when the steering wheel is steered from the neutral position in a state where the auxiliary torque is generated is shown. In the operation experiment of the electric power steering apparatus 1 in FIG. 7, an addition value obtained by adding the steering force first-order time differential proportional value, the steering force second-order time differential proportional value, and the steering speed processing value is set as the correction current instruction value. As shown in FIG. 7, it can be seen that the vehicle is steered with a substantially constant steering torque from the time of steering disclosure. That is, as shown in FIG. 5 and FIG. 6, there is no protruding portion of the mountain-like steering torque at the start of steering, and the change width of the steering torque that frequently changes along the time axis that existed after the start of steering. Decreased. As a result, a good steering feeling could be obtained. Specifically, the mountain-shaped steering torque that existed at the start of steering in the operation experiment shown in FIG. 6 is set to the corrected current instruction value using the steering force second-order time differential proportional value in the operation experiment in FIG. As a result, the steering torque became substantially constant. In addition, the change width of the steering torque that frequently changes along the time axis existing after the start of steering in the operation experiment shown in FIG. 6 is the correction current using the steering speed processing value in the operation experiment of FIG. Decrease by setting the indicated value. In addition, in the series of processes in which an output instruction value based on the assist current instruction value is set and power is supplied to the motor based on the output instruction value, there is a characteristic that the response of the auxiliary torque to the steering force is delayed. In the steering device 1, the shortage amount of the auxiliary torque with respect to the steering force is reduced by setting the correction current instruction value using the steering force first-order time differential proportional value.

As described above, in this embodiment, when the driver steers the steering wheel, the steering force and the steering speed generated by the steering are detected. Next, an assist current instruction value is set based on the detected steering force. Further, based on the rotation direction of the steering wheel and the direction of the steering torque, it is determined whether or not the steering wheel is in the steering wheel return state in which the steering wheel returns to the neutral position from the steering rotational position. The corrected current instruction value is calculated. The corrected current instruction value includes a steering force first-order time derivative proportional value that is proportional to the first-order time derivative of the steering force and a steering force second-order time derivative that is proportional to the second-order time derivative of the steering force. The added value is set. Next, the assist current instruction value and the correction current instruction value are added, and this addition value is set as the output instruction value. Next, electric power is supplied to the motor 2 based on the output instruction value. Steering of the steering wheel is assisted by driving of the motor 2 supplied with electric power.

Thus, since electric power is supplied to the motor 2 based on the output instruction value including the corrected current instruction value using the second-order time derivative of the steering force, the steering force is increased when the steering force increases in a short time. As the second-order time derivative increases, the current supplied to the motor 2 increases and the auxiliary torque increases. Therefore, for example, the motor 2 and the speed reduction mechanism connected to the steering wheel are in a stopped state, such as when the driver starts steering the steering wheel while the steering angle is maintained. When a high steering force is required to move the motor 2, the speed reduction mechanism, etc., the motor 2 is driven by the increased electric power as the second-order time derivative of the steering force increases, and the auxiliary torque increases. . Therefore, the steering force required to rotate the motor 2 in a stopped state can be reduced, and the steering feeling can be improved. In particular, the assist torque can be increased appropriately at the start of steering when the driver performs minute steering for the course correction on the steering wheel at the neutral position while the vehicle is traveling straight ahead, so that a good steering fee can be obtained. You can get a ring.

Further, in the steering wheel return state, the self-aligning torque generates a force in the direction of decreasing the steering angle and the motor 2 is being driven, so that a high steering force is not required and the assist torque based on the assist current instruction value is used. An appropriate steering feeling can be obtained. Therefore, if the addition value obtained by adding the correction current instruction value to the assist current instruction value is set as the output instruction value, the steering may be lightened and the steering feeling may be deteriorated. Therefore, the correction current instruction value is changed to the assist current instruction value. The assist current instruction value is set as the output instruction value without adding.

In addition, an assist current instruction value based on the steering force is set, and a correction current instruction value using a first-order time derivative of the steering force is set, which is an addition value of the correction current instruction value and the assist current instruction value. The auxiliary torque is increased by supplying electric power to the motor 2 based on the output instruction value. Therefore, for example, in the series of processes for setting the assist current instruction value based on the steering force and supplying power to the motor 2 based on the output instruction value including the assist current instruction value, the response of the auxiliary torque to the steering force In the electric power steering apparatus 1 having the characteristic that the delay is delayed, the shortage of the auxiliary torque with respect to the steering force can be reduced.

Also, as the steering speed increases due to steering to the steering wheel, the auxiliary torque increases. Therefore, for example, when there is a mechanical resistance such as the motor 2 or the speed reduction mechanism connected to the steering wheel, such as when the steering wheel is increased, the auxiliary torque increases as the steering speed increases. The steering force required to steer the steering wheel against mechanical resistance such as the motor 2 and the speed reduction mechanism can be reduced, and the steering feeling can be improved.

As mentioned above, although the embodiment to which the invention made by the present inventor is applied has been described, the present invention is not limited by the description and the drawings that form part of the disclosure of the present invention according to this embodiment. That is, it should be added that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on this embodiment are all included in the scope of the present invention.

The present invention can be used as an electric power steering device for various vehicles.

1: Electric power steering device 2: Motor 3: Steering force sensor (steering force detection means)
4: Steering angle sensor (steering speed detection means)
6: Inverter (power supply means)
7: Battery (power supply means)
11: Steering force calculation unit (steering force detection means)
12: Steering speed calculation unit (steering speed detection means)
13: Handle state detection unit (handle state detection means)
20: Assist instruction value setting unit (assist instruction value setting means)
32: 1st-order time differential calculation unit (calculation means)
35: Second-order time differential calculation section (calculation means)
37: Steering speed processing value setting unit (steering speed processing value setting means)
40: Correction instruction value addition unit (correction instruction value setting means)
50: Output instruction value setting unit (output instruction value setting means)

Claims

Steering force detection means for detecting the steering force input to the steering wheel;
An assist instruction value setting means for setting an assist current instruction value based on the steering force detected by the steering force detection means;
A calculation means for calculating a second-order time derivative of the steering force detected by the steering force detection means;
Correction instruction value setting means for setting a correction current instruction value using the second-order time derivative of the steering force calculated by the arithmetic means;
Output instruction value setting means for adding the assist current instruction value set by the assist instruction value setting means and the correction current instruction value set by the correction instruction value setting means, and setting the added value as an output instruction value;
A motor coupled to the steering wheel;
An electric power steering apparatus comprising: power supply means for supplying electric power to the motor based on the output instruction value set by the output instruction value setting means.
The electric power steering apparatus according to claim 1,
A steering wheel state detection means for detecting whether or not the steering wheel is in a steering wheel return state in which the steering wheel returns from a steering rotational position to a neutral position;
The output instruction value setting means sets the assist current instruction value set by the assist instruction value setting means as an output instruction value when the handle state detection means detects that the steering wheel return state is present. Electric power steering device.
The electric power steering apparatus according to claim 1 or 2,
The calculation means calculates a first-order time derivative of the steering force detected by the steering force detection means,
The electric power steering apparatus, wherein the correction instruction value setting means sets the correction current instruction value by further using the first-order time derivative of the steering force calculated by the calculation means.
The electric power steering device according to claim 1, wherein
Operation speed detection means for detecting the steering speed;
Steering speed processing value setting means for setting a steering speed processing value according to the steering speed detected by the steering speed detection means,
The electric power steering apparatus, wherein the correction instruction value setting unit further sets a correction current instruction value by further using the steering speed processing value set by the steering speed processing value setting means.