JP2006160010A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of accurately estimating static friction by a simple structure. <P>SOLUTION: The electric power steering device 1 adding steering auxiliary force by a motor 5 to a steering system according to a steering state, comprises a rotation angle detecting means 4 detecting a rotation angle of the motor 5; an electric current supplying means 6 supplying the electric current to the motor 5; and a static friction estimating means 6 supplying the electric current while the motor 5 is stopped, and estimating static friction on the basis of a current value supplied to the motor 5 when the rotation angle of the motor 5 starts to change. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus that applies a steering assist force by a motor to a steering system.

  The electric power steering device controls the driving of the motor according to the steering torque and the vehicle speed input by the driver, and adds a steering assist force to the steering system by the motor. Since there is static friction in the steering system due to friction of the motor itself and friction of the suspension, the electric power steering apparatus is affected by static friction. Therefore, when static friction is not considered in the steering assist force, a feeling of catching occurs when steering is started, and the steering feeling near the neutral position of the steering is deteriorated. Further, when steering is performed on the vehicle side such as a lane keeping device, if the motor is driven and controlled without taking this static friction into consideration, the tire may not be steered or the tire may be cut too much.

Therefore, some electric power steering apparatuses estimate the static friction and add a steering assist force by a motor in consideration of the estimated static friction (see Patent Document 1). As a method for estimating the static friction, a method is adopted in which the angular velocity of the motor, the back electromotive force of the motor, the current of the motor or the steering angular velocity is detected, and the static friction is estimated from the steep change.
Japanese Patent No. 3481468

  Since the conventional static friction estimation method uses a steep change such as the angular velocity of the motor, the time derivative of each sensor signal is obtained. Therefore, when noise is present in each sensor signal, there is a possibility that the noise is detected as a steep change, so that the estimation accuracy of static friction deteriorates. Therefore, when a filter process is performed on the sensor signal in order to remove noise, a separate filter is required as hardware, or the control software becomes complicated if it is removed by software, resulting in an increase in cost. In addition, steep changes such as the angular velocity of the motor may be removed by the filtering process, so that the estimation accuracy of static friction is deteriorated and reliability is lowered.

  Accordingly, an object of the present invention is to provide an electric power steering apparatus that estimates static friction with a simple configuration and high accuracy.

  An electric power steering apparatus according to the present invention is an electric power steering apparatus that adds a steering assist force by a motor to a steering system according to a steering state, and includes a rotation angle detection unit that detects a rotation angle of the motor, and a current flowing through the motor. Current supply means for supplying static current and static friction estimation for supplying static current when the motor is stopped and estimating static friction based on the current value supplied to the motor when the rotation angle of the motor starts to change Means.

  In this electric power steering apparatus, when the motor is stopped, current is supplied to the motor by the current supply means. In the electric power steering apparatus after the current is started to be supplied, the rotation angle detection means detects the rotation angle of the motor, and detects when the rotation angle of the motor starts to change (when the motor starts to rotate from the stop). . In the electric power steering apparatus, the static friction is estimated based on the current value supplied to the motor when the rotation angle starts to change by the static friction estimation means. That is, when the current starts to be supplied to the motor, the motor remains stopped due to the influence of static friction. When the current supplied to the motor is gradually increased, the torque generated by the motor also increases. Eventually, the motor torque exceeds the static friction force, and the motor starts to rotate. Therefore, the motor torque generated by the current supplied when the motor starts rotating from the stop becomes the motor torque necessary for the static friction force. Thus, in the electric power steering apparatus, it is possible to estimate the static friction with a simple configuration. Further, in the electric power steering apparatus, it is only necessary to detect the moment when the rotation angle is changed from the stopped state, so that the static friction estimation accuracy is very high.

  The electric power steering apparatus according to the present invention may include a canceling unit that cancels the rotation in the steering system due to the rotation of the motor when the rotation angle changes from the stopped state of the motor.

  In this electric power steering apparatus, when the static friction is estimated, the rotation in the steering system generated by the rotation of the motor is canceled by the canceling unit. That is, when a current is supplied to the motor in order to estimate the static friction, the steering wheel moves somewhat through the steering shaft when the motor rotates. Therefore, the canceling means provided between the motor and the steering wheel gives the canceling means the action of canceling the rotation in the steering system before the rotation by the motor is transmitted to the steering wheel. As a result, the steering wheel does not move when estimating the static friction, so that the driver does not feel uneasy. The canceling means is, for example, a gear ratio variable device provided in the middle of the steering shaft.

  According to the present invention, static friction can be estimated with high accuracy by a simple configuration.

  Embodiments of an electric power steering apparatus according to the present invention will be described below with reference to the drawings.

  In the present embodiment, the electric power steering apparatus according to the present invention is applied to an electric power steering apparatus that applies a steering assist force by a brushless motor. The electric power steering apparatus according to the present embodiment uses a motor rotation angle sensor necessary for driving and controlling a brushless motor, and estimates the static friction of the steering system by the static friction estimation process in the ECU. In this embodiment, there are two embodiments, the first embodiment is a basic configuration of static friction estimation, and the rotation of the motor when the second embodiment estimates static friction. This also includes means for canceling the rotation of the steering system. In the present embodiment, the rotation angle of the motor and the direction of the steering torque are represented by positive and negative, the positive value is the right rotation direction, and the negative value is the left rotation direction.

  With reference to FIG.1 and FIG.2, the electric power steering apparatus 1 which concerns on 1st Embodiment is demonstrated. FIG. 1 is a configuration diagram of an electric power steering apparatus according to the first embodiment. FIG. 2 is an example of a motor map showing the relationship between the motor drive current and the motor rotational torque.

  In the electric power steering apparatus 1, steering assist torque is set according to various states of the vehicle, and the steering assist torque is applied to the steering system by a motor. In particular, the electric power steering apparatus 1 can estimate the static friction (friction torque) of the steering system. For this purpose, the electric power steering apparatus 1 includes a steering torque sensor 2, a vehicle speed sensor 3, a motor rotation angle sensor 4, a motor 5, an ECU [Electronic Control Unit] 6, and the like.

  In the first embodiment, the motor rotation angle sensor 4 corresponds to the rotation angle detection means described in the claims, and the ECU 6 corresponds to the current supply means and the static friction estimation means described in the claims. .

  The steering torque sensor 2 is a sensor that detects the direction and magnitude of the steering torque. The steering torque sensor 2 transmits a steering torque signal TS indicating its direction and magnitude to the ECU 6. The vehicle speed sensor 3 transmits a vehicle speed signal SS indicating the detected value to the ECU 6. The motor rotation angle sensor 4 is a sensor that detects the direction and magnitude of the rotation angle of the motor 5. The motor rotation angle sensor 4 transmits a motor rotation angle signal AS indicating its direction and magnitude to the ECU 6.

  The motor 5 is a brushless motor, and the current flowing through the coil is controlled based on the motor rotation angle detected by the motor rotation angle sensor 4. The motor 5 is connected to the ECU 6, and a control current CI based on the motor rotation angle is supplied from the ECU 6. The motor 5 is rotationally driven in a direction corresponding to the control current CI, and generates a rotational torque corresponding to the control current CI.

  The electric power steering device 1 may be a column drive type in which the motor 5 is provided with respect to a steering shaft (not shown) or a rack drive type in which the motor 5 is provided with respect to a rack shaft (not shown). . In any type, the motor 5 applies a predetermined torque to the steering shaft or the rack shaft via a speed reducer (not shown).

  The ECU 6 is an electronic control unit including a CPU [Central Processing Unit], a ROM [Read Only Memory], a RAM [Random Access Memory], a motor drive circuit, and the like. The ECU 6 controls the driving of the motor 5 by performing a steering assist control process, a static friction estimation process, and the like based on the detection signals TS, SS, AS from the various sensors 2, 3, 4.

  The steering assist control process will be described. The ECU 6 obtains the steering assist torque (direction and magnitude) based on the vehicle speed based on the vehicle speed signal SS, the steering torque based on the steering torque signal TS, and the like using the steering assist torque setting map. At this time, the ECU 6 calculates the vehicle speed from the rotational speed of each wheel based on the vehicle speed signal SS. The ECU 6 sets a drive current command value (direction and magnitude) necessary for generating the direction and magnitude of the steering assist torque. Further, a control current CI corresponding to the drive current command value is generated in the motor drive circuit of the ECU 6, and the generated control current CI is supplied to the motor 5. At this time, the ECU 6 feedback-controls the motor 5 based on the motor rotation angle by the motor rotation angle signal AS so that the drive current command value is obtained.

  The static friction estimation process will be described. The ECU 6 executes a static friction estimation process each time the ignition switch is turned on. First, the ECU 6 determines whether or not the steering torque is zero based on the steering torque based on the steering torque signal TS in order to confirm that there is no steering input from the driver. Further, the ECU 6 confirms whether or not the drive current command value is 0 in order to confirm that the motor 5 is in a stopped state. Further, the ECU 6 resets the rotation angle of the motor 5 to zero. At this time, the ECU 6 confirms whether the motor rotation angle based on the motor rotation angle signal AS is zero.

  When the ECU 6 confirms that there is no steering input from the driver and the motor 5 is in a stopped state, the ECU 6 sets the drive current command value slightly increased by a constant very small amount. Each time the drive current command value is set slightly increased, the motor drive circuit of the ECU 6 generates a control current CI corresponding to the drive current command value, and supplies the generated control current CI to the motor 5. Every time the slightly increased control current CI is supplied to the motor 5, the ECU 6 determines whether or not the absolute value of the motor rotation angle based on the motor rotation angle signal AS has changed from zero. Incidentally, when the absolute value of the motor rotation angle is 0, the friction torque of the static friction is larger than the rotation torque of the motor 5 via the speed reducer, and the motor 5 remains stopped. At the moment when the absolute value of the motor rotation angle changes from 0, the friction torque of static friction becomes equal to the rotation torque of the motor 5 via the speed reducer, and the motor 5 starts to rotate from the stopped state.

  When the ECU 6 determines that the absolute value of the motor rotation angle has changed from 0, the ECU 6 holds the drive current command value at the start of the change. Then, the ECU 6 uses the motor map (see FIG. 2) to obtain the rotational torque of the motor 5 when the control current CI corresponding to the drive current command value is supplied from the held drive current command value. The motor map is a map showing the relationship between the drive current supplied to the motor 5 and the generated rotational torque, and is set with a rotational torque that increases as the drive current increases. The motor map is obtained in advance by experiments or the like, and is held in the ECU 6. Further, the ECU 6 converts the friction torque of the static friction from the obtained rotational torque based on the gear ratio of the speed reducer between the motor 5 and the steering shaft or the rack shaft.

  In the electric power steering apparatus 1, in order to compensate for the static friction of the steering system, the estimated friction torque is used when obtaining the steering assist torque. In addition, when this vehicle is equipped with a device such as a lane keeping device that performs steering on the vehicle side, in order to compensate for the static friction of the steering system, the estimated friction torque is added to the added steering torque. It may be.

  With reference to FIG. 1, the operation | movement at the time of estimating the static friction in the electric power steering apparatus 1 is demonstrated. In particular, the static friction estimation process in the ECU 6 will be described with reference to the flowchart of FIG. FIG. 3 is a flowchart showing a static friction estimation process in the ECU of FIG.

  The driver turns on the ignition switch. Then, the ECU 6 starts the static friction estimation process. The steering torque sensor 2 detects the steering torque and transmits a steering torque signal TS to the ECU 6. The motor rotation angle sensor 4 detects the rotation angle of the motor 5 and transmits a motor rotation angle signal AS to the ECU 6. The vehicle speed sensor 3 detects the rotational speed of each wheel, and transmits a vehicle speed signal SS to the ECU 6. The ECU 6 calculates the vehicle speed from the detected rotational speed.

  The ECU 6 determines whether or not the steering torque is 0 (S1). In the ECU 6, when the steering torque is not 0, the process of S1 is repeatedly executed. If the steering torque is determined to be 0 in S1, the ECU 6 determines whether or not the drive current command value is 0 (S2). In the ECU 6, when the drive current command value is not 0, the process of S2 is repeatedly executed. If the drive current command value is determined to be 0 in S2, the ECU 6 resets the rotation angle of the motor 5 to 0 (S3).

  When the above conditions are satisfied, the ECU 6 integrates and sets a certain minute amount as the drive current command value with respect to the previous drive current command value, and sends the control current CI according to the drive current command value from the motor drive circuit to the motor. 5 (S4).

  The motor 5 generates a rotational torque corresponding to the supplied control current CI. And this rotational torque is added to a steering shaft or a rack axis | shaft via a reduction gear. When the applied torque is smaller than the friction torque of static friction, the motor 5 remains stopped (rotation angle is 0), and the steering shaft or the rack shaft also remains stopped. On the other hand, when the applied torque becomes larger than the friction torque of the static friction, the motor 5 rotates (the rotation angle changes from 0), and the steering shaft rotates or the rack shaft moves in the vehicle width direction.

  Each time the process of S4 is executed, the ECU 6 determines whether or not the absolute value of the rotation angle of the motor 5 has changed from 0 (S5). If it is determined in S5 that the absolute angle of the rotation angle is 0, the ECU 6 returns to the process of S4, and further sets the drive current command value slightly increased by a certain minute amount, and uses the slightly increased control current CI as the motor. 5 (S4).

  When it is determined in S5 that the absolute value of the rotation angle has changed from 0, the ECU 6 uses the motor map to determine the rotational torque of the motor 5 based on the drive current command value at that time (S6). Further, the ECU 6 calculates the friction torque of the steering system from the obtained rotational torque using the gear ratio of the reduction gear (S7).

  According to this electric power steering apparatus 1, static friction is estimated with a simple configuration in which a current is gradually supplied from a stopped state of the motor 5 and a friction torque is obtained from a drive current value when the rotation angle of the motor 5 changes. be able to. In addition, since the electric power steering apparatus 1 only detects the time when the motor 5 starts to rotate from the stopped state, the static friction can be estimated with high accuracy.

  With reference to FIG. 4, an electric power steering apparatus 11 according to a second embodiment will be described. FIG. 4 is a configuration diagram of an electric power steering apparatus according to the second embodiment. In addition, in the electric power steering apparatus 11, the same code | symbol is attached | subjected about the structure similar to the electric power steering apparatus 1 which concerns on 1st Embodiment, and the description is abbreviate | omitted.

  The electric power steering device 11 is the same device as the electric power steering device 1, but cancels the rotation of the steering wheel due to the rotation of the motor 5 so that the steering wheel does not move when estimating the static friction. For this purpose, the electric power steering apparatus 11 includes a steering torque sensor 2, a vehicle speed sensor 3, a motor rotation angle sensor 4, a motor 5, an ECU [Electronic Control Unit] 16, and the like. 17 is used.

  In the second embodiment, the motor rotation angle sensor 4 corresponds to the rotation angle detection means described in the claims, and the ECU 16 corresponds to the current supply means and the static friction estimation means described in the claims. The gear ratio variable device 17 corresponds to canceling means described in the claims.

  The gear ratio variable device 17 is a device that changes the steering gear ratio (the ratio of the steering angle of the steering wheel to the turning angle of the tire) according to the vehicle speed. The gear ratio variable device 17 is provided at an intermediate portion of the steering shaft, and changes the rotation ratio between the steering wheel side and the pinion side of the steering shaft. Therefore, the steering shaft is separated into the steering wheel side and the pinion side via the gear ratio variable device 17. The gear ratio variable device 17 is connected to the ECU 16 and receives a cancel signal CS (rotation direction and rotation angle) from the ECU 16. When the gear ratio varying device 17 receives the cancel signal CS, the gear ratio variable device 17 rotates the pinion side steering shaft by the rotation angle in the rotation direction indicated by the cancel signal CS.

  The ECU 16 is the same ECU as the ECU 6 according to the first embodiment, but also has a process for canceling the rotation of the steering wheel in the static friction estimation process. Therefore, the ECU 16 controls the driving of the motor 5 and transmits the cancel signal CS to the gear ratio variable device 17 to operate it. Here, only the process added to the static friction estimation process in the ECU 6 in the static friction estimation process in the ECU 16 will be described.

  Every time the slightly increased control current CI is supplied to the motor 5, the ECU 16 obtains the angular velocity of the motor 5 by time-differentiating the motor rotation angle based on the motor rotation angle signal AS. Then, the ECU 16 determines whether or not the motor angular velocity (differential value) has changed from zero. In this way, instead of determining the change in the motor rotation angle, the change in the motor angular velocity is determined because the angular velocity rises steeply even with a slight change in the rotation angle. This is to detect as fast as possible.

  When the ECU 16 determines that the motor angular velocity has changed from 0, the direction opposite to the direction in which the steering shaft rotates (and thus the direction in which the steering wheel is steered) from the motor rotation angle (rotation direction and magnitude) at that time. Is set as the rotation direction, and the rotation angle of the steering shaft on the pinion shaft side by the rotation of the motor 5 is obtained. Then, the ECU 16 sets a cancel signal CS indicating the rotation direction and rotation angle, and transmits it to the gear ratio variable device 17.

  With reference to FIG. 4, the operation | movement at the time of estimating the static friction in the electric power steering apparatus 11 is demonstrated. In particular, the static friction estimation process in the ECU 16 will be described with reference to the flowchart of FIG. In the operation description here, only points different from the operation description in the first embodiment will be described in detail. FIG. 5 is a flowchart showing a static friction estimation process in the ECU of FIG. In the flowchart shown in FIG. 5, the same step numbers are assigned to the same processes as those in the flowchart shown in FIG. 3 according to the first embodiment.

  The ECU 16 calculates the friction torque of the static friction by the processes of S1 to S7. At this time, every time the process of S4 ends, the ECU 16 time-differentiates the rotation angle of the motor 5 and calculates the angular velocity of the motor 5 (S8). Then, the ECU 6 determines whether or not the motor angular velocity (differential value) has changed from 0 (S9). If it is determined in S9 that the motor angular velocity has not changed, the ECU 6 returns to the process of S4. In this case, since the rotation angle of the motor 5 has not changed, it is determined that the absolute angle of the rotation angle is 0 in S5.

  If it is determined in S9 that the motor angular velocity has changed, the ECU 6 sets a cancel signal CS indicating the rotation direction and rotation angle for canceling steering wheel steering, and transmits it to the gear ratio variable device 17 (S10). ). Then, the gear ratio variable device 17 rotates the pinion side steering shaft by the rotation angle in the rotation direction set in the cancel signal CS. Therefore, the rotation of the motor 5 is canceled by the gear ratio variable device 17 and is not transmitted to the steering shaft (and thus the steering wheel) on the steering wheel side.

  According to the electric power steering apparatus 11, the same effect as that of the electric power steering apparatus 1 according to the first embodiment is obtained, and the steering wheel does not rotate when estimating the static friction. Therefore, the driver does not feel uncomfortable by rotating the steering wheel without permission. Further, in the electric power steering device 11, the change of the motor 5 can be detected quickly by detecting the change in the angular velocity, and the rotation of the motor 5 can be canceled before the rotation of the motor 5 is transmitted to the steering wheel. it can.

  As mentioned above, although embodiment which concerns on this invention was described, this invention is implemented in various forms, without being limited to the said embodiment.

  For example, in the present embodiment, the present invention is applied to an electric power steering apparatus including a brushless motor, but the present invention can also be applied to an electric power steering apparatus including another motor. Moreover, although it was set as the structure which detects the rotation angle of a motor with the motor rotation angle sensor provided with a brushless motor, when it is not a brushless motor, it is good also as a structure provided with a motor rotation angle sensor as a rotation angle detection means, It may be a means for estimating the rotation angle of the motor from the current value and voltage value of the motor, or a means for calculating from the angular velocity of the motor or the angular acceleration of the motor.

  In the present embodiment, the motor torque is calculated from the motor drive current using the motor map, but the motor torque is calculated from the motor drive current using a predetermined calculation formula. It is good.

  Further, in the second embodiment, the gear ratio variable device is used as the canceling unit. However, other devices may be used as long as the device can cancel the rotation of the steering system due to the rotation of the motor, or a dedicated device. The canceling means may be configured.

  In the second embodiment, the present invention is applied to a rack drive type electric power steering device. However, if the gear ratio variable device is small and can be provided in the vicinity of the steering wheel of the steering shaft, the column drive type is also used. Applicable.

It is a lineblock diagram of the electric power steering device concerning a 1st embodiment. It is an example of the motor map which shows the relationship between the drive current of a motor, and the rotational torque of a motor. It is a flowchart which shows the static friction estimation process in ECU of FIG. It is a block diagram of the electric power steering device which concerns on 2nd Embodiment. It is a flowchart which shows the static friction estimation process in ECU of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,11 ... Electric power steering device, 2 ... Steering torque sensor, 3 ... Vehicle speed sensor, 4 ... Motor rotation angle sensor, 5 ... Motor, 6, 16 ... ECU, 17 ... Gear ratio variable device

Claims (2)

An electric power steering device for adding a steering assist force by a motor to a steering system according to a steering state,
Rotation angle detection means for detecting the rotation angle of the motor;
Current supply means for supplying current to the motor;
Static friction estimating means for supplying static current when the motor is in a stopped state and estimating static friction based on the current value supplied to the motor when the rotation angle of the motor starts to change. Electric power steering device.   2. The electric power steering apparatus according to claim 1, further comprising canceling means for canceling rotation in the steering system due to rotation of the motor when a rotation angle changes from a stopped state of the motor.

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