JP4061980B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering equipment for assisting steering by transferring torque generated by an electric motor to a steering mechanism.
[0002]
[Prior art]
For example, in an electric power steering device that assists steering by applying torque generated by an electric motor to a steering mechanism, an absolute steering angle sensor that outputs a signal corresponding to the rotational position (absolute steering angle) of the steering wheel is provided as an additional function. The target current value corresponding to the detection signal of the absolute steering angle sensor is set, and the drive control of the electric motor is performed based on the target current value. Further, in recent vehicles, based on the absolute rudder angle detected by the absolute rudder angle sensor, the driving force of the engine and / or the braking force of the wheels is controlled to stabilize the posture of the vehicle (stability).・ Control is performed.
[0003]
[Problems to be solved by the invention]
However, since the absolute rudder angle sensor is expensive, the electric power steering apparatus provided with this absolute rudder angle sensor has a problem of high cost.
[0004]
Accordingly, an object of the present invention is to provide an electric power steering apparatus having a configuration capable of detecting an absolute steering angle of a steering mechanism (steering wheel) without using an absolute steering angle sensor.
[0006]
[Means for Solving the Problems and Effects of the Invention]
In order to achieve the above object, the invention according to claim 1 controls the electric motor (M) in accordance with the operation of the operating member (11), and generates torque generated from the electric motor by the steering mechanism (12, 13, 14) is an electric power steering device which assists steering by providing motor rotation angle detection means (23, 211) for detecting the rotation angle of the electric motor and the steering mechanism based on the rotation speed of the vehicle wheel. Based on the neutral position detected by the neutral position detector and the rotation angle detected by the motor rotation angle detector, the absolute steering angle of the steering mechanism is detected. detecting the absolute steering angle detecting means and (212), seen including a steering torque detecting means (22) for detecting a steering torque applied to the operation member, the upper The neutral position detecting means is such that the rotational speeds of the left and right wheels of the vehicle are greater than zero, the rotational speeds of the left and right wheels are substantially the same, and the steering torque detected by the steering torque detecting means is substantially zero. An electric power steering device that detects a steering angle of the steering mechanism at a certain time as a neutral position .
[0007]
In addition, the alphanumeric characters in parentheses represent corresponding components in the embodiments described later. The same applies hereinafter.
[0008]
According to the present invention, the neutral position of the steering mechanism is detected based on the rotational speed (wheel speed) of the vehicle wheel. Then, the absolute steering angle of the steering mechanism is detected based on the detected neutral position and the rotation angle of the electric motor detected by the motor rotation angle detection means. Therefore, since an expensive absolute steering angle sensor is not required, the cost can be reduced as compared with an electric power steering apparatus provided with this absolute steering angle sensor. Further, a space for arranging the absolute rudder angle sensor becomes unnecessary.
[0010]
The neutral position of the steering mechanism is the steering angle of the steering mechanism when the vehicle is traveling straight. When the vehicle is traveling straight, the wheel speeds of the left and right wheels are greater than zero, and the wheel speeds of the left and right wheels are substantially equal. Therefore, if the rotational speeds of the left and right wheels are greater than zero and the rotational speeds of the left and right wheels are substantially the same, it is determined that the vehicle is traveling straight, and the steering angle of the steering mechanism at this time is set to the neutral position. be able to.
[0012]
According to a second aspect of the present invention, the steering mechanism includes a rack bar (14), and torque generated from the electric motor is mechanically transmitted to the rack bar via a speed reducer (15). The electric power steering apparatus according to claim 1.
According to a third aspect of the present invention, the absolute rudder angle detection means uses the rotation angle detected by the motor rotation angle detection means when the neutral position detection means detects the neutral position of the steering mechanism as a reference rotation angle. The electric power steering according to claim 1 or 2 , wherein the absolute steering angle of the steering mechanism is calculated based on a change amount of the rotation angle of the electric motor from the reference rotation angle. Device.
[0013]
In the configuration in which the torque generated by the electric motor is transmitted to the steering mechanism to achieve steering assistance, the rotation angle of the electric motor corresponds to the steering angle (relative steering angle) of the steering mechanism. For example, when the rotation of the electric motor is decelerated at a constant reduction ratio and transmitted to the steering mechanism, between the rotation angle of the electric motor and the steering angle of the steering mechanism,
The relationship of motor rotation angle × (1 / reduction ratio) = steering angle of the steering mechanism is established.
[0014]
Therefore, as described in claim 3 , the absolute steering angle of the steering mechanism is the rotation angle of the electric motor from the reference rotation angle with the rotation angle of the electric motor when the steering mechanism is in the neutral position as the reference rotation angle. It can be calculated based on the amount of change.
[0015]
According to a fourth aspect of the present invention, there is provided an electric power steering apparatus that controls an electric motor in accordance with an operation of an operation member and applies a torque generated from the electric motor to a steering mechanism to assist steering , and the steering mechanism of the steering mechanism Steering angle change detecting means (23, 211; 24) for outputting a detection signal corresponding to the angle change, and neutral position detecting means (212; for detecting the neutral position of the steering mechanism based on the rotational speed of the vehicle wheel). 217) and an absolute steering angle detection means (212; for detecting an absolute steering angle of the steering mechanism) based on the neutral position detected by the neutral position detection means and the detection signal output from the steering angle change detection means. and 217), seen including a steering torque detecting means (22) for detecting a steering torque applied to the operation member, the neutral position detecting means, the car The left and right wheels have a rotational speed greater than zero, the left and right wheels have substantially the same rotational speed, and the steering torque detected by the steering torque detecting means is substantially zero. An electric power steering apparatus that detects a steering angle as a neutral position .
[0016]
According to the present invention, the absolute steering angle of the steering mechanism can be detected without using an expensive absolute steering angle sensor.
[0017]
The steering angle change detecting means may directly detect the steering angle change amount of the steering mechanism and output a signal corresponding to the detected steering angle change amount (24) . electric movement motors (relative) detects the rotational angle, or may be designed to output a signal corresponding to the rotation angles of the detection (23,211).
[0018]
That the difference between the rotational speeds of the left and right wheels of the vehicles is less than a predetermined value close to zero, since the wheel speed of the left and right wheels is that substantially equal, the difference between the rotational speeds of the left and right wheels is equal to or less than the predetermined value Ah is, the steering torque Ru substantially Reidea steering torque that is detected by the detection means state, the vehicle can be determined that the state in which the straight, the rotational position at this time of the steering mechanism to a neutral position Can do.
[0019]
Furthermore, as described in claim 5, the steering mechanism includes a rack bar (14), and torque generated from the electric motor is mechanically transmitted to the rack bar via a speed reducer (15). Also good.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0022]
FIG. 1 is a block diagram for explaining an electrical configuration of an electric power steering apparatus according to an embodiment (first embodiment) of the present invention. The electric power steering apparatus is configured such that the electronic control unit 21 drives and controls an electric motor M (for example, a brushless motor) based on a steering torque applied from the steering wheel 11 to the steering shaft 12. The steering torque applied to the steering shaft 12 is transmitted to the rack bar 14 via the pinion gear 13 to cause the rack bar 14 to linearly move in the vehicle width direction (longitudinal direction of the rack bar 14). The linear motion of the bar 14 is converted into the steering force of the front left and right wheels for steering by a tie rod or a knuckle arm (not shown). Further, the generated torque of the electric motor M is mechanically transmitted to the rack bar 14 via the speed reducer 15 as a steering assist force.
[0023]
In order to detect steering torque, a torque sensor 22 is provided in association with the steering shaft 12. Specifically, the steering shaft 12 has a configuration in which an input shaft coupled to the steering wheel 11 side and an output shaft provided with the pinion gear 13 are connected by a torsion bar, and the torque sensor 22 includes the steering wheel 11. The direction and magnitude of the twist generated in the torsion bar when the is operated is detected as the steering torque. A signal representing the steering torque detected by the torque sensor 22 is supplied to the electronic control unit 21.
[0024]
When the electric motor M is a brushless motor, a rotation angle sensor 23 for detecting the rotation angle of the electric motor M (rotation position of the rotor) is attached to the electric motor M. The rotation angle sensor 23 is composed of, for example, a resolver that outputs a signal corresponding to the rotational position of the rotor, or a rotary encoder that outputs a pulse signal every time the rotor rotates by a certain angle. The output signal of the rotation angle sensor 23 is also given to the electronic control unit 21.
[0025]
The electronic control unit 21 further includes a vehicle speed signal indicating a traveling speed (vehicle speed) of the vehicle via an interface such as a CAN (Controller Area Network) constructed with another controller mounted on the vehicle. A wheel speed signal representing the rotational speed (wheel speed) of each wheel of the vehicle is input.
[0026]
The electronic control unit 21 includes a microcomputer and the like. The rotation angle detection unit 211 that detects the motor rotation angle based on the output signal of the rotation angle sensor 23 by the program processing by the microcomputer, and the steering wheel 11. Each function of the absolute steering angle detection unit 212 that detects the absolute steering angle that is the rotational position of the (steering shaft 12) is realized.
[0027]
The electronic control unit 21 also has a motor target that is a current value to be supplied to the electric motor M based on the steering torque detected by the torque sensor 22, the vehicle speed, and the absolute steering angle detected by the absolute steering angle detection unit 212. A motor target current calculation unit 213 that calculates a current value, a motor current detection circuit 214 that detects a drive current (motor current) actually supplied to the electric motor M, and a motor calculated by the motor target current calculation unit 213 A subtraction unit 215 that obtains a deviation between the target current value and the motor current detected by the motor current detection circuit 214, and an electric motor based on the deviation obtained by the subtraction unit 215 and the motor rotation angle detected by the rotation angle detection unit 211. And a current control unit 216 that controls the current flowing through the motor M. The motor target current calculation unit 213 includes A feedback control of the electric motor M based on the calculated target motor current value I. Each function of the motor target current calculation unit 213, the subtraction unit 215, and the current control unit 216 is realized by software by program processing by a microcomputer.
[0028]
The absolute steering angle detection unit 212 detects the absolute steering angle based on the wheel speed signal, the detection signal of the torque sensor 22, and the output signal of the rotation angle detection unit 211.
[0029]
Specifically, when the ignition key switch of the vehicle is turned on, the absolute steering angle detection unit 212 first detects the neutral position of the steering wheel 11 (the rotational position of the steering wheel 11 when the vehicle is traveling straight). In the vehicle straight running state, the wheel speed of each wheel is greater than zero, and the wheel speeds of the left and right wheels are substantially equal (while the vehicle is traveling on a curve, the wheel speed of the outer wheel is greater than the wheel speed of the inner wheel. ). Further, since the steering wheel 11 is not operated in the straight traveling state of the vehicle, the steering torque is almost zero. Therefore, the absolute rudder angle detection unit 212, when each of these conditions is satisfied, that is, if each wheel speed is greater than zero, the wheel speeds of the left and right wheels are substantially equal, and the steering torque is substantially zero, A straight traveling state is determined, and the rotational position of the steering wheel 11 at this time is set as a neutral position.
[0030]
After detecting the neutral position of the steering wheel 11, the absolute steering angle detection unit 212 determines the steering wheel based on the detected neutral position of the steering wheel 11 and the motor rotation angle detected by the rotation angle detection unit 211 thereafter. 11 detects the absolute steering angle corresponding to the rotation angle from the neutral position. That is, the rotation of the electric motor M is decelerated at a constant reduction ratio (for example, 7 to 30) by the reduction gear 15 and transmitted to the rack bar 14. ,
Since there is a relationship of motor rotation angle × (1 / reduction ratio) = rotation angle of the steering shaft 12, the absolute steering angle is the reference rotation with the motor rotation angle when the steering wheel 11 is in the neutral position as the reference rotation angle. It can be calculated by multiplying the change amount of the motor rotation angle from the angle by (1 / reduction ratio). The absolute steering angle detected in this way is given to the motor target current calculation unit 213, and is also transmitted to the controller that controls the driving force of the engine and / or the braking force of the wheels via the interface such as CAN in order to stabilize the vehicle posture. Is done.
[0031]
As described above, in the electric power steering apparatus of this embodiment, the absolute steering angle of the steering wheel 11 is detected based on the wheel speed, the steering torque, and the motor rotation angle. Therefore, since an expensive absolute steering angle sensor is not required, the cost can be reduced as compared with an electric power steering apparatus provided with this absolute steering angle sensor. Further, the space near the steering shaft 12 can be afforded as much as the space for arranging the absolute steering angle sensor is unnecessary.
[0033]
FIG. 2 is a block diagram for explaining an electrical configuration of an electric power steering apparatus according to another embodiment (second embodiment) of the present invention. In FIG. 2, parts corresponding to the parts shown in FIG. 1 are denoted by the same reference numerals as in FIG. Moreover, since the part which attached | subjected the same referential mark has a function similar to the case of the above-mentioned embodiment, the detailed description about these parts is abbreviate | omitted below.
[0034]
In this embodiment, in relation to the steering wheel 11, for example, a relative rudder that detects the steering angle (relative steering angle) of the steering wheel 11 with reference to the rotational position of the steering wheel 11 immediately after turning on the ignition key switch of the vehicle. An angle sensor 24 is provided. Then, the electronic control unit 210 detects the absolute steering angle of the steering wheel 11 based on the vehicle speed, the wheel speed, the steering torque, and the relative steering angle detected by the relative steering angle sensor 24, and the detected absolute steering angle. The electric motor M is controlled based on the above.
[0035]
Specifically, the electronic control unit 210 has an absolute steering angle detection unit 217 realized by a program process executed by the microcomputer, and the absolute steering angle detection unit 217 is connected to an interface such as CAN. Vehicle speed signal and wheel speed signal, torque sensor 22 detection signal, and relative steering angle sensor 24 detection signal.
[0036]
The absolute steering angle detection unit 217 detects the neutral position of the steering wheel 11 when the vehicle speed is equal to or higher than a predetermined speed (for example, 5 km / h). The detection of the neutral position is performed by the same method as in the case of the first embodiment described above. That is, if the difference between the wheel speeds of the left and right wheels is not more than a predetermined value (for example, 0.1 km / h) that is close to zero and the steering torque is not more than a predetermined value (for example, 0.2 Nm) that is close to zero, It is determined that the vehicle is traveling straight, and the rotation position of the steering wheel 11 at this time is set as a neutral position. The condition that the difference between the wheel speeds of the left and right wheels is not more than a predetermined value close to zero is substantially the same as the condition that the wheel speeds of the left and right wheels are substantially equal, and the steering torque is not more than a predetermined value that is close to zero. Is substantially the same as the condition that the steering torque is substantially zero. Therefore, the neutral position detection method in this embodiment is substantially the same as the neutral position detection method in the first embodiment. The same can be said.
[0037]
After detecting the neutral position, the absolute steering angle detection unit 217 captures the detection signal of the relative steering angle sensor 24 at a predetermined control cycle, and the relative steering angle represented by the captured detection signal is compared with the relative steering angle when the neutral position is detected. The relative steering angle (steering angle midpoint) detected by the steering angle sensor 24 is converted into an absolute steering angle. That is, by subtracting the relative rudder angle at the time of neutral position detection from the relative rudder angle detected by the relative rudder angle sensor 24, an absolute rudder angle that is a rudder angle based on the neutral position of the steering wheel 11 is obtained. Then, the absolute steering angle acquired for each control cycle is given to the motor target current calculation unit 213 and also given to the controller for vehicle posture stabilization via an interface such as CAN.
[0038]
As described above, even with the configuration of this embodiment, the absolute steering angle can be detected without using an expensive absolute steering angle sensor, and the same effect as in the case of the first embodiment can be obtained.
[0040]
Further, the neutral position of the steering wheel 11 is detected when the vehicle speed becomes equal to or higher than a predetermined speed. However, when the wheel speed becomes equal to or higher than the predetermined rotational speed, the neutral position of the steering wheel 11 may be detected. Since there is a certain relationship between the wheel speed and the vehicle speed, the neutral position of the steering wheel 11 can be obtained even if the condition that the vehicle speed is equal to or higher than the predetermined speed is replaced with the condition that the wheel speed is equal to or higher than the predetermined rotation speed. Can be detected satisfactorily.
[0041]
As a method for detecting the neutral position of the steering wheel 11, for example, the time differential value of the steering torque detected by the torque sensor 22 is not more than a predetermined value other than the method described in the first or second embodiment, Further, when the time differential value (steering angular velocity) of the steering angle of the steering wheel 11 is equal to or less than a predetermined value, it is determined that the vehicle is in a straight traveling state, and the rotational position of the steering wheel 11 at this time is set to the neutral position. . However, since the output signal of the torque sensor 22 includes many unstable elements such as noise components, in this method, the process of removing the unstable elements from the output signal of the torque sensor 22 prior to the detection of the neutral position ( For example, it is necessary to perform an averaging process), and it takes time to detect the neutral position. On the other hand, in the detection method of the first or second embodiment, when the condition that the steering torque is not more than a predetermined value close to zero or the condition that the steering torque is substantially zero is omitted, the steering wheel 11 neutral position can be detected in a short time, so that good steering assistance and vehicle attitude stability control can be performed immediately after the start of operation of the steering wheel 11.
[0042]
FIG. 3 is a flowchart for explaining the neutral position return control performed when the vehicle is parked.
[0043]
For example, there is a case where the steering wheel 11 is cut into one side for garage entry or width adjustment, and the vehicle is parked while the steering wheel 11 is cut. In such a case, when the vehicle is started, the vehicle may travel in a direction that the driver does not plan. In particular, if the driver once leaves the vehicle after parking, the driver assumes that the vehicle will go straight when starting the vehicle, so the starting direction of the vehicle becomes a direction that the driver does not plan.
[0044]
Therefore, in a vehicle equipped with the electric power steering device according to the first or second embodiment described above, the steering wheel 11 (the steering shaft 12, the pinion gear 13, the rack bar 14, etc.) is set by the electric power steering device when parked. It is preferable that neutral position return control for returning the steering mechanism) to the neutral position is performed.
[0045]
For example, the neutral position return control by the electric power steering apparatus according to the first embodiment is performed in response to the detection of the parking state of the vehicle by the microcomputer provided in the electronic control unit 21 (see FIG. 1) (steps). This is performed immediately after the detection of the parking state (step S2).
[0046]
When the vehicle is parked, for example, a vehicle speed signal input to the electronic control unit 21 via an interface such as CAN, a detection signal of a shift position sensor that detects the position of the shift lever of the automatic transmission, and hand brake on / Detected based on the detection signal of the handbrake sensor that detects OFF That is, the microcomputer of the electronic control unit 21 determines that the vehicle speed is zero, the shift lever is in the parking position, and the hand brake is turned on (the hand brake is applied). Detect as.
[0047]
The microcomputer that detects the parking state of the vehicle then controls the electric motor M so that the absolute steering angle of the steering wheel 11 detected by the absolute steering angle detection unit 212 becomes zero. Thereby, the steering wheel 11 is returned to the neutral position, and the left and right wheels for steering are directed in the direction when the vehicle is traveling straight. Therefore, even if the driver once leaves the vehicle after parking, there is no risk that the vehicle will travel in a direction that the driver does not plan when the vehicle is started.
[0048]
FIG. 4 is a diagram conceptually showing an arrangement example of a motor drive circuit for generating a drive current for the electronic control unit 21 (210) and the electric motor M. The electronic control unit 21 is housed in a sensor circuit housing 221 attached to the torque sensor 22 together with a signal output circuit (torque sensor circuit) of the torque sensor 22. On the other hand, the motor drive circuit is a circuit including a power element, a large-capacity electrolytic capacitor, a relay, and the like, and is housed in a driver housing 25 attached to the housing of the electric motor M independently of the electronic control unit 21. . The electronic control unit 21 and the motor drive circuit are electrically connected by an analog signal line 26 that transmits a signal (analog electric signal) for controlling on / off of the power element in the motor drive circuit. .
[0049]
Since it is difficult to reduce the size of the motor drive circuit, in a configuration in which the motor drive circuit is included in the electronic control unit, the portion that accommodates the electronic control unit (the portion corresponding to the sensor circuit housing 221) is small. Is difficult. On the other hand, in the above configuration, since the motor drive circuit is independent of the electronic control unit 21, the sensor circuit housing 221 can be reduced in size, and an empty space can be created in the vicinity of the torque sensor 22.
[0050]
Also, since the motor drive circuit needs to change its capacity according to the vehicle type (size of the electric motor), in the configuration in which the motor drive circuit is included in the electronic control unit, it is necessary to prepare an electronic control unit corresponding to the vehicle type However, the configuration in which the motor drive circuit is independent from the electronic control unit 21 has an advantage that the common electronic control unit 21 can be used regardless of the vehicle type.
[0051]
Although the embodiment of the present invention has been described above, the present invention can be implemented in other forms, and various design changes can be made within the scope of the matters described in the claims.
[Brief description of the drawings]
FIG. 1 is a block diagram for explaining an electrical configuration of an electric power steering apparatus according to an embodiment (first embodiment) of the present invention.
FIG. 2 is a block diagram for explaining an electrical configuration of an electric power steering apparatus according to another embodiment (second embodiment) of the present invention.
FIG. 3 is a flowchart for explaining neutral position return control;
FIG. 4 is a diagram conceptually illustrating an arrangement example of an electronic control unit and a motor drive circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Steering wheel 12 Steering shaft 13 Pinion gear 14 Rack bar 15 Reduction gear 21 Electronic control unit 22 Torque sensor 23 Rotation angle sensor 24 Relative steering angle sensor 210 Electronic control unit 211 Rotation angle detection part 212 Absolute steering angle detection part 213 Motor target current calculation 216 Current control unit 217 Absolute steering angle detection unit M Electric motor

Claims (5)

An electric power steering device that controls an electric motor in accordance with an operation of an operation member and assists steering by giving a torque generated from the electric motor to a steering mechanism,
Motor rotation angle detection means for detecting the rotation angle of the electric motor;
Neutral position detecting means for detecting the neutral position of the steering mechanism based on the rotational speed of the wheels of the vehicle;
Absolute steering angle detection means for detecting the absolute steering angle of the steering mechanism based on the neutral position detected by the neutral position detection means and the rotation angle detected by the motor rotation angle detection means ;
Look including a steering torque detecting means for detecting a steering torque applied to the operation member,
In the neutral position detecting means, the rotational speeds of the left and right wheels of the vehicle are greater than zero, the rotational speeds of the left and right wheels are substantially the same, and the steering torque detected by the steering torque detecting means is substantially zero. An electric power steering apparatus characterized by detecting the steering angle of the steering mechanism at a neutral position as a neutral position .   The electric power steering apparatus according to claim 1, wherein the steering mechanism includes a rack bar, and torque generated from the electric motor is mechanically transmitted to the rack bar via a speed reducer. The absolute rudder angle detection means uses the rotation angle detected by the motor rotation angle detection means when the neutral position detection means detects the neutral position of the steering mechanism as a reference rotation angle, and determines from the reference rotation angle. 3. The electric power steering apparatus according to claim 1, wherein an absolute steering angle of the steering mechanism is calculated based on a change amount of a rotation angle of the electric motor. An electric power steering device that controls an electric motor in accordance with an operation of an operation member and assists steering by giving a torque generated from the electric motor to a steering mechanism ,
Rudder angle change detecting means for outputting a detection signal according to the rudder angle change of the steering mechanism;
Neutral position detecting means for detecting the neutral position of the steering mechanism based on the rotational speed of the wheels of the vehicle;
An absolute steering angle detection means for detecting an absolute steering angle of the steering mechanism based on a neutral position detected by the neutral position detection means and a detection signal output from the steering angle change detection means ;
Look including a steering torque detecting means for detecting a steering torque applied to the operation member,
In the neutral position detecting means, the rotational speeds of the left and right wheels of the vehicle are greater than zero, the rotational speeds of the left and right wheels are substantially the same, and the steering torque detected by the steering torque detecting means is substantially zero. An electric power steering apparatus characterized by detecting the steering angle of the steering mechanism at a neutral position as a neutral position .   The electric power steering apparatus according to claim 4, wherein the steering mechanism includes a rack bar, and torque generated from the electric motor is mechanically transmitted to the rack bar via a speed reducer.

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