JP2008195203A - Steering device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering device for a vehicle capable of easily and inexpensively estimating a road surface μ, regardless of a traveling state of the vehicle. <P>SOLUTION: A current sensor 34 of this steering device 1 measures current consumption consumed to vibrate a rack shaft 32 at a prescribed vibration period by a turning actuator 33. A friction coefficient estimating part detects a road surface friction coefficient between the road surface and steered wheels 31 based on the current consumption. As a result, the road surface friction coefficient can be detected, regardless of a tire slip ratio, without providing a rotational speed detector for each of the steered wheels 31, and thereby the road surface friction coefficient can be detected, regardless of the traveling state. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technology for improving a steer-by-wire vehicle steering apparatus.

  Conventionally, the steering shaft coupled to the steering wheel and the steering mechanism that steers the steered wheels are mechanically separated, and the steering actuator provided in the steering mechanism is electrically connected according to the steering amount of the steering wheel. A so-called steer-by-wire vehicle steering apparatus for controlling has been proposed.

  In such a steer-by-wire vehicle steering apparatus, the steering shaft and the steering mechanism are mechanically separated, so that a road surface reaction force such as a road surface frictional force is not transmitted to the steering wheel. Therefore, in a steer-by-wire vehicle steering apparatus, a reaction force actuator coupled to the steering shaft is provided, and a steering reaction force is applied to the steering wheel using the reaction force actuator, thereby causing a road surface reaction generated on the steered wheels. The force is virtually transmitted to the steering wheel. As a result, the driver can obtain an operation feeling as if the steering shaft and the steering mechanism are mechanically connected.

Conventionally, such road friction force (road friction coefficient (μ)) is determined by the tire slip condition (tire slip ratio) based on slip detection during braking by a wheel speed sensor and side slip detection by a yaw rate sensor. It was calculated and estimated from the regression coefficient of the tire slip ratio.
However, according to such a method, the road surface μ cannot be estimated when traveling at a constant speed when the brake operation is not performed or when traveling straight ahead when the steering wheel is not operated.

Therefore, the estimated road surface μ for acceleration / deceleration travel is calculated based on the acceleration and the regression coefficient of the tire slip ratio, and the estimated road surface μ for constant speed travel is calculated in advance for each tire slip ratio and road surface μ. Calculated based on the relationship between the set vehicle speed and the tire slip ratio, and depending on the estimated accuracy for each of these estimated road surface μ values for acceleration / deceleration driving and estimated road surface μ values for constant speed driving A technique has been proposed in which the road surface μ is finally estimated based on the weighted road surface μ estimated value for acceleration / deceleration traveling and the road surface μ estimated value for constant speed traveling (for example, Patent Document 1).
According to such a technique, even during acceleration / deceleration driving where acceleration / deceleration occurs due to braking operation or the like, even when driving at a constant speed where braking operation or the like is not performed and acceleration / deceleration does not occur, the road surface μ Was able to be estimated.
JP-A-2005-29016

  However, since such a technique estimates the road surface μ from the tire slip rate, a rotational speed detector is required for each wheel, the configuration tends to be complicated and expensive, and the tire is slipping. In other cases (for example, when the vehicle speed is 0), it is difficult to detect the road surface μ. For this reason, the steer-by-wire vehicle steering apparatus has a problem that an appropriate steering reaction force cannot be applied in a state where the tire does not slip.

  The present invention has been made in view of these problems, and an object of the present invention is to provide a vehicle steering apparatus that can easily and inexpensively estimate the road surface μ regardless of the traveling state of the vehicle.

  (1) Steering wheel (for example, equivalent to the steering wheel 21 in FIG. 1), steering angle detection means for detecting the steering angle of the steering wheel (for example, equivalent to the steering angle sensor 24 in FIG. 1), and vehicle speed are detected. Vehicle speed detection means (e.g., corresponding to the vehicle speed sensor 61 in FIG. 1), and sets a target rudder angle based on the steering angle and the vehicle speed, and is driven according to the set target rudder angle. In the vehicle steering apparatus, the motor torque generated by the steering actuator (for example, equivalent to the steering actuator 33 in FIG. 1) is applied to the rack shaft (for example, equivalent to the rack shaft 32 in FIG. 1). Drive control means for controlling the steered actuator (for example, corresponding to the drive control unit 53 in FIG. 2), and current measuring means for measuring current consumption of the steered actuator For example, when the steering actuator controls the rack shaft to vibrate at a predetermined vibration cycle by the drive control means, the current measurement means measures the current sensor 34. A vehicle having road surface friction coefficient detecting means (for example, equivalent to the friction coefficient estimating unit 54 in FIG. 2) for detecting a road surface friction coefficient between a road surface and a wheel based on current consumption of a steering actuator. Has proposed a steering device.

  According to the invention of (1), the current measuring means measures the consumption current consumed by the turning actuator to vibrate the rack shaft at a predetermined vibration period. Then, the road surface friction coefficient detecting means detects the road surface friction coefficient between the road surface and the wheel based on the current consumption. Thereby, since the road surface friction coefficient can be detected based on the current consumption of the steering actuator, it is not necessary to provide a rotational speed detector for each wheel, and the road surface friction coefficient can be detected regardless of the tire slip ratio. Therefore, the road surface friction coefficient can be detected regardless of the traveling state.

  (2) In the vehicle steering apparatus according to (1), when the road surface friction coefficient detection means controls the steering actuator to vibrate the rack shaft at a predetermined vibration period by the drive control means, A vehicular friction coefficient between a road surface and a wheel is detected based on a current consumption of the steering actuator measured by a current measuring unit and the vehicle speed detected by the vehicle speed detecting unit. A steering device is proposed.

  According to the invention of (2), the road surface friction coefficient detecting means detects the road surface friction coefficient based on the consumed current and the vehicle speed consumed to vibrate the rack shaft at a predetermined vibration cycle. Thereby, the road surface friction coefficient according to the vehicle speed can be detected. Therefore, for example, the road surface friction coefficient can be detected even when the vehicle speed is 0 and the tire does not slip.

  (3) The vehicle steering device according to (1) or (2) further includes a reaction force actuator (for example, corresponding to the reaction force motor 23 in FIG. 1) that applies a steering reaction force to the steering wheel, and the drive control The means applies the reaction force so that a steering reaction force corresponding to the steering angle detected by the steering angle detection means and the road surface friction coefficient detected by the road surface friction coefficient detection means is applied to the steering wheel. A vehicle steering apparatus characterized by controlling an actuator has been proposed.

  According to the invention of (3), the drive control means controls the reaction force actuator so as to apply a steering reaction force according to the steering angle and the road surface friction coefficient to the steering wheel. As a result, information on the road surface friction coefficient is transmitted to the driver via the steering wheel, and the driver can perform steering according to the road surface condition.

  According to the present invention, since the road surface friction coefficient can be detected based on the current consumption of the steering actuator, it is not necessary to provide a rotational speed detector for each wheel, and the road surface friction coefficient can be detected regardless of the tire slip ratio.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

<Configuration of vehicle steering device>
FIG. 1 is a schematic diagram of a vehicle steering apparatus 1 according to an embodiment of the present invention.
The vehicle steering apparatus 1 includes a steering mechanism 20 to which a steering operation by a driver is input, a steering mechanism 30 that steers a pair of steered wheels 31 and 31 based on the steering operation of the steering mechanism 20, and the steering. And a control device 50 that controls the mechanism 20 and the steering mechanism 30. The vehicle steering device 1 of the present invention is a so-called steer-by-wire (SBW) type vehicle steering device in which the steering mechanism 20 and the steering mechanism 30 are mechanically separated.

  The steering mechanism 20 includes a steering wheel 21 that can be steered by the driver, a substantially rod-shaped steering shaft 22 that rotatably supports the steering wheel 21, a reaction force motor 23 that applies torque to the steering shaft 22, and a reaction force. And a reaction force torque sensor 25 that detects a torque (steering reaction force) generated by the force motor 23.

  The output shaft of the reaction force motor 23 is connected to the steering shaft 22, so that the steering reaction force acting in the direction for returning the steering wheel 21 to the neutral position and the direction for returning to the neutral position are opposite. It is possible to generate a return resistance force that acts in the direction of. Here, the reaction force motor 23 and the steering shaft 22 are connected by a worm gear mechanism, but the present invention is not limited to this.

  The steering shaft 22 is provided with a steering angle sensor 24 as steering angle detection means for detecting a steering angle (rotation angle) from the neutral position of the steering wheel 21 connected to the steering shaft 22. In the present embodiment, the steering angle of the steering wheel 21 is 0 at the neutral position. Further, the neutral position of the steering wheel 21 corresponds to the position of the steering wheel 21 that is controlled by the control device 50 so that the steered wheels 31 and 31 are in a straight traveling state.

  The steered mechanism 30 includes a substantially rod-shaped rack shaft 32, a steered actuator 33 that applies steered power to the rack shaft 32, and a current sensor 34 that serves as a current measuring unit that measures current consumption of the steered actuator 33. And steered wheels 31, 31 connected to both ends of the rack shaft 32. The steered actuator 33 is driven according to the rotation of the steering wheel 21. Steering wheels 31 and 31 are connected to both ends of the rack shaft 32 via steering rods 35 and 35, tie rods 36 and 36, and knuckle arms 37 and 37, respectively.

  The steering actuator 33 is connected to the rack shaft 32 by a rack and pinion mechanism. As a result, the turning power imparted by the turning actuator 33 is converted into the linear motion of the rack shaft 32 and the steering rods 35, 35, and the steered wheels 31, The steering angle of these steered wheels 31 and 31 is changed. The rack shaft 32 is provided with a steering angle sensor 38 that detects the steering angles of the steered wheels 31 and 31. Specifically, the steering angle sensor 38 is composed of a potentiometer that detects the operation amount of the steering rod 35.

  In addition to the steering angle sensor 24, the current sensor 34, and the steering angle sensor 38, the control device 50 includes a vehicle speed sensor 61 as vehicle speed detection means for detecting the vehicle speed of the vehicle, a yaw rate sensor 62 for detecting the yaw rate of the vehicle, and the like. The steering mechanism 20 and the steered mechanism 30 are controlled based on the input signal from. Here, the steering mechanism 20 and the turning mechanism 30 are connected to the control device 50 via a reaction force motor drive circuit 51 and a turning actuator drive circuit 52, respectively.

The reaction force motor drive circuit 51 drives the reaction force motor 23 based on the output from the control device 50, and is applied to the steering wheel 21 according to the traveling state of the vehicle such as the frictional force of the road surface and the operation state by the driver. Steering reaction force or return resistance force. Here, the reaction force motor drive circuit 51 receives the target steering reaction force determined by the control device 50 in accordance with the running state of the vehicle and the operation state of the steering wheel 21. The reaction force motor drive circuit 51 drives the reaction force motor 23 so that the steering reaction force of the reaction force motor 23 detected by the reaction force torque sensor 25 matches the target steering reaction force.
As a result, a steering reaction force or a return resistance force can be applied to the steering wheel 21, so that the driver is as if the steering wheel 21 and the steered wheels 31, 31 are mechanically connected. Operation feeling can be obtained.

The steered actuator drive circuit 52 drives the steered actuator 33 based on the output from the control device 50, and steers the steered wheels 31, 31 by moving the rack shaft 32. Here, the control instruction steering angle δ determined by the control device 50 in accordance with the traveling state of the vehicle and the operation state of the steering wheel 21 is input to the steering actuator drive circuit 52. The steered actuator drive circuit 52 drives the steered actuator 33 so that the steered angles of the steered wheels 31, 31 detected by the steered angle sensor 38 coincide with the control instruction steered angle δ.
Thereby, in the vehicle steering device 1, the characteristic of the angle ratio of the steered wheels 31, 31 to the steered amount (steering angle) of the steering wheel 21, that is, the steering characteristic can be automatically set.

  Here, in the vehicle steering apparatus 1 of the SBW system, since the steering mechanism 20 and the steering mechanism 30 are mechanically separated, the road surface reaction force (road surface μ) generated in the steered wheels 31, 31 is the steering wheel 21. Basically, the driver cannot grasp road surface information such as the road surface μ. Therefore, in the vehicle steering apparatus 1, road surface information is transmitted to the driver by controlling the steering reaction force against the steering wheel 21 to be different according to the road surface μ and the like.

<Method of estimating road friction coefficient (μ)>
Hereinafter, a method for estimating the road surface μ in the vehicle steering apparatus 1 will be described with reference to FIGS.
FIG. 2 is a control block diagram of a method for estimating the road surface μ, and FIG. 3 is a reference data map regarding the relationship between the vehicle speed and the current consumption of the turning actuator. FIG. 4 is a control flow for the road surface μ estimation method.

  As shown in FIG. 2, the control block for the road surface μ estimation method includes a vehicle speed sensor 61, a current sensor 34, a steering actuator 33, a drive control unit 53 that forms part of the control device 50, and a friction coefficient estimation. Unit 54 and storage unit 55.

  The drive control unit 53 of the control device 50 controls the steering actuator 33 via the steering actuator drive circuit 52 so as to vibrate the rack shaft 32 at a predetermined vibration cycle that does not affect the behavior of the vehicle. The current sensor 34 measures the current consumed by the steering actuator 33 at this time.

The storage unit 55 of the control device stores a reference data map regarding the relationship between the vehicle speed and the current consumption of the steering actuator.
As shown in FIG. 3, the reference data map is composed of the vehicle speed and the current consumed by the steering actuator 33. What is indicated by a solid line in FIG. 3 indicates a reference current consumption according to the vehicle speed. The reference current consumption corresponds to, for example, a current consumed by the turning actuator 33 when the rack shaft 32 is vibrated at a predetermined vibration cycle on a normal road surface (asphalt in fine weather).

  Then, the friction coefficient estimating unit 54 of the control device 50 calculates the friction coefficient (road surface μ) of the road surface from the current consumption of the steering actuator 33 measured by the current sensor 34, the vehicle speed detected by the vehicle speed sensor 61, and the reference data map. Is estimated. That is, the friction coefficient estimation unit 54 estimates the road surface μ from the difference between the standard consumption current in the reference data map and the consumption current consumed by the turning actuator 33.

  Here, when the road surface μ is high, a large force is required to vibrate the rack shaft 32 at a predetermined vibration period, so that the current consumption consumed by the steering actuator 33 increases. On the other hand, when the road surface μ is low, not so much force is required to vibrate the rack shaft 32 at a predetermined vibration period, so that the current consumption consumed by the steering actuator 33 is low.

  That is, when the current consumption of the steering actuator 33 measured by the current sensor 34 is higher than the reference current consumption (point P in FIG. 3), the friction coefficient estimation unit 54 estimates that the road surface μ is high, and the current sensor When the consumption current of the steering actuator 33 measured by 34 is lower than the reference consumption current (point Q or point R in FIG. 3), the friction coefficient estimation unit 54 estimates that the road surface μ is low. In particular, the friction coefficient estimation unit 54 estimates the road surface μ from the difference between the reference consumption current and the consumption current of the turning actuator 33. Therefore, when the consumption current of the turning actuator 33 is a point R in FIG. The road surface μ is estimated to be lower than when the current consumption of the steering actuator 33 is the point Q in FIG. Note that point Q and point R in FIG. 3 indicate current consumption of the steering actuator 33 at the same vehicle speed.

  Next, the procedure for estimating the road surface μ in the control device 50 configured as described above will be described with reference to the flowchart of FIG.

  First, in step S101, the drive control unit 53 of the control device 50 controls the steered actuator 33 so as to vibrate the rack shaft 32 at a predetermined vibration cycle. Here, the predetermined vibration period refers to one that does not affect the behavior of the vehicle. In step S <b> 102, the current consumption consumed by the steering actuator 33 to vibrate the rack shaft 32 is measured by the current sensor 34.

  In step S103, the vehicle speed is measured by the vehicle speed sensor 61. In step S104, the friction coefficient estimation unit 54 compares the measured current with a reference current consumption (FIG. 3) corresponding to the vehicle speed. In the embodiment, the current consumed by the steering actuator 33 when the rack shaft 32 is vibrated at a predetermined vibration cycle on the road surface in fine weather paved with asphalt is set as the reference consumption current.

  In step S105, the friction coefficient estimation unit 54 determines whether or not the measured current is higher than the reference consumption current. If this determination is YES, the process proceeds to step S106, and if NO, the process proceeds to step S107. In step S106, the friction coefficient estimation unit 54 estimates that the road surface μ is higher than the road surface in fine weather paved with asphalt, and ends the process. Moreover, in step S107, the friction coefficient estimation part 54 estimates that the road surface μ is lower than the road surface in fine weather paved with asphalt, and ends the processing.

  As described above, in the embodiment, the friction coefficient estimation unit 54 estimates the road surface μ by comparing the current consumed by the steering actuator 33 and the reference consumption current when the rack shaft 32 is vibrated at a predetermined vibration period. .

<Steering reaction force control processing>
The road surface μ estimated by the friction coefficient estimator 54 is transmitted to the driver by the steering reaction force against the steering wheel 21.
Hereinafter, the steering reaction force control process in the vehicle steering apparatus 1 will be described with reference to FIG.

  As shown in FIG. 5, the control block for the steering reaction force control process includes a steering angle sensor 24, a reaction force motor 23, a drive control unit 53 and a friction coefficient estimation unit 54 that form part of the control device 50, and Consists of

The steering angle sensor 24 detects the rotation angle of the steering wheel 21, and the friction coefficient estimation unit 54 of the control device 50 estimates the road surface μ. The drive control unit 53 of the control device 50 sets the target steering reaction force from the rotation angle of the steering wheel 21 and the road surface μ, and the steering reaction force corresponding to the target steering reaction force is applied to the steering shaft 22 via the reaction force motor drive circuit 51. The reaction force motor 23 is controlled so as to apply a force.
Thereby, a steering reaction force according to the road surface μ and the rotation angle of the steering wheel 21 can be applied to the steering wheel 21.

Therefore, for example, the drive control unit 53 of the control device 50 can set the target steering reaction force to be large when the road surface μ is high. Thus, when the road surface μ is high, a large force is required for steering the steering wheel 21, and the steering wheel 21 can be prevented from rotating much.
For example, the drive control unit 53 of the control device 50 can set the target steering reaction force to be small when the road surface μ is low. Thereby, not much force is required for steering the steering wheel 21 and the steering wheel 21 rotates easily, so that the road surface μ is low can be transmitted to the driver.

  Thus, by using the drive control unit 53 of the control device 50, an appropriate steering reaction force can be applied to the steering wheel 21 according to the road surface μ and the like.

In particular, since the road surface μ can be easily estimated using a device provided in a conventional SBW vehicle steering device, the road surface μ is detected without adding a new device, and the information is used as a steering reaction force. Can be reflected.
Further, since the road surface μ is estimated based on the reference current consumption according to the vehicle speed, for example, the road surface μ can be estimated even when the vehicle speed is 0 (stopped), and the steering wheel is also used when the vehicle speed is 0. An appropriate steering reaction force can be applied to 21.

  As mentioned above, although embodiment of this invention has been explained in full detail with reference to drawings, the concrete structure is not restricted to these, The design etc. of the range which does not deviate from the summary of this invention are included.

It is a lineblock diagram showing the steering device for vehicles concerning one embodiment of the present invention. It is a block diagram regarding the estimation control of the road surface friction coefficient of the steering apparatus for vehicles which concerns on the said embodiment. It is a figure which shows the reference data map about the road surface friction coefficient which concerns on the said embodiment. It is a flow regarding the estimation control of the road surface friction coefficient of the vehicle steering device according to the embodiment. It is a block diagram regarding control of the steering reaction force of the steering device for vehicles concerning the embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Vehicle steering device, 20 ... Steering mechanism, 21 ... Steering wheel, 24 ... Steering angle sensor, 30 ... Steering mechanism, 31, 31 ... Steering wheel, 32 ... Rack shaft, 33 ... Steering actuator, 34 ... Current Sensor 38 rudder angle sensor 50 control device 53 drive control unit 54 friction coefficient estimation unit 61 vehicle speed sensor

Claims (3)

Steering wheel,
Steering angle detecting means for detecting a steering angle of the steering wheel;
Vehicle speed detection means for detecting the vehicle speed,
For a vehicle in which a target rudder angle is set based on the steering angle and the vehicle speed, and motor torque generated by a steering actuator driven according to the set target rudder angle is applied to a rack shaft. In the steering device,
Current measuring means for measuring current consumption of the steering actuator;
Drive control means for controlling the steering actuator;
When the turning actuator controls the turning shaft to vibrate the rack shaft at a predetermined vibration period, the road surface and the wheel are controlled based on the current consumption of the turning actuator measured by the current measuring means. And a road surface friction coefficient detecting means for detecting a road surface friction coefficient.   The road surface friction coefficient detecting means consumes the turning actuator measured by the current measuring means when the driving control means controls the turning actuator to vibrate the rack shaft at a predetermined vibration period. The vehicle steering apparatus according to claim 1, wherein a road surface friction coefficient between a road surface and a wheel is detected based on an electric current and the vehicle speed detected by the vehicle speed detection means. A reaction force actuator for applying a steering reaction force to the steering wheel;
The drive control means applies a steering reaction force according to the steering angle detected by the steering angle detection means and the road surface friction coefficient detected by the road surface friction coefficient detection means to the steering wheel. The vehicle steering apparatus according to claim 1, wherein the reaction force actuator is controlled.

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