JP2005225354A - Steering device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent control interference between respective actuators in a steer-by-wire system steering device for a vehicle equipped with a plurality of actuators. <P>SOLUTION: The steering device is equipped with two motors driving a steering rack 3 and a controller 11 controlling the motors 6, 7. The controller 11 makes a total target torque to be generated by respective motors 6, 7 summation of the feedforward component excluding a front wheel turning angle and the feedback component except that, and determines distribution torque to respective motors 6, 7 so that the feedback component is distributed only to the motor 6. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention belongs to a technical field of a steering apparatus for a vehicle by a so-called steer-by-wire system in which a steering wheel and a steering gear for steering a front wheel are mechanically separated.

  The conventional steering control device is driven to displace the steered shaft according to the operation amount of the steering handle. However, the steered shaft motor includes two steered shaft motors serving as driving sources at this time. By driving the motors simultaneously, the steered shaft is displaced.

In this way, by providing two drive systems, even when a failure occurs in one of the steered shaft motors, the steered shaft can be driven to be displaced by the other steered shaft motor. The situation where steering becomes impossible is avoided (see, for example, Patent Document 1).
JP-A-4-38270

  However, in the above-described conventional steering control device, the control of the two turning shaft motors is based on the operation amount of the steering handle and the displacement amount of the turning shaft for both the turning shaft motors. Since the same calculated control amount is given, the target position of the two steered shaft motors will shift due to the effects of mechanical displacement error, electrical detection error, etc., and each other will perform other controls. There was a problem of interference.

  The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a vehicle steering apparatus capable of preventing control interference between a plurality of actuators.

In order to achieve the above-described object, in the vehicle steering apparatus of the present invention, the front wheel steering steering gear mechanically separated from the steering wheel that receives the steering input, and the front wheel steering steering gear are connected to Based on a plurality of actuators that generate torque to be steered and a target turning angle corresponding to a signal including at least a steering wheel angle and a front wheel turning angle, to the total target torque to be generated by the plurality of actuators and to each actuator corresponding thereto In a vehicle steering apparatus comprising: torque determining means for determining the distribution torque of the actuator; and actuator driving means for controlling the actual torque of each actuator based on the distribution torque.
The torque determining means sets the total target torque to be generated by the plurality of actuators as the sum of the feedforward component not including the front wheel turning angle and the other feedback component,
In addition, the distribution torque to each actuator is determined so that the feedback amount is distributed to only one actuator.

  Here, the Ford forward distribution to each actuator is free, and may be distributed to the actuator to which the feedback is distributed.

  In the present invention, since only one actuator is responsible for the feedback of the total target torque, the target position shift between the actuators does not occur, and the control interference between the plurality of actuators can be prevented.

  Hereinafter, the best mode for carrying out the vehicle steering system of the present invention will be described based on the first embodiment.

First, the configuration will be described.
FIG. 1 is a configuration diagram of a vehicle including the steer-by-wire system according to the first embodiment.
In FIG. 1, 1 is a handle, 2 is a handle angle sensor for detecting the steering amount of the handle, 3 is a steering rack, 4 is a tie rod, 5 is a tire (front wheel), 6 and 7 are motors (actuators), and 8 and 9 are A transmission for transmitting the torque of the motors 6 and 7 to the steering rack 3, 10 is a rotation angle sensor attached to the rotation shaft of the motor 6, 11 is a controller (torque determination means) for calculating a target torque of the motors 6 and 7, 12 , 13 are drivers (actuator driving means) for controlling the motor current so that the actual torques of the motors 6 and 7 coincide with the target torques of the motors 6 and 7, respectively. It is assumed that the relationship between the rotation of the motor 6 and the tire 5 is known in advance, and the rotation angle sensor 10 of the motor 6 is a sensor of a turning angle (steering amount) δ.

  The steer-by-wire feature is that the steering wheel 1 and the steering rack 3 are not mechanically connected, and the displacement of the steering rack 3, that is, the actual turning angle δ of the tire 5 is controlled based on the steering wheel angle θ.

Next, the operation will be described.
[Target turning angle calculation]
The control procedure by the controller 11 is as follows.
First, the target turning angle δ ^* is calculated based on the steering wheel angle θ. An example is shown in the following formula (1).
δ ^* = G (v) · θ (1)

  Here, G (v) corresponds to the steering gear ratio. v represents the vehicle speed and indicates variable vehicle speed. At low speeds, attempts are being made to increase G (v) to make the steering response quicker and improve maneuverability. On the other hand, at high speeds, G (v) is reduced to slow down the steering response, thereby improving running stability. In addition, a method for improving the vehicle behavior with respect to the steering wheel by giving dynamic characteristics is also being studied.

[Target total torque calculation]
Next, the total torque to be generated by the motors 6 and 7 (converted around the turning axis δ) is calculated so that the actual turning angle δ matches the target turning angle δ ^* . In order to realize this servo system, a two-degree-of-freedom control system is used.

The configuration of the two-degree-of-freedom control system is shown in FIG. P (s) is the model to be controlled, and F (s) is the target value response of the actual turning angle δ to the target turning angle δ ^* . F (s) · δ ^* is expressed as a target turning angle correction value δ ^** . C (s) represents a feedback controller.

First, an example of P (s) derivation method is shown. The model around the turning shaft is approximated by the following formula (2).
^{_{T d = I d · s 2}} δ + C d · sδ + ξN f (s) / D f (s) · δ ... (2)
Here, s represents a differential with a Laplace operator, T _d is the total torque of the motors 6 and 7 (converted value around the turning shaft), I _d is the motors 6 and 7, the transmissions 8 and 9, and the steering rack. 3, tie rods 4, the moment of inertia, C _d around the turning axis of the front wheel steering device including the tire 5 is viscosity coefficient around the turning axis of the turning device. Further, ξ is a caster rail, and N _f (s) / D _f (s) is a transfer function from the turning angle δ to the front wheel lateral force (total of left and right wheels).

When this is expressed as a transfer function, P (s) appearing in the following equation (3) is obtained.
δ = [D _f (s) / {I _d · s ² + C _d · s + ξN _f (s)}] · T _d = P (s) · T _d … (3)
For example, F (s) has a first-order lag characteristic. When it is written as a transfer function, the following equation (4) is obtained.
F (s) = 1 / (T _a · s + 1) (4)
Here, Ta represents _a delay time. FIG. 3 shows the response of the target turning angle correction value δ ^** when the target turning angle δ ^* changes stepwise at time zero.

  The feedback controller C (s) is designed using an optimal regulator or the like based on P (s). This design method is a well-known technique and will not be described here.

Next, the operation of the two-degree-of-freedom control system will be described. A block diagram showing the entire system including the actual control target represented by P ₀ (s) is shown in FIG.

Suppose now that P ₀ (s) completely matches P (s). At that time, it can be seen that the actual turning angle δ satisfies the following formula (5).
y = F (s) / P (s) · P ₀ (s) · δ ^* = F (s) · δ ^* (5)
As a result, the input of the feedback controller C (s) becomes zero. In summary, if the plant modeling is accurate, there will be no feedback. In other words, the feedback component compensates for the modeling error of the plant.

  The sum of the target torques (converted around the turning axis δ) of the motors 6 and 7 is the sum of the output of F (s) / P (s) and the output of C (s). The former will be referred to as feedforward and the latter as feedback.

[Target torque distribution]
Next, the distribution of the target torque (total value) will be described. An example of distribution is shown in FIG. In FIG. 5, α represents the ratio of the feed-forward for the motor 6 (with the rotation angle sensor).

As shown in FIG. 6, this α may be changed depending on the vehicle speed. An example of setting this ratio is shown below.
The ratio of feedback power and feedforward power at a certain vehicle speed
x: 1-x (where x> 0.5)
It is assumed that it is known in advance by trial operation that the share of feed forward is large.

At that time, the feed forward ratio α is set as shown in the following equation (6).
α = (1-2 · x) / (2-2 · x) (6)
Also, when the feedback share is large, α is set to zero.

[Target torque distribution function]
As shown in FIG. 2, the feedforward component is given by F (s) / P (s) · δ ^* . The target turning angle δ ^* is obtained by the driver's steering operation as shown in the equation (1), and does not change even when the turning angle changes. Therefore, as shown in FIG. 5, since the target rotational angle of the motor 7 does not exist when the distribution torque of the motor 7 is only a part of the feedforward, the deviation of the target rotational angle between the motors as in the conventional case is eliminated. Will not occur and no interference will occur.

  Furthermore, since the feedback is performed by the motor 6 having the rotation angle sensor (steering angle sensor) 10, it is difficult for the feedback to diverge even if the feedback gain is set large. This is because there is no backlash due to gears or the like between the sensor 10 and the motor 6 which is an actuator.

In addition, since the target turning angle δ ^* is generated by the steering operation as is apparent from the equation (1), the feedforward component F (s) / P (s) · δ ^* is a noise component that repeats positive and negative. Is not included. Therefore, even if there is play in the motor 7 and the steering rack 3 that are in charge of the feedforward component, the influence of play can be suppressed by the amount of back and forth.

[Distribution of feed forward according to vehicle speed]
The effect of changing the distribution α to the motor 6 for the feedforward according to the vehicle speed will be described. The feedback component is caused by modeling errors. Although an example of a model is shown in Equation (2), in general, modeling such as low-speed stationary and centering torque due to vehicle body lifting is difficult, and many models vary depending on the vehicle speed.

  Therefore, it can be said that the feedback generated by the modeling error is dependent on the vehicle speed. Now, if the feedback amount is smaller than the feed forward amount, it is better to share a part of the feed forward (ratio α) to the motor 6 in terms of miniaturization of the motor, prevention of heat generation, and durability. It can be said that there is. That is, it can be said that it is advantageous to obtain the ratio of the feedback and the feed-forward for each vehicle speed in advance by trial operation or the like and change the distribution α according to the vehicle speed v as shown in FIG.

Next, the meaning of equation (6) will be described. Now, the power distribution β of the motor 6 based on Equation 6 is calculated. From Figure 5 and Equation (6),
β = (1-x) · α + x = (1-x) · (1-2 · x) / (2-2 · x) + x = 0.5 (7)
That is, the distribution of the motor 6 and the motor 7 is equal. As a result, the motor can be used more effectively.

Next, the effect will be described.
In the vehicle steering apparatus according to the first embodiment, the following effects can be obtained.

  (1) The controller 11 determines the total target torque from the feedforward amount not including the front wheel turning angle and the other feedback amount, and distributes the feedback amount only to the motor 6. , 7 is determined, control interference between the motors 6 and 7 can be prevented.

(2) The controller 11 sets the feedforward amount of the total target torque to F (s) / P (s) δ * ×, and sets the feedback amount to {F (s) × δ ^* −δ} × C (s) The torque distribution to the motors 6 and 7 is determined as follows. That is, the target turning angle δ ^* is obtained by the driver's steering operation, and does not change even when the turning angle δ changes. Therefore, by setting the distribution torque of the motor 7 to only a part of the feedforward, the target rotation angle of the motor 7 does not exist, so that the deviation of the target rotation angle between the motors as in the conventional case does not occur and the control is performed. Interference can be prevented.

  (3) Since the rotation angle sensor 10 is attached to the rotation shaft of the motor 6 to which the feedback of the total target torque is distributed, and there is no backlash due to gears between the rotation angle sensor 10 and the motor 6, a large feedback gain is set. Even in this case, the control is difficult to diverge. Therefore, it is possible to increase the control gain by setting a large feedback gain.

  (4) Since the controller 11 changes the feedforward amount for each of the motors 6 and 7 according to the vehicle speed, the motor 11 can reduce the size of the motor, prevent heat generation, and share the feedforward portion larger than the feedback amount. Improved durability can be achieved.

  (5) Since the controller 11 sets the feed-forward distribution in the direction in which the distribution of the motors 6 and 7 becomes equal, the motor can be used more effectively by equalizing the load on each motor. .

(Other examples)
Although the best mode for carrying out the present invention has been described based on the first embodiment, the specific configuration of the present invention is not limited to the first embodiment. Although an example using two motors has been described, the number of motors is not limited to two.

1 is a configuration diagram of a vehicle including a steer-by-wire system according to a first embodiment. 1 is a configuration diagram of a two-degree-of-freedom control system of Embodiment 1. FIG. It is a figure which shows the target value response of actual steering angle (delta). It is a block diagram which shows the whole system of a 2 degree-of-freedom system. It is a figure which shows the example of allocation of target torque (total value). It is a figure which shows an example of the feedforward distribution part according to a vehicle speed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Handle 2 Handle angle sensor 3 Steering rack 4 Tie rod 5 Tire 6, 7 Motor 8, 9 Transmission 10 Rotation angle sensor 11 Controller 12, 13 Driver

Claims (5)

A steering gear for steering the front wheels mechanically separated from the steering wheel that receives the steering input;
A plurality of actuators coupled to the front-wheel steering steering gear for generating torque for steering the front wheels;
Torque determining means for determining a total target torque to be generated by the plurality of actuators and a distribution torque to each actuator according to the target turning angle according to a signal including at least a steering wheel angle and a front wheel turning angle;
Actuator driving means for controlling the actual torque of each actuator based on the distributed torque;
In a vehicle steering apparatus comprising:
The torque determining means sets the total target torque to be generated by the plurality of actuators as the sum of the feedforward component not including the front wheel turning angle and the other feedback component,
In addition, the vehicle steering apparatus is characterized in that a distribution torque to each actuator is determined so that a feedback amount is distributed to only one actuator. The vehicle steering apparatus according to claim 1,
When the target turning angle is δ ^* , the target value response of the actual turning angle δ to the target turning angle δ ^* is F (s), the controlled model is P (s), and the feedback controller is C (s) ,
The torque determining means includes
F (s) / P (s) δ * × is the total target torque feedforward,
A vehicle steering apparatus characterized in that a torque distribution to each actuator is determined with a feedback amount as {F (s) × δ ^* −Δ} × C (s). The vehicle steering apparatus according to claim 1 or 2,
A vehicle steering apparatus, wherein a front wheel turning angle sensor for detecting a front wheel turning angle is attached to a proximity position of an actuator to which a feedback amount is distributed or to the actuator. The vehicle steering apparatus according to any one of claims 1 to 3,
Vehicle speed detecting means for detecting the vehicle speed is provided;
The vehicle torque steering device according to claim 1, wherein the torque determination means changes a feed forward distribution to each actuator in accordance with a vehicle speed. The vehicle steering device according to claim 4,
The vehicle steering apparatus according to claim 1, wherein the torque determination unit sets a feed-forward distribution in a direction in which the distribution of each actuator becomes equal.

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