JP5263181B2 - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of changing steering modes smoothly and reducing the load of arithmetic processing of a CPU. <P>SOLUTION: The electric power steering device includes: a steering torque detection means, which detects steering torque applied to the steering; a motor, which generates an assist force that assists the operation of the steering wheel; and a motor control means, which controls the motor based on the steering torque and vehicle speed. In this device, the motor control means is provided with a vehicle speed switching means, which, when a steering mode switching signal is input, converts the vehicle speed into alternate vehicle speed using false vehicle speed parameter that shows the correspondence relationship between the alternate vehicle speed and the vehicle speed in each steering mode and performs assist control based on the converted alternate vehicle speed. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  TECHNICAL FIELD The present invention relates to an electric power steering apparatus that applies an assist force by a motor to a steering system of a vehicle, and in particular, a plurality of steering modes can be switched according to a driver's selection, and smooth switching of assist characteristics at the time of switching is realized. The present invention relates to an electric power steering device that can be used.

  An electric power steering device that applies a steering assist force (assist) to a steering device of a vehicle by a rotational force of a motor is applied to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a reduction gear. A steering assist force is applied. Such a conventional electric power steering apparatus performs feedback control of the motor current in order to accurately generate the steering assist torque. In feedback control, the motor applied voltage is adjusted so that the difference between the current command value and the detected motor current value is small. Generally, the adjustment of the motor applied voltage is a duty ratio of PWM (pulse width modulation) control. It is done by adjusting.

  A general configuration of such an electric power steering apparatus will be described with reference to FIG. A column shaft 2 of the handle 1 is connected to a tie rod 6 of a steered wheel via a reduction gear 3, universal joints 4A and 4B, and a pinion rack mechanism 5. The column shaft 2 is provided with a torque sensor 10 that detects the steering torque of the handle 1 according to the torsion bar torsion, and a motor 20 that assists the steering force of the handle 1 is connected to the column shaft via the reduction gear 3. 2 is connected. Electric power is supplied from the battery 14 to the control unit 30 that controls the power steering device, and an ignition key signal is input via the ignition key 11. The control unit 30 calculates the current command value I of the assist command based on the steering torque Tr detected by the torque sensor 10 and the vehicle speed Vel detected by the vehicle speed sensor 12, and based on the calculated current command value I. The current supplied to the motor 20 is controlled.

  The control unit 30 is mainly composed of a CPU (or MPU or MCU). FIG. 2 shows general functions executed by a program inside the CPU.

  The function and operation of the control unit 30 will be described with reference to FIG. 2. The steering torque Tr detected and input by the torque sensor 10 and the vehicle speed Vel from the vehicle speed sensor 12 are input to the steering assist command value calculation unit 31. A steering assist command value Iref is calculated using the assist map. The calculated steering assist command value Iref is limited and output by the maximum output limiter 32 due to overheat protection conditions and the like, and the current command value I whose maximum output is limited is input to the subtractor 33.

  The calculation of the steering assist command value Iref in the steering assist command value calculation unit 31 can be further performed using the steering angle in addition to the steering torque Tr and the vehicle speed Vel.

  The subtracting unit 33 obtains a deviation ΔI (= I−i) between the current command value I and the current i of the motor 20 that is fed back, and the deviation ΔI is controlled by the current control unit 34 to control the controlled current control value E. Is input to the PWM control unit 35, the duty ratio is calculated, and the motor 20 is PWM driven via the inverter 36. Electric power is supplied to the inverter 36 from the battery 14 via the power supply relay 13, and the motor current i of the motor 20 is detected by the motor current detection circuit 37 and input to the subtraction unit 33 and fed back.

  Here, when the vehicle is traveling, it is required to change the steering operation for each traveling state. For example, the steering mode required when the road surface is dry and wet is different, and different steering modes are required depending on the sex, age, driving experience, and the like. Furthermore, it is necessary to set different steering modes for traffic and on mountain roads. For these situations, it is necessary to provide a switching means that can smoothly switch between various steering modes.

  Therefore, Patent Document 1 (Japanese Patent No. 2998929) proposes an electric power steering apparatus including a control unit capable of switching a plurality of control mode units having different target current signal characteristics under a predetermined condition. The control means uses a new value for one of the target current signal before switching or the target current signal after switching and the previous value for the other, and processes either one or the other within a certain processing time. It has switching means to calculate the target current signal at the time of transition by using it alternately every time, and the transition from the target current signal before switching of the control mode means to the target current signal after switching of the control mode means with time I try to change it continuously. That is, in the control means of Patent Document 1, target current signals before and after switching the control mode means are calculated, and the characteristics are gradually changed by the transition coefficient.

Japanese Patent No. 2999828 JP 2003-19972 A JP 2009-113550 A

  However, although the electric power steering apparatus of Patent Document 1 can smoothly switch between the control modes, the target current before and after switching is changed based on the steering torque and the vehicle speed in order to gradually change the characteristic of the assist characteristic. The signal is calculated and controlled by a gradual change function consisting of a transfer coefficient. In this case, since the assist characteristic calculation before and after switching and the gradual change function calculation must be provided, the calculation processing capacity of the CPU is increased, and there is a possibility that other control functions may be hindered in calculation troubles. is there. Therefore, it is necessary to reduce the processing load of the CPU so as not to hinder the calculation of other control functions.

  The present invention has been made under the circumstances as described above, and an object of the present invention is to smoothly switch the steering mode according to the traveling state of the vehicle, for example, the road surface state, traffic jam, and the driver's preference. Another object of the present invention is to provide an electric power steering device that can reduce the load of arithmetic processing of a CPU.

The present invention is based on the steering torque detecting means for detecting the steering torque applied to the steering, the vehicle speed detecting means for detecting the vehicle speed, the motor for generating the assist force for assisting the steering operation on the steering wheel, the steering torque and the vehicle speed. Steering assist command value, and a steering assist command calculation unit having a gradually increasing and decreasing function corresponding to the sudden change in the vehicle speed, and the motor based on the steering assist command value output from the steering assist command calculation unit. The above-described object of the present invention relates to an electric power steering apparatus including a motor control means for controlling, and includes a plurality of pseudo vehicle speed parameters indicating a correspondence relationship between an alternative vehicle speed in each steering mode and the vehicle speed, and is input. The pseudo vehicle speed parameter is referred to according to the steering mode corresponding to the steering mode switching signal. Converting the vehicle speed to the substitute vehicle speed, the converted the substitute vehicle speed includes a vehicle speed switching means to be input to the steering assist command calculating section, said motor control means, when the steering mode switching signal is inputted, the This is achieved by performing assist control based on the steering assist command value calculated by the steering assist command calculating unit based on the steering torque and the alternative vehicle speed .

Furthermore, the above-mentioned object of the present invention is achieved more effectively by the fact that the pseudo vehicle speed parameter is in a map format, a gain format, or an offset format. In addition, the object of the present invention is to limit the maximum output of the converted alternative vehicle speed so that the vehicle speed switching means does not cause a sudden change , and set the alternative vehicle speed with the maximum output limited to the steering assist command. This is achieved more effectively by being input to the calculation unit .

  The electric power steering apparatus according to the present invention converts the actual vehicle speed into an alternative vehicle speed for each steering mode according to the pseudo vehicle speed parameter using the conventional assist characteristic map, and performs assist control based on the converted alternative vehicle speed. Like to do. Originally, since the electric power steering apparatus has a gradual change function corresponding to a sudden change in the vehicle speed, a smooth switching of the steering mode can be obtained. Further, it is not necessary to calculate the assist amount before and after the switching as in Patent Document 1, and only the alternative vehicle speed is calculated, so the load on the calculation device (CPU) can be reduced.

It is a lineblock diagram showing an outline of an electric power steering device. It is a block diagram which shows the general structural example of a control unit. BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram which shows the outline | summary of the electric power steering apparatus which concerns on Example 1 of this invention. It is a block diagram which shows the structural example of the control unit which concerns on Example 1 of this invention. It is a block diagram which shows the example of an internal structure of the vehicle speed switching part which concerns on Example 1 of this invention. It is a characteristic view which shows an example (map format) of the pseudo vehicle speed parameter which concerns on Example 1 of this invention. It is a figure which shows an example of the change of the steering command value at the time of switching in the electric power steering device which concerns on Example 1 of this invention. It is a time chart which shows the operation example at the time of the switching of the electric power steering apparatus which concerns on Example 1 of this invention. It is a characteristic view which shows an example (gain form) of the pseudo vehicle speed parameter which concerns on Example 2 of this invention. It is a characteristic view which shows an example (offset form) of the pseudo vehicle speed parameter which concerns on Example 3 of this invention.

  Switching the vehicle steering mode means changing the assist amount that the drive motor 20 assists the steering operation with respect to the same steering torque Tr, and means a change in the steering assist command value Iref that controls the motor 20. doing. The normal steering assist command value Iref is calculated based on the steering torque Tr and the vehicle speed Vel. Therefore, when the steering mode is switched, if the steering torque Tr or / and the vehicle speed Vel are changed, the assist amount can be changed, and the steering mode can be switched.

  Further, the normal steering assist command calculation unit 31 is equipped with a gradual decrease and gradual increase function (so-called ramp function or gradual change function) in order to obtain a good steering feeling when the vehicle speed Vel changes suddenly. For example, Patent Document 2 (Japanese Patent Application Laid-Open No. 2003-19972) discloses an electric power steering device that gradually changes the steering assist command value to the same range to the steering assist command value corresponding to the changed vehicle speed. Further, Patent Document 3 (Japanese Patent Laid-Open No. 2009-113550) is limited when the steering assist command value is changed in accordance with a change in vehicle speed when the predetermined threshold value is not exceeded, and the threshold value is exceeded. An electric power steering device that changes the steering assist command value at a different change rate is disclosed. That is, when a sudden change in the vehicle speed occurs, the steering assist command value can be smoothly changed by providing a gradually increasing and decreasing function.

  Therefore, when switching the steering mode, it is conceivable to switch to another steering mode by changing the vehicle speed.

In the present invention, when the steering mode is switched, when calculating the steering assist command value Iref for controlling the motor 20, the vehicle speed Vel detected by the vehicle speed sensor 12 is not used, but each predetermined steering mode is determined. The detected vehicle speed Vel is converted into the alternative vehicle speed Vela according to the pseudo vehicle speed parameter, and the assist control is performed based on the converted alternative vehicle speed Vela. Thus, the steering mode can be switched by using the alternative vehicle speed, and the steering mode can be switched smoothly by the gradually increasing and decreasing function corresponding to the sudden change of the vehicle speed originally provided in the electric power steering apparatus.
Example 1
FIG. 3 is a configuration diagram showing an outline of the electric power steering apparatus according to the first embodiment of the present invention, corresponding to FIG. The electric power steering apparatus according to the first embodiment includes a steering mode changeover switch 17, and can switch among three types of steering modes ST1 to ST3. The steering mode changeover switch 17 is provided within the reach of the driver, generates a switching signal SW for the steering modes ST1, ST2 and ST3 according to the operation of the driver, and inputs the generated switching signal SW to the control unit 30. To do. In this embodiment, only three types of steering modes ST1 to ST3 are provided. However, as long as a pseudo vehicle speed parameter corresponding to each steering mode is provided, it is naturally possible to realize three or more types of steering modes. It is.

  FIG. 4 is a block diagram illustrating a configuration example of the control unit 30 of the electric power steering apparatus according to the present embodiment, and is a configuration diagram corresponding to FIG. 2 described above. The description is omitted. The control unit 30 according to the present embodiment is provided with a vehicle speed switching unit 38. The vehicle speed switching unit 38 inputs the vehicle speed Vel detected by the vehicle speed sensor 12 and also receives the switching signal SW from the steering mode switching switch 17 and according to the pseudo vehicle speed parameter corresponding to the switching signal SW, The input vehicle speed Vel is converted into an alternative vehicle speed Vela.

  The auxiliary command value calculation unit 31 inputs the alternative vehicle speed Vela converted by the vehicle speed switching unit 38 and the steering torque Tr detected by the torque sensor 10, and refers to the assist map based on the alternative vehicle speed Vela and the steering torque Tr. The steering assist command value Iref is calculated. The electric power steering device performs assist control based on the calculated steering assist command value Iref.

  FIG. 5 is a block diagram illustrating a configuration example of the vehicle speed switching unit 38. The vehicle speed switching unit 38 includes a steering mode determination unit 381, an alternative vehicle speed conversion unit 382, and an output limiting unit 383. The steering mode determination unit 381 determines the tearing modes ST1 to ST3 based on the input switching signal SW, and outputs the vehicle speed Vel to the alternative vehicle speed conversion unit 382.

  The alternative vehicle speed conversion unit 382 has three pseudo vehicle speed parameters 382-1 to 382-3, and sets the pseudo vehicle speed parameters 382-1 to 382-3 according to the steering modes ST1 to ST3 determined by the steering mode determination unit 381. Referring to, vehicle speed Vel is converted into alternative vehicle speeds Vela1 to Vela3. The simulated vehicle speed parameters 382-1 to 382-3 are parameters indicating a correspondence relationship between the vehicle speed Vel detected by the vehicle speed sensor 12 and the alternative vehicle speeds Vela1 to Vela3 corresponding to the steering modes ST1 to ST3 after switching. And the like, and are stored in a storage device such as a ROM. The electric power steering apparatus according to the present embodiment has three types of steering modes ST1 to ST3. When the steering mode ST1 is set, the vehicle speed Vel is converted into the alternative vehicle speed Vela1 according to the pseudo parameter 382-1, and the steering mode ST2 is set. When set to, the vehicle speed Vel is converted to the alternative vehicle speed Vela2 according to the pseudo parameter 382-2, and when set to the steering mode ST3, the vehicle speed Vel is converted to the alternative vehicle speed Vela3 according to the pseudo parameter 382-3.

  As shown in FIG. 5, the alternative vehicle speed conversion unit 382 converts the vehicle speed Vel to the alternative vehicle speeds Vela1 to Vela3, respectively, according to the pseudo vehicle speed parameters 382-1 to 382-3 corresponding to the determined steering modes ST1 to ST3. And input to the output limiting unit 383. The output restricting unit 383 restricts the maximum output of the alternative vehicle speeds Vela 1 to Vela 3 so that sudden fluctuation does not occur, and the alternative vehicle speed Vela with the maximum output restricted is input to the steering assist command calculation unit 31.

  As shown in FIG. 6, the simulated vehicle speed parameters 382-1 to 382-3 of the vehicle speed switching unit 38 of the electric power steering apparatus according to the present embodiment have a one-to-one correspondence between the vehicle speed Vel and the alternative vehicle speeds Vela1 to Vela3 in the form of a map. The vehicle speed Vel directly outputs the alternative vehicle speeds Vela1 to Vela3 by referring to the respective pseudo vehicle speed parameters. Since the assist amount decreases as the vehicle speed increases with respect to a certain steering torque Tr, the steering wheel becomes lighter in the order of the steering mode ST2, the steering mode ST1, and the steering mode ST3.

  The operation at the time of switching will be described using the following example. For example, when the steering torque Tr is constant and the vehicle speed Vel is 30 km / h, when the driver switches from the steering mode ST1 to the steering mode ST3, the alternative vehicle speed is 30 km according to the pseudo vehicle speed parameter shown in FIG. From / h to 0 km / h, the change in the steering assist command value Iref should change suddenly from point A to point B as shown in FIG. However, since the normal steering assist command calculation unit 31 has a gradual change function corresponding to a sudden change in the vehicle speed Vel, the steering assist command value Iref gradually changes from the point A to the point B. Then, the assist force for assisting the driver's steering operation increases, the steering wheel becomes lighter, and the mode is smoothly switched to the steering mode ST3.

FIG. 8 is a time chart showing the simulation results of this example. FIG. 8B is a curve showing a change in the current i flowing through the motor 20 of the electric power steering apparatus, the solid line is the behavior according to the present invention, and the dotted line is the behavior when the function of the present invention is not provided. FIG. 8C is a curve showing a change in steering torque Tr related to steering, and FIG. 8D is a curve showing switching of the steering mode of the vehicle. The simulation was performed on the premise that the steering torque Tr is constant after the time point t1. At time t0, the ignition key is turned on under the condition of the steering mode ST2, and the driver starts assisting the steering by the motor 20 based on the steering torque Tr. At time t1, the steering mode ST2 is switched to the steering mode ST1, the motor current is controlled based on the alternative vehicle speed Vela1 converted according to the pseudo vehicle speed parameter 382-1, and the motor current i changes from I1 to I2. . However, since there is a gradual change function, the motor current i gradually increases from I1 to I2. At time t2, the current i flowing through the motor 20 becomes I2, and the mode is switched to the steering mode ST2. Similarly, at time t3, the steering mode ST1 is switched to the steering mode ST3, and the motor current i gradually changes from I2 to I3. At time t4, the motor current i becomes I3, and the electric power steering apparatus switches to the steering mode ST3. As described above, the electric power steering apparatus according to the present embodiment can smoothly switch between the three defined steering modes ST1 to ST3.
(Example 2)
In the first embodiment described above, the pseudo vehicle speed parameter of the vehicle speed switching unit 38 is a one-to-one correspondence between the vehicle speed Vel and the alternative vehicle speeds Vela1 to Vela3, but other forms are also possible. FIG. 9 is a diagram showing another example (Example 2) of the pseudo vehicle speed parameter, and shows the relationship between the vehicle speed Vel and the gain with respect to the vehicle speed. That is, instead of directly obtaining the alternative vehicle speed as in the first embodiment, a gain for the vehicle speed Vel is temporarily obtained using the pseudo vehicle speed parameter, and the alternative vehicle speed Vela is obtained by multiplying the vehicle speed Vel by the gain. .
(Example 3)
Except for the pseudo vehicle speed parameter of the one-to-one relationship between the vehicle speed Vel of the first embodiment and the alternative vehicle speeds Vela1 to Vela3 and the gain pseudo vehicle speed parameter of the second embodiment, an offset type pseudo vehicle speed parameter is also possible. As shown in FIG. 10, the horizontal axis represents the vehicle speed Vel, and the vertical axis represents the offset corresponding to the vehicle speed in each steering mode. When obtaining the alternative vehicle speed Vela, the vehicle speed switching unit 38 obtains an offset corresponding to the input vehicle speed Vel according to the offset pseudo parameter, and obtains the alternative vehicle speed Vela by adding the vehicle speed Vel and the offset.

DESCRIPTION OF SYMBOLS 10 Torque sensor 12 Vehicle speed sensor 13 Power supply relay 14 Battery 17 Steering mode changeover switch 20 Motor 31 Steering assistance command calculating part 32 Maximum output control part 33 Subtraction part 34 Current control part 35 PWM control part 36 Inverter 37 Motor current detection circuit 38 Vehicle speed switching Part

Claims (5)

Steering torque detecting means for detecting steering torque applied to the steering;
Vehicle speed detection means for detecting the vehicle speed;
A motor that generates an assist force for assisting steering of the steering wheel;
A steering assist command calculation unit that calculates a steering assist command value based on the steering torque and the vehicle speed, and has a gradually decreasing and increasing function corresponding to a sudden change in the vehicle speed;
In an electric power steering apparatus comprising: motor control means for controlling the motor based on a steering assist command value output from the steering assist command calculation unit ;
A plurality of pseudo vehicle speed parameters indicating a correspondence relationship between the alternative vehicle speed of each steering mode and the vehicle speed are provided, and the pseudo vehicle speed parameter is referred to according to the steering mode corresponding to the input steering mode switching signal. Vehicle speed switching means for converting a vehicle speed to the alternative vehicle speed and inputting the converted alternative vehicle speed to the steering assist command calculation unit;
Said motor control means, said when the steering mode switching signal is input, the steering torque and the substitute vehicle speed to perform the assist control based on the steering assist command value calculated by the steering assist command calculating section, based An electric power steering device. The electric power steering apparatus according to claim 1 , wherein the pseudo vehicle speed parameter is in a map format. The electric power steering apparatus according to claim 1 , wherein the pseudo vehicle speed parameter is in a gain format. The electric power steering apparatus according to claim 1 , wherein the pseudo vehicle speed parameter is in an offset format. The vehicle speed switching means limits the maximum output of the converted alternative vehicle speed so as not to cause a sudden fluctuation, and inputs the alternative vehicle speed with the maximum output limited to the steering assist command calculation unit. The electric power steering device according to any one of claims 1 to 4 .