JP2008296679A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device which is not affected by noise when switching between a first mode and a second mode. <P>SOLUTION: This electric power steering device includes a control signal correction means which determines a difference between the present current deviation in a digital format and a current deviation in the digital format obtained before the last sampling or earlier samplings of the data of the present current deviation and adds a value obtained by multiplying the difference by a coefficient to a motor current control value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

Detailed description

  The present invention relates to an electric power steering device used for assisting steering of a vehicle steering wheel.

  FIG. 4 shows a block diagram of an electric power steering apparatus 100 according to the prior art.

  In FIG. 4, 101 indicates a torque sensor that detects a steering torque of a handle (not shown), and 102 indicates a vehicle speed sensor that detects a vehicle speed. Reference numeral 103 denotes target value calculation means provided in the subsequent stage of the torque sensor 101 and the vehicle speed sensor 102. The target value calculation means 103 inputs the steering torque a and the vehicle speed b and outputs a current command signal c. The sensor signal according to claim 1 is constituted by the steering torque a and the vehicle speed b.

  The target value calculation means 103 has a built-in table T for calculating a current command signal c from the steering torque a and the vehicle speed b.

  A subtracter 104 is provided following the target value calculation means 103. The subtractor 104 is a device that obtains a difference between the current command signal c and the actually measured assist current value and outputs it as a current deviation value e. The actually measured assist current value is a current value actually flowing in the motor M described later, and is detected by the motor current detecting means 105.

  The current deviation value e is input to the subsequent proportional control means 106 and the integration control means 107. The proportional control means 106 is a device that receives the current deviation value e, multiplies the current deviation value e by a coefficient α, and outputs the result as a proportional control value f.

The integration control unit 107 includes an adder 108, a delay operator 109, and a gain adjustment unit 110. The lag operator 109 is a current deviation value e (i-1), e (i-2), e (i-3), e prior to the current current deviation value e (i) output from the subtractor 104. ,, And output devices.

The adder 108 repeats a loop for sequentially adding e (i-1), e (i-2), e (i-3), to the current deviation value e (i), thereby obtaining a current deviation value. The integration of e is executed and an integration control signal g is output. The gain adjusting unit 110 is a device that multiplies the integration control signal g by a coefficient β and outputs it.

  An adder 111 is provided following the proportional control means 106 and the integral control means 107. The adder 111 is a device that adds the proportional control value f and the integral control value g and outputs the sum as a motor current control value h.

  A PWM control unit 112 is provided following the adder 111. The PWM control unit 112 is a device that inputs the motor current control value h and performs PWM control of the subsequent motor driving unit 113 based on the motor current control value h.

  A motor circuit 114 is provided at the subsequent stage of the motor driving means 113. The motor circuit 114 includes four switching elements F1, F2, F3, and F4 and a DC motor M. The motor circuit 114 is provided between the power source 115 and the ground, and is configured such that electric power is supplied from the power source 115 via the current detection resistor 116.

The motor circuit 114 is composed of an H bridge circuit in which two switching elements F1 and F2 on the high side and two switching elements F3 and F4 on the low side are bridge-connected, and the two switching elements F1 on the high side. , F2 and the two low-side switching elements F3, F4 are provided with the steering assist DC motor M. Each of the switching elements F1, F2, F3, and F4 is configured by a power transistor such as an FET. The gate of each FET is connected to the motor drive means 113, and a drive signal is input from the motor drive means 113 to each FET.

  The switching element F1 and the switching element F4 are paired, and the switching element F2 and the switching element F3 are paired.

  Here, the modes in which the four switching elements F1, F2, F3, and F4 operate include a first mode and a second mode. The first mode is a mode in which the two switching elements F3 or F4 on the low side are always in the ON state and the switching elements F1 and F2 on the high side that are paired with the switching element F3 or F4 are PWM-controlled. . The second mode is a mode in which the switching elements F1 and F4, and the switching elements F2 and F3 are PWM-controlled, respectively.

  By the way, in the case of the first mode, since only the high-side switching element F1 or F2 is PWM-controlled, there is an advantage that the number of times of switching is small and heat generation due to loss during switching is small. There is a problem as shown in FIG.

FIG. 5 is a diagram illustrating a current flowing through the motor circuit 114 in the first mode. FIG. 5A illustrates a current flowing through the motor circuit 114 when the motor M is rotating forward. It is assumed that the switching elements F1 and F4 are conductive during normal rotation of the motor M.

FIG. 5B shows a current flowing through the motor circuit 114 when the high-side FET is turned off in the first mode. That is, when the high-side FET is turned off in the first mode, current flows in the circuit formed by the switching element F4, the parasitic diode D3 of the switching element F3, and the motor M, and therefore flows through the current detection resistor 116. There is no configuration. Considering this situation with an actual vehicle, there is no problem when the driver steers the steering wheel, but the steering wheel is released and the steering wheel automatically returns to the neutral position by the vehicle's self-aligning torque. At the time of return, a regenerative current is generated due to the counter electromotive voltage generated by the motor. However, for the above reason, the current at this time cannot be detected in the first mode, and the current flowing through the motor M cannot be controlled. For this reason, there is a problem in that smooth rotation cannot be obtained when the handle is returned and abnormal noise is generated due to this.

For this reason, Patent Document 1 discloses an invention in which steering assist of the steering wheel is basically controlled in the first mode, while return control of the steering wheel is executed in the second mode.
Japanese Patent No. 2857555

  However, Patent Document 1 has the following problems. FIG. 6 is a characteristic diagram showing the relationship between PWM control and assist current. In FIG. 6, the horizontal axis represents PWM control, that is, the duty ratio, and the vertical axis represents assist current. In FIG. 6, the dotted line indicates the characteristics of the first mode, and the solid line indicates the characteristics of the second mode.

  In the first mode, the assist current of the motor M is controlled based on the characteristic indicated by the dotted line in FIG. 6, but in the second mode, the assist current is controlled based on the characteristic indicated by the solid line in FIG. To do. Therefore, due to the current difference S between the first mode characteristic and the second mode characteristic, the current difference S appears as noise N as shown in FIG.

  Generation of the noise N will be described with reference to FIG. FIG. 7 shows the input torque on the horizontal axis and the assist current on the vertical axis. In the first quadrant of FIG. 7, it is assumed that the input torque increases in the direction indicated by the arrow A in FIG. 7 while being controlled in the second mode, and is switched to the first mode. In this case, as shown in FIG. 7, noise N (1) in the direction of increasing current is generated based on the current difference S (shown in FIG. 6) between the second mode and the first mode. On the other hand, it is assumed that the input torque decreases in the direction of arrow B in FIG. 7 while being controlled in the first mode, and the mode is switched to the second mode. In this case, based on the current difference S (shown in FIG. 6) between the second mode and the first mode, noise N (2) in the direction in which the current decreases is generated.

  Furthermore, in addition to the above-mentioned causes, noise based on the poor response of the integration control means 107 is also added to the noise N.

  When the noise N flows to the motor M, it is transmitted as an impact to the driver, causing not only an uncomfortable feeling during driving, but also a undesirable phenomenon during driving.

  On the other hand, if the characteristic of the second mode shown in FIG. 6 can be specified, that is, if the form of the characteristic line of the second mode can be specified, the difference S between the characteristic of the second mode and the characteristic of the first mode is set in advance as a fixed value. Anticipating and correcting the assist current with the difference S is expected to prevent the noise N from occurring.

  However, when the difference S between the characteristic of the second mode and the characteristic of the first mode is to be specified in this way, there are the following problems.

  That is, the characteristics of the second mode vary depending on the characteristics of the motor M itself, the length of the harness, and the like. That is, the characteristic line of the second mode varies depending on the characteristics of the motor M itself, the length of the harness, and the like. For this reason, it is difficult to specify the difference S (shown in FIG. 6) between the second mode and the first mode in advance.

The motor M acts as a generator when rotated by an external force from the output shaft side. The current flowing through the motor M is determined based on the sum of the power generated by the motor M and the power of the power source 115. For this reason, as shown in FIG. 8, the characteristic line of the second mode fluctuates. In FIG. 8, the center characteristic line indicates the characteristic when the motor M is in the locked state. The right characteristic line indicates the characteristic when an external force in the same direction as the control direction is acting on the motor M. Further, the characteristic line on the left shows the characteristic when an external force opposite to the control direction is acting on the motor M.

  Thus, since the current characteristic of the second mode characteristic line varies depending on the power generation condition of the motor M, the second mode characteristic line cannot be specified. As a result, the first mode and the second mode By obtaining the difference S in advance as a fixed value and preventing the generation of noise by the fixed value, the assist current of the motor M could not be controlled so as not to be affected by the noise.

  The present invention has been made in view of the problems of the background art, and an object thereof is to provide an electric power steering device that is not affected by noise when switching between the first mode and the second mode. For the purpose.

  The invention according to claim 1 includes a vehicle speed sensor that detects a vehicle speed, a torque sensor that detects a steering torque of a steering wheel, a steering assist motor, and an H bridge circuit that includes four switching elements. A motor circuit for driving the motor; motor driving means for driving the motor circuit; a current command signal corresponding to sensor signals output from the vehicle speed sensor and the torque sensor; and an actually measured assist current flowing through the motor; Integration control means for inputting and integrating the current deviation value obtained by subtracting in the form of digital data and outputting it as a motor current control value, and PWM control means for PWM controlling the motor drive means based on the motor current control value The PWM control includes switching elements on the low side of the four switching elements. In the electric power steering apparatus including the first mode in which the high-side switching element is PWM-controlled and the second mode in which all the four switching elements are PWM-controlled, the current current deviation value digital data is 1 Control signal correction means for obtaining a difference between one or a plurality of previous digital data and the digital data of the current current deviation value, and adding a value obtained by multiplying the difference by a coefficient to the motor current control value; It is characterized by having.

  Since the assist current is controlled by calculating the difference between the current current deviation value and one or more previous current deviation values and immediately adding the difference to the motor current control value, the integral control means Even if the responsiveness is poor, the assist current can be immediately and satisfactorily controlled without being affected by noise.

  FIG. 1 is a block diagram of an electric power steering apparatus 1 according to this embodiment. FIG. 2 is a diagram for explaining the operation. The electric power steering apparatus 1 includes a torque sensor 101, a vehicle speed sensor 102, a target value calculation means 103, a subtractor 104, a motor current detection means 105, a proportional control means 106, an integral control means 107, an adder 108, a PWM control means 112, The motor driving unit 113 and the motor circuit 114 are provided in the same manner as the electric power steering apparatus 100 of the background art.

  As shown in FIG. 1, the electric power steering apparatus 1 according to this embodiment includes a control signal correction unit 2. The control signal correction unit 2 includes a subtracter 3 and a gain control unit 4. The subtractor 3 obtains a difference between the current current deviation value e (i) and the previous current deviation value e (i-1) input from the delay operator 109, and outputs the difference signal j. It is. Here, the previous current deviation value e (i-1) is a digital current deviation value used when the integration control means 107 performs integration, and is based on the current current deviation value e (i). Is the current deviation value e (i-1) captured at the timing of the previous sampling. Note that two or more current deviation values before sampling may be captured.

The subtractor 3 of the control signal correcting means 2 is a device that executes the following arithmetic expression (1) and outputs a difference signal j. The gain control means 4 is a device that obtains a correction control signal k by multiplying the difference signal j by a coefficient γ and outputs the correction control signal k to the adder 111. In the adder 111, the correction control signal k is added to the motor current control value h.
j = [− {current current deviation value e (i)} + {current deviation value e (i−1)} acquired by the previous sampling]] (1)
Further, the noise can be easily canceled or reduced by adjusting the coefficient γ.

  Next, the operation will be described. Suppose that the input torque increases in the direction of arrow A in FIG. In the background art, when switching from the second mode to the first mode, noise N (1) in which the current increases is generated.

  On the other hand, in this embodiment, in this case, the output of the control signal correction unit 2 becomes negative based on the arithmetic expression (1). That is, in this case, when the current current deviation e (i) is compared with the previous current deviation e (i-1), the current current deviation e (i) is larger. For this reason, as shown in the arithmetic expression (1), by outputting a negative value from the control signal correction means 2, the noise N (1) is canceled as shown in FIG. By reducing, the noise N (2) disappears or decreases.

  Next, it is assumed that the input torque decreases as shown in the arrow B direction in FIG. In this case, the mode is switched from the first mode to the second mode. In the background art, noise N (2) in which the current decreases is generated.

  On the other hand, in this embodiment, in this case, the output of the control signal correction unit 2 becomes positive based on the arithmetic expression (1). That is, in this case, when the current current deviation e (i) is compared with the previous current deviation e (i-1), the current current deviation e (i) is smaller. For this reason, a positive value is output from the control signal correction means 2 and is canceled or reduced by the noise N (2) as shown in FIG. Decrease.

  In the above description, the case where the noises N (1) and N (2) generated in the first quadrant are eliminated or reduced in FIG. 7 has been described. However, the noise N generated in the third quadrant is eliminated, The same applies to the case of reduction.

  As described above, the noise N is eliminated or reduced by the correction control signal k output from the control signal correction means 2, and good control without feeling uncomfortable during driving is performed. It is possible.

  As shown in FIG. 1, in the present embodiment, the current current deviation value e (i) is subtracted from the current deviation value e (i-1) captured at the previous sampling timing. Since the correction control signal k obtained in this way is inputted to the PWM control means 112 to immediately control the assist current, the assist control is immediately and satisfactorily executed even if the integration control means 107 has poor responsiveness. Therefore, noise N as shown in FIG. 7 does not occur.

  FIG. 3 is an enlarged view of a part of the characteristic diagram shown in FIG. In general, the output value of the integrator has a phase delay of 90 degrees with respect to the input value, and the response is poor. In particular, as shown in FIG. 6, the characteristics of the second mode have a small slope and poor response when the current is small. Therefore, as shown by the alternate long and short dash line in FIG. There is a phenomenon that the assist current suddenly rises after the threshold value is exceeded. In this case, when the assist current suddenly rises, a sense of incongruity may be felt at the start of the assist.

  However, in this embodiment, since the correction control signal k output from the control signal correction unit 2 is applied to the PWM control unit 112, the assist current rises quickly as shown by the solid line in FIG. Thus, the power steering control can be executed smoothly. For this reason, it is possible to travel well without feeling uncomfortable at the start of steering.

It is a block block diagram of the electric power steering device which concerns on this embodiment. (This embodiment) It is a figure explaining an effect | action. (This embodiment) It is a figure explaining an effect | action. (This embodiment) It is a block block diagram of the electric power steering device which concerns on background art. (Background technology) It is a block diagram of a motor circuit. (Background technology) It is a figure which shows the relationship between PWM control and assist current in the 1st mode and the 2nd mode. (Background technology) It is a figure which shows the relationship between input torque and assist current. (Background technology) It is a figure which shows the state which the form of the characteristic line of the 2nd mode shown in FIG. 6 changes with forward rotation and reverse rotation. (Background technology)

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 2 Control signal correction | amendment means 101 Torque sensor 102 Vehicle speed sensor 104 Motor circuit 107 Integration control means 112 PWM control means 113 Motor drive means M Motor F1-F4 Switching element

Claims (1)

A vehicle speed sensor for detecting the vehicle speed, a torque sensor for detecting the steering torque of the steering wheel, a motor for assisting steering of the steering wheel, and a motor circuit configured to include an H bridge circuit including four switching elements, and driving the motor; A current deviation value obtained by subtracting a motor driving means for driving the motor circuit, a current command signal corresponding to the sensor signal output from the vehicle speed sensor and the torque sensor, and an actually measured assist current flowing through the motor. At least integration control means for inputting and integrating as digital data and outputting as a motor current control value, and PWM control means for PWM controlling the motor drive means based on the motor current control value,
The PWM control includes a first mode in which the high-side switching elements are PWM-controlled while the low-side switching elements of the four switching elements are on, and a second mode in which the four switching elements are PWM-controlled. In the power steering device,
A difference between one or a plurality of digital data before the current current deviation value digital data and the current current deviation value digital data is obtained, and a value obtained by multiplying the difference by a coefficient is used as the motor. An electric power steering apparatus comprising control signal correction means for adding to a current control value.

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