JP2008174089A - Electric power steering control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To alleviate a processing load of a CPU without changing hardware. <P>SOLUTION: A steering auxiliary command value computing portion 10, a phase compensator 20, a convergence controller 60, and an inertia compensating part 70 carry out computing processing on the basis of variable gains K<SB>1</SB>, K<SB>2</SB>, K<SB>6</SB>and K<SB>7</SB>generated by vehicle speed response maps 13, 23, 63 and 73 according to a vehicle speed signal V and recorded. These variable gains K<SB>1</SB>, K<SB>2</SB>, K<SB>6</SB>and K<SB>7</SB>are updated in a predetermined period (for example, a period of 50 ms) which is set in advance. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an electric power steering control device that applies a steering assist force to a steering device by a motor when a steering wheel steers a steering handle.

  An electric power steering device mounted on a vehicle such as an automobile assists a steering person by applying a steering assist force to the steering device by an output torque of a motor.

  A general schematic configuration of such an electric power steering apparatus is shown in FIG. As shown in FIG. 7, the electric power steering apparatus includes a torque sensor 83 that detects the steering torque of the shaft 82 that is directly connected to the steering handle 81, a vehicle speed sensor 84 that detects the traveling speed of the vehicle, and detection of these sensors. An electric power steering control device (hereinafter referred to as ECU) 85 that calculates a steering assist force based on the signal, a motor 86 that generates rotational torque based on a signal output from the ECU 85, and the generated rotational torque to the steering mechanism. Transmission reduction gear 87, battery power supply 89 that supplies current to ECU 85 by turning on ignition key 88, universal joints 90a and 90b that transmit the rotational movement of steering handle 81 to the wheels, rack and pinion 91, and tie rod 92.

  FIG. 8 is a block diagram showing a schematic configuration of the ECU 85. The ECU 85 includes a microprocessor (MPU) 851 including a CPU and a recording medium (for example, ROM, RAM, etc.), a motor drive circuit 852, and a motor current detection circuit 853. The CPU stores a program stored in the internal memory of the MCU 851. By executing this, a current control value E for driving the motor 86 is generated based on the steering torque signal T detected by the torque sensor 83 and the vehicle speed signal V detected by the vehicle speed sensor 84, and this current control value is also generated. Feedback control is performed so that the deviation between E and the motor current i detected by the motor current detection circuit 853 becomes small. The CPU executes these control programs at a predetermined cycle based on a clock generation circuit (not shown).

  The application range of the electric power steering apparatus configured as described above has been extended to not only mini-passengers but also large vehicles such as ordinary vehicles and RVs in recent years. Large automobiles may have a large vehicle weight, and require a larger steering assist force, while further operability and safety are required. Further, in order to ensure these safety and operability, the vehicle speed signal V or the like is actively used, for example, a vehicle speed sensitivity map showing the relationship between the vehicle speed signal V and the control parameter is set in advance, and current control is performed. It is known that it is used for both the generation of the value E and the compensation of the current control value E, and the motor control of the electric power steering control device is highly functional.

  As described above, motors have been increased in size, and motor control functions for ensuring operability and safety have been advanced. For this reason, an increase in storage capacity of the recording medium in the electric power steering control device is inevitable. In this situation, the processing load on the CPU in the MPU is increasing.

  On the other hand, as a technique for reducing the processing load of the conventional CPU, there is a process when the processing load increases and a normal process, and when the processing load increases, the process is shifted to the increased processing. In some cases, the processing load is reduced (see, for example, Patent Document 1).

  In addition, in data communication between a plurality of CPUs, when data is the same, a technique is known in which processing load is reduced by not communicating the data (for example, Patent Documents). 2).

JP 2006-90356 A JP 2002-236659 A

  However, in the example described in Patent Document 1 described above, an increase in ROM capacity due to the addition of processing in preparation for an increase in processing load, or an increase in processing load due to processing for determining whether or not the processing load has increased. I hated it.

  Further, the time-series fluctuation of the vehicle speed is smaller than that of the steering torque, and therefore the detection of the vehicle speed signal V detected by the vehicle speed sensor 84 has a longer cycle than the calculation process of the current control value E such as 20 ms or 40 ms. (See FIG. 6). However, in general, processing in the vehicle speed sensitivity map is performed in the same manner as the calculation processing of the current control value E, for example, at a cycle of 1 ms. Therefore, the inventors of the present invention paid attention to this, and as a result of intensive studies, found out as one of the specific causes of the processing burden on the CPU.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an electric motor capable of reducing the processing load of the CPU and suppressing the manufacturing cost without changing hardware. It is to provide a power steering control device.

  In order to achieve the above-described object, an electric power steering control device according to the present invention is characterized by the following (1) and (2).

(1) Steering torque detecting means for detecting a steering torque generated in the steering handle and outputting a steering torque signal, vehicle speed detecting means for detecting a vehicle speed and outputting a vehicle speed signal, at least the steering torque signal and the vehicle speed Steering assist command value calculating means for calculating a steering assist command value based on the signal, compensation calculating means for correcting and calculating the steering assist command value based on the vehicle speed, and based on the corrected steering assist command value An electric power steering apparatus comprising: current command value calculating means for calculating a current command value; and motor drive control means for controlling drive of a motor based on the current command value. The steering assist command value calculating means, the compensation calculating means, Performs a calculation process based on a control parameter generated and recorded according to the vehicle speed signal, and the control parameter is preset. The update process is performed at a predetermined cycle.
(2) In the electric power steering control device according to (1), when the vehicle speed signal is equal to the vehicle speed signal of one cycle before, the update process of the control parameter is omitted.

  According to the electric power steering control device described in (1) above, since the control parameter is updated at a predetermined cycle set in advance, the processing load on the CPU can be reduced without changing the hardware. It is possible to reduce the manufacturing cost.

  Further, according to the electric power steering control device described in (2) above, when the vehicle speed signal is the same as that before one cycle, the process of updating the control parameter is omitted, so the processing load of the CPU Can be further reduced.

  According to the present invention, it is possible to reduce the processing load on the CPU without changing hardware, and to reduce the manufacturing cost.

  Embodiments of an electric power steering control device according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a hardware configuration of an electric power steering control device according to an embodiment of the present invention.

  In FIG. 1, an electric power steering control device (hereinafter also referred to as ECU) 1 includes a bus 100, a nonvolatile memory 109, an A / D converter 110, an interface (I / F) 111, a clock generation circuit 112, a CPU 113, and a ROM 114. , RAM 115, RD converter 116, PWM controller 117, motor drive circuit 118, and motor current detection circuits 119 and 120.

  The bus 100 transmits and receives data among the A / D converter 110, the interface 111, the CPU 113, the ROM 114, the RAM 115, and the like.

  The A / D converter 110 includes a steering torque signal T output from the torque sensor 4, a current detection value output from the motor current detection circuits 119 and 120, a motor rotation angle signal output from the RD converter 116, and the motor 3. Converts the voltage between terminals into a digital signal.

  The interface 111 counts the vehicle speed signal (pulse signal) V output from the vehicle speed sensor 2, converts it to a digital signal, and outputs it to the bus 100.

  A ROM 114 connected to the bus 100 is used as a memory for storing control programs such as a motor 3 control program, a PWM controller 117 calculation program, and a motor 3 output torque compensation program, which will be described later. It is used as a work memory for operating the program.

  The non-volatile memory 109 is constituted by, for example, an EEPROM or a flash memory, and can hold the contents stored in the memory even after the ignition key is turned off. Further, it is also used for recording and holding data of a vehicle speed sensitivity map (to be described later) and gain (control parameter) data generated corresponding to the vehicle speed signal V with reference to the vehicle speed sensitivity map. The vehicle speed response map is set in advance and can be rewritten from the outside.

  The PWM controller 117 performs pulse width modulation on the signal representing the torque of the motor 3 and converts it into duty command value pulse signals W, V, U, Wb, Vb, Ub. Here, the pulse signals W, V, and U represent positive-phase three-phase signals, and the pulse signals Wb, Vb, and Ub represent negative-phase three-phase signals.

  The motor drive circuit 118 is composed of three inverter circuits for generating currents of W, U, and V phases that drive the motor 3. Each of these inverter circuits consists of two switching transistors cascaded between a power supply voltage and a ground potential, and positive phase duty command value pulse signals W, V, U are input to the gates of the upper switching transistors. The lower-stage switching transistors receive opposite-phase duty command value pulse signals Wb, Vb, Ub. As a result, the upper and lower switching transistors perform complementary operations, and alternately turn on and off to generate drive currents Iu, Iv, and Iw of the motor 3 having a desired pulse width. In order to prevent the switching transistors at the upper and lower stages from being turned on at the same time, both before and after the on-time of W, V, U and Wb, Vb, Ub of the duty command value pulse signals of the normal phase and the reverse phase. A time (dead time) in which both the switching transistors are turned off is provided. Thereby, it is possible to avoid a short circuit between two switching transistors connected in cascade.

  The RD converter 116 supplies an excitation current to the resolver 5 and outputs an output signal from the resolver 5 to the A / D converter 110 as a rotation angle signal.

  The motor current detection circuits 119 and 120 are configured by current-voltage conversion elements such as resistors, detect the drive currents Iu and Iw of the motor 3, and output current detection values of voltages corresponding to the currents. The detected current value is corrected for voltage fluctuation by a power supply voltage correction circuit (not shown), amplified by the amplifier circuits 121 and 122, and then converted into a digital signal by the A / D converter 110.

  FIG. 2 is a block diagram showing functions of the CPU 113 constituting the ECU 1, that is, a control program executed by the CPU 113 is shown for each block. The same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof is simplified or omitted.

  As shown in FIG. 2, the ECU 1 corrects the torque system that performs control using the steering torque signal T, the current control system that performs control related to the driving of the motor, and the output torque (steering assist command value) of the motor. It consists of a compensation system. The torque system includes a steering assist command value calculation unit 10 and a differential controller 30, and the current control system includes a subtractor 97, a current controller 98, a PWM controller 117, a motor drive circuit 118, and a motor current detector 119. The compensation system includes a phase compensator 20, a convergence controller 60, an inertia compensator 70, and a SAT estimation compensator 80.

  The steering torque signal T is detected by the torque sensor 4 and input to the steering assist command value calculation unit 10, the differentiation controller 30, and the SAT estimation compensation unit 80.

  The steering assist command value calculation unit 10 outputs a steering assist command value I to be supplied to the motor based on the steering torque signal T and the vehicle speed signal V, and inputs the steering assist command value I to the phase compensator 20. The steering torque is greatest when the vehicle is stopped, and the steering torque is reduced as the vehicle speed increases. Therefore, the steering assist command value calculator 10 supplies the steering torque signal T to the motor 3. By changing the relationship with the steering assist command value I according to the vehicle speed signal V, the steering feeling is improved and the vehicle behavior is stabilized.

Phase compensator 20 performs phase compensation on the steering assist command value I, and outputs a steering assist command value I _P which phase compensation is applied to the subtracter 95 and the estimated SAT compensator 80. The phase compensator 20 takes in the vehicle speed signal V, removes the peak value at the resonance frequency of the resonance system composed of the inertia element and the spring element included in the output torque from the motor 3, and the response and stability of the control system. To compensate for the phase shift of the resonance frequency that hinders the above, to improve the transient characteristics or stabilize the control system.

  The differential controller 30 takes in the steering torque signal T, corrects the steering assist command value I according to the fluctuation of the steering torque signal T, suppresses the fluctuation of the output torque by the motor 3, and near the steering neutral point. Improves control responsiveness and realizes smooth and smooth steering. The output result of the partial controller 30 is output to the subtracter 95.

  On the other hand, the motor angular velocity estimation unit 40 estimates the motor angular velocity ω based on the output signal of the resolver 5. The motor angular velocity ω is input to the convergence controller 60, the motor angular acceleration estimator 50, and the SAT estimation compensator 80, respectively. Further, the motor angular acceleration estimator 50 estimates the motor angular acceleration α by subjecting the motor angular velocity ω to differentiation processing, for example, and outputs it to the inertia compensator 70 and the SAT estimation compensator 80.

  The convergence controller 60 receives the vehicle speed signal V and the motor angular velocity ω as inputs, and corrects the steering assist command value I in a direction that prevents the steering handle from rotating in order to improve the convergence of the vehicle. A brake is applied to the swinging motion of the steering handle, and the behavior of the steering handle after steering is stabilized.

  Then, the inertia compensator 70 receives the motor angular acceleration α and the vehicle speed signal V, and inputs the steering assist according to the change in the inertia system related to the steering system, the pinion rack mechanism, the motor 3 and the reduction gear. The command value I is corrected to suppress fluctuations in the auxiliary torque. Thus, the inertia of the drive system is prevented from being transmitted to the steering person, and the steering feeling is improved.

The SAT estimation compensator 80 receives the steering torque signal T, the steering assist command value _IP , the motor angular acceleration α, and the motor angular velocity ω, and corrects the steering assist command value I in a direction that assists the operation of the steering handle. To improve the return of the steering wheel after steering.

Here, the SAT estimation compensator 80 will be described in more detail with reference to FIG.
When the steering wheel steers the steering handle, a steering torque Th is generated, and the motor 3 generates an assist torque (steering assist force) Tm according to the steering torque Th (corresponding to the steering torque signal T). As a result, the wheels are steered and SAT is generated as a reaction force. Further, at that time, torque serving as steering steering resistance is generated by the inertia J and friction (static friction) Fr of the motor 3. Considering the balance of these forces, the following equation of motion can be obtained:

J · α (s) + Fr · sign (ω) + SAT = Tm + Th (1)
Here, when the above equation (1) is Laplace transformed with an initial value of zero and solved for SAT, the following equation (2) is obtained.

      SAT (s) = Tm (s) + Th (s) −J · α (s) −Fr · sign (ω (s)) (2)

Since the assist torque Tm can be estimated from the steering assist command value I _P, the estimated SAT compensator 80 according to the above (2) can be corrected steering assist command value I to estimate the SAT.

Returning again to FIG. 2, the description will be continued.
The adder 93 adds the output of the inertia compensator 70 and the output of the SAT estimation compensator 80 and outputs the result to the adder 94. The adder 94 adds the output of the adder 93 and the output of the convergence controller 60 and outputs the result to the subtracter 95.

Subtractor 95, an output steering assist command value I _P of the differential controller 30 and addition operation, and the output of the adder 94 from the result of the addition operation to subtraction processing, the result as the torque command value It outputs to the current command value calculation part 96 comprised with a 2-3 phase converter etc.

  Next, the subtractor 97 subtracts the outputs of the current detectors 119 and 120 from the current command value calculated by the current command value calculation unit 96 and outputs the result to the current controller 98. The current controller 98 takes in the output signal of the subtractor 97 and calculates a voltage command value based on the output signal. Further, the duty ratio is calculated from the voltage command value by the PWM controller 117, the inverter circuit is driven by the motor drive circuit 118, and the voltage is applied to the motor 3.

  Next, referring to FIG. 4, a control program execution process for the steering assist command value calculation unit 10, the phase compensator 20, the convergence controller 60, and the inertia compensation unit 70 that performs calculation processing by taking in the vehicle speed signal V will be further described. . The same constituent elements as those in FIGS. 1 and 2 are denoted by the same reference numerals or corresponding reference numerals, and description thereof will be simplified or omitted.

The steering assist command value calculation unit 10 receives the steering torque signal T, multiplies the transfer function G ₁ by the calculator 11, and then multiplies a variable gain (control parameter) K ₁ correlated with the vehicle speed signal V by the amplifier 12. Thus, the steering assist command value I is calculated. The processing of this control program is executed by the CPU 113, and for example, the cycle is 1 ms.

The phase compensator 20 takes in the output of the steering assist command value calculator 10 and multiplies the transfer function G ₂ by the calculator 21 and the variable gain K ₂ correlated with the vehicle speed signal V by the amplifier 22 and outputs the result. The processing of this control program is executed by the CPU 113, for example, with a period of 2 ms.

Similarly, the convergence control unit 60 and the inertia compensator 70 take in signals and multiply the transfer functions G ₆ and G ₇ by the arithmetic units 61 and 71 and the variable gains K ₆ and K ₇ by the amplifiers 62 and 72, respectively. Is output. Further, for example, the control program in the convergence controller 60 is executed in a cycle of 4 ms, and the control program in the inertia compensator 70 is executed in a cycle of 1 ms.

Here, the variable gains K ₁ , K ₂ , K ₆ , and K ₇ are updated based on the individually corresponding vehicle speed response maps 13, 23, 63, and 73. Further, the vehicle speed sensitive map 13,23,63,73 are predefined and the vehicle speed signal V, and the relationship between the control parameters of the variable gain _{K 1, K 2, K 6} , K 7 by a curve, operability In consideration of safety, for example, the larger the vehicle speed signal V, the smaller the variable gains K ₁ , K ₂ , K ₆ , K ₇ are set.

That is, the CPU 113 sequentially calculates the values of the variable gains K ₁ , K ₂ , K ₆ , K ₇ corresponding to the vehicle speed signal V with reference to the vehicle speed sensitivity maps 13, 23, 63, 73 and records them in the RAM 115. The held variable gains K ₁ , K ₂ , K ₆ , K ₇ are updated (see FIG. 1). Therefore, the steering assist command value calculation unit 10, the phase compensator 20, the convergence controller 60, and the inertia compensation unit 70 are updated to the variable gains K ₁ , K ₂ , K ₆ , and K ₇ that are sequentially updated. Based on the calculation processing.

In addition, since the change in the actual vehicle speed is slight compared to the steering torque or the like, the updating process of the variable gains K ₁ , K ₂ , K ₆ , and K ₇ using these vehicle speed sensitivity maps 13, 23, 63, 73 is as follows: It is assumed that the processing is performed in a cycle longer than the processing cycle of the steering assist command value calculation unit 10, the phase compensator 20, the convergence controller 60, and the inertia compensation unit 70, for example, in a cycle of 50 ms.

  Here, taking the comparative example shown in FIG. 5, the present embodiment will be further described while comparing the present embodiment with the comparative example according to FIG. In the comparative example, the vehicle speed sensitivity maps 113, 123, 163, and 173 are stored in the control programs of the steering assist command value calculation unit 10, the phase compensator 20, the convergence controller 60, and the inertia compensation unit 70, respectively. A case where the control program is included and executed in the cycle of each control program is shown, and FIG. 6 shows the execution of the control program of the steering assist command value calculation unit 10 as a representative one.

  In FIG. 6, (a) represents a torque signal input at a cycle of 1 ms, and (b) represents a vehicle speed signal input at a cycle of 50 ms. (C) As shown in (1), the calculation processing of the steering assist command value calculation unit 10 is performed at a cycle of 1 ms corresponding to the steering torque signal T input at a cycle of 1 ms.

Furthermore, here, in the comparative example, the process of calculating the gain K ₁ according to the vehicle speed signal V is executed with reference to the vehicle speed sensitivity map 113 at a cycle of 1 ms. On the other hand, in the present embodiment, the vehicle speed sensitivity map 13 provided in a separate stage is executed in 50 ms in accordance with a vehicle speed signal input at a cycle of 50 ms. For this reason, as shown in (d), in the comparative example, a constant load is always applied to the CPU 113, but in this embodiment, the burden on the CPU 113 is small except when the vehicle speed signal V is input.

The variable gains K ₁ , K ₂ , K ₆ , and K _{7 that} are generated and updated according to the vehicle speed signal V are generated and updated each time corresponding to the vehicle speed signal V acquired at a period of 50 ms. Although explained as a thing, when the value of vehicle speed signal V is the same as the last time, processing generated according to vehicle speed signal V may be omitted. In this case, each time the vehicle speed signal is sequentially input, it is recorded and held in the RAM 115 (see FIG. 1), and it is determined whether or not the newly input vehicle speed signal has the same value as compared with the previous one. The

Therefore, according to the present embodiment, the steering assist command value calculation unit 10, the phase compensator 20, the convergence controller 60, and the inertia compensation unit 70 are converted into the vehicle speed signal V by the vehicle speed response map 13, 23, 63, 73. depending arithmetic processing performed based on the variable gain _{K 1, K 2, K 6} , K 7 to be recorded held are generated, and these variable gain _{K 1, K 2, K 6} , K 7 are set in advance Since the update process is performed at a predetermined cycle (for example, a cycle of 50 ms), it is possible to reduce the load of the arithmetic processing of the CPU 113. Moreover, since it can be easily realized by changing the control program, the hardware is not changed, and therefore the manufacturing cost of the electric power steering control device can be suppressed.

  This is the end of the description of specific embodiments. However, aspects of the present invention are not limited to these embodiments, and modifications, improvements, and the like can be made as appropriate. For example, in the present embodiment, the processing cycle of each control program is shown as a specific numerical value, but is not limited to this, and can be appropriately selected within a range where the present invention can be applied.

  In the present embodiment, most of the processing is performed by software. However, part or all of the processing may be realized by hardware such as FPGA (Field Programmable Gate Array). The present invention may be any control that uses the vehicle speed, and can be applied to various control systems such as a robust control system in addition to the above-described control.

  The present invention is applicable to all electric power steering devices regardless of the type of electric power steering device (column type, pinion type, rack type) and the type of motor (with brush, brushless, etc.).

It is a block diagram which shows the hardware constitutions of the electric power steering control apparatus which concerns on embodiment of this invention. It is a block diagram which shows the function of CPU which comprises ECU of the electric power steering control apparatus which concerns on embodiment of this invention. It is a schematic diagram which shows the mode of the torque generate | occur | produced between a road surface and steering. It is a block diagram which shows a part of process of the torque command value production | generation of the electric power steering control apparatus which concerns on embodiment of this invention. It is a block diagram which shows a part of process of the torque command value generation which concerns on the conventional electric power steering control apparatus. It is a timing chart for explaining operation in processing of torque command value generation of an electric power steering control device concerning an embodiment of the present invention. It is a figure which shows schematic structure of a general electric power steering apparatus. It is a block diagram which shows schematic structure of ECU.

Explanation of symbols

1 ECU
2 Torque sensor (steering torque detection means)
3 Motor 4 Vehicle speed sensor (vehicle speed detection means)
10 Steering assist command value calculator (steering assist command value computing means)
13, 23, 63, 73 Vehicle speed sensitivity map 16 Current command value calculation unit (current command value calculation means)
20 Phase compensator (correction calculation means)
60 Convergence controller (correction calculation means)
70 Inertia compensator (correction calculation means)
113 CPU
_{K 1, K 2, K 6} , K 7 variable gain (control parameter)

Claims (2)

Steering torque detecting means for detecting steering torque generated in the steering handle and outputting a steering torque signal, vehicle speed detecting means for detecting vehicle speed and outputting a vehicle speed signal, and at least the steering torque signal and the vehicle speed signal A steering assist command value calculating means for calculating a steering assist command value based on the correction, a compensation calculating means for correcting the steering assist command value based on the vehicle speed, and a current command value based on the corrected steering assist command value. In an electric power steering apparatus comprising a current command value calculating means for calculating the motor and a motor drive control means for driving and controlling the motor based on the current command value,
The steering assist command value calculation means and the compensation calculation means perform a calculation process based on a control parameter generated and recorded and held in accordance with the vehicle speed signal, and the control parameter is set in a predetermined cycle. An electric power steering control device characterized in that an update process is performed in When the vehicle speed signal is equal to the vehicle speed signal one cycle before,
The electric power steering control device according to claim 1, wherein the update process of the control parameter is omitted.

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