JP2007185991A - Electric power steering system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering system including a motor for generating steering auxiliary torque to a steering shaft according to steering torque applied to the steering shaft and a control unit for controlling the motor according to a current value of the motor detected by a current detector, capable of suppressing heat generation without increasing the capacity of a heat sink in the control unit. <P>SOLUTION: This electric power steering system including the motor for generating steering auxiliary torque to a steering shaft according to steering torque applied to the steering shaft and the control unit for controlling the motor according to a detected value of the motor by a current detector cools down a heat generating area in the control unit using Peltier elements. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric power steering device that applies a steering assist force by a motor to a steering system of a vehicle, and more specifically, cools a heat generating portion such as a motor drive circuit portion of a control unit that controls the motor. The present invention relates to the electric power steering apparatus.

  When a vehicle is parked in a parking space or the like, there may be a case where the steering is continuously turned back or stopped at a low speed. In this case, a large steering assist force (assist torque) is required, and the time for continuously flowing the maximum current of the motor increases. As a result, a heat generating part, a motor, etc. in the control unit generate heat and cause a failure, which may cause a failure or malfunction of a heat-sensitive component or the heat generating part itself. In order to prevent this, control for limiting the maximum current of the motor is generally performed. However, due to this control, the steering wheel may become heavy during steering, which is inconvenient when it is necessary to perform repeated steering repeatedly.

  In recent years, the output of electric power steering devices has also been increased to accommodate large vehicles, and semiconductor elements such as field effect transistors (hereinafter referred to as “FETs”) that can control large currents are mounted. The maximum current of the motor is also increasing.

  However, since the amount of heat generation increases as the maximum current of the motor increases in this way, heat dissipation measures become an important issue.

  Therefore, it is conceivable to increase the capacity of the heat radiating plate of the control unit. As a result, the size of the control unit increases as the cost increases. There were drawbacks.

  The present invention has been made under the circumstances as described above, and an object of the present invention is to provide a motor that applies a steering assist torque to the steering shaft in accordance with the steering torque generated in the steering shaft, and the current detector detected by the current detector. In an electric power steering apparatus having a control unit for controlling the motor based on a detected current value of the motor, the electric power steering apparatus can suppress heat generation without increasing the capacity of a heat radiating plate or the like in the control unit. Is to provide.

  According to the present invention, there is provided a motor that applies a steering assist torque to a steering shaft in accordance with a steering torque generated in a steering shaft, and a control unit that controls the motor based on a current detection value of the motor detected by a current detector. This is achieved by providing an electric power steering device characterized in that the heat generating part in the control unit is cooled by a Peltier element.

  The above-mentioned object of the present invention is achieved more effectively by providing an electric power steering device in which the heat generating part is a drive circuit part of the motor.

  According to another aspect of the present invention, there is provided an electric power steering apparatus, wherein the Peltier element is disposed between a heat sink and a substrate on which the motor drive circuit unit is mounted. Achieved more effectively.

  The object of the present invention is to provide an electric power steering device in which the Peltier element is driven and cooled based on the temperature of the drive circuit unit of the motor obtained by measurement or calculation. This is achieved more effectively.

  Further, the above object of the present invention is to provide an electric power steering device characterized in that electric power is supplied to the Peltier element by PWM control and the duty ratio is varied to perform temperature control. Effectively achieved.

  Further, the above object of the present invention is more effective by providing an electric power steering device characterized in that the temperature of the drive circuit section of the motor is measured by a thermistor installed in the vicinity of the heat generating section. Is achieved.

  The above-mentioned object of the present invention is achieved more effectively by providing an electric power steering apparatus characterized in that the temperature of the drive circuit section of the motor is calculated from the detected current value.

  According to another aspect of the present invention, there is provided an electric power steering apparatus, wherein the temperature of the drive circuit unit of the motor is calculated from the detected current value and a Peltier element drive current or a Peltier element drive PWM duty ratio. This is achieved more effectively.

  Further, the object of the present invention is that the Peltier element is driven and cooled by a Peltier element driving current value or a Peltier element driving PWM duty ratio mapped in advance for each temperature obtained by the measurement or calculation. This is achieved more effectively by providing an electric power steering device characterized by the above.

  The object of the present invention is to provide an electric power steering device in which the Peltier element is driven and cooled when the temperature obtained by the measurement or calculation exceeds a predetermined temperature. This is achieved more effectively.

  Further, the object of the present invention is that the Peltier element is driven when the temperature obtained by the measurement or calculation exceeds a predetermined temperature and is cooled, but when the temperature rises, This is achieved more effectively by providing an electric power steering apparatus characterized by increasing the Peltier element driving current or the Peltier element driving PWM duty ratio stepwise according to the temperature.

  In addition, the above object of the present invention is that the Peltier element is driven and cooled from the time when the temperature obtained by the measurement or calculation exceeds a predetermined temperature, and the Peltier element drive current even if the temperature starts to decrease. Alternatively, this can be achieved more effectively by providing an electric power steering device characterized by not changing the Peltier element drive PWM duty ratio.

  Still further, the object of the present invention is to provide an electric power steering device characterized in that the Peltier device stops driving when the temperature obtained by the measurement or calculation falls below a predetermined temperature. Is achieved more effectively.

  As described above, the present invention uses the cooling characteristics of the Peltier element to forcibly cool heat-generating components such as FETs. According to the present invention, the capacity of the heat sink and the like is increased. It is possible to provide an electric power steering device that can suppress heat generation without any problems. This also has the advantage that the steering wheel does not become heavy in the middle even when turning back and forth repeatedly, and inconvenience is not felt.

  The contents of the present invention will be described below with reference to the accompanying drawings. The present invention is not necessarily limited to the following examples, and it goes without saying that the configuration can be variously changed without departing from the scope of the claims.

  FIG. 1 is a diagram illustrating a general configuration example of an electric power steering apparatus. In this electric power steering apparatus, the column shaft 2 of the steering handle 1 is coupled to a tie rod 6 of a steering 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 steering handle 1, and a motor 20 that assists the steering force of the steering handle 1 is connected to the column shaft 2 via the reduction gear 3. ing. The control unit 30 that controls the electric power steering apparatus is supplied with electric power from the battery 14 and also receives an ignition key signal from the ignition key 11. The control unit 30 detects the steering torque value detected by the torque sensor 10. Based on T and the vehicle speed V detected by the vehicle speed sensor 12, an assist command steering assist command value I is calculated using an assist map or the like, and supplied to the motor 20 based on the calculated steering assist command value I. To control the current.

  The control unit 30 is mainly composed of a CPU (or MPU or MCU), and general functions and operations executed by programs in the CPU are as shown in FIG.

The steering torque T detected and input by the torque sensor 10 is phase-compensated by the phase compensator 31 in order to increase the stability of the steering system, and the phase-compensated steering torque TA is input to the steering assist command value calculator 32. Is done. In addition, the vehicle speed V detected by the vehicle speed sensor 12 is also input to the steering assist command value calculation unit 32. The steering assist command value calculation unit 32 refers to an assist map (lookup table) 33 based on the input steering torque TA and vehicle speed V, and a steering assist command value that is a control target value of the current supplied to the motor 20. Iref is determined.
The steering assist command value Iref is input to the subtraction unit 30A and also input to the feedforward differential compensation unit 34 for increasing the response speed, and the deviation (Iref-i) obtained by the subtraction unit 30A is a proportional calculation unit 35. And is input to the integral calculation unit 36 for improving the characteristics of the feedback system. The output of the proportional calculator 35 and the output of the integral calculator 36 are respectively input to the adder 30B, the output of the differential compensator 34 is also added to the adder 30B, and the current command value E, which is the addition result of the adder 30B. Is input to the motor drive circuit 37 as a motor drive signal. The motor current value i of the motor 20 is detected by the motor current detection circuit 38, and the motor current detection value i is input to the subtraction unit 30A and fed back.

  FIG. 3 shows a configuration example of the motor drive circuit 37. This motor drive circuit 37 includes an FET gate drive circuit 371 for driving the gates of the field effect transistors (FETs) FET1 to FET4 based on the current command value E from the adder 30B, an H bridge circuit comprising FET1 to FET4, FET1 and A boosting power source 372 for driving the high side of the FET 2 is formed. The FET1 and FET2 are turned ON / OFF by a PWM signal having a duty ratio D1 determined based on the current command value E, and the magnitude of the current Ir that actually flows through the motor 20 is controlled. FET3 and FET4 are driven by a PWM signal having a duty ratio D2 defined by a predetermined linear function equation (D2 = a · D1 + b, where a and b are constants) in a region where the duty ratio D1 is small, and the duty ratio D2 is also 100%. After reaching the value, it is turned ON / OFF according to the rotation direction of the motor 20 determined by the sign of the PWM signal.

  In the present embodiment, as described above, the Peltier element 40 cools the portion of the motor drive circuit 37 that generates heat and rises in temperature.

  FIG. 4 is a sectional view showing the cooling structure. As shown in the figure, the Peltier element 40 is disposed between a substrate 41 on which a motor drive circuit 37 part including FET1 to FET4 and the like is mounted, and a heat radiating plate 42. Specifically, the substrate 41 on which the motor drive circuit 37 is mounted is fixed to the upper surface of the heat radiating plate 42 with screws 43, and a recess 42 c is formed in the central portion of the heat radiating plate 42. It is arrange | positioned inside the hollow 42c. The heat radiation surface 40a (that is, the heat radiation plate 42 side) and the cooling surface 40b (that is, the substrate 41 side) of the Peltier element 40 are respectively coated with greases 44a and 44b that are excellent in thermal conductivity. The heat radiation surface 40a and the upper surface of the recess 42c of the heat radiation plate 42, and the cooling surface 40b of the Peltier element 40 and the lower surface of the substrate 41 are in close contact with each other. Note that the drive terminal 40 t of the Peltier element 40 is directly connected to the substrate 41. A thermistor 45 is provided on the upper surface of the substrate 41. The thermistor 45 measures the ambient temperature of heat-generating components such as FET1 to FET4. Here, since the structure and function of the Peltier element 40 are known, the description thereof is omitted.

  The Peltier element 40 is driven and cooled based on the temperature measured by the thermistor 45 (this is abbreviated as “thermistor temperature”).

  FIG. 5 is an explanatory diagram of a map control method as an example. That is, in this control method, the thermistor temperature is set for each arbitrary temperature, and the Peltier element drive current or the Peltier element drive PWM duty ratio for the drive signal of the Peltier element 40 is determined and mapped for each temperature in advance. The drive control of the Peltier element 40 is performed at a PWM duty ratio suitable for the thermistor temperature.

  Further, a feedback control method can be adopted as another control method.

  In this control method, drive control of the Peltier element 40 is started from the time when the thermistor temperature exceeds an arbitrary temperature, for example, 50 ° C. When driving control of the Peltier element 40 is started, driving is started with a Peltier element driving current or a Peltier element driving specified value. For example, the power supplied to the Peltier element 40 is controlled at a PWM duty ratio of 50%. Thereafter, every time the thermistor temperature rises by a specified temperature, for example, 1 ° C., the Peltier element driving current or the Peltier element driving duty ratio is increased by a specified value, for example, 3% PWM duty ratio. When the temperature starts to drop, the duty ratio at that time is fixed, and the control is continued until a predetermined temperature, for example, 45 ° C. is reached.

  As another control method, a simple control method can be adopted. Similar to the feedback control method, this control method starts driving control of the Peltier element 40 from the time when the thermistor temperature exceeds an arbitrary temperature, for example, 50 ° C. However, unlike the feedback control method, the Peltier element driving current or the Peltier element driving PWM duty ratio is not changed from the start of driving control of the Peltier element 40 until a predetermined temperature, for example, 45 ° C. is reached. When the temperature falls to a predetermined temperature, for example, 45 ° C., the driving of the Peltier element 40 is stopped.

  The layout of the Peltier element 40, the heat radiating plate 42, and the substrate 41 is not limited to the layout shown in FIG. 4, but can be freely laid out depending on design factors and the like as long as cooling and heat dissipation are possible.

  Further, a plurality of FETs may be cooled by one Peltier element, or the same number of Peltier elements as FETs may be used, and one FET may be cooled by one Peltier element. When using a plurality of Peltier elements, it is more effective to use a plurality of thermistors and control each Peltier element individually.

  Moreover, although the thermistor temperature was used in the said Example, the same effect can be acquired even if it uses the temperature measured using another temperature measuring element and a temperature measuring device.

  Further, the same effect can be obtained even if the estimated temperature value is used instead of the actually measured value such as the thermistor temperature. For example, the estimated temperature value is obtained by calculating electric power from the current command value E input to the motor drive circuit 37 from the adder 30B shown in FIG. The driving of the Peltier element is controlled using the value. Since the calculation for estimating the temperature rise is a known calculation, detailed description thereof is omitted.

  Further, the temperature drop value due to cooling can be estimated from the drive current of the Peltier element. A temperature closer to the actually measured value may be estimated from the temperature increase value and the temperature decrease value, and the drive of the Peltier element may be controlled using the value.

  Further, the motor drive circuit is not limited to the motor drive circuit 37 shown in FIG. 3 used in the above embodiment, and even if this is a motor circuit for driving a multiphase DC motor, it can be cooled by the Peltier element 40, An effect can be obtained.

  Furthermore, in the above embodiment, the embodiment of the method for cooling the FET has been described, but the same effect can be obtained for a heat generating component other than the FET, such as a CPU or a relay.

  The main configuration of the present invention has been described above, but as described above, the present invention is not necessarily limited to such an embodiment.

It is a block diagram which shows an example of an electric power steering device. It is a block diagram which shows the internal structure of a control unit. It is a connection diagram which shows an example of a motor drive circuit. It is sectional drawing which shows the cooling structure of a motor drive circuit part. It is explanatory drawing of the cooling control method by map control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering handle 2 Steering shaft 3 Reduction gear 5 Pinion rack mechanism 6 Tie rod 10 Torque sensor 11 Ignition key 12 Vehicle speed sensor 13 Relay 14 Battery 20 Motor 30 Control unit 37 Motor drive circuit 40 Peltier element 41 Substrate 42 Heat sinks 44a, 44b Grease 45 Thermistor

Claims (13)

  An electric motor comprising a motor that applies a steering assist torque to the steering shaft in accordance with a steering torque generated in the steering shaft, and a control unit that controls the motor based on a detected current value of the motor detected by a current detector. In the power steering apparatus, an electric power steering apparatus characterized in that a heat generating part in the control unit is cooled by a Peltier element.   The electric power steering apparatus according to claim 1, wherein the heat generating unit is a drive circuit unit of the motor.   3. The electric power steering apparatus according to claim 1, wherein the Peltier element is disposed between a substrate on which the drive circuit unit of the motor is mounted and a heat radiating plate. 4.   The electric power steering according to any one of claims 1 to 3, wherein the Peltier element is driven and cooled based on a temperature of a drive circuit unit of the motor obtained by measurement or calculation. apparatus.   5. The electric power steering apparatus according to claim 1, wherein electric power is supplied to the Peltier element by PWM control, and the duty ratio is varied to perform temperature control. 6.   5. The electric power steering apparatus according to claim 4, wherein the temperature of the drive circuit unit of the motor is measured by a thermistor installed in the vicinity of the heat generating unit.   The electric power steering apparatus according to claim 4, wherein the temperature of the drive circuit unit of the motor is calculated based on the detected current value.   5. The electric power steering apparatus according to claim 4, wherein the temperature of the driving circuit unit of the motor is calculated by the current detection value and a Peltier element driving current or a Peltier element driving PWM duty ratio.   5. The Peltier element is driven and cooled by a Peltier element driving current value or a Peltier element driving PWM duty ratio mapped in advance for each temperature obtained by the measurement or calculation. Electric power steering device.   5. The electric power steering apparatus according to claim 4, wherein the Peltier element is driven and cooled when the temperature obtained by the measurement or calculation exceeds a predetermined temperature. 6.   Even if the Peltier element is driven and cooled from the time when the temperature obtained by the measurement or calculation exceeds a predetermined temperature and the cooling is performed, the Peltier element is gradually changed according to the temperature. 11. The electric power steering apparatus according to claim 10, wherein a drive current or a Peltier element drive PWM duty ratio is increased.   The Peltier element is driven and cooled when the temperature obtained by the measurement or calculation exceeds a predetermined temperature, and the Peltier element driving current or the Peltier element driving PWM duty ratio is changed even when the temperature starts to decrease. The electric power steering apparatus according to claim 10, wherein the electric power steering apparatus is not provided.   The electric power steering apparatus according to any one of claims 10 to 12, wherein the Peltier element stops driving when a temperature obtained by the measurement or calculation falls below a predetermined temperature.

Images