JP2008265381A - Electric power steering apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device enabling the consistent operation for a long period by preventing the shortening of the lifetime of an auxiliary power source attached to a main power source by repeating the charging and discharging. <P>SOLUTION: A chargeable/dischargeable auxiliary power source 8 is provided on a power supply circuit with a motor 5 for the steering assist being connected to a main power source 7. When the load on the motor 5 is small, the auxiliary power source 8 is connected to the main power source 7 and charged by the operation of an assist control ECU 6. When the load on the motor 5 is large, the auxiliary power source 8 is connected to the side of the motor 5 and discharged. A temperature detector 9 for detecting the temperature of the auxiliary power source 8 is provided, the resistance of a variable resistor 81 connected to the auxiliary power source 8 is changed by the operation of the assist control ECU 6 based on the detected temperature of the temperature detector 9, and the charging/discharging time constant of the auxiliary power source 8 is changed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus including a motor driven by power supplied from an on-vehicle power source as a generation source of steering assist force.

  An electric power steering device that drives a steering assist motor in response to a rotation operation of a steering member such as a steering wheel and assists steering by adding the generated force of the motor to a steering mechanism is used as a generation source of the steering assist force. This motor is driven by power supplied from the on-board battery, so that it is possible to reduce the direct power burden of the engine for assisting the steering and to contribute to improving the fuel consumption of the vehicle.

  On the other hand, as a motor for assisting steering, a motor with high output is used assuming steering assist force at the time of low speed traveling or stopping against a large road reaction force, that is, so-called steering steering. Therefore, there is a problem that the burden on the in-vehicle battery becomes large.

  In order to cope with such problems, an auxiliary power source that can be charged and discharged is arranged in parallel with the in-vehicle battery as the main power source, and when the motor load for steering is heavy, in addition to the power supply from the main power source, the auxiliary power source An electric power steering device is proposed that is configured to reduce the burden on the main power source by driving the motor by discharging, while charging the auxiliary power source by supplying power from the main power source when the load on the motor is small. (For example, refer to Patent Document 1).

The auxiliary power supply is a capacitor provided in the power supply circuit that connects the steering assist motor to the in-vehicle battery as the main power supply, and is switched between the discharge position on the motor side and the charging position on the main power supply side by switching means It is possible. The assist control ECU that drives and controls the steering assist motor issues an operation command to the switching means according to the magnitude of the load of the motor, and the switching means responds to the discharge position when the motor load is large. In addition, when the motor load is small, the operation is switched to the charging position.
JP 2003-320942 A

  In the electric power steering apparatus configured as described above, a large steering assist force required for stationary steering can be realized without increasing the capacity of the in-vehicle battery as a main power source. For example, when stationary steering is repeatedly executed during garage entry, parallel parking, etc., and charging / discharging is frequently switched, the auxiliary power supply self-heats due to the action of the charging / discharging current flowing through the internal resistance. There was a problem that continuation of the high temperature state due to heat generation deteriorated the life of the auxiliary power supply.

  The present invention has been made in view of such circumstances, and prevents the life of the auxiliary power source attached to the main power source from deteriorating due to repeated charging and discharging, and enables stable operation over a long period of time. An object is to provide an electric power steering apparatus.

  An electric power steering apparatus according to a first aspect of the present invention is provided with an auxiliary power source capable of charging and discharging in a power supply circuit that connects a steering assist motor to a main power source. In the electric power steering apparatus that is connected to the main power source for charging, and the auxiliary power source is connected to the motor for discharging when the motor is under a heavy load, a temperature detector that detects the temperature of the auxiliary power source; Time constant changing means for changing the charge / discharge time constant of the auxiliary power supply, and control means for controlling the time constant changing means so that the charge / discharge time constant is increased or decreased according to the temperature detected by the temperature detector. It is characterized by providing.

  An electric power steering apparatus according to a second aspect of the present invention is characterized in that the time constant changing means in the first aspect is a variable resistor connected in series to the auxiliary power source.

  In the electric power steering apparatus according to the first aspect of the invention, the temperature of the auxiliary power source is detected by the temperature detector, and the charge / discharge time constant of the auxiliary power source is changed according to the detected temperature level. When the temperature of the power supply is high, charging and discharging of the auxiliary power supply can be performed slowly to suppress heat generation due to internal resistance, and the life of the auxiliary power supply due to self-heating can be prevented from deteriorating. .

  In the electric power steering apparatus according to the second aspect of the invention, the charge / discharge time constant can be continuously changed from large to small by increasing / decreasing the resistance of a variable resistor connected in series to the auxiliary power source, according to the temperature of the auxiliary power source. Detailed change control of the time constant becomes possible, and the life deterioration of the auxiliary power source due to self-heating can be more reliably prevented.

  Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof. FIG. 1 is a schematic diagram showing an overall configuration of an electric power steering apparatus according to the present invention. In this figure, an example of application to a vehicle equipped with a rack and pinion type steering mechanism 1 is shown, but it goes without saying that the present invention can be applied regardless of the type of the steering mechanism. .

  The rack-and-pinion type steering mechanism 1 crosses the rack housing 10 in the middle of the rack housing 10, which is supported in an axially movable manner in a rack housing 10 that extends in the left-right direction of a vehicle body (not shown). A pinion shaft 2 rotatably supported inside the pinion housing 20 is provided. Both ends of the rack shaft 11 are protruded to the outside of both sides of the rack housing 10, and these protruding ends are connected to left and right front wheels 13, 13 as steering wheels via respective tie rods 12, 12. . Further, the upper end of the pinion shaft 2 protruding outside the pinion housing 20 is connected to a steering wheel 30 as a steering member via the steering shaft 3.

  A pinion (not shown) is integrally formed at the lower part of the pinion shaft 2 extending inside the pinion housing 20, and this pinion has an appropriate length on the outer surface of the middle portion of the rack shaft 11 at the intersection with the rack housing 10. Is engaged with a rack provided. The steering shaft 3 is rotatably supported inside a cylindrical housing 31 and is attached to the interior of a passenger compartment (not shown) while maintaining a tilted posture with the front facing down via the housing 31. A pinion shaft 2 is connected to the protruding end of the steering shaft 3 downward, and a steering wheel 30 is fixed to the protruding end.

  With the above configuration, when the steering wheel 30 is rotated for steering, this rotation is transmitted to the pinion shaft 2 via the steering shaft 3, and the rotation of the pinion shaft 2 is caused by the engagement of the pinion and the rack. The rack shaft 11 is converted into a movement in the axial direction, and by this movement, the left and right front wheels 13 and 13 are pushed and pulled through the respective tie rods 12 and 12 for steering.

  A torque sensor 4 for detecting a steering torque applied to the steering shaft 3 by the operation of the steering wheel 30 is provided in the middle of the housing 31 that supports the steering shaft 3. A steering assist motor 5 is provided below the torque sensor 4. Is installed.

  The torque sensor 4 divides the steering shaft 3 to be detected into two upper and lower axes that are coaxially connected by a torsion bar having a known torsion characteristic, and the torsion bar is twisted between these two axes. It has a known configuration for detecting the relative angular displacement by an appropriate means.

  The steering assisting motor 5 is attached to the outside of the housing 31 with its axis substantially orthogonal, and the rotation of the output shaft of the motor 5 extending inside the housing 31 is used to rotate the output shaft of the motor 5. Thus, the speed is reduced and transmitted to the steering shaft 3.

  The steering assisting motor 5 attached in this way is connected to the assist control ECU 6. The assist control ECU 6 includes a CPU, a ROM, and a RAM, and integrally includes an arithmetic control unit that performs a predetermined control operation by the operation of the CPU according to a control program stored in the ROM, and a drive circuit of the motor 5. It is connected to a main power source 7 and an auxiliary power source 8 using a vehicle-mounted battery as described later. The assist control ECU 6 is provided with a detected value of the steering torque by the torque sensor 4 and a detected value of the temperature of the auxiliary power supply 8 from a temperature detector 9 attached to the auxiliary power supply 8.

  The assist control ECU 6 performs an assist control operation for controlling the steering assist motor 5 based on the detection result of the steering torque given from the torque sensor 4. In this assist control operation, a detected value of steering torque is taken at a predetermined sampling period, and this detected value is applied to a preset control map to determine a target value (target assist force) of the steering assist force to be generated. This is a known control operation in which the drive circuit of the steering assist motor 5 is operated to generate the target assist force, and the steering assist motor 5 is driven by power supplied from the main power supply 7 and the auxiliary power supply 8.

  The target auxiliary force determined based on the steering torque is used after being corrected based on the detection result of the running state that affects the steering such as the vehicle speed and the yaw rate. For example, the correction by the vehicle speed is a stable driving without wobbling by suppressing the steering assist force generated by the motor 5 at a low speed when the road surface reaction force applied to the front wheels 13 and 13 is small and giving the steering wheel 30 a rigidity. Conversely, when the road surface reaction force is large and the vehicle is running at a low speed, the steering assist force generated by the motor 5 is increased, the steering wheel 30 is operated lightly, and the labor burden required for steering is reduced. It will be done.

  On the other hand, the assist control ECU 6 sets the power supply circuit by the main power supply 7 and the auxiliary power supply 8 based on the magnitude of the load of the motor 5 driven as described above and the temperature detection value of the auxiliary power supply 8 given from the temperature detector 9. The following power supply control operation is performed as a control target.

  FIG. 2 is a diagram illustrating a schematic configuration of the power feeding circuit. As shown in the figure, the assist control ECU 6 is connected to a positive electrode and a negative electrode of a main power source 7 using an in-vehicle battery so that power can be supplied constantly. The auxiliary power supply 8 is a capacitor 8a having an internal resistance 8b, and is connected in parallel to the main power supply 7 and the assist control ECU 6 via a changeover switch 80. The auxiliary power supply 8 is connected in series with a variable resistor 81 as time constant changing means.

  The changeover switch 80 is configured to be switchable between a charging position indicated by a solid line in the drawing and a discharging position indicated by a two-dot chain line. When the changeover switch 80 is switched to the charging position, the auxiliary power supply 8 is connected to the main power supply 7 and is charged until there is no potential difference from the main power supply 7 and charges are accumulated in the capacitor 8a. On the other hand, when the changeover switch 80 is switched to the discharge position, the auxiliary power supply 8 is connected to the assist control ECU 6, and the charge accumulated in the capacitor 8a is discharged to the assist control ECU 6.

  During the charging / discharging performed as described above, the temperature of the auxiliary power supply 8 rises due to the heat generated by the internal resistor 8b through which the charging / discharging current flows. The temperature of the auxiliary power supply 8 that rises in this way is detected by the temperature detector 9 as described above, and is given to the assist control ECU 6.

  An operation command is given to the changeover switch 80 from the assist control ECU 6, and the changeover switch 80 is switched to one of the above-described charging position and discharging position in accordance with this operation command. The operation command of the assist control ECU 6 is also given to the variable resistor 81 connected in series to the auxiliary power supply 8, and the resistance of the variable resistor 81 is configured to be changed according to the operation command. is there.

  FIG. 3 is a flowchart showing the content of the power feeding control operation performed by the assist control ECU 6. The power feeding control operation according to this figure is repeatedly executed at predetermined control cycles in parallel with the assist control operation described above.

First, the assist control ECU 6 takes in the detected temperature t of the auxiliary power source 8 given from the temperature detector 9 (step S1), and compares this detected temperature t with the reference temperature t ₀ (step S2). The reference temperature t ₀ used for this comparison is a temperature that is expected to cause the life of the auxiliary power supply 8 to be deteriorated. For example, the reference temperature t ₀ is determined in advance based on the specifications of the capacitor 8a constituting the auxiliary power supply 8.

If the assist control ECU6 is that issues an operation command to the variable resistor 81 in response to the comparison in step S2, it is determined the detected temperature t of the temperature detector 9 exceeds the reference temperature t ₀ (step S2: YES the), sets the resistance value of the variable resistor 81 to the large (step S3), and conversely, if the detected temperature t is equal to or less than the reference temperature t ₀ (step S2: NO), a variable The resistance value of the resistor 81 is set to a small value (step S4), and the process proceeds to step S5.

  The rise in temperature of the auxiliary power supply 8 corresponds to internal energy loss that occurs in the capacitor 8a due to charging and discharging. This internal energy loss W (J) is given by the following equation.

In the equation (1), C is the capacitance (F) of the capacitor 8a, and V is the charging voltage (V) of the capacitor 8a, that is, the power supply voltage of the main power supply 7. In the equation (1), R is the discharge resistance (Ω) of the capacitor 8a, that is, the load resistance of the motor 5 including the drive circuit, and R _C is the resistance value (Ω) of the internal resistance 8b of the auxiliary power supply 8. ). Each of these values is given as a constant value specific to the component of the power feeding circuit.

  On the other hand, T in the equation (1) is a charging / discharging time constant of the auxiliary power supply 8 (capacitor 8a), and this time constant T can be changed depending on the resistance value of the variable resistor 81. . As apparent from the equation (1), the internal energy loss W of the capacitor 8a is small when the charging / discharging time constant T is large, and is large when the charging / discharging time constant T is small. By increasing the charging / discharging time constant T, the internal energy loss W of the capacitor 8a can be maintained at a low level, and the temperature rise of the auxiliary power supply 8 due to charging and discharging can be suppressed.

  The operation of the assist control ECU 6 after step S5 is an operation for issuing an operation command to the changeover switch 80 according to the magnitude of the load of the motor 5 and switching the changeover switch 80 to the discharging position or the charging position, as in the conventional case. The control ECU 6 checks the magnitude of the load on the steering assist motor 5 (step S5). If the load is in a heavy load state (step S5: YES), the control switch 6 switches the changeover switch 80 to the discharge position (step S6). If it is in a small load state (step S5: NO), the changeover switch 80 is switched to the charging position (step S7), and one control operation is completed.

  The magnitude determination of the load in step S5 is made, for example, by comparing the target auxiliary force determined in the assist control ECU 6 in the assist control operation described above with a preset reference auxiliary force. As a result of this comparison, if it is determined that a large load is necessary to achieve the target assist force, the motor 5 is supplied with power from the main power source 7 because switching to the discharge position is performed in step S6. And the auxiliary power supply 8 is discharged, and a large steering assist force can be generated. On the other hand, when it is determined that the vehicle is in a small load state, switching to the charging position is performed in step S7, and the auxiliary power source 8 is charged by power feeding from the main power source 7, and the motor 5 during this period is switched from the main power source 7. It is driven by power supply.

When the above charging / discharging is repeatedly performed, the temperature of the auxiliary power supply 8 rises due to self-heating. However, in the electric power steering device according to the present invention, the assist control ECU 6 performs the above-described operations in steps S2 to S4. When the temperature of the auxiliary power supply 8 exceeds the reference temperature t ₀ , the resistance value of the variable resistor 81 becomes large, and charging / discharging is performed under a large time constant T. Therefore, the temperature of the auxiliary power supply 8 is further increased. It is possible to suppress the deterioration of the life of the auxiliary power source 8 and to perform a stable operation over a long period of time.

In the above embodiment, the variable resistor 81 is used as the time constant changing means, and the charge / discharge time constant T can be changed stepwise or continuously by changing the resistance value of the variable resistor 81. Yes, for example, by determining a plurality of reference temperatures t ₀ and making a stepwise or continuous change based on the comparison result between the reference temperature t ₀ and the detected temperature t of the temperature detector 9, the auxiliary power source 8 caused by self-heating is provided. It is possible to more reliably prevent the deterioration of the lifespan.

1 is a schematic diagram showing an overall configuration of an electric power steering apparatus according to the present invention. It is a figure which shows schematic structure of an electric power feeding circuit. It is a flowchart which shows the content of electric power feeding control operation.

Explanation of symbols

  5 Motor, 7 Main power supply, 8 Auxiliary power supply, 9 Temperature detector, 81 Variable resistor (Time constant changing means)

Claims (2)

A power supply circuit for connecting a steering assist motor to a main power supply is provided with a chargeable / dischargeable auxiliary power supply. When the motor is under a small load, the auxiliary power supply is connected to the main power supply for charging, and the motor has a large load. Sometimes, in the electric power steering device that discharges by connecting the auxiliary power source to the motor,
A temperature detector for detecting the temperature of the auxiliary power source;
Time constant changing means for changing the charge / discharge time constant of the auxiliary power source;
An electric power steering apparatus comprising: control means for controlling the time constant changing means so as to increase or decrease the charge / discharge time constant according to the temperature detected by the temperature detector.   The electric power steering apparatus according to claim 1, wherein the time constant changing means is a variable resistor connected in series to the auxiliary power source.

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