JP5233638B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus that performs control to suppress overheating of a steering assist motor.

  An electric power steering device mounted on a vehicle includes a motor that is driven in accordance with a steering torque applied to a steering member, and transmits a driving force generated by the motor to a steering mechanism of the vehicle, thereby assisting steering. It is carried out. In such an electric power steering apparatus, the temperature of the motor or the drive circuit is increased or decreased by the current flowing through the motor or the drive circuit that drives the motor according to the history of steering. When the motor or the drive circuit is overheated due to the history of steering, there is a risk that malfunctions such as malfunction or damage to parts occur.

  In the conventional electric power steering apparatus, in order to prevent problems due to overheating, for example, a temperature detector is provided on a substrate on which a control unit and a drive circuit are mounted, and the temperature of the substrate is detected. When the temperature detected by the temperature detector exceeds the allowable temperature, the current supplied to the motor is limited to a threshold value or less. The threshold for limiting the current is increased or decreased according to the temperature of the motor or drive circuit corresponding to the steering history. Then, when the temperature of the substrate becomes equal to or higher than the allowable temperature by lowering the threshold when the temperature of the motor or the drive circuit becomes high, a current limited to the threshold or lower is supplied to the substrate or the motor. As a result, the temperature of each component on the board and the motor is prevented from further rising due to the supplied current, and problems due to overheating are prevented.

  By the way, in the electric power steering apparatus that limits the current as described above, when the engine is stopped for a long time, the temperature of the substrate from which the supply of electric power is cut is sufficiently lowered. For this reason, it is not necessary to perform control to limit the current immediately after the starter switch for starting the engine is turned on. However, when the starter switch is turned on after the engine is stopped and before the temperature of the substrate decreases, it is necessary to perform control to limit the current immediately after the starter switch is turned on. The substrate and the motor are generally provided apart from each other, and it is necessary to estimate the motor temperature from the substrate temperature.

Therefore, Patent Document 1 discloses an electric power steering apparatus that estimates the temperature of a motor and controls current when power supply to an electric control unit that controls driving of the motor is cut off and then the power is turned on again. Has been proposed. The electric power steering device described in Patent Document 1 directly detects the temperature of a specific part of the electric control unit, and based on the cooling time obtained from the detected temperature, and the cooling characteristics of the electric control unit and the motor. The motor temperature is estimated. And the control which restrict | limits an electric current below the threshold set based on the estimated temperature is performed.
Japanese Patent No. 3578048

  In Patent Document 1, when the temperature of the motor is estimated to be higher than the actual temperature, the current is surely limited, and the temperature increase of the motor or the electric control unit can be prevented. However, when the temperature of the motor is estimated to be lower than the actual temperature, the current is not limited even if the current needs to be limited, and the temperature of the motor or the electric control unit further increases. As a result, there is a risk that problems due to overheating may occur. For this reason, in the electric power steering apparatus of patent document 1, it is influenced by estimated temperature and cannot prevent the malfunction by overheating reliably.

  The present invention has been made in view of such circumstances, and an object of the present invention is to prevent the current from being unnecessarily limited when the starter switch is turned on, and to limit the current more safely. And it is providing the electric power steering device which can prevent the malfunction by overheating reliably.

  An electric power steering apparatus according to the present invention detects a steering assist motor to which a current corresponding to a steering torque applied to a steering member is supplied, and the temperature of a specific part that is heated by driving the motor. An electric power steering apparatus comprising: a detection unit; and a control unit that controls the current to be equal to or less than a current limit value that is changed according to the temperature of the specific part when the temperature detected by the detection unit exceeds an allowable temperature. A storage means for storing the current limit value when the engine is stopped as a limit value before engine stop, and a starter switch for starting the engine that corrects the temperature of the specific part detected by the detection means. Determining means for determining a temperature correction value at the time based on a limit value before stopping the engine stored in the storage means; and the starter switch The temperature correction value is added to the temperature of the specific part detected by the detection means when the starter switch is turned on for a predetermined time after the switch is turned on, and the specific value detected by the detection means is detected. Temperature setting means for correcting the temperature of the part.

  In addition, the electric power steering apparatus according to the present invention further includes a gradual decrease unit that gradually decreases the temperature correction value determined by the determination unit with an elapsed time after the starter switch is turned on.

  Furthermore, the electric power steering apparatus according to the present invention includes an outside air temperature detecting means for detecting an outside air temperature, and the temperature correction value and / or the temperature setting means based on the outside air temperature detected by the outside air temperature detecting means. And a correction unit that corrects the temperature set by.

  The electric power steering apparatus according to the present invention includes an outside air temperature detecting means for detecting an outside air temperature, a calculating means for calculating a temperature difference between the outside air temperature detecting means and the detecting means, and a calculation by the calculating means. As a result, when the temperature difference is smaller than a predetermined value, it further comprises a prohibiting means for prohibiting the temperature setting by the temperature setting means.

  In the present invention, the temperature of the specific part is set to a temperature higher than the detected temperature by adding a temperature correction value determined based on the limit value before the stop to the temperature detected when the engine is stopped. To do. Since the limit value is changed according to the temperature of the specific part, the temperature of the specific part before stopping can be estimated from the limit value before stopping the engine. Therefore, since the temperature correction value is determined in consideration of the temperature of the specific part before the stop, even when the temperature correction value is set higher by adding the temperature correction value when the starter switch is turned on, the specific part The temperature can be kept from becoming higher than necessary. As a result, even if the detected temperature does not match the actual motor temperature, it is possible to prevent the current from being unnecessarily limited based on the temperature set appropriately high, and to make the current safer. It is possible to reliably prevent problems due to overheating.

  Further, when the motor temperature is estimated, it may coincide with the actual motor temperature, but may be estimated higher or lower than the actual temperature. For this reason, the present invention, which is set higher than the detected temperature for a predetermined time after the starter switch is turned on so that the current is easily limited, is more reliably compared with the case of estimating the temperature. It is possible to prevent problems caused by

  In the present invention, the temperature correction value set when the starter switch is turned on is reduced over time to bring it closer to the detected actual temperature. Thereby, the possibility that the steering assist force of the motor is insufficient can be reduced by restricting the current unnecessarily.

  Furthermore, the present invention corrects the determined temperature correction value and / or the temperature set by the temperature setting means in accordance with the outside air temperature. As a result, when the outside air temperature is low, the temperature of the portion that rises due to the driving of the motor decreases earlier, so that the current can be appropriately limited by correcting according to the outside air temperature.

  In the present invention, when the temperature difference between the outside air temperature and the temperature of the specific part is small, the temperature correction value is added to the temperature of the specific part, and the setting of the temperature higher than the detected temperature is prohibited. That is, it is prohibited to set the current higher than the detected temperature to easily limit the current to the motor. When the engine is stopped and a sufficient time has elapsed, the temperature of the specific part that has been raised due to the driving of the motor is lowered to a temperature close to the outside air temperature. When the temperature difference between the two is small, the possibility of malfunction due to overheating is low. For this reason, by restricting the current more than necessary, it is possible to reduce a situation in which the current corresponding to the steering torque of the motor is not sufficiently supplied and the steering of the steering member becomes heavy.

  Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof.

(Embodiment 1)
FIG. 1 is a schematic diagram showing a configuration of an electric power steering apparatus according to the present invention. The electric power steering apparatus includes a rack and pinion type steering mechanism 1. The steering mechanism 1 includes a rack shaft 10 that is supported so as to be movable in the axial direction inside a rack housing 11 that extends in the left-right direction of a vehicle body (not shown), and a pinion housing 19 that intersects the rack housing 11 in the middle. It has the well-known structure provided with the pinion shaft 2 rotatably supported inside.

  Both ends of the rack shaft 10 projecting outward from both sides of the rack housing 11 are connected to left and right front wheels 13, 13 as steering wheels via separate tie rods 12, 12. Further, the upper end of the pinion shaft 2 protruding outside from the pinion housing 19 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 19, and the pinion is formed in an intermediate portion of the rack shaft 10 at an intersection with the rack housing 11. Meshed with the rack.

  The steering shaft 3 is rotatably supported inside a cylindrical housing 31 and is attached to the interior of a vehicle compartment (not shown) with the front facing down via the housing 31. The pinion shaft 2 is connected to the lower end of the steering shaft 3 that projects downward from the housing 31, and the steering wheel 30 is fixed to the upper end of the steering shaft 3 that projects upward from the housing 31.

  With the above configuration, the steering shaft 3 is rotated by the rotation operation of the steering wheel 30 for steering, and this rotation is transmitted to the pinion shaft 2, and the rotation of the pinion shaft 2 is performed on the rack shaft at the meshing portion between the pinion and the rack. Thus, the movement of the rack shaft 10 is transmitted to the left and right front wheels 13 and 13 via the respective tie rods 12 and 12 for steering.

  In the middle of the housing 31 that supports the steering shaft 3, a torque sensor 4 that detects a steering torque applied to the steering shaft 3 by a rotation operation of the steering wheel 30 is provided. A steering assist motor 5 is attached below the torque sensor 4.

  The steering assist motor 5 is attached to the outside of the housing 31 with its axis substantially orthogonal, and, for example, a worm fixed to an output end extending inside the housing 31 is externally fixed to the steering shaft 3. It is engaged with the wheel, and the rotation of the motor 5 is decelerated by a worm and a worm wheel (not shown) and transmitted to the steering shaft 3 to assist the steering performed as described above. The motor 5 is connected to a motor driving unit 7 that drives and controls the motor 5.

  The motor drive unit 7 is connected to the in-vehicle battery 9 via an ignition switch (hereinafter referred to as IG switch) 15, and power is supplied from the in-vehicle battery 9. In addition, the motor drive unit 7 is connected to the assist control unit 6 and receives a PWM signal from the assist control unit 6 to drive the motor 5 by PWM. Similarly to the motor drive unit 7, the assist control unit 6 is connected to the in-vehicle battery 9 via the IG switch 15, and power is supplied from the in-vehicle battery 9.

  The IG switch 15 is an engine starter switch that starts when the engine is turned on. In the present embodiment, when the IG switch 15 is turned off, the engine is stopped, and power to the assist control unit 6 and the motor drive unit 7 is cut off.

  FIG. 2 is a block diagram showing a configuration of the assist control unit 6. The assist control unit 6 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory) connected by an internal bus. The following units are operated by the CPU according to a control program stored in the ROM. It is comprised so that control may be performed. The assist control unit 6 detects the steering torque value detected by the torque sensor 4, the vehicle speed value detected by the vehicle speed sensor 8, the motor current value detected by the motor current detection unit 50, and the outside air temperature detection unit 16. The outside air temperature is input respectively.

  The assist control unit 6 includes a phase compensation unit 61, a target drive current calculation unit 62, a current limiting unit (control means) 63, a temperature detection unit 64, a subtractor 65, a PWM signal generation unit 66, a storage unit 67, and a temperature correction unit. (Temperature setting means) 68 is provided. The phase compensation unit 61 is given a steering torque value from the torque sensor 4. In order to stabilize the control system, the phase compensation unit 61 performs a phase compensation process such as advancing the phase with respect to the steering torque value given by the torque sensor 4, for example. The steering torque value is given to the target drive current calculation unit 62. The target drive current calculation unit 62 is given a vehicle speed value by the vehicle speed sensor 8.

  The target drive current calculation unit 62 has an assist control map (not shown) showing the relationship between the steering torque value and the target drive current value, and applies the given steering torque value to this assist control map to achieve target drive. The current value is obtained, and the obtained drive current value is given to the current limiting unit 63. The target drive current value is a motor current value required for the motor 5 to generate an assist force necessary for assisting steering. There are a plurality of assist control maps for each vehicle speed value, and the target drive current calculation unit 62 selects one assist control map corresponding to the vehicle speed value, and obtains the target drive current value based on the selected assist control map. It is configured as follows.

  A temperature detection unit 64 and a temperature correction unit 68, which will be described later, are connected to the current limiting unit 63. From the temperature detection unit 64 or the temperature correction unit 68, the temperature in the assist control unit 6 or corrected assist control. The temperature in part 6 is given. The current limiting unit 63 sets the target driving current value obtained by the target driving current calculating unit 62 to the current limiting value when the given temperature exceeds a permissible temperature set in advance, for example, stored in the ROM. Restrict to:

  The current limit value is a threshold value used when limiting the motor current supplied to the motor 5, has an upper limit value, and decreases or increases according to the steering history of the steering wheel 30. Further, the steering history is a history of operation of the steering wheel 30 and is estimated from the target drive current value and is stored in a storage unit such as a RAM as needed.

  For example, when the steering wheel 30 is frequently operated at the time of entering the garage, the motor 5 is supplied with a motor current, so that the motor 5 or the assist control unit 6 that increases the temperature due to the driving of the motor 5 increases the temperature. To do. For this reason, limiting the motor current supplied to the motor 5 can prevent the motor 5 or the assist control unit 6 from being overheated.

  A storage unit 67 is connected to the current limiting unit 63, and the current limit value is stored in the storage unit 67. The storage unit 67 is, for example, an EEPROM (Electrically Erasable and Programmable Read Only Memory), and the current limiting unit 63 stores the current limit value used for limiting the motor current in a nonvolatile manner. The storage unit 67 stores the current limit value without receiving power supply. Therefore, the current limit value is stored in the storage unit 67 even while the IG switch 15 is turned off. The storage unit 67 may be not only an EEPROM, but also a static RAM or a flash memory, and may be any storage medium that does not erase the stored contents even when the IG switch 15 is in an off state. The current limit value stored in the storage unit 67 is read by the temperature correction unit 68. In the following description, the current limit value stored in the storage unit 67 is referred to as “current limit value Ioff”.

  The temperature detection unit 64 is, for example, a thermistor provided on a circuit board that constitutes the assist control unit 6, and is a temperature sensor that detects the temperature T in the assist control unit 6. The temperature T detected by the temperature detection unit 64 is given to the current limiting unit 63 or the temperature correction unit 68. The temperature correction unit 68 is connected to the outside air temperature detection unit 16 and is given the outside air temperature detected by the outside air temperature detection unit 16.

  The temperature correction unit 68 has a temperature correction map shown in FIGS. 3 and 4 to be described later, and the current limit value Ioff read from the storage unit 67 and the outside air temperature detected by the outside air temperature detection unit 16 are The temperature correction value dT is determined by applying to these maps. The temperature correction value dT is a correction value for setting the temperature T detected by the temperature detection unit 64 immediately after the IG switch 15 is turned on to be higher than the detection value. Then, the temperature correction unit 68 adds the obtained temperature correction value dT to the temperature detected by the temperature detection unit 64 and gives the result to the current limiting unit 63.

  The subtracter 65 is also given a motor current value output by the motor current detector 50 that detects the current flowing through the motor 5. The subtractor 65 obtains a deviation between the target drive current value (current limit value when limited by the current limiter 63), which is an output value of the target drive current calculation unit 62, and the motor current, and calculates the deviation by PWM. The signal generation unit 66 is provided. The PWM signal generation unit 66 generates a PWM signal based on the deviation given from the subtractor 65, the PWM signal generation unit 66 gives the generated PWM signal to the motor drive unit 7, and the motor drive unit 7 The motor 5 is PWM driven by switching between a coil of each phase (not shown) 5 and a power source and a ground terminal.

  The assist control unit 6 configured as described above generates a PWM signal of a target drive current value that generates a motor current necessary for assisting the steering of the motor 5, and the assist control unit 6 exceeds a predetermined temperature. When the temperature rises, the target drive current value is controlled to be equal to or less than the current limit value, and the assist control unit 6 is prevented from overheating.

  Next, a correction map used when the assist control unit 6 performs temperature correction in the temperature correction unit 68 will be described. FIG. 3 is a diagram illustrating an example of a map for determining the temperature correction value dT from the current limit value and the outside air temperature. FIG. 4 is a diagram illustrating an example of a map for determining the temperature correction value dT from the elapsed time. These maps may be stored in the ROM of the assist control unit 6 or may be stored in storage means in the temperature correction unit 68.

  The map shown in FIG. 3 associates the current limit value Ioff and the temperature correction value dT stored in the storage unit 67 for each of a plurality of outside air temperatures. When the IG switch 15 is turned on, the temperature correction unit 68 corresponds to the outside air temperature detected by the outside air temperature detecting unit 16 and the current limit value Ioff read from the storage unit 67 with reference to the map of FIG. The temperature correction value dT to be acquired is acquired. As described above, the temperature correction value dT is determined based on the current limit value Ioff before the IG switch 15 is turned off.

  When steering is frequently performed and the motor current needs to be limited, the current limit value becomes low. Therefore, in the map of FIG. 3, when the current limit value Ioff before turning off the IG switch 15 is low, the temperature correction value dT is set high, and the temperature detected after the IG switch 15 is turned on is set higher. It has become. Further, the temperature correction value dT is set to increase as the outside air temperature decreases. That is, when the outside air temperature is low, the temperature detecting unit 64 may detect a value lower than the actual temperature. Therefore, a high temperature correction value dT is set for the low outside air temperature, and the temperature detecting unit 64 detects the outside air temperature. The temperature to be set is set high.

  A map in which the current limit value Ioff and the temperature correction value dT are associated may be prepared for each outside air temperature. In FIG. 3, the temperature correction value dT is corrected according to the outside air temperature. However, the temperature obtained by adding the temperature correction value dT to the detected temperature T may be corrected according to the outside air temperature. Good.

  The map shown in FIG. 4 associates the elapsed time t after the IG switch 15 is turned on with the percentage of the temperature correction value dT. The temperature correction value dT determined by the map of FIG. 3 is a value immediately after the IG switch 15 is turned on. As shown in the map of FIG. 4, the temperature correction value dT is the value after the IG switch 15 is turned on. Decrease over time. For example, the temperature correction value dT when two minutes have passed since the IG switch 15 is turned on is approximately 60% of the temperature correction value dT determined by the map of FIG. When about 5 minutes have elapsed since the IG switch 15 was turned on, the temperature correction value dT becomes “0”.

  Next, an operation performed by the assist control unit 6 will be described. FIG. 5 is a flowchart for explaining the operation executed by the assist control unit 6. FIG. 6 is a flowchart for explaining the temperature correction / current limiting process executed by the assist control unit 6.

  First, when the IG switch 15 is turned on, the assist control unit 6 reads the current limit value Ioff stored in the storage unit 67 (S10). The current limit value Ioff is stored in the storage unit 67 before the IG switch 15 is turned off. And the assist control part 6 detects the temperature T in the assist control part 6 by the temperature detection part 64 (S11). Then, the assist control unit 6 determines whether or not the current limit value Ioff is close to the initial value (S12). Here, the initial value is the upper limit value of the current limit value, and the range that approximates the initial value is not particularly limited and can be changed as appropriate. When the current limit value Ioff is not close to the initial value (S12: NO), the assist control unit 6 determines the current limit value (hereinafter referred to as the current limit value Ion) after the IG switch 15 is turned on as the current The limit value Ioff is set (S13). That is, immediately after the IG switch 15 is turned on, the assist control unit 6 limits the motor current using the current limit value Ioff before the IG switch 15 is turned on.

  The assist control unit 6 executes temperature correction / current limiting processing (S14). In the temperature correction / current limiting process, the assist control unit 6 takes in the outside air temperature from the outside air temperature detecting unit 16 (S21). Then, the assist control unit 6 applies the current limit value Ioff read in S10, the temperature T detected in S11, and the outside air temperature captured in S21 to the map of FIG. 3, and determines the temperature correction value dT (S22). . Thereafter, the assist control unit 6 applies the elapsed time t after the IG switch 15 is turned on to the map of FIG. 4 and corrects the temperature correction value dT determined in S22 (S23).

  Next, the assist control unit 6 adds the temperature correction value dT to the temperature T detected in S11 (S24). Then, the assist control unit 6 determines whether or not the temperature [T + dT] as a result of addition in S24 exceeds the allowable temperature (S25). If the allowable temperature is not exceeded (S25: NO), the assist control unit 6 moves the process to S27. When the allowable temperature is exceeded (S25: YES), the assist control unit 6 performs current limiting process control (S26). That is, when the target drive current value obtained by the target drive current calculation unit 62 from each value such as the vehicle speed value and the steering torque value exceeds the current limit value Ion set in S13, the current limit value is less than the current limit value Ion. Based on the control result, a PWM signal to be supplied to the motor drive unit 7 is generated. When the target drive current value does not exceed the current limit value Ion, a PWM signal is generated based on the target drive current value obtained by the target drive current calculation unit 62.

  In S27, it is determined whether or not a predetermined time has elapsed since the IG switch 15 was turned on. Immediately after the IG switch 15 is turned on, the temperature correction value dT becomes a value determined from the map of FIG. 3, and gradually decreases with the passage of time after the IG switch 15 is turned on. Accordingly, when the predetermined time (about 5 minutes in FIG. 4) has elapsed, the temperature correction value dT becomes “0”. That is, if the predetermined time has not elapsed (S27: NO), the assist control unit 6 returns the process to S23, and corrects the temperature correction value dT from the elapsed time using the map of FIG.

  Thus, the motor current is limited by a safe value by setting the detected temperature high for a predetermined time after the IG switch 15 is turned on. Thereby, overheating of the motor 5 or the assist control part 6 can be prevented reliably.

  When the predetermined time has elapsed (S27: YES), the assist control unit 6 sets the current limit value Ion set to the current limit value Ioff in S13 based on the steering history (S28). Thereafter, the assist control unit 6 moves the process to S15. On the other hand, when the current limit value Ioff is close to the initial value in S12 (S12: YES), the assist control unit 6 hardly limits the motor current before the IG switch 15 is turned off. The current limit value Ion after the determination and the IG switch 15 is turned on is set to an initial value (S18). Thereafter, the assist control unit 6 moves the process to S15.

  The assist control unit 6 performs an overheat control process (S15). In the overheat control process here, the assist control unit 6 performs control to limit the motor current based on the current limit value Ion set in S28 or S18, and prevents the assist control unit 6 or the motor 5 from being overheated. . In S15, the current limit value Ion set in S28 or S18 is changed according to the steering history.

  Next, the assist control unit 6 determines whether or not the IG switch 15 is turned off (S16). If the IG switch 15 is not turned off (S16: NO), the overheat control process of S15 is repeated. On the other hand, when the IG switch 15 is turned off (S16: YES), the assist control unit 6 stores the current limit value used in the overheat control process of S15 in the storage unit 67 (S17), and the operation process of FIG. Exit. Note that, until the current limit value is stored in the storage unit 67 after the IG switch 15 is turned off, for example, a timer and a relay are provided to delay until the power is completely cut off.

  The current limit value stored in S17 is read when the IG switch 15 is turned on, and is applied to the determination of the temperature correction value dT as described above.

  As described above, the electric power steering apparatus of the present embodiment limits the current of the motor 5 based on the temperature higher than the detected temperature for a predetermined time after turning on the IG switch 15. For this reason, even if the detected temperature does not coincide with the actual temperature of the motor 5, immediately after the IG switch 15 is turned on by controlling the current more safely at a temperature higher than the detected temperature. Therefore, it is possible to reliably prevent problems due to overheating. Further, the temperature correction value dT can be set to an appropriate value by determining based on the current limit value before the IG switch 15 is turned off, thereby preventing the detected temperature from becoming higher than necessary.

  In the present embodiment, the assist control unit 6 includes the temperature detection unit 64 and determines the temperature correction value dT based on the temperature in the assist control unit 6, but the motor drive unit 7 or the motor 5 It is also possible to detect the temperature of another part that rises in temperature due to the driving of and to determine the temperature correction value dT based on that temperature.

  In the present embodiment, the timing for storing the current limit value in the storage unit 67 is when the IG switch 15 is turned off. However, the current limit unit 63 reduces the current limit value based on the steering history. Every time, that is, whenever the current limit value fluctuates, it may be stored in the storage unit 67. In this case, the power to the assist control unit 6 can be cut off at the same time as the IG switch 15 is turned off, and it is necessary to install a relay for providing a time difference for storing the current limit value after the IG switch 15 is turned off. Disappears.

(Embodiment 2)
Next, a second embodiment of the present invention will be described. In the second embodiment, when correcting the temperature detected by the temperature detection unit 64 in the first embodiment, it is determined whether or not to correct the temperature based on the temperature difference between the temperature in the assist control unit and the outside air temperature. To do. Hereinafter, differences from the first embodiment will be described.

  FIG. 7 is a block diagram illustrating a configuration of the assist control unit. The assist control unit 60 includes a phase compensation unit 61, a target drive current calculation unit 62, a current limiting unit 63, a temperature detection unit 64, a subtractor 65, a PWM signal generation unit 66, a storage unit 67, a temperature correction unit 68, and a temperature correction prohibition. The configuration has a portion 69. The temperature correction prohibition unit 69 is given the outside air temperature detected by the outside air temperature detection unit 16 and the temperature detected by the temperature detection unit 64, and calculates a temperature difference between the given temperatures. The temperature correction prohibiting unit 69 is connected to the current limiting unit 63. When the calculated temperature difference is an allowable temperature difference, the current limiting unit 63 performs current limiting based on the temperature corrected by the temperature correcting unit 68. Prohibit to do. That is, the current limiting unit 63 performs current limiting based only on the temperature detected by the temperature detection unit 64.

  As described in the first embodiment, the temperature of the assist control unit 60 rises due to the motor 5 or the driving of the motor 5. For this reason, when the IG switch 15 is turned on immediately after being turned off, the temperature in the assist control unit 60 is not lowered, and the temperature difference from the outside air temperature detected by the outside air temperature detecting unit 16 becomes large. On the other hand, when the IG switch 15 is turned on after a sufficient time has passed since the IG switch 15 is turned off, the temperature in the assist control unit 60 is lowered and the temperature difference from the outside air temperature is reduced. Therefore, if the temperature difference between the given temperatures is an allowable temperature difference, the temperature correction prohibition unit 69 determines that the assist control unit 60 is sufficiently cooled, and the temperature correction of the temperature detected by the temperature detection unit 64 is performed. Is prohibited. Thereby, when it is not necessary to limit the motor current for replenishing the steering, it is possible to avoid the trouble that the rotation operation of the steering wheel 30 becomes heavy. The allowable temperature difference may be determined based on a difference between the temperature at which the assist control unit 60 can determine that the cooling has been performed and the average temperature of the outside air temperature according to the season, or may be determined based on other conditions.

  Next, operations performed by the assist control unit 60 will be described. FIG. 8 is a flowchart for explaining the operation executed by the assist control unit 60.

  When the IG switch 15 is turned on, the assist control unit 60 first reads the current limit value Ioff stored in the storage unit 67 (S30). The assist control unit 60 detects the temperature T in the assist control unit 60 by the temperature detection unit 64 (S31). Then, the assist control unit 60 determines whether or not the current limit value Ioff is close to the initial value (S32). When the current limit value Ioff is close to the initial value (S32: YES), the assist control unit 60 determines that the motor current is hardly limited before the IG switch 15 is turned off, and the IG switch The current limit value Ion after 15 is turned on is set to an initial value (S38). Thereafter, the assist controller 60 moves the process to S39.

  When the current limit value Ioff is not close to the initial value (S32: NO), the assist control unit 60 takes in the outside air temperature Tout from the outside air temperature detecting unit 16 (S33). Then, the assist control unit 60 calculates a temperature difference (T−Tout) between the temperature T and the outside air temperature Tout (S34). As a result of the calculation, the assist control unit 60 determines whether or not the temperature difference (T-Tout) is an allowable temperature difference (S35). Specifically, the assist control unit 60 determines whether the temperature difference (T-Tout) is greater than or less than a threshold value, and determines that the temperature difference is less than or equal to the threshold value. When it is an allowable temperature difference (S35: YES), the assist control part 60 moves a process to S38.

  On the other hand, when the difference is not the allowable temperature difference (S35: NO), the assist control unit 60 determines that the temperature in the assist control unit 60 has not decreased, and the current limit stored in the storage unit 67 as the current limit value Ion. The value is set to Ioff (S36). That is, immediately after the IG switch 15 is turned on, the assist control unit 60 limits the motor current using the current limit value Ioff before the IG switch 15 is turned on. Then, the assist control unit 60 performs temperature correction / current limiting processing (S37). The temperature correction / current limiting process is the same as the process from S21 to S28 described in FIG. 6 of the first embodiment. Thereafter, the assist controller 60 moves the process to S39.

  The assist control unit 60 performs an overheat control process (S39). In the overheat control process here, the assist control unit 60 performs control to limit the motor current based on the current limit value Ion set in S36 or S38, and prevents the assist control unit 60 or the motor 5 from being overheated. . Next, the assist control unit 60 determines whether or not the IG switch 15 is turned off (S40). If the IG switch 15 is not turned off (S40: NO), the overheat control process of S39 is repeated. On the other hand, when the IG switch 15 is turned off (S40: YES), the assist control unit 60 stores the current limit value used in the overheat control process of S39 in the storage unit 67 (S41), and ends this process. . Note that, until the current limit value is stored in the storage unit 67 after the IG switch 15 is turned off, for example, a timer and a relay are provided to delay until the power is completely cut off.

  As described above, in the second embodiment, when the temperature difference between the temperature in the assist controller 60 and the outside air temperature is an allowable temperature difference, the temperature detected by the temperature detector 64 is not corrected. Based on the temperature detected by the temperature detector 64, an overheat control process is performed. As a result, by limiting the current more than necessary, it is possible to reduce a situation in which the current corresponding to the steering torque of the motor 5 is not sufficiently supplied and the steering of the steering wheel 30 becomes heavy.

  The preferred embodiments of the present invention have been specifically described above. However, each configuration, processing operation, and the like can be changed as appropriate, and are not limited to the above-described embodiments.

It is a mimetic diagram showing the composition of the electric power steering device concerning the present invention. It is a block diagram which shows the structure of an assist control part. It is a figure which shows an example of the map which determines a temperature correction value from an electric current limiting value and external temperature. It is a figure which shows an example of the map which determines a temperature correction value from elapsed time. It is a flowchart for demonstrating the operation | movement which an assist control part performs. It is a flowchart for demonstrating the temperature correction and electric current limitation process which an assist control part performs. It is a block diagram which shows the structure of an assist control part. It is a flowchart for demonstrating the operation | movement which an assist control part performs.

Explanation of symbols

  5 motor, 6 assist control unit, 7 motor drive unit, 16 outside air temperature detection unit, 63 current limiting unit, 64 temperature detection unit, 67 storage unit, 68 temperature correction unit

Claims (4)

A steering assist motor to which a current corresponding to a steering torque applied to the steering member is supplied, a detection means for detecting the temperature of a specific part that rises in temperature when the motor is driven, and the detection means detects In an electric power steering apparatus comprising a control means for controlling the current below a current limit value that is changed according to the temperature of the specific part when the temperature exceeds an allowable temperature,
Storage means for storing the current limit value when the engine is stopped as a limit value before stopping the engine;
Determination that corrects the temperature of the specific part detected by the detection means and determines a temperature correction value when the starter switch for starting the engine is turned on based on the limit value before engine stop stored in the storage means Means,
The temperature correction value is added to the temperature of the specific part detected by the detection means when the starter switch is turned on for a predetermined time after the starter switch is turned on, and the detection means detects An electric power steering apparatus comprising: temperature setting means for correcting the temperature of the specific part. 2. The electric power steering apparatus according to claim 1, further comprising a gradual decrease unit that gradually decreases the temperature correction value determined by the determination unit according to an elapsed time after the starter switch is turned on. An outside air temperature detecting means for detecting the outside air temperature;
The correction means for correcting the temperature correction value and / or the temperature set by the temperature setting means based on the outside air temperature detected by the outside air temperature detecting means. The electric power steering device described in 1. An outside air temperature detecting means for detecting the outside air temperature;
A calculating means for calculating a temperature difference between the temperatures detected by the outside air temperature detecting means and the detecting means;
The electric power steering apparatus according to claim 1, further comprising: a prohibiting unit that prohibits temperature setting by the temperature setting unit when a temperature difference is smaller than a predetermined value as a result of calculation by the calculating unit.

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