JP5119958B2 - 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, when steering is repeatedly performed, the motor or the drive circuit generates heat due to the current flowing in the motor or the drive circuit that drives the motor. And when a motor or a drive circuit overheats, malfunctions, such as malfunction or damage of components, may arise. For this reason, in a conventional electric power steering device, for example, a temperature detector is provided on a substrate on which a control unit and a drive circuit are mounted, and the temperature detected by the temperature detector is supplied to the motor when the temperature exceeds an allowable temperature. By limiting the current to be generated, further temperature rise of each component and motor on the board is prevented, 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. In general, since the electric power steering apparatus is provided so that the substrate and the motor are separated from each other, it is necessary to estimate the temperature of the motor from the temperature of the substrate.

Therefore, Patent Document 1 proposes an electric power steering device that estimates the temperature of a motor and performs control to limit current when a starter switch is turned on. The electric power steering device described in Patent Document 1 directly detects the temperature of a specific part of an electric control unit that drives and controls the motor, and cools the cooling time obtained from the detected value, and the cooling of the electric control unit and the motor. The motor temperature is estimated based on the characteristics. Based on the estimated motor temperature, control is performed to limit the current.
Japanese Patent No. 3578048

  However, when the engine is stopped, the current to the steering assist motor is cut off, so the temperature of the specific part of the electric control unit after being turned off regardless of the length of time it is turned off. Some cooling. Therefore, in Patent Document 1 in which the temperature of the motor is estimated and the current is limited based on the estimated temperature, when the motor temperature is estimated to be lower than the actual temperature, the current is rarely limited. If it is estimated to be higher than the temperature, there is a possibility that the current is limited even if the current is not actually limited. Therefore, the electric power steering apparatus of Patent Document 1 has a problem that the steering feeling of the steering member after the starter switch is turned on depends on the estimated temperature.

  The present invention has been made in view of such circumstances, and an object of the present invention is to prevent the steering feeling of the steering member from deteriorating by suppressing unnecessary current limitation when the starter switch is turned on. An object of the present invention is to provide an electric power steering device that can be used.

  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. In an electric power steering apparatus comprising: a detection unit; and a control unit that controls the current below a 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. Temperature storage means for storing the temperature of the specific part detected by the detection means when the engine is stopped, and limit value storage for storing the limit value when the engine is stopped as a limit value before stop And the temperature of the specific part detected by the detection means when the starter switch for starting the engine is turned on, and the temperature storage means The limit value is stored in the limit value storage means according to the temperature difference calculated by the calculation means for a predetermined time after the starter switch is turned on, and a calculation means for calculating the temperature difference between the temperatures. And setting means for setting the value to be greater than or equal to the pre-stop limit value.

  In the electric power steering apparatus according to the present invention, when the temperature difference calculated by the calculation unit is less than T1, the setting unit sets the limit value before stop stored in the limit value storage unit. When the temperature difference calculated by the first setting means for setting the value and the calculation means is not less than T1 and less than T2 (T2> T1), the limit value is stored in the limit value storage means Second setting means for setting a value obtained by adding a predetermined value to the previous limit value, and third setting means for setting the limit value to an upper limit value when the temperature difference calculated by the calculation means is equal to or greater than T2. It is characterized by having.

  Furthermore, the electric power steering apparatus according to the present invention is configured to determine the T1 and / or the T2 based on the outside air temperature detecting means for detecting the outside air temperature and the outside air temperature detected by the outside air temperature detecting means. And a means.

  In the present invention, when the current is controlled so as to be equal to or less than the limit value changed according to the temperature of the specific part, the starter switch is turned on based on the temperature difference between before the engine is stopped and after the engine is started The predetermined time is set to be equal to or greater than the limit value stored before the stop. Thus, when the starter switch is turned on, for example, even if the detected or estimated temperature of the specific part is higher than the allowable temperature, the temperature of the specific part is set higher than before stopping by setting the limit value higher. Since it is slightly lowered, the current can be prevented from being limited more than before stopping. As a result, when the starter switch is turned on, unnecessary current limitation can be suppressed, and the steering feeling of the steering member can be prevented from deteriorating.

  Further, by using the temperature difference and, for example, the cooling characteristics of the specific part, it is possible to estimate the time during which the engine is stopped, which is the cooling period. And if the estimated time is short, setting the limit value to the limit value before stop, which is the minimum value of the set value range, will make the limit value higher than necessary and limit the necessary current. Can be prevented.

  Further, according to the present invention, the limit value stored before the stop, before the stop, depending on whether the temperature difference is less than T1, T1 or more and less than T2, or T2 or more. A value obtained by adding a predetermined value to the limit value and an upper limit value are set. If the limit value is set higher than necessary, the necessary current will not be limited, so the current limit is set appropriately by setting the limit value higher stepwise based on the temperature difference. Unnecessary current limitation can be suppressed.

  Furthermore, in the present invention, T1 and / or T2 are determined based on the outside air temperature. When the outside air temperature is low or high, the temperature of the specific part also fluctuates accordingly, so the threshold value for setting the limit value is determined based on the outside air temperature. , Current can be limited appropriately.

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

  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 63, a temperature detection unit 64, a subtractor 65, a PWM signal generation unit 66, and a storage unit 67. 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 is connected to the current limiting unit 63. 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. Then, the temperature in the assist control unit 6 is given from the temperature detection unit 64 to the current limiting unit 63. The current limiting unit 63 sets the target drive current value obtained by the target drive current calculation unit 62 to be equal to or less than the current limit value when the given temperature exceeds a permissible temperature set in advance, for example, stored in the ROM. To be limited.

  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 temperature of the assist control unit 6 is increased due to the driving of the motor 5 or the motor 5. 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 temperature detection unit 64 and the current limiting unit 63 are connected thereto. The storage unit 67 stores the temperature detected by the temperature detection unit 64 and the current limit value used for limiting the motor current in the current limit unit 63 in a nonvolatile manner. The storage unit 67 stores the temperature and the current limit value without receiving power supply. Accordingly, the storage unit 67 stores various data even while the IG switch 15 is turned off and the engine is stopped. 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 and the temperature stored in the storage unit 67 are read by the current limit unit 63. In the following description, the current limit value stored in the storage unit 67 is referred to as “current limit value Ioff”, and the temperature is referred to as “temperature Toff”.

  In addition, the current limiting unit 63 calculates a temperature difference Ta between the temperature T detected by the temperature detection unit 64 and the temperature Toff stored in the storage unit 67. Further, the outside air temperature detection unit 16 is connected to the current limiting unit 63, and the outside air temperature detected by the outside air temperature detection unit 16 is given. The current limiting unit 63 sets a current limiting value based on the calculated temperature difference Ta and the outside air temperature for a predetermined time after the IG switch 15 is turned on. Then, when the temperature T detected by the temperature detection unit 64 exceeds the allowable temperature, the current limiting unit 63 determines that the target drive current value obtained by the target drive current calculation unit 62 is based on the temperature difference Ta and the outside air temperature. Limit the current to the current limit value or less. In the following description, the current limit value set by the current limiter 63 for a predetermined time after the IG switch 15 is turned on is referred to as “current limit value Ion”.

  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, an operation performed by the assist control unit 6 will be described. FIG. 3 is a flowchart for explaining the operation executed by the assist control unit 6.

  The assist control unit 6 starts the operation of FIG. 3 when the IG switch 15 is turned on, and reads the current limit value Ioff and the temperature Toff stored in the storage unit 67 (S10). The current limit value Ioff and the temperature Toff are stored in the storage unit 67 before the IG switch 15 is turned off. Then, the assist control unit 6 determines whether or not the current limit value Ioff is approximate to the upper limit value (S11). Here, the range that approximates the upper limit value is not particularly limited, and can be changed as appropriate.

  When the current limit value Ioff is not close to the upper limit value (S11: NO), the assist control unit 6 detects the temperature T in the assist control unit 6 by the temperature detection unit 64 (S12). Then, the assist control unit 6 calculates the temperature difference Ta between the temperature Toff before the IG switch 15 is turned off and the temperature T after the IG switch 15 is turned on (S13). Specifically, the calculation is performed by T−Toff. The assist control unit 6 determines the time during which the IG switch 15 is turned off based on the calculated temperature difference Ta. For example, when the temperature difference is small, it is determined that the off time is short, and when the temperature difference is large, it is determined that the off time is long.

  Next, the assist controller 6 takes in the outside air temperature from the outside air temperature detector 16 (S14), and sets threshold values T1 and T2 (S15). The threshold values T1 and T2 are both threshold values for determining the magnitude of the temperature difference Ta calculated in S13, and by determining the magnitude based on the threshold value, the time during which the IG switch 15 is turned off is determined. To do. The temperature difference Ta changes according to the outside air temperature. For example, when the outside air temperature is low, the temperature difference Ta is large, and when the outside air temperature is high, the temperature difference Ta is small. Therefore, the threshold values T1 and T2 for determining the magnitude of the temperature difference Ta are set according to the outside air temperature.

  Subsequently, the assist control unit 6 determines whether or not the temperature difference Ta is less than the threshold value T1 in the current limiting unit 63 (S16). When the temperature difference Ta is less than the threshold value T1 (S16: YES), the assist control unit 6 determines that the time during which the IG switch 15 is off is short, and sets the current limit value Ion to the current limit value Ioff. (S17). That is, the assist control unit 6 limits the motor current by the current limit value Ioff before being turned off for a predetermined time after the IG switch 15 is turned on. Thereafter, the assist controller 6 moves the process to S21.

  On the other hand, when the temperature difference Ta is not less than the threshold value T1 (S16: NO), the assist control unit 6 determines whether or not the temperature difference Ta is equal to or greater than the threshold value T1 and less than the threshold value T2 (S18). When the temperature difference Ta is greater than or equal to the threshold value T1 and less than the threshold value T2 (S18: YES), the assist control unit 6 adds the current limit value Ion to the current limit value Ioff by a predetermined value α, and from the current limit value Ioff. A high value is set (S19). Thereafter, the assist controller 6 moves the process to S21.

  When the temperature difference Ta is equal to or greater than the threshold T1 and not less than the threshold T2 (S18: NO), the assist control unit 6 determines that the time during which the IG switch 15 is off is long, and sets the current limit value Ion to the upper limit. A value is set (S20). Thereafter, the assist controller 6 moves the process to S21.

  In S21, overheat control is performed based on the current limit value Ion set in S17, S19, or S20 (S21). Then, the assist control unit 6 determines whether or not a predetermined time has elapsed since the IG switch 15 was turned on (S22). If the predetermined time has not elapsed (S22: NO), the assist control unit 6 returns the process to S21 and performs overheat control based on the current limit value Ion set in S17, S19, or S20. Specifically, the assist control unit 6 determines 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 when the temperature T detected by the temperature detection unit 64 exceeds the allowable temperature. However, when the current limit value Ion is exceeded, the current limit value Ion is controlled to be equal to or less. And based on the controlled result, the PWM signal given to the motor drive part 7 is produced | generated. Further, when the temperature T does not exceed the allowable temperature, or when the target drive current value does not exceed the current limit value Ion, the PWM signal is based on the target drive current value obtained by the target drive current calculation unit 62. Is generated.

  Thus, for a predetermined time after the IG switch 15 is turned on, the motor current is limited by the current limit value Ion set to be equal to or greater than the current limit value Ioff based on the calculated temperature difference Ta. As a result, the motor current is not limited more than before the IG switch 15 is turned off, and the unnecessary motor current can be limited to prevent the steering force from becoming insufficient.

  If the predetermined time has elapsed (S22: YES), the assist control unit 6 moves the process to S24. On the other hand, when the current limit value Ioff is close to the upper limit value in S11 (S11: YES), the assist control unit 6 hardly limits the motor current before the IG switch 15 is turned off. The current limit value after the determination and the IG switch 15 is turned on is set to the upper limit value (S23). Thereafter, the assist control unit 6 moves the process to S24.

  In S24, the assist control unit 6 performs an overheat control process (S24). In the overheat control process here, the assist control unit 6 responds to the current limit value set to the upper limit value in S23 or the steering history when the temperature T detected by the temperature detection unit 64 exceeds the allowable temperature. Based on the set current limit value, control for limiting the motor current is performed, and overheating of the assist control unit 6 or the motor 5 is prevented.

  Next, the assist control unit 6 determines whether or not the IG switch 15 is turned off (S25). When the IG switch 15 is not turned off (S25: NO), the overheat control process of S24 is repeated. On the other hand, when the IG switch 15 is turned off (S25: YES), the assist control unit 6 stores the current limit value used in the overheat control process of S24 and the temperature T detected by the temperature detection unit 64 in the storage unit 67. Store (S26) and end the operation process of FIG. Note that, until the current limit value and the temperature are 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 and temperature stored in S26 are read when the IG switch 15 is turned on, and are applied to the calculation of the temperature difference Ta and the setting of the current limit value Ion as described above.

  As described above, in the present embodiment, the temperature difference between the assist control unit 6 before the IG switch 15 is turned off and after the IG switch 15 is turned on is calculated, and the current limit value is determined according to the calculated temperature difference. Ion is set to be equal to or greater than the current limit value Ioff before turning off. Thereby, it is possible to prevent the steering feeling of the steering member from deteriorating by suppressing unnecessary current limitation.

  In the present embodiment, the assist control unit 6 has the temperature detection unit 64 and determines the temperature correction value based on the temperature in the assist control unit 6, but the motor drive unit 7 or the motor 5, etc. The temperature of the part that generates heat due to the driving of the motor 5 may be detected, and the temperature correction value may be determined 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. Further, each time the temperature detected by the temperature detection unit 64 changes, the temperature may be stored in the storage unit 67. In this case, at the same time as the IG switch 15 is turned off, the power to the assist control unit 6 can be cut off, and a relay is provided to provide a time difference for storing the current limit value or temperature after the IG switch 15 is turned off. There is no need to do it.

  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 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

Claims (3)

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 limit value to be changed according to the temperature of the specific part when the temperature exceeds an allowable temperature,
Temperature storage means for storing the temperature of the specific part detected by the detection means when the engine is stopped;
Limit value storage means for storing the limit value when the engine is stopped as a limit value before stop;
A calculation means for calculating a temperature difference between the temperature of the specific part detected by the detection means when the starter switch for starting the engine is turned on and the temperature stored in the temperature storage means;
A setting for setting the limit value to be equal to or greater than the limit value before stop stored in the limit value storage unit according to the temperature difference calculated by the calculation unit for a predetermined time after the starter switch is turned on. And an electric power steering device. The setting means includes
A first setting means for setting the limit value to a limit value before stop stored in the limit value storage means when the temperature difference calculated by the calculation means is less than T1;
When the temperature difference calculated by the calculating means is not less than T1 and less than T2 (T2> T1), the limit value is a value obtained by adding a predetermined value to the limit value before stop stored in the limit value storage means Second setting means for setting to
The electric power steering apparatus according to claim 1, further comprising third setting means for setting the limit value to an upper limit value when a temperature difference calculated by the calculation means is equal to or greater than T2. An outside air temperature detecting means for detecting the outside air temperature;
The electric power steering apparatus according to claim 2, further comprising: a determining unit that determines the T1 and / or the T2 based on an outside air temperature detected by the outside air temperature detecting unit.

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