JP2004032997A - Motor drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a miniaturization and cost reduction of a switching device for a drive control circuit without sacrificing a drive responsiveness when starting or braking a DC motor. <P>SOLUTION: When starting the DC motor, an energization is carried out at 100 % duty ratio without limiting an energized current of the DC motor. At this moment, a time during which an energized current of the DC motor continues to exceed a current limit value Vref is counted with a timer. When the time reaches a preset time t38 (a little longer than the energizing time for starting under normal conditions), a current limiting operation is commenced which limits the current with the preset current limit value Vref. In this case, during normal operation, an energization for starting will be finished before the counted time of the timer reaches the time t38 and the current limiting operation will not be performed. For this reason, the energized current can be limited to a lower current value by the current limiting operation, thereby protecting the switching device, when a motor locking occurs, without sacrificing the responsiveness of the DC moor. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a motor drive device having a function of limiting a current flowing to a DC motor.

For example, some electronic throttle systems for automobiles use a DC motor as a drive source for a throttle valve. In this system, in order to increase the responsiveness of the throttle valve, when the motor is started, a current is supplied to the DC motor at a duty of 100% to increase the operating speed of the throttle valve. In the reverse direction to brake the DC motor so that the throttle valve is quickly stopped at the target throttle opening. Furthermore, in this system, when the DC motor is locked due to foreign matter being caught in the throttle valve or the like, a large current continues to flow in the DC motor, so that the state in which the throttle valve does not approach the target throttle opening continues for a predetermined time. In some cases, when the motor is locked, the DC motor is deenergized to protect the switching element of the drive control circuit.

For example, in a temporary slight lock state due to freezing of moisture adhering to the throttle valve, if the drive is continued for a while, the lock state may be recovered and normal drive may be possible. Therefore, if the time until the DC motor is turned off and the DC motor is deenergized (lock determination time) is too short when the motor is started or braked, the motor drive will stop immediately even in the temporary slight lock state. There is a problem that it is done. Therefore, it is preferable to set the lock determination time to some extent long. However, as the lock determination time becomes longer, the time during which a large current flows through the switching element of the drive control circuit becomes longer. Or a switching element having a small on-resistance (heat generation) and a large chip size needs to be used, which has a disadvantage of increasing the manufacturing cost of the drive control circuit.

In view of this, there is a configuration in which the switching element of the drive control circuit can be reduced in size and cost by limiting the current supplied to the DC motor to a certain value or less (for example, see Patent Document 1). However, in this case, the current is limited even at the time of starting the motor or braking which requires a relatively large torque, so that the driving torque and the braking force are insufficient, and the driving response of the throttle valve is deteriorated. There is a disadvantage that.
Japanese Patent Publication No. Hei 9-501817

The present invention has been made in view of such circumstances, and therefore has as its object to reduce the size and cost of the switching element of the drive control circuit without sacrificing the drive response at the time of starting or braking the motor. It is another object of the present invention to provide a motor drive device capable of supplying a current to a DC motor for a certain long time in expectation of a normal state when the motor is locked.

By the way, in a normal operating state where no motor lock occurs, the time required for starting and braking the motor is short. Even if power flows, the power loss (heat generation) of the switching element in the drive control unit is small, and a large rated element that can drive a large current for a long time and a large chip size element with low on-resistance are required as the switching element. And not.

Focusing on this point, according to the motor drive device of the first aspect of the present invention, during the period corresponding to the start, the start is performed by limiting the current flowing to the DC motor at a high predetermined current value [Vref (H)]. Alternatively, the current flowing to the DC motor after the elapse of the period may be limited to a predetermined current value [Vref (L)] lower than the high predetermined current value. In this case, at the time of startup, the current is limited from the beginning, but the current limit value is initially set to a high current value [Vref (H)], and then switched to a low current value [Vref (L)] to control the drive. Protect the switching elements of the unit. Therefore, the initial current limit value [Vref (H)] can be set to a high current value that does not impair the start-up performance, and the switching element can be reduced in size and cost while improving the start-up performance. it can.

Further, as in claim 2, during the period corresponding to the braking, the braking is performed by limiting the current flowing to the DC motor at a high predetermined current value [Vref (H)], and after the lapse of the period, the current flowing to the DC motor is reduced. The current value may be limited to a predetermined current value [Vref (L)] lower than the high predetermined current value. In this manner, the motor torque during braking can be increased, and the braking performance can be improved, as in the case of the start of claim 1. Is limited to a low predetermined current value [Vref (L)], so that heat generation of the switching element due to braking can be reduced.

The DC motor may be connected to an H-bridge drive circuit. With this configuration, the current flowing through the DC motor can be flowed in both the forward direction and the reverse direction, and both the activation and the braking of the DC motor can be performed.

(4) It is preferable that a current detecting means for detecting a current flowing through the DC motor be provided. By doing so, it is possible to limit the current while detecting the actual current flowing through the DC motor.

Further, the determining means determines whether or not the state limited to the low predetermined current value has continued for a predetermined time or more, and if it is determined that the state has been continued for a predetermined time or more, the DC motor It is preferable to shut off the power supply to the power supply. With this configuration, it is possible to prevent the DC motor from being continuously energized while the DC motor is in the locked state.

Further, the present invention is applied to an electronic throttle system, wherein a DC motor is connected to a throttle valve of a vehicle engine, and an accelerator signal from an accelerator sensor connected to an accelerator pedal of the vehicle and a throttle valve are applied. The throttle valve control means may control the throttle valve to a desired opening based on the throttle signal from the connected throttle opening sensor. In this way, it is possible to improve the drive response of the electronic throttle system and reduce the cost of the drive control unit of the DC motor.

In this case, the state in which the difference between the desired throttle valve opening and the actual throttle valve opening based on the throttle signal is equal to or greater than the predetermined value continues for at least the predetermined time set longer than the period. In such a case, it is preferable to cut off the power supply to the DC motor. With this configuration, it is possible to prevent the DC motor from being continuously energized while the electronic throttle is locked.

Further, as in claim 8, a drive control unit for driving the throttle valve to a desired throttle valve opening by driving the DC motor is provided, and the drive control unit supplies a current to the DC motor in a stopped state to drive the throttle valve. When the desired throttle valve opening changes while the throttle valve is kept at a constant opening, current is supplied to the DC motor so that the actual throttle valve opening approaches the desired throttle valve opening. When the DC motor is started, the drive control unit starts the DC motor by limiting the current flowing to the DC motor at a high predetermined current value [Vref (H)] during a period corresponding to the start, and after starting the period, flows the current to the DC motor. The current may be limited to a predetermined current value [Vref (L)] lower than a high predetermined current value.

Further, as claimed in claim 9, a drive control unit for driving the throttle valve to a desired throttle valve opening by driving a DC motor is provided, and the drive control unit determines that the actual throttle valve opening is the desired throttle valve opening. When approaching a predetermined range preset for the throttle valve opening, a current is supplied to the DC motor to apply a brake to the throttle valve. Braking is performed by restricting the current flowing at a high predetermined current value [Vref (H)], and after that period, the current flowing to the DC motor is limited to a predetermined current value [Vref (L)] lower than the high predetermined current value. It may be configured as follows.

[Example 1]

Hereinafter, an embodiment (1) in which the present invention is applied to an electronic throttle system will be described with reference to FIGS. First, a schematic configuration of the entire system will be described with reference to FIG. A throttle valve 12 provided in the middle of an intake pipe 11 of the engine is driven by a DC motor 13. The throttle valve 12 is urged in a closing direction by a return spring (not shown), and is forcibly returned to a substantially closed position where the throttle valve 12 can be idle when a failure occurs. Therefore, the DC motor 13 needs a torque that can drive the throttle valve 12 in the opening direction against the return spring. Therefore, when starting from a stopped state or braking in an operating state, the DC motor 13 is energized. It is necessary to secure the torque by increasing the current. The opening of the throttle valve 12 is detected by a throttle opening sensor 14, and the detection signal is taken into an engine control circuit 15. The engine control circuit 15 functions as a throttle valve control unit that controls the ignition timing and the fuel injection amount and also controls the opening of the throttle valve 12.

On the other hand, the depression amount of the accelerator pedal 16 is detected by the accelerator sensor 17, and the detection signal is taken into the engine control circuit 15. The engine control circuit 15 outputs to the drive control circuit 18 drive command signals A1 to A4 corresponding to the accelerator depression amount taken from the accelerator sensor 17, and the drive control circuit 18 drives the DC motor 13 to thereby control the throttle valve. 12 is driven to a target throttle opening set according to the accelerator depression amount. It should be noted that the drive control circuit 18 and the engine control circuit 15 (throttle valve control means) constitute a drive control section referred to in the claims.

The drive control circuit 18 includes a drive logic circuit 19 to which the four drive command signals A1 to A4 are input from the engine control circuit 15, an H-bridge type drive circuit 20 for driving the DC motor 13, and a current flowing through the DC motor 13. And a current detecting circuit 21 for detecting the current. The drive control circuit 18 starts and brakes the current flowing through the DC motor 13 without limiting the current flowing through the DC motor 13 during a predetermined period corresponding to starting and braking, and starts and brakes the current flowing through the DC motor 13 after the elapse of the period. Is limited so as not to exceed a current limit value smaller than the current flowing at the time. Therefore, if the motor lock occurs, the current flowing through the DC motor 13 is limited by the current limit value. If the motor lock is released during this current limiting operation, the current limit is released. However, if the opening of the throttle valve 12 does not approach the target throttle opening even after the predetermined period has elapsed, the engine is stopped. The control circuit 15 determines that the motor is locked, sets all the drive command signals A1 to A4 to low level, and cuts off the power supply to the DC motor 13.

Next, a detailed configuration of the drive control circuit 18 will be described with reference to FIG. The drive circuit 20 is configured by connecting four switching elements, for example, MOSFETs 22 to 25 in an H-bridge type, and has a direct current between an intermediate connection point between the right MOSFETs 22 and 25 and an intermediate connection point between the left MOSFETs 23 and 24. The positive terminal and negative terminal of the motor 13 are connected. The high side of the drive circuit 20 is connected to the + terminal side of a power supply 26 such as a battery, and the low side of the drive circuit 20 is connected to a current detection circuit 21 (current detection means). The current detection circuit 21 includes a current detection resistor 27 connected between the low side and the ground side of the drive circuit 20, and a differential amplifier circuit 28 that amplifies a potential difference between both ends of the current detection resistor 27. .

Next, a detailed configuration of the drive logic circuit 19 will be described. The output of the current detection circuit 21 (the voltage corresponding to the current flowing through the DC motor 13) is input to the + input terminal of the comparator 30, and is compared with the reference voltage Vref # input to the-input terminal. This reference voltage Vref # is set to a voltage corresponding to a current limit value at the time of the current limit operation. The current limit value is set to a low current limit value such that MOSFETs 22 to 25 are not damaged even if current is continuously supplied to some extent at the time of motor lock. (That is, a current limit value lower than the current generated by starting or braking). Each time the current flowing through the DC motor 13 exceeds the current limit value, the output of the comparator 30 is inverted to a high level, and this high level signal is input to the set terminals S of the two set priority type RS latches 31 and 32. . The outputs of the timers 33 and 34 are input to the reset terminals R of the RS latches 31 and 32, respectively.

On the other hand, when a high-level signal indicating that the current flowing through the DC motor 13 exceeds the current limit value is input to the set terminal S from the comparator 30 to the set terminal S, the RS latch 31 performs a set operation and outputs the AND gate 39 from the output terminal Q. And a high-level signal to both the timer 33 and the timer 33. The timer 33 is a timer for setting a time during which the energization of the DC motor 13 is temporarily turned off every time the energization current of the DC motor 13 exceeds the current limit value during the current limiting operation. When a high level signal is input to the timer 33, the counting operation of the internal counter is started. When the counting of a preset time is completed, a high level signal is output from the output terminal Q to the reset terminal R of the RS latch 31. . As a result, the RS latch 31 performs a reset operation and outputs a low-level signal from the output terminal Q to both the AND gate 39 and the timer 33. When the low level signal is input, the timer 33 resets the internal counter and inverts the output of its own output terminal Q to a low level.

As described above, by forming a closed loop by the RS latch 31 and the timer 33, the output terminal Q of the RS latch 31 is connected to the DC motor 13 whenever the current flowing through the DC motor 13 exceeds the current limit value during the current limiting operation. A high-level signal is output only for the time when the power is temporarily turned off (see FIG. 4).

The output of the output terminal Q of the timer 34 is input to the reset terminal R of the other RS latch 32. The timer 34 receives the output of its own output terminal Q at an input terminal T via a delay circuit 35 and an inverter 36. Thus, when the output of the output terminal Q of the timer 34 is inverted to the low level, the output of the delay circuit 35 is inverted to the low level with a delay of a certain time, and at the same time, the output from the inverter 36 is input to the input terminal T of the timer 34. A high level signal is input. Accordingly, the timer 34 outputs a high-level signal from the output terminal Q when the internal counter starts counting and the counting of the preset time t34 ends. The high-level signal is input to the inverter 36 with a delay of a predetermined time by the delay circuit 35, and the low-level signal is input from the inverter 36 to the input terminal T of the timer 34. As a result, the timer 34 resets the internal counter and inverts the output of the output terminal Q to low level. As described above, by forming a closed loop by the timer 34, the delay circuit 35, and the inverter 36, the output terminal Q of the timer 34 becomes high level by the delay time of the delay circuit 35 every fixed time t34 set in the timer 34. A signal is output (see FIG. 3).

The output of the output terminal Q of the timer 34 is input to the reset terminal R of the RS latch 32 and the clock input terminal CK of the D flip-flop (DFF) 37. The output terminal Q of the RS latch 32 is connected to the data input terminal D of the D flip-flop 37.

When a high-level signal indicating that the current flowing through the DC motor 13 has exceeded the current limit value is input to the set terminal S from the comparator 30 to the set terminal S, the RS latch 32 performs a set operation to output the D flip-flop 37 from the output terminal Q. A high level signal is output to the data input terminal D. Further, the RS latch 32 performs a reset operation on the reset terminal R in response to a high-level signal for each fixed time t34 input from the timer 34, and outputs a low-level signal from the output terminal Q to the data input terminal D of the D flip-flop 37. I do.

On the other hand, when the output level of the timer 34 input to the clock input terminal CK rises from the low level to the high level, the D flip-flop 37 outputs the output level of the output terminal Q of the RS latch 32 input to the data input terminal D. And outputs a signal level corresponding to the stored level from the output terminal Q of the D flip-flop 37 to the input terminal T of the timer 38.

As described above, the operation of the RS latch 32 and the D flip-flop 37 causes the output of the D flip-flop 37 when the current flowing through the DC motor 13 exceeds the current limit value within the time t34 set in the timer 34. A high-level signal is output from the terminal Q to the input terminal T of the timer 38.

In this case, the time t34 set in the timer 34 is a time for temporarily turning off the energization of the DC motor 13 when the energizing current of the DC motor 13 exceeds the current limit value during the current limiting operation, and resuming energization after the temporarily energizing off. The time is set to be longer than the sum of the time until the current limit value is exceeded again. As a result, the output of the output terminal Q of the D flip-flop 37 is maintained at the high level during the current limiting operation.

On the other hand, when the timer 38 receives a high-level signal from the output terminal Q of the D flip-flop 37 indicating that the current flowing through the DC motor 13 continues to exceed the current limit value, the internal counter starts counting. Then, the times t1a and t2a (see FIG. 3) in which the supplied current continues to exceed the current limit value are counted. Thereafter, when the timer 38 finishes counting for a preset time t38 (see FIG. 4), the output terminal Q outputs a high-level signal (current limit operation start signal) to one input terminal of the AND gate 39. When a low-level signal indicating that the current flowing through the DC motor 13 is equal to or less than the current limit value is input from the output terminal Q of the D flip-flop 37, the timer 38 resets the internal counter and sets the output terminal. From Q, a low level signal is output to one input terminal of the AND gate 39.

In this case, the time t38 set in the timer 38 determines the time at which the current limiting operation is started when the time for energizing the start of the DC motor 13 or the time for braking is increased. The time is set to be slightly longer than the time for energization and braking. As a result, as shown in FIG. 3, in the activation energization and braking during normal operation, the actual throttle opening approaches the target throttle opening before the count times t1a and t2a of the internal counter of the timer 38 reach the time t38. Since the startup energization and the braking are completed, the current limiting operation does not work, and the startup and the brake are performed in a state where the energization current of the DC motor 13 is not limited, and the drive responsiveness at the time of the startup and the braking is enhanced.

The output of the AND gate 39 is high only when both the output of the timer 38 and the output of the RS latch 31 input to both terminals are high. As a result, the output of the AND gate 39 is maintained at the low level during normal operation (see FIG. 3), and during the current limiting operation, the energizing of the DC motor 13 is temporarily stopped every time the energizing current of the DC motor 13 exceeds the current limit value. The output of the AND gate 39 is inverted to the high level only during the time when it is turned off (see FIG. 4).

The output of the AND gate 39 is input to the OR gates 40 and 41 and also to the AND gates 43 and 44 via the inverter 42. Drive command signals A1 to A4 output from the engine control circuit 15 are input to the OR gates 40 and 41 and the AND gates 43 and 44, respectively. The outputs of the OR gates 40 and 41 are applied to the gates of the high-side MOSFETs 22 and 23 via the protection control circuit 45 and the pre-drivers 46 and 47. Thus, the high-side MOSFETs 22 and 23 are turned on when the high-side drive command signals A1 and A2 are at the high level, and when the output of the AND gate 39 is at the high level (the current supply is temporarily turned off during the current limiting operation). Also during the current limit operation, the high-side MOSFETs 22 and 23 are turned on, and the energy remaining in the coil of the DC motor 13 is circulated through the circulation path 50 while the power is turned off during the current limiting operation.

On the other hand, the outputs of the AND gates 43 and 44 are applied to the gates of the low-side MOSFETs 24 and 25 via the protection control circuit 45 and the pre-drivers 48 and 49. Accordingly, the low-side MOSFETs 24 and 25 are turned on when the low-side drive command signals A3 and A4 are at the high level and the output of the inverter 42 is at the high level. During normal operation, as shown in FIG. 3, the output of the AND gate 39 is maintained at a low level, so that the output of the inverter 42 is maintained at a high level. As a result, during normal operation, the low-side drive command signals A3 and A4 pass through the AND gates 43 and 44 as they are, and when the low-side drive command signals A3 and A4 are at a high level, the low-side MOSFETs 24 and 25 are turned on, and The motor 13 is energized.

Further, in the current limiting operation, as shown in FIG. 4, the output of the AND gate 39 is set to the high level for the time for temporarily turning off the energization of the DC motor 13 every time the energization current of the DC motor 13 exceeds the current limit value. Because of the inversion, the output of the inverter 42 is inverted to a low level for a time period during which the energization of the DC motor 13 is temporarily turned off every time the energization current of the DC motor 13 exceeds the current limit value. As a result, even if the low-side drive command signal A3 (or A4) is at a high level, the output of the AND gate 43 (or 44) is temporarily low whenever the current flowing through the DC motor 13 exceeds the current limit value. Level. Thereby, at the time of the current limiting operation, the low-side MOSFET 24 (or 25) is temporarily turned off each time the current flowing through the DC motor 13 exceeds the current limit value, and the current flowing through the DC motor 13 is suppressed to the current limit value or less. Can be

The protection control circuit 45 prevents a so-called through current in which the high-side and low-side MOSFETs 22 to 25 connected to both terminals of the DC motor 13 are simultaneously turned on and an overcurrent flows, or Logic such as overcurrent protection control for forcibly turning off the MOSFETs 22 to 25 when the current flows is included.

Next, the normal operation will be described with reference to FIG. During a period t0 when the throttle 12 is stopped and the throttle opening does not change, the engine control circuit 15 maintains the drive command signal A1 at a high level in order to maintain the throttle valve 12 at a constant opening against the return spring. At the same time, by switching the drive command signal A3 between a high level and a low level at a predetermined duty ratio, the low-side left MOSFET 24 is turned on / off at a predetermined duty ratio while the high-side right side MOSFET 22 is maintained in an on state. Then, a current is caused to flow through the DC motor 13 in the direction of arrow B (positive direction) in FIG. 2 at a predetermined duty ratio to maintain the throttle valve 12 at a constant opening.

During the holding energization period t0, the drive command signal A2 is switched to the high level only during the low level period each time the drive command signal A3 is at the low level. By turning on the MOSFET 23 on the left side, the energy remaining in the coil of the DC motor 13 is circulated through the circulation path 50.

Thereafter, when the accelerator pedal 16 is depressed to change the target throttle opening, the engine control circuit 15 starts the DC motor 13 at a 100% duty ratio as follows, and changes the actual throttle opening to the target throttle opening. Start energization that approaches During the activation energizing period t1, the drive command signals A1 and A3 are held at a high level, thereby holding both the high-side right side MOSFET 22 and the low-side left side MOSFET 24 in the on state, and directing the DC motor 13 to the arrow B in FIG. A current is caused to flow in the direction (positive direction) at a duty ratio of 100%, the starting torque is increased, and the operating speed of the throttle valve 12 is increased. Therefore, the current limiting operation does not work during the startup energizing period t1 during normal operation. This is because the count time t1a at startup (time during which the supplied current exceeds the current limit value) by the internal counter of the timer 38 does not reach the time t38 at which the current limiting operation is started.

When the engine control circuit 15 detects that the actual throttle opening approaches a predetermined range set in advance to the target throttle opening during the startup energization period t1, the engine energization period t1 ends, and the engine is turned on. The brake is energized to apply a brake to the throttle valve 12 and stop at the target throttle opening. During the braking period t2, both the MOSFET 23 on the high side left side and the MOSFET 25 on the low side right side are kept in the ON state, and a current is passed through the DC motor 13 in the direction of arrow C in FIG. The braking force is increased to quickly stop the throttle valve 12 at the target throttle opening. Therefore, the current limiting operation does not work during the brake period t2 during normal operation. This is because the count time t2a during braking by the internal counter of the timer 38 (the time when the supplied current exceeds the current limit value) does not reach the time t38 when the current limiting operation is started. After the throttle valve 12 stops at the target throttle opening (period t3), the same holding energization control as before the activation of the DC motor 13 (period t0) is performed.

Next, the operation at the time of motor lock will be described with reference to FIG. FIG. 4 shows an operation example when the motor lock occurs at the timing tx immediately after the start energization with the 100% duty ratio is started. When the motor lock occurs, even if the startup energization with the 100% duty ratio is continued, the startup energization is continued for a while because the throttle valve 12 does not approach the target throttle opening. Thus, when the count time t1a at startup (time during which the supplied current exceeds the current limit value) by the internal counter of the timer 38 reaches the time t38 at which the current limit operation starts, the current limit operation starts as follows. Is done.

(4) When the count time t1a at startup by the internal counter of the timer 38 reaches the time t38 at which the current limiting operation is started, the output of the timer 38 is inverted to a high level. The AND gate 39, to which the output of the timer 38 and the output of the RS latch 31 are input, is connected to the output of the RS latch 31 during a high level period (that is, every time the energizing current of the DC motor 13 exceeds the current limit value). It is inverted to the high level only for the time when the power is temporarily turned off. Thus, each time the AND gate 39 is inverted to a high level, the high level signal is inverted to a low level signal by the inverter 42 and input to the AND gate 43. For this reason, even if the low-side drive command signal A3 is at a high level, the output of the AND gate 43 temporarily goes to a low level every time the current flowing through the DC motor 13 exceeds the current limit value. Thereby, at the time of the current limiting operation, the low-side MOSFET 24 is temporarily turned off each time the current flowing through the DC motor 13 exceeds the current limit value, and the current flowing through the DC motor 13 is suppressed to the current limit value or less.

During the current limiting operation, the output of the OR gate 41 is inverted to the high level during the off-period of the low-side MOSFET 24 (the high-level period of the AND gate 39) to turn on the MOSFET 23 on the left side of the high-side. The energy remaining in the coil is circulated through the circulation path 50.

(4) During this current limit operation period, when it is detected that the motor lock is released and the throttle valve 12 approaches a predetermined range set in advance to the target throttle opening, the operation shifts to energization of the brake. When the application of the brake is started, as shown in FIG. 3, the current supplied to the DC motor 13 temporarily drops below the current limit value, so that the output of the D flip-flop 37 is inverted to low level, Is reset, and the output of the timer 38 is inverted to a low level. As a result, the current limiting operation is released, and a current flows through the DC motor 13 in the direction of arrow C (reverse direction) of FIG. 2 at a duty ratio of 100%, and the movement of the throttle valve 12 is braked.

On the other hand, if the opening of the throttle valve 12 does not approach the target throttle opening even if the current limiting operation is continued to some extent, the energization of the DC motor 13 is cut off by the engine control circuit 15 as follows. You. The engine control circuit 15 counts the time during which the state in which the difference between the actual throttle opening and the target throttle opening is equal to or more than a predetermined value at the time of startup, and determines that the motor is locked when the time reaches a predetermined time t4. Then, all the drive command signals A1 to A4 are set to low level, and the energization to the DC motor 13 is cut off.

Alternatively, the engine control circuit 15 inputs a current limit operation monitor signal indicating that the current limit operation period is being output from the timer 38 indicated by a broken line in FIG. The time when the high level state continues is counted, and when the time reaches a predetermined time t5, all the drive command signals A1 to A4 are set to the low level, and the energization to the DC motor 13 is cut off. You may do it. Although the operation example of FIG. 4 is an example when the motor lock occurs during the energization of the start, the control is similarly performed when the motor lock occurs during the braking.

In the embodiment (1) described above, during the start energization period (brake energization period) set to a time slightly longer than the start energization and the brake time during the normal operation of the DC motor 13, the energization current of the DC motor 13 is set. (Braking) is performed without limiting the starting torque, so that the starting torque (braking force) can be increased as compared with the case where the current is limited from the start (start of braking), and the drive response of the throttle valve 12 is improved. Can be.

Moreover, if the state in which the energizing current of the DC motor 13 is larger than the current limit value for the preset energizing period (brake energizing period) continues for a preset time t38, it is determined that there is a possibility of motor lock. Since the energizing current is limited to a low current value, the current flowing through the MOSFETs 22 to 25 can be limited to a low current value, and the heat generated by the MOSFETs 22 to 25 can be reduced. As a result, even when the motor is locked, it is possible to allow the electric current to flow through the DC motor 13 for a relatively long period of time. In the case of the temporary slight lock state, the drive torque can be continuously applied for a while to recover the normal state. . In addition, since the heat generated by the MOSFETs 22 to 25 is small, the size and cost of the MOSFETs 22 to 25 can be reduced. This makes it possible to satisfy the demand for cost reduction of the drive circuit 20 without sacrificing the drive response of the throttle valve 12.
[Example 2]

Next, an embodiment (2) applied to a system having a sufficient torque of the DC motor 13 will be described with reference to FIGS. In the embodiment (1), the current is not limited during the start energizing period (brake energizing period). However, in the embodiment (2), the current flowing through the DC motor 13 is set during the start energizing period (brake energizing period). When starting (braking) is performed by limiting the starting current (braking performance) at a high current value that does not impair the starting performance (braking performance), and there is a possibility of motor lock, the limit value of the current flowing to the DC motor 13 after the lapse of the period. Is switched to a lower current limit value. Hereinafter, portions different from the embodiment (1) will be described.

In the embodiment (1), the reference voltage Vrefｒｅ (the voltage corresponding to the current limit value) input to the negative input terminal of the comparator 30 is a fixed value. In the present embodiment (2), the negative input terminal of the comparator 30 is different. Is provided with a reference voltage switching circuit 51 for switching the reference voltage Vref # input to the two stages of a voltage Vref (H) corresponding to a high current limit value and a voltage Vref (L) corresponding to a low current limit value. The reference voltage switching circuit 51 has three resistors 52 to 54 connected in series between a power supply voltage Vcc side and a ground side, and has a reference voltage switching terminal connected to both ends of one of the resistors 54 on the ground side. The collector and the emitter of the transistor 55 are connected, and the intermediate connection point between the resistors 52 and 53 is connected to the negative input terminal of the comparator 30.

In the embodiment (1), the output of the timer 38 and the output of the RS latch 31 are input to the AND gate 39. However, in the embodiment (2), the output of the RS latch 31 is eliminated without the AND gate 39. Is input directly to the OR gates 40 and 41, and the output of the RS latch 31 is also input to the AND gates 43 and 44 via the inverter 42. The output terminal Q of the timer 38 is connected to the base of the reference voltage switching transistor 55, and the reference voltage Vref # (current limit value) is switched by the output of the timer 38. Other configurations are the same as those in the embodiment (1).

Next, the normal operation will be described with reference to FIG. Normally, the output of the timer 38 is maintained at a low level, so that the reference voltage switching transistor 55 is maintained in an off state. In this state, reference voltage Vref # input from reference voltage switching circuit 51 to comparator 30 is maintained at voltage Vref (H) corresponding to the high current limit value. Here, assuming that the resistance values of the three resistors 52 to 54 of the reference voltage switching circuit 51 are R52 to R54, Vref (H) is calculated by the following equation. Vref (H) = Vcc × (R53 + R54) / (R52 + R53 + R54) The high reference voltage Vref (H) is set so that the current limit value becomes a high current value that does not impair the starting performance (braking performance). .

When the accelerator pedal 16 is depressed and the target throttle opening changes, the energization of the start is performed, the actual throttle opening is brought close to the target throttle opening, and then the brake energization is performed, as in the first embodiment. Then, the throttle valve 12 is stopped at the target throttle opening. At the start of the start-up energization, a current flows through the DC motor 13 at a duty ratio of 100%. During this start-up energization period t1, the energization current of the DC motor 13 is set to a high current limit set by a high reference voltage Vref (H). Each time the value exceeds the value, the output of the RS latch 31 becomes high level for the time set by the timer 33, and this high level signal is inverted to a low level signal by the inverter 42 and input to the AND gate 43. For this reason, even when the low-side drive command signal A3 is at a high level, the output of the AND gate 43 is temporarily at a low level every time the current flowing through the DC motor 13 exceeds a high current limit value. As a result, the low-side MOSFET 24 is temporarily turned off each time the energizing current of the DC motor 13 exceeds the high current limit value, and the energizing current of the DC motor 13 is suppressed below the high current limit value.

During this current limiting operation, the output of the OR gate 41 is inverted to the high level during the off-period of the low-side MOSFET 24 (the high-level period of the RS latch 31) to turn on the MOSFET 23 on the left side of the high-side. The energy remaining in the coil is circulated through the circulation path 50.

(4) When it is detected that the throttle valve 12 is approaching the target throttle opening within a predetermined range set in advance by such activation, the activation energization period t1 is ended and the brake is energized. At the start of braking, a current flows through the DC motor 13 in the reverse direction at a duty ratio of 100%. During the brake energizing period t2, the energizing current of the DC motor 13 is set to a high current set at a high reference voltage Vref (H). Each time the limit value is exceeded, the output of the RS latch 31 goes high for the time set by the timer 33, and, similarly to the start energization described above, the output current of the DC motor 13 temporarily exceeds the high current limit value. And the energizing current of the DC motor 13 is suppressed to a high current limit value or less.

As in the first embodiment, after the throttle valve 12 stops at the target throttle opening (period t3), the same holding energization control as before the DC motor 13 is started (period t0) is performed.

Next, the operation at the time of motor lock will be described with reference to FIG. FIG. 7 shows an operation example when a motor lock occurs at a time tx immediately after the start energization is started. In this case, even if the startup energization is performed with a high current limit value, the startup energization is continued for a while because the throttle valve 12 does not approach the target throttle opening. Thus, when the count time t1a at startup (time during which the supplied current exceeds the high current limit value) by the internal counter of the timer 38 reaches the time t38, the current limit value is reduced as follows.

When the count-up time t1a by the internal counter of the timer 38 reaches the time t38, the timer 38 outputs a high-level signal to the base of the reference voltage switching transistor 55. Thereby, transistor 55 is turned on, both ends of one resistor 54 of reference voltage switching circuit 51 are short-circuited, and reference voltage Vref # input from reference voltage switching circuit 51 to comparator 30 corresponds to a low current limit value. The voltage is switched to the voltage Vref (L). This low reference voltage Vref (L) is calculated by the following equation.

Vref (L) = Vcc × R53 / (R52 + R53) The low current limit value set by the low reference voltage Vref (L) is such a low current that the MOSFETs 22 to 25 are not damaged even if the energization is continued to some extent during motor lock. It is set to be a value.

In this manner, when the reference voltage Vref # input to the comparator 30 is switched to the voltage Vref (L) corresponding to the low current limit value, every time the energizing current of the DC motor 13 exceeds the low current limit value, RS The output of the latch 31 becomes high level for the time set by the timer 33, and this high level signal is inverted to a low level signal by the inverter 42 and input to the AND gate 43. As a result, the low-side MOSFET 24 is temporarily turned off each time the energizing current of the DC motor 13 exceeds the low current limit value, and the energizing current of the DC motor 13 is suppressed below the low current limit value. At this time, while the low-side MOSFET 24 is off, the high-side left MOSFET 23 is turned on, and the energy remaining in the coil of the DC motor 13 is circulated through the circulation path 50.

If the opening of the throttle valve 12 does not approach the target throttle opening even if the current limiting operation using such a low current limiting value is continued to some extent, the DC motor 13 is operated in the same manner as in the above embodiment (1). Cut off the power supply to. Note that the operation example in FIG. 7 is an example in which the motor lock occurs during the energization of the start. However, the same control is performed when the motor lock occurs during the braking. In the embodiment (2) described above, the same effect as in the embodiment (1) can be obtained.

In the embodiments (1) and (2), the current limiting operation is controlled by the drive logic circuit 19 constituted by hardware. However, the current limiting operation is controlled by program control by a microcomputer. Is also good. Further, the current limit value may be reduced to two or more levels as time elapses during the current limit operation performed when there is a possibility of motor lock.

Further, in the above-described embodiments (1) and (2), even when the motor lock occurs during the brake energizing period, the current limiting operation is performed after the predetermined period elapses, similarly to the case where the motor lock occurs during the activation energizing period. Although the current limiting operation is performed, the current limiting operation may be performed only for one of the activation and the braking. Further, the H-bridge type driving circuit 20 may be configured by switching elements other than the MOSFETs 22 to 25.
In addition, the scope of application of the present invention is not limited to the electronic throttle system, and the present invention can be applied to various devices using a DC motor as a drive source.

FIG. 1 is a schematic configuration diagram of an entire system showing an embodiment (1) in which the present invention is applied to an electronic throttle system. Electric circuit diagram of the drive control circuit of the embodiment (1) FIG. 6 is a time chart showing signal waveforms of respective units during a normal operation of the embodiment (1). FIG. 6 is a time chart showing signal waveforms of various parts when the motor is locked according to the first embodiment. Electric circuit diagram of the drive control circuit of the embodiment (2) FIG. 6 is a time chart showing signal waveforms of respective units during a normal operation of the embodiment (2). FIG. 6 is a time chart showing signal waveforms of various parts when the motor is locked according to the embodiment (2).

Explanation of reference numerals

12 ... Throttle valve,
13 ... DC motor,
14. Throttle opening sensor
15. Engine control circuit (drive control unit, throttle valve control means)
16 ... accelerator pedal,
17 ... accelerator sensor,
18 ... drive control circuit (drive control unit)
19 ... Drive logic circuit,
20 ... Drive circuit,
21 ... current detection circuit (current detection means)
22-25 ... MOSFET (switching element),
30 ... Comparator,
33, 34 ... timer,
35 ... delay circuit,
38 ... Timer,
51: reference voltage switching circuit
52-54 ... resistance,
55 ... transistor.

Claims (9)

In a motor drive device including a drive control unit that starts a DC motor by flowing a current to a DC motor in a stopped state,
The drive control unit performs the startup by limiting the current flowing to the DC motor at a high predetermined current value [Vref (H)] during a period corresponding to the startup, and after the lapse of the period, reduces the current flowing to the DC motor to the high current. A motor driving device characterized in that the current is limited to a predetermined current value [Vref (L)] lower than the predetermined current value. In a motor drive device including a drive control unit that applies a current to a DC motor in an operating state to brake the DC motor,
The drive control unit performs braking by limiting the current flowing to the DC motor at a high predetermined current value [Vref (H)] during a period corresponding to the brake, and after the lapse of the period, reduces the current flowing to the DC motor to the high current. A motor driving device characterized in that the current is limited to a predetermined current value [Vref (L)] lower than the predetermined current value. The motor driving device according to claim 1 or 2,
The motor drive device, wherein the DC motor is connected to an H-bridge drive circuit. The motor drive device according to any one of claims 1 to 3,
A motor driving device, further comprising current detection means for detecting a current flowing through the DC motor. The motor drive device according to any one of claims 1 to 4,
A determining means for determining whether or not the state limited to the low predetermined current value [Vref (L)] has continued for a predetermined time or more; and when the determining means determines that the state has continued for a predetermined time or more. A motor driving device for shutting off the power supply to the DC motor. The motor drive device according to any one of claims 1 to 4,
The DC motor is connected to a throttle valve of a vehicle engine, and the drive control unit includes an accelerator signal from an accelerator sensor connected to an accelerator pedal of the vehicle and a throttle signal from a throttle opening sensor connected to the throttle valve. A motor drive device comprising: throttle valve control means for controlling a desired throttle valve opening based on a signal. The motor driving device according to claim 6,
When the state in which the difference between the desired throttle valve opening and the actual throttle valve opening based on the throttle signal is equal to or more than a predetermined value continues for a predetermined time longer than the period, the DC motor A motor drive device characterized in that the power supply to the motor is cut off. A drive control unit that drives the throttle valve to a desired throttle valve opening degree by driving a DC motor,
The drive control unit controls the actual throttle valve opening when a desired throttle valve opening changes in a state in which a current is supplied to the DC motor in a stopped state and the throttle valve is held at a constant opening. Start the DC motor by passing a current to the DC motor so as to approach the desired throttle valve opening,
During the period corresponding to the start, the drive control unit performs the start by limiting the current flowing to the DC motor at a high predetermined current value [Vref (H)], and after the lapse of the period, reduces the current flowing to the DC motor to the high current. A motor driving device characterized in that the current is limited to a predetermined current value [Vref (L)] lower than the predetermined current value. A drive control unit that drives the throttle valve to a desired throttle valve opening degree by driving a DC motor,
The drive control unit applies a current to the DC motor to apply a brake to the throttle valve when the actual throttle valve opening approaches a predetermined range preset with respect to the desired throttle valve opening. ,
The drive control unit performs braking by limiting the current flowing to the DC motor at a high predetermined current value [Vref (H)] during a period corresponding to the brake, and after the lapse of the period, reduces the current flowing to the DC motor to the high current. A motor driving device characterized in that the current is limited to a predetermined current value [Vref (L)] lower than the predetermined current value.

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