Motor control device

Abstract

To provide a technology that suppresses a vehicle from rolling backward at the start of driving.SOLUTION: A control device controls a motor for driving an electric vehicle. The control device includes an inverter that generates a drive current supplied to a coil of the motor, a control unit that controls operation of the inverter, and a detection unit that detects a magnitude of the drive current. In the control device, when the electric vehicle is started, the control unit controls the inverter such that the motor enters a short-brake state. The detection unit detects a peak current value generated in the inverter while short-brake control is being performed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This specification discloses a technique related to a motor control device. [Background technology]

[0002] Patent Document 1 discloses a control device for a motor that drives an electric vehicle. In Patent Document 1, in order to prevent the vehicle from rolling down an uphill road, rolling down is predicted while the vehicle is decelerating. If it is determined that rolling down will occur, the motor is controlled based on the prediction result to prevent rolling down when the vehicle starts moving. In other words, Patent Document 1 controls the motor feedforward based on the result of rolling down prediction during deceleration, and controls the motor torque to prevent rolling down. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-255808 Summary of the Invention [Problem to be solved by the invention]

[0004] The control device of Patent Document 1 can prevent the vehicle from rolling back when the vehicle is temporarily stopped during driving. However, when driving starts (when the vehicle is started), the control device system is also restarted, so feedforward control of the motor is not possible. Therefore, if the vehicle is parked on an uphill road, the control device of Patent Document 1 cannot prevent the vehicle from rolling back when driving starts. The purpose of this specification is to provide a technology that prevents the vehicle from rolling back when driving starts. [Means for solving the problem]

[0005] A first technology disclosed in this specification is a control device that controls a motor for driving an electric vehicle, and may include an inverter that generates a drive current to be supplied to a coil of the motor, a control unit that controls the operation of the inverter, and a detection unit that detects the magnitude of the drive current. In this control device, the control unit may control the inverter so that the motor is in a short brake state when the electric vehicle is started, and the detection unit may detect a peak current value generated in the inverter while short brake control is being performed.

[0006] The second technology disclosed in this specification is a control device of the first technology, wherein the control unit may determine the drive current to be supplied to the coil based on the peak current value when releasing the short brake control. [Effects of the Invention]

[0007] According to the first technique, even when the electric vehicle is parked on an uphill road, it is possible to prevent the electric vehicle from rolling back when it is started (when it begins to drive). Furthermore, even when the electric vehicle is parked on a downhill road, it is possible to prevent the electric vehicle from suddenly accelerating when it is started. Specifically, according to the first technique, when the electric vehicle is started, the inverter is controlled so that the motor is in a short brake state. While the motor is in the short brake state, a current is supplied to the motor so that a torque that prevents the motor from rotating (stops the vehicle) is generated. Then, by detecting the peak current value while the motor is under short brake control, it is possible to estimate the torque required for the electric vehicle to start. As a result, even when the electric vehicle is parked on an uphill road, it is possible to prevent the electric vehicle from rolling back when it starts (or from suddenly starting if it is parked on a downhill road).

[0008] The "peak current value" refers to the maximum or minimum current value detected by the detection unit when the motor is in a short braking state. For example, if the current value detected when an electric vehicle parked on an uphill road is short-braked is "positive," and the current value detected when an electric vehicle parked on a downhill road is short-braked is "negative," the peak current values ​​can be considered to be the "maximum current value" and the "minimum current value," respectively.

[0009] According to the second technique, when the short brake state is released (effectively when motor control is started), a current value that does not cause a slippage (or sudden acceleration) can be applied to the motor (coil). As a result, the distance and time of a slippage (or sudden acceleration) of the electric vehicle are reduced, improving the drivability of the electric vehicle. [Brief explanation of the drawings]

[0010] [Figure 1] A schematic diagram of a control device is shown. [Figure 2] 4 shows a timing chart relating to the rotation speed of the motor after the electric vehicle is started. [Figure 3] 1 illustrates motor control for an electric vehicle parked on an uphill road. [Figure 4] 1 illustrates motor control for an electric vehicle parked on a downward-sloping road. [Figure 5] 1 shows the control flow of the control device. DETAILED DESCRIPTION OF THE INVENTION

[0011] (Control device) The control device 1 will be described with reference to FIG. 1. The control device 1 controls a motor 9 for driving an electric vehicle (not shown). Specifically, the control device 1 controls the current value (torque) applied to a coil (not shown) of the motor 9. The control device 1 is activated when the electric vehicle is started, and controls the driving of the motor 9 while the electric vehicle is driving (including when it is stopped). The control device 1 includes an inverter 7, a control unit 3, and a detection unit 5. The inverter 7 uses current supplied from a power source (not shown) to generate a driving current to be supplied to the coil of the motor 9. The motor 9 is driven by the current supplied from the inverter 7, and the electric vehicle runs. Note that the basic structure of the inverter 7 is known, so a detailed description of the inverter 7 will be omitted.

[0012] The control unit 3 controls the operation of the inverter 7. Specifically, the control unit 3 controls the current value that the inverter 7 applies to the motor 9, thereby controlling the rotation speed and rotation direction of the motor 9. Furthermore, when the electric vehicle is started, the control unit 3 controls the inverter 7 so that the motor 9 is in a short brake state after the electromagnetic brake is unlocked. In other words, when the electric vehicle is started, the control unit 3 grounds each phase of the inverter 7 to prevent the motor 9 from rotating. Note that the control unit 3 performs short brake control on the motor 9 for only several tens of milliseconds after the electric vehicle begins to start. Therefore, the user (driver) will hardly feel that the electric vehicle is not running even though it has started.

[0013] The detector 5 detects the current value (drive current) occurring in the inverter 7 during the short brake control period. Specifically, the detector 5 detects the peak current value occurring in the inverter 7 during the short brake control period. The detector 5 also transmits the detected peak current value to the controller 3.

[0014] After the short brake control is completed, the control unit 3 determines the drive current to be supplied to the coil of the motor 9 based on the peak current value detected by the detection unit 5, and controls the inverter 7.

[0015] (Motor control) The state of the motor 9 from when the electric vehicle is started until the electric vehicle starts to move (the motor 9 starts to drive) will be described with reference to Figure 2. Note that Figure 2 shows the state of the motor 9 when the electric vehicle parked on an uphill road starts to move (move forward).

[0016] First, after the electric vehicle starts, when the driver steps on the accelerator after timing t1, the accelerator signal is turned on. Then, after timing t2, the electromagnetic brake is released. Until the electromagnetic brake is released (from the start of the electric vehicle to timing t2), no drive current is supplied to the motor 9, so the rotation speed of the motor 9 is "0." After the electromagnetic brake is released, the control device 1 controls the inverter 7 so that the motor 9 is in a short brake state until timing t3 (several tens of milliseconds). While the motor 9 is under short brake control (timing t2 to t3), a current for executing short brake control is generated in the inverter 7. In other words, a current for preventing the motor 9 from rotating in the opposite direction to the desired direction is generated in the inverter 7. As a result, the electric vehicle remains substantially stopped while under short brake control.

[0017] At timing t3, the short brake control is released, the rotation speed of the motor 9 increases, and the electric vehicle starts to travel. At timing t3, the control device 1 supplies the motor 9 with the peak current value detected while the short brake control was in effect. As described above, during the short brake control, a current is generated in the inverter 7 to prevent the motor 9 from rotating in reverse (a current to maintain the motor rotation speed at "0"). Therefore, by supplying the peak current value to the motor 9 at timing t3, it is possible to prevent the motor 9 from rotating in reverse (the electric vehicle from sliding down), as shown by curve 2.

[0018] If, as in conventional control devices, driving of the motor 9 is started at timing t3 without taking into account the peak current value during short brake control (in reality, there are cases where short brake control is not performed, in which case driving of the motor 9 starts at timing t2), the motor 9 will rotate in the reverse direction, causing the electric vehicle to roll over, as shown by curve 4. By supplying the motor 9 with the peak current value that occurs during short brake control when starting driving of the motor 9, the control device 1 can prevent the electric vehicle from rolling over when the electric vehicle starts moving, even when the electric vehicle is started.

[0019] The control of the motor 9 will be described in more detail with reference to Figures 3 and 4. Figures 3 and 4 also show the state of the motor 9 when the electric vehicle moves forward. Curve 10 in Figure 3 shows the current value generated in the inverter 7 during short brake control (timings t2 to t3) of an electric vehicle parked on an uphill road. Curve 12 shows the current value applied to the motor 9 after the motor 9 starts to drive (timing t3). Curve 14 shows the current value applied to the motor 9 after the motor 9 starts to drive when a conventional control device is used.

[0020] Furthermore, curve 20 in Figure 4 shows the current value generated in inverter 7 during short brake control of an electric vehicle having the same motor 9 as in Figure 3 and parked on a downward slope road. Curve 22 shows the current value applied to motor 9 after motor 9 starts to drive. Curve 24 shows the current value applied to motor 9 after motor 9 starts to drive when a conventional control device is used.

[0021] As shown in FIG. 3, during short brake control, the current value generated in the inverter 7 changes as shown by curve 10 depending on the load on the motor 9 (the load that prevents the rotation of the motor 9). In the control device 1, the detection unit 5 detects the maximum current value (current value Imax), which is the peak current, and changes the current applied to the motor 9 so that the current value at the start of driving the motor 9 (immediately after driving starts) becomes current value Imax. Thereafter, the current value applied to the motor 9 is gradually increased from current value Imax, as shown by curve 12. This prevents the motor 9 from rotating in the reverse direction after driving starts (after timing t3 in FIG. 2), making it possible to prevent the electric vehicle from slipping back when starting off (see also curve 2 in FIG. 2).

[0022] On the other hand, as shown by curve 14, if the current value applied to the motor 9 is gradually increased from zero after the motor 9 starts to drive, the motor 9 may rotate in the reverse direction until the current value Imax is reached. As a result, the electric vehicle may slip back when starting off.

[0023] As shown in FIG. 4, when an electric vehicle is parked on a downward-sloping road, the current value generated in inverter 7 during short brake control of an electric vehicle having the same motor 9 as shown in FIG. 3 changes in the opposite direction to when the electric vehicle is parked on an upward-sloping road, as shown by curve 20 (see also FIG. 3). In this case, in control device 1, detection unit 5 detects the minimum current value (current value Imin), which is the peak current, and changes the current applied to motor 9 so that the current value at the start of driving of motor 9 (immediately after driving starts) becomes current value Imin. Thereafter, the current value applied to motor 9 is gradually increased (the absolute value of the current is reduced) from current value Imin, as shown by curve 22. In other words, current is applied so that motor 9 rotates in the reverse direction.

[0024] Note that the current value Imin is the peak current value detected during short brake control, so even if a current greater than the peak current value (smaller than the absolute value of the peak current value) is applied to the motor 9, the motor 9 will not actually rotate in reverse. If a current greater than the peak current value is applied to the motor 9, the motor 9 will not rotate or will rotate gradually in the desired direction. Therefore, the rotation of the motor 9 is suppressed, and it is possible to suppress the electric vehicle from suddenly starting when it starts moving.

[0025] On the other hand, as shown by curve 24, even if the current value applied to the motor 9 is reduced from zero after the motor 9 starts to drive, the rotation of the motor 9 is not sufficiently suppressed, and the motor 9 may rotate excessively immediately after the motor 9 starts to drive. As a result, the electric vehicle may suddenly take off when starting off.

[0026] When the electric vehicle is parked on a flat road, almost no current flows in the inverter 7 during short brake control (the peak current value is zero). Therefore, when the motor 9 starts to drive, the control device 1 gradually increases the current value from zero to the peak current value.

[0027] The control flow performed by the control device 1 will be described with reference to FIG. 5. First, the control device 1 determines whether or not the electromagnetic brake has been released after the electric vehicle has started (step S2). If release of the electromagnetic brake is detected (step S2: YES), the control unit 3 causes the inverter 7 to start short brake control (step S4). The control unit 3 causes short brake control to be executed for a preset period (predetermined time). If release of the electromagnetic brake is not detected (step S2: NO), the control unit 3 does not start short brake control and continues to detect that the electromagnetic brake is being released.

[0028] During the short brake control period, the detection unit 5 continues to detect the current value generated in the inverter 7 (step S6) and detects the peak current value generated in the inverter 7 (step S6). After that, if the period of the short brake control has elapsed for a predetermined time (step S10: YES), the short brake control is terminated, a drive current is applied to the motor 9, and driving of the motor 9 is started (step S12). Note that the detection of the current value generated in the inverter 7 continues until the period of the short brake control reaches the predetermined time (step S10: NO).

[0029] (Advantages of Control Device 1) When the electric vehicle is started, the control device 1 puts the motor 9 into a short brake state before supplying a drive current to the motor 9, and detects the peak current value generated in the inverter 7 during short brake control. As a result, when supplying a drive current to the motor 9, the control device 1 can determine the drive current to be supplied to the motor 9 based on the peak current value generated in the inverter 7. In order to prevent the electric vehicle from rolling over or suddenly accelerating when it starts traveling, it is necessary to supply a drive current to the motor 9 that corresponds to the gradient of the road, the weight of the electric vehicle, etc., when supplying a drive current to the motor 9. Furthermore, the peak current value generated in the inverter 7 during short brake control varies depending on the gradient of the road, the weight of the electric vehicle, etc. When starting to drive the motor 9, the control device 1 supplies the current to the motor 9 using the peak current value generated in the inverter 7 during short brake control, thereby preventing rolling over or suddenly accelerating with high precision.

[0030] (Other embodiments) In the above embodiment, an example has been described in which the peak current value generated in the inverter during short brake control is supplied to the motor when starting to drive the motor. However, a current different from the peak current value may be applied to the motor when starting to drive the motor. For example, a current obtained by adding a predetermined coefficient to (or multiplying by) the peak current value may be applied to the motor when starting to drive the motor. Adding a predetermined coefficient to (or multiplying by) the peak current value can shorten the time it takes for the electric vehicle to start moving or smooth out speed changes when starting to move. The important thing is to determine the drive current to be supplied to the motor based on the peak current value generated in the inverter during short brake control when starting to drive the motor.

[0031] Although the embodiments of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. Furthermore, the technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings simultaneously achieves multiple objectives, and achieving one of these objectives itself has technical utility. [Explanation of symbols]

[0032] 1: Control device 3: Control unit 5: Detection unit 7: Inverter 9: Motor Imax: Peak current value Imin: Peak current value

Claims

1. A control device that controls a motor for driving an electric vehicle, an inverter that generates a drive current to be supplied to a coil of the motor; a control unit that controls the operation of the inverter; a detection unit that detects the magnitude of the drive current, the control unit controls the inverter so that the motor is in a short brake state when the electric vehicle is started, The detection unit detects a peak current value generated in the inverter while short brake control is being performed.

2. The control device according to claim 1, The control unit determines the drive current to be supplied to the coil based on the peak current value when the short brake control is released.

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