JP2015139239A - Motor drive device of electric vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor driving device of an electric vehicle capable of allowing the vehicle to reduce its speed preventing its wheels from locking, and to run at an appropriate speed, while achieving cost reduction.SOLUTION: A motor driving device of an electric vehicle comprises a power generation brake control part 24, which generates a brake force by short-circuiting a motor coil to substitute a driving control part 23 for control. The power generation brake control part 24 comprises: a switch 4; driving wheel revolution speed detection means 26; driven wheel revolution speed detection means 27; driving wheel reference revolution speed calculation means 28; and duty ratio control means 29. The duty ratio control means 29 controls a duty ratio, which is a ratio of a short-circuit time to a whole operation time of the power generation brake control part 24, so as to control a revolution of a driving wheel 7 detected by the driving wheel revolution speed detection means 26 to follow the reference revolution speed.

Description

  The present invention relates to a motor drive device for an electric vehicle, and more particularly to a technique capable of decelerating to an appropriate vehicle speed when an electric motor for driving driving is short-circuited to generate a braking force.

  The power generation brake is a kind of brake system in vehicles and equipment driven by electric power, and is also called a dynamic brake. This power generation brake is widely used in railway vehicles and industrial equipment. The power generation brake stops the normal driving by stopping the power supply to the motor, and when applying the brake, set the circuit to which the resistor is connected so that the motor is short-circuited, and the normal output side (vehicle In this case, the motor generates an electromotive force (Fleming's right-hand rule) by rotating the wheel. When this electromotive force is input to its own motor, a rotational resistance opposite to that of normal driving is generated in the motor (Fleming's left-hand rule is generated), and a braking force is obtained for the motor.

JP 2012-196104 A

  For example, a vehicle traveling on a downhill is naturally accelerated by gravity acceleration regardless of the driver's operation. When decelerating during such downhill travel, the brake pedal must be depressed more strongly than when traveling on a horizontal road. However, on a downhill when the road surface μ is low (for example, when the road surface is frozen), if the brake pedal is stepped on strongly, the wheel locks and the posture of the vehicle body becomes unstable. If the brake is provided with an ABS function, the wheel can be prevented from locking, but the cost is increased due to the ABS function. In addition, since ABS does not work at vehicle speeds below the low speed range, it may not be possible to exert a desired braking force.

  When the vehicle is an electric vehicle, a motor for driving that has a high response speed is provided. Therefore, the regenerative brake is controlled while monitoring the rotation speed of the motor, and the wheels can be prevented from locking. However, for example, when the battery is fully charged, the regenerative brake may not be used.

  In a vehicle not provided with an ABS function, a technology has been proposed in which a power generation brake is used when a regenerative brake cannot be used, and the vehicle is decelerated without locking wheels (Patent Document 1). However, even on a downhill, decelerating the vehicle too much causes traffic jams and wastes time. Even when decelerating downhill, it is desirable to travel at an appropriate speed while ensuring safety.

  An object of the present invention is to provide a motor drive device for an electric vehicle capable of decelerating the vehicle without locking the wheels and traveling at an appropriate speed after reducing the cost. It is.

The motor drive device for an electric vehicle according to the present invention includes an electric motor 3 that rotationally drives the drive wheels 7, and a drive control unit 23 that applies an on / off command to the plurality of drive elements 17a and 17b to perform PWM control of the electric motor 3. In the electric vehicle motor drive apparatus provided,
In place of the control by the drive control unit 23, a power generation brake control unit 24 for generating a braking force by short-circuiting the motor coil 19 of the electric motor 3 by providing an on / off command to the plurality of drive elements 17a and 17b is provided. ,
This power generation brake control unit 24
A switch 4 for switching control from the drive control unit 23 to the power generation brake control unit 24;
Drive wheel rotation speed detection means 26 for detecting the rotation speed of the drive wheel 7;
Driven wheel rotational speed detection means 27 for detecting the rotational speed of the driven wheel 6;
From the current rotational speed of the driven wheel 6 detected by the driven wheel rotational speed detection means 27 and the set ideal slip ratio, the reference rotational speed of the drive wheel 7 is calculated according to a predetermined rule. Drive wheel reference rotation speed calculation means 28;
The power generation brake control unit 24 is PWM-controlled to short-circuit the entire brake operation time so that the rotation speed of the drive wheel 7 detected by the drive wheel rotation speed detection means 26 follows the reference rotation speed. And duty ratio control means 29 for controlling the duty ratio as a ratio of time.
The set ideal slip ratio is, for example, a slip ratio (for example, 0. 0) that maximizes the grip force of the wheel on each road surface such as a dry asphalt road surface, a wet asphalt road surface, and a frozen road surface. 1 to 0.2) is set.
The predetermined rule is set by experiment, simulation, or the like.

According to this configuration, during normal travel, the drive control unit 23 performs PWM control of the electric motor 3 to rotationally drive the drive wheels 7. Drive wheel rotation speed detection means 26 and driven wheel rotation speed detection means 27 detect the rotation speeds of drive wheel 7 and driven wheel 6, respectively.
When the driver turns on the switch 4 when traveling downhill, the control is switched from the drive control unit 23 to the power generation brake control unit 24. The drive wheel reference rotation speed calculation means 28 in the power generation brake control unit 24 calculates the reference rotation speed of the drive wheel 7 from the detected current rotation speed of the driven wheel 6 and the set ideal slip ratio.

  The duty ratio control means 29 controls the duty ratio so that the rotation speed of the drive wheel 7 detected by the drive wheel rotation speed detection means 26 follows the reference rotation speed. This duty ratio is a ratio of the time for short-circuiting with respect to the entire operation time of the power generation brake control unit 24. By autonomously controlling the duty ratio, the rotational speed of the drive wheel 7 is adjusted. Even during downhill travel, the power generation brake control unit 24 causes the motor coil 19 of the electric motor 3 to be short-circuited to generate a braking force without excessively decelerating the vehicle. In this case, the cost can be reduced as compared with the case where the vehicle is decelerated using ABS or the like. Therefore, the vehicle can be decelerated and the vehicle can travel at an appropriate speed without reducing the cost, while reducing the cost. Further, according to the power generation brake control unit 24, a desired braking force can be exhibited even at a vehicle speed below the low speed range.

When the control is switched to the power generation brake control unit 24 by the switch 4, the host control means 1 of the power generation brake control unit 24 may perform control to invalidate the accelerator command. For example, when the accelerator command is validated when the control is switched to the power generation brake control unit 24, the grip force of the wheels may be undesirably reduced. In this case, when the control is switched to the power generation brake control unit 24, the host control means 1 performs control to invalidate the accelerator command, thereby realizing fail-safe.
The electric motor 3 may constitute the in-wheel motor drive device 11.

  An electric vehicle motor driving apparatus according to the present invention includes: an electric motor that rotationally drives driving wheels; and a motor drive for the electric vehicle that includes a drive control unit that applies an on / off command to a plurality of driving elements to perform PWM control of the electric motor. In the apparatus, a power generation brake control unit that generates a braking force by short-circuiting a motor coil of the electric motor by giving an on / off command to the plurality of drive elements instead of the control by the drive control unit is provided. The control unit includes a switch for switching control from the drive control unit to the power generation brake control unit, drive wheel rotation number detection means for detecting the rotation number of the drive wheel, and driven wheel rotation number for detecting the rotation number of the driven wheel. It is determined from the detection means, the current rotation speed of the driven wheel detected by the driven wheel rotation speed detection means, and the set ideal slip ratio. In accordance with the rules, the drive wheel reference rotation speed calculation means for calculating the reference rotation speed of the drive wheel and the rotation speed of the drive wheel detected by the drive wheel rotation speed detection means are made to follow the reference rotation speed. And a duty ratio control means for controlling a duty ratio which is a ratio of a time for short-circuiting with respect to an entire operation time of the power generation brake control unit. For this reason, it is possible to decelerate the vehicle without locking the wheels and to travel at an appropriate speed after reducing the cost.

1 is a block diagram of a conceptual configuration of a motor drive device for an electric vehicle according to a first embodiment of the present invention. It is a block diagram of a conceptual structure which shows the electric vehicle carrying the motor drive device with a top view. It is a block diagram which shows the conceptual structure of the inverter apparatus of the same electric vehicle. It is explanatory drawing of the short circuit connection form of the inverter of the inverter apparatus. It is a block diagram which shows the structure of the electric power generation brake control part of the motor drive device. It is a figure which shows the relationship between the slip ratio of various road surfaces, and driving force. It is a block diagram which shows the control loop of the drive control part and power generation brake control part in the motor drive device. It is a flowchart which shows the control algorithm of the motor drive device.

  A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of a conceptual configuration of a motor drive device for an electric vehicle according to this embodiment. The motor drive device includes a VCU (vehicle control unit) 1, an inverter device 2, an electric motor 3, and a switch 4. The VCU 1 is a computer-type electric control unit that performs integrated control and cooperative control of the entire vehicle, and is also referred to as “ECU”. The inverter device 2 gives a drive current to each electric motor 3 for driving driving according to the drive command sent from the VCU 1.

  The VCU 1 and the inverter device 2 are connected so as to be able to transmit signals to each other by a controller area network (abbreviation: CAN) communication or the like. The figure shows an example in which the left and right wheels are applied to a vehicle driven by an electric motor 3 respectively. The electric motor 3 includes a three-phase synchronous motor, for example, an embedded magnet type synchronous motor. During normal travel, a torque command indicating the accelerator operation amount output from the accelerator operation sensor 5 is input to the VCU 1 and distributed to the inverter devices 2 and 2 for the electric motors 3 and 3 from the VCU 1. When the driver turns on the switch 4 when traveling downhill, each inverter device 2 generates a braking force by short-circuiting the motor coil of each electric motor 3.

  FIG. 2 is a block diagram of a conceptual configuration showing, in plan view, an electric vehicle equipped with this motor drive device. This electric vehicle is a four-wheeled vehicle in which the wheels 7 that are the left and right rear wheels of the vehicle body are driving wheels and the wheels 6 that are the left and right front wheels are driven wheels. The front wheels 6 and 6 are steering wheels. The wheels 7 and 7 serving as driving wheels are driven by independent electric motors 3. The rotation of the electric motor 3 is transmitted to the wheel 7 via the speed reducer 10 and the wheel bearing 9.

  The electric motor 3, the speed reducer 10, and the wheel bearing 9 constitute an in-wheel motor drive device 11 that is one assembly part. In the in-wheel motor drive device 11, the electric motor 3 is installed in the vicinity of the wheel 7, and a part or the whole is disposed in the wheel 7. Each of the wheels 6 and 7 is provided with, for example, an electric or hydraulic brake (not shown). These electric or hydraulic brakes are configured to be capable of braking independently of a power generation brake that generates a braking force by short-circuiting the motor coil.

  The VCU 1 has torque distribution means 1a. This torque distribution means 1a is based on the accelerator opening signal output from the accelerator operating means 12, the deceleration command output from the brake operating means 13, and the turning command output from the steering means 14, and the electric motors 3 for the left and right wheels. , 3 are generated as torque command values and output to each inverter device 2. The torque distribution unit 1a distributes the braking torque command value for causing the electric motor 3 to function as a regenerative brake and the braking torque command value for operating the brake when a deceleration command output from the brake operation unit 13 is received. Have

  As the braking torque command value to function as the regenerative brake, for example, the torque command value of the acceleration / deceleration command given to each of the electric motors 3 and 3 is given as a negative command value. The accelerator operation means 12 includes an accelerator pedal and an accelerator operation sensor 12a that detects an operation amount of the accelerator pedal. The brake operation means 13 includes a brake pedal and a sensor 13a that detects an operation amount of the brake pedal.

  FIG. 3 is a block diagram showing a conceptual configuration of the inverter device 2 of the electric vehicle. The inverter device 2 includes a power circuit unit 15 that is a power conversion circuit unit provided for each electric motor 3, and a motor control unit 16 that controls the power circuit unit 15. The motor control unit 16 has a function of outputting information such as detection values and control values related to the in-wheel motor drive device 11 (FIG. 2) to the VCU 1.

The power circuit unit 15 includes an inverter 17 that converts the DC power of the battery 8 into three-phase AC power that is used to drive the electric motor 3, and a PWM driver 18 that is a means for controlling the inverter 17.
The inverter 17 is composed of a plurality of drive elements 17a and 17b that are semiconductor switching elements, and each of the three phases (U, V, and W phases) of the electric motor 3 is combined by an on / off combination of the drive elements 17a and 17b. The drive current is output as a pulse waveform.

  Two drive elements 17 a and 17 b of the inverter 17 are connected in series to three phase circuit units connected in parallel between the positive voltage side circuit unit and the negative voltage side circuit unit connected to the battery 8. The portion between the two drive elements 17 a and 17 b in each phase circuit section is connected to the motor coil 19 of each phase of the electric motor 3. A diode is connected in parallel to each drive element 17a, 17b. A smoothing circuit 20 using a smoothing capacitor is provided between the positive voltage side circuit section and the negative voltage side circuit section.

  The PWM driver 18 performs pulse width modulation on the input current command and gives an on / off command to each of the drive elements 17a and 17b. The pulse width modulation is performed, for example, so as to obtain a current output driven by a sine wave. The PWM driver 18 that is a weak electric circuit portion of the power circuit portion 15 and the motor control unit 16 constitute an arithmetic unit 21 that is a weak electric circuit portion in the inverter device 2. The computing unit 21 includes a computer, a program executed on the computer, and an electronic circuit.

The electric motor 3 is provided with angle detection means 22 for detecting the angle of the motor rotor.
The motor control unit 16 includes a drive control unit 23 that performs control according to the magnetic pole position according to the angle detected by the angle detection unit 22. During normal travel, the drive control unit 23 performs PWM control of the electric motor 3 to rotationally drive the drive wheels. The drive control unit 23 outputs three-phase AC voltage command values Vu, Vv, and Vw by a predetermined circuit in accordance with a torque command value given from the torque distribution unit 1a of the VCU 1 that is a host control unit. The power circuit unit 15 converts the voltage command values Vu, Vv, and Vw output from the drive control unit 23 as described above, and outputs motor drive currents Iu, Iv, and Iw.

In this embodiment, instead of the control by the drive control unit 23, an on / off command is given to the plurality of drive elements 17a, 17b, thereby generating a braking force by short-circuiting the motor coil 19 of the electric motor 3. 24 is provided.
As shown in FIG. 4, when the inverter 17 is composed of a total of six drive elements 17a and 17b, all the three drive elements 17a on the positive voltage side (upper side in FIG. 4) are turned off and the negative voltage side ( By turning on all the three drive elements 17b (lower side in FIG. 4), the motor coil 19 of the electric motor 3 is short-circuited. When all the six drive elements 17a and 17b are turned off, there is no power input / output, and the electric motor 3 is in a free state.

FIG. 5 is a block diagram illustrating a configuration of the power generation brake control unit 24.
The power generation brake control unit 24 includes a switch 4 and a short-circuit current control unit 25. The switch 4 is a switch for switching control from the drive control unit 23 to the power generation brake control unit 24 and can be switched by the driver. The switch 4 may be automatically switched by a gyro sensor or the like that senses the vehicle posture. When the control is switched to the power generation brake control unit 24 by the switch 4, the VCU 1 performs control to invalidate the accelerator command. The short-circuit current control means 25 is means for controlling the short-circuit current of the electric motor 3 when the inverter 17 (FIG. 4) is in a short-circuit connection state. The short-circuit current control means 25 performs current control by PWM drive, and specifically controls the short-circuit current using the drive control unit 23.

In the current control by PWM driving of the short-circuit current, the connection form of the inverter 17 (FIG. 3) is changed to the short-circuit connection form of FIG. 4, and the three drive elements 17b on the negative voltage side to be turned on are simultaneously turned on and off. This is done by controlling the pulse width giving the ON time.
As shown in FIG. 5, the short-circuit current control unit 25 includes a drive wheel rotation number detection unit 26, a driven wheel rotation number detection unit 27, a drive wheel reference rotation number calculation unit 28, and a duty ratio control unit 29. .

  The drive wheel rotation speed detection means 26 always detects the rotation speed of the drive wheel 7 from the angle detection means 22, for example. The driven wheel rotational speed detection means 27 always detects the rotational speed of the driven wheel 6. For example, a rotation sensor 30 is provided in a wheel bearing or the like that rotatably supports the driven wheel 6, and the rotation speed of the driven wheel 6 is detected from the detection value of the rotation sensor 30.

The drive wheel reference rotation speed calculation means 28 is a drive wheel according to a predetermined rule from the current rotation speed of the driven wheel 6 detected by the driven wheel rotation speed detection means 27 and the set ideal slip ratio λmin. 7 is calculated.
FIG. 6 is a diagram showing the relationship between the slip ratio of various road surfaces and the driving force. The slip ratio λ of the wheel with respect to the road surface is minimum between λ = 0.1 and 0.2 regardless of whether it is a dry asphalt road surface, a wet asphalt road surface, or a frozen road surface. There is a value, that is, a value that maximizes the gripping force. Accordingly, the reference rotational speed Nmax of the drive wheel is calculated according to the following equation, with λ = 0.1 to 0.2 being an ideal slip ratio λmin.

(Nmax−N1) / N1 = λmin
However, N1: rotational speed of the driven wheel As shown in FIG. 5, the duty ratio control means 29 variably controls the duty ratio so that the detected rotational speed of the drive wheel 7 follows the reference rotational speed. This duty ratio is a ratio of the time for short-circuiting with respect to the entire operation time of the power generation brake control unit 24.

FIG. 7 is a block diagram illustrating a control loop of a drive control unit and a power generation brake control unit in the motor drive device.
During normal travel, as shown in the lower control loop of FIG. 7, an accelerator torque command indicating the accelerator operation amount is input to VCU1 (FIG. 1), and each inverter device 2 ( Is given in FIG. The accelerator torque command is converted into a current command by each inverter device 2 (FIG. 1). The drive control part 23 (FIG. 3) in each inverter apparatus 2 obtains the electric current sent through an electric motor from the electric current detection means using PID controller 31a, and performs electric current feedback control. The electric current command calculated by the PID controller 31a is subjected to pulse width modulation, and the electric motor 3 is rotationally driven by giving an ON / OFF command to each drive element at a duty ratio of 50%, for example. Therefore, the drive wheel can be driven to rotate.

  When the driver turns on the switch 4 (FIG. 5) during downhill travel, the control loop is switched to the power generation brake control unit surrounded by the dotted line frame in FIG. In this power generation brake control loop, the rotation speed of the driven wheel is detected by the rotation sensor 30 (FIG. 5). Further, the drive wheel rotation speed detection means always detects the rotation speed of the drive wheel from the angle detection means 22 provided in the electric motor 3.

  The current slip ratio is calculated from the detected rotational speed of the driving wheel and the rotational speed of the driven wheel, and the power generation brake control unit 24 (FIG. 5) in each inverter device 2 (FIG. 1) uses the PID controller 31b. Thus, the duty ratio is variably controlled so that the rotational speed of the drive wheel follows the reference rotational speed Nmax (that is, the current slip ratio follows the ideal slip ratio λmin).

  For example, when the slope of the downhill is steep, all the driving elements on the negative voltage side are turned on with a duty ratio of 100%, and the rotational speed of the driving wheel is reduced to the maximum. For example, when the slope of the downhill is a gentle angle, all the driving elements on the negative voltage side are turned off at a duty ratio of 0%, the electric motor 3 is in a free state, and the vehicle running on the downhill is Drive at an appropriate vehicle speed due to gravitational acceleration. By using the power generation brake in this way, when the vehicle travels downhill on a low μ road, for example, the vehicle can travel at an appropriate vehicle speed without being locked.

FIG. 8 is a flowchart showing a control algorithm of the motor drive device. This will be described with reference to FIGS. 3, 4 and 5 as appropriate. After the start of this process, the power generation brake control unit 24 determines whether or not the switch 4 is on (step S1), and determines that the switch 4 is not on (step S1: NO), and validates the accelerator command (step S2). ). Then return.
If it is determined that the switch is on (step S1: YES), the VCU 1 performs control to invalidate the accelerator command (step S3).

  Next, the drive wheel rotation speed detection means 26 of the inverter device 2 detects the rotation speed of the drive wheel 7 (step S4), and the driven wheel rotation speed detection means 27 detects the rotation speed of the driven wheel 6 (step S5). . The power generation brake control unit 24 calculates the current slip ratio from the detected rotation speed of the driving wheel 7 and the rotation speed of the driven wheel 6 (step S6), and the power generation brake control unit 24 performs the current slip rate by PID control. The duty ratio is variably controlled so that the slip ratio follows the ideal slip ratio λmin (step S7). Then return.

  According to the motor drive apparatus described above, for example, when the driver turns on the switch 4 during downhill travel, the control is switched from the drive control unit 23 to the power generation brake control unit 24. The drive wheel reference rotation speed calculation means 28 in the power generation brake control unit 24 calculates the reference rotation speed of the drive wheel 7 from the detected current rotation speed of the driven wheel 6 and the set ideal slip ratio λmin. .

  The duty ratio control means 29 controls the duty ratio so that the rotation speed of the drive wheel 7 detected by the drive wheel rotation speed detection means 26 follows the reference rotation speed. This duty ratio is a ratio of the time for short-circuiting with respect to the entire operation time of the power generation brake control unit 24. By autonomously controlling the duty ratio, the rotational speed of the drive wheel 7 is adjusted. Even during downhill travel, the power generation brake control unit 24 causes the motor coil 19 of the electric motor 3 to be short-circuited to generate a braking force without excessively decelerating the vehicle. In this case, the cost can be reduced as compared with the case where the vehicle is decelerated using ABS or the like. Therefore, the vehicle can be decelerated and the vehicle can travel at an appropriate speed without reducing the cost, while reducing the cost.

  When the control is switched to the power generation brake control unit 24 by the switch 4, the VCU 1 that is the upper control means of the power generation brake control unit 24 performs control to invalidate the accelerator command. For example, when the accelerator command is validated when the control is switched to the power generation brake control unit 24, the grip force of the wheels may be undesirably reduced. In this case, when the control is switched to the power generation brake control unit 24, fail safe can be realized by the VCU 1 performing control to invalidate the accelerator command.

  In the wheel drive device according to this embodiment, an example in which the in-wheel motor drive device is adopted has been shown, but the present invention is not limited to this, and an on-board type may be used. In addition, as the speed reducer in the wheel drive device, for example, a cycloid type speed reducer, a planetary speed reducer, a two-axis parallel speed reducer, and other speed reducers can be applied, and a so-called direct motor type that does not employ a speed reducer. It may be. In the present specification, “electric vehicle” is a concept including all vehicles that obtain driving force from electric power.

DESCRIPTION OF SYMBOLS 3 ... Electric motor 4 ... Switch 6 ... Drive wheel 7 ... Drive wheel 11 ... In-wheel motor drive device 17a, 17b ... Drive element 19 ... Motor coil 23 ... Drive control part 24 ... Power generation brake control part 26 ... Drive wheel rotation speed detection Means 27 ... Driven wheel rotational speed detection means 28 ... Drive wheel reference rotational speed calculation means 29 ... Duty ratio control means

Claims (3)

In an electric vehicle motor drive device comprising: an electric motor that rotationally drives a drive wheel; and a drive control unit that PWM-controls the electric motor by giving an on / off command to a plurality of drive elements.
A power generation brake control unit that generates a braking force by short-circuiting the motor coil of the electric motor by providing an on / off command to the plurality of drive elements instead of the control by the drive control unit,
This power generation brake control unit
A switch for switching control from the drive control unit to the power generation brake control unit;
Drive wheel rotation speed detection means for detecting the rotation speed of the drive wheel;
Driven wheel rotational speed detection means for detecting the rotational speed of the driven wheel;
A drive wheel reference that calculates a reference rotation speed of the drive wheel according to a predetermined rule from the current rotation speed of the driven wheel detected by the driven wheel rotation speed detection means and a set ideal slip ratio. A rotation speed calculating means;
Percentage of time for which the power generation brake control unit is PWM-controlled to short-circuit the entire brake operation time so that the rotation speed of the drive wheel detected by the drive wheel rotation speed detection means follows the reference rotation speed Duty ratio control means for controlling the duty ratio,
An electric vehicle motor drive device comprising:   2. The motor drive device for an electric vehicle according to claim 1, wherein when the control is switched to the power generation brake control unit by the switch, the host control means of the power generation brake control unit performs control to invalidate an accelerator command. Motor drive device for automobiles.   3. The motor drive device for an electric vehicle according to claim 1, wherein the electric motor is an in-wheel motor drive device.

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