JPH088722B2 - Electric differential drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a motor drive of a vehicle, in which the left and right wheels are affected by a torque imbalance caused by a difference in rotational speed between an inner wheel and an outer wheel generated when the wheel travels in a curve. The present invention relates to a device for performing well-balanced driving by controlling electric motors separately coupled to wheels.

[Conventional technology]

FIG. 4 shows a drive mechanism of an electric vehicle,
The front wheels 1 and 2 are driven by electric motors 5 and 6, respectively, and are controlled by left and right independent control devices 7 and 8. In the figure, 3 and 4 are rear wheels.

Conventionally, such vehicle drive has been driven by a DC motor. This is because the starting torque is large and the speed control is easy. The method shown in FIG. 5 has been put into practical use as one method for achieving torque balance by driving a DC motor.

In FIG. 5, L is a left wheel electric motor, and R is a right wheel electric motor. Since the two motors are connected in series, the same current flows. The vehicle moves on a curve,
When a speed difference occurs between the two electric motors, the sharing of the armature voltage changes according to the speed difference. Therefore, if the field is kept constant, the torques of both motors will be balanced. When the field current is controlled so as to be inversely proportional to the armature voltage, the output balance of both motors is maintained.

One of the drawbacks of the method of FIG. 5 is that when one of the vehicles runs idle, the full voltage is applied to the electric motor that drives the wheels of the vehicle, resulting in the voltage saturation and the loss of the driving force. It will be.

On the other hand, with the improvement of the AC motor drive technology using an inverter, the need for maintenance-free and application in adverse environments has increased, and there is a strong demand for AC conversion of this drive device.

To meet this demand, there is a method of increasing the secondary resistance of the electric motor, but there is a drawback that the efficiency is extremely lowered.

[Problems to be solved by the invention]

The present invention has been invented in view of the above conventional problems, and in an apparatus that individually drives the left and right wheels of a vehicle with an AC electric motor that is fed by an inverter, a left-right speed difference is generated during curved traveling. However, even if both torques or outputs are balanced and one wheel spins,
It is an object of the present invention to provide a control method in which the speed difference does not rise above a set value and the driving force can always be secured.

[Means for solving problems]

The present invention detects the torque difference between the left and right induction motors that drive the left and right drive wheels, regulates the maximum width of the torque difference, and then adds the torque difference signal from the speed setting value according to the sign and The values are subtracted and given as speed command values for the induction motor control circuit.

〔Example〕

Hereinafter, the present invention will be specifically described based on the embodiments shown in the drawings.

FIG. 1 shows a block diagram of the present invention. Electric motors 5 and 6 for driving the left and right wheels are fed by individual inverters 10 and 11, respectively, and each inverter can electrically detect torque or output. It has a function (torque detection blocks 12 and 13). In the figure, 14 is a deviation detector, 15 is a first-order lag element for signal smoothing, 16 is a torque limiting block for preventing idling, 17 and 18 are subtractors and adders, and 19 respectively.
Is a frequency setting device, 20 is a rectifier, and 21 is a braking block that gives the inverter a braking function.

The difference between the torque or output (KW) detected by the torque detection blocks 12 and 13 of the left and right inverters 10 and 11 is detected by the deviation detector 14, the deviation is smoothed via the first-order lag element 15, and the smoothed deviation is calculated. Input to torque limit block 16. The torque limiting block 16 is composed of, for example, a function generator, and is proportional to the above deviation within a predetermined range, and outputs a constant feedback value above or below the deviation. This feedback value and the output of the frequency setting device 19 are subtracted by the subtractor 17 and also added by the adder 18, and this is added to each inverter 10, 11.
It is fed back as the frequency command of. The polarity of the feedback is to lower the frequency of the heavier load inverter and increase the lighter load frequency.

In this way, the torque of the load can be changed due to the speed difference. By detecting the difference, the two inverters 10, 11 can be connected.
Differentiate the frequency command of to maintain balance.

For torque or output detection, modern inverters use active current or active power calculation to calculate torque or output for purposes such as automatic voltage compensation, stall prevention, and load meter (load monitoring). It has a function to detect a signal corresponding to.

Further, for the purpose of the present invention, since the induction motor itself has a slip and a slight torque imbalance can be tolerated, the accuracy of the torque or the output detection need not be strict.

In addition, each inverter can be equipped with a detection function, and the method of finding the difference can be taken one step further to directly detect the inverter DC main circuit current difference with a single DC current transformer (CT) as shown in FIG. .

DC current is pulse width modulated (PWM) with constant DC voltage
In the case of the method, it is almost proportional to the output power, and in the pulse amplitude modulation (PAM) method in which the output voltage is controlled by changing the DC voltage, it is almost proportional to the torque.

By providing the limiting circuit 16 in the torque or output deviation feedback circuit as shown in FIG. 1, it is possible to limit the speed difference when the wheels are idling and to secure the driving force. Further, by inserting a dead zone as shown in FIG. 3, it is possible to perform a stable operation against a detection error and the like.

〔The invention's effect〕

As described above, according to the present invention, in a device that individually drives the left and right wheels of a vehicle, by adding a simple circuit that feeds back the torque or output (electric power) deviation of the left and right drive devices to an inverter frequency command,
The effect of the differential gear (differential gear) can be electrically obtained, and the vehicle can be driven economically and stably.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, and FIG.
The figure is a block diagram showing another embodiment using a DC current transformer,
FIG. 3 shows the case where a dead band is provided in the feedback signal,
A graph showing the relationship between the torque deviation and the feedback value,
FIG. 4 is an explanatory view of a drive mechanism of an electric vehicle, and FIG. 5 is a block diagram of a differential drive device using a DC motor. 1,2: Front wheel 3,4: Rear wheel 5,6: Motor 10,11: Inverter 12,13: Torque detection block 14: Deviation detector 15: 1st delay element 16: Torque limit block 17: Subtractor 18: Adder 19: Frequency setter 20: Rectifier 21: Braking function block

Claims (1)

[Claims] Claims: 1. Left and right individual induction motors for driving left and right drive wheels, individual inverters for driving these induction motors, individual torque detecting means for detecting torque of each induction motor, and each inverter. An electric differential drive comprising a frequency setting device for giving a reference frequency to a deviation detector for detecting the torque difference between the left and right induction motors detected by the torque detecting means, and smoothing the deviation. And a torque limiting means for restricting the maximum width of the output of this primary delay element, and adding and subtracting the torque difference signal whose maximum width is restricted from the speed set value according to the sign of the signal. An electric differential drive device is further provided with an adder and a subtracter, which are given as speed command values of the induction motor control circuit, respectively.