JPS62131782A - Driver for dc motor - Google Patents

Abstract

PURPOSE:To prevent a torque from decreasing at low speed rotation time after starting by setting a reference value inversely proportional to a rotating speed at this time. CONSTITUTION:The output of a pulse encoder 32 is converted by a frequency/ voltage converter 34 to a voltage signal E1. A voltage converter 38 outputs a reference signal E2 inversely proportional to the signal E1 to a Schmitt trigger 46. A voltage signal E3 across a shunt resistor 4 of a motor circuit is applied to the comparison input side of the trigger 46. The output signal S5' of the trigger 45 is output through a waveform shaper 54 to a motor control means 16. Thus, acceleration of the motor and operating feeling at starting time can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a DC motor drive device, and particularly to a DC motor drive device that employs a chopper control method.

[Conventional technology]

Generally, electric vehicles such as electric vehicles are equipped with a DC motor as a drive source, and the DC motor is driven by a drive device that employs various control methods.

As a control method for this DC motor, a chopper control method has traditionally been widely used.This chopper control method not only controls the speed but also controls the motor current (armature current) of the DC motor to a predetermined limit value. I try to do that.

Furthermore, as seen in Japanese Patent Laid-Open No. 58-79405, attempts have been made to detect the rotational speed of a DC motor and control the motor current in conjunction with chopper control, thereby improving riding comfort, etc. .

[Problem that the invention seeks to solve]

However, in each of the above-mentioned conventional technologies, the relationship between the rotation speed and torque of the DC motor is as shown in FIG.
In reality, there is a temporary drop in torque due to the characteristics peculiar to the chopper control system in the low rotational speed region immediately after startup, so when this DC motor is installed in an electric vehicle, it is difficult to reduce the running torque. Due to this deficiency, not only was smooth acceleration not possible after the start of driving, but there was also an inconvenience that the operating feel was not good.

[Purpose of the invention]

An object of the present invention is to provide a DC motor drive device that can improve the disadvantages of the prior art, eliminate the drop in torque during low-speed rotation after starting, and provide smoother rotation. purpose.

[Means for solving problems]

Therefore, in the present invention, in a DC motor drive device including a motor control means for forming a drive signal corresponding to a rotational speed command signal and controlling energization to a driving DC motor based on the drive signal, A rotation detecting means for detecting the rotational speed of a motor and outputting a signal proportional to the rotational speed, a voltage converting means for converting an output signal from the rotation detecting means into a voltage inversely proportional to the signal and outputting it, and the voltage converting means. A reference value based on the output voltage from the means is constantly compared with a voltage value based on the motor current of the DC motor, and if necessary, the driving of the motor control means is forcibly stopped so that the motor current reaches a predetermined limit value. The present invention aims to achieve the above object by providing a motor current control means for controlling the motor current so as not to exceed the current.

[Created/Used]

The driving DC motor is controlled by a motor control means that functions based on a rotational speed command signal. In this case, the rotation speed of the DC motor is detected by the rotation detection means, the output signal from the rotation detection means is converted by the voltage conversion means into a voltage inversely proportional to the rotation speed, and this voltage is applied to the motor current control means. It will be done. This motor current control means constantly compares a reference value based on the output voltage from the voltage conversion means and a voltage value based on the motor current of the DC motor, and is necessary to prevent the motor current from exceeding a predetermined limit value. The drive of the motor control means is forcibly controlled in accordance with the above.

In this control, the reference value based on the motor rotation speed is
Since it is set sequentially to be inversely proportional to the rotation speed at that point, the above reference value can be set to be higher during low speed rotation, thereby eliminating the drop in torque at low speed rotation after starting. can.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 4. This embodiment shows a case where the present invention is applied to an electric vehicle as an electric vehicle.

In FIG. 1, 2 indicates a driving DC motor, and 4 indicates a shunt resistor for motor current detection connected between the DC motor 2 and ground. Further, numeral 6 indicates an on-vehicle battery, and numeral 8 is a power supply circuit configured as shown in the figure by a three-terminal regulator 10 and capacitors 12 and 14, and receives power from the battery 8 and generates a YCC power supply for the logic circuit. shows.

Further, in this embodiment, the DC motor 2 is provided with a motor control means 16 for controlling the supply of electricity from the battery 6 to the DC motor 2 based on a chipper control method, and a motor control means 16 for controlling the current and rotation of the DC motor 2. A control section 18 is provided which controls the function of the motor control means 16 intermittently depending on the number of motors and controls the motor current to a predetermined limit value.

Of these, the motor control means 16 includes a comparator 2
0 is provided, and the inverting input terminal of the comparator 20 receives a sawtooth wave signal Sl from a reference signal generator (not shown).
(see Fig. 3(a)), and a rotational speed command signal (accelerator signal) S2 (see Fig. 3(a)) output from the accelerator section (not shown) of the electric vehicle is applied to the non-inverting input terminal. This causes the comparator 2 to
From the output terminal of 0, a square wave pulse-shaped output signal S3 as shown in FIG. 2(b) is output.

Furthermore, the output terminal of the comparator 20 is connected to a diode 2.
2 to an amplifier circuit in which transistors 24, 26, 28, etc. are connected as shown.

Among these, the emitter side of the final stage transistor 28 is connected to the power supply side end of the DC motor 2, and the collector side is connected to the positive end of the battery 6. Here, the diode 30 attached to the DC motor 2 and the shunt resistor 4 is used as a flywheel for smooth motor rotation.

Therefore, the output signal S3 of the comparator 20 acts as a drive signal for the motor 2, and when the signal S3 reaches the logic level H, the transistor 24
is turned on and is energized by the transistor 26.2.
8 operate sequentially, and the battery 6 supplies electricity to the motor 2, causing the motor 2 to rotate. Here, the rotation of the motor 2 is performed by a pulse width variable m (PWM) method according to the rate at which the signal S3 is at the logic level H per unit time. Further, when the signal S3 is at the logic level L, the motor current is commutated to the motor 2 via the diode 30.

On the other hand, the aforementioned control section 18 is provided between the motor circuit section and the output end of the comparator 20 of the motor control means 16 as shown in the figure.

To explain this in more detail, the output shaft of the DC motor 2 is equipped with a pulse encoder 32 for detecting the rotation speed. It has the function of forming a pulse signal of rotation speed). A frequency/voltage converter (hereinafter simply referred to as rF/V converter) 34 is provided on the output side of this pulse encoder, and this F/V converter 34 converts the input pulse signal in proportion to its frequency. In addition to converting it into a voltage signal E1 (see FIG. 2(a)),
The F/V converter 34 is configured to output the voltage to the voltage conversion means 38 via a buffer amplifier 36 provided on the output side.

Here, the pulse encoder 32 and the F/■ converter 34 constitute a rotation detecting means 40.

The voltage conversion means 38 is an operational amplifier (operational amplifier) 42
The variable power supply circuit includes a function generating circuit 5 having a main part thereof and a variable power supply circuit having a current booster transistor 44 as a main part. As shown in FIG. 2(b), this voltage conversion circuit 38 has a function of forming a voltage signal E2 that is inversely proportional to the input voltage signal El (that is, 9 rotations), and this voltage signal E2 is output to a Schmitt trigger circuit 46, which is provided at the next stage and serves as motor current control means.

On the other hand, the voltage across the shunt resistor 4 in the motor circuit section is applied to a differential amplifier circuit 48 provided to accurately detect the motor current. The voltage signal E3 detected and amplified by the differential amplifier circuit 48 is applied to the comparison input side of the Schmitt trigger circuit 46.

The Schmitt trigger circuit 46 has an operational amplifier 50 as its main part, uses the voltage E2 from the voltage conversion means 38, which changes in inverse proportion to the motor rotational speed, as a power supply voltage, and also uses the voltage E2 for comparison based on this voltage E2. The configuration is such that a reference voltage is formed. For this reason, this Schmitt trigger circuit 46 has two threshold levels Ll,
As shown in FIG. 2(c), L2 changes in inverse proportion to the motor rotation speed, and as the rotation speed increases, its level width becomes narrower. Therefore, this Schmitt trigger circuit 46 lowers its output signal S5' to the logic level L at the time when the voltage E3 to be compared changes from a value smaller than the threshold level L1 and exceeds this level L1. When the voltage E3 becomes smaller than the threshold level L2, the output signal S5' is raised to the logic level H (see FIG. 3(d)).In this case, the threshold level Ll , L2 are set corresponding to the motor current limit value of the DC motor 2, and the level L1 is set to correspond to the motor current limit value of the DC motor 2.
It is set to a value greater than 2.

The output signal S5' of the Schmitt trigger circuit 46, which operates based on such a function, is output to a waveform shaping circuit 54 whose main part is a comparator 52. This waveform shaping circuit 54 uses a manually generated binary signal S5.
After shaping the waveform of ', it is outputted from its output terminal as a control signal S5 (see FIG. 3(e)). The output end of this waveform shaping circuit 54 is a diode 56.
to the output terminal of the comparator 20 of the motor control means 16. Therefore, when the control signal S5 is at the logic level L, the operation of the motor control means 16 is forcibly stopped, and when the control signal S5 is at the logic level H, the operation of the motor control means 1 is forcibly stopped.
It has a configuration that has no involvement in 6. As a result, the final motor drive signal S4 corresponds to the AND of the signals S3 and 85, as shown in FIG. 3<r>.

Next, the overall operation of this embodiment will be explained.

Now, for example, a sawtooth signal S as shown in FIG. 3(a)
1 and speed command signal S2 are output,
The comparator 20 outputs a pulse-like signal S3 as shown in FIG. This signal S3 drives the DC motor 2 as described above so that the speed corresponds to the speed command signal S2.

In this state, the rotation speed of the motor 6 increases at a constant rate as shown in FIG.
), it gradually decreases in inverse proportion to the rotation speed, as shown by the broken line.

As a result, when the rotational speed of the DC motor 2 is low as described above, the threshold level L1 of the Schmitt trigger circuit 46 is large, and the threshold level L1 and L
The level difference between 2 and 3 becomes larger than when rotating at high speed. Therefore, if the voltage signal E3 based on the motor current of the DC motor 2 changes as shown by the solid line in FIG.
.

That is, the output signal S5 of the waveform shaping circuit 54 becomes as shown in FIG. In other words, the time T1 from when the DC motor 2 is started until the output of the Schmitt trigger circuit 46 falls to the logic level L can be set longer than when the threshold level is constant based on high-speed rotation. (See Figure 3(e)).

In this way, the threshold level L1. By setting L2 appropriately, the ratio of the H level of the motor drive signal S4 when the rotation speed is low immediately after the DC motor 2 is started can be set higher. Therefore, the motor current of the DC motor 2 is also controlled to have a higher limit value when the rotational speed is low than when the rotational speed is high.

By the way, the torque of the DC motor 2 is proportional to the motor current, so if such motor current control is executed, the torque generated by the DC motor 2 during low speed rotation will be reduced as shown by the solid line in Figure 4. , it is possible to raise the torque more reliably than in the case where the threshold is constant (see the broken line in the figure), and it is possible to improve the drop in torque as in the conventional example.

Therefore, in this embodiment, when starting the electric vehicle, the torque of the DC motor 2, which is the drive source, can be kept relatively high and constant, making it possible to improve the acceleration performance and operational feeling when starting.

Note that although the above embodiments have been described with reference to the case where the present invention is applied to an electric vehicle, the present invention is not necessarily limited thereto, and may be applied to other electric vehicles or mechanical devices.

〔Effect of the invention〕

Since the present invention is configured and functions as described above, it is possible to set a higher motor current limit value when the DC motor rotates at low speed than when it rotates at high speed, so that a predetermined rotation control for the DC motor can be performed. In addition, the present invention can be applied to electric vehicles, for example, because the torque, which is proportional to the motor current, can be increased by a predetermined amount during low-speed rotation to improve the drop in torque that occurs in the conventional example. By doing so, it is possible to provide an excellent DC motor drive device that further improves the acceleration performance and the operating feeling when starting.

[Brief explanation of drawings]

FIG. 1 is a further block circuit diagram according to an embodiment of the present invention, FIG. 2(a) is a graph diagram for explaining the operation of the frequency/voltage converter, and FIG. 2(b) is a voltage converting means. Figure 3 (C) is a graph diagram showing the relationship between the rotation speed of the DC motor and the threshold level of the Schmitt trigger circuit. A waveform diagram for explaining the operation of each part of the embodiment shown in the figure, Figure 4 is a graph diagram showing the relationship between the rotation speed and torque of the embodiment shown in Figure 1, and Figure 5 is a graph diagram for the conventional example. It is a graph diagram showing the relationship between the rotation speed and torque. 2...DC motor, 16...Motor control means, 38...Voltage conversion means, 40...
... Rotation detection means, 46 ... Motor current control means. Patent applicant: Suzuki Motor Co., Ltd. Figure 2 Figure 3

Claims (3)

[Claims] (1) A DC motor drive device comprising a motor control means for forming a drive signal corresponding to a rotational speed command signal and controlling energization of the drive DC motor based on the drive signal, A rotation detecting means for detecting the rotation speed and outputting a signal proportional to the rotation speed; a voltage conversion means for converting the output signal from the rotation detection means into a voltage inversely proportional to the signal and outputting the voltage; A reference value based on the output voltage of the DC motor is constantly compared with a voltage value based on the motor current of the DC motor, and if necessary, the drive of the motor control means is forcibly stopped so that the motor current does not exceed a predetermined limit value. What is claimed is: 1. A direct current motor drive device comprising a motor current control means for controlling the current. (2) The DC motor drive device according to claim 1, wherein the motor control means is configured to form a drive signal using a chopper control method. (3) The DC motor drive device according to claim 1, wherein the motor current control means is a Schmitt trigger circuit.