Electricity: motive power systems – Battery-fed motor systems
Reexamination Certificate
1995-03-21
2001-05-15
Wysocki, Jonathan (Department: 2837)
Electricity: motive power systems
Battery-fed motor systems
Reexamination Certificate
active
06232729
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control device for a motor employed for an electric vehicle and, more particularly, to a motor control device which is designed to prevent the deterioration of a storage battery or the like by preventing an excessive increase in the regenerative braking amount of the motor.
2. Description of the Related Art
FIG. 6
is a block diagram showing a motor control device for an electric vehicle. The motor control device for the electric vehicle is equipped with a motor
1
, which is operatively connected to driving wheels (not shown), and a driver circuit
2
which is connected to the motor
1
to drive the motor
1
. The motor control device is further provided with a controller
3
for controlling the motor via the driver circuit
2
, a storage battery
4
for supplying power to the motor
1
, the driver circuit
2
and the controller
3
, a brake stroke sensor
5
which is provided on an operating section of each brake (not shown) for detecting an the operating amount of the corresponding brake and supplying the detected operating amount of the brake to the controller
3
, and a revolution detector
6
which is provided on the motor
1
for detecting the number of revolutions (i.e., rpm) of the motor
1
and supplying the detected number of revolutions to the controller
3
.
FIG. 7
shows the relationship between regenerative power and a maximum regenerative torque with respect to the number of revolutions per minute of the motor
1
. As it is obvious from the chart, the relationship between the regenerative power and the maximum regenerative torque satisfies the expression given below:
Regenerative power∝Max. regenerative torque×Number of revolutions (rpm)
Decelerating a vehicle at a fixed deceleration value gives good deceleration feeling without causing a shock to a driver and/or passenger. To achieve this, it is necessary to regenerate the motor of the electric vehicle at a fixed torque, so the regenerative power is apropriately set as shown in a diagram of FIG.
8
. According to
FIG. 8
, the regenerative torque becomes constant when a set rpm N
0
or more is reached. Further, in an actual vehicle, regenerating the motor so far as the rpm becomes zero causes a shock or the like immediately before reverse rotation or stoppage of the motor
1
. For this reason, there are some cases where the regenerative torque is reduced to zero at a certain rpm, as shown in FIG.
9
.
As stated above, FIG.
8
and
FIG. 9
show an example of the regenerative torque corresponding to the rpm of the motor
1
.
FIG. 10
shows the regenerative torque (brake regenerative torque) of the motor
1
with respect to the output value of the brake stroke sensor
5
.
FIG. 11
shows the relationship between the regenerative torque generated by a wheel brake and the rpm. The regenerative power shown in FIG.
8
and
FIG. 9
corresponds to the engine brake of a gasoline-powered automobile and the regenerative power is so set that it is applied when an accelerator pedal, which is not shown, is fully released. The regenerative braking amount, which is the regenerative torque of the vehicle, is designed to be equal to the sum of the regenerative torque generated by the aforesaid wheel brake and the regenerative torque corresponding to the engine brake.
Hence, as the brake operating amount or the rpm of the motor
1
increases, the regenerative braking amount accordingly increases, causing the rechargeable storage battery
4
to be charged with an excessively large magnitude of current. At this time, the voltage of the storage battery
4
increases with the charging current and such an increase is significant when the storage battery is fully charged, as illustrated in FIG.
12
.
The above-mentioned motor control device for an electric vehicle is incapable of suppressing the regenerative braking amount of the motor, presenting the following problems. As described above, in certain cases, the regenerative braking amount considerably increases and if the voltage of the storage battery
4
increases to exceed a maximum permissible voltage level, then the controller
3
, the driver circuit
2
and other component units will be damaged. Likewise, if the storage battery charging current increases to exceed a maximum permissible current level, then the storage battery
4
may be deteriorated or broken.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a motor control device for an electric vehicle which is capable of preventing a considerable increase in the regenerative braking amount, thereby protecting various component units from damage and also preventing the storage battery from being deteriorated or broken.
To this end, according to one aspect of the present invention, there is provided a motor control device for an electric vehicle which has a motor powered by a rechargeable battery, the motor control device comprising: voltage detecting means for detecting a voltage of the rechargeable battery; and regenerative braking amount control means for suppressing a regenerative braking amount of the motor by controlling the motor in such a manner that a voltage of the battery detected by the voltage detecting means stays at a predetermined voltage value or less at the time of regenerative braking of the motor.
With this arrangement, the regenerative braking amount control means serves to protect component units associated with the motor from damage which would otherwise be caused if a high voltage greater than the permissible maximum voltage is applied to the component units.
In accordance with another aspect of the invention, there is provided a motor control device for an electric vehicle which has a motor powered by a rechargeable battery, the motor control device comprising: current detecting means for detecting a charging current for the rechargeable battery; and regenerative braking amount control means for suppressing a regenerative braking amount of the motor by controlling the motor in such a manner that a charging current for the battery detected by the current detecting means stays at a predetermined current value or less at the time of regenerative braking of the motor.
With this arrangement, the regenerative braking amount control means serves to protect the battery from deterioration or breakage which would otherwise be caused if a large charging current greater than the permissible maximum current is supplied to the battery.
In a preferred from of the invention, the regenerative braking amount control means gradually decreases the regenerative braking amount at fixed intervals to control the regenerative braking amount. This serves to prevent a sudden decrease in the braking force of the vehicle.
In another preferred form of the invention, the regenerative braking amount control means decreases the regenerative braking amount in accordance with a deviation of an actual voltage of the battery from the predetermined voltage value. This serves to suppress the voltage of the battery so as not to exceed the predetermined voltage value in a reliable manner.
In a further preferred form of the invention, the regenerative braking amount control means decreases the regenerative braking amount in accordance with a deviation of an actual current of the battery from the predetermined current value. This serves to suppress the current of the battery so as not to exceed the predetermined current value.
Preferably, there may be provided means for notifying a driver of the vehicle of an operating condition of the motor.
Preferably, the motor is frequency-, voltage-, current-, or power-controlled.
REFERENCES:
patent: 3657625 (1972-04-01), Miller et al.
patent: 3735220 (1973-05-01), Renner et al.
patent: 4554999 (1985-11-01), Kamaike
patent: 4787021 (1988-11-01), Hokari et al.
patent: 5359308 (1994-10-01), Sun et al.
Mitsubishi Denki & Kabushiki Kaisha
Sughrue Mion Zinn Macpeak & Seas, PLLC
Wysocki Jonathan
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