Motor vehicles – Power – Electric
Reexamination Certificate
2000-02-14
2002-08-13
Johnson, Brian L. (Department: 3618)
Motor vehicles
Power
Electric
C180S065100, C180S065800
Reexamination Certificate
active
06431297
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for driving an electric car by inverter-controlled motors through a gear mechanism.
2. Description of the Prior Art
FIGS. 1A
,
1
B, and
2
show an apparatus for driving a car according to a prior art. The apparatus has a large gear
11
, a small gear
12
, an AC motor
13
, an inverter
14
, a filter reactor
15
, and a feeder system
16
. The large gear
11
is coaxial to and directly connected to a wheel shaft
10
and is mechanically arranged to mesh with the small gear
12
. The AC motor
13
generates torque, which is amplified at an amplification factor defined by a gear ratio of the small gear
12
and large gear
11
, thereby providing acceleration and deceleration force to drive the car. Also shown are a truck
9
and a smoothing capacitor
8
.
The problems of the prior art will be explained. To transmit large torque, each tooth of each gear must have a size (an area) larger than a predetermined value. Mechanical strength and a limited underfloor space restrict the maximum numbers of teeth of gears to restrict a maximum gear ratio. This puts limits on a torque amplification factor of gears and the speed of a motor. Namely, the prior art restricts the speed of the motor of the car driving apparatus, and therefore, is impossible to reduce the size, weight, and cost of the apparatus by using the merit of operating the motor at high speed.
Inverters used to supply electricity to motors for driving a car usually operate on an input DC voltage of about 1500 V. This voltage is extremely high compared with an input DC voltage of about 280 V for standard inverters. As a result, the inverters for cars cause a serious harmonic induction problem. In addition, the inverters for cars are designed according to special specifications, and therefore, involve high costs.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide an apparatus for driving and controlling a car, capable of increasing a gear ratio defined by small gears driven by AC motors and a large gear directly connected to a wheel shaft. The apparatus is small, light, and low-cost because it can operate the AC motors at high speed. The first object of the present invention is achieved by directly connecting a large gear to a wheel shaft, meshing the large gear with small gears, connecting the small gears to AC motors, and connecting the AC motors to AC sides of inverters, respectively. This arrangement distributes and reduces torque applied to the small gears, to decrease torque to be transmitted by each small gear. This enables the cross-sectional area of each tooth of each small gear to be reduced, thereby enabling a gear ratio defined by the gears to be increased.
A second object of the present invention is to provide an apparatus for driving a car, capable of reducing an input DC voltage for an inverter for driving an AC motor to a standard inverter level, minimizing the harmonic induction problem, and improving reliability by using low-cost, mass-produced standard inverters. The second object of the present invention is achieved by connecting small gears to AC motors, respectively, driving the AC motors by inverters, respectively, connecting the DC input sides of the inverters in series in multiple stages, and supplying power thereto from a high-voltage power source. This arrangement reduces an input DC voltage for each inverter to a standard inverter level.
More precisely, a first aspect of the present invention provides an apparatus for driving and controlling a car, having a large gear directly connected to a wheel shaft, small gears meshing with the large gear, AC motors connected to the small gears, respectively, and inverters connected to the AC motors, respectively, for supplying power thereto. The DC input sides of the inverters are connected in series. A positive terminal of one of the inverters arranged in the first stage and a negative terminal of one of the inverters arranged in the last stage are connected to a high-voltage DC power source.
This apparatus distributes torque to the small gears to drive the large gear that is directly connected to the wheel shaft. Each small gear bears small torque, and therefore, each tooth of each gear may have small mechanical strength. This means that the cross-sectional area of each tooth of each small gear may be reduced, the number of teeth of the large gear meshing with the small gears may be increased, a gear ratio defined by the small and large gears may be increased, and the size, weight, and cost of the apparatus may be reduced by operating the motors at high speed. DC input terminals of the inverters are connected in series to receive power from the high-voltage DC power source, while an input DC voltage to each inverter is dropped to a standard inverter level. This minimizes the harmonic induction problem. Since the apparatus may employ mass-produced standard inverters as they are, it is producible at low cost and high reliability.
Each of the inverters may have an inverter controller that receives a DC source voltage value detected on a power-source feeder line and an input voltage value detected at the inverter, finds a difference between the input voltage value and a quotient obtained by dividing the DC source voltage value by the number of the series-connected inverters, and corrects an output torque command for the inverter according to the difference. This arrangement suppresses a DC voltage imbalance caused by the individual differences of the series-connected inverters and prevents an input overvoltage to the inverters due to the DC voltage imbalance that may stop the apparatus.
Each of the inverters may have a short-circuit switch between the positive and negative DC input terminals thereof, to short-circuit the inverter if the inverter fails, so that the remaining inverters may continue to operate. Even if some inverters fail, this arrangement minimizes torque reduction and continues the operation of the car.
The apparatus may have a breaker for breaking the DC power to the DC input sides of the inverters, if at least one of the inverters fails so that the car must be operated with the remaining inverters, and at the same time, if the value of a DC source voltage exceeds the sum of allowable input DC voltage values of the remaining inverters. If some inverters fail so that the car must be operated with the remaining inverters, and at the same time, if a DC input overvoltage that is above the withstand voltage values of the remaining inverters is applied to the remaining inverters, the breaker opens to prevent the breakdown of the remaining inverters.
The apparatus may have an inverter controller for preparing an inverter output voltage command according to a composite value of output currents of the inverters so that the inverters may provide pulse patterns according to the same voltage command. This arrangement automatically equalizes DC voltage and continues the powering operation of the car without a special balance control of DC voltage.
A frame of each AC motor may electrically be short-circuited with a power source ground. The apparatus may have an inverter controller for providing a phase difference for a triangular wave that is used to form a PWM pulse pattern of each inverter. This arrangement minimizes a high-frequency leakage current to the ground due to the PWM switching of the inverters and maintains the quality of signals and communication.
The apparatus may have an inverter controller for each of the inverters, for calculating an output effective power value according to an input DC voltage value and an input DC current value both detected at the inverter, calculating an effective power command value according to a motor angular frequency and a torque command value related to the inverter, calculating a difference between the output effective power value and the effective power command value, and correcting the torque command value according to the difference. This arrangement suppresses an output torque imbal
Johnson Brian L.
Kabushiki Kaisha Toshiba
Shriver J. Allen
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