Electricity: battery or capacitor charging or discharging – One cell or battery charges another – Vehicle battery charging
Reexamination Certificate
2000-09-21
2001-10-16
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
One cell or battery charges another
Vehicle battery charging
Reexamination Certificate
active
06304056
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application is related to co-pending U.S. Patent application Ser. No. 09/667,196 entitled “Pulsed Charge Starter/Alternator Control System” filed Sep. 21, 2000 and U.S. Patent Application Ser. No. 09/666,582 entitled “Power Delivery Circuit With Boost For Energetic Starting In A Pulsed Charge Starter/Alternator System” filed Sep. 21, 2000 both of which are incorporated herein by reference and commonly owned by the assignee of the present invention.
BACKGROUND
The present invention relates to electrical systems for motor vehicles and more particularly, to a pulsed charge power delivery circuit for a vehicle having a combined starter/alternator.
Combined starter/alternators such as those known in the art are disclosed in U.S. Pat. Nos. 4,720,638; 4,916,345; 5,001,412; 5,097,140 and 5,469,820. A combined starter/alternator as used in a motor vehicle can be used as a motor to crank and start the engine as well as a generator to provide electrical power to the vehicle electrical systems. When operated as a starter motor, the starter/alternator is supplied with current from the battery and is operated to rotate the engine crankshaft. The engine crankshaft is rotated until the engine fires and continues to run on its own power. When used as a generator, the running engine is coupled to the starter/alternator which, in turn, produces a three-phase output that is rectified to a steady state DC output that is used to maintain the charge on the vehicle energy storage device to meet the vehicle electrical load requirements.
When operating as a generator, the efficiency of the starter/alternator is defined as the ratio of the input power to the output power. Such generators have both fixed and variable losses. Some of these losses are associated with the switching circuitry such as the inverter used to rectify the output of the generator. There are three primary classifications of losses: mechanical losses, electrical losses, and magnetic losses. Mechanical losses are primarily due to the rotation of the rotor and include bearing friction loss and windage loss. Magnetic losses include eddy current-current loss and hysteresis loss. All of these losses can be grouped into two categories, namely, fixed losses and variable losses. Fixed losses are losses that do not change with load when the machine is operating at a known speed. Therefore, rotational losses are one part of fixed losses. In the case of a wound field machine where the field current is required to set up the required flux in the machine, the power supplied to the field lining is also considered a fixed loss. On the other hand, variable losses are losses that vary with the load current. All of the copper or resistive losses are included in this category. Since the losses associated with the starter/alternator when operating as a generator are only partially load dependent, the system exhibits low efficiencies at low power levels. At higher output power levels, the output power rises relative to the losses and correspondingly, the system efficiency rises as well. This continues up to a peak efficiency torque point whereafter additional torque input into the generator does not result in a significant increase in power output and, hence, the efficiency falls off.
It has been found that operating a starter/alternator at a continuous power output approximately equal to the vehicle electrical load demand such as 500 W is a low efficiency output for a typical starter/alternator. Accordingly, there is a need for a starter/alternator control system having increased efficiency.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an improved pulsed charge power delivery circuit for a starter/alternator system. It is another object of the invention to provide a pulsed charge power delivery circuit for a starter/alternator system having improved efficiency.
According to the present invention, the foregoing and other objects are attained by a method of charging a primary energy storage device in a vehicle including a secondary energy storage device and an engine coupled to a combined starter/alternator. The method comprises the steps of operating the starter/alternator as a generator at approximately a peak efficiency value, and electrically connecting the starter/alternator and the secondary energy storage device for a first predetermined period of time such that the starter/alternator charges the secondary energy storage device. Once the secondary energy storage device reaches a desired charge value, the starter/alternator and the secondary energy storage device are disconnected. The method also electrically connects the primary and secondary energy storage devices such that the secondary energy storage device charges the primary energy storage device. This continues until the charge on the secondary energy storage device reaches a minimum charge value, at which time, the starter/alternator is again operated at a peak efficiency value and connected to the secondary energy storage device. In this way, the starter/alternator pulse-charges the secondary energy storage device which, in turn, maintains the desired charge on the primary energy storage device. Alternatively, the primary and secondary energy storage devices can be continuously electrically connected.
One advantage of the present invention is that it has improved efficiency as compared to conventional starter/alternator charging systems. Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.
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Degner Michael W
Gale Allan Roy
Tamor Michael Alan
Ford Global Technologies Inc.
Stec Jennifer
Tso Edward H.
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