Power supply circuit and method for a motor vehicle electrical accessory load

• US 20030184935A1
• Filed: 03/28/2002
• Published: 10/02/2003
• Est. Priority Date: 03/28/2002
• Status: Active Grant

• Current Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Original Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Inventors: Enzinna, Donald John, Vetter, Stephan Michael
• Granted Patent: US 6,917,502 B2
• Time in Patent Office: Days
• US Class Current: 361/72
• CPC Class Codes: H02J 7/0032 disconnection of loads if battery is not under charge, e.g. in vehicle if engine is not running

Abstract

An improved circuit supplies electrical power to a vehicle accessory load, such as a load that is powered through a vehicle accessory load connector or cigarette lighter plug. The circuit utilizes battery voltage comparator and timer switching circuitry to interrupt the supply of power to the accessory load if the engine-driven alternator fails to charge the storage battery for at least a predefined time interval (i.e., when the vehicle engine is not running), and to automatically re-establish electrical power supply to the load when battery charging resumes (i.e., when engine operation resumes).

Claims

1. A power supply circuit for an accessory load of a motor vehicle including a storage battery and an engine driven mechanism coupled to the storage battery for producing supplemental electrical energy during engine operation, the power supply circuit comprising:

a switch mechanism having a first state in which the accessory load is connected to the storage battery, and a second state in which the accessory load is disconnected from the storage battery;

comparator means for measuring a terminal voltage of the storage battery and comparing the measured voltage to a reference voltage that is higher than a nominal open-circuit terminal voltage of the battery but lower than a minimum voltage produced by the engine driven mechanism during engine operation; and

a timer circuit responsive to the comparison of the measured voltage to the reference voltage for establishing the state of said switch mechanism such that the first state of the switch mechanism is established whenever the measured voltage exceeds the reference voltage, and the second state of the switch mechanism is established when the measured voltage is below the reference voltage for at least a predefined time interval.

2. The power supply circuit of claim 1, wherein the second state of the switch mechanism is established to disconnect the accessory load from the storage battery whenever an output of the timer circuit is active, and wherein the comparator means prevents said output from being active whenever the measured voltage exceeds the reference voltage.

3. The power supply circuit of claim 2, wherein the output of the timer circuit is produced by a counter that receives and counts clock pulses produced by a pulse generator, and such output becomes active when the pulse count reaches a reference count corresponding to said predefined time interval.

4. The power supply circuit of claim 3, wherein said comparator means continuously resets the pulse count of said counter whenever the measured voltage exceeds the reference voltage.

5. The power supply circuit of claim 1, wherein the vehicle includes an accessory load connector, the power supply circuit is connected to the accessory load connector, and the accessory load is connected to the power supply circuit.

6. A method of supplying electrical power to an accessory load of a motor vehicle including a storage battery and an engine driven mechanism coupled to the storage battery for producing supplemental electrical energy during engine operation, the control method comprising the steps of:

measuring a terminal voltage of the storage battery;

comparing the measured voltage to a reference voltage that is higher than a nominal open-circuit terminal voltage of the battery but lower than a minimum voltage produced by the engine driven mechanism during engine operation; and

connecting the accessory load to the storage battery whenever the measured voltage exceeds the reference voltage, and disconnecting the accessory load from the storage battery when the measured voltage is below the reference voltage for at least a predefined time interval.