Apparatus and method for protecting a motor control circuit

• US 4,691,149 A
• Filed: 10/11/1985
• Issued: 09/01/1987
• Est. Priority Date: 10/11/1985
• Status: Expired due to Fees

• Current Assignee: Caterpillar Industrial Incorporated Mentor Ohio
• Original Assignee: Caterpillar Incorporated
• Inventors: Pickering, William, Baumgartner, Kenneth A.
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): Keane, Patrick C.
• Application Number:
  US06/786,580
• Time in Patent Office: 690 Days
• Field of Search: 318/331, 318/333, 318/563, 318/341, 361/88, 361/101, 361/90, 361/91, 361/92, 361/93, 361/1, 361/23, 361/63, 361/65, 361/18, 361/33, 307/240, 363/124
• US Class Current: 388/809
• CPC Class Codes: H02H 7/0833 for electric motors with control arrangements
• CPC Class Codes: H03K 17/0826 in bipolar transistor switches
• CPC Class Codes: Y10S 388/903 Protective, e.g. voltage or current limit
• CPC Class Codes: Y10S 388/92 Chopper

Abstract

Motor control circuits having solid-state switching elements are commonly used on industrial vehicles such as lift trucks. A short circuit condition in the motor circuit can cause catastrophic failure of the semiconductor switching element. The instant invention detects such a short circuit condition and modifies the motor control signals supplied by a chopper circuit to a switching element. The apparatus includes a trigger circuit for receiving the motor control signals and sensing a voltage across the motor produced in response to electrical power delivered from a power supply.

Claims

1. Apparatus for sensing a short circuit condition of a motor control circuit, comprising:

a battery having first and second battery poles;

a transistor having an emitter terminal, a base terminal, and a collector terminal connected to one of said battery first and second poles;

a motor having a first motor terminal connected to the other of said battery first and second poles, and a second motor terminal connected to said transistor emitter terminal;

chopper means for controllably producing motor control signals;

clock means for periodically producing a reset signal;

a first logic gate having a second input terminal, an output terminal, and a first input terminal connected to said transistor emitter terminal;

a latch having an output terminal, a first input terminal connected to said first logic gate output terminal, and a second input terminal connected to said clock means; and

a second logic gate having a first input terminal connected to said latch output terminal, a second input terminal connected to said chopper means, and an output terminal connected to said transistor base terminal and said first logic gate second input terminal.

2. Apparatus for sensing a short circuit condition of a motor control circuit, comprising

power supply means for providing a source of electrical power;

a motor connected across said power supply means;

chopper means for controllably producing motor control signals;

switch means for receiving said motor control signals and delivering electrical power from said power supply means to said motor in response to said received motor control signals, said switch means being serially connected between said motor and said power supply means;

means for sensing voltages across said motor produced in response to said delivered electrical power and producing voltage level signals in response to said sensed voltages;

trigger means for receiving each of said motor control signals and said voltage level signals, and controllably producing a trigger signal in response to receiving said motor control signals and failing to receive said voltage level signals;

clock means for periodically producing a reset signal; and

inhibit means for controllably modifying said motor control signals in response to receiving said trigger signal; and

wherein said trigger means includes a first logic gate having a first input terminal connected to the junction of said switch means and said motor, a second input terminal connected to said inhibit means, and an output terminal, and said inhibit means includes a latch having a first input terminal connected to said first logic gate output terminal, a second input terminal connected to said clock means, and an output terminal, and a second logic gate, having a first input terminal, connected to said latch output terminal, a second input terminal connected to said chopper means, and an output terminal connected to said switch means and said first logic gate second input terminal.

3. Apparatus for sensing a short circuit condition of a motor control circuit, comprising:

power supply means for providing a source of electrical power;

a motor connected across said power supply means;

chopper means for controllably producing motor control signals;

switch means for receiving said motor control signals and delivering electrical power from said power supply means to said motor in response to said received motor control signals, said switch means being serially connected between said motor and said power supply means;

means for sensing voltages across said motor produced in response to said delivered electrical power and producing voltage level signals in response to said sensed voltages;

trigger means for receiving each of said motor control signals and said voltage level signals and controllably producing a trigger signal in response to receiving said motor control signals and failing to receive said voltage level signals;

clock means for periodically producing a reset signal; and

inhibit means for controllably modifying said motor control signals in response to receiving said trigger signal; and

wherein said trigger means includes a first logic gate having a first input terminal connected to the junction of said switch means and said motor, a second input terminal connected to said inhibit means, and an output terminal, and said inhibit means includes a latch having a first input terminal connected to said first logic gate output terminal, a second input terminal connected to said clock means, and an output terminal, and a second logic gate, having a first input terminal, connected to said latch output terminal, a second input terminal connected to said chopper means, and an output terminal connected to said switch means and said first logic gate second input terminal, and wherein said inhibit means ceases to modify said motor control signals in response to receiving said clock signal in the absence of said trigger signal.