Thyristor motor control circuit

Claim 2

A control system for an electric traction motor of a batterypowered vehicle, comprising, in combination: a first thyristor connected in series with said motor and contacts of a first contactor means across a battery; means for controlling the duty cycle of said first thyristor; first timing circuit means responsive to a first enabling signal and operative to provide an output pulse after a predetermined time delay; operatorcontrolled switch means for connecting an operating coil of said first contactor means in series with a second thyristor across said battery and for applying said first enabling signal tO said first timing circuit, said output pulse from said first timing circuit being connected to turn on said second thyristor; and detection circuit means connected between said first thyristor and said first timing circuit for preventing said timing circuit from responding to said enabling signal if said first thyristor is shorted.

Claim 3

A system according to claim 1 wherein said first timing circuit comprises a capacitor charging circuit connected to fire a unijunction transistor to provide said output pulse, and wherein said detection circuit means comprises diode means connected to divert said enabling signal to prevent capacitor charging if said first thyristor is shorted.

Claim 4

A system according to claim 1 having a relaxation oscillator connected to fire a third thyristor to turn off said second thyristor, and means responsive to said detection means for enabling said oscillator while said first thyristor is turned on and for resetting said oscillator as said first thyristor is turned off, whereby said oscillator is prevented from firing said third thyristor each time said first thyristor is turned off within a predetermined time after being turned on.

Claim 5

A system according to claim 1 wherein said first timing circuit means comprises a capacitor having a first terminal connected to one terminal of said battery and a second terminal connected to receive said first enabling signal, one terminal of said first thyristor being connected to said one terminal of said battery, and wherein said detection circuit means comprises resistance means connected to said capacitor through a first diode to discharge said capacitor upon conduction of said first diode, second diode means normally biasing said first diode to conduction, and a third diode connected between said second diode and a second terminal of said first thyristor to cut off said first diode when said first thyristor is conductive.

Claim 6

A system according to claim 1 having means responsive to conduction of said first thyristor for turning off said second thyristor if a conduction period of said first thyristor exceeds a predetermined duration, and in which said first timing circuit means may provide a further output pulse to re-fire said second thyristor to re-energize said operating coil.

Claim 7

A system according to claim 2 having normally-open contacts of a by-pass contactor connected to by-pass said first thyristor; a second timing circuit responsive to a second enabling signal and operative to provide an output pulse after a predetermined time delay; said operator-controlled switch means being operable to connect the operating coil of said by-pass contactor in series with a third thyristor across said battery and to apply a second enabling signal to said second timing circuit; and wherein said detection circuit means is connected to allow said capacitor charging circuit to repetitively charge and fire said unijunction transistor if said first thyristor is failed open; and means responsive to firing of said unijunction transistor for preventing said second enabling signal from enabling said second timing circuit.

Claim 8

A system according to claim 3 having means responsive to a predetermined position of said operator-controlled switch means for energizing a by-pass contactor to by-pass said first thyristor, and means responsive to movement of said switch means to said predetermined position for disabling said oscillator.

Claim 9

A system according to claim 3 having circuit means interconnecting said third thyristor and said first timing circuit means whereby firing of said third thyristor disables said first timing circuit means and prevents said second thyristor from being turned on.

Claim 10

A system according to claim 8 wherein said circuit means includes switch means interconnecting said third thyristor and said first timing circuit means, said switch means being operable between a first position in which firing of said third thyristor disables said first timing circuit means to prevent said second thyristor from being Turned on, and a second position in which after said third thyristor has been turned on said first timing circuit means may re-fire said second thyristor to re-energize said operating coil of said first contactor means and turn off said third thyristor.

Claim 11

A control system for an electric traction motor of a battery-powered vehicle, comprising, in combination: a first thyristor connected in series with said motor and contacts of a first contactor means across a battery; means for controlling the duty cycle of said first thyristor; cyclically-operable first timing circuit means responsive to a first enabling signal and operative to provide an output pulse after a predetermined time delay; operator-controlled switch means for connecting an operating coil of said first contactor means in series with a second thyristor across said battery and for applying said first enabling signal to said first timing circuit, said output pulse from said first timing circuit being connected to turn on said second thyristor; and means responsive to conduction of said first thyristor for preventing said first timing circuit from providing output pulses, whereby said operating coil of said first contactor will not be energized if said first thyristor is shorted, said first timing circuit means will provide one output pulse to fire said second thyristor if said first thyristor is operable and turns on and off, and said first timing circuit means will provide repeated output pulses if said first thyristor is failed open.

Claim 12

A control system for an electric traction motor of a battery-powered vehicle, comprising, in combination: a first thyristor connected in series with said motor and contacts of a first contactor means across a battery; means for controlling the duty cycle of said first thyristor; cyclically-operable first timing circuit means responsive to a first enabling signal and operative to provide an output pulse after a predetermined time delay; operator-controlled switch means for connecting an operating coil of said first contactor means in series with a second thyristor across said battery and for applying said first enabling signal to said first timing circuit, said output pulse from said first timing circuit being connected to turn on said second thyristor; and means responsive to conduction of said first thyristor for preventing said first timing circuit from providing output pulses, whereby said operating coil of said first contactor will not be energized if said first thyristor is shorted, said first timing circuit means will provide one output pulse to fire said second thyristor if said first thyristor is operable and turns on and off, and said first timing circuit means will provide repeated output pulses if said first thyristor is failed open.

Claim 13

A control system according to claim 10 having normally-open contacts of a by-pass contactor connected to by-pass said first thyristor, a second timing circuit normally operable after receipt of a second enabling signal from said operator-controlled switch means to energize the operating coil of said by-pass contactor, and means responsive to said repeated output pulses for preventing operation of said second timing circuit.

Claim 14

A control system for an electric traction motor of a battery-powered vehicle, comprising, in combination: electronic switching means connected in series with said motor across a battery; pulse generating means for controlling the duty cycle of said electronic switching means; an operator speed control; control means adjustable over a range of operation of said operator speed control for controlling said pulse generating means; a by-pass contactor means having an operating coil and having a pair of normally-open contacts connected in parallel with said electronic switching means; a first timing circuit means normally operable after receipt of a first enabling signal for a predetermined time to energize said operating coil of said by-pass contactor means to close said normally-open contacts; switch means operated by said operator speed control for applying said first enabling signal to said first timing circuit means when said operator speed control is adjusted to a predetermined position; and circuit means responsive to non-conduction of said electronic switching means for preventing said first timing circuit means from energizing said operating coil.

Claim 15

A control system for an electric traction motor of a battery-powered vehicle, comprising, in combination: electronic switching means connected in series with said motor across a battery; pulse generating means for controlling the duty cycle of said electronic switching means; an operator speed control; control means adjustable over a range of operation of said operator speed control for controlling said pulse generating means; a by-pass contactor means having an operating coil and having a pair of normally-open contacts connected in parallel with said electronic switching means; a first timing circuit means normally operable after receipt of a first enabling signal for a predetermined time to energize said operating coil of said by-pass contactor means to close said normally-open contacts; switch means operated by said operator speed control for applying said first enabling signal to said first timing circuit means when said operator speed control is adjusted to a predetermined position; and circuit means responsive to non-conduction of said electronic switching means for preventing said first timing circuit means from energizing said operating coil.

Claim 16

A system according to claim 12 wherein said first timing circuit means comprises an RC charging circuit connected to be charged by said first enabling signal, thyristor means connected in series with said operating coil across said battery, and means responsive to a predetermined charge level in said RC charging circuit for turning on said thyristor means to energize said operating coil, and wherein said circuit means comprises means operable upon non-conduction of said electronic switching means to discharge said charging circuit.

Claim 17

A system according to claim 12 in which said switch means is connected to apply said first enabling signal to said first timing circuit means through said operating coil, said first enabling signal being of insufficient magnitude to cause said operating coil to close said normally-open contacts.

Claim 18

A system according to claim 12 having contacTs of a directional contactor means connected in series with said motor and said electronic switching means, and wherein said circuit means comprises a second timing circuit operable to energize an operating coil of said directional contactor means.

Claim 19

A system according to claim 15 wherein said second timing circuit comprises a relaxation oscillator circuit operable during oscillation to prevent said first timing circuit from energizing said operating coil of said by-pass contactor means, and means responsive to conduction of said electronic switching means for preventing oscillation of said oscillator circuit.

Claim 20

In a control system for an electric traction motor of a battery-powered lift truck having electronic switching means and contacts of a directional contactor connected in series with said motor across a battery, and means for controlling the duty cycle of said electronic switching means, the combination of: a relaxation oscillator timing circuit operable after receipt of an enabling signal for a predetermined time to discharge and close a first electronic switch to energize an operating coil of said directional contactor, means responsive to conduction of said electronic switching means for preventing said enabling signal from re-operating said oscillator timing circuit, means responsive to conduction of said electronic switching means for a predetermined time interval for closing a second electronic switch, said first and second electronic switches being interconnected so that closure of one opens the other, whereby a system fault which causes said electronic switching means to conduct for said predetermined time each time it is caused to conduct will cause said directional contactor to be repeatedly opened and closed, thereby providing an audible signal to warn an operator of the presence of said fault, and whereby eventual disappearance of said fault while said motor is operating will terminate the repeated opening of said directional contactor and allow said motor to continue to operate without stopping.

Claim 21

In a control system for an electric traction motor of a battery-powered lift truck having electronic switching means and contacts of a directional contactor connected in series with said motor across a battery, and means for controlling the duty cycle of said electronic switching means, the combination of: a relaxation oscillator timing circuit operable after receipt of an enabling signal for a predetermined time to discharge and close a first electronic switch to energize an operating coil of said directional contactor, means responsive to conduction of said electronic switching means for preventing said enabling signal from re-operating said oscillator timing circuit, means responsive to conduction of said electronic switching means for a predetermined time interval for closing a second electronic switch, said first and second electronic switches being interconnected so that closure of one opens the other, whereby a system fault which causes said electronic switching means to conduct for said predetermined time each time it is caused to conduct will cause said directional contactor to be repeatedly opened and closed, thereby providing an audible signal to warn an operator of the presence of said fault, and whereby eventual disappearance of said fault while said motor is operating will terminate the repeated opening of said directional contactor and allow said motor to continue to operate without stopping.