Lift truck control providing time delay in operation of directional contactor

• US 4,081,725 A
• Filed: 12/30/1975
• Issued: 03/28/1978
• Est. Priority Date: 12/30/1975
• Status: Expired due to Term

• Current Assignee: AC Material Handling Corporation
• Original Assignee: Allis-Chalmers Energy Incorporated (Archer Ltd.)
• Inventors: Gilmore, Thomas P., Schmidt, Harvey E., Henry, Luke F., Murphy, Howard G.
• Primary Examiner(s): Schaefer, Robert K.
• Assistant Examiner(s): Indyk, Eugene S.
• Application Number:
  US05/645,325
• Time in Patent Office: 819 Days
• Field of Search: 318/139, 318/447, 318/484, 317/13 R
• US Class Current: 318/139
• CPC Class Codes: H02H 7/0844 Fail safe control, e.g. by comparing control signal and controlled current, isolating motor on commutation error

Abstract

A chopper motor-controller for regulating a lift truck traction motor incorporates means for detecting faults which may cause the truck to run out of control, such as the high speed bypass contacts which shunt the semiconductor power switch being welded closed, and for disabling the controller in response thereto and also has time delay means for preventing a directional contactor from closing in on a fault before the fault detecting means can operate to disable the controller. The disclosed controller may alternatively be connected to require the operator to relax the accelerator foot pedal when starting or changing direction or to permit change of direction while the foot pedal is depressed.

Claims

1. In a vehicle driven by a reversible electric motor provided with a field winding and having a chopper controller for regulating the speed of said motor including a load current carrying semiconductor power switch in series with said motor and being switchable periodically from a nonconductive state to a conductive state and also including means controlled by a speed regulating member on said vehicle for selectively varying the average load current to said motor carried by said power switch;

forward and reverse directional contactors adapted when operated to connect said field winding in a direction so as to rotate said motor in the forward and reverse directions respectively,

a high speed contactor having a pair of normally open bypass contacts in shunt to said power switch, whereby said motor runs at full speed when said high speed contactor is operated,

means including a direction switch having forward and reverse positions for selectively completing energizing circuits to said forward and to said reverse contactors respectively and also having a neutral position between said forward and reverse positions in which both of said directional contactors are released,

time delay means in series with said direction switch and said forward and reverse contactors responsive to actuation of said direction switch to said forward position or to said reverse position for completing an energizing circuit to the selected directional contactor after a first predetermined time interval,

fault detection means for sensing closure of said bypass contacts for a second predetermined time interval, which is less than said first predetermined interval, and for disabling said chopper controller in response thereto,

means responsive to operation of said speed regulating member to adjacent its maximum speed position for disabling said fault detecting means and for operating said high speed contactor,

said time delay means being set to its initial condition and said fault detection means being disabled when said direction switch is in said neutral position and said fault detection means being enabled when said direction switch is operated to either said forward position or to said reverse position, and

sequence-of-operation controlling means for preventing operation of either directional contactor if said speed regulating member is away from its minimum speed position at the instant said direction switch is actuated from said neutral position to either said forward position or to said reverse position and wherein said sequence-of-operation controlling means includes a pair of normally closed contacts connected in said directional contactor energizing circuits and which are opened when said speed regulating member is away from its minimum speed position and prevent subsequent operation of either directional contactor, in response to actuation of said direction switch between said forward and reverse positions, until said speed regulating member is at its minimum speed position, and wherein said sequence-of-operation controlling means also includes a pair of contacts in series with said time delay means and said directional contactors which contacts are open when said speed regulating member is at its minimum speed position and are closed to complete said directional contactor energizing circuits when said speed regulating member is partially operated.

2. In a vehicle driven by a reversible electric motor provided with a field winding and having means including a triggerable load current carrying semiconductor power switch in series with said motor and being switchable periodically between a nonconductive state and a conductive state and also having means including a foot pedal on said vehicle for selectively varying the average load current supplied by said power switch to said motor to thereby control the speed thereof,

forward and reverse directional contactors arranged when operated to connect said field winding in a direction to rotate said motor in the forward and in the reverse direction respectively,

a high speed contactor having a pair of normally open bypass contacts in shunt to said power switch, whereby said motor runs at full speed when said high speed contactor is operated,

direction switch means having forward and reverse positions for selectively operating said forward and reverse contactors respectively and also having a neutral position therebetween in which both of said directional contactors are released,

time delay means in series with said direction switch means and said directional contactors responsive to actuation of said direction switch means to said forward position or to said reverse position for completing an energizing circuit to the selected directional contactor after a first predetermined time interval,

fault sensing means for detecting either when said bypass contacts are closed for a second predetermined time interval, which is less than said first predetermined interval, or when said power switch fails to pulse for said second predetermined interval, and for removing electrical power from said directional contactors in response thereto,

means responsive to operation of either of said directional contactors for applying a train of triggering pulses to said power switch,

switch means responsive to depression of said foot pedal to adjacent its maximum speed position for disabling said fault detecting means and said triggering pulse applying means and for operating said high speed contactor,

said fault sensing means being disabled and said time delay means being reset when said direction switch means is in said neutral position and being enabled when said direction switch means is operated to said forward position or to said reverse position, and

sequence-of-operation controlling means including a pair of normally closed foot switch contacts controlled by said foot pedal and connected in series with the operating coils of both said directional contactors for preventing operation of either directional contactor when said foot pedal is depressed at the instant said direction switch means is actuated from said neutral position to either said forward position or to said reverse position, and wherein said sequence-of-operation controlling means also includes a pair of normally open foot switch contacts controlled by said foot pedal and arranged in series relation with said normally closed foot switch contacts and also with the operating coils of both said directional contactors, and a control relay having a operating coil, a pair of normally closed contacts in series with said operating coil and said normally closed foot switch contacts and a pair of normally open contacts in shunt to said normally closed foot switch contacts.

3. In combination with a vehicle driven by an electric motor and having a chopper controller for regulating motor speed including a semiconductor power switch in series with said motor and means controlled by a foot pedal for selectively varying the average current supplied by said power switch to said motor,

forward and reverse directional contactors adapted when operated to connect said motor to rotate in the forward and in the reverse directions respectively,

direction switch means having forward and reverse positions for selectively completing energizing circuits to said forward and to said reverse directional contactors respectively,

time delay means in series with said direction switch means and said directional contactors responsive to actuation of said direction switch means to said forward position or to said reverse position to complete an energizing circuit to the selected directional contactor after a first predetermined time delay,

a high speed contactor having a pair of normally open bypass contacts in shunt to said power switch,

fault detecting means for sensing closure of said bypass contacts and for disabling said chopper controller in response thereto, said fault detecting means being enabled upon actuation of said direction switch means to said forward position or to said reverse position,

said direction switch means having a neutral position between said forward position and said reverse position in which said directional contactor energizing circuits are open and said time delay means is set to its initial condition and said fault detecting means is disabled,

means responsive to depression of said foot pedal to adjacent its full speed position for operating said high speed contactor and for disabling said fault detecting means, whereby said directional contactors cannot close in on a fault which might cause said vehicle to run out of control before said fault detecting means disables said chopper controller, and

sequence-of-operation controlling means including a switch operated by said foot pedal and having a pair of normally closed contacts connected in said energizing circuits to said directional contactors for preventing operation of said directional contactors if said foot pedal is depressed when said direction switch means is actuated from said neutral position to said forward position or to said reverse position, and wherein said switch also has a pair of normally open contacts (FS2) connected in said directional contactor energizing circuits in series with said time delay means (TD) and with said pair of normally closed contacts (FS1), and wherein said sequence-of-operation controlling means also includes control relay means (CR) responsive to operation of said direction switch means (DS) to said forward position (F'"'"') or to said reverse position (R'"'"') at a time when said normally closed contacts (FS1) are engaged for completing an electrical path (CR2) in shunt to said pair of normally closed contacts (FS1), whereby said control relay means (CR) cannot be operated unless said foot pedal (FS) is relaxed and said directional contactors cannot operate until said control relay means (CR) is operated and said foot pedal (FS) is subsequently depressed to close said pair of normally open contacts (FS2).

4. In combination with a vehicle driven by an electric motor and having a chopper controller for regulating motor speed including a semiconductor power switch in series with said motor and means controlled by a foot pedal for selectively varying the average current supplied by said power switch to said motor,

forward and reverse directional contactors adapted when operated to connect said motor to rotate in the forward and in the reverse directions respectively,

direction switch means having forward and reverse positions for selectively completing energizing circuits to said forward and to said reverse directional contactors respectively,

time delay means in series with said direction switch means and said directional contactors responsive to actuation of said direction switch means to said forward position or to said reverse position to complete an energizing circuit to the selected directional contactor after a first predetermined time delay,

a high speed contactor having a pair of normally open bypass contacts in shunt to said power switch,

fault detecting means for sensing closure of said bypass contacts and for disabling said chopper controller in response thereto, said fault detecting means being enabled upon actuation of said direction switch means to said forward position or to said reverse position,

said direction switch means having a neutral position between said forward position and said reverse position in which said directional contactor energizing circuits are open and said time delay means is set to its initial condition and said fault detecting means is disabled,

means responsive to depression of said foot pedal to adjacent its full speed position for operating said high speed contactor and for disabling said fault detecting means, whereby said directional contactors cannot close in on a fault which might cause said vehicle to run out of control before said fault detecting means disables said chopper controller, and

sequence-of-operation controlling means including a switch operated by said foot pedal and having a pair of normally closed contacts connected in said energizing circuits to said directional contactors for preventing operation of said directional contactors if said foot pedal is depressed when said direction switch means is actuated from said neutral position to said forward position or to said reverse position, and wherein said direction switch means is adapted, when a low impedance (S1) is connected in shunt to said pair of normally closed contacts (FS1), to release one directional contactor and operate the other, even though said foot pedal (FS) is depressed, when said direction switch means (DS) is operated between said forward (F'"'"') and reverse (R'"'"') positions.

5. In the combination of claim 4 wherein said switch also has a pair of normally open contacts (FS2) connected in said directional contactor energizing circuits in series with said time delay means (TD) and said pair of normally closed contacts (FS1), whereby relaxation of said foot pedal (FS) from said high speed position when said pair of normally closed contacts (FS1) have said low impedance shunt (S1) will reset said time delay means (TD) and release said directional contactor and permit said fault detecting means (FD) to operate if said bypass contacts (1A1) are shorted.

6. In a vehicle driven by a reversible electric motor provided with a field winding and having a chopper controller for regulating the speed of said motor including a load current carrying semiconductor power switch in series with said motor and being switchable periodically from a nonconductive state to a conductive state and also including means controlled by a speed regulating member on said vehicle for selectively varying the average load current to said motor carried by said power switch;

forward and reverse directional contactors adapted when operated to connect said field winding in a direction so as to rotate said motor in the forward and reverse directions respectively,

a high speed contactor having a pair of normally open bypass contacts in shunt to said power switch, whereby said motor runs at full speed when said high speed contactor is operated,

means including a direction switch having forward and reverse positions for selectively completing energizing circuits to said forward and to said reverse contactors respectively and also having a neutral position between said forward and reverse positions in which both of said directional contactors are released,

time delay means in series with said direction switch and said forward and reverse contactors responsive to actuation of said direction switch to said forward position or to said reverse position for completing an energizing circuit to the selected directional contactor after a first pedetermined time interval,

fault detection means for sensing closure of said bypass contacts for a second predetermined time interval, which is less than said first predetermined interval, and for disabling said chopper controller in response thereto,

means responsive to operation of said speed regulating member to adjacent its maximum speed position for disabling said fault detecting means and for operating said high speed contactor,

said time delay means being set to its initial condition and said fault detection means being disabled when said direction switch is in said neutral position and said fault detection means being enabled when said direction switch is operated to either said forward position or to said reverse position, and

sequence-of-operation controlling means for preventing operation of either directional contactor if said speed regulating member is away from its minimum speed position at the instant said direction switch is actuated from said neutral position to either said forward position or to said reverse position, said sequence-of-operation controlling means including a pair of normally closed contacts connected in said directional contactor energizing circuits and which are opened when said speed regulating member is away from its minimum speed position and prevent subsequent operation of either directional contactor, in response to actuation of said direction switch between said forward and reverse positions, until said speed regulating member is at its minimum speed position, and wherein said means for selectively completing energizing circuits to said forward and reverse contacts is adapted, when a low impedance is connected in shunt to said pair of normally closed contacts, to release one directional contactor and operate the other, even though said speed regulating member is away from said minimum speed position, when said direction switch is operated between said forward and reverse positions and through said neutral position.