Electricity: motive power systems – Motor-reversing – Automatic and/or with time-delay means
Patent
1982-12-30
1985-01-29
Dobeck, B.
Electricity: motive power systems
Motor-reversing
Automatic and/or with time-delay means
318291, 318293, 318300, H02P 312
Patent
active
044968884
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a control system for a d.c. motor.
BACKGROUND ART
Control systems have previously been proposed for electric vehicle motors in which there are interlocks between various driver operable controls and control devices in the control system to prevent damage to the system. For example, one such interlock may be provided to prevent a control device in the form of a contactor controlling the connection of the motor for reverse and forward motoring from being operated except when the vehicle is at rest. Such an interlock, which will be referred to hereinafter as "a speed interlock", necessitates the provision of means determining whether or not the vehicle is in motion.
In the previous proposals the control system has included a speed transducer which is used both for providing logic signals for use in the speed interlock functions and for providing analog signals for the control system. The speed transducer was a mechanical device driven by the traction motor and producing a pulse train, the frequency of which was proportional to speed. Such a transducer added considerably to the cost and complication of the control system and, being a mechanical device, required maintenance.
It is an object of the invention to provide a control system for an electric vehicle traction motor incorporating at least one speed interlock function but no mechanical speed transducer.
DISCLOSURE OF INVENTION
In accordance with the invention there is provided a control system for a d.c. motor comprising control means for varying the connections of the motor armature winding and/or field winding so as to enable the motor to operate in a plurality of different modes, and speed interlock means for preventing operation of said control means to change the motor connections from at least one mode to at least one other mode whilst the motor is running characterised in that said interlock means is sensitive to the voltage across the armature winding of the motor and means are provided for supplying a field current to the field winding when said interlock means is required to be operative.
Thus, when a change over from forward drive to reverse drive is demanded, for example, the speed interlock means will be required to be operative at a time when the field and armature currents would otherwise be zero. When it is required for the speed interlock means to be operative a current pulse is applied to the field winding. If the motor is at rest the voltage across the armature winding will be zero. If, on the other hand, the motor is running, a voltage signal will be generated by the motor which signal is detected and used to prevent the change-over.
Alternatively it can be arranged for the field current to have a predetermined minimum level below which it is never allowed to fall.
BRIEF DESCRIPTION OF DRAWINGS
An example of the invention as applied to an electrical vehicle d.c. traction motor control system is shown in the accompanying drawings in which,
FIG. 1 is a block diagram of the armature and field winding current controls,
FIG. 2 is a block diagram of a logic circuit associated with the circuit of FIG. 1,
FIG. 3 is an electrical circuit diagram of the armature current control portion of FIG. 1,
FIG. 4 is an electrical circuit diagram of an armature chopper circuit and current signal generator circuit forming part of FIG. 1,
FIG. 5 is an electrical circuit diagram of a field current control circuit portion of FIG. 1,
FIG. 6 is an electrical circuit diagram of a field chopper circuit forming part of FIG. 1, and
FIGS. 7a, 7b and 7c together make up the electrical circuit diagram of the logic circuit of FIG. 2.
BEST MODE OF CARRYING OUT THE INVENTION
Referring firstly to FIG. 1, the armature current control makes use of an armature chopper circuit 10 which is shown in detail in FIG. 4. Three thyristor drive circuits 11, 12, 13 control the chopper circuit 10, these drive circuits deriving their input from a Schmitt bistable circuit 14. This Schmitt bistable circuit 14 receives its input from a
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Dobeck B.
Lucas Industries Limited
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