Electricity: motive power systems – Braking – Automatic and/or with time-delay means
Patent
1979-07-23
1982-08-31
Truhe, J. V.
Electricity: motive power systems
Braking
Automatic and/or with time-delay means
318341, H02P 516
Patent
active
043474675
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a control circuit for a d.c. motor.
BACKGROUND ART
Known circuits have often included means sensitive to the speed of the motor in the form of a transducer mechanically driven by the motor (or by the vehicle transmission). Generally speaking the transducer produces an a.c. signal which varies in frequency with the speed of the motor. Such a transducer is, however, considered to be an undesirably expensive component of the control system and it is an object of the invention to provide a control system of the general kind referred to in which no mechanical speed transducer is utilized.
DISCLOSURE OF INVENTION
In accordance with the present invention a d.c. motor control circuit includes a chopper circuit with a main switch element arranged to be turned on or off to control the supply of power to the motor and speed sensitive means including means sensitive to the ratio of the on and off times of the main switch element of the chopper circuit.
The invention is particularly, but not exclusively, applicable to control circuits of the known kind in which there is a motor current demand signal generator which generates a demand signal, a feedback circuit for producing a feedback signal corresponding to the actual motor current and means for switching the main switch element on when the feedback signal falls more than a set amount below the demand signal and for switching the main switch element off when the feedback signal rises more than a set amount above the demand signal. In such a circuit the speed sensitive means may provide an input to the demand signal generator to vary the demand signal independently of a demand input to the demand signal generator from a driver's accelerator pedal device or the like.
Where the motor is of the type having separate armature and field windings, it is known to provide a separate chopper circuit for the field winding, so as to enable the field current to be reduced when the vehicle speed reaches a level that the armature back e.m.f. becomes such that the demanded armature current cannot be achieved. In such a system the signal which is generated to control the reduction of field current may also be employed as a signal which is indicative of speed.
BRIEF DESCRIPTION OF DRAWINGS
An example of the invention is shown diagrammatically in the accompanying drawings in which:
FIG. 1 is a block diagram of the control system,
FIG. 2 is a circuit diagram of an armature chopper circuit included in FIG. 1,
FIG. 3 is a circuit diagram of a part of the control system of FIG. 1, and
FIGS. 4 to 6 are graphs showing the speed/maximum armature current characteristics of the control for forward motoring, braking and reverse motoring modes respectively.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring firstly to FIG. 1 the system, which is for the control of a d.c. traction motor, with separately excited field winding 10, makes use of an armature current chopper circuit 11 which controls the current flowing in the motor armature 12. A Hall-effect current sensing circuit 13 is used to produce a feedback signal corresponding to the actual current flowing in the armature.
As shown in FIG. 2 the chopper circuit 11 includes a main thyristor 14, a commutating thyristor 15 and a third thyristor 16. The thyristor 14 connects one terminal of the motor armature 12 to a negative supply rail 17 via a main fuse 18, the anode-cathode of the thyristor 14 being shunted by a resistor 19 and a capacitor 20. The other terminal of the armature 12 is connected via a contact 21 to a positive supply rail 22. This other terminal of the armature 12 is also connected by a diode 23 and fuse 24 in series to the rail 17 to provide a current path for armature current during braking i.e. when the contact 21 is open. A recirculation diode 25 connects the first-mentioned armature terminal to the rail 22 to provide a current recirculation path to carry continuing (but decaying) armature current when the thyristor 14 is not conducting.
The thyristor 15 has its anode connec
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Lucas Industries Limited
Moose Richard M.
Truhe J. V.
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