TRACTION MOTOR SPEED REGULATION FOR PROPULSION SYSTEMS PROVIDING SMOOTH STEPLESS CHANGES IN SPEED AND AUTOMATIC WHEEL SLIP CONTROL

• US 3,764,867 A
• Filed: 11/14/1972
• Issued: 10/09/1973
• Est. Priority Date: 11/14/1972
• Status: Expired due to Term

• Current Assignee: Russell M. Smith
• Original Assignee: Russell M. Smith
• Inventors: Smith, Russell M.
• Primary Examiner(s): Dobeck, B.
• Application Number:
  US05/306,411
• Time in Patent Office: 329 Days
• Field of Search: 318/52,79,109,111
• US Class Current: 318/52
• CPC Class Codes: B60L 2200/26 Rail vehicles
• CPC Class Codes: B60L 3/10 Indicating wheel slip ; Correction of wheel slip
• CPC Class Codes: H02P 5/685 electrically connected in series, i.e. carrying the same current
• CPC Class Codes: Y02T 10/64 Electric machine technologies in electromobility

Abstract

A traction motor tractive effort regulator for propulsion systems employing multiple series type direct current traction motors and providing smooth stepless changes in tractive effort together with automatic wheel slip control. Current controlling resistors are are connected in series circuit relationship with the respective serially connected field and armature windings of a string of serially connected traction motors across a main power source of direct current excitation. Main control switches are provided for variably controlling the value of the current controlling resistors connected in series, series-parallel and/or parallel circuit relationship with the traction motors for variably controlling the torque of the motors and hence the tractive effort of the vehicle. Means are provided for supplying a separate excitation source of direct current connected across the respective field windings of the direct current traction motors in parallel with and in addition to the excitation provided by the main power source. Ancillary control means are included for varying the magnitude of the separate direct current excitation supplied through the respective field windings independently of and in conjunction with the main current controlling resistors. The separate excitation source of direct current is connected across the respective field windings of the traction motor with a polarity such that the separate direct current excitation adds to the normal excitation direct current supplied from the main power source through the variable current control resistor, and the ancillary control means controls the magnitude of the separate direct current excitation supplied to the respective field windings in a manner to steplessly control the magnitude of the armature current and hence the tractive effort of the respective traction motors during each step change in value of the series current controlling resistors whereby smooth, stepless changes in torque of the traction motors can be achieved with the regulator. For this purpose current sensing devices are coupled to the respective traction motors for deriving an output indication of the tractive effort. The output indication of actual tractive effort is compared to an input reference signal in a suitable comparator which derives an output error command signal that controls operation of the ancillary control means. The ancillary control means in turn controls the magnitude of the separate direct current excitation supplied to the respective field windings independently of and complementary with the main current controlling resistors whereby smooth, stepless changes in motor torque are achieved. Additionally, wheel slippage detecting devices are provided for detecting slippage of the respective traction motors and deriving an output indication of such slippage. A wheel slip control circuit is responsive to the wheel slippage detector and is coupled to control the ancillary control means for the slipping traction motor so as to reduce the field current of the slipping motor, and thereby quickly reduce its tractive effort. Simultaneously, the wheel slip control circuit provides an increase in field current to the nonslipping traction motors so as to maintain the tractive effort of each nonslipping motor substantially constant by appropriately decreasing the armature current or at least preventing an increase in the armature current.

Claims

1. In a traction motor torque regulator for propulsion systems employing multiple series type direct current traction motors having the field and armature windings thereof connected in series electrical circuit relationship and with which smooth stepless changes in speed of operation of the traction motors is provided, the improvement comprising variable impedance means connected in series circuit relationship with the respective serially connected field and armature windings of the traction motors across a main power source of direct current excitation, main power control means for variably controlling the value of said variable impedance means to thereby variably control the torque of the direct current traction motors, means for supplying a separate excitation source of direct current connected across the respective field windings of the direct current traction motors in parallel with and in addition to the main power source, and ancillary control means for varying the magnitude of the separate direct current excitation supplied through the respective field windings independently of and in conjunction with the main power control means, the separate excitation source of direct current being connected across the respective field windings of the traction motors with a polarity such that the separate direct current excitation adds to the normal excitation direct current supplied to the respective field windings by the main power source through the variable impedance means and the ancillary control means controls the magnitude of the separate direct current excitation supplied to the respective field windings in a manner to control the armature current and hence the tractive effort of the respective traction motors whereby smooth stepless changes in speed of the traction motors can be achieved with the regulator.

2. A motor torque regulator according to claim 1 further including traction motor tractive effort sensing means coupled to the respective traction motors for deriving an output indication of the tractive effort thereof, means for generating an input command tractive effort reference signal representative of a desired command level of tractive effort, comparison means for comparing the input command tractive effort reference signal to the derived output indication of the measured actual tractive effort of the traction motors and deriving an output error control signal representative of any difference, and feedback means for coupling the output error control signal derived from said comparison means back to control operation of said ancillary control means for varying the magnitude of the separate direct current excitation supplied to the respective field windings independently of and complementary with the main speed control means whereby smooth stepless changes in the speed of the traction motors is achieved.

3. A motor torque regulator according to claim 1 further including wheel slippage detection means for detecting slippage of the respective series type direct current traction motors and deriving an output indication of any slippage, and wheel slip control means responsive to the wheel slippage detecting means and coupled to control the ancillary control means for the slipping traction motor to reduce the field current of the slipping motor and thereby quickly reduce the tractive effort of the slipping traction motor without a corresponding reduction in the tractive effort of the remaining series non-slipping traction motors.

4. A motor torque regulator according to claim 3 further including means comprising a part of the wheel slip control means for automatically controlling the ancillary control means for the respective non-slipping traction motors to increase the field current of the non-slipping motors in series with the slipping motor automaticaLly in response to the detection of a wheel slippage condition and thereby maintain the traction effort of the propulsion system.

5. A motor torque regulator according to claim 3 further including rate sensing and control means comprising a part of said wheel slip control means for controlling the reduction in field current of the slipping motor in accordance with the rate of slippage.

6. A motor torque regulator according to claim 2 further including wheel slippage detection means for detecting slippage of the respective series type direct current traction motors and deriving an output indication of any slippage, and wheel slip control means responsive to the wheel slippage detecting means and coupled to control the ancillary control means for the slipping traction motor to reduce the field current of the slipping motor and thereby quickly reduce the tractive effort of the slipping traction motor without a corresponding reduction in the tractive effort of the remaining series non-slipping traction motors.

7. A motor torque regulator according to claim 6 further including means comprising a part of the wheel slip control means for automatically controlling the ancillary control means for the respective non-slipping traction motors to increase the field current of the non-slipping motors in series with the slipping motor automatically in response to the detection of a wheel slippage condition and thereby maintain the traction effort of the propulsion system.

8. A motor torque regulator according to claim 7 further including rate sensing and control means comprising a part of said wheel slip control means for controlling the reduction in field current of the slipping motor in accordance with the rate of slippage.

9. A motor torque regulator according to claim 2 wherein said tractive effort sensing means comprises means for measuring the armature current of the respective traction motors, means for measuring the traction motors terminal voltage, and multiplier means responsive to the armature current measuring means and the traction motors terminal voltage measuring means for multiplying these two quantities and deriving an output indication of the actual measured tractive effort of the traction motors, and said means for generating an input command tractive effort reference signal comprises a function generator responsive to an input throttle command signal representative of the desired power commanded by an operator of the propulsion system, an input line voltage signal representative of the actual value of the main power direct current excitation voltage, and an input measured actual speed signal representative of the actual speed of the propulsion system, said function generator serving to combine these input parameters and deriving an output command tractive effort reference signal that is supplied to the comparison means.

10. A motor torque regulator according to claim 9 further including error signal comparison means responsive to the output from said first mentioned comparison means and to an input reference level error signal for deriving a second output torque controlling signal that is supplied to and controls operation of said main torque control means for variably controlling the value of said variable impedance means to thereby variably control the torque of the direct current traction motors.

11. A motor torque regulator according to claim 10 further including wheel slippage detection means for detecting slippage of the respective series type direct current traction motors and deriving an output indication of any slippage, and wheel slip control means responsive to the wheel slippage detecting means and coupled to control the ancillary control means for adjusting the value of the field current of a slipping motor in a direction to quickly reduce the tractive effort of a slipping traction motor without a corresponding reduction in the tractive effort of the remaining non-slipping traction motors.

12. A motor torque regulator according to claim 11 Further including means comprising a part of the wheel slip control means for automatically controlling the ancillary control means for the respective non-slipping traction motors to increase the field current of the non-slipping motors in series with the slipping motor automatically in response to the detection of a wheel slippage condition and thereby maintain the traction effort of the propulsion system.

13. A motor torque regulator according to claim 12 further including rate sensing and control for controlling the reduction in field current of the slipping motor and the increase in current of the non-slipping motor in accordance with the rate of slippage.

14. A motor torque regulator according to claim 12 wherein said wheel slip control means comprises comparison bridge measurement means responsive to the output from said wheel slippage detecting means for deriving an unbalance output control signal indicative of a slipping traction motor, means for supplying the unbalance output control signal thus derived directly from the comparison bridge means to the ancillary control means for varying the magnitude of the direct current excitation supplied to the respective field winding of a slipping motor in a direction to reduce field current of the slipping motor, and inverse current signal generating means responsive to the unbalance output control signal developed by the comparison bridge measurement means for supplying inverse actuating control signals to the ancillary control means for varying the magnitude of the direct current excitation supplied to the respective field windings of the non-slipping motors in a direction to increase the field current of the non-slipping motors, and wherein the wheel slippage detecting means comprises tachometer generators for measuring the speed of the traction motor armatures, voltage measuring reactors for measuring the traction motor armature voltages, and the like.

15. A motor torque regulator according to claim 14 further including rate responsive circuit means coupled to said comparison bridge measurement means for deriving an unbalance output control signal indicative of slippage in a traction motor which varies in accordance with the rate of wheel speed whereby corrective additional excitation current is supplied to the respective field windings of the slipping and the non-slipping traction motors according to the rate of wheel slippage.

16. A motor torque regulator according to claim 14 wherein the wheel slip control means comprises a diode comparison bridge and the wheel slippage detecting means comprises tachometer generators for measuring the speed of the respective traction motors, diode rectifier bridge means for the respective tachometer generators having one set of diagonally opposite terminals connected across a respective tachometer generator output and a remaining set of diagonally opposite terminals connected across a load resistor, all of the load resistors having one end thereof connected to one terminal of a low voltage direct current power source and having the remaining ends thereof connected through respective ancillary control means for varying the magnitude of the direct current excitation supplied to the respective field windings of the respective traction motors and serially through respective parallel connected resistor-diode coupling networks to the mid-tap point of a pair of serially connected diodes constituting arms of the diode comparison bridge, and amplifier means connected across the diode comparison bridge and supplied from the remaining terminal of the low voltage power source for feeding back an inverse polarity correction signal to the ancillary control means for the non-slipping motors for varying the magnitude of the direct current excitation supplied to the respective field windings of the non-slipping traction motors.

17. A motor torque regulator according to claim 16 further including rate responsive circuit means coupled to the respective diode bridge means and to the respectIve ancillary control means of the respective traction motors for deriving unbalance output control signals indicative of slippage in the traction motors which varies in accordance with the rate of wheel speed whereby corrective additional excitation current supplied to the field windings of the respective slipping and non-slipping traction motors is adjusted according to the rate of wheel slippage.

18. A motor torque regulator according to claim 14 wherein the wheel slip control means comprises a diode comparison bridge and the wheel slippage detecting means comprises a voltage measuring reactor for measuring the speed of the respective traction motors, diode rectifier bridge means for the respective voltage measuring reactors with one set of opposite terminals connected across a respective voltage measuring reactor output and a remaining set of diagonally opposite terminals connected across a load resistor, all of the load resistors having one end thereof connected to one terminal of a low voltage direct current power source and having the remaining ends thereof connected through respective ancillary control means for varying the magnitude of the direct current excitation supplied to the respective field windings of the respective traction motors and serially through respective parallel connected resistor-diode coupling networks to the mid-tap point of a pair of serially connected diodes constituting arms of the diode comparison bridge, and emitter-follower amplifier means connected across the diode comparison bridge and supplied from the remaining terminal of the low voltage power source for feeding back an inverse polarity correction signal to the ancillary control for varying the magnitude of the direct current excitation supplied to the respective field windings of the non-slipping traction motors.

19. A motor torque regulator according to claim 18 further including rate responsive circuit means coupled to the respective diode bridge means and to the respective ancillary control means of the respective traction motors for deriving unbalance output control signals indicative of slippage in the traction motors which varies in accordance with the rate of wheel speed whereby corrective additional excitation current supplied to the field windings of the respective slipping and non-slipping traction motors is adjusted according to the rate of wheel slippage.

20. A motor torque regulator according to claim 12 wherein the field windings of said series type direct current traction motors have fewer turns than otherwise normally are provided for similar motors of the same given rating and specifications whereby auxiliary excitation current is required under most conditions to provide rated tractive effort by the motors.

21. A motor torque regulator according to claim 4 wherein the field windings of said series type direct current traction motors have fewer turns than otherwise normally are provided for similar motors of the same given rating and specifications whereby auxiliary excitation current is required under most conditions to provide rated tractive effort by the motors.

22. A motor torque regulator according to claim 1 wherein the field windings of said series type direct current traction motors have fewer turns than otherwise normally are provided for similar motors of the same given rating and specifications whereby auxiliary excitation current is required under most conditions to provide rated tractive effort by the motors.