Vehicle Propulsion Control Apparatus and Method

The present application is related to a patent application Ser. No. 902,001 now U.S. Pat. No. 4,282,466 that was filed Apr. 27, 1978 by T. C. Matty and entitled Transit Vehicle Motor Effort Control Apparatus and Method, which is assigned to the same assignee and the disclosure of which is incorporated herein by reference.

In an article entitled Alternative Systems For Rapid Transit Propulsion And Electrical Braking, published in the Westinghouse Engineer for March, 1973, at pages 34-41, there is described a thyristor chopper control system for propulsion and electrical braking of transit vehicles. The thyristor chopper provides a propulsion system that is superior in smoothness and ease of maintaining a given speed, which latter feature is desired for automatic train control.

It is known in the prior art to operate a vehicle propulsion motor with a programmed microprocessor controlling a chopper that determines the average current of that motor as described in the above cross referenced patent application and in U.S. Pat. No. 4,095,153 of T. C. Matty, et al.

It is known in the prior art to provide a slipslide control system for a vehicle, such as a transit car, as described in an article published in The Westinghouse Engineer for September, 1970 at pages 143-149, wherein once a pair of wheels is slipping or sliding then corrective action is taken to reduce the tractive or braking effort applied to the axle to permit those wheels to regain the speed equivalent to train speed. The desired tractive or braking effort is then reapplied.

U.S. Pat. No. 3,069,606 discloses the utilization of an auxiliary field for a DC traction motor arranged in a bridge circuit and operative with a train vehicle to respond to differences in the speeds of selected motors to limit the motor speed for protecting a motor against excessive voltage and excessive speed.

U.S. Pat. No. 3,783,339 discloses the provision of two tachometers coupled with a moving vehicle, such that the output of a first tachometer leads the signal provided by the second when the vehicle is traveling forward and the output of the second tachometer leads the signal provided by the first when the vehicle is traveling in a reverse direction, for the purpose of controlling the movement of the vehicle.

In response to a sensed predetermined difference between the speeds of the wheels of a moving vehicle, as determined by respective tachometers coupled with the vehicle wheels, when a loss of tractive effort occurs, the propulsion motor currents are reduced and then reapplied at one or more adaptively controlled rates in accodance with the level of tractive effort at which that loss occurred for minimizing the resulting lost tractive effort time product.

FIG. 1 functionally shows a prior art propulsion motor control apparatus in relation to input signals and output signals operative with the motor control apparatus.

FIG. 2 illustrates the operation of the prior art slip/slide control apparatus;

FIG. 3 shows a side view of a prior art transit vehicle operative with a roadway track;

FIG. 4 shows a bottom view of a prior art transit vehicle including a speed sensing tachometer coupled with each motor driven wheel and axle assembly;

FIG. 5 schematically illustrates the prior art slip/slide control operation for propulsion motor control apparatus in accordance with the signal operation of FIG. 1;

FIG. 6 schematically illustrates the present slip/slide control operation for propulsion motor control apparatus including the provision of the plurality of wheel speed signals to the slip/slide brake blend controller; and

FIG. 7 illustrates a modified operation of the present slip/slide control apparatus; and

FIG. 8 illustrates another modification of the present slip/slide control apparatus.

In FIG. 1 there is shown a functional illustration of the prior art vehicle motor control apparatus in relation to the input signals and the output signals generally operative therewith, and including a CPU microprocessor 94 operative with a PROM programmable memory 96 and a scratch pad RAM random access memory 98 used for intermediate storage. An application control program, such as the program listing included in the Appendix, is stored in the programmable memory 96. The microprocessor 94 can be an INTEL 8080, the random access memory 98 can be an INTEL 8108, and the programmable memory 96 can be an INTEL 1702 programmable read only memory, which items are currently available in the open marketplace. There are four illustrated general categories of input and output signals relative to the processor controlled operation of a transit vehicle. The digital input signals are supplied through digital input 100 from the transit vehicle and include the slip/slide signal SLIP, the thyristor temperature sensor thermal overload signal THOUL, and the one or more power circuit condition indication signals LCOC. The analog input signals are supplied through analog input 102 and include the first propulsion motor leg current I1, the second propulsion motor leg current I2, the line current IL, the line voltage LV, the primary power request or brake request control signal P, the mode request signal BRK, the air pressure in the vehicle support bag members providing load weighed current request signal IRW, the analog phase signal IP and the vehicle actual speed signal S. The digital output signals are supplied through digital output 104 to the controlled transit vehicle and include the line switch control signal LS, the power brake mode control signal P/B, the field shunt control signal FS, the first braking resistor control signal BC1, the second braking resistor control signal BC2, the third braking resistor control signal BC3, the fourth braking resistor control signal BC4, the phase zero control signal .phi..sub.o, the timing signal BOOST, the ON suppress control signal SUPP and the zero speed signal ZS. The analog output current request signal I+ is supplied through analog output 106 going to an analog phase controller 108, which is operative to supply the control signal ON to fire the chopper thyristor T1, the control signal OFF to fire the commutating chopper thyristor T2, the control signal T5 for the T5 thyristor in the propulsion motor control chopper apparatus, the thyristor control signal T6 and the analog phase indication signal IP going to analog input 102. The time period associated with turning the chopper ON and OFF is at a constant frequency of 283 Hz, that defines the clock time interval for the program cycle and for checking the process operation. During each of the 283 time intervals per second, the program cycle operates through the application program. It was necessary in the prior art for some of the input signals to be filtered to slow down the effects of noise transients and the like, but the computer program now samples the input signals 283 times every second, so if desired each signal can be checked during each program cycle and if the signal stays the same as it was before the proper response can be provided.

The master controller provides a tractive effort request to the train control system operative with each vehicle, and provides a P signal which selects a desired propulsion effort. This signal goes from 0 to 100 milliamps and establishes how much propulsion power or braking effort is desired by a particular train vehicle. The P signal is decoded to determine the proper motor current to generate the proper tractive effort. In addition, there is a confirming signal, called the BRK signal which determines when the propulsion power and when braking effort is applied. The purpose of the BRK signal is to control the power switching at the correct time to avoid one car braking while another car is in propulsion. Contact closures in the power circuitry are detected to establish that the power contacts have been made up properly and to readjust the settings in the logic. For instance, in field shunt operation, the amount of motor current is adjusted to keep from getting an undesired physical jerk of the vehicle. A failsafe reading of the P signal level is made such that, should the P signal be lost, the train control automatically goes into a brake mode. The prior art propulsion control apparatus determines which switches to close and when to close them to modify the power circuit properly. A dynamic brake feedback signal DBFB is sent to the mechanical brake control from the analog output 106 for providing the blending of mechanical brake necessary to maintain the deceleration level required by the P signal. The P signal is in reality a vehicle acceleration or deceleration request.

The propulsion control apparatus shown in FIG. 1 provides output pulses to the main power thyristors to tell them when to turn ON and when to turn OFF. When a command signal is sensed, for example, if the vehicle is in propulsion or power mode and the command signal desires the vehicle to brake, the control apparatus senses any difference between the desired motor current and the actual motor current and ramps down the actual current as required. When the current gets down to a desired level, the control apparatus opens all the propulsion switches and reconnects for a brake operation, then ramps the motor current back up again to the level established by the desired brake operation.

The prior art propulsion motor control apparatus of FIG. 2 has a power circuit 24 which includes the power supply 26 connected through the relay operated line switch 28 to the chopper and line filter 30. The motor control apparatus 14 controls the line switch 28 with the signal LS, and the status of the line switch is fed back through the indication signal LCOC to the motor control apparatus 14. The power supply 26 can have a nominal rating of 750 volts, but can vary above 900 volts and down to about 450 volts. During motor braking, regeneration is determined as a function of filter capacitor voltage. At above 975 volts the line switch opens. The line reactor 32 operates to smooth out current changes. The motor control box 34 is utilized to set up the motor circuit in either power or brake and to adjust the braking resistors during brake. The motor reactor 36 then connects with the propulsion motor 16.

The power and brake signal generator 38 provides an output tractive effort controlling P signal to the motor control apparatus 14 in response to a tractive effort request signal 40 from the operator's master controller 42. The front end controls 44 are provided to enable or disable the generator 38 in response to inputs, such as an overspeed condition to clamp the P signal to a low level value. The motor current apparatus 14 provides a feedback output signal DBFB indicative of the level of electric dynamic braking effort, as determined by sensed motor currents in the brake mode of operation. The load weight sensor 48 provides an input signal to the motor control apparatus 14 in accordance with the weight of the vehicle.

In FIGS. 1 and 2 there is shown a prior art motor control apparatus coupled with the vehicle carried motor and brake control apparatus components as well known to persons skilled in the art. Four tachometers T.sub.1, T.sub.2, T.sub.3 and T.sub.4 are shown in FIG. 2, which are respectively coupled with the four drive motors and support wheel axles of the vehicle. The slip/slide brake blend controller 55 , which can be a well known Westinghouse Air Brake Co. Model F2 Unit, Part No. 585819 and shown by drawing EA 8515-51, that is presently available in the open market, responds to the speed signal from each of the tachometers T.sub.1, T.sub.2, T.sub.3 and T.sub.4 to sense a predetermined difference between any two of the provided speed signals to establish that one of a slip or a slide operational condition of the vehicle is occurring. A slip occurs during acceleration and a slide occurs during braking of the vehicle. The slip/slide controller 55 provides an output 10 for controlling the pneumatic brake apparatus 12 of the vehicle and provides a signal SLIP to the digital input of the motor control apparatus 14 for removing the tractive effort provided by the propulsion motors of the vehicle, which are schematically shown as motors 16, 18, 20 and 22 in FIG. 2. It should be understood that a power circuit, similar to the illustrated power circuit 24, is also provided for each of the motors 18, 20 and 22 and operative with the motor control apparatus 14. The brake apparatus 12 can include tread brakes operative with the outside of the vehicle wheels and responsive to changes in controlling air pressure as determined by the slip/slide controller SS. The slip/slide controller SS provided signal SLIP to the digital input of the motor control apparatus 14, depending upon whether the vehicle is in power or brake mode, causes the motor control apparatus 14 to back off on the current to the motors 16, 18, 20 and 22 and then reapply that motor current at a predetermined jerk-limited rate.

The prior art motor control arrangement shown in FIGS. 1 and 2 is commercially in use at the present time as part of the east-west line of the Sao Paulo Brazil Metro, which is discussed in an article published in the Conference Record of the IAS Annual Meeting of the IEEE Industry Applications Society for October 1977, at pages 1105-1109.

In FIG. 3 there is shown a prior art transit vehicle 45 operative with a roadway track 47. When the vehicle 45 is operating under conditions of limited adhesion between the wheels 49 and the roadway track 47, it is the prior art practice to sense this condition in relation to a predetermined difference in selected wheel speeds and to remove the tractive effort applied through the wheels and then reapply this tractive effort at a constant jerk limited rate such as 2 miles per hour per second that was used for normal operation of the vehicle. If an adhesion limit were again reached, the tractive effort would be removed and then reapplied at the same normal rate. This was repeatedly done until the adhesion limit problem no longer occurred.

In FIG. 4 there is illustrated one prior art arrangement of the drive motors 16, 18, 20 and 22 coupled with respective axles and wheel units 50, 52, 54 and 56. The motor control apparatus 14 carried by the vehicle 58 responds to two or more of the respective motor speed signals S1, S2, S3 and S4, preferably with at least one from each end of the vehicle.

In FIG. 5 there is shown a plot of acceleration rate versus time to illustrate the prior art slip/slide control of vehicle propulsion motors. In response to the P signal, a jerk limited application of tractive effort is applied to the vehicle by the motors 16, 18, 20 and 22 at a rate such as 2 miles per hour per second in accordance with curve section 62. When a slip or slide condition is sensed, which occurs when the adhesion limit 60 is reached, the signal SLIP is activated by the controller 55 and is supplied to the motor control apparatus. The applied tractive effort, is then removed to zero in accordance with curve section 64. The tractive effort is then reapplied at the same rate in accordance with curve section 66 until the adhesion limit is reached at location Y on the curve 60, where the tractive effort again goes to zero in accordance with curve section 68. This operation is repeated until the adhesion limit condition shown by curve 60 discontinues such that the applied tractive effort at the same constant jerk rate of curve section 70 increases up to the requested acceleration rate shown by curve 72. If there were no more slip conditions, the applied tractive effort would then level off in accordance with the curve 72. The tractive effort force applied to the vehicle can be determined by multiplying the acceleration rate times the mass of the vehicle.

In FIG. 6 there is shown the here provided tractive effort control operation in accordance with the present invention. The applied tractive effort as shown by curve section 80 is removed to zero as shown by curve section 84 if a particular wheel-axle unit such as unit 52 shown in FIG. 3 is sensed to be slipping at location A on the adhesion limit curve. The CPU 94 shown in FIG. 1 within the motor control 14 shown in FIG. 2, is programmed to remember in storage the value of the tractive effort at location A on adhesion limit curve 82, and then adaptively controls the rate or rates at which tractive effort is reapplied in order to minimize and reduce the resulting lost tractive effort time product.

Included in the appendix A is a program listing operative with an Intel 8080 microprocessor 94 to provide the slip/slide responsive tractive effort control of vehicle motors in accordance with the present invention as shown in FIG. 6. In the program TER is the tractive effort request and TERJ is the jerk limited tractive effort request signal that determines the output current request signal I+ that is supplied to the analog phase controller within the motor control apparatus 14 for determining the control signal T1 to fire the chopper main thyristor ON, the control signal T2 to fire the commutating thyristor ON and turn OFF the main thyristor and the control signal T5 for the turn ON of the dynamic brake thyristor, as shown in the above referenced published article in the Westinghouse Engineer for March 1973. In the program TERJS corresponds with the location A shown in FIG. 6 where the adhesion limit is reached and the wheel-axle unit slips or slides depending on operation in power or brake mode. The value of the tractive effort TERJS establishes the break point shown as location B in FIG. 6 which governs the rate at which the tractive effort is reapplied. For example the tractive effort increase rate in accordance with curve section 86 can be the same as the tractive effort increase rate or vehicle acceleration of about 2 MPHPS of curve section 80. At B, which is about 0.825 of the tractive effort at location A, the vehicle acceleration rate shown by curve section 87 is selected to be more gradual such as 1 MPHPS in power and 0.5 MPHPS in brake in an effort to avoid another loss of adhesion condition and keep the vehicle moving along the roadway track. If the adhesion limit curve 82 is again reached at tractive effort C, then the tractive effort applied to the vehicle is removed as shown by curve section 88. The tractive effort is then again applied to the vehicle in accordance with curve section 90 at a higher than normal rate such as 2.25 MPHPS until a tractive effort known to be a predetermined fraction such as 0.825 times the last known adhesion limit C has been reached. The acceleration in accordance with curve section 92 is then followed, such as 0.5 MPHPS in power and 0.25 MPHPS in brake, in an effort to avoid another loss of adhesion. This operation is repeated until the adhesion limit 82 no longer is present.

It is desired that the blank area shown in FIG. 6 under the curve 82 and without cross hatching should be maximized, since tractive effort is being applied in relation to this blank area under the curve 82.

When the microprocessor 94 in response to the signal SLIP determines that there is a loss of adhesion in relation to curve 82 shown in FIG. 6, the level of tractive effort at which the loss occurred, such as successively location A, then B, then C, then D, etc., is remembered. A subsequent brake point or knee, such as B, which can typically be about 0.825 times A, is used to delineate the following two jerk limited rates at which tractive effort is reapplied and is set on the basis of the previous remembered adhesion limit. If this is the first loss of adhesion at location A since the requested level of tractive effort was obtained, values are set for: Jerk Limited RATE 1 of about 2 MPHPS which is applied up to the knee B and jerk limited RATE 2 of about 1 MPHPS in power and 0.5 MPHPS in brake which is applied after the knee B. RATE 1 can be set higher such as 3 MPHPS in power than the normal jerk rate of about 2 MPHPS in power shown by curve Section 80 and RATE 2 is typically lower, such as 1 MPHPS in power and 0.5 MPHPS in brake, than the normal jerk rate in order to maximize the blank area under the desired tractive effort versus time curve 81.

If adhesion is lost again before the requested level of tractive effort shown by curve 81 is achieved, the microprocessor 94 again remembers the adhesion limit level of tractive effort, sets the level of the following knee and removes tractive effort. This time, RATE 1 and RATE 2 are modified in order to increase the blank area under the desired tractive effort versus time curve 81. To accomplish this, RATE 1 is increased and RATE 2 is decreased. This process continues repeatedly until the requested level of tractive effort as shown by curve 81 is achieved.

In FIG. 7, there is illustrated the operation of the program listing included in Appendix B, which is operative with the microprocessor 94 to provide a doubling of the acceleration rate for each of predetermined time intervals that occur after a previous slip or slide and without another slip or slide condition, as sensed by the slip/slide brake blend controller SS. For example, in FIG. 7, there is shown a previous loss of adhesion at location R, and the tractive effort is removed as shown by curve section 200. The tractive effort is again applied as shown by curve section 202 until location S, which can be 0.825 times R, has been reached. Then a lower acceleration as shown by curve section 204 is followed for a predetermined time period, such as 3 seconds and assuming no slip or slide condition is detected. At location T, the acceleration rate of curve section 204 is doubled to determine the acceleration rate of curve section 206. Then after this same time period, if no slip or slide condition is detected, at location U the acceleration rate is again doubled for curve section 208. This same operation is repeated for up to five such time periods without sensing another slip or slide condition, when the vehicle acceleration rate goes back to the original normal rate, such as 2 MPHPS up to the desired tractive effort shown by curve 81.

In FIG. 8 there is shown a modification of the present invention as provided with the operation of the program listing included in Appendix C to additionally minimize the lost tractive effort time product, as represented by the cross hatched areas under the requested level of tractive effort as shown by curve 81. When a loss of adhesion is sensed by the slip/slide brake blend controller 55 for a given wheel-axle unit, such as occurs at location G on the adhesive limit curve 82, the microprocessor 94 remembers the level of tractive effort at location G and removes tractive effort as shown by curve section 94 to a tractive effort level H which has a predetermined relationship with tractive effort level G, such as one-half. Then tractive effort is reapplied in accordance with curve section 96 until knee I where the rate of tractive effort application is lowered, such as previously described in relation to FIG. 7. This operation repeatedly continues as shown in FIG. 7 until the requested level of tractive effort as shown by curve 81 is achieved.

In each of Appendix A, B and C, there is included an instruction program listing that has been prepared to control the operation of the here disclosed propulsion control apparatus and method. The instruction program listing is written in the assembly language of the Intel 8080 microprocessor. Many of these microprocessors have already been supplied to customers, including technical instruction and descriptive documentation to explain to persons skilled in this art the operation of the microprocessor apparatus. These instruction program listings are included to provide an illustration of suitable embodiments of the present invention. These instruction program listings at the present time are more or less development programs and have not been extensively debugged through the course of practical operation for the real time propulsion control of a vehicle. It is well known by persons skilled in this art that most real time control application programs contain some minor bugs, and it usually takes varying periods of actual operation time to identify and routinely correct the more critical of these bugs.

In relation to the program listing included in the above cross referenced patent application, PI is TER and PO is TERJ of the program listings included in appendices A, B and C.