Vehicle propulsion control apparatus and method

The propulsion control apparatus for a vehicle including a plurality of motor driven wheel units detects a slip or slide operation of at least one wheel unit in accordance with a predetermined difference between sensed motor currents, and reduces the tractive effort of those wheel units until the sensed motor currents no longer have that difference.

CROSS REFERENCE TO RELATED APPLICATION 
The present application is related to a patent application Ser. No. 
902,001, filed Apr. 27, 1978 and entitled "Transit Vehicle Motor Effort 
Control Apparatus and Method" by T. C. Matty, now issued as U.S. Pat. No. 
4,282,466, which is assigned to the same assignee and the disclosure of 
which is incorporated herein by reference. 
BACKGROUND OF THE INVENTION 
It is known in the prior art to control the speed of a vehicle propulsion 
direct current series motor by a chopper apparatus including a thyristor 
switch device in series with the motor. Speed control of the motor is 
provided by varying the width of the voltage pulses supplied to the motor 
such that the resulting average power supplied to the motor establishes 
the operational speed thereof. A commutation circuit including a charge 
capacitor has been used to provide a biased voltage across a conducting 
thyristor device for commutating the conduction of that thyristor device. 
A traction motor is operative in a motoring mode when the passenger 
vehicle is being propelled or accelerated along a track and in a brake 
mode when the vehicle is being stopped or decelerated. 
As described in a published article in the Westinghouse Engineer for March 
1973 at pages 34 through 41, the average voltage supplied to the motor 
armature is controlled by adjusting the ratio of chopper off time to the 
chopper on time, with the resulting average motor armature current 
determining the motor torque for moving the vehicle along a track. In the 
motoring or power mode of operation, the motors of a vehicle are connected 
by mechanical switches in relation to a direct current voltage source such 
that current is supplied through a chopper when the chopper is on and 
through the motors to ground. When the chopper is turned off, the energy 
stored in the motor reactor and the inductance of the motor field 
maintains current flow in the motor circuit through a free wheeling diode. 
In the brake or deceleration mode of operation, the motors in the prior 
art are reconnected by mechanical change-over switches with the motors 
operative as self-excited generators to provide dynamic or regenerative 
braking of the vehicle. With the chopper on, the motor current increases 
and with the chopper off, the motor current is forced into the power 
supply through the free-wheeling diode by the motor reactor. 
It is known in the prior art to provide a slip slide 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 to 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. 
SUMMARY OF THE INVENTION 
In a vehicle propulsion motor control apparatus, a plurality of DC series 
motors is coupled with respective wheel units of the vehicle and provided 
in a bridge circuit arrangement of those motors, with one current sensing 
device operative with a first branch of that bridge circuit and another 
current sensitive device operative with a second branch of that bridge 
circuit to sense the current in each armature leg of the bridge 
arrangement in relation to each of a motor mode and a brake mode of 
operation of those motors. The back EMF across each motor armature is 
proportional to RPM and the current of that motor. If the RPM of the 
respective motors in each branch circuit is the same, the motor current 
for each branch circuit will be the same. A control microprocessor senses 
any difference between the motor currents of the two branch circuits for 
detecting and controlling the slip or spin of any one or more wheel units 
in relation to the other wheel units of the vehicle.

DESCRIPTION OF A PREFERRED EMBODIMENT 
FIG. 1 shows a prior art motor control apparatus for a plurality of vehicle 
propulsion motors operative in the power mode. The motors are well known 
DC series motors each including an armature and a field winding, with the 
first and second motor armature A1 and A2 being connected in a first 
bridge circuit including the first and second motor field windings F1 and 
F2 while the third and fourth motor armatures A3 and A4 are connected in a 
second bridge circuit including the third and fourth motor field windings 
F3 and F4 such that the four motors are connected with two in series and 
the two groups of two motors being connected in parallel as determined by 
closing the mechanical switches 1, 2, 3 and 4 and by opening the 
mechanical switches 5 and 6. In the power mode, a chopper C is used to 
regulate the current in the motor circuit 10. Turning the chopper C on 
builds up currents in the motors by completing the circuit from the DC 
power supply 12 through the motors in the motor circuit 10 to ground. When 
the chopper C is turned off, the energy stored in the motor reactor MR and 
the inductance of the motors in the motor circuit 10 maintains current 
flow through the free-wheeling diode FWD. The operation of the chopper C 
in this regard is described in greater detail in the above-referenced 
published article in the Westinghouse Engineer for March 1973 and in the 
above cross-referenced application. 
The average voltage applied to the motors is controlled by adjusting the 
ratio of the off time to the ON time of the chopper C. This adjustment is 
made by the control apparatus 14 in response to the effort request P 
signal and the motor currents I1 and I2 from the current sensing 
transducers TD1 and TD2 for maintaining the desired average motor current 
and therefore the average motor torque. The chopper C switches at the 
normal cycle time frequency of approximately 218 Hz. 
FIG. 2 shows a prior art motor control apparatus for a plurality of vehicle 
propulsion motors operative in the brake mode. For the brake mode of 
operation, the motors are changed to the arrangement as shown in the motor 
circuit 16 of FIG. 2 by means of well-known power brake changeover 
mechanical switches B1, B2, B3, B4 and B5 in accordance with the 
above-referenced article in the Westinghouse Engineer for March 1973 and 
as shown in the above cross-referenced application. The circuit shown in 
FIG. 2 is arranged for regenerative or dynamic braking with the motors 
operative as self-excited generators. The fields are connected to force 
load division between the paralleled generators. In regenerative braking, 
the function of the chopper C is the same as is its function in the power 
mode with the on/off ratio being regulated to maintain the desired current 
and with the greater motor current providing the greater braking to the 
vehicle. When the chopper C is turned on, the current in the motor circuit 
16 increases. When the chopper C is turned off, the current flowing in the 
motor is forced back to the power supply 12 through the free-wheeling 
diode FWD by the motor reactor MR. The control apparatus 14 for logically 
controlling the operation of the chopper C during the brake mode also 
monitors the voltage 18 across the line filter capacitor FC and the line 
voltage 20 to control the chopper on/off ratio in response to the P signal 
in such a manner as to prevent the capacitor voltage 18 from exceeding the 
line voltage 20. When the capacitor voltage 18 approaches the line voltage 
20, the thyristor T5 is fired such that the generated current is then 
supplied through the dynamic braking resistor R5 as desired. 
In FIG. 3, there is shown a prior art transit vehicle 26 operative with a 
roadway track 28 and including wheel units 30, 32, 34 and 36. 
FIG. 4 shows an under-view of the vehicle 26 shown in FIG. 3 and includes a 
plurality of propulsion motors coupled with the respective wheel units, 
with the motor 38 being coupled with the wheel unit 30, the motor 40 being 
coupled with the wheel unit 32, the motor 42 being coupled with the wheel 
unit 34 and the motor 44 being coupled with the wheel unit 36. Motor 
control apparatus 46 is operative to control the operation of the 
respective propulsion motors 38, 40, 42 and 44. 
In FIG. 5, there is shown the motor control apparatus 46 shown in FIG. 4 to 
provide desired power and brake control of the propulsion motors 50 and 
the air brakes 52. An operator's console 54 is provided for the vehicle 
operator and which determines the tractive effort request from a P signal 
generator 56 operative with each of a microprocessor logic apparatus 58 
and a B3 brake control 60. The microprocessor logic apparatus 58 operates 
with the propulsion motor control circuits 50 shown in FIGS. 1 and 2. The 
B3 brake control is a well-known prior art brake control presently 
available from the Westinghouse Air Brake Company as Part No. 584631 for a 
single end car and as Part No. 585636 for a double end car. The 
microprocessor logic apparatus 58 determines the operation of propulsion 
motor circuits 50 which are operative with the motors 38, 40, 42 and 44 
shown in FIG. 4. The air brakes are well-known air brakes. 
FIG. 6 shows the prior art microprocessor logic apparatus 58 shown in FIG. 
5 such as described in the above cross-referenced application, which 
description is incorporated herein by reference. 
FIGS. 7A and 7B show a flow chart for the application program provided to 
derive a tractive effort request TER from the P signal for the 
microprocessor logic apparatus 58 of FIG. 5. The TER routine flow chart 
provides at step 150 a display output. At step 152, a check is made to see 
if the current request is greater than actual motor current plus 63 
amperes to see if substantially more current is being asked for than is 
actually being obtained. If so, something might be wrong, so at step 154, 
the TER and TER1 are set equal to 0. If the operation appears to be okay 
at step 152, at step 156, a check is made to see if the mode word 
indicates how the motor circuit, is set up such as in brake mode, in power 
mode or in neither. If it is neither and unconfirmed, the program goes to 
TER0 and at step 154, sets the indicated values to zero as before. If the 
motor circuit is set up at step 158, a check is made to see if there is a 
request for power or a request for brake. If power is requested, at step 
160 a check is made to see if the vehicle is in coast. If so, at step 154, 
TER and TER1 are set to zero. If the vehicle is not coasting, at step 162 
the P signal is checked to see if it is less than 65 milliamps, and if it 
is, at step 154, TER and TER1 are set to zero. If not, at step 164 the 
intermediate value P1 is set equal to AP, which is the P signal stored in 
RAM minus 65 milliamps. If the request was for brake at step 158, then at 
step 166 a check is made to see if the stored P signal AP is greater than 
55 milliamps and not in the brake range. If so, go to step 154 as before. 
If okay, at step 168 the intermediate value P1 is set equal to 55 
milliamps minus the stored P signal AP. At step 170, a check is made to 
see if P1 is less than or equal to 35 milliamps. If not, at step 172 P1 is 
set equal to 35 milliamps. In power the P signal should be from 65 to 100 
milliamps which is a difference of 35 milliamps, and in brake the P signal 
should be from 20 to 55 milliamps which is again a 35 milliamps 
difference. The program goes to step 174 where a check is made to see if 
the motor circuit is set up in power, and if so, at step 176 P2 is set 
equal to three times P1. If the motor circuit is in brake, at step 178 P2 
is set equal to 2.75 times P1. In power the vehicle has a 3 MPH per second 
maximum acceleration rate, and in brake the vehicle has a 2.75 MPH per 
second maximum deceleration rate. At step 180, TER1 is set equal to P2. 
Then limits are applied to P2 such as at step 182, if P2 is greater than 
TEL1, it is limited to TEL1 at step 184. At step 186 if P2 is greater than 
TEL3, at step 188 it is limited to TEL3. At step 190 if P2 is greater than 
TEL7, it is limited at step 192 to TEL7. The same checking and limiting is 
repeated at steps 194 and 196 for TEL9 at steps 198 and 200 for TEL10, the 
phase angle limit bit, at steps 202 and 204 for TEL11, at steps 206 and 
208 for TEL12, and at steps 210 and 212 for TEL13. AT step 214 the 
tractive effort request TER is set equal to P2. 
With the motor arrangement shown in FIG. 4, the vehicle 26 can be moving 
along the track 28 with the propulsion of only the motors 38 and 40 of the 
front truck or with the propulsion of only the motors 42 and 44 of the 
rear truck, when there is some operational problem with the motors of one 
of the trucks. In effect, a respective current transducer as shown in 
FIGS. 1 and 2 is provided to sense the motor current of each truck and to 
operationally check the wheel units of one truck in relation to the wheel 
units of the other truck. 
In the flow chart for the slip/slide application control program of the 
present invention shown in FIG. 8, at step 250 a check is made to see if 
both motor loops or branch circuits are in operation. If not, at step 252, 
the current difference IDIF is set to zero since this mode with the motors 
of one truck not operating does not permit detecting a slip or slide 
condition of the vehicle. If so, at step 254 a check is made to see if 
I1ADJ is greater than I2ADJ. The signal I1ADJ comes from transducer TD1, 
with a determined offset being subtracted from the actual current reading. 
The signal I2ADJ comes from the transducer TD2, with an offset subtracted. 
At one of steps 256 or 258, the smaller motor current is subtracted from 
the larger to give IDIF, the branch motor current difference. At step 260, 
a check is made to see if IDIF is greater than 50 amps, which would 
indicate that one wheel unit is slipping or sliding in relation to the 
other wheel unit and in relation to the adhesion level of the track on 
which the vehicle is operating. If it is, at step 262 the slip slide bit 
SS is set and a slip slide annunciator bit SSA is set in the RV output 
word. The slip slide bit SS goes to the B3 brake control 60 to indicate a 
slip/slide condition is detected and it is desired to back off on the air 
brake effort. The slip slide annunciator bit SSA turns on a light on the 
operator's console to indicate to the operator the detection of a slip or 
slide condition. At step 264, the tractive effort limit TEL9 is set equal 
to zero. At step 266, the flag bit in the TLRF word is set for 
troubleshooting and to find out which tractive effort limit is in effect. 
At step 268, the timer T9 is reset to zero. If there was not a current 
difference of 50 amps at step 260, at step 270, the tractive effort limit 
TEL9 is set up to the high value FF. At step 272, the flag bit in the TLRF 
word is cleared. At step 274, a check is made to see if the timer T9 has 
timed up to greater than 0.15 second. If it has, at step 276 the slip 
slide bit SS is reset and the slip slide annunciator bit SSA is reset in 
the RV output word. 
The actual tractive effort request is then determined in the TER program 
shown in FIGS. 7A and 7B. The P signal is converted to tractive effort 
request and then limits are applied in relation to TEL9 from the 
slip/slide program shown in FIG. 8. 
The control apparatus shown in FIG. 5 includes a control panel as part of 
the operator's console that determines the P signal and the brake signal 
on the line 57, which is actually a line for each of these signals. The 
microprocessor logic apparatus 58 responds to the P signal for determining 
the acceleration or deceleration rates to be provided by the propulsion 
motor control 50. 
If a wheel unit slip is detected in power or a wheel unit slide is detected 
in brake, the motor branch current difference IDIF will become greater 
than 50 amperes, and the limit TEL9 is set to the low value zero at step 
264 of the FIG. 8 program to result in P2 being set equal to TEL9 at step 
196 and then TER being set to P2 at step 214 of the FIGS. 7A and 7B 
program. 
As shown in FIG. 9, at time T1 the wheel starts to slip and the current 
difference IDIF shown by curve 280 begins to increase. At time T2 the 
current difference IDI exceeds 50 amps and TEL9 shown by curve 282 is set 
to zero, causing TERJ to start to decrease in a jerk limited manner which 
causes motor current shown by curve 286 to begin to decrease. At time T3 
the current difference is decreased to the point where IDIF no longer 
exceeds 50 amps, and TEL9 is set to FF again, allowing TERJ to start to 
increase, which causes IM to increase. At time T4 the current difference 
has increased to the point where IDIF exceeds 50 amps, and TEL 9 is again 
set to 00; causing TERJ to decrease and causing IM to decrease. The motor 
current will tend to oscillate around the adhesion level 290 at which the 
wheels would adhere to the rail. 
In brake operation, the P signal generator 56 provides a brake signal when 
the operator's console 54 establishes that the vehicle should be in the 
brake mode of operation. The setting of the slip/slide bit SS at step 262 
in conjunction with this brake signal from the P signal generator 56 
causes the B3 brake controller 60 to cut back on the braking effort in a 
manner similar to that shown in relation to the power operation in FIG. 9. 
The mechanical delays in the operation of the air brake system provide a 
similar time delayed oscillation of the vehicle substantially along the 
available wheel adhesion level in the brake mode of operation. 
In the control operation of the trolley vehicle shown in FIGS. 3 and 4, the 
input P signal becomes tractive effort request TER which is then jerk 
limited to TERJ and multiplied by weight adjust to give TERW representing 
the actual torque desired from the propulsion motors. The TERW signal 
determines the actual motor currents of the propulsion motors. A look-up 
table in the control CPU memory shown in FIG. 6 responds to the TERW input 
and determines the desired current request IR which is then output to the 
analog phase controller to establish the on/off duty cycle of the chopper 
for establishing the desired average motor current. 
As shown in FIGS. 1 and 2, a current transducer TD1 and TD2 are provided in 
each motor branch path to give I1 and I2 which are compared to see if they 
are equal. If they are equal, this indicates no slip or slide condition. 
If these currents are not equal, then a determination is made to establish 
which one is greater, and the smaller is subtracted from the larger with 
the difference being stored in the microprocessor memory. A check is made 
to see if this difference is greater than a predetermined amount, such as 
50 amperes. If it is, the vehicle is considered to be in a slip or a slide 
mode of operation and the tractive effort request TER is set to zero. This 
results in TERJ the jerk limit tractive effort request to begin ramping 
down and the weight adjusted tractive effort request TERW similarly begins 
to ramp down. In power operation, this will reduce the torque at all 
vehicle wheels that are trying to accelerate and will stop any tendency to 
spin of those wheels. Depending upon the track adhesion level, the torque 
will be lowered as shown in FIG. 9 until no wheel spin occurs. When the 
current differential for a cycle of the controlled microprocessor becomes 
less than 50 amperes, then the tractive effort request TER will go back up 
to the level established by the P signal until some later cycle when the 
current differential again becomes greater than 50 amperes. This cyclical 
operation can cause the jerk limited tractive effort request TERJ to 
reduce to a lower average value where the motor currents are such that no 
slip or slide condition causes the current differential to become greater 
than 50 amperes. 
The typical trolley vehicle also includes air operated mechanical brakes in 
addition to the electric brakes. The air brakes are released when a slip 
or slide condition is determined. In effect, a time delay is provided 
before the full release of the air brakes such that there can result in a 
cyclic on and off ramp adjustment of the average brake effort provided by 
the air brakes in a manner similar to the on and off adjustment of the 
effective electric brake effort that is provided by the propulsion motors. 
The phase angle is controlled by the on/off ratio of the chopper such that 
for 100% phase angle, the chopper is on all the time and for 0% phase 
angle, the chopper is off all the time. The current request IR from the 
microprocessor logic apparatus 58 causes the phase angle controller 108 to 
provide on and off firing pulses which control the respective motor 
currents. The motor currents I1 and I2 are read back into the control 
logic for each cycle of control CPU 94 operation to determine if the 
tractive effort request TER should or should not be set to zero for the 
next cycle of operation. 
The equation describing the armature back EMF is: 
EQU V.sub.emf =K.phi..omega. 
where .phi. is the flux of the motor field windings, .omega. is the 
rotational speed of the motor, and K is a proportionality constant. From 
this equation, it can be seen that if the rotational speed .omega. is 
increased due to a wheel slipping on ice or the like, then the back EMF of 
the armature would also increase which would decrease the voltage across 
the field winding. This would in turn decrease the current through the 
field. There are hall effect current transducers in each motor branch to 
sense the motor currents in each branch. There will normally be some small 
differences between the currents of each branch shown in FIGS. 1 and 2 due 
to the fact that no two motors are exactly the same. When the difference 
between these currents exceeds some predetermined amount such as 50 
amperes, the chopper will start to decrease its on/off ratio and begin 
lowering the chopper voltage. This will lower the current in the motor 
circuit branches until the difference between the branch currents 
approaches and stays at approximately 50 amperes and provide a restricted 
operation of the wheel units. It will maintain this restricted operation 
situation until the wheels get enough traction to stop spinning and then 
the P signal will determine the tractive effort request to establish the 
motor currents in accordance with normal and desired operation of the 
vehicle control apparatus. 
GENERAL DESCRIPTION OF INSTRUCTION PROGRAM LISTING 
In Appendix A and Appendix B, there are included instruction program 
listings that have been prepared to control a passenger vehicle in 
accordance with the here-disclosed control system and method and the 
respective flow charts shown in FIGS. 7 and 8. These instruction program 
listings are written in the assembly language of the Intel 8080 computer 
system. Many of these computer systems have already been supplied to 
customers, including customer instruction books and descriptive 
documentation to explain to persons skilled in this art the operation of 
the hardware logic and the executive software of this digital computer 
system. 
In relation to the program listing included in the above cross-referenced 
application PI is TER, PO is TERJ and PN is AP in relation to the program 
listings here included. 
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