Inference-based manual pulldown control of an automatic transmission

A shift pattern control for a multiple speed ratio transmission wherein an inference-based control overrides the normal shift pattern to automatically achieve manual pulldown operation under conditions for which such operation would be advised and expected. The inference-based control is achieved with a fuzzy logic technique by which vehicle parameters influencing the desirability of manual pulldown operation are measured or estimated, and used to establish an aggregate measure of the overall need for engine braking and downshifting. In the preferred embodiment, the fuzzy logic parameters include vehicle speed, grade load, engine throttle position, time of braking and time of deceleration. The parameters are applied to membership functions to indicate the truthfulness of the specified conditions, and logical combinations of the truth indications are formed, weighted to reflect their criticality, and combined to form an aggregate measure of the overall need for pulldown operation.

This invention relates to speed ratio scheduling in a motor vehicle 
automatic transmission, and more particularly, to an inference-based 
override of the normal speed ratio schedule under conditions for which a 
manual pulldown would be suggested. 
BACKGROUND OF THE INVENTION 
Vehicles having automatic transmissions are typically equipped with a 
driver manipulated transmission range selector positionable to one of a 
number of sectors for indicating a desired operating range of the 
transmission. The forward operating range is defined by a Drive sector and 
one or more manual pulldown sectors corresponding to the various forward 
speed ranges provided by the transmission. 
To operate the vehicle in a forward range, the selector is ordinarily moved 
to the Drive sector, and the speed ratio selection is carried out 
automatically in accordance with an empirically determined shift pattern 
based on engine load (throttle position) and vehicle speed. For any given 
engine load, for example, the shift pattern may dictate a first vehicle 
speed above which an upshift should be initiated, and a second vehicle 
speed below which a downshift should be initiated. 
However, the predetermined shift pattern is not especially suited to 
operation in hilly terrain. During such operation, the driver is 
encouraged to move the range selector to a manual pulldown position. In 
addition to downshifting the transmission to the indicated speed ratio, 
the manual pulldown configures the transmission to enable engine braking 
and inhibits upshifting to a higher speed ratio. 
SUMMARY OF THE PRESENT INVENTION 
The present invention is directed to an improved shift pattern control for 
a multiple speed ratio transmission, wherein an inference-based control 
overrides the normal shift pattern to automatically achieve manual 
pulldown operation under conditions for which such operation would be 
advised and expected. 
The inference-based control is achieved with a fuzzy logic technique by 
which vehicle parameters influencing the desirability of manual pulldown 
operation are measured or estimated, and used to establish an aggregate 
measure of the overall need for engine braking and downshifting. In the 
preferred embodiment, the fuzzy logic parameters include vehicle speed, 
grade load, engine throttle position, time of braking, time of 
deceleration, and coast-acceleration time. The parameters are applied to 
membership functions to indicate the truthfulness of the specified 
conditions, and logical combinations of the truth indications--such as low 
vehicle speed and high negative grade load--are formed, weighted to 
reflect their criticality, and combined to form an aggregate measure of 
the overall need for pulldown operation. 
When the magnitude of the aggregate measure reaches predetermined 
thresholds, the control automatically initiates manual pulldown 
downshifting consistent with the severity of the driving conditions. When 
the driving conditions become less severe, the transmission is 
successively upshifted as the aggregate measure falls below the respective 
predetermined thresholds. The effect of the control is to automatically 
provide manual pulldown operation when and to an extent consistent with 
the vehicle operation. If the driver initiates a manual pulldown to a 
speed ratio lower than the inference-based speed ratio, the manual 
pulldown is given priority.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring particularly to FIGS. 1a and 1b, the reference numeral 10 
generally designates a motor vehicle drivetrain including an engine 12 and 
a parallel shaft transmission 14 having a reverse speed ratio and four 
forward speed ratios Engine 12 includes a throttle mechanism 16 
mechanically connected to an operator manipulated device, such as an 
accelerator pedal (not shown) for regulating engine output torque, such 
torque being applied to the transmission 14 through the engine output 
shaft 18. The transmission 14 transmits engine output torque to a pair of 
drive axles 20 and 22 through a torque converter 24 and one or more of the 
fluid operated clutching devices 26-34, such clutching devices being 
applied or released according to a predetermined schedule for establishing 
the desired transmission speed ratio. 
Referring now more particularly to the transmission 14, the impeller or 
input member 36 of the torque converter 24 is connected to be rotatably 
driven by the output shaft 18 of engine 12 through the input shell 38. The 
turbine or output member 40 of the torque converter 24 is rotatably driven 
by the impeller 36 by means of fluid transfer therebetween and is 
connected to rotatably drive the shaft 42. A stator member 44 redirects 
the fluid which couples the impeller 36 to the turbine 40, the stator 
being connected through a one-way device 46 to the housing of transmission 
14. 
The torque converter 24 also includes a clutching device 26, also referred 
to herein as the torque converter clutch or TCC, comprising a clutch plate 
50 connected to rotate with the turbine 40. The clutch plate 50 has a 
friction surface 52 formed thereon adaptable to be engaged with the inner 
surface of the input shell 38 to form a direct mechanical drive between 
the engine output shaft 18 and the transmission shaft 42. The clutch plate 
50 divides the space between input shell 38 and the turbine 40 into two 
fluid chambers: an apply chamber 54 and a release chamber 56. 
When the fluid pressure in the apply chamber 54 exceeds that in the release 
chamber 56, the friction surface 52 of clutch plate 50 is moved into 
engagement with the input shell 38 as shown in FIG. 1, thereby engaging 
the TCC 26 to provide a mechanical drive connection in parallel with the 
torque converter 24. When the fluid pressure in the release chamber 56 
exceeds that in the apply chamber 54, the friction surface 52 of the 
clutch plate 50 is moved out of engagement with the input shell 38 thereby 
uncoupling such mechanical drive connection and permitting slippage 
between the impeller 36 and the turbine 40. The circled numeral 5 
represents a fluid connection to the apply chamber 54 and the circled 
numeral 6 represents a fluid connection to the release chamber 56. A fluid 
exhaust line 55 returns fluid from the torque converter 24 to a cooler 
(not shown). 
A positive displacement hydraulic pump 60 is mechanically driven by the 
engine output shaft 18 through the input shell 38 and impeller 36, as 
indicated by the broken line 62. Pump 60 receives hydraulic fluid at low 
pressure from the fluid reservoir 64 and supplies pressurized fluid to the 
transmission control elements via output line 66. A pressure regulator 
valve (PRV) 68 is connected to the pump output line 66 and serves to 
regulate the fluid pressure (hereinafter referred to as line pressure) in 
line 66 by returning a controlled portion of the fluid therein to 
reservoir 64 via the line 70. In addition, pressure regulator valve 68 
supplies fluid pressure for the torque converter 24 via line 74. While the 
pump and pressure regulator valve designs are not critical to the present 
invention, a representative pump is disclosed in the Schuster U.S. Pat. 
No. 4,342,545 issued Aug. 3, 1982, and a representative pressure regulator 
valve is disclosed in the Vukovich U.S. Pat. No. 4,283,970 issued Aug. 18, 
1981, such patents being assigned to the assignee of the present 
invention. 
The transmission shaft 42 and a further transmission shaft 90 each have a 
plurality of gear elements rotatably supported thereon. The gear elements 
80-88 are supported on shaft 42 and the gear elements 92-102 are supported 
on shaft 90. The gear element 88 is rigidly connected to the shaft 42, and 
the gear elements 98 and 102 are rigidly connected to the shaft 90. Gear 
element 92 is connected to the shaft 90 via a freewheeler or one-way 
device 93. The gear elements 80, 84, 86 and 88 are maintained in meshing 
engagement with the gear elements 92, 96, 98 and 100, respectively, and 
the gear element 82 is coupled to the gear element 94 through a reverse 
idler gear 103. The shaft 90, in turn, is coupled to the drive axles 20 
and 22 through gear elements 102 and 104 and a conventional differential 
gear set (DG) 106. 
A dog clutch 108 is splined on the shaft 90 so as to be axially slidable 
thereon, and serves to rigidly connect the shaft 90 either to the gear 
element 96 (as shown) or the gear element 94. A forward speed relation 
between the gear element 84 and shaft 90 is established when dog clutch 
108 connects the shaft 90 to gear element 96, and a reverse speed relation 
between the gear element 82 and shaft 90 is established when the dog 
clutch 108 connects the shaft 90 to the gear element 94. 
The clutching devices 28-34 each comprise an input member rigidly connected 
to a transmission shaft 42 or 90, and an output member rigidly connected 
to one or more gear elements such that engagement of a clutching device 
couples the respective gear element and shaft to effect a driving 
connection between the shafts 42 and 90. The clutching device 28 couples 
the shaft 42 to the gear element 80; the clutching device 30 couples the 
shaft 42 to the gear elements 82 and 84; the clutching device 32 couples 
the shaft 90 to the gear element 100; and the clutching device 34 couples 
the shaft 42 to the gear element 86. Each of the clutching devices 28-34 
is biased toward a disengaged state by a return spring (not shown). 
Engagement of the clutching device is effected by supplying fluid pressure 
to an apply chamber thereof. The circled numeral 1 represents a fluid 
passage for supplying pressurized fluid to the apply chamber of clutching 
device 28; the circled numeral 2 and letter R represent a fluid passage 
for supplying pressurized fluid to the apply chamber of the clutching 
device 30; the circled numeral 3 represents a fluid passage for supplying 
pressurized fluid to the apply chamber of the clutching device 32; and the 
circled numeral 4 represents a fluid passage for directing pressurized 
fluid to the apply chamber of the clutching device 34. 
The various gear elements 80-88 and 92-100 are relatively sized such that 
engagement of first, second, third and fourth forward speed ratios are 
effected by engaging the clutching devices 28, 30, 32 and 34, 
respectively, it being understood that the dog clutch 108 must be in the 
position depicted in FIG. 1 to obtain a forward speed ratio. A neutral 
speed ratio or an effective disconnection of the drive axles 20 and 22 
from the engine output shaft 18 is effected by maintaining all of the 
clutching devices 28-34 in a released condition. The speed ratios defined 
by the various gear element pairs are generally characterized the ratio of 
the turbine speed N.sub.t to output speed N.sub.o. Representative N.sub.t 
/N.sub.o ratios for transmission 14 are as follows: 
______________________________________ 
First 2.368 Second 1.273 
Third 0.808 Fourth 0.585 
Reverse 1.880 
______________________________________ 
The fluid control elements of the transmission 14 include a manual valve 
140, a directional servo 160 and a plurality of electrically operated 
fluid valves 180-190. The manual valve 140 operates in response to 
operator demand and serves, in conjunction with directional servo 160, to 
direct regulated line pressure to the appropriate fluid valves 182-188. 
The fluid valves 182-188, in turn, are individually controlled to direct 
fluid pressure to the clutching devices 28-34. The fluid valve 180 is 
controlled to direct fluid pressure from the pump output line 66 to the 
pressure regulator valve 68. The fluid valve 190 is controlled to direct 
fluid pressure from the PRV output line 74 to TCC 26. The directional 
servo 160 operates in response to the condition of the manual valve 140 
and serves to properly position the dog clutch 108. 
The manual valve 140 includes a shaft 142 for receiving axial mechanical 
input from a range selector 144 which is positioned by the operator of the 
motor vehicle to obtain a desired transmission gear range. Fluid pressure 
from the pump output line 66 is applied as an input to the manual valve 
140 via the line 148, and the valve outputs include a forward (F) output 
line 150 for supplying fluid pressure for engaging forward speed ratios 
and a reverse (R) output line 152 for supplying fluid pressure for 
engaging the reverse speed ratio. Thus, when the range selector 144 is 
moved to the D4, D3 or D2 positions, line pressure from the line 148 is 
directed to the forward (F) output line 150. 
When the range selector 144 is in the R position, line pressure from the 
line 148 is directed to the reverse (R) output line 152. When the range 
selector 144 is in the N (neutral) or P (park) positions, the input line 
148 is isolated, and the forward and reverse output lines 150 and 152 are 
connected to an exhaust line 154 which is adapted to return any fluid 
therein to the fluid reservoir 64. 
The directional servo 160 is a fluid operated device and includes an output 
shaft 162 connected to a shift fork 164 for axially shifting the dog 
clutch 108 on shaft 90 to selectively enable either forward or reverse 
speed ratios. The output shaft 162 is connected to a piston 166 axially 
movable within the servo housing 168. The axial position of the piston 166 
within the housing 168 is determined according to the fluid pressures 
supplied to the chambers 170 and 172. The forward output line 150 of 
manual valve 140 is connected via line 174 to the chamber 170 and the 
reverse output line 152 of manual valve 140 is connected via the line 176 
to the chamber 172. 
When the range selector 144 is in a forward range position, the fluid 
pressure in the chamber 170 urges piston 166 rightward as viewed in FIG. 1 
to engage the dog clutch 108 with the gear element 96 for enabling 
engagement of a forward speed ratio. When the range selector 144 is moved 
to the R position, the fluid pressure in chamber 172 urges piston 166 
leftward as viewed in FIG. 1a to engage the dog clutch 108 with the gear 
element 94 for enabling engagement of the reverse speed ratio. In each 
case, it will be remembered that the actual engagement of the second or 
reverse speed ratio is not effected until engagement of the clutching 
device 30. 
The directional servo 160 also operates as a fluid valve for enabling the 
reverse speed ratio. To this end, the directional servo 160 includes an 
output line 178 connected to the electrically operated fluid valve 186. 
When the operator selects a forward speed ratio and the piston 166 of 
directional servo 160 is in the position depicted in FIG. 1, the passage 
between lines 176 and 178 is cut off; when the operator selects the 
reverse gear ratio, the passage between the lines 176 and 178 is open. 
The electrically operated fluid valves 180-190 each receive fluid pressure 
at an input passage thereof from the pump 60 or PRV 68, and are 
individually controlled to direct fluid pressure to the pressure regulator 
valve 68 or respective clutching devices 26-34. The fluid valve 180 
receives line pressure directly from pump output line 66, and is 
controlled to direct a variable amount of such pressure to the pressure 
regulator valve 68, as indicated by the circled letter V. The fluid valves 
182, 184 and 188 receive fluid pressure from the forward output line 150 
of manual valve 140, and are controlled to direct variable amounts of such 
pressure to the clutching devices 34, 32 and 28, as indicated by the 
circled numerals 4, 3 and 1, respectively. The fluid valve 186 receives 
fluid pressure from the directional servo output line 178, and is 
controlled to direct a variable amount of such pressure to the clutching 
device 30, as indicated by the circled numeral 2 and the circled letter R. 
The fluid valve 190 is adapted to alternately connect the release chamber 
56 of torque converter 24 to fluid pressure line 74 and exhaust line 192, 
as indicated by the circled numeral 6. The apply chamber 54 of TCC 26 is 
supplied with fluid pressure from the fluid pressure line 74 via the 
orifice 194, as indicated by the circled numeral 5. 
Each of the fluid valves 180-190 includes a spool element 210-220, axially 
movable within the respective valve body for directing fluid flow between 
input and output passages. When a respective spool element 210-220 is in 
the rightmost position as viewed in FIG. 1b, the input and output passages 
are connected. Each of the fluid valves 180-190 includes an exhaust 
passage, as indicated by the circled letters EX, such passage serving to 
drain fluid from the respective clutching device when the spool element is 
shifted to the leftmost position as viewed in FIG. 1b. In FIG. 1b, the 
spool elements 210 and 212 of fluid valves 180 and 182 are shown in the 
rightmost position connecting the respective input and output lines, while 
the spool elements 214, 216, 218 and 220 of the fluid valves 184, 186, 188 
and 190 are shown in the leftmost position connecting the respective 
output and exhaust lines. 
Each of the fluid valves 180-190 includes a solenoid 222-232 for 
controlling the position of its spool element 210-220. Each such solenoid 
222-232 comprises a plunger 234-244 connected to the respective spool 
element 210-220 and a solenoid coil 246-256 surrounding the respective 
plunger. One terminal of each such solenoid coil 246-256 is connected to 
ground potential as shown, and the other terminal is connected to an 
output line 258-268 of a control unit 270 which governs the solenoid coil 
energization. As set forth hereinafter, the control unit 270 pulse width 
modulates the solenoid coils 246-256 according to a predetermined control 
algorithm to regulate the fluid pressure supplied to the pressure 
regulator 68 and the clutching devices 26-34, the duty cycle of such 
modulation being determined in relation to the desired magnitude of the 
supplied pressures. 
With respect to the TCC 26, open converter operation is achieved by 
deenergizing the coil 256 of fluid valve 190 so that the spool element 220 
assumes the position depicted in FIG. 1b. In this case, the fluid pressure 
in line 74 is directed to the release chamber 56 of torque converter 24, 
creating a pressure differential across clutch plate 50 which disables 
engagement of TCC 26. The fluid supplied to release chamber 56 via valve 
190 and the fluid supplied to apply chamber 54 via orifice 194 are both 
exhausted via exhaust line 55 of FIG. 1a. 
When it is desired to engage the TCC 26, the coil 256 of valve 190 is pulse 
width modulated to lessen the fluid pressure in the release chamber 56 of 
torque converter 24. This creates a pressure differential across clutch 
plate 50 which moves the friction element 52 into engagement with input 
shell 38 to initiate TCC engagement. 
While the fluid valves 180-190 have been illustrated as spool valves, other 
types of valves could be substituted therefor. By way of example, valves 
of the ball and seat type could be used. In general terms, the fluid 
valves 180-190 may be mechanized with any three-port pulse width modulated 
valving arrangement. 
Input signals for the control unit 270 are provided on the input lines 
272-285. A position sensor (S) 286 responsive to movement of the manual 
valve shaft 142 provides an input signal to the control unit 270 via line 
272. Speed transducers 288, 290 and 292 sense the rotational velocity of 
various rotary members within the transmission 14 and supply speed signals 
in accordance therewith to the control unit 270 via lines 274, 276 and 
278, respectively. The speed transducer 288 senses the velocity of the 
transmission shaft 42 and therefore the turbine or transmission input 
speed N.sub.t ; the speed transducer 290 senses the velocity of the drive 
axle 22 and therefore the transmission output speed N.sub.o ; and the 
speed transducer 292 senses the velocity of the engine output shaft 18 and 
therefore the engine speed N.sub.e. 
The position transducer 294 is responsive to the position of the engine 
throttle 16 and provides an electrical signal in accordance therewith to 
control unit 270 via line 280. A pressure transducer 296 senses the 
manifold absolute pressure (MAP) of the engine 12 and provides an 
electrical signal to the control unit 270 in accordance therewith via line 
282. A temperature sensor 298 senses the temperature of the oil in the 
transmission fluid reservoir 64 and provides an electrical signal in 
accordance therewith to control unit 270 via line 284. Finally, a brake 
switch BR provides an indication of service brake application on line 285. 
The control unit 270 responds to the input signals on input lines 272-285 
according to a predetermined control algorithm as set forth herein, for 
controlling the energization of the fluid valve solenoid coils 246-256 via 
output lines 258-268. As such, the control unit 270 includes an 
input/output (I/O) device 300 for receiving the input signals and 
outputting the various pulse width modulation signals, and a microcomputer 
302 which communicates with the I/O device 300 via an address-and-control 
bus 304 and a bi-directional data bus 306. Flow diagrams representing 
suitable program instructions for developing the pulse width modulation 
outputs in accordance with the teachings of this invention are depicted in 
FIGS. 5-9. 
As indicated above, the present invention is directed to an inference-based 
control of the shift scheduling which provides improved control when 
operating the vehicle in hilly terrain. The base or default shift 
scheduling is performed by table look-up as graphically depicted in FIG. 
2. For any engine throttle position TPS, the table provides an upshift 
vehicle speed above which an upshift to the next higher speed ratio is 
desired, and a downshift vehicle speed below which a downshift to the next 
lower speed ratio is desired. 
The shift schedule of FIG. 2 provides adequate control of transmission 
shifting while the vehicle is operating in relatively flat terrain, but 
may result in unnecessary shifting and excessive brake usage when 
operating in hilly terrain. When ascending a hill, the normal shift 
schedule yields an appropriate speed ratio by downshifting, if necessary, 
as the driver increases the engine throttle setting to maintain a given 
speed, but generates an upshift at the crest of the hill when the driver 
reduces the throttle setting. The upshift effectively obviates engine 
braking effects, and the operator must then rely on the service brakes to 
regulate vehicle speed while going down the hill. A similar situation 
occurs when driving on a winding ascent; that is, the transmission 
upshifts when the driver reduces the throttle setting upon entering a 
curve, necessitating a subsequent downshift after negotiating the curve. 
To avoid inappropriate shifting and excessive braking when driving in hilly 
terrain, the driver is encouraged to move the range selector 144 to one of 
the manual pulldown positions D3, D2 or D1, thereby downshifting the 
transmission to the indicated speed ratio. In this mode, the transmission 
will not upshift beyond the indicated speed ratio, and engine braking is 
available. 
An experienced driver may initiate manual pulldown shifting several times 
in the course of a few miles in hilly terrain, but inexperienced drivers 
tend to leave the range selector 144 in the Drive position regardless of 
the terrain. 
The present invention is directed to a shift control which supplements the 
normal shift schedule to automatically provide manual pulldown operation 
when driving in hilly terrain, based on information inferred from various 
vehicle operating parameters. For example, the control unit may infer the 
need for a manual pulldown when low vehicle speed and highly negative 
grade occur concurrently. A number of such parameter combinations, 
referred to herein as control rules, are monitored during the course of 
vehicle operation. When the need for manual pulldown operation is 
sufficiently great, the control unit overrides the normal shift schedule, 
effectively initiating manual pulldown operation. 
In the illustrated embodiment, the control unit 270 utilizes five control 
rules: (1) low vehicle speed (VSLOW) AND large negative grade (GLNEG); (2) 
large negative grade AND low throttle setting (TPSLOW); (3) low vehicle 
speed AND large negative grade AND long brake time (BRKTIML); (4) low 
vehicle speed AND long deceleration time (DECTIML); and (5) low vehicle 
speed AND long deceleration time AND long coast acceleration time 
(CACCTIML). The degree of truthfulness of the individual parameter 
conditions are determined by table look-up, as graphically illustrated by 
graphs of FIGS. 3a-3f. In each case, the degree of truthfulness is 
represented by a numerical result, referred to herein as a truth value, 
between zero (no truthfulness) and one (high truthfulness). In the VSLOW 
table of FIG. 3a, for example, the numerical result is one at 0 MPH, 
decreasing with increasing speed, and zero for speeds of 60 MPH or higher. 
Once the truth values for the various parameters are determined, they are 
applied to the control rules defined above to produce a truth value result 
for each control rule. For example, if the truth values of "low vehicle 
speed" and "large negative grade" were 0.6 and 0.9, respectively, the 
truth value of the first control rule would be the lower of the truth 
values or 0.6. The control rule truth values are weighted to account for 
their criticality, and then summed to form an overall result which 
determines if, and to what extent, manual pulldown shifting is 
appropriate. 
The table of FIG. 4 illustrates an example where weighting factors are 
applied to five control rule values to form an overall result of 83.2. In 
this example, a result of 64 or higher indicates the need for a single 
ratio manual pulldown--that is, to the D3 quadrant. Similarly, a result of 
128 or higher indicates the need for a manual pulldown to the D2 quadrant, 
and a result of 192 or higher indicates the need for a manual pulldown to 
the D1 quadrant. In the illustrated example, the inference-based control 
would thus initiate manual pulldown to the D3 quadrant. In the illustrated 
embodiment, no individual control rule value can be high enough to 
initiate manual pulldown operation (that is, each is less than 64), 
requiring some truthfulness of more than one control rule. In other 
applications, it may be desirable to give certain control rules more 
authority. 
The above-described control results in a shift control system that does not 
downshift or upshift at distinct speeds, grades or acceleration levels. 
Rather, manual pulldown shifting occurs when the preponderance of the 
inferences indicates that manual pulldown operation should occur. 
The flow diagrams of FIGS. 5, 6a-6b, 7a-7d, 8a-8b and 9 represent program 
instructions to be executed by the microcomputer 302 of control unit 270 
in mechanizing the ratio shifting control of this invention. The flow 
diagram of FIG. 5 represents a main or executive program which calls 
various subroutines for executing particular control functions as 
necessary. The flow diagrams of FIGS. 6a-6b, 7a-7d, 8a-8b and 9 represent 
the functions performed by those subroutines which are pertinent to the 
present invention. 
Referring to the main loop program of FIG. 5, the reference numeral 330 
designates a set of program instructions executed at the initiation of 
each period of vehicle operation for initializing the various tables, 
timers, etc., used in carrying out the control functions of this 
invention. Following such initialization, the instruction blocks 332-354 
are repeatedly executed in sequence, as designated by the flow diagram 
lines connecting such instruction blocks and the return line 356. 
Instruction block 332 reads and conditions the various input signals 
applied to I/O device 300 via the lines 272-285, and calculates various 
terms used in the control algorithms, including the input torque Ti, the 
torque variable Tv and the seed ratio No/Ni. 
The block 333 determines the grade load GL, as described above, and is set 
forth in detail in the flow diagram of FIGS. 6a-6b, as indicated. The 
block 334 detail in the flow diagram of FIGS. 7a-7d as indicated. The 
block 335 pertains to Fuzzy Counter Processing Logic, and is set forth in 
detail in the flow diagram of FIGS. 8a-8b as indicated. The block 336 
determines the desired speed ratio, Rdes, in accordance with a number of 
inputs including present ratio Ract, throttle position TPS, vehicle speed 
Nv, range selector position RSEL, and the inference-based pulldown 
considerations, and is set forth in detail in the flow diagram of FIG. 9, 
as indicated. 
The blocks designated by the reference numeral 358 include the decision 
block 338 for determining if a shift is in progress, as indicated by the 
"SHIFT IN PROGRESS" flag; the decision block 340 for determining if the 
actual speed ratio Ract (that is, No/Nt) is equal to the desired speed 
ratio Rdes determined at instruction block 336; and the instruction block 
342 for setting up the initial conditions for a ratio shift. The 
instruction block 342 is only executed when decision blocks 338 and 340 
are both answered in the negative. In such case, instruction block 342 
serves to set the old ratio variable (Rold) equal to Ract and to set the 
"SHIFT IN PROGRESS" flag. If a shift is in progress, the execution of 
blocks 340 and 342 is skipped, as indicated by the flow diagram line 360. 
If no shift is in progress, and the actual ratio equals the desired ratio, 
the execution of instruction block 342 and the blocks designated by the 
reference numeral 362 is skipped, as indicated by the flow diagram line 
364. 
The blocks designated by the reference numeral 362 include the decision 
block 344 for determining if the shift is an upshift or a downshift; the 
instruction block 346 for developing pressure commands for the on-coming 
and off-going clutches if the shift is an upshift; and the instruction 
block 348 for developing the pressure commands for the on-coming and 
off-going clutches if the shift is a downshift. Instruction block 350 
determines pressure commands for the PRV and the nonshifting clutches, 
converts the commands to a PWM duty cycle based on the operating 
characteristics of the various actuators, and energizes the actuator coils 
accordingly. The development of suitable pressure commands and PWM duty 
cycle control given a desired speed ratio is described in detail in the 
U.S. Pat. No. 4,653,350 to Downs et al., issued on Mar. 31, 1987, and 
assigned to General Motors Corporation. 
Referring to the grade load determination flow diagram of FIGS. 6a-6b, the 
decision block 366 is first executed to determine if a shift is in 
progress. If so, the remainder of the routine is skipped. If the service 
brake is depressed, as determined at block 368, the execution of blocks 
370-382 is skipped to freeze the current values of Tax and Taccel. If the 
transmission range selector 142 is in Reverse, as determined at block 370, 
the block 372 is executed to set the axle and acceleration torque terms 
Tax and Taccel to zero. If the range selector 142 is in Neutral, as 
determined at block 374, the block 376 is executed to set the axle torque 
term Tax to zero. The axle and acceleration torque terms Tax and Taccel 
are also zeroed if the vehicle speed Nv is less than a predefined value 
K1, such as 20 MPH, as determined at block 377. 
The blocks 378-382 determine the non-zero values of the axle and 
acceleration torque terms Tax and Taccel. The axle torque Tax is 
determined according to the expression: 
EQU Tax=Tin*Ract*K2 
and then subjected to a first order lag filter, as indicated at block 380. 
The acceleration torque term is determined according to the expression: 
EQU Taccel=K4*d(Nv)/dt 
where K4 represents the nominal vehicle weight and d(Nv)/dt represents the 
acceleration of the vehicle. 
The aerodynamic and rolling resistance torque terms Taero and Tro are then 
determined at blocks 384 and 386 according to the respective expressions: 
EQU Taero=Nv.sup.2 *K5, and 
EQU Tro=K6 
The block 388 is then executed to determine the new grade load term GL(NEW) 
according to the expression: 
EQU GL(NEW)=Tax-K7-Taero-Taccel-Tro 
The block 390 is then executed to develop a filtered grade load term GLfilt 
according to the expression: 
EQU GLfilt=GLfilt+K8(GL(NEW)-GLfilt) 
where K8 is a gain constant. 
The Fuzzy Downshift Logic flow diagram of FIGS. 7a-7d determines and sums 
the values of the five control rules, determines the appropriate pulldown 
speed ratio, and develops an inference-based pulldown request. The truth 
values for the six parameter conditions: TPS LOW, VSLOW, GLNEG, RKTIML, 
DECTIML and CACCTIML are determined at instruction blocks 450 and 460-468 
by table look-up substantially as described above in reference to the the 
graphs of FIGS. 3a-3f. 
As noted at block 460, the VSLOW parameter is determined as a function of 
the fuzzy logic vehicle speed term FZVSPEED. Normally, this term is set 
equal to the measured vehicle speed Nv, as indicated at block 458. Under 
the condition defined by blocks 452-456, however, the execution of block 
458 is skipped, and FZVSPEED is temporarily held at its entry value. This 
condition, defined by (1) a fuzzy-logic induced pulldown being in effect, 
(2) the engine throttle setting being less than a reference value REFTPS, 
and (3) the actual vehicle speed Nv increasing, occurs after climbing a 
hill and beginning a subsequent descent. In this condition, an upshift is 
undesired, and when detected, the current vehicle speed value FZVSPEED is 
frozen so that the control rules which include VSLOW are maintained at a 
relatively high value. This operates to maintain the fuzzy pulldown until 
the driver increases the throttle setting above the reference REFTPS, 
indicating that engine braking is no longer desired. 
The blocks 470-474 apply the VSLOW and GLNEG truth values determined at 
blocks 460 and 462 to the first control rule: VSLOW AND GLNEG. The lower 
of the two truth values, determined at block 470, satisfies the logical 
AND operator, and is suitably weighted by gain factor K1 and stored in the 
control rule truth term TRUTH1. The blocks 476-480 apply the TPSLOW and 
GLNEG truth values determined at blocks 450 and 462 to the second control 
rule: TPSLOW AND GLNEG. The lower of the two truth values, determined at 
block 476, is suitably weighted by gain factor K2 and stored in the 
control rule truth term TRUTH2. The blocks 482-492 apply the VSLOW, GLNEG 
and BRKTIML truth values determined at blocks 460, 462 and 464 to the 
third control rule: BRKTIML AND GLNEG AND VSLOW. 
The lowest of the three truth values, determined by blocks 482-486, is 
suitably weighted by gain factor K3 and stored in the control rule truth 
term TRUTH3. The blocks 494-502 apply the VSLOW and DECTIML truth values 
determined at blocks 460 and 466 to the fourth control rule: VSLOW AND 
DECTIML. The lower of the two truth values, determined at block 494, is 
suitably weighted by gain factor K4 and stored in the control rule truth 
term TRUTH4 as well as the temporary variable x. The blocks 504-508 apply 
the VSLOW, DECTIML and CACCTIML truth values determined at blocks 460, 466 
AND 468 to the fifth and final control rule: VSLOW AND DECTIML AND 
CACCTIML. The lowest of the three truth values, determined in conjunction 
with the variable x at block 504, is suitably weighted by gain factor K5 
and stored in the control rule truth term TRUTH5. Finally, the block 510 
is executed to sum the control rule truth terms TRUTH1, TRUTH2, TRUTH3, 
TRUTH4 and TRUTH5 in the term TRUTHSUM. 
The blocks 512-534 are then executed to determine the value of FUZZQUAD, 
which defines the pulldown gear corresponding to the value of TRUTHSUM. 
The value of FUZZQUAD, initialized to four, represents the highest 
available forward speed ratio, based on the value of TRUTHSUM. If TRUTHSUM 
is less than or equal to 64, as determined by blocks 516-520, the block 
522 is executed to set FUZZQUAD to four; if TRUTHSUM is between 64 and 
128, block 524 is executed to set FUZZQUAD to three; and if TRUTHSUM is 
greater than or equal to 128, the block 526 is executed to set FUZZQUAD to 
two. If the FUZZQUAD is set to three or two, as determined at block 518 
and 512, respectively, the respective block 530 or 532 is executed to 
increase the value of TRUTHSUM by a hysteresis creating amount K. The 
hysteresis operates to reduce the likelihood of oscillation between 
different values of FUZZQUAD when TRUTHSUM has a value of approximately 64 
or 128. 
The blocks 536-556 concern determination of the term FUZZQ2, which is the 
inference-based pulldown command generated by the Fuzzy Downshift Logic. 
In other words, FUZZQUAD represents the pulldown quadrant which appears to 
be desired per the inference-based control rules, while FUZZQ2 represents 
the pulldown quadrant actually commanded by the Fuzzy Downshift Logic. As 
described below in reference to the flow diagram of FIG. 9, the Desired 
Ratio Determination Logic utilizes the state of FUZZQ2 in determining the 
desired ratio Rdes. 
The block 536 is first executed to compare the states of FUZZQUAD and 
FUZZQ2. If FUZZQUAD is less than FUZZQ2, the blocks 538-546 are executed 
to determine if FUZZQ2 should be decremented to a lower pulldown quadrant. 
If a coast downshift is in progress, as determined at block 538, the state 
of FUZZQ2 is not changed. If a coast downshift is not in progress and the 
blocks 540-544 are satisfied, the block 546 is executed to set FUZZQ2 
equal to FUZZQUAD, effectively decrementing FUZZQ2 by one or more 
quadrants. 
The block 540 determines if the desired pulldown quadrant FUZZQUAD agrees 
with the shift pattern result Rdes. If so, the block 546 is executed to 
set the inference-based pulldown command FUZZQ2 equal to FUZZQUAD. If not, 
the blocks 542-544 are executed to detect a condition in which braking 
activity has just ceased. The block 542 determines if either of the 
brake-dependent control rule values (that is, TRUTH3 and TRUTH4) are at 
least partially responsible for the TRUTHSUM value giving rise to the need 
for manual pulldown operation. If not, block 546 is executed to set FUZZQ2 
equal to FUZZQUAD, as above. If so, but the brake is now released, as 
determined at block 544, the execution of block 546 is skipped since 
further downshifting would not be appropriate. Significantly, the control 
does not modify the TRUTHSUM and FUZZQUAD values in this situation. Thus, 
if the driver subsequently reapplies the brakes, the inference-based 
pulldown shift will occur without delay. 
If FUZZQUAD is greater than FUZZQ2, the blocks 548-556 are executed to 
update the fuzzy logic speed value FZVSPEED to the measured speed Nv and 
to determine if FUZZQ2 should be incremented to a higher pulldown 
quadrant. If an inference-based pulldown is not required--in other words, 
if the shift pattern is requesting the inference-based pulldown command 
FUZZQ2--the block 546 is executed to immediately increment the indicated 
pulldown quadrant by setting FUZZQ2 equal to FUZZQUAD. The above condition 
is determined at block 550 by the status of the FUZZY ACTIVE flag, 
described below in reference to the flow diagram of FIG. 9. If an 
inference-based pulldown is required and the delay timer FZQDELAY has been 
satisfied, as determined at blocks 550-552, the blocks 554 and 556 are 
executed to increment FUZZQ2 by one quadrant and to clear or reset the 
delay timer FZQDELAY. It will be seen that the delay timer, described 
below in reference to the flow diagram of FIGS. 8a-8b, thereby serves to 
separate the upshifts in time, improving the shift pleaseability. 
The Fuzzy Logic Counter Processing Logic flow diagram of FIGS. 8a-8b serves 
to update certain of the inference-based parameters and timers utilized in 
the Fuzzy Downshift Logic of FIGS. 7a-7d. The brake, deceleration and 
coast-acceleration timers are progressively increased in value so long as 
the respective condition is true and progressively decreased in value 
whenever the condition is not true. The blocks 560-572 are directed to 
increasing the timer values, while the blocks 574-584 are directed to 
decreasing the timer values. 
If the vehicle service brakes are applied, as determined at block 560, the 
block 562 is executed to increment brake timer term BRKTIME. If the brakes 
are not applied, and the vehicle acceleration exceeds a minimum reference 
amount K, as determined at blocks 560 and 564, the block 566 is executed 
to increment the coast acceleration timer term CACCTIME. If the vehicle 
deceleration exceeds a vehicle speed dependent threshold THRESH determined 
at block 568, as determined at block 570, the deceleration timer term 
DECTIME is incremented at block 572. The threshold is scheduled in 
relation to the vehicle speed so that increased deceleration is required 
at lower vehicle speeds in order to increase the value of DECTIME. 
The blocks 580-584 are executed to decrement all three timer terms unless 
at least one of the conditions defined by blocks 574-578 is met. The first 
condition, engine throttle position TPS less than a reference K, inhibits 
decrementing if the accelerator pedal is substantially released. The 
second condition, defined by block 576, inhibits decrementing of the 
timers when the service brakes are applied. The third condition defines a 
situation in which the brake is off and the engine throttle setting is 
increasing at a relatively high rate, a situation which occurs as the 
vehicle begins an ascent and the driver attempts to maintain a given 
vehicle speed. In this situation, decrementing the timer values is 
inhibited since upshifting would not be appropriate. If none of the 
conditions are met--that is, the throttle setting is non-zero but 
reasonably steady, and the brakes are not applied--a quasi-steady-state 
condition is indicated, and the timer values are decremented, reducing the 
values of TRUTH3, TRUTH4 and TRUTH5. 
The blocks 586-596 control the value of the delay timer term FZQDELAY. At 
block 586, the current state of FUZZQ2 is compared with its state after 
the previous execution of the Fuzzy Logic Counter Processing Logic, 
designated as FUZZQ2(LAST). If the state of FUZZQ2 is lower than the 
previous state, upshifting is not required and the blocks 588-590 are 
executed to clear/reset the delay timer term FZQDELAY and to reinitialize 
the previous state term FUZZQ2(LAST) in accordance with the current value 
of FUZZQ2. If the state of FUZZQ2 is at least as high as the previous 
state, the blocks 592-594 and 590 are executed to determine if the delay 
timer term FZQDELAY should be incremented, and then to re-initialize the 
previous state term FUZZQ2(LAST) as described above. Essentially, the 
timer term FZQDELAY is incremented at block 596 if (1) the change in 
engine throttle position DTPS is less than a reference K, and (2) the 
current value of the term is less than or equal to the reference time 
defined at block 552 of FIG. 7d. 
The DTPS condition of block 592 is included to prevent incrementing of the 
delay timer when the vehicle nears the bottom of a hill and the driver 
begins increasing the throttle to climb another hill. In this situation, 
an upshift would be inappropriate as noted above in reference to block 578 
of FIG. 8a, and the control responds by further delaying an upshift; see 
FIG. 7d, blocks 552-554. 
Referring to the Desired Speed Ratio Determination flow diagram of FIG. 9, 
the block 600 is first executed to address the normal shift pattern 
look-up table as a function of engine throttle position TPS and vehicle 
speed Nv to determine the desired speed ratio Rdes. If the inference-based 
pulldown command FUZZQ2 is at least as high as the scheduled ratio Rdes, 
as determined at block 602, the blocks 604-610 are executed to clear set 
the FUZZY ACTIVE flag (referenced above with respect to block 550 of FIG. 
7d), and to compare Rdes with the manual range selector position RSEL. 
Essentially, the desired ratio Rdes is reset in accordance with RSEL so 
long as (1) the actual ratio Ract is higher than RSEL, and (2) engine 
speed constraints would not be violated by shifting to the ratio 
designated by RSEL. 
If the inference-based pulldown command FUZZQ2 is less than Rdes, the block 
612 is executed to set the FUZZY ACTIVE flag. If FUZZQ2 is at least as 
great as the range selector position RSEL or the actual ratio Ract, as 
determined at blocks 614-616, the blocks 606-610 are executed to reset the 
desired ratio Rdes as described above. Otherwise, the block 620 is 
executed to set the desired ratio Rdes equal to the inference-based 
pulldown command FUZZQ2 unless the engine speed constraints would be 
violated, as determined at block 618. 
In the manner described above, the control of this invention automatically 
initiates manual pulldown shift operation based on the inferred need for 
such operation. Drivers who are unfamiliar with the recommended operating 
procedures for driving in hilly terrain will enjoy the operational 
advantages (such as reduced shift busyness and increased brake life) which 
were heretofore attained only by experienced drivers. 
While the invention is described in reference to the illustrated 
embodiment, it is expected that various modifications will occur to those 
skilled in the art, and it should be understood that controls 
incorporating such modifications may fall within the scope of this 
invention, which is defined by the appended claims.