Method and control system for controlling AMT system including detection of erroneous gear neutral indication

A control method/system for an automatic/semi-automatic mechanical transmission system (10) is provided including logic rules by which a faulty input signal indicative of a gear neutral condition (GNS=.phi.) can be detected and, in the event of such detection, a fail safe mode of operation is implemented.

BACKGROUND OF THE INVENTION 
This invention relates to automatic and semi-automatic power transmissions 
providing a plurality of gear reduction ratios, such as vehicular 
automatic mechanical transmissions (i.e. "AMTs"), and, to control systems 
and methods therefor. In particular, the present invention relates to 
control systems and methods for vehicular automatic/semi-automatic 
mechanical transmission systems wherein gear selection and/or shift 
decisions are made and/or executed based upon measured and/or calculated 
parameters such as engagement condition of the transmission, vehicle or 
transmission output shaft speed, transmission input shaft speed, engine 
speed, throttle position, rate of change of throttle position, rate of 
change of vehicle and/or engine speed and the like. More particularly, the 
present invention relates to a method/system for controlling an AMT system 
utilizing sensors for providing input signals indicative of the presence 
of a transmission gear neutral condition, engine, transmission input shaft 
and transmission output shaft rotational speeds, etc. including sensing of 
a faulty signal from the gear neutral sensors and modifying the system 
operation logic in response to detection of such fault. 
DESCRIPTION OF THE PRIOR ART 
The use of automatic and/or semi-automatic transmissions of both the 
automatic mechanical type utilizing positive clutches and of the planetary 
gear type utilizing frictional clutches is well known in the prior art, as 
are control systems therefor. Electronic control systems utilizing 
discrete logic circuits and/or software controlled microprocessors for 
automatic transmissions wherein gear selection, shift execution and/or 
shift decisions are made based upon certain measured and/or calculated 
parameters such as the presence of a transmission gear neutral condition, 
vehicle speed (or transmission output shaft speed), transmission input 
shaft speed, engine speed, rate of change of vehicle speed, rate of change 
of engine speed, throttle position, rate of change of throttle position, 
full depression of the throttle (i.e. "kickdown"), actuation of the 
braking mechanism, currently engaged gear ratio, and the like are known in 
the prior art. Examples of such automatic/semi-automatic transmission 
control systems for vehicles may be seen by reference to U.S. Pat. Nos. 
4,722,248; 4,722,237; 4,676,115; 4,648,290; 4,361,060; 4,551,802; 
4,527,447; 4,425,620; 4,463,427; 4,081,065; 4,073,203; 4,253,348; 
4,038,889; 4,226,295; 3,776,048; 4,208,929; 4,039,061; 3,974,720; 
3,478,851; 3,942,393 and 4,595,986, the disclosures of which are all 
hereby incorporated by reference. 
While the above referenced automatic/semi-automatic transmission control 
systems, and similar systems, are effective to control an automatic 
transmission by selecting and/or engaging a desired gear ratio which will 
tend to optimize the fuel economy and/or performance of the vehicle in 
view of the sensed parameters and then commanding a shift into the 
selected gear ratio, such control systems were not totally acceptable as 
the predetermined programs utilized did not include logic routines, or 
methods, to recognize and identify a fault in the input signals from the 
gear neutral condition sensors and/or could not modify the predetermined 
program to provide an acceptable response to such a sensed fault. 
An AMT control method for sensing gear neutral and not gear neutral sensor 
faults, and for modifying the control logic in tolerance to such faults, 
is disclosed in U.S. Pat. No. 4,702,127, the disclosure of which is hereby 
incorporated by reference. While this control method/system is an 
improvement over the then existing prior art, it was not totally 
satisfactory as faulty gear neutral signals during a shifting operation 
were not detected and/or the response to such faults allowed continued 
vehicle operation under conditions which could lead to undesirable vehicle 
operation and/or damage to the transmission system. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, the drawbacks of the prior art 
have been overcome or minimized by providing a control system, preferably 
an electronic control system, and control method, for 
automatic/semi-automatic mechanical transmission systems wherein gear 
selection and shift decisions are made and/or executed based upon measured 
and/or calculated parameters including at least input signals indicative 
of the presence of a gear neutral condition, transmission input shaft 
speed and transmission output shaft speed. Other inputs/parameters, such 
as signals indicative of throttle position and/or rate of change of 
throttle position, condition of the master clutch, currently engaged gear 
ratio, operation of the vehicle brakes, and the like are also utilized to 
make decisions for control of the AMT system. 
The predetermined logic rules or programs by which the various input 
signals are processed include a method for detecting a fault in the input 
signals from the gear neutral sensors and a method for modifying the 
predetermined logic in response to a sensed fault to provide an acceptable 
set of logic rules for limited (i.e. limp home/limp off road) continuing 
operation of the system until such time as the fault is corrected. 
A gear neutral condition sensor input signal is considered to be faulty if 
the value thereof is not indicative of the true engaged or disengaged 
condition of the transmission or transmission section monitored thereby. 
The above is accomplished by establishing a set of relationships between 
the gear neutral condition input signals, the transmission input shaft 
speed signal and the transmission output shaft speed signal which, under 
defined conditions, must be true. If, under the defined conditions, these 
relationships are not true, a fault in the input signals from one or more 
of the sensors exists, and various relationships are evaluated to identify 
the one or more faulty sensors. If the gear neutral sensor is in fault, 
the logic routines are modified to allow a continued system operation in 
only the currently engage ratio for limp home/limp off road purposes until 
such time as the fault is corrected. 
This invention detects a false transmission neutral indication for 
automatically/semi-automatically controlled manual transmissions that 
utilizes a sensor to indicate that the transmission is in a neutral state. 
In actuality, the sensor usually senses a position of a shift rail rather 
than of the engaged gear. The coupling to the sensor is through a shift 
yoke member being driven by an air pressurized shift rail to a dog clutch 
for the engaged gear. A false transmission neutral indication can readily 
occur due to deflections of the mechanical members, wear at the dog 
clutch, shift yoke and/or sensor mechanism, a malfunctioning sensor and 
the like. 
The AMT control algorithms require the indication of a transmission neutral 
signal prior to taking any action to bring the transmission jaw clutch 
members to synchronous. Once the sensor indicates neutral, the control 
actuates a system component that applies a torque to the input of the 
transmission bringing the engaging jaw clutch members to synchronous for 
the gear selected. The control system continuously monitors the input 
speed and output speed of the transmission and calculates a speed 
difference across the gears to be engaged, called error. At the same time, 
the system continuously calculates the speed difference for the last gear 
the transmission was in, called FLTERROR. If the transmission is truly in 
neutral, the value of error will decrease and the value of FLTERROR will 
increase as the input shaft approaches synchronous rotational speed for 
the ratio to be engaged. Using these facts, an algorithm was designed, 
such that, during a shift and when the sensor indicates that the 
transmission is in neutral and a system component is commanded to apply a 
torque to the input of the transmission the value of FLTERROR is monitored 
and compared to a calibration value for a short period of time. The 
selection of the calibration value is based upon the speed steps between 
gears, minimum obtainable error values, and mechanical backlash between 
the measuring speed sensors. If during that period of time, the value of 
FLTERROR does not exceed the calibration value, a fault is declared. This 
fault indicates that the transmission has not come out of gear, even 
though the sensor indicates that it has. Continuing to apply a torque to 
the input of the transmission further prevents it for coming to neutral 
due to torque lock on the clutches. Once the fault is established the 
system reselects the last gear and prohibits any further gear selections. 
Since it has already been established that the transmission did not come 
out of the last gear, no further synchronization is required. The control 
system allows the vehicle to continue to operate in the last gear until 
the vehicle comes to a stop, at which time the vehicle is rendered 
disabled. 
Accordingly, it is an object of the present invention to provide a new and 
improved control method/system for automatic mechanical transmission 
systems which involves sensing and identifying a fault in the gear neutral 
sensors and modifying the logic routines or algorithms by which the system 
is operated in response to sensed fault. 
This and other objects and advantages of the present invention will become 
apparent from a reading of the description of the preferred embodiment 
taken in connection with the attached drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In this disclosure, certain terminology will be used for convenience and 
reference only and will not be limiting. For example, the terms "forward" 
and "rearward" will refer to directions forward and rearward of the 
transmission or transmission shift bar housing assembly as normally 
mounted in a vehicle. The terms "rightward" and "leftward" will refer to 
directions in the drawings in connection with which the terminology is 
used. The terms "inwardly" and "outwardly" will refer to directions toward 
and away from, respectively, the geometric center of the apparatus being 
described. The terms "upward" and "downward" will refer to directions as 
taken in the drawings in connection with which the terminology is used. 
All foregoing terms include the normal derivatives and equivalents 
thereof. 
FIG. 1 schematically illustrates an automatic mechanical transmission 
system 10 including an automatic multi-speed compound change gear 
transmission 12 driven by a throttle controlled engine 14, such as a well 
known diesel engine, through a master clutch 16. An engine brake, such as 
an exhaust brake 17 for retarding the rotational speed of engine 14 and/or 
an input shaft brake 18 which is effective to apply a retarding force to 
the input shaft upon disengagement of master clutch 16 may be provided as 
is known in the prior art. The output of automatic transmission 12 is 
output shaft 20 which is adapted for driving connection to an appropriate 
vehicle component such as the differential of a drive axle, a transfer 
case or the like as is well known in the prior art. 
The above mentioned power train components are acted upon and monitored by 
several devices, each of which will be discussed in greater detail below. 
These devices include a throttle position or throttle opening monitor 
assembly 22 which senses the position of the operator controlled vehicle 
throttle or other fuel throttling device 24, a fuel control device 26 for 
controlling the amount of fuel to be supplied to engine 14, an engine 
speed sensor 28 which senses the rotational speed of the engine, a clutch 
operator 30 which engages and disengages clutch 16 and which also supplies 
information as to the status of the clutch, an input brake operator 31, a 
transmission input shaft speed sensor 32, a transmission operator 34 which 
is effective to shift the transmission 12 into a selected gear ratio and 
to provide a signal indicative of the gear neutral condition and/or 
currently engaged ratio, and a transmission output shaft speed sensor 36. 
A vehicle brake monitor 38 senses actuation of vehicle brake pedal 40. 
A transmission operator for an AMT system including a gear neutral switch 
may be seen by reference to U.S. Pat. No. 4,445,393, the disclosure of 
which is hereby incorporated by reference. The above mentioned devices 
supply information to and/or accept commands from a central processing 
unit or control 42. The central processing unit 42 may include analogue 
and/or digital electronic calculation and logic circuitry, the specific 
configuration and structure of which forms no part of the present 
invention. The central processing unit 42 also receives information from a 
shift control assembly 44 by which the vehicle operator may select a 
reverse (R), neutral (N), or forward drive (D) mode of operation of the 
vehicle. An electrical power source (not shown) and/or source of 
pressurized fluid (not shown) provides electrical and/or pneumatic power 
to the various sensing, operating and/or processing units. A fault 
indicator or alarm 46 may display the identity of a specific fault or 
simply signal the existence of an unidentified fault. Drive train 
components and controls therefor of the type described above are known in 
the prior art and may be appreciated in greater detail by reference to 
above mentioned U.S. Pat. Nos. 4,445,393; 4,361,060; 3,776,048; 4,038,889; 
4,226,295; 4,702,127 and 4,722,237. 
Sensors 22,28,32,36,38 and 44 may be of any known type or construction for 
generating analogue or digital signals proportional to the parameter 
monitored thereby. Similarly, operators 17,18,26,30 and 34 may be of any 
known electrical, pneumatic or electropneumatic type for executing 
operations in response to command signals from processing unit 42 and/or 
for providing input signals thereto. Fuel control 26 will normally supply 
fuel to engine 14 in accordance with the operator's setting of throttle 24 
but may supply a lesser (fuel dip) or greater (fuel boost) amount of fuel 
in accordance with commands from control unit 42. 
A portion of a typical transmission operator 34 may, for purposes of 
example only, be seen by reference to FIG. 2. Briefly, a shift fork 50 is 
carried by a shift rail 56 for axial movement therewith. A pair of opposed 
fluid actuated pistons, 58 and 60, are slidably and sealingly received in 
selectively pressurized cylinders, 62 and 64, respectively. A rod member 
66 is axially movable with shift rod 56 and shift fork 50 and defines a 
pair of grooves, 68 and 70, separated by land 72. A spring biased plunger 
74 cooperates with the land 72 to open gear neutral switch 76 and with 
grooves 68 and 70 to close gear neutral switch 76. The gear neutral switch 
76 thus provides a gear neutral signal (GNS) having a first value (GNS=.0. 
) to indicate the gear neutral condition and a second value (GNS=1) to 
indicate the not gear neutral condition. 
The gear neutral sensor input signal, GNS, if not previously declared 
faulty, is utilized by the AMT controller, or central processing unit, 42, 
to control shifting of automatic/semiautomatic mechanical transmission 12. 
For example, during a shift sequence when the transmission is being 
shifted from a previously engaged gear (GR.sub.L) into neutral, if the GNS 
indicates a gear neutral condition exists, the synchronization procedure 
may proceed. Also, after synchronization has occurred and the transmission 
12 is being shifted into the most recently selected gear (GR.sub.S), if 
the GNS signal indicates that a not gear neutral condition exists, the 
transmission is considered engaged, or at least partially engaged, and the 
master clutch 16 may be re-engaged. 
In the case of a fully automated AMT system 10, a purpose of the central 
processing unit 42 is to select, in accordance with a program (i.e. 
predetermined logic rules) and current or stored parameters, the optimal 
gear ratio at which the transmission should be operating and, if 
necessary, to command a gear change, or shift, into the selected optimal 
gear ratio based upon the current and/or stored information. 
The various functions to be performed by central processing unit 42, and a 
preferred manner of performing same may be seen in greater detail by 
reference to U.S. Pat. No. 4,595,986 assigned to the assignee of this 
invention and to published Society of Automotive Engineers SAE paper No. 
831776 published November 1983, the disclosures of which are hereby 
incorporated by reference. 
The gear neutral switch or sensor 76 provides signals for processing by the 
central processing unit 42 which are important for optimal operation of 
the clutch operator 30, optimal selectiion of desired gear ratio and 
optimal synchronization of transmission 12 during an upshift or downshift. 
It is important that the inputs (GNS=.0. or GNS=1) provided by sensor 76 
be periodically verified, and, if a fault is detected, the faulty sensor 
be identified and a modified logic be utilized to control system 10 which 
is the identified faulty sensor. 
The method of the present invention for verifying the inputs from the gear 
neutral sensor 76, for identifying a faulty input signal GNS, and for 
adapting an appropriate fault logic is schematically illustrated on FIG. 
3. The symbol ".0." is utilized to identify an equal, or substantially 
equal condition and the symbol "&gt;" is utilized to identify a greater than 
relationship. As stated above, the control or CPU 42 receives various 
input signals and processes these and/or stored information in accordance 
with a program of predetermined logic rules to issue command output 
signals for operation of the AMT system 10. 
A typical five forward speed, single reverse speed, change gear mechanical 
transmission, or transmission 12 for use within system 10 is schematically 
illustrated in FIG. 4. 
Transmission 12 is a simple transmission, or transmission section, of the 
twin countershaft type which is well known in the art, and which may be 
understood in greater detail by reference to U.S. Pat. Nos. 3,105,395; 
4,735,109 and 4,152,949, the disclosure of which are incorporated by 
reference. 
The illustrated transmission comprises an input shaft 114 carrying an input 
gear 116 for rotation therewith. Input shaft 114 is intended to be driven 
by prime mover 14 through a master clutch or torque converter as is well 
known in the art. A pair of substantially identical countershafts 118 and 
118A are rotatably mounted in a housing (not shown) by means of bearings 
120 120A. A main or output shaft 22 is provided which is preferably 
floatingly and/or pivotally mounted in the transmission housing. 
Each of the countershafts 120 and 120A carries countershaft gears 
124,126,128,130 and 132 fixed thereto for rotation therewith. Countershaft 
gear 124 is constantly meshed with the input gear 116. Third speed 
mainshaft gear 134 surrounds main shaft 122 and is constantly meshed with 
and supported by the countershaft gears 126. Second speed mainshaft gear 
136 surrounds main shaft 122 and is constantly meshed with and supported 
by countershaft gears 128. First speed mainshaft gear 138 surrounds main 
shaft 122 and is constantly meshed with and supported by countershaft 
gears 130. The reverse mainshaft gear 140 surrounds mainshaft 122, and is 
constantly meshed with and supported by a pair of idler gears (not shown) 
which, in turn, are constantly meshed with and driven by countershaft 
gears 132. Preferably, as is well known in the art, mainshaft gears 
134,136,138 and 140 are radially movable relative to mainshaft 122. The 
advantages of utilizing a floating mainshaft 22 and/or floating mainshaft 
gears are well known in the art and may be appreciated in greater detail 
by reference to the aforementioned U.S. Pat. No. 3,105,395. 
Axially slidable clutches 142,144 and 146 are mounted, preferably by a 
splined connection, to mainshaft 122 for axial sliding movement relative 
thereto, and for rotation therewith. Clutch 142 may be moved to the left 
from the neutral position shown to selectively couple the mainshaft 122 
directly with input gear 116 and input shaft 114 for fourth or direct 
drive of transmission 110 or moved rightwardly from the position shown to 
engage mainshaft gear 134 with mainshaft 122 for third speed operation of 
transmission 12. Clutch 144 may be moved from the position shown 
leftwardly to engage mainshaft gear 136 with mainshaft 122 for second 
speed operation or may be moved rightwardly from the position shown to 
engage mainshaft gear 138 with mainshaft 122 for first speed operation of 
transmission 12. Clutch 146 may be moved rightwardly from the position 
shown to engage mainshaft gear 140 with mainshaft 122 for reverse 
operation of transmission 12. Of course, clutches 142, 144 and 146 may be 
positive clutches, blocked clutches and/or synchronized clutches. 
A shift fork or yoke 148 is received in a groove in clutch 142 for 
controlling the axial position of clutch 142 relative to mainshaft 122. A 
shift fork 50 is received in a groove in clutch 144 for axially 
controlling the position of clutch 144 relative to mainshaft 122. A shift 
fork 152 is received in an axial groove in clutch 146 for controlling the 
axial position of clutch 146 relative to mainshaft 122. 
Shift bar housing assembly 34 includes three axially movable shift bars, 
also called shift rails or shift rods 154,156 and 158 which are 
substantially parallel and independently axially slidable in substantially 
parallel bores 162, 164 and 166, respectively, in shift bar housing. Shift 
bar housing is mountable to the transmission housing (not shown) in a 
conventional manner. Shift fork 148 is axially movable with shift bar 154, 
shift fork 150 is axially movable shift bar 156 and shift fork 152 is 
axially movable with shift bar 158. Of course, various levers and/or other 
mechanical/fluid connections may be interposed between the shift bars and 
the shift fork as is well known in the art. 
Central processing unit 42 will provide a signal indicative of desired 
engaged gear (GR.sub.s) ratio to a valve assembly 172, which will 
typically comprise a plurality of individually controllable valves, such 
as solenoid valves, or the like. Valve assembly 172 is fluidly connected 
to a source of pressurized fluid, preferably a compressible fluid such as 
compressed air, from a source 174 which is preferably regulated by a 
regulator valve 176. Pressurized fluid valve assembly 172 may be of any 
one of a plurality of designs, and will provide pressurized fluid to the 
shift bar housing assembly to selectively axially position the shift bars. 
The command signals from controller valve assembly 172 may be fluid, 
electrical, mechanical or a combination thereof, as is well known in the 
art. Preferably, central processing unit 42 microprocessor based as 
illustrated in U.S. Pat. No. 4,595,986 and transmission 12 is utilized in 
an automatic mechanical transmission system of the type illustrated in 
U.S. Pat. No. 4,361,060, the disclosure of which is hereby incorporated by 
reference. 
Transmission 10 is illustrated as utilizing positive, non-synchronized jaw 
clutches, as is well known in the art. Of course, frictional clutches, 
synchronized positive clutches and/or blocked clutches as are more fully 
described in U.S. Pat. Nos. 4,194,410; 3,924,484 and 3,799,002, the 
disclosures of which are hereby incorporated by reference, may be 
utilized. As only one of the clutches should be engaged at any one time to 
avoid damage to the transmission, shift bar housing assembly will include 
an interlock mechanism to prevent movement of more than one of the shift 
bars 154, 156 and 158 from the neutral axial positions thereof at a given 
time 
The details of construction of transmission or transmission section 12 and 
of the shift coils and clutches may be appreciated in greater detail by 
reference to above-mentioned U.S. Pat. Nos. 3,105,395; 3,799,002; 
4,722,237 and 4,735,109. 
This invention detects a false transmission neutral (GNS=.0.) indication 
for automatically/semiautomatically controlled mechanical transmissions 
that utilize a sensor 76 to indicate that the transmission is in a neutral 
state. In actuality, the sensor senses a position of a shift rail 136 or 
138 rather than the engaged gear 56. The coupling to the sensor is through 
a shift yoke member 50 being driven by an air pressurized shift rail to a 
dog clutch 144 for the engaged gear. A false transmission neutral 
indication can readily occur due to deflections of the mechanical members, 
wear at the dog clutch, shift yoke or sensor mechanism, a malfunctioning 
sensor and the like. 
Its purpose is to detect a false transmission neutral indication and 
provide a failsafe condition upon the detection of such a fault. 
Should the signal be in error, and not be detected, damage to other system 
components may result along with the possibility of unsafe vehicle 
operation. 
Upon sensing a command from CPU 42 to shift transmission from a last 
engaged gear ratio, GR.sub.L, to a selected gear ratio, GR.sub.S, and upon 
receiving an indication from the gear neutral sensors 76 that the 
transmission is in the gear neutral condition (GNS=.0.), periodically, 
preferably at least once during each period of time in which the various 
mechanical actuators can react to a command output signal, the logic or 
control method utilized in processing unit 42 will attempt to verify the 
nonfaulty operation of the gear neutral sensors 76, and, if a fault is 
detected, modify the control logic in a manner to provide failsafe 
modified operation. 
Assuming central processing unit 42 is a microprocessor based control unit, 
a complete cycle of processing current and stored parameters and issuing 
command output signals can be accomplished in less than 15-20 milliseconds 
while a typical actuator, such as a solenoid controlled valve or the like, 
will require a minimum of 20-30 milliseconds to cause even initial 
movements of an operator such as clutch operator 30. 
The gear neutral sensor circuit can fail in one of two ways, namely GNS can 
indicte a gear neutral condition (i.e. GNS=.0.) when the transmission 12 
is actually not in neutral or the GNS circuit can indicate a not gear 
neutral condition (i.e. GNS=1) when the transmission 12 is actually in 
neutral. Upon detecting either type of fault, the GNS signal from sensor 
76 is considered faulty, is ignored, a fault indicator, such as indicator 
46, is actuated, and the logic is modified. 
Preferably, the first step is to verify the non-faulty operation of the 
gear neutral sensor indication (GNS=.0.) and if verified, to proceed with 
the remainder of the control algorithm. 
Typically, the control algorithms for system 10 require the indication of a 
transmission neutral signal prior to taking any action to bring the 
transmission to synchronous. Once the sensors 76 indicate neutral, the 
control actuates a system component a fuel control for a burst of fuel or 
an input shaft brake that applies a torque to the input of the 
transmission bringing it to synchronous for the gear selected. The control 
system continuously monitors the input speed IS and output speed OS of the 
transmission and calculates a speed difference across the gears to be 
engaged, called error. At the same time, the system continuously 
calculates the speed difference for the last gear the transmission was in, 
called FLTERROR. If the transmission is truly in neutral, the value of 
error will decrease and the value of FLTERROR will increase as the input 
shaft approaches synchronous. Using these facts, an algorithm was 
designed, such that, during a shift and when the sensor indicates that the 
transmission is in neutral and a system component is commanded to apply a 
torque to the input of the transmission the value of FLTERROR is monitored 
and compared to a calibration value for a short period of time. The 
selection of the calibration value is based upon the speed steps between 
gears, minimum obtainable error values, and mechanical backlash between 
the measuring speed sensors. If during that period of time, the value of 
FLTERROR does not exceed the calibration value (REF), a fault is declared. 
This fault indicates that the transmission has not come out of gear, even 
though the sensor indicates that it has. Continuing to apply a torque to 
the input of the transmission further prevents it from coming to neutral 
due to torque lock on the clutches. Once the fault is established the 
system reselects the last gear and prohibits any further gear selections. 
Since it has already been established that the transmission did not come 
out of the last gear, no further synchronization is required. The control 
system allows the vehicle to continue to operate in the gear the fault 
occurred in (i.e. the last gear ratio GR.sub.L) until the vehicle comes to 
a stop, at which time the vehicle is rendered disabled. 
In a simple transmission, FLTERROR equals IS-OS*GR.sub.L while in a 
compound transmission, to calculate FLTERROR across the supposedly 
disengaged gear, FLTERROR equals [(IS/GR.sub.LF)-(GR.sub.LR *OS) ] where 
GR.sub.LF and GR.sub.LR are, respectively, the front and rear 
[(IS/GR.sub.LF)-(GR.sub.LR *OS)] transmission section ratios in the last 
engaged transmission ratio. 
The calibration value, REF, and the time during which a torque is applied 
to the input shaft 114 of the transmission will preferably vary with ratio 
steps between last gear ratio GR.sub.L and selected gear ratio GR.sub.S, 
system backlash time required to come out of gear (usually not in excess 
of 100 milliseconds) and sensor accuracy. Further, for a more accurate 
system, FLTERROR may be integrated with respect to time to determine a 
relative rotation between expected input and output shaft positions which 
may be compared to a system backlash value. 
Although the AMT system 10 has been described as utilizing a microprocessor 
based control 42 and the methods and operations carried out as software 
modes or algorithms, it is clear that the operations can also be carried 
out in electronic/fluidic logic circuits comprising discrete hardware 
components. 
Clutch operator 30 is preferably controlled by the central processing unit 
42 and may engage and disengage master clutch 16 as described in 
above-mentioned U.S. Pat. No. 4,081,065. Transmission 12 may include 
synchronizing means, such as an accelerator and/or a brake mechanism as 
described in U.S. Pat. No. 3,478,851, hereby incorporated by reference. 
The transmission 12 is preferably, but not necessarily, of the twin 
countershaft type as is seen in U.S. Pat. No. 3,105,395, hereby 
incorporated by reference. 
Although the present invention has been set forth with a certain degree of 
particularity, it is understood the various modifications are possible 
without departing from the spirit and scope of the invention as 
hereinafter claimed.