Control and method for controlling AMT system including manually operated engine compression brake

A method and control for controlling an AMT system (10) having an operator actuated engine compression brake (17) is provided including sensing vehicle deceleration and monitoring throttle position (THL), vehicle brake actuation (BRK) and engine compression brake (ECB) actuation to select one of three (50, 52, 54) mutually exclusive vehicle deceleration downshift shift profiles.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to automatic/semiautomatic power transmissions 
providing a plurality of gear reduction ratios, such as 
automatic/semiautomatic mechanical transmissions (i.e. "AMTs"), and, to 
control systems and methods therefor. In particular, the present invention 
relates to control systems and methods for automatic/semiautomatic 
mechanical transmission systems wherein gear selection and shift decisions 
are made and/or executed based upon measured and/or calculated parameters 
such as 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 control and method for 
controlling an AMT system including a manually operated engine compression 
brake during sensed vehicle deceleration by modifying the downshift logic 
in response to sensed throttle, vehicle brake and/or engine compression 
brake operation. 
2. Description of the Prior Art 
The use of 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 and shift decisions are made based upon certain 
measured and/or calculated parameters such as 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 /semiautomatic transmission control systems for 
vehicles may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,595,986; 
4,576,065; 4,569,255; 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 and 3,942,393, and European 
Pat. No. 0 071,353, the disclosures of which are all hereby incorporated 
by reference. 
Automatic control systems/subsystems for automatically controlling the 
engagement and disengagement of AMT system vehicle master clutches, 
especially during vehicle start from stop operations, are known in the 
prior art as may be seen by reference to U.S. Pat. Nos. 4,081,065; 
4,401,200; 4,413,714; 4,432,445, 4,509,625 and 4,576,263, the disclosures 
of all of which are hereby incorporated by reference. 
While the above referenced automatic/semiautomatic transmission control 
systems, especially the system illustrated in U.S. Pat. Nos. 4,081,065; 
4,361,060; 4,595,986; 4,576,065; 4,569,255 and 4,576,263, and similar 
systems, are effective to control the vehicle automatic/semiautomatic 
transmission system operations under most conditions, under certain 
vehicle deceleration conditions, the logic did not accurately sense 
vehicle operating conditions/operator intentions and some downshifts were 
performed in other than the most desirable manner. 
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/semiautomatic mechanical transmission systems wherein gear 
selection and shift decisions, especially vehicle deceleration downshift 
decisions, are made and/or executed based upon measured and/or calculated 
parameters including at least input signals indicative of engine speed, 
throttle position, vehicle speed, operation of the vehicle brakes and 
operation of the vehicle engine compression brake. Other 
inputs/parameters, such as signals indicative of the transmission input 
shaft speed, rate of change of throttle position, condition of the master 
clutch, currently engaged gear ratio, and the like, may also be utilized 
to make decision for control of the AMT system. The various input signals 
are processed to provide downshift logic rules whereby the AMT system will 
perform transmission downshifts in a manner most suited for vehicle 
operating conditions. 
The above is accomplished by providing a transmission control system 
including a central processing unit generating shift patterns (i.e., shift 
points) based upon sensed or calculated parameters processed by a central 
processing unit in accordance with predetermined logic rules or programs. 
The predetermined logic rules or programs by which the various input 
signals are processed include a method for detecting or predicting at 
least four distinct vehicle deceleration operating conditions. These 
vehicle deceleration operating conditions include a coasting condition 
wherein the vehicle operator is allowing the vehicle to decelerate at a 
relatively low rate determined by road conditions and vehicle inertia, a 
moderate braking condition wherein the vehicle is decelerated at a 
relatively moderate rate by the operator's application of the vehicle 
brakes only, a maximum braking condition wherein the operator is applying 
the vehicle brakes and the engine compression brake to achieve a maximum 
available vehicle deceleration rate, and a vehicle performance required 
condition wherein the vehicle is decelerating while the operator is 
maintaining the throttle control at greater than a predetermined reference 
value. 
In both the maximum braking condition and the performance required 
condition of vehicle deceleration, it is highly desirable that the 
transmission be downshifted such that, after completion of the downshift, 
the engine speed will be at a relatively maximum value, such as the 
governed engine speed, to provide maximum performance and for maximum 
engine compression braking. In the coasting mode of operation, it is 
desirable that the transmission be downshifted at relatively low engine 
speed such that, after the downshift, the engine speed will be at a 
relatively low value allowing smooth deceleration of the vehicle to 
continue. In the moderate braking condition, it is desirable that the 
transmission be downshifted at engine speeds such &hat, after completion 
of the downshift, the engine speed will provide a degree of engine 
compression for retarding motion of the vehicle, but will not be unduly 
harsh to provide an objectionably rough ride for the vehicle operator 
and/or to provide a sudden deceleration of the vehicle which may be 
dangerous to those vehicles following the vehicle in which the AMT system 
is installed. 
The above is accomplished by providing predetermined logic rules or 
programs by which the above discussed vehicle deceleration operating 
conditions can be sensed and/or predicted. The central processing unit 
receives signals indicative of vehicle speed, throttle position, engine 
compression brake actuation, and vehicle brake actuation. If, during 
deceleration of the vehicle, either throttle position exceeds a 
predetermined reference value and/or the engine compression brake is 
actuated, the logic declares a performance/maximum braking condition and 
the downshift shift profiles are set to provide downshifting at engine 
speeds which, assuming relatively constant speed during the shift 
transient, will resolve in the engine speed being at a maximum value upon 
completion of the downshift. It, during vehicle deceleration conditions, 
throttle position does not exceed the predetermined reference value and 
the engine compression brake is not actuated while the vehicle brakes are 
actuated, the logic declares a moderate vehicle braking condition and the 
downshift shift profiles are set to provide a moderately high engine RPM 
upon completion of transmission downshifting. If, during vehicle 
deceleration, throttle position fails to exceed the predetermined 
reference value, and both the engine compression brake and the vehicle 
brakes are not actuated, the logic declares a vehicle coasting condition 
and downshift shift point profiles are selected to provide a relatively 
low engine speed upon completion of downshifting. 
Accordingly, it is an object of the present invention to provide a new and 
improved control and control method for an automatic/semi-automatic 
mechanical transmission system including a manually operated engine 
compression brake which senses and/or predicts various types of vehicle 
deceleration operating conditions and modifies the downshift shift 
profiles accordingly. 
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 
FIG. 1 schematically illustrates an automatic mechanical transmission 
system 10 including an automatic multi-speed compound change gear 
transmission 12 driven by a throttle control engine 14, such as a well 
known diesel engine, through a master friction clutch 16. An engine 
compression brake, such as an exhaust brake 17, for retarding the rotation 
speed of engine 14 and/or an input shaft brake 18, which is effective to 
apply a retarding force to the transmission input shaft upon disengagement 
of master clutch 16, may be provided as is well known in the 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. 
Exhaust brakes, also known as engine compression brakes, such as the well 
known "Jake Brake" are well known in the heavy-duty truck industry. 
The above-mentioned power train components are acted upon and/or 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 control 
vehicle throttle or other fuel throttling device 24, a fuel control device 
26 for controlling the amount of fuel to be supplied to the engine 14, an 
engine speed sensor 28 which senses the rotational speed of the engine 14, 
a clutch operator 30 which engages and disengages clutch 16, and which may 
also supply information as to the status of the clutch, an input shaft 
brake operator 31, a transmission operator 34, which is effective to shift 
the transmission 12 into a selected gear ratio and preferably to provide a 
signal indicative of the currently engaged ratio, and a transmission 
output shaft speed sensor 36. A vehicle brake monitor 38 senses actuation 
of the vehicle brake pedal 40 while an engine compression brake monitor 41 
senses actuation of the engine compression brake actuator 43. 
The above-mentioned devices supply information to and/or except commands 
from a central processing unit or control 42. The central processing unit 
42 may include analog and/or digital electronic calculation and logic 
circuitry, the specific configuration and structure of which circuitry 
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) provide electrical 
and/or pneumatic power to the various sensing, operating and/or processing 
units. 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. 4,595,986; 4,576,065; 
4,569,255; 4,361,060; 4,226,295; 4,038,889 and 3,776,048. 
Sensors 22, 28, 32, 36, 38, 41 and 44 may be of any known type or 
construction for generating analog or digital signals proportional to 
and/or indicative of the parameter monitored thereby. Similarly, operators 
17, 18, 26, 30 and 34 may be of any known electrical, pneumatic or 
electro-pneumatic type for executing operations in response to command 
signals on processing unit 42. Fuel control 26 will normally supply fuel 
to engine 14 in accordance with the operator setting of throttle 24, but 
may supply a lessor (fuel dip) or greater (fuel boost) amount of fuel in 
accordance with commands from control unit 42. 
In addition to the above-mentioned direct inputs, the central processing 
unit 42 may be provided with circuitry and/or logic routines for 
differentiating the input signals from sensors 28 and/or 36 to provide 
calculated signals indicative of the rate of acceleration of the engine 
and/or vehicle, means to compare the input signals from sensors 31 and 36 
to calculate a currently engaged gear ratio, means to compare the current 
engaged gear ratio with the signal from sensor 36 to provide a calculated 
engine speed, means to sense full throttle and means to differentiate the 
signal from sensor 22 to calculate the rate of change of the throttle 
position sensor. 
The central processing unit 42 may also comprise a memory means for storing 
certain input and/or calculated information and means for clearing the 
memory means upon the occurrence of a predetermined event. The memory 
means incorporated into the central processing unit 42 may store 
information such as the direction of the last shift (i.e. upshift or 
downshift), position of a throttle, rate of change of throttle position, 
vehicle speed or the like. The memory means may be reset upon the 
occurrence of a specified event, such as engine or vehicle speed being 
less than and of greater than a predetermined limit or limits, full 
application of a throttle, operator throttle setting exceeding a 
predetermined limit, the occurrence of a gear change, etc. 
It is understood that, given a known drive train, output speed and vehicle 
speed are related in a known manner. Also, assuming a fully engaged master 
clutch 16, input shaft speed and engine speed are equal and signals 
indicating any two of the input shaft/engine speed, currently engaged gear 
ratio and output shaft/vehicle speed is sufficient to specify all three 
parameters. 
The purpose of the central processing unit 42 is to select, in accordance 
with a program (i.e. predetermined logic rules) and current and stored 
parameters, the optimal gear ratio at which the transmission 12 should be 
operating and, if necessary, to command a gear change, or shift, into the 
selected optimal gear ratio. Ideally, decisions by the central processing 
unit 42 as to the proper gear ratio that should be selected and engaged, 
are based upon accurate sensing and/or predicting of current operating 
conditions and driver demands. 
One of the primary purposes of the central processing units programs or 
logic rules is to generate shift patterns, or shift point profiles. FIG. 3 
illustrates only the three vehicle deceleration downshift shift profiles 
50, 52 and 54 of the present invention. The shift point profiles generated 
by the central processing unit will determine if the transmission should 
remain in the currently engaged ratio, should be upshifted to the next 
highest ratio, or should be downshifted to the next lower ratio. In 
certain situations, multiple upshifts or downshifts may be selected. The 
shift point profiles graphically illustrated in FIG. 3 are a function 
above throttle position, expressed as a percentage of maximum throttling 
position, and of engine speed. Downshifts occur if the operating point 
moves to the left of the active downshift shift point profile. The engine 
speed may be directly sensed or, preferably, as calculated engine speed 
which will not vary during a shift transient, as is known in the prior 
art. As is well known, assuming a relatively constant vehicle speed during 
a shift transient, the engine speed, upon completion of a downshift, will 
be greater than the engine speed prior to the downshift, by a factor of 
the ratio step. Accordingly, the greater the engine speed at which 
downshifts are commanded, the greater the engine speed upon completion of 
the downshift. 
Referring to FIG. 3 and assuming a transmission ratio step of about 28% to 
32% for transmission 12, dashed line 56, 58 and 60 represent the expected 
engine speeds at completion of downshifts performed accordance with 
downshift shift profiles 50, 52 and 54, respectively. Assuming engine 14 
to be a diesel engine having a maximum governed speed of about 2100 RPM, 
as represented by line 62, downshifting in accordance with downshift shift 
profile 50, will provide maximum engine performance and/or maximum engine 
compression braking, downshifting in accordance with downshift shift 
profile 52 will provide a more moderate, less harsh, engine compression 
braking while downshifting in accordance with downshift shift profile 54 
provide relatively little, if any, engine compression braking. 
Accordingly, upon sensing the vehicle deceleration operating conditions 
indicating a need for vehicle performance and/or maximum vehicle braking, 
it is desirable that the logic utilized downshift shift profile 50, upon 
sensing a vehicle coasting condition, that the logic utilize the downshift 
shift profile 54 and upon sensing a moderate vehicle braking condition, 
that the logic utilize the downshift shift profile 52. 
Assuming, for purposes of illustration, that transmission 12 is a twelve 
forward speed transmission having substantially equal ratio steps of about 
30% and that engine 12 is a diesel engine governed to a maximum engine 
rotational speed of 2100 RPM, the relative consequences of selecting 
vehicle deceleration shift point profiles 50, 52 or 54 may be seen be 
reference to FIGS. 2A and 2B, which are vehicle deceleration downshift 
speed charts. Briefly, the speed charts illustrated in FIGS. 2A and 2B 
illustrate the engaged transmission ratio at a specified engine speed and 
vehicle speed. The shift points obtained by utilizing downshift shift 
profile 52 are illustrated in solid lines in both FIGS. 2A and 2B. The 
transmission ratio and engine rotational speed characteristics obtained by 
utilizing the maximum performance/maximum engine braking downshift profile 
50 is illustrated in dotted lines in FIG. 2A, while the transmission ratio 
and engine rotational speed characteristics obtained by utilizing the 
coast mode downshift shift profile 54 is illustrated in dotted lines in 
FIG. 2B. 
Referring to FIG. 2A, it may be appreciated that by utilizing the maximum 
performance/maximum engine compression braking downshift profile 50, and 
assuming that vehicle speed remains relatively constant during the 
relatively rapid shift transient, the engine speed at completion of a 
downshift will be approximately the governed engine speed. As is well 
known in the prior art, maximum performance and maximum engine braking are 
obtained in a diesel engine when the diesel engine is operating at or near 
its maximum governed engine RPM. It is noted that in the lower gear 
ratios, shift point profile 50 is selected such that the engine RPM at 
completion of a downshift is somewhat less than maximum governed engine 
speed to prevent unduly harsh and potentially damaging and dangerous 
vehicle operation. 
Selection of an appropriate vehicle deceleration downshift shift profile 
50, 52 or 54, does, of course, require that the logic rules accurately 
predict the current vehicle deceleration operating conditions and vehicle 
operator intentions. FIG. 4 schematically illustrates logic rules by which 
the sensed input parameters may be utilized to predict the current vehicle 
deceleration/operator intention conditions. Upon a determination that the 
vehicle is decelerating, as may be obtained by monitoring the signal from 
transmission output shaft speed sensor 36 and differentiating same, the 
logic will process input signals from the throttle position sensor 22 
(THL), the brake actuator sensor (BRK) and the engine compression brake 
sensor (ECB). 
If the throttle signal (THL) is greater than a predetermined reference 
signal, which reference signal may be 0% throttle, this is an indication 
that the vehicle is decelerating due to adverse road conditions, such as 
operation on a relatively steep hill, and that the operator desires 
performance. Accordingly, upon sensing a throttle position signal greater 
than the predetermined reference, the logic will declare a performance 
required vehicle deceleration condition and the performance/maximum 
braking downshift shift profile 50 will be utilized. If a signal 
indicating operator actuation of the engine compression brake (ECB) is 
received, this is an indication of the operator requiring a maximum 
braking effort and the logic will declare a maximum braking required 
vehicle deceleration condition and will utilize the performance/maximum 
braking downshift shift point profile 50. If the vehicle is decelerating 
without the presence of a throttle position signal (THL) and without the 
presence of an engine compression brake (ECB) signal, while a signal 
indicating operator actuation of the vehicle brakes (BRK) is received, the 
logic will declare a moderate braking vehicle deceleration condition and 
the moderate braking downshift shift point profile 52 will be utilized. If 
the vehicle is decelerating in the absence of all of the throttle position 
(THL) signal, engine compression brake (ECB) and vehicle brake (BRK) 
signals, the logic will declare a coasting vehicle deceleration condition 
and the coasting downshift shift point profiles 54 will be utilized. 
Accordingly, it may be seen that by the control, and the control method, of 
the present invention, predetermined logic rules are provided allowing the 
central processing unit 42 of an AMT system 10 to process available input 
parameters to determine if a vehicle deceleration condition exists, and, 
if such a condition is sensed, to predict the conditions and/or operator 
intentions causing the vehicle deceleration conditions and to select 
appropriate downshift shift point profiles in view of the predicted 
condition. 
Although the present invention has been set forth with a certain degree of 
particularity, it is understood that various modifications are possible 
without departing from the spirit and the scope of the invention as 
hereinafter claimed.