METHOD OF ESTIMATING VEHICLE DECELERATION
DURING A TRANSMISSION GEAR SHIFT
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for estimating deceleration of a
wheeled vehicle during a transmission gear shift.
2. Background Art
Wheeled vehicles, such as automobiles and trucks, have transmissions that
adapt the power of an engine to meet varying road and load conditions. Such
transmissions may have an input shaft connected to an engine and an output shaft
adapted to drive vehicle traction wheels. The torque provided to the vehicle traction
wheels by the output shaft is interrupted during a transmission gear shift. As a result,
the speed of the vehicle may decrease during the gear shift.
Shift control systems, such as that disclosed in United States Patent No.
5,272,939, use an engine torque value and a vehicle acceleration value to predict
whether a shift is feasible before commencing a gear shift. These inputs must be heavily
filtered or dampened to reduce noise due to vehicle driveline dynamics, such as the
torsional vibrations. This filtering causes the filtered signals to lag real time signals and
can result in late transmission gear shifts. In addition, the vehicle acceleration value is
obtained by differentiating a shaft rotational velocity signal. Differentiating the
rotational velocity signal increases the signal noise by a significant order of magnitude
and may lead to suboptimal shift decisions that reduce fuel economy and degrade
transmission performance.
SUMMARY OF THE INVENTION
According to the present invention, a method for estimating deceleration
of a vehicle during a transmission gear shift is provided. The method includes the steps
of determining an expected vehicle deceleration during a transmission gear ratio shift to
a target gear ratio as a function of a first signal and a second signal and outputting the
expected vehicle deceleration value to a shift decision control unit for implementing a
transmission gear shift. The first signal is indicative of an engine torque and the second
signal is indicative of an input shaft rotational speed. The first signal may be measured
at the transmission output shaft or may be provided by an engine control module. The
second signal may also be measured at the transmission output shaft.
The expected vehicle deceleration during the transmission gear shift may
be calculated using the torque on the transmission due to vehicle drag forces, gross
vehicle weight, and a constant. The constant may be a function of the axle ratio of the
vehicle and the radius of a tire disposed on the vehicle.
According to another aspect of the invention, the method may comprise
the steps of providing a set of initial values for a current time period, determining a set
of estimated values for a future time period, providing an estimated vehicle deceleration
value to a shift decision control unit, calculating a set of error values, calculating a set of
correction values, and adjusting the set of estimated values using the set of correction
values.
The set of initial values may include an engine torque value, an input
shaft rotational speed value, and a vehicle deceleration value. The set of estimated
values for a future time period may include an estimated engine torque value, an
estimated input shaft rotational speed rotational value, and an estimated vehicle
deceleration value. The step of providing the engine vehicle deceleration value to a shift
decision control unit may be performed after adjusting the set of estimated values using
the set of correctional values.
The set of error values may be based on the first signal, the second signal,
and a subset of the set of estimated values. The subset of the set of estimated values
may comprise the estimated engine torque value and the estimated input shaft rotational
speed value. The set of estimated values may be used as the set of initial values in a
future time period. The set of correction values may be calculated using the set of error
values and a set of predetermined coefficients.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic view of a vehicle and the resistive forces acting on
the vehicle.
Figure 2 is a schematic view of a vehicle transmission system.
Figure 3 is a flowchart of one embodiment of a method for determining
deceleration of the vehicle during a transmission gear shift.
Figure 4 is a flowchart of another embodiment of the method for
determining deceleration of the vehicle during the transmission gear shift.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
Figure 1 shows a vehicle 10 traveling up a slight grade. Three resistive
forces are shown acting on the vehicle 10. The first force 12 represents the aerodynamic
drag on the vehicle 10. The second force 14 represents the rolling resistance due to the
road surface and frictional effects. The third force 16 represents the grade resistance
due to gravitational forces on the vehicle 10 caused by the slope of the road. These
forces act to decelerate the vehicle 10 during a transmission gear shift.
Figure 2 shows a transmission system 20 of the vehicle 10. The
transmission system 20 includes an engine 22 connected to a transmission 24 via an input
shaft 26. The transmission 24 includes a number of gear ratios 28 and an output shaft
30 that is adapted to drive vehicle traction wheels. Specifically, the output shaft 30 is
connected to a differential 32 that is connected to a pair of axles 34 that are each
connected to a vehicle wheel 36. When a gear ratio is engaged, the engine torque at the
input shaft 26 is transmitted through the transmission 24 to the output shaft 30,
differential 32, and axles 34 to turn the vehicle wheels 36.
The transmission system 20 includes a shift decision control unit 38 that
processes inputs to determine whether a gear shift should be executed. These inputs
include a rotational velocity signal and an engine torque signal. The rotational velocity
signal may be provided by an input shaft speed sensor 40 or an output shaft speed sensor
42. The engine torque value may be provided by one or more torque sensors, such as an
input shaft torque sensor 44 or an output shaft torque sensor 46, or by an engine control
module 48 that monitors engine performance. In the present invention, the rotational
velocity signal and the engine torque signal do not need to be filtered before being
provided to the shift decision control unit 38.
The shift decision control unit 38 is connected to actuators (not shown)
that shift the transmission 24 from a current gear ratio to a desired target gear ratio.
When a decision is made to shift the transmission, the input shaft 26 is temporarily
disengaged from the output shaft 30. As a result, the resistive forces 12, 14, 16 shown
in Figure 1 can decrease the speed of the vehicle 10 and consequently reduce the
rotational velocity of the output shaft 30. By predicting the vehicle deceleration due to
these resistive vehicle drag forces, a more accurate shift decision may be determined.
Referring to Figure 3, a flowchart of one embodiment of the present
invention is shown. At 60, a set of initial values for a current time period (n) is
provided. The initial value set includes a current engine torque (Enginetorquen), current
input shaft rotational velocity (Speedn), and current torque due to resistive forces acting
on the vehicle (Dragtorquen). Each initial value may be arbitrarily selected or may be
based on test data or other quantitative assessments of the vehicle and transmission
system performance.
Next, at 62, a set of estimated values for a future time period (n +1) are
calculated. The estimated value set includes a predicted torque due to resistive forces
acting on the vehicle (Dragtorquen+i), a predicted engine torque (Enginetorquen-w), and a
predicted input shaft rotational speed (Speedn+i). Dragtorquen+i and Enginetorquen-i are
set equal to their initial values, Dragtorquen and Enginetorquen, respectively. The
predicted input shaft rotational speed (Speedn+i) is determined by the relationship:

The constant C is determined as a function of the vehicle axle ratio and
the tire radius. The value of the constant C depends on the units of measurement used.
For example, if U.S. customary weights and measurements are used, (e.g., distance
measured in feet and force measured in pounds), the constant C is determined by the
expression:

In the next block 64, a set of error values is determined based on the
difference between the estimated values and actual measured values. Specifically,
Errorenginetorque is the difference between the measured engine torque (Enginetorqueactuai)
and the estimated engine torque (Enginetorquen+i) and is determined by the expression:

Likewise, Errorspecd is the difference between the measured input shaft rotational speed
(Speedacnui) and die estimated input shaft rotational speed (Speedn+i) and is determined by
the expression:

Next, at 66, a set of correction values is determined using the set of error
values and correction coefficients. The correction coefficients are constants and are
designated BO, Bl, B2, B3, B4, and B5. Their values may be established arbitrarily or
may be tailored to the particular powertrain characteristics of the vehicle as determined
through testing and performance assessments. In the present embodiment, three
correction values are determined. The first correction value (Correctiondragwrque) is
determined by the expression:

The second correction value (Correctioncngii«orque) for the engine torque is determined by
the expression:

The third correction value for the rotational speed (Correctionspeed) is determined by the
expression:

At 68, the set of correction values is used to determine a new set of initial
values for the next iteration. Specifically, the following expressions are used:
Finally, at 70, the value of Dragtorquen is outputted to the shift decision
control unit 38. The shift decision control unit 38 then uses this value as an input in a
shift control algorithm to determine whether a vehicle shift from a current transmission
gear ratio to a target transmission gear ratio should be implemented. The process then
returns to block 62 and the process repeats for the next time period.
Referring to Figure 4, a flowchart of an alternate embodiment of the
present invention is shown. The individual steps 80, 82, 84, 86, 88 and 90 coincide
with the steps in Figure 3. However, the sequence of steps is altered such that the step
of outputting the value of Dragtorquen to the shift decision control unit 38 takes place
earlier in the process. Specifically, Dragtorquen is outputted in step 84 after the set of
initial values is determined at 82, but before error values are calculated at 86.
While embodiments of the invention have been illustrated and
described, it is not intended that these embodiments illustrate and describe all possible
forms of the invention. Rather, the words used in the specification are words of
description rather than limitation, and it is understood that various changes may be made
without departing from the spirit and scope of the invention.
WE CLAIM
1. A method for estimating deceleration of a wheeled vehicle (10) during a
transmission gear shift, the vehicle having a transmission system (20)
comprising an engine (22), a transmission (24) having a plurality of gear
ratios (28), an input shaft (26) driven by the engine, an output shaft (30)
adapted to drive a vehicle wheel (36), a first signal indicative of an engine
torque, and a second signal indicative of an input shaft rotational speed,
the method comprising the steps of:
determining as a function of the first signal indicative of the engine torque
and the second signal indicative of the input shaft rotational speed, an
expected vehicle deceleration value (Dragtorquen+1) during a transmission
gear ratio shift to a target gear ratio; and
outputting the expected vehicle deceleration value to a shift decision
control unit (38) for implementing a transmission gear shift.
2. The method as claimed in claim 1 wherein the first signal indicative of the
engine torque is measured at the output shaft (30) of the transmission
(24).
3. The method as claimed in claim 1 wherein the first signal indicative of the
engine torque is provided by an engine control module (48).
4. The method as claimed in claim 1 wherein the second signal indicative of
the input shaft rotational speed is measured at the output shaft (30) of
the transmission (24).
5. The method as claimed in claim 1 wherein the expected vehicle
deceleration during the transmission gear shift is determined as a function
of the expression
Dragtorquen * C/W
where:
Dragtorquen is the torque due to vehicle drag forces (12, 14, 16) at a time
n,
W is the gross vehicle weight, and
C is a constant
6. The method as claimed in claim 5 wherein the value for the constant (C)
is a function of the expression
307*(Ratioaxie2/Radiustire2)
Where:
RatiOaxie is the axle ratio of the vehicle, and
Radius^ is the radius of the tire disposed on the vehicle.
7. A method for estimating deceleration of a wheeled vehicle (10) during a
transmission gear shift, the vehicle having a transmission system (20)
comprising an engine (22), a transmission (24) having a plurality of gear
ratios (28), an input shaft (26) driven by the engine, an output shaft (30)
adapted to drive a vehicle wheel (36), a first signal indicative of an engine
torque, and a second signal indicative of an input shaft rotational speed,
the method comprising the steps of:
providing a set of initial values for a current time period (n) including an
engine torque value (Enginetorquen), an input shaft rotational speed value
(Speedn) and a vehicle deceleration value (Dragtorquen);
determining a set of estimated values for a future time period (n+1)
including an estimated engine torque value (Enginetorquen+i), an
estimated input shat rotational speed value (Speedn+0, and an estimated
vehicle deceleration value (Dragtorquen+i);
providing the estimated vehicle deceleration value (Dragtorque n+i) to a
shift decision control unit (38) for implementing a transmission gear shift;
determining a set of error values (Errorengineteorque, Errorspeed) based on the
first signal, the second signal, and a subset of the set of estimated values;
determining a set of correction values (Correctiondragtorque/ Corresctionspeed,
Correctionenginetorque) based on the set of error values including an engine
torque correction value, an input shaft rotational speed correction value,
and a vehicle deceleration corrections values;
adjusting the set of estimated values using the set of correction values;
and
using the set of estimated values as the set of initial values in the future
time period.
8. The method as claimed in claim 7 wherein the subset of the set of
estimated values comprises the estimated engine torque value
(Enginetorquen+i).
9. The method as claimed in claim 8 wherein the set of error values is
determined by subtracting the estimated engine torque value from the
first signal and by subtracting the estimated input shaft rotational speed
values from the second signal.
10.The method as claimed in claim 7 wherein the set of correction values
(Correctiondragtorque, Correctionspeed, Correctionenginetorque) is calculated using
the set of error values (Errorengineteorque, Errorspeed) and a set of
predetermined coefficients (BO, Bl, B2, B3, B4, B5).
11.The method as claimed in claim 7 wherein the first signal indicative of the
engine torque is measured at the output shaft of the transmission.
12.The method as claimed in claim 7 wherein the first signal indicative of the
engine torque is provided by an engine control module (48).
13.The method as claimed in claim 7 wherein the second signal indicative of
the input shaft rotational speed is measured at the output shaft of the
transmission.
14. A method for estimating deceleration of a wheeled vehicle (10) during a
transmission gear shift, the vehicle having a transmission system (20)
comprising an engine (22), a transmission (24) having a plurality of gear
ratios (28), an input shaft (26) driven by the engine, an output shaft (30)
adapted to drive a vehicle wheel (36), a first signal indicative of an engine
torque, and a second signal indicative of an input shaft rotational speed,
the method comprising the step of:
providing a set of initial values for a current time period (n) including an
engine torque value (Enginetorquen), an input shaft rotational speed value
(Speedn), and a vehicle deceleration value (Dragtorquen);
determining a set of estimated values of a future time period (n+1)
including an estimated engine torque value (Enginetorquen+i), an
estimated input shaft rotational speed value (Speedn+i), and an estimated
vehicle deceleration value (Dragtorquen+i);
determining a set of error values (Errorengineteorque/ Errorspeed) based on the
first signal, the second signal, and a subset of the set of estimated values;
determining a set of correction values (Correctiondragtorque/ Correctionspeed,
Correctionenginetorque) based on the set of error values including an engine
torque correction value, an input shaft rotational speed correction value,
and a vehicle deceleration correction value;
adjusting the set of estimated values using the set of correction values;
providing the estimated vehicle deceleration value to a shift decision
control unit (38) for implementing a transmission gear shift; and
using the set of estimated values as the set of initial values in the future
time period.
15.The method as claimed in claim 14 wherein the first signal indicative of
the engine torque is measured at the output shaft of the vehicle
transmission.
16.The method as claimed in claim 14 wherein the first signal indicative cf
the engine torque is provided by an engine control module (48).
17.The method as claimed in claim 14 wherein the second signal indicative of
the input shaft rotational speed is measured at the output shaft of the
transmission.
18.The method as claimed in claim 14 wherein the subset of the set of
estimated values comprises the estimated engine torque value and the
estimated input shaft rotational speed value.
19.The method as claimed in claim 18 wherein the set of error values is
determined by subtracting the estimated engine torque value from the
first signal and by subtracting the estimated input shaft rotational speed
value from the second signal.

The invention relates to a method for estimating deceleration of a wheeled
vehicle (10) during a transmission gear shift, the vehicle having a transmission
system (20) comprising an engine (22), a transmission (24) having a plurality of
gear ratios (28), an input shaft (26) driven by the engine, an output shaft (30)
adapted to drive a vehicle wheel (36), a first signal indicative of an engine
torque, and a second signal indicative of an input shaft rotational speed, the
method comprising the steps of, determining as a function of the first signal
indicative of the engine torque and the second signal indicative of the input shaft
rotational speed, an expected vehicle deceleration value (Dragtorquen+1) during
a transmission gear ratio shift to a target gear ratio; and outputting the expected
vehicle deceleration value to a shift decision control unit (38) for implementing a
transmission gear shift.