Interrelated power delivery controls – including engine control – Transmission control – Anticreep
Reexamination Certificate
2001-11-29
2003-10-21
Marmor, Charles A. (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Anticreep
Reexamination Certificate
active
06634987
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority of Korea patent Application No. 10-2000-71894, filed on Nov. 30, 2000.
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a creep-control method for an automatic transmission of a vehicle, and more particularly, to a creep-control method wherein a second shift-speed is maintained to prevent rearward rolling on a slope and shift shock is reduced by optimal shift control from the second shift-speed to a target shift-speed when a creep-control state is released.
(b) Description of the Related Art
A conventional automatic transmission, equipped with a torque converter, performs shift control based on a variety of inputs regarding a driving state of a vehicle.
FIG. 1
shows a block diagram of a control apparatus for a conventional automatic transmission.
As shown in
FIG. 1
, the control apparatus includes a driving-state detecting unit
10
for detecting a plurality of vehicle driving-state factors, a transmission control unit (referred to as “TCU” hereinafter)
20
for determining an optimal shift pattern for the detected driving state and for controlling hydraulic shifting according to the determined optimal shift pattern, and an actuator unit
30
for performing hydraulic shifting according to the control of the TCU
20
.
The driving-state detecting unit
10
includes a throttle valve open-angle detector
11
for detecting an open-angle of the throttle valve, a vehicle speed detector
12
for detecting a speed of the vehicle, a shift-lever position detector
13
for detecting a position of the shift lever, a turbine-speed detector
14
for detecting a revolution speed of the turbine in a torque converter (not shown), and an engine-speed detector
15
for detecting a revolution speed of the engine.
When the shift-lever is in a forward range such as a drive “D” range, a second “2” range, and a low “L” range, rotational torque of the engine is transmitted to an output shaft of the automatic transmission even if the vehicle is stopped because the transmission maintains a predetermined shift-speed. The control of the transmission to maintain the predetermined shift-speed at a very low vehicle speed is called creep-control, and the phenomenon whereby rotational torque is transmitted to the output shaft under creep-control is called a creep phenomenon. The predetermined shift-speed can be either of the first shift-speed and the second shift-speed.
FIGS. 2
a
,
2
b
,
2
c
,
3
a
, and
3
b
are speed diagrams for a conventional four-speed automatic transmission, wherein
FIG. 2
a
shows a state in which the vehicle is driven in a first shift-speed, and
FIG. 3
a
shows a state in which the vehicle is driven in a second shift-speed.
A shift mechanism of the transmission receives engine torque via a turbine of a torque converter through a rear clutch in the first and second shift-speeds. Therefore, the revolution speed of the rear clutch in the first and second shift-speeds can be understood as the revolution speed of an input element of the shift mechanism in those shift-speeds.
In the second shift-speed where a kick-down band brake is operated, a first operating element N
1
as shown in the far right of
FIG. 3
a
is stopped.
In the first shift-speed, the rear clutch N
4
and the first operating element N
1
revolve at opposite sides of a one-way clutch OWC.
More particularly, the first operating element N
1
rotates in an opposite direction to the rotation of the rear clutch N
4
, the rear clutch N
4
acting as an input element in the first shift-speed, because a second operating element on which the one-way clutch OWC acts is prevented from rotating backward.
Therefore, in a normal driving state, the rotational speed of the input element of the rear clutch N
4
is changed according to the speed diagram of
FIG. 2
a
and is transmitted to an output element of a third operating element N
3
.
However, when the vehicle is stopped, the output element of the third operating element N
3
is also stopped. Therefore, the rear clutch N
4
, engaged with the third operating element through a gear mechanism, is also stopped. Accordingly, revolution speeds of each of the first, second, third, and fourth operating elements N
1
, N
2
, N
3
, and N
4
are as shown in
FIG. 2
b.
A difference between the engine speed and the revolution speed of the rear clutch N
4
implies that slip corresponding to the speed difference occurs in the torque converter.
The torque converter transmits engine torque to the shift mechanism when slip occurs, and accordingly the shift mechanism of the automatic transmission changes revolution speed and torque of the engine, and outputs the changed speed and torque through the output element. Therefore, the output torque acts as a driving torque of the vehicle.
The driving torque of the vehicle acts as a driving force to drive the vehicle on a plane even when an accelerator pedal is not depressed, and it also acts as a force that prevents rearward rolling when the vehicle is stopped on a slope.
However, if the driving torque output from the output element is not sufficient, the vehicle may roll rearward on a steep slope when a driver takes his/her foot from a brake pedal.
FIG. 2
c
shows how the speed diagram may be changed when a vehicle is stopped on a slope and a brake pedal is released.
Gravitational force acts rearward on the vehicle when the vehicle is stopped on a slope and a brake pedal is released. However, the second operating element N
2
cannot have a negative revolution speed rate because of the one-way clutch OWC if the shift mechanism of the automatic transmission is set to the first shift-speed.
Therefore, if the torque transmitted to the shift mechanism is not sufficient, the speed diagram can pivot anti-clockwise around the center of the second operating element N
2
, and accordingly the output element N
3
can turn backward, which implies that the vehicle rolls rearward.
In the prior art in which an idle revolution speed of the engine is preset to be high, the problem of rearward vehicle rolling is not significant because of high torque transmitted to the shift mechanism. However, in the recent progression of engine control methods, it has been a trend that idle rpm of the engine is controlled as low as possible because it lowers fuel consumption. Therefore, rearward rolling of a vehicle on a slope has become more problematic in recently produced vehicles.
The prior art in which the shift mechanism of an automatic transmission is maintained at a first shift-speed also causes inconvenience in that a brake pedal must be pushed with a high force to keep the vehicle stationary.
The problem of rearward rolling on a slope and the inconvenience of applying the high braking force needed to hold the vehicle stationary according to the prior art can be solved by maintaining the shift mechanism at a second shift-speed for creep-control, which is herein-after explained in detail with reference to
FIG. 3
b.
In the second shift-speed, the first operating element N
1
is stopped and the second operating element N
2
is prevented from turning backward because of the one-way clutch OWC.
Therefore, the point of the output element N
3
in the speed diagram cannot be lowered below 0 even in the case when gravitational force acts as a rearward rolling force on the vehicle on a slope, because the speed diagram has a fixed point of the first operating element N
1
, and the second operating element N
2
cannot turn backward.
However, maintaining the shift mechanism in the second shift-speed may cause another problem.
When the accelerator pedal is depressed, the shift mechanism must be transformed into a first shift-speed from the second shift-speed. However, sudden release of the first operating element N
1
may cause a shift shock resulting from a sudden stop of the second operating element by the function of the one-way clutch OWC because the vehicle, and more particularly the second operating element N
2
, may gain a certain amount of speed during the time between rel
Abdelnour Dennis
Hyundai Motor Company
Marmor Charles A.
LandOfFree
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