Interrelated power delivery controls – including engine control – Transmission control – Transmission controlled by engine
Reexamination Certificate
2001-09-18
2003-10-28
Estremsky, Sherry (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Transmission controlled by engine
C477S143000
Reexamination Certificate
active
06638196
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a shift control apparatus for an automatic transmission and, especially, to a shift control apparatus for executing such a proper shift as is done by a changeover of friction elements, of which one friction element is brought into disengagement whereas another friction element is brought into engagement.
BACKGROUND ART
In the automatic transmission, there is a shift to be executed by the so-called “changeover of friction elements”, in which one friction element is brought into disengagement as the working oil pressure lowers whereas another friction element is brought into engagement as the working oil pressure rises.
Herein: the friction elements to be changed over from an engaging state to a disengaging state at the time of said changeover shift will be called the “disengagement side friction elements”; the working oil pressure will be called the “disengagement side working oil pressure”; and the friction elements to be switched from the disengaging state to the engaging state will be called the “engagement side friction elements”; and the working oil pressure will be called the “engagement side working oil pressure”.
At said changeover shift, the control to lower the disengagement side working oil pressure for bringing the disengagement side friction element into disengagement and the control to raise the engagement side working oil pressure for bringing the engagement side friction element into engagement are known in the prior art, as disclosed in Unexamined Published Japanese Patent Application No. 1-224549, for example.
By raising an engagement side working oil pressure P
C
from a shift command instant t
1
, as illustrated in FIG.
13
(
a
), an engagement side friction element is stroked against a return spring, and it is detected by an oil pressure switch to be turned ON at P
C
=P
1
that the engagement side friction element ends a loss stroke.
A disengagement side working oil pressure P
0
is so abruptly lowered to P
4
for the time period from a shift command instant t
1
to an instant of the loss stroke end detection of the engagement side friction element as to take an engaging capacity just before the disengagement side friction element starts to slip, and is so slowly lowered till an instant t
5
as to effect the aforementioned changeover, until it is abruptly lowered to 0.
On the other hand, the engagement side working oil pressure P
C
is so abruptly raised to an initial pressure P
2
that the aforementioned changeover may be started at and after the detection instant t
2
of the loss stroke end of the engagement side friction element to start a torque phase, and is further raised at a predetermined slow shelf pressure gradient to a pressure P
3
, at which an inertia phase ends, until it is raised to the highest level till an instant t
7
.
In a common sense, during the shelf pressure control of the engagement side working oil pressure P
C
, the engagement side friction element has to share the transmission input torque. It is, therefore, ordinary that the shelf pressure of the engagement side working oil pressure P
C
is raised, as indicated by a broken line, as an engine throttle opening degree TVO increases.
When the throttle opening degree TVO is high, therefore, the engagement side working oil pressure P
C
is abruptly raised for advancing the torque phase from the instant t
3
to a later instant t
4
.
Here in the shift control apparatus of the prior art thus far described, the changing rate at the time when the engagement side working oil pressure P
C
is raised to the initial shelf pressure from the detection instant t
2
of the loss stroke end of the engagement side friction element is given a constant gradient independently of the throttle opening degree TVO. Therefore, this gradient has to be relatively steepened for ending the torque phase within a predetermined short time period even for a high throttle opening degree, and the following problem may occur.
Here, the time-series changes of a turbine speed N
t
(or a transmission input speed) and a transmission output torque T
O
at a high throttle opening degree for determining the engagement side working oil pressure P
C
, as indicated by a broken line, are illustrated in FIG.
13
B. On the other hand, the time-series changes of a turbine speed N
t
(or the transmission input speed) and the transmission output torque T
O
at a low throttle opening degree for determining the engagement side working oil pressure P
C
, as indicated by a solid line, are illustrated in FIG.
13
C.
At the high throttle opening degree, the transmission output torque T
O
is relatively high, as illustrated in
FIG. 13B
, even if the torque falls at T
OT
in the torque phase, the transmission output torque T
O
does not take a negative value, and no serious tossing shock occurs just after the fall.
However, the changing rate at which the engagement side working oil pressure P
C
is raised to the initial shelf pressure from the loss stroke ending instant t
2
of the engagement side friction element has a constant gradient independently of the throttle opening degree TVO. As apparent from the comparison of the turbine speed N
t
illustrated in
FIGS. 13B and 13C
, therefore, the shift advances at a rate similar to that of the high throttle opening degree even at the low throttle opening degree having the small transmission output torque T
O
so that the turbine speed N
t
reaches that (i.e., the speed equal to a transmission output speed N
o
because N
t
e of the shift to the 3rd speed having a gear ratio
1
in the case of
FIG. 13
) after the shift. At the low throttle opening degree, therefore, the rising rate (or the torque phase advancing rate) of the engagement side working oil pressure P
C
during that period is excessive high, and the transmission output torque T
O
is relatively low, as illustrated in FIG.
13
C. Hence, there is caused the so-called “zero cross of the transmission output torque”, in which the fall T
OT
in the torque phase makes the transmission output torque T
O
once negative and then returns it to a positive value. There arises a problem that a serious tossing shock T
OS
is caused just after the zero cross.
Here, the zero cross of the transmission output torque reverses the direction of the torque for a short time thereby to generate a backlash noise between the gears in the gear transmission mechanism of the automatic transmission to cause the noise, as indicated as the sound pressure level in FIG.
13
C.
This problem of the backlash or the aforementioned serious tossing shock T
OS
is easily transmitted to the passenger at the low throttle opening degree because the transmission output torque T
O
is intrinsically low, and it has to be avoided.
In the aforementioned control of the prior art, on the other hand, the instant t
3
at which the disengagement side working oil pressure P
O
is to be abruptly lowered is usually controlled by an orifice control valve disposed in the hydraulic circuit, and this orifice control valve acts when the engagement side working oil pressure P
C
exceeds its set pressure. Thus, there arises a second problem that the disengagement side working oil pressure P
O
abruptly drops.
The set pressure of the orifice control valve is constant. Therefore, the set pressure has to be set at a high level so as to prevent the racing of the engine, i.e., an abrupt rise in the engine speed, which might otherwise be caused when the engaging capacities of the individual friction elements on the engagement side and the disengagement side become short for a shifting action at a high throttle opening degree TVO.
Where the orifice control valve is given a high set value, the engaging capacity of the disengagement side friction element is excessive at the shifting action for an intermediate or low throttle opening degree TVO. As a result, the transmission output torque T
O
drops (or falls) and abruptly rises (or tosses) in the deep and long torque of the torque phase. As a result, the drivability or riding comfortableness of the v
Murasugi Takashi
Otake Kazunari
Sano Takashi
Estremsky Sherry
Foley & Lardner
Jatco LTD
Lewis Tisha D.
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