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Claims  |
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What is claimed is:
1. A gear shift shock reducing apparatus of a hydraulic control system for
an automatic transmission including a driving member operatively connected
to the output shaft of an engine of an automotive vehicle, a driven
member, and frictional units having fluid operated actuating means
selectively made operative and inoperative for producing a plurality of
gear ratios between the driving and driven members, comprising:
means for generating a line fluid pressure;
means for generating a kickdown fluid pressure under a kickdown condition;
a manual valve provided operatively between said line fluid pressure
generating means and the respective fluid operated actuating means of the
frictional units;
a shift valve provided operatively between said manual valve and at least
one of the fluid operated actuating means of the frictional units, said
shift valve having a valve spool movable into a position providing
communication between said line fluid pressure generating means through
said manual valve and said at least one of the fluid operated actuating
means; and
a pressure reducing valve provided operatively between said at least one of
the fluid operated actuating means and said manual valve and having a
valve member movable into a position providing communication between said
at least one of the fluid operated actuating means and said manual valve
through said shift valve, said pressure reducing valve communicating with
said kickdown fluid pressure generating means for producing an actuating
fluid pressure which is not higher than said line fluid pressure in
response to the absence of said kickdown fluid pressure, said valve member
of said fluid pressure reducing valve including a first pressure-acting
area which is selectively exposed to said actuating said pressure to which
said at least one of the fluid operated actuating means is selectively
exposed and a second pressure-acting area, opposite to said first
pressure-acting area, which is selectively exposed to said kickdown fluid
pressure, said valve member of said pressure reducing valve being held in
said position providing communication between said at least one of the
fluid operated actuating means and said manual valve through said shift
valve when said second pressure-acting area is exposed to said kickdown
fluid pressure.
2. A gear shift shock reducing apparatus as claimed in claim 1, wherein
said pressure reducing valve communicates with said line fluid pressure
generating means and responsive to said line fluid pressure upon producing
said actuating fluid pressure, said valve member of said pressure reducing
valve including a third pressure-acting area, opposite to said first
pressure-acting area, which is exposed to said line fluid pressure.
3. A gear shift shock reducing apparatus as claimed in claim 2, wherein
said pressure reducing valve includes a spring biasing said valve member
of said pressure reducing valve toward said position providing
communication between said at least one of the fluid operated actuating
means and said manual valve through said shift valve.
4. A gear shift shock reducing apparatus as claimed in claim 3, wherein
said pressure reducing valve has a drain port and said valve member has
two axially spaced first and second lands which have the same diameter and
a third land which is axially spaced from said second land and is smaller
in diameter than said second land, said first land having said first
pressure-acting area, said second land and third land defining
therebetween said third pressure-acting area, said third land having said
second pressure-acting area, said first land selectively opening or
closing said drain port.
5. A gear shift shock reducing apparatus as claimed in claim 3, wherein
said pressure reducing valve has a drain port, and wherein said valve
member of said pressure reducing valve has two axially spaced first and
second lands, said second land being smaller in diameter than said first
land, said first land having said first pressure-acting area, said second
land having said second pressure acting area, said first and second lands
defining therebetween said third pressure acting area, said first land
selectively opening or closing said drain port.
6. A shock reducing apparatus of a hydraulic control system for an
automatic transmission including a driving member operatively connected to
the output shaft of an engine of an automotive vehicle, a driven member,
and frictional units having fluid operated actuating means selectively
made operative and inoperative for producing a plurality of gear ratios
between the driving and driven members, comprising:
a throttle pressure valve means for generating a throttle fluid pressure;
a pressure regulator valve means for generating a line fluid pressure
variable with said throttle fluid pressure;
means for generating a kickdown fluid pressure under a kickdown condition;
a manual valve provided operatively between the fluid pressure regulator
valve means and the respective fluid operated actuating means of the
frictional units;
a shift valve provided operatively between said manual valve and one of the
fluid operated actuating means of the frictional units, said shift valve
having a valve spool movable into a position providing communication
between said pressure regulator valve means and said at least one of the
fluid operated actuating means; and
a pressure reducing valve provided operatively between said at least one of
the fluid operated actuating means and said manual valve and having a
valve member movable into a position providing communication between said
at least one of the fluid operated actuating means and said manual valve
through said shift valve, said fluid pressure reducing valve communicating
with said kickdown fluid pressure generating means for producing an
actuating fluid pressure variable with said throttle fluid pressure in
response to the absence of said kickdown fluid pressure, said valve member
of said fluid pressure reducing valve including a first pressure-acting
area which is selectively exposed to said actuating fluid pressure to
which said at least one of the fluid operated actuating means is
selectively exposed and a second pressure-acting area, opposite to said
first pressure-acting area, which is selectively exposed to said kickdown
fluid pressure, said valve member of said pressure reducing valve being
held in said position providing communication between said at least one of
the fluid operated actuating means and said manual valve through said
shift valve when said second pressure-acting area is exposed to said
kickdown fluid pressure.
7. A gear shift shock reducing apparatus as claimed in claim 6, including a
pressure modifier valve provided operatively between said throttle
pressure valve means and said pressure regulator valve means, said
pressure modifier valve being selectively communicable with said throttle
pressure valve means and responsive to said throttle fluid pressure for
producing a modified fluid pressure which is variable with said throttle
fluid pressure, and wherein said pressure regulator valve means
communicates with said pressure modifier valve and responsive to said
modified fluid pressure upon generating said line fluid pressure, and
wherein said pressure reducing valve communicates with said pressure
regulator valve means and is responsive to said line fluid pressure upon
producing said actuating fluid pressure, said valve member of said
pressure reducing valve including a third pressure-acting area, opposite
to said first pressure-acting area, which is exposed to said line fluid
pressure.
8. A shock reducing apparatus of a hydraulic control system for an
automatic transmission including a driving member operatively connected to
the output shaft of an engine of an automotive vehicle, a driven member,
and frictional units including a first frictional unit and a second
frictional unit, having fluid operated actuating means selectively made
operative and inoperative for producing a plurality of gear ratios between
the driving and driven members, comprising:
means for generating a throttle fluid pressure;
means selectively communicable with said throttle fluid pressure generating
means for producing a modified fluid pressure variable with said throttle
fluid pressure;
means communicating with said modified fluid pressure generating means for
generating a line fluid pressure variable with said modified fluid
pressure;
means for generating a kickdown fluid pressure under a kickdown condition;
a manual valve provided operatively between the fluid pressure regulator
valve and the respective fluid operated actuating means of the frictional
units;
shift valves, each provided operatively between said manual valve and each
of the fluid operated actuating means of the first and second frictional
units, each shift valve having a valve spool movable into a position
providing communication between said line fluid pressure generating means
and the corresponding fluid operated actuating means; and
pressure reducing valves, each provided operatively between each of the
fluid operated actuating means of the first and second frictional units
and said manual valve and having a valve member movable into a position
providing communication between the corresponding fluid operated actuating
means and said manual valve through said corresponding shift valve, said
fluid pressure reducing valve communicating with said line fluid pressure
generating means and said kickdown fluid pressure generating means and
responsive to said kickdown fluid pressure for producing an actuating
fluid pressure variable with said line fluid pressure in response to the
absence of said kickdown fluid pressure, said valve member of each of said
fluid pressure reducing valves including a first pressure-acting area
which is selectively exposed to said actuating fluid pressure to which
said corresponding fluid operated actuating means is selectively exposed,
a second pressure-acting area, opposite to said first pressure-acting
area, which is selectively exposed to said kickdown fluid pressure, and a
third pressure-acting area, opposite to said first pressure-acting area,
which is exposed to said line fluid pressure, said valve member of each of
said pressure reducing valves being held in said position providing
communication between said corresponding fluid operated actuating means
and said manual valve through said corresponding shift valve when said
second pressure-acting area is exposed to said kickdown fluid pressure. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gear shift shock reducing apparatus for
a hydraulic control system of an automatic transmission.
2. Description of the Prior Art
In automatic transmissions, a shift is made automatically between gears
either by supplying a fluid pressure, for example, a line pressure, to a
corresponding friction unit or by discharging the fluid pressure from the
same as a result of an upshift or downshift operation of a gear shift
valve. During a gear shifting operation, the driver feels a shock (often
called as a "gear shift shock") because the gear ratio (a gear reduction
ratio) to be used changes, thus changing the output torque of the
transmission.
The amount of the gear shift shock is determined by the amount of the
torque capacity of a friction element in relation to the amount of torque
required to the friction element in accordance with the driving torque of
an engine, and if the amount of the required torque to the friction
element is greater than the amount of torque capacity thereof, the amount
of the gear shift shock increases, while, if the required amount of torque
is smaller than the amount of torque capacity, the coupling force of the
friction element is insufficient, allowing the friction element to slip,
thus not only preventing the transmission of the driving power without any
loss, but also causing a serious and a damaging overheating of the
friction element. Accordingly, it is known to design each friction element
such that the torque capacity thereof is slightly larger than necessary in
order to avoid these problems.
Since the automatic transmission can not avoid the above-mentioned shock,
it has been the conventional practice to use an accumulator a as shown in
FIG. 1 to cope with this problem. Referring to the accumulator a, if a
shift valve is actuated to start feeding a line pressure P.sub.L through
an orifice c to a friction element d, the operating oil pressure for said
friction element P.sub.A is fed to a chamber e. The accumulator a is fed
with the line pressure P.sub.L within a chamber f, wherein an accumulator
piston g receives a downward force by the oil pressure P.sub.A within the
chamber e (pressure receiving area A) and an upward force by the oil
pressure P.sub.L within the chamber f (pressure receiving area B). The
piston g further receives an upward force by a spring h, thus a
equilibrium equation of the forces acting upon the piston g is expressed
by the following equation if a spring force by the spring h is represented
by F.sub.s.
P.sub.A .times.A=P.sub.L .times.B+F.sub.s
P.sub.A =(B/A)P.sub.L +(Fs/A) (1)
Explaining now a change in the oil pressure P.sub.A vs. time (a change in
the torque capacity of the friction element d), as is apparently shown
together with a change in an output axle torque of a transmission vs. time
in FIG. 2, when the line pressure is fed to the friction element d after
the shift valve b is actuated, the oil pressure P.sub.A increases to
P'.sub.A during a period beginning at the initiation of coupling and
ending at the initiation of the subsequent gear change because of a
sliding resistance in the friction element. Subsequently, when the gear
change begins to take place as a result of the coupling of the friction
element, the oil pressure P".sub.A increases up to P.sub.A" because of
the occurrence of a reaction at this time. The oil pressure P.sub.A begins
to move the piston g downwardly against the pressure within the chamber f
and the spring force Fs of the spring h. The oil pressure value P".sub.A
is expressed using said equation (1) as follows:
P".sub.A =(B/A)P.sub.L +(Fs/A) (2)
Since A>B and the spring force Fs is small, the oil pressure P".sub.A takes
a value that is a reduced value from the line pressure P.sub.L by a
constant rate and since this reduced pressure is fed to the friction
element d, the torque capacity of the friction element is initially
suppressed small. During the downward movement of the piston g wherein the
torque capacity of the friction element d is suppressed small, said
friction element completes its coupling action and thereafter the piston g
reaches its lower limit position. When the piston g has reached the low
limit position, the accumulator stops effecting said pressure reducing
function, thus allowing the oil pressure P.sub.A to increase to the same
value as that of the line pressure P.sub.L.
In the above-mentioned manner, the accumulator a regulates the actuating
oil pressure P.sub.A to provide a torque capacity which varies in
agreement with the required torque of the friction element d that is shown
by the one dot chain line in FIG. 2 although slightly larger than the
latter, thus decreasing a gear shift shock without causing the occurrence
of a slip of the friction element.
However, the accumulator a is relatively bulky, which measures, in
diameter, 30.about.35 mm and, in length, 60.about.65 mm, as compared to
the shift valve b which measures, in diameter, about 10.about.15 mm, thus
making it difficult to arrange the accumulator within a limited space
provided by an automatic transmission, thus causing a bulky size of a
hydraulic control portion of the automatic transmission. Besides, where
the accumulator a is to be used, when a release of the friction element d
is necessary in response to an inoperative position (a downshifted
position) of the shift valve b, this release must be effected quickly.
Thus, in order to disable the function of the orifice c upon release of
the friction element d, a one-way valve as shown b i in FIG. 1 has been
necessiated which prevents a flow of oil from the shift valve b toward the
friction element d, thus causing a complicated and expensive structure of
the automatic transmission as a result of an increase in the number of
component parts.
Further, the accumulator a performs the before-mentioned pressure reducing
function even under a kickdown condition (a condition when an accelerator
pedal is fully depressed) in the same manner as its function under normal
conditions, thus providing inconveniences which will be hereinafter
explained. FIG. 3 shows a typical example of a shift pattern of an
automatic transmission, and as will be apparently understood from this
figure, shift points under a kickdown condition are shifted toward a
higher vehicle speed side as compared to the corresponding shift points
under normal conditions. It is to be noted that because the engine speed
is high, the required torque capacity to the friction element should be
high upon making a shift at high vehicle speeds as compared to the
required capacity upon making a shift under low vehicle speeds even if a
driving torque is the same, so that unless the torque capacity is large
enough for the required torque capacity, a slippage time period of the
friction element prolongs, causing an excessive wear of the friction
element during a running condition wherein a kickdown occurs frequently,
resulting in a braking. However, the above-mentioned accumulator performs
the pressure reducing function not only under normal condition but also
under a kickdown condition in the same manner, thus running short of a
torque capacity of the friction element under the kickdown condition, thus
failing to meet the demanded torque capacity as mentioned above.
SUMMARY OF THE INVENTION
The present invention resides in a gear shift shock reducing apparatus for
a hydraulic control system of an automatic transmission which has been
developed to realize a conception that the above-mentioned problems can be
solved at once for all if, instead of, the above-mentioned accumulator, a
pressure reducing valve is employed which is constructed and arranged as
to perform a pressure reducing function under normal condition except a
kickdown condition in a similar manner to the above-mentioned accumulator,
but stops effecting its pressure reducing function under the kickdown
condition.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a diagram of a conventional gear shift shock reducing apparatus;
FIG. 2 is a torque capcity vs. time characteristic provided by the
conventional apparatus shown in FIG. 1;
FIG. 3 is a graph showing a shift pattern curves of the automatic
transmission;
FIG. 4 is a schematic view of a power train of the automatic transmission;
FIGS. 5A,5B and 5C when combined show a shift shock reducing apparatus for
a hydraulic control system of the automatic transmission according to the
present invention;
FIG. 6 is a torque capacity vs. time characteristic provided by the
apparatus shown in FIG. 5; and
FIG. 7 is a sectional view of a modification of the pressure reducing
valves used in the apparatus according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be explained in connection with an
illustrated embodiment.
POWER TRAIN IN FIG. 4
FIG. 4 shows the construction of a power train of a three-forward speed and
one-reverse speed automatic transmission comprising a crank shaft 100 to
be driven by an engine, a torque converter 101, an input shaft 102, a
front clutch 104, a rear clutch 105, a second brake 106, a low-and-reverse
brake 107, a one-way clucth 108, an intermediate shaft 109, a first
planetary gear assembly 110, a second planetary gear assembly 111, an
output shaft 112, a first governor valve 113, a second governor valve 114,
and an oil pump 115. The torque converter 101 comprises a pump impeller P,
a turbine runner T, and a stator S, of which the pump impeller P is driven
by the crank shaft 100 so that the torque converter working oil contained
therein is caused to swirl and imparts torque to the turbine runner T
which is secured to the input shaft 102. The torque is further transmitted
through the input shaft 102 to the change-speed gearing arrangement. The
startor S is mounted about a sleeve 116 with the one-way clutch 103
interposed therebetween. The one-way clutch 103 is constructed and
arranged in such a manner as to permit a rotation of the stator S in the
same direction as the direction of rotation of the crank shaft 100, viz.,
the direction indicated by the arrow (abbreviated hereinafter as forward
rotation) and to prevent the opposite rotation of the stator S
(abbreviated hereinafter as opposite direction). The first planetary gear
assembly 110 comprises an internally toothed gear 117 rotatable with an
intermediate shaft 109, a sun gear 119 rotatable with a hollow
transmission shaft 118, not less than two planet pinions 120, each meshing
with the internally toothed gear 117 and the sun gear 119 so that it
rotates and moves along an orbit, and a front planet carrier 121 rotatable
with the output shaft 112 and having the planet pinions 120 thereon, while
the second planetary gear assembly 111 comprises an internally toothed
gear 122 rotatable with the output shaft 112, a sun gear 123 rotatable
with the hollow transmission shaft 118, not less than two planet pinions
124, each meshing with the internally toothed gear 122 and the sun gear
123 so that it rotates and moves along an orbit, and a rear planet carrier
125 having the planet pinions 124 thereon. The front clutch 104 is
operative to connect the transmission input shaft 102 to be driven by the
turbine runner T to the hollow transmission shaft 118 rotatable in unision
with the both sun gears 119 and 123 through a drum 126, while, the rear
clutch 105 is operative to connect the input shaft 102 to the internally
toothed gear 117 of the first planetary gear assembly 110 through the
intermediate shaft 109. The second brake 106 is operative to tighten a
band winding the drum 126 secured to the hollow transmission shaft 118 so
as to fix the both sun gears 119 and 123, while, the low-and-reverse brake
107 is operative to fix the rear planet carrier 125 of the second
planetary gear assembly 111. The one-way clutch 108 is so constructed and
arranged as to permit the forward rotation of the rear planet carrier 125
but prevent the opposite rotation thereof. The first governor valve 113
and second valve 114 are fixed to the output shaft 112 and are operative
to produce a governor pressure corresponding to the vehicle speed.
Description will be hereinafter made of the power transmission paths which
are established when the selector lever is in the D (the forward automatic
drive) position.
Under this condition, the rear clutch 105 serving as the forward input
clutch is engaged. The power from the engine and having past through the
torque converter 101 is transmitted, through the input shaft 102 and rear
clutch 105, to the internally toothed gear 117 of the first planetary gear
assembly 110. The rotation of the internally toothed gear 117 causes the
planet gears 120 to rotate in the forward direction. Accordingly, the sun
gear 119 tends to rotate in the opposite direction, causing the sun gear
123, rotatable in unison with the sun gear 119, of the second planetary
gear assembly 111 to tend to rotate in the opposite direction, thus
causing the planet gears 124 to rotate in the forward direction. The
one-way clutch 108 is operative to prevent the sun gear 123 from rotating
the rear planet carrier 125 in the opposite direction, thus serving as a
forward reaction brake. As a result, the internally toothed gear 122 of
the second planetary gear assembly 111 rotates in the forward direction.
It therefore follows that the output shaft 112 rotatable with the
internally toothed gear 122 also rotates in the forward direction, thereby
producing the first forward drive gear ratio. When, under this condition,
the second brake 106 is applied after the vehicle speed has increased,
similarly to the first gear condition, the power which has past through
the input shaft 102 and the rear clutch is transmitted to the internally
toothed gear 117. The second brake 106 is operative to fix the drum 126 to
prevent rotation of the sun gear 119, thus serving as a reaction brake in
the forward direction. Accordingly, the planet pinions 120 rotate and move
along an orbit around the sun gear 119 which is held stationary with the
result that the front planet carrier 121 and the output shaft 112
rotatable with the front planet carrier rotate in the forward direction at
a speed, although with a reduction ratio, higher than the first gear
condition, thereby producing the second forward drive gear ratio. When,
after the vehicle speed has increased further, the second brake 106 is
released and the front clutch 104 is engaged, the power delivered to the
input shaft 102 splits into one part transmitted through the rear clutch
105 to the internally toothed gear 117 and into the remaining part
transmitted through the front clutch 104 to the sun gear 119. Therefore,
the internally toothed gear 117 and the sun gear 119 are interlocked with
each other to rotate together with the front planet carrier 121 and the
output shaft 112 at a common revolution speed in the forward direction,
thereby producing the third forward drive gear ratio. Under this
condition, the front clutch 104 and the rear clutch 105 may be referred to
as an input clutch and there is no reaction brake so that the planetary
gear assemblies do not lend themselves to multiplication of torque.
The power transmission path to be established when the selector lever is in
the R (reverse drive gear) position will be hereinafter described.
When this position is selected, both of the front clutch 104 and the
low-and-reverse brake 107 are engaged and applied, respectively. The power
from the engine having past through the torque converter 101 is
transmitted from the input shaft 102 through the front clutch 104 and the
drum 126 to the sun gears 119 and 123. Since, under this condition, the
rear planet carrier 125 is fixed by the low and reverse brake 107, the
rotation of the sun gears 119 and 123 in the forward direction causes the
internally toothed gear 122 to rotate at a reduced speed in the opposite
direction with the result that the output shaft 112 rotatable with the
internally toothed gear 122 rotates in the opposite direction, thereby
producing the reverse drive gear ratio.
HYDRAULIC CONTROL SYSTEM
FIGS. 5A, 5B and 5C when combined show a hydraulic circuit diagram showing
a gear shift shock reducing apparatus according to the present invention
as incorporated in the hydraulic control system of the above described
automatic transmission, which control system comprises a regulator valve
1, a manual valve 2, a 1-2 shift valve 3, a 2-3 shift valve 4, a 3-2 down
shift valve 5, a line pressure booster valve 6, a pressure modifier valve
7, a throttle valve 8, a throttle failsafe valve 9, a throttle modulator
valve 10, a pressure reducing valve 11 for a manual first gear range, an
accumulator 12, a 2-3 timing valve 13, a 3-2 timing valve 14, and gear
shift shock reducing valves 15 and 15', all these devices being connected
through the illustrated circuit network to the torque converter 101, the
rear clutch 105, a band brake 106' for said second brake (ref. FIG. 1),
the low-and-reverse brake 107, the governor valves 113 and 114, and the
oil pump 115; and the gear shift shock reducing apparatus comprises the
pressure reducing valves 15 and 15' as the major component elements of the
apparatus.
REGULATOR VALVE 1
Referring to FIG. 5A, the oil pump 115 is driven by the engine through the
crank shaft 100 and the pump impeller P of the torque converter 101 and is
operative to suck in an oil free from dust from an illustrated oil
reservoir through an oil strainer (not shown) and feed the oil to a line
pressure circuit 16 when the engine is in operation. The regulator valve 1
which is adapted to regulate the pressure of the oil to a predetermined
level comprises a valve spool 1b, which is urged by means of a spring 1a
to slidably move toward a raised position indicated by the left half of
the spool in FIG. 5A, within a housing 1c, and also comprises four
chambers 1d, 1e, 1f and 1g. To the chambers 1d and 1f are fed an oil
pressure from the line pressure circuit 16 by way of oil passages 17 and
18, respectively. To the chamber 1e is fed a line pressure through an oil
passage 22 from a port 2b of a manual valve 2 when the manual valve 2
assumes one of D, II and I ranges, as will be hereinafter described. A
land 1'b of the spool 1b is slightly smaller, in diameter, than the inner
diameter of the corresponding rib 1'c so as to define therebetween a small
clearance which serves as a variable orifice. Through this clearance, the
oil within the chamber 1f is drained off at all times by a drain port 1 at
a rate which is determined by an amount of overlap between the 1'b and the
rib 1'c thus allowing a line pressure to be produced within the line
pressure circuit 16 which increases in proportion to the amount of
overlap. A land 1"b of the spool 1b is slightly smaller than the bore 1"c
of a housing 1c, thus defining therebetween a clearance, and through this
clearance the oil within the chamber 1f is supplied through an oil passage
19 to the torque converter 101, an oil cooler 20 and various kinds of
portions within the transmission which need lubrication.
MANUAL VALVE 2
The line pressure developed in the line pressure circuit 16 is directed to
the manual valve 2 shown in FIG. 5C, which serves as a fluid-flow
direction change-over valve adapted to provide communication from the line
pressure circuit 16 selectively to any one of the ports 2a, 2b, 2c and 2d
when the selector lever (not shown) is manipulated for gear selection, the
valve comprising a valve spool 2f which is slidably mounted within a
housing 2e. The valve spool 2f has six positions, viz., a neutral position
(N), an automatic forward drive position (D), a manual second gear
position (II), a manual first gear position (I), and a parking position
(P) and allows the line pressure circuit 16 to commnicate with the ports
indicated by the sign "o" in the following table when the spool 2f is
moved selectively to each of the positions as a result of the above
mentioned selecting operation. The ports which are not in communication
with the line pressure circuit 16 are all made open to the openings on
both sides of the housing 2 e, thus serving as drain ports.
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Ports
Ranges 2a 2b 2c 2d
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R o
N
D o
II o o
I o o o
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GOVERNOR VALVES 113, 114
Referring to FIG. 5B, the first governor valve 113 and the second governor
valve 114 are operative to develop a governor pressure having a magnitude
corresponding to a vehicle speed under forward driving condition of a
vehicle. As will be understood from the Table as above, when the manual
valve 2 is in any one of the forward drive gear positions D, II and I, the
line pressure is first fed to the second governor valve 114 through the
circuit 22 from the port 2b communicating with the line pressure circuit
16, and when the vehicle is running, the line pressure is regulated by the
second governor valve 114, thus providing a governor pressure
corresponding to the vehicle speed, this governor pressure being fed to
the first governor valve 113. When the vehicle speed increases beyond a
predetermined value, the first governor pressure 113 begins to allow the
governor pressure being introduced thereto into the governor pressure
circuit 23. This governor pressure is fed through the circuit 23 to the
1-2 shift valve 3, the 2-3 shift valve 4, and the 3-2 downshift valve 5 so
as to regulate the operation of these valves in the manner described
hereinlater.
1-2 SHIFT VALVE 3
Referring to FIG. 5B, the 1-2 shift valve 3 comprises within a housing 3a
two valve spools 3b and 3c which are axially arranged in line with each
other with their adjacent opposed end faces abutting with each other and
which are slidably mounted. Acting upon that end face of the valve spool
3b which is more remote from the valve spool 3c is a spring 3d, while,
that end face of the spool 3c which is more remote from the valve spool 3b
is exposed to a chamber 3e. The valve spool 3b is formed with lands 3f,
3g, and 3k which are larger in diameter in this sequence, while, the
housing 3a is formed with ribs 3i, 3j, and 3k which correspond to these
lands, respectively. The valve spool 3c is further formed with lands 3l
and 3m, and lands 3n and 3o which is larger, in diameter, than the former
two, while, the housing 3a is formed with two ribs 3p and 3q cooperating
with the land 3l and a rib 3r cooperating with the land 3m. As
illustrated, connected to the 1-2 shift valve 3 are the governor pressure
circuit 23, a kickdown pressure circuit 24, and a gear shift control
pressure circuit 25, and further connected to the 1-2 shift valve is an
oil passage 27 which is selectively and alternatively communicated with an
oil passage 26 or a drain port 3s depending upon the axial position of the
land 3l. The governor pressure circuit 23 communicates with the chamber
3e, while, the kickdown pressure circuit 24 is allowed to communicate with
a groove between the lands 3f and 3g when the valve spool 3b is in the
position indicated by the right half thereof or allowed to communicate
with a groove between the lands 3g and 3h and a groove between the lands
3f and 3g when the valve spool 3b is in the position indicated by the left
half thereof. The gear | | |
