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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to an automatic transmission for vehicle and more
particularly to a fluid pressure control system for governing a planetary
or epicyclic gear trains employed in the transmission.
As used herein, the term "low position" refers to a high ratio differential
achieved by the planetary gear trains adapted for the slowest travelling
speed of the vehicle.
The term "second position" refers to a middle level ratio differential
achieved by the gear trains adapted for the middle level vehicle
travelling speed.
The term "top position" refers to a position in which the entire mechanism
of the gear trains is locked together as a unit and is rotated in integral
with an input shaft for achieving a higher travelling speed of the
vehicle.
In known automatic transmission, there is usually a time lag in restoring
the gear trains to the original mode of operation of low ratio
differential after sudden or urgent acceleration, so-called "kick down",
of the vehicle is completed by a high ratio differential.
SUMMARY OF THE INVENTION
A principal object of the present invention therefore is to provide a fluid
pressure control system having improved means for restricting the throttle
pressure to a predetermined threshold value so that the pressure control
system is enabled to restore the gear trains to its original position of
low ratio differential as soon as acceleration of the vehicle by a high
ratio differential is ceased.
The foregoing object and others are attained according to at least one
aspect of the present invention through the provision of valve means to
restrict the throttle pressure under a threshold predetermined value so
that the gear trains may be restored to its original position against such
restricted throttle pressure readily.
Thus, in the disclosed embodiments, a pressure restricting valve is
provided fluidically connected to the throttle valve to have the throttle
pressure in excess of the predetermined one to escape into a reservoir
under the atmospheric pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic view of a transmission gearing according to the
invention;
FIG. 2 is a diagrammatic illustration of a fluid control system for the
transmission gearing;
FIGS. 3 and 4 are diagrammatic illustrations of different embodiments of
fluid control systems according to the present invention; and
FIG. 5 is a graph showing throttle pressure and pedal strokes which actuate
the engine throttle valve.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1 is shown an outline of an automatic transmission with which
cooperates the fluid pressure control system according to the invention.
An input shaft 1 drives a first middle shaft 2 through a torque convertor
3. An oil pump 4 is driven by means of the vehicle engine, not shown,
through the input shaft 1 and the oil pumped thereby is transmitted into
the oil pressure control circuit as will be described in detail as the
description proceeds. The first middle shaft 2 drives a second middle
shaft 5 through a clutch 6. On the second shaft 5 is free running fit a
hollow shaft 7. At one end of the hollow shaft 7 is formed with second sun
gear 8 and at the other end thereof is provided with a second clutch 9.
The second middle shaft 5 has a first sun gear 10 at its right hand end.
The first sun gear 10 meshes with a middle gear 11a of planetary gear set
generally indicated by the reference character 11. The planetary gear set
11 is rotatably supported on a planetary carrier 12. The planetary gear
set 11 also has gears 11b and 11c both integral with the other gear 11a.
The gear 11b meshes with a third sun gear 17 which is fast on an output
shaft 13 of the fluid transmission. The gear 11c meshes with an idle gear
14 through an intermediate gear (not shown), and the idle gear in turn
meshes with the second sun gear 8. The carrier 12 is rotatable coaxially
with the second middle shaft 5. The input shaft 1, the first second middle
shafts 2 and 5 and the output shaft 13 are in alignment with one another.
The governor 15 is driven by the output shaft 13 and its output pressure
is proportional to a rotational speed of the output shaft 13. The governor
is of conventional construction and its operation and use is well known in
the art so that the detailed description is not required for full
understanding of the invention. The reference character 16 indicates
another oil pump driven by the output shaft 13. The output fluid pressure
from the oil pump 16 is governed by the valve 15 in dependency upon the
rotational speed of the output shaft 13. Such output fluid pressure is
used for the control system according to the invention as hereinbelow
described as the discussion proceeds.
A brake 18 is provided for achieving prohibition and allowance of the
rotation of the hollow shaft 7. Another brake 19 is provided for achieving
prohibiting and allowing rotation of the carrier 12. The brakes 18 and 19
operate due to fluid pressure applied thereto from the oil pump 4 or 16. A
brake 20 prevents the carrier from in one direction rotation while
permitting the reverse direction rotation as one-way brake.
In the application of the gear trains, there are four modes of operation.
The first mode of operation is achieved by keeping the gear trains in the
low position, the second mode of operation is achieved by keeping the gear
trains in the second position, and the third mode of operation is achieved
by keeping the gear trains in the top position. The fourth mode of
operation is achieved when the gear trains is in a position in which the
output shaft is driven in the inverse rotational direction, rearward
travelling of the vehicle being thus effected.
In the first mode of operation, the clutch 6 and the brake 19 are in their
operation position while the clutch 9 and the brake 18 are in rest
position. As a result, the input torque is transmitted from the input
shaft 1 via torque convertor 3, first middle shaft 2, clutch 6, second
middle shaft 5, first sun gear 10, middle gear 11a, gear 11b, third sun
gear 17 and output shaft 13 to driving wheels of the vehicle (not shown).
In the mode, the carrier is kept stationary. The low position, namely the
highest ratio differential of the gear trains results from the first mode
and the large pulling power of the vehicle is obtained at the travelling
speed.
In the second mode of operation, the clutch 6 is in act and clutch 9 and
brake 18 are in the rest position while the brake 19 is replaced by the
brake 20. Since the brake 20 is operative in preventing the carrier 12
from rotating in a reaction torque direction in the low position, the same
low position is achieved in that second mode of operation. If the brake 18
becomes operated in the second mode of operation, the second sun gear 8
becomes stationary and the carrier 12 is applied the reverse direction
reaction torque. As a result, the brake 20 permits rotation of the carrier
in such rotational direction. Since the second sun gear 8 is stationary
and the carrier 12 is rotatable, rotation of the first sun gear 10 is
transmitted to the output shaft 13 with a result that the shaft 13 is
rotated with a ratio differential lower than that of the low position. A
middle level travelling speed thus may be effected for the vehicle.
In the third mode of operation, both clutches 6 and 9 are in act while the
brakes 18 and 19 are in rest position. As a result, both sun gears 10 and
8 become integral as a unit. The entire mechanism of the gear trains is
locked together as a unit and is rotated in integral with the first middle
shaft 2 and the output shaft 13. The top position is thus effected and the
high travelling speed of the vehicle is achieved.
In the fourth mode of operation, the clutch 9 and the brake 19 are in act
while the clutch 6 and the brake 18 are inoperative. The carrier 12 is
kept stationary and the second sun gear 8 becomes driving gear so that the
sun gear 8 drives, via idle gear 14, gear 11c, gear 11b and the third sun
gear 17, the output shaft 13 in the direction reverse to that of the first
to third modes of operation. The rearward travelling of the vehicle is
thus effected.
If both clutches 6 and 9 and both brakes 18 and 19 are all in the rest
position, no torque is transmitted from the input shaft 1 to the output
shaft 13. This mode is referred to as "neutral mode" hereinafter.
In FIG. 2, an oil pump 4 is driven by the vehicle engine, not shown, and
the oil pumped thereby is transmitted into the pressure control circuit. A
regulator valve, generally indicated by the reference character 31,
includes ports 32 to 38. The pressurized oil from the pump 4 is
transmitted into port 32 through means of conduit 39 and into port 33
through means of conduit 39 and a branch conduit on which is disposed a
check valve 40. The pressurized oil is also transmitted into the port 35
through means of conduit 39. A conduit 41 connects the port 36 with a
reservoir 42. A suction pipe 43 of the pump 4 leads to the reservoir 42.
The torque converter 3 is supplied the lubricant oil through means of
conduit 47 from the port 34. A check valve 48 is connected to the torque
converter 3 through means of conduit 49 to have the fluid escape at a
pressure exceeding a predetermined value. An orifice 34a is provided on
the conduit 47 to keep the fluid pressure to the converter at a lower
value than that of pressure which is applied to the clutches and brakes.
The ports 32 and 33 are connected to the manually shiftable valve,
generally indicated by the reference character 44, through means of
conduit 45.
The regulator valve 31 includes a valve spool 50 having three lands 50a,
50b, and 50c and fluid chambers 51 and 52. The lands are of the same
diameter and cooperate with the ports selectively to regulate the input
pressure as a pressure suitable to apply to the clutches and the brakes.
Such suitable or proper fluid pressure is referred to hereinafter as "line
pressure". The spool 50 is applied on its lowermost end the line pressure.
The land 50c is applied on its face the line pressure within the chamber
52 and land 50a is applied on its lower end face the line pressure from
the port 32. An orifice 32a is provided at the port 32 for preventing the
spool from vibration when the line pressure is applied through the conduit
45 and port 32.
The chamber 51 is connected fluidically to a first shift valve, generally
indicated by the reference character 60, through means of conduits 53 and
69 and the chamber 52 is fluidically connected to the manual shift valve
44 through means of conduit 54. When the oil pressure is applied to the
lower face of the lower land 50a, and/or lower end face of the spool 50
through the ports 32 and 38 respectively the opening and closing of a
discharging port 36 of the valve 31 is controlled by means of the land 50c
of the valve spool against the biasing force of a restoring spring 55,
which is associated with the end of spool 50 opposite that end upon which
is disposed land 50a. The pressure applied to the lower face of the land
50a may be associated with a line pressure transmitted into chamber 51 as
more fully described as the discussion proceeds. As a result of such
controlling achieved by the land 50c and the port 36, a regulated output
line pressure is supplied to the conduit 45 owing to a calibration
threshold of the spring 44. Such regulated line pressure may be decreased
by supplying the line pressure into the lowermost chamber 51 of the valve
31, by an amount which is proportional to an area of the lowermost end
face of the spool 50. This is intended to provide a comparatively lower
line pressure for the clutch 6 and the first brake 18 when the second mode
of operation is initiated and to prevent an enertial shock as would
otherwise be exhibited each time the gear train in FIG. 1 changes the mode
of operation. The pump 16 which is driven by the output shaft 13 supplies
fluid pressure and the governor 15 causes the output pressure of the pump
to vary by an amount which is proportional to rotation speed of the shaft
13 representing normally a travelling speed of the vehicle. Immediately
after the initiation of operation, an output pressure of the pump 16
overcomes a calibration threshold of a spring of a check valve 56. The
fluid pressure is applied to the conduit 45 in addition to the precedingly
applied pressure by the other pump 4. The total pressure is higher than
the precedingly supplied pressure by the pump 4 alone. a result the spool
50 of the regulator valve 31 is upward moved a distance which is
proportional to a resulting biasing force of the spring 55.
The pressure regulation which precedingly performed by the port 36 and the
land 50c is thereafter replaced by pressure regulation of the land 50b and
port 36 which repeatedly or intermittently permits the ports 36 and 33 to
connect.
From the foregoing it will be understood that after the pump 16 has become
driven by initiation of travel of the vehicle, the ports 35 and 36 are
connected and the pump 4 is in idling position. It will be further
understood that the check valve 40 is thereafter closed and the check
valve 56 is opened. Since rotational speed of the engine varies by a large
amount, such substitutional employment of the pump 16 is effective to
avoid difficulty in calculating a large regulating capacity of a
regulating valve as would continuously operate throughout both engine
idling and subsequent vehicle travelling periods.
A shift valve 60 similarly includes a valve spool 61, having six lands 61a
to 61f. The lands 61a to 61c and 61f are of the same diameter. The land
61d is of smaller diameter than any one of the upwardly disposed lands and
the land 61e is of smaller diameter than the land 61d. The valve 60
further includes a spring 62 associated with an end portion of the spool
61 opposite that end upon which is disposed land 61e which normally biases
the spool 61 in the downward direction as seen in FIG. 1. The chamber 63a
is connected with the manually operable valve 44 through conduit 67 while
the other chambers 63b and 63d are connected with the valve 44 through
conduit 66. The valve 60 has ports 64a, 64b, 64c, 64d and 64e. The ports
64a and 64d lead to the reservoir 42. The port 64e leads to the brake 19
through conduit 68 and port 64 c leads to an engaging chamber 18e of the
brake 18 through conduit 69. The port 64b leads via a branch conduit 70'
and conduit 70 to the manually operable valve 44. The chamber 63c is
connected via conduit 71 with another shift valve 80.
The second shift valve 80 includes also a valve spool 81 having three lands
81a, 81b and 81c, and a spring 82 associated with the end of spool 81
opposite that end which is disposed land 81c, which normally biases the
spool 81 in the upward direction as viewed in FIG. 2. The lands 81a, 81b
and 81c are of the same diameter. The shift valve is normally urged to the
position shown in FIG. 2 as a result of the biasing force of spring 82,
and the lowermost chamber 83a is connected via conduit 771 to the chamber
63c of the valve 60. The chamber 83b defined between the lands 81a and 81b
is connected via means of conduit 84 to the manual shift valve 44. The
chamber 83c is connected through means of conduit 54 to the manually shift
valve 44 while being connected through means of another conduit 86 to a
control valve 100. A port 86' is connected to the reservoir 42. The
uppermost land 81c exposes its end face to the fluid pressure within the
said chamber 63e.
The control valve 100 includes a valve spool 101, having two lands 101a and
101b which has a small hole 102 for applying fluid pressure to lower the
spool downwardly. Both lands 101a and 101b are of the same diameter. A
pair of compression springs 103 and 104 are arranged to normally bias the
spool in the upward direction as viewed in FIG. 2. The uppermost extremity
of each of the springs is together anchored to the retainer 105 but the
lowermost end of the spring 103 is anchored to an outer annular piston 106
and the inner spring 104 is anchored at its lowermost end to the inner
piston 107. The outer piston exposes its face to fluid pressure within a
chamber 108 while the inner piston exposes its face to fluid pressure
within a chamber 109. The chamber 109 is connected through means of
conduit 110 to a accumulator tank 111. The conduit 110 has a branch
conduit 112 leading to the clutch 9 and a disengaging chamber 18d of brake
18. The conduit 112 further has a branch conduit 115 which leads to port
113 and has an orifice 114. The accumulator tank 111 includes a piston 116
and a spring 117 associated with the back of the piston 116 which normally
biases the piston in the upward direction as seen in the view. The valve
100 has an uppermost port 118 which is connected to the conduits 86
leading to the valve 80. The other ports 119 and 120 lead to the reservoir
42 through means of conduit, not shown.
A throttle valve 130 includes a plug 131 having two lands 131a and 131b of
the same diameter, movable within the left end portion thereof, a valve
spool 132 having a plurality of lands 132a, 132b and 132c, and a spring
133, which is interposed between plug 131 and valve spool 132, for urging
the plug 131 into the rest position of the pedal 135. A chamber 136 is
defined within the right end portion of the valve 130 and has spring 137
disposed therewithin. Ports 138 and 139 are together connected to the
chamber 108 of the control valve 100. Ports 140 and 141 are connected with
a second regulator 150 through means of conduit 151 and its branch
conduits. A port 142 is connected to the manual shift valve 44 through
means of conduits 143 and 70.
The other ports 144, 145 and 146 are connected with the reservoir 42.
The second regulator valve 150 includes a spool 152 having two lands 153
and 154 disposed thereon, and a spring 155 associated with the end of
spool 152 opposite that end upon which is disposed land 153 which normally
biases the spool 152 in the leftward direction as viewed in the FIG. 2. A
port 154 is connected to the reservoir 42. The land 153 has a small hole
157 which connects a chamber defined between the two lands 153 and 154 to
another chamber defined between the internal end face of the valve 150 and
the land 153 so that fluid pressure applied through the port 158 urges the
spool against the spring 155.
The manual shift valve 44 includes a valve spool 160 having a plurality of
lands 44a, 44b, 44c and 44d. An annular groove 161 engages a manual shift
valve lever (not shown) to be axially shifted by the driver to vairous
positions designated L, 2, D, N, R, and P so that the clutches and brakes
are selectively actuated by the line pressure through the control system.
The operation of the embodiment in FIG. 2 will now be described hereinbelow
in detail. Assume that the manual shift valve 160 is positioned to the low
position designated L. The line pressure from the pump 4 or 16 is
regulated by means of the regulator valve 31 and is supplied to conduit
45. Such line pressure is able to be transmitted to the conduits 66 and 67
through means of chamber between the lands 44b and 44c of the valve 44.
The second brake 19 is thus able to engage as a result of the line
pressure being transmitted through the conduit 66, chamber 63d and conduit
68 and this line pressure is also supplied via conduit 66 to chamber 63b
of the first shift valve 60. Further the pressure is transmitted to the
chamber 63a through conduit 67. It should be noted that there is no chance
for the spool 61 of the valve 60 to move to the other positions until the
manual shift valve 44 is shifted to other positions due to fluid pressures
in the chambers 63a, 63b and 63c which overcome the spring 62 and the
maximum of the varying governor pressure in the chamber 63e.
The governor 15 produces a pressure by an amount which is proportional to a
rotational speed of the output shaft 13. Such out put pressure is
transmitted to the chamber 63e through its exhaust conduit as viewed in
FIG. 2.
A chamber 44f of the manual shift valve 44 permits, in the mode in FIG. 2,
the line pressure to be transmitted via conduit 70 to the first clutch 6
to operate thereof. The fluid pressure within the conduit 70 is also
transmitted via its branch conduit 70' to the port 64b and in turn to a
chamber defined between the lands 61a and 61b, which at this time, such
chamber is closed. It should be noted that in such mode of operation, the
second clutch 9 and disengaging chamber 18d of the first brake 18 are
connected to the reservoir through conduits 112 and 115, port 113, chamber
101e, and port 118 of the second regulator valve 100, conduit 86, chamber
83c of the second shift valve 80, conduit 54, chamber 44g defined between
lands 44a and 44b and port 44h of the manual shift valve 44. The engaging
chamber 18e of the brake 18 is connected to the reservoir through conduit
69 and ports 64c and 64d. From the foregoing it will be understood that
the first clutch 6 and the second brake 19 are in action while the second
clutch 9 and the first brake 18 are disengaged.
Now referring to FIG. 1, it will be understood that the carrier 12 is
stationary and sun gear 10 is in driving position. The clutch 9 and brake
18 are released. The output shaft 13 effects high ratio differential in
the above mentioned mode of operation.
When the manual shift valve 44 is displaced from the above mentioned state
to the second position designated 2, the land 44b blocks communication
between the port 44l and the conduit 66. As a result, the brake 19 becomes
applied no fluid pressure and released. No change is offered in applying
fluid pressure to the other clutches or brake so that the preceding mode
of operation continues until the governor pressure increases to a
threshold calibration value. Such continuation of the previous mode is
effected through substitutional actuation of the one-way brake 20. When
the vehicle travelling speed increases, the governor pressure follows by
an amount which is normally proportional to the rotational speed of the
output shaft 13 or the travelling speed of the vehicle. At the stage when
a predetermined threshold value is reached, the governor pressure within
the chamber 63e and spring 62 overcomes a biasing force of fluid pressure
within the chambers 63a and 63c. The fluid pressure within the chamber 63c
is a throttle pressure which will be described hereinafter in detail.
The governor pressure is transmitted to the upper chamber 63e and the spool
61 of the first shift valve 60 is thus lowered to connect the engaging
chamber 18e via conduit 69, port 64c and port 64b, conduits 70' and 70 and
manual shift valve 44 to the line pressure conduit 45. Such line pressure
is thus able to actuate the brake 18 to engage, the second sun gear 8 of
the transmission being held stationary. The second position is achieved
automatically. The reverse takes place also automatically in case of
decrease of the governor pressure to a lower value than the threshold
calibration value. It will be noted that the disengaging chamber 18d is
connected in the above phase to the reservoir through conduits 112, 115,
second regulator valve 100, conduit 86, chamber 83c of the second shift
valve 80, conduit 54 and port 44h of the manual shift valve 44, the
engaging of the brake 18 being thus permitted.
The operation of the throttle valve 130 will now be described in detail
hereinbelow. When the input pressure is supplied to the throttle valve 130
from the manual shift valve 44 through conduits 70, 143 and port 142, the
spool 132 operates to produce a regulated pressure by reciprocation as a
throttle pressure by an amount of compression of the spring 133 which is
proportional to a degree to which the engine throttle valve, not shown, is
opened. The line pressure delivered into chamber 132d of valve 130 is then
transmitted into the right hand chamber defined by lands 132b and 132c via
ports 139 and 138. The spool 132 is therefore leftward moved against
spring 133 so as to close the inlet port 142. Immediately after or at the
same time when the inlet 142 is closed, the land 132a opens the outlet
port 141 to permit fluid pressure in chamber 132d to escape via outlet
port 141, conduit 151 and its branch conduit, port 140 and outlet port 144
to the reservoir. The fluid pressure in chambers 132d and the other
chamber between lands 132b and 132c is decreased upon that escape and
hence the spool 132 is moved to the original position shown by the spring
133. The spool 132 flutteringly repeats the cycle of reciprocation during
the period of depression of the pedal 135 by the driver, and the desired
regulated output throttle pressure which is proportional to or determined
by the force of the compressed restoring spring 133 (degree of depression
of the pedal) is thus obtained at outlet 139.
In the normal travelling, the throttle valve performs the above mentioned
operation and produced an output pressure regulated as a throttle pressure
which is proportional to the amount by which the pedal 135 is depressed.
However, when the pedal is suddenly depressed to meet a requirement for
increasing the travelling speed of the vehicle, a different operation of
the throttle valve is effected. The plug 131 of the throttle valve 130 is
shifted to the right by such sudden depression with its land 131a closing
port 144 leading to the reservoir so that input pressure in chamber 132d
escapes via port 141 and conduit 151 into the reducing valve 150. The
reducing valve 150 operates to produce an predetermined threshold pressure
by the known reciprocal movement of the spool 152 associated by the force
of the calibration threshold of the spring 155 and the exhausting port
154. The fluid pressure within the first chamber between the lands 153 and
154 transmitted through the orifice 157 into the second chamber between
the land 153 and the internal end face of the valve 150. The spool 152 is
accordingly moved to the right against the spring 155 to permit the fluid
in the first chamber to escape through the outlet port 159 to the
reservoir, thus reducing the fluid pressure. Fluid pressure in excess of
the predetermined threshold valve is thus exhausted through the port 159
and the fluid pressure in chamber 132d of the throttle valve 130
controlled so as to vary below the maximum of such predetermined threshold
value determined by the spring 155. By such operation, an output pressure
in excess of the predetermined value is prevented from being transmitted
through the conduit 72 to the second regulator valve 100 and through
conduits 72 and 72' to the valve 80.
The operation of the second regulator valve or control valve 100 is then
described in detail hereinbelow. In the position shown in FIG. 2, the
uppermost port 118 of the second regulator valve 100 is connected to the
reservoir through conduit 86, chamber 83c, conduit 54, chamber 44g and
port 44h of the manual shift valve 44. When the spool 81 of the second
shift valve 80 is shifted in the downward direction, the chamber 83c is
isolated from the reservoir by its uppermost land 81c while being
connected to the line pressure conduit 45 through conduit 84, and the
chamber defined between the lands 44d and 44c of the spool 160, assuming
that the chamber 44f is shifted to the left to connect conduit 84 thereto.
The line pressure supplied within the chamber 101e of the valve 100 is then
transmitted via branch conduit 115, orifice 114 and conduit 112 to the
chamber 111a of the accumulator tank 11, chamber 109 of the second
regulator valve 100, disengaging chamber 18d of the brake 18 and the
second clutch 9. By such line pressure in the chamber 101e, the spool 101
is downward moved against the biasing force of the springs 103 and 104 to
have the fluid escape through the port 120 into the reservoir if
pressurization in the chamber 101e exceeds the predetermined threshold
value. The resulting output pressure from the chamber 101e is thus a
pressure regulated by an amount which is proportional to the amount by
which the springs are compressed. The outer spring 103 is compressed by
the throttle pressure from throttle valve 130 variable to an amount which
is proportional to the amount by which the pedal 135 is depressed. The
provision of spring 103 and outer piston 106 is contemplated to keep the
output pressure in chamber 101e proportional to the throttle pressure in
chamber 108, so that a proportional tightening force is applied to the
clutch 9 to the torque to be transmitted. The provision of spring 104 and
inner piston 107 is contemplated to cause the piston 101a to gradually
increase the output pressure in chamber 101e.
The clutches and brakes of the embodiment are usually employed in the form
of multiple disc type or band type frictional clutch and brake. It should
be noted that, for given purpose, the frictional force or tightening force
exerted in such frictional device is proportional to depression of the
pedal, so that the larger the depression of the pedal the greater will be
the frictional force. The variable throttle pressure from the throttle
valve 130 meets such requirement.
Since the line pressure within the chamber 101e of the second regulator
valve 100 is transmitted through orifice 114 to the chamber 109, the
resulting pressure in the chamber 109 is lower than the line pressure.
Such resulting pressure is further regulated by action of the compression
spring 117 and piston 116 of the accumulator tank 111. The resulting
pressure in the chamber 109 serves to upwardly move the inner piston 107
to thereby further compress the spring 104 and in turn increase the
threshold value of the line pressure in the chamber 101e. Such cycle of
pressurization is repeated for a while immediately after the application
of the line pressure is initiated to the chamber 103e, and gradual
increase of output pressure thus resulting. The gradual increase is
effective to prevent the clutches and brakes from a shocking operation
resulting from a sudden change of travelling speed of the vehicle, such
gradual increase being translated exactly into increase of input pressure
to the clutches and brakes.
When the spool 160 of the manual shift valve 44 is shifted to the D
position, the line pressure is transmitted to the chamber 83b of the valve
80 through conduit 84 on connection of the conduit 84 with the chamber
44f, which is at this time connected to the line pressure conduit 45
through port 44k. The line pressure in the chamber 83b remains closed
within the chamber 83b until the spool 81 is downward moved by a governor
pressure within the chamber 63e which exceeds a predetermined threshold
value.
Such downward movement of the spool 81 causes the chamber 83c to be
isolated from the conduit 54 connected to the reservoir while being
connected to the conduit 86 leading to the second regulator valve or
control valve 100, namely to its chamber 101e. The chamber 83c is further
connected by such shift down to the conduit 84 leading to line pressure in
D position. The line pressure transmitted to the chamber 101e is thence
transmitted to the second clutch 9 and disengaging chamber 18d of the
brake 18. Reverse takes place in dependency upon the decrease of the
governor pressure over the predetermined threshold one.
It will be noted that in D position of the manual shift valve 44, the shift
valve 60 is of course downward shiftable due to the governor pressure
which imposes also downward shift of the spool of the shift valve 80.
It will be further noted that in the D position, the gear trains varies
automatically from low position to the second position and further to the
top position. Reverse takes place from the top or second place.
When the spool 160 of the manual shift valve 44 is in the position
designated N in FIG. 2, each clutch and each brake is freed from the line
pressure and no torque is transmitted from the input shaft 1 to the output
shaft 13. The neutral position is thus achieved.
Referring to FIG. 3, a different embodiment of the the invention will be
described hereinbelow in detail. In FIG. 3, parts which are the same as
those shown in FIG. 2 are given the same number. A reducing valve 200
includes a valve spool 201 having a pair of lands 203 and 202 to define
therebetween a chamber 204, and a compressed spring 205 interposed between
the spool end and internal end face of the valve 200 to normally bias the
spool 201 to the left. The land 202 have a small hole 206 to communicate
the chamber 204 with another chamber defined between the left end face of
the land 202 and the left internal end face of the valve 200.
A port 207 leads to the reservoir 42; port 208 is connected to a conduit
210 which connects the pump 16 and the port 140 of the throttle valve 130
through the check valve 56 and another check valve 211 of inversely
operational character to the check valve 56. The port 209 is connected to
the manual shift valve 44 through conduit 212.
The operation of the reducing valve 200 is the same as that of the reducing
valve 150 of the first embodiment in FIG. 2 except that the fluid pressure
in the chamber 132d of the throttle valve 130 is beforehand regulated to a
predetermined threshold value by the reducing valve 200 the operation of
which is similar to that of the valve 150 as aforementioned. The valve 200
is supplied a line pressure from the pump 4 through conduit 45, chamber
44f of the manual shift valve 44 and conduit 212 or from the pump 16
through conduit 210. Such input pressure within the chamber 204 of the
valve 200 is regulated to the predetermined threshold value. The threshold
value is translated into exactly the pressure in the chamber 44f of the
valve 44 and into the throttle valve 130. In case of the sudden depression
of the pedal 135, the excessively increased pressure in the chamber 132d
is transmitted through conduit 151, check valve 211 and conduit 210 into
the chamber 204 of the valve 200 so that the output pressure from the
throttle valve 130 is regulated to the predetermined threshold value. Such
output valve pressure is then applied to the valves 100, 80 and 60 to
thereby operate in the normal condition particularly in permitting prompt
restoring of these device to their original position without any time lag
after required sudden acceleration of the vehicle is attained.
Referring to FIG. 4, still further different embodiment will be decribed
hereinbelow. Parts which are the same as those shown in FIG. 2 are given
the same number. The other parts are given in a 300 series. A reducing
valve 300 includes a valve spool 301 having a pair of lands 302 and 303 to
define therebetween a chamber 304, and a compressed spring 305 interposed
between the spool end and internal end face of the valve 300 to normally
bias the spool 301 to the left. The land 302 has a small hole 306 to
communicate the chamber 304 with another chamber defined between left end
face of the land 302 and the left internal end face of the valve 300. The
valve 300 has further ports 307 to 310. The port 307 leads to the
reservoir 42, port 308 is connected to a conduit 311 leading to the pump
16. The port is connected via conduit 312 to conduit 143, 70 and 31 | | |
