Hydraulically operated continuously variable transmission

A hydraulically operated continuously variable transmission includes a hydraulic motor coupled to an output shaft and having a motor swash plate and a motor cylinder supporting an annular array of slidable motor plungers held in slidable contact with the motor swash plate, a distribution member integral with the motor cylinder, a hydraulic pump coupled to an input shaft in sliding contact with the distribution member and having a pump swash plate movable with the motor cylinder and a pump cylinder supporting an annular array of slidable pump plungers held in slidable contact with the pump swash plate, a closed hydraulic circuit interconnecting the hydraulic pump and the hydraulic motor, the pump cylinder being coaxially surrounded by the motor cylinder with a hydraulically hermetic chamber defined therebetween, and a replenishing pump operatively coupled to the input shaft and connected to the closed hydraulic circuit through a replenishing oil passage. The replenishing oil passage partly extends in the distribution member, and the distribution member has an oil passage defined therein and interconnecting the replenishing oil passage and the hydraulically hermetic chamber. A relief valve is disposed in the oil passage in the distribution chamber, the relief valve being openable when the pressure of oil in the replenishing oil passage exceeds a prescribed level.

BACKGROUND OF THE INVENTION 
The present invention relates to a hydraulically operated continuously 
variable transmission, and more particularly to a hydraulically operated 
continuously varible transmission having a relief valve disposed in a 
distribution member for releasing oil from a replenishing oil passage into 
an oil chamber. 
Hydraulically operated continuously variable transmissions are known in the 
art as disclosed in Japanese Laid-Open Patent Publication No. 56-143857, 
for example. 
In such hydraulically operated continuously variable transmissions, a 
hydraulic pump and a hydraulic motor are interconnected by a closed 
hydraulic circuit. Japanese Laid-Open Patent Publication No. 57-76357 also 
discloses a hydraulically operated transmission. 
SUMMARY OF THE INVENTION 
In view of the drawbacks of conventional hydraulically operated 
continuously variable transmissions, it is an object of the present 
invention to provide a hydraulically operated continuously variable 
transmission which is capable of introducing excess oil from a 
replenishing oil passage into a hydraulically hermetic chamber without 
greatly varying the conventional structure and size. 
According to the present invention, there is provided a hydraulically 
operated continuously variable transmission comprising an output shaft, a 
hydraulic motor coupled to the output shaft and having a motor swash plate 
and a motor cylinder supporting an annular array of slidable motor 
plungers held in slidable contact with the motor swash plate, a 
distribution member integral with the motor cylinder, an input shaft, a 
hydraulic pump coupled to the input shaft in sliding contact with the 
distribution member and having a pump swash plate movable with the motor 
cylinder and a pump cylinder supporting an annular array of slidable pump 
plungers held in slidable contact with the pump swash plate, a closed 
hydraulic circuit interconnecting the hydraulic pump and the hydraulic 
motor, the pump cylinder being coaxially surrounded by the motor cylinder 
with a hydraulically hermetic chamber defined therebetween, a replenishing 
pump operatively coupled to the input shaft and connected to the closed 
hydraulic circuit through a replenishing oil passage, the replenishing oil 
passage partly extending in the distribution member, the distribution 
member having an oil passage defined therein and interconnecting the 
replenishing oil passage and the hydraulically hermetic chamber, and a 
relief valve disposed in the oil passage in the distribution member, the 
relief valve being openable when the pressure of oil in the replenishing 
oil passage exceeds a prescribed level. 
The above and other objects, features and advantages of the present 
invention will become more apparent from the following description when 
taken in conjunction with the accompanying drawings in which preferred 
embodiments of the present invention are shown by way of illustrative 
example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Like or corresponding parts are denoted by like or corresponding reference 
numerals throughout the several views. 
FIG. 1 shows a hydraulically operated continuously variable transmission 
CVT according to an embodiment of the present invention for use on a motor 
vehicle such as an automobile, the transmission CVT basically comprising a 
hydraulic pump P of the fixed displacement type coupled to an input shaft 
2 driven by an engine E and a hydraulic motor M of the variable 
displacement type disposed coaxially with the hydraulic pump P. The 
hydraulic pump P and the hydraulic motor M are coupled in a closed 
hydraulic circuit C. The hydraulic motor M is operatively coupled to 
wheels W through an output shaft 11 a forward/reverse gear assembly G, an 
auxiliary shaft 18, and a differential D. 
The closed hydraulic circuit C includes a higher pressure oil passage Ch 
interconnecting the outlet port of the hydraulic pump P and the inlet port 
of the hydraulic motor M and a lower pressure oil passage Cl 
interconnecting the outlet port of the hydraulic motor M and the inlet 
port of the hydraulic pump P. The higher and lower pressure oil passages 
Ch, Cl are interconnected by a clutch valve 116. The input shaft 2 drives 
a replenishing pump F having an outlet port connected to the higher and 
lower oil passages Ch, Cl through a replenishing oil passage 137 and a 
pair of check valves 138. The replenishing pump F, when actuated, supplies 
working oil from an oil tank T through the replenishing oil passage 137 to 
the closed hydraulic circuit C to compensate for an oil shortage in the 
circuit C. A relief valve 150 is connected to the replenishing oil passage 
137. When the oil pressure in the replenishing oil passage 137 exceeds a 
prescribed pressure level, the relief valve 150 is opened to release oil 
which is introduced into a hydraulically hermetic chamber 31 of the 
hydraulic pump P. A pressure control valve 50 coupled between the chamber 
31 and the oil tank T is opened when the oil pressure in the chamber 31 
exceeds a prescribed pressure level. The pressure level set for opening 
the pressure control valve 50 is lower than the pressure level set for the 
relief valve 150. 
The clutch valve 116 comprises a restriction valve switchable between an 
open position in which the higher and lower pressure oil passages Ch, Cl 
are interconnected and a fully closed position in which the higher and 
lower pressure oil passages Ch, Cl are disconnected from each other, the 
clutch valve 116 having an intermediate open position. When the clutch 
valve 116 interconnects the higher and lower pressure oil passages Ch, Cl, 
no oil pressure is supplied to the hydraulic motor M and hence the 
transmission is in a neutral condition with the hydraulic motor M being 
inoperative. When the clutch valve 116 disconnects the higher and lower 
pressure oil passages Ch, Cl from each other, working oil circulates 
between the hydraulic pump P and the hydraulic motor M to transmit driving 
power for thereby causing the motor vehicle to run. When the clutch valve 
116 is in the intermediate open position, working oil circulates at a rate 
dependent on the opening of the clutch valve 116, which is thus held in a 
"partly engaged" condition. 
The structure of the continuously variable transmission CVT will be 
described in detail with reference to FIG. 2. The continuously variable 
transmission CVT is housed in a transmission case 1 composed of a pair of 
longitudinally separate case members 1a, 1b. 
The hydraulic pump P has a pump cylinder 4 splined at 3 to an input shaft 
2, a plurality of cylinder holes or bores 5 defined in the pump cylinder 4 
in a circular pattern around the input shaft 2, and a plurality of pump 
plungers 6 slidably fitted respectively in the cylinder holes 5. The power 
of the engine is transmitted through a flywheel 7 to the input shaft 2. 
The hydraulic motor M has a motor cylinder 8 disposed concentrically in 
surrounding relation to the pump cylinder 4 and rotatable relatively 
thereto, a plurality of cylinder holes or bores 9 defined in the motor 
cylinder 8 in a circular pattern around the center of rotation thereof, 
and a plurality of motor plungers 10 slidably fitted respectively in the 
cylinder holes 9. 
The motor cylinder 8 has axially opposite ends on which output and support 
shafts 11, 12 are coaxially mounted, respectively. The output shaft 11 is 
rotatably supported on the axial end wall of the case member 1a by means 
of a needle bearing 13, and the support shaft 12 is rotatably supported on 
the axial end wall of the case member 1b by means of a ball bearing 14. 
The input shaft 2 extends through the end wall of the case member 1a in a 
fluid-tight manner, and is disposed concentrically in the output shaft 11. 
A plurality of needle bearings 15 are disposed between the inner surface 
of the output shaft 11 and the outer surfce of the input shaft 2, so that 
the input shaft 2 and the pump cylinder 4, and the output shaft 11 and the 
motor cylinder 8 are relatively rotatable. 
Parallel to the output shaft 11, the auxiliary shaft 18 is rotatably 
supported on the opposite end walls of the transmission case 1 by a roller 
bearing 16 and a ball bearing 17. The forward/reverse gear assembly G is 
located between the auxiliary shaft 18 and the output shaft 11. 
The forward/reverse gear assembly G comprises a pair of driver gears 19, 20 
fixedly mounted on the output shaft 11, a driven gear 21 rotatably 
supported on the auxiliary shaft 18 in mesh with the driver gear 19, a 
driven gear 22 rotatably supported on the auxiliary shaft 18 in radial 
alignment with the other driver gear 20, an intermediate gear 23 meshing 
with the driver gear 20 and the driven gear 22, a driven clutch gear 24 
fixed to the auxiliary shaft 18 between driver clutch gears 21a, 22a 
integral with the opposite surfaces of the driven gears 21, 22, and a 
clutch member 25 for selectively coupling the driver clutch gears 21a, 22a 
to the driven clutch gear 24. A shift fork 26 engages in the clutch member 
25 for selectively moving the same axially into engagement with the driver 
clutch gear 21a and the driven clutch gear 24 or the driver clutch gear 
22a and the driven clutch gear 24. 
The auxiliary shaft 18 has an integral gear 28 held in mesh with an input 
gear 27 of the differential D. In response to operation of the clutch 
member 25, the differential D is operated selectively in forward and 
reverse directions of the motor vehicle. 
As shown in FIG. 2, the hydraulically hermetic chamber 31 is defined betwen 
the motor cylinder 8 and the pump cylinder 4, and a pump swash plate 32 is 
supported in the chamber 31 inwardly of the motor cylinder 8 in facing 
relation to the end face of the pump cylinder 4. An annular unitary pump 
shoe 33 is held in slidable contact with the pump swash plate 32. 
The pump plungers 6 and the pump shoe 33 are relatively swingably coupled 
by connecting rods 44. A presser ring 34 supported on the motor cylinder 8 
by a roller bearing 42 is held against an inner peripheral step of the 
pump shoe 33. A spring holder 35 is held against the presser ring 34, the 
spring holder 35 being coupled to the input shaft 2 through splines 36 
which allow axial movement of the spring holder 35 on the input shaft 2 
but prevent rotation of the spring holder 35 relatively to the input shaft 
2. A coil spring 37 is disposed around the input shaft 2 between the 
spring holder 35 and the pump cylinder 4 for normally pressing the spring 
holder 35 to cause the presser ring 34 to push the pump shoe 33 
resiliently toward the pump swash plate 32. The spring holder 35 has a 
partly spherical surface contacting a complementary partly spherical 
surface of the presser ring 34. Therefore, the spring holder 35 is neatly 
held against the presser ring 34 for transmitting the resilient force from 
the spring 37 to the presser ring 34. 
The chamber 31 is divided into a first chamber 31a near the pump swash 
plate 32 and a second chamber 31b near the pump cylinder 4 by the pump 
shoe 33, the presser ring 34, and the spring holder 35. 
The pump swash plate 32 and the pump shoe 33 have mutually sliding surfaces 
with their inner peripheral edges facing into the first chamber 31a, so 
that lubricating oil leaking from between these sliding surfaces flow into 
the first chamber 31a. To lubricate the sliding surfaces of the pump swash 
plate 32 and the pump shoe 33, an annular hydraulic pocket 38 is defined 
in the front surface of the pump shoe 33 and communicates through oil 
holes 39, 30, 41 defined in the pump shoe 33, the connecting rods 44, and 
the pump plungers 6 with pump chambers 45 defined between the pump 
plungers 6 and the pump cylinder 4. Therefore, oil under pressure in the 
pump chambers 45 is supplied through the oil holes 41, 40, 39 to the 
hydraulic pocket 38 for thereby lubricating the sliding surfaces of the 
pump shoe 33 and the pump swash plate 32. At the same time, oil pressure 
in the hydraulic pocket 38 is applied to the pump shoe 33 to bear the 
projecting thrust of the pump plungers 6, so that the pressure of contact 
between the pump shoe 33 and the pump swash plate 32 can be reduced. 
An annular lubricating chamber 43 is defined around the sliding surfaces of 
the pump swash plate 32 and the pump shoe 33 by means of the motor 
cylinder 8, the pump swash plate 32, the pump shoe 33, and a roller 
bearing 42, the lubricating chamber 43 being part of the second chamber 
31b. 
Oil under pressure in the hydraulic pocket 38 leaks along the sliding 
surfaces of the pump shoe 33 and the pump swash plate 32 into the 
lubricating chamber 43 at all times. The oil that has thus leaked first 
fills the lubricating chamber 43 as lubricating oil, and then leaks into 
the second chamber 31b through the roller bearing 42. Therefore, the 
lubricating chamber 43 is always replenished with new lubricating oil 
which can reliably lubricate the sliding surfaces of the pump shoe 33 and 
the pump swash plate 32 even from outside of the pump shoe 33. 
Into the second chamber 31b, there oil flows the lubricating chamber 43 and 
also lubricating oil from the sliding surfaces of the pump plungers 6 and 
the cylinder holes 5 and the sliding surfaces of the pump cylinder 4 and a 
distribution member 46. 
The spring holder 35 has a passage 47 by which the first and second chamber 
31a, 31b are held in communication with each other. Between the output 
shaft 11 and the input shaft 2, there is defined a first discharge 
passage 48 communicating with the first chamber 31a and coupled through a 
second discharge passage 49, the pressure control valve 50, a and a third 
discharge passage 51 to the oil tank on the bottom of the transmission 
case 1. 
As shown in FIG. 4, the pressure control valve 50 comprises a bottomed 
cylindrical spool valve body 52 for allowing and cutting off fluid 
communication between the second and third discharge passages 49, 51, and 
a spring 53 for normally urging the spool valve body 52 in a direction to 
cut off such fluid communication. The end wall of the case member 1a of 
the transmission case 1 has a bottomed hole 54 parallel to the input shaft 
2. The spool valve body 52 is slidably fitted in the bottomed hole 54, 
defining an oil chamber 55 between the bottom of the hole 54 and the spool 
valve body 52. A support member 57 is also inserted in the bottomed hole 
54, the support member 57 being prevented from moving toward the open end 
of the bottomed hole 54 by means of a retaining ring 56 fitted in the 
bottomed hole 54. The spring 53 is disposed between the support member 57 
and the spool valve body 52. The spool valve body 52 is therefore caused 
to slide in the bottom hole 54 until the hydraulic pressure in the oil 
chamber 55 which tends to open the pressure control valve 50 and the 
spring force of the spring 53 which tends to close the pressure control 
valve 50 are counterbalanced. 
The oil chamber 55 is held in communication with the second discharge 
passage 49 which is defined in the end wall of the case member 1a. An 
annular groove 58 is defined in a n inner peripheral surface of the 
bottomed hole 54 and held in communication with the third discharge 
passage 51. The annular groove 58 is selectively brought into and out of 
communication with the oil chamber 55 by the spool valve body 52. 
Therefore, when the oil pressure in the oil chamber 55, i.e, the chamber 
31, exceeds a level set by the spring 53, the pressure control valve 50 is 
opened to adjust the oil pressure in the chamber 31 to a prescribed level. 
Intermeshing bevel gears 61, 62 are fixed respectively to the confronting 
ends of the pump cylinder 4 and the pump shoe 33. The bevel gears 61, 62 
are synchronous gears having the same number of teeth. When the pump 
cylinder 4 is rotated by the input shaft 2, the pump shoe 33 is 
synchronously rotated through the bevel gears 61, 62. On rotation of the 
pump shoe 33, those pump plungers 6 which run along an ascending side of 
the inclined surface of the pump swash plate 32 are moved in a discharge 
stroke by the pump swash plate 32, the pump shoe 33, and the connecting 
rods 44, and those pump plungers 6 which travel along a descending side of 
the inclined surface of the pump swash plate 32 are moved in a suction 
stroke. 
In the hydraulic motor M, an annular motor swash plate 63 confronting the 
motor cylinder 8 is fitted in an annular swash plate holder 64. The swash 
plate holder 64 has a pair of integral trunnions 65 projecting outwardly 
from its opposite sides and pivotally supported in the transmission case 
1. Therefore, the motor swash plate 63 can be tilted together with the 
swash plate holder 64 about the axis of the trunnions 65. 
The tip ends of the respective motor plungers 10 are relatively swingably 
coupled to a plurality of motor shoes 66 held in slidable contact with the 
motor swash plate 63. To keep the respective motor shoes 66 in slidable 
contact with the motor swash plate 63, a presser plate 67 which holds the 
backs of the motor shoes 66 is rotatably supported by a ring 69 fastened 
to the swash plate holder 64 by means of bolts 68. The motor shoes 66 and 
the motor plungers 10 where they are coupled project through the presser 
plate 67 at a plurality of circumferentially spaced positions. The presser 
plate 67 is therefore rotatable with the motor shoes 66. 
Each of the motor shoes 66 has a hydraulic pocket 70 defined in its front 
face slidably contacting the motor swash plate 63. Oil chambers 71 defined 
between the closed ends of the cylinder holes 9 and the respective motor 
plungers 10 communicate with the corresponding hydraulic pockets 70 
through joined oil holes 72, 73 defined in the motor plungers 10 and the 
motor shoes 66. Therefore, oil under pressure in the oil chambers 71 is 
supplied through the oil holes 72, 73 into the hydraulic pockets 70 to 
apply a pressure to the motor shoes 66 for bearing the projecting thurst 
of the motor plungers 10. The pressure thus applied to the motor shoes 66 
reduces the pressure of contact between the motor shoes 66 and the motor 
swash plate 63, and causes oil to lubricate the sliding surfaces of the 
motor shoes 66 and the motor swash plate 63. 
A cylindrical partition 74 is fitted against the inner peripheral surface 
of the swash plate holder 64 in confronting relation to the inner 
peripheral surface of the presser plate 67 with a small gap therebetween. 
The partition 74, the swash plate holder 64, and the presser plate 67 
jointly define a lubricating chamber 75 accommodating the sliding surfaces 
of the motor shoes 66 and the motor swash plate 63. 
Oil under pressure in the respective hydraulic pockets 70 leaks along the 
sliding surfaces of the motor shoes 66 and the motor swash plate 63 at all 
times. The oil that has thus leaked first fills the lubricating chamber 75 
as lubricating oil, and then leaks out through the gap around the presser 
plate 67. Therefore, the lubricating chamber 75 is always replenished with 
new lubricating oil which can reliably lubricate the sliding surfaces of 
the motor shoes 66 and the motor swash plate 63 even from outside of the 
motor shoes 66. 
If the pressure in the lubricating chamber 75 approaches the pressure in 
the hydraulic pockets 70, the ability of the hydraulic pockets 70 to 
hydraulically support the motor shoes 66 would be impaired. To prevent 
this, the gap around the presser plate 67 is suitably selected dependent 
on the amount of oil leakage from the hydraulic pockets 70 so that the 
lubricating chamber 75 will hold oil under an approximately atmospheric 
pressure condition. 
A servomotor 81 for tilting the swash plate holder 64, i.e., the motor 
swash plate 63 is disposed in the transmission case 1. The servomotor 81 
comprises a servo cylinder 82 fixed to the transmission case 1, a servo 
piston 85 slidably disposed in the servo cylinder 82 and dividing the 
interior space of the servo cylinder 82 into a lefthand oil chamber 83 and 
a righthand oil chamber 84, a piston rod 86 integral with the servo piston 
85 and movably extending through the end wall of the servo cylinder 82 
near the lefthand oil chamber 83 in a fluid-tight manner, and a pilot 
valve 88 having an end slidably fitted in a valve hole 87 defined in the 
servo piston 85 and the piston rod 86 and movably extending through the 
end of the servo cylinder 82 near the righthand oil chamber 84 in a 
fluid-tight manner. 
The piston rod 86 is coupled to the swash plate holder 64 by a pin 89. An 
oil passage 90 defined in the servo cylinder 82 is held in communication 
with the lefthand oil chamber 83 for supplying oil pressure to act on the 
servo piston 85. The servo piston 85 and the piston rod 86 have a passage 
91 for bringing the righthand oil chamber 84 into communication with the 
valve hole 87 in response to rightward movement of the pilot valve 88, and 
a passage 92 for bringing the righthand oil chamber 84 into communication 
with the lefthand oil chamber 83 in response to leftward movement of the 
pilot valve 88. The valve hole 87 communicates with the oil tank at the 
bottom of the transmission case 1 through a return passage 93. 
The servo piston 85 is operated in amplified movement by following the 
lefthand and righthand movement of the pilot valve 88 under the oil 
pressure from the oil passage 90. In response to movement of the servo 
piston 85, the swash plate holder 64, i.e., the motor swash plate 63 can 
be angularly shifted or adjusted between the most inclined position (as 
shown) and the right-angle position where the motor swash plate 63 lies 
perpendicularly to the motor plungers 10. Upon rotation of the motor 
cylinder 8, the motor swash plate 63 reciprocally moves the motor plungers 
10 into and out of the cylinder holes 9. The stroke of the motor plungers 
10 can continuously be adjusted by the inclination of the motor swash 
plate 63. 
The closed hydraulic circuit C is formed between the hydraulic pump P and 
the hydraulic motor M through the distribution member 46 and a 
distribution ring 97. When the pump cylinder 4 is rotated by the input 
shaft 2, high-pressure working oil discharged from the pump chambers 45 
accommodating therein the pump plungers 6 in the discharge stroke flows 
into the oil chambers 71 of the cylinder holes 9 accommodating therein the 
motor plungers 10 which are in the expansion stroke. Working oil 
discharged from the oil chambers 71 accommodating therein the motor 
plungers 10 in the compression stroke flows back into the pump chambers 45 
accommodating therein the pump plungers 6 in the suction stroke. During 
this time, the motor cylinder 8, i.e., the output shaft 11 is rotated by 
the sum of the reactive torque applied by the motor plungers 10 in the 
discharge stroke to the motor cylinder 8 through the motor swash plate 63 
and the reactive torque received by the motor plungers 10 in the expansion 
stroke from the motor swash plate 63. 
The transmission ratio of the motor cylinder 8 to the pump cylinder 4 is 
given by the following equation: 
##EQU1## 
It can be understood from the above equation that the transmission ratio 
can be varied from 1 to a desired value by varying the displacement of the 
hydraulic motor M that is determined by the stroke of the motor plungers 
10, from zero to a certain value. 
The motor cylinder 8 comprises axially separate first through fourth 
members or segments 8a through 8d. The first member 8a includes the output 
shaft 11 as a unitary element, and accommodates the pump swash plate 32 
therein. The cylinder holes 9 are defined in the second, third, and fourth 
members 8b through 8d. The third member 8c serves as the distribution 
member 46. The fourth member 8d has the support shaft 12 as a unitary 
element. 
The first and second members 8a, 8b are coupled to each other by means of a 
plurality of bolts 98. The second, third, and fourth members 8b, 8c, 8d 
are relatively positioned by knock pins 99, 100 fitted in positioning 
holes defined in their mating end faces, and are firmly coupled together 
by means of a plurality of bolts 101. 
The input shaft 2 has an inner end portion rotatably supported centrally in 
the distribution member 46 by a needle bearing 105. The pump cylinder 4 is 
resiliently held against the distribution member 46 by the spring 37. 
A support plate 107 is fixed to an outer end surface of the case member 1b 
by means of bolts 106. To the support plate 107, there is securely coupled 
a cylindrical fixed shaft 108 projecting into the support shaft 12 of the 
motor cylinder 8. The distribution ring 97 slidably held against the 
distribution member 46 is eccentrically supported on the inner end of the 
fixed shaft 108. The distribution ring 97 divides an interior space 109 in 
the fourth member 8d of the motor cylinder 8 into an inner chamber 110 and 
an outer chamber 111. The distribution member 46 has an outlet port 112 
and an inlet port 113. The outlet port 112 provides fluid communication 
between the pump chambers 45 that receive the pump plungers 6 operating in 
the discharge stroke and the inner chamber 110. The inlet port 13 provides 
fluid communication between the pump chambers 45 that receive the pump 
plungers 6 operating in the suction stroke and the outer chamber 111. The 
distribution member 46 also has a number of communication ports 114 
defined therein and through which the oil chambers 71 of the motor 
cylinder 8 communicate with the inner chamber 110 or the outer chamber 
111. 
Therefore, upon rotation of the pump cylinder 4, high-pressure working oil 
discharged by the pump plungers 6 in the discharge stroke flows from the 
outlet port 112 via the inner chamber 110, and those communication ports 
114 which communicate with the inner chamber 110 into the oil chambers 71 
receiving the motor plungers 10 which are in the expansion stroke, thereby 
imposing a thrust on these motor plungers 10. Working oil discharged by 
the motor plungers 10 operating in the compression stroke flows through 
those communication ports 14 which communicate with the outer chamber 111 
and the inlet port 113 into the pump chambers 45 receiving the pump 
plungers 6 in the suction stroke. Upon such circulation of the working 
oil, hydraulic power can be transmitted from the hydraulic pump P to the 
hydraulic motor M as described above. 
The fixed shaft 108 has a peripheral wall having two, for example, radial 
bypass ports 115 through which the inner and outer chambers 110, 111 
communicate with each other. The clutch valve 116 in the form of a 
cylindrical clutch valve is rotatably fitted in the fixed shaft 108 for 
selectively opening and closing the ports 115. The clutch valve 116 has 
valve holes 117 defined in its peripheral wall near the distal end 
thereof, and a control connector 119 on the opposite end to which a 
control shaft 118 coupled to a clutch control device (not shown) is 
connected. The clutch valve 116 serves as a clutch for selectively 
connecting and disconnecting the hydraulic pump P and the hydraulic motor 
M. 
When the clutch valve 116 is rotated about its own axis to fully open the 
valve holes 117 in full registry with the bypass ports 115, the clutch is 
in an "OFF" position. When the bypass ports 115 are fully closed by 
shifting the valve holes 117 out of registry therewith, the clutch is in 
an "ON" position. When the bypass ports 115 are partly opened by slightly 
shifting the valve holes 117, the clutch is in a "partly ON" (partly 
engaged) position. With the clutch OFF as shown, working oil discharged 
from the outlet port 112 into the inner chamber 110 flows through the 
bypass ports 115 and the outer chamber 111 directly into the inlet port 
113, making the hydraulic motor M inoperative. When the clutch is ON, the 
above oil flow is shut off, and workin oil is circulated from the 
hydraulic pump P to the hydraulic motor M, allowing hydraulic power to be 
transmitted from the hydraulic pump P to the hydraulic motor M. 
The clutch valve 116 houses therein a hydraulic servomotor 121 actuatable 
by a pilot valve 20. The servomotor 121 has a servo piston 122 including a 
valve rod 123 which is of a diameter smaller than the inside diameter of 
the clutch valve 116. The valve rod 123 projects into the inner chamber 
110 and has a distal end on which a closure valve 124 is pivotally mounted 
for closing the outlet port 112. When the servo piston 122 is moved to the 
left until the closure valve 124 is held closely against the distribution 
member 46, the outlet port 112 is closed. The outlet port 112 is closed 
when the motor swash plate 73 is vertically positioned (as viewed in FIG. 
2) for the transmission ratio of 1. With the outlet port 112 closed, the 
pump plungers 6 are hydraulically locked to cause the pump cylinder 4 to 
mechanically drive the motor cylinder 8 through the pump plungers 6 and 
the pump swash plate 32. As a result, the thrust of the motor plungers 10 
on the motor swash plate 63 is eliminated, and so is the load on the 
various bearings. 
The fixed shaft 108 and the support plate 107 have an oil passage 139 
communicating with the inner chamber 110 and an oil passage 140 
communicting with the outer chamber 111. The support plate 107 has an oil 
passage 141 communicating with the oil passage 90 connected to the 
servomotor 81. A changeover valve 142 is disposed in the support plate 107 
for selectively communicating the oil passages 139, 140 with the oil 
passage 141. The changeover valve 142 operates to communicate one of the 
oil passages 139, 140 which is of a higher oil pressure, with the oil 
passage 141. Therefore, the servomotor 81 for tilting the motor swash 
plate 63 of the hydraulic motor M is supplied with the higher oil pressure 
from the inner chamber 110 or the outer chamber 111. 
The pilot valves 88, 120 of the respective servomotors 81, 121 are coupled 
to ends of links 127, 128, respectively. The other end of the link 127 is 
coupled to a rotatable shaft 129 which can be rotated about its own axis 
by an actuator (not shown), the shaft 129 having a cam 130 supported 
thereon. The other end of the link 128 supports thereon a cam follower 131 
slidingly contacting the cam 130. When the servomotor 81 is operated to 
vertically position the motor swash plate 63, the servomotor 121 is 
operated by the link 127, the cam 130, the cam follower 131, and the link 
128 to enable the closure valve 124 to close the outlet port 112. 
The replenishing pump F is mounted on an outer surface of the end wall of 
the case member 1a. The replenishing pump F is driven by the input shaft 2 
for feeding working oil from the oil tank on the bottom of the 
transmission case 1. The replenishing pump F has an outlet port 136 
communicating through an axial central replenishing oil passage 137 
defined in the input shaft 2 with the inner chamber 110 via the check 
valve 138 and also with the outer chamber 111 via the other check valve 
(not shown). The replenishing pump F therefore supplies oil to 
automatically compensate for any oil leakage from the closed hydraulic 
circuit C composed of the hydraulic pump P and the hydraulic motor M. 
As shown in FIG. 5, the distribution member 46 has an oil passage 151 
communicating with the replenishing oil passage 137 and an oil passage 152 
communicating with the second chamber 31b of the chamber 31, with the 
relief valve 150 being disposed in the distribution member 46 between the 
oil passages 151, 152. 
The relief valve 150 comprises a bottomed cylindrical spool valve body 153 
for allowing and cutting off fluid communication between the oil passages 
151, 152, and a spring 154 for normally urging the spool valve body 153 in 
a direction to cut off such fluid communication. The distribution member 
46 has a bottomed hole 155 defined therein and opening at an outer side 
surface thereof. The spool valve body 153 is slidably fitted in the 
bottomed hole 155, defining an oil chamber 156 between the bottom of the 
hole 155 and the spool valve body 153. A support member 158 is also 
inserted in the bottomed hole 155, the support member 158 being prevented 
from moving toward the open end of the bottomed hole 155 by means of a 
retaining ring 157 fitted in the bottomed hole 155. The spring 154 is 
disposed between the support member 158 and the spool valve body 153. The 
spool valve body 153 is therefore caused to slide in the bottom hole 155 
until the hydraulic pressure in the oil chamber 156 which tends to open 
the relief valve 150 and the spring force of the spring 154 which tends to 
close the relief valve 150 are counterbalanced. 
The oil chamber 156 is held in communication with the oil passage 151. An 
annular groove 159 is defined in an inner peripheral surface of the 
bottomed hole 155 and held in communication with the oil passage 152. The 
annular groove 59 is selectively brought into and out of communication 
with the oil chamber 156 by the spool valve body 153. 
Therefore, when the oil pressure in the oil chamber 156, i.e., the 
replenishing oil passage 137, exceeds a level set by the spring 154, the 
relief valve 150 is opened to inttroduce oil released from the 
replenishing oil passage 137 into the chamber 31 via the oil passage 152. 
The pressure level set for opening the pressure control valve 50 is lower 
than the pressure level set for opening the relief valve 150. 
Operation of the hydraulically operated continuously variable transmission 
thus constructed is as follows: 
The second chamber 31b of the chamber 31 defined between the pump cylinder 
4 and the motor cylinder 8 is supplied with most of the oil that has 
leaked from between the sliding surfaces of the shoe 33 and the swash 
plate 32, oil that has leaked from between the sliding surfaces of the 
pump cylinder 4 and the distribution member 46, and oil that has leaked 
from between the sliding surfaces of the plungers 6 and the cylinder holes 
5. When the relief valve 150 is opened, working oil that has been released 
from the replenishing oil passage 137 is also introduced into the second 
chamber 31b. The first chamber 31a communicating with the second chambeer 
31b through the passage 47 is supplied with the remainder of the oil that 
has leaked from between the sliding surfaces of the shoe 33 and the swash 
plate 32. The leaked oil sealed in the chamber 31 is discharged via the 
discharge passages 48, 49, 51 when the pressure control valve 50 is 
opened. 
Excess oil from the replenishing oil passage 137 communicating with the 
replenishing pump F is supplied to the chamber 31 through the relief valve 
150 in the above manner. Since the oil passage 151, 152 are defined in the 
distribution member 46, with the relief valve 150 disposed therebetween, 
excess oil from the replenishing pump F can be introduced into the chamber 
31 without varying the conventional structure and size. 
FIG. 6 shows a hydraulically operated continuously variable transmission 
according to another embodiment of the present invention. This embodiment 
differs from the preceding embodiment only in that the third discharge 
passage 51 connected to the pressure control valve 50 is defined in the 
case member 1a of the transmission case 1 such that the third discharge 
passage 51 communicates with an oil reservoir 160 defines in an end of the 
auxiliary shaft 18. The roller bearing 16 and the gear assembly G can 
therefore be effectively lubricated with oil from the oil reservoir 160. 
According to still another embodiment shown in FIG. 7, the pressure control 
valve 50 is dispensed with, and a plurality of discharge holes 171 are 
defined in the motor cylinder 8 near the motor swash plate 63, the 
discharge holes 171 communicating with the chamber 31. The motor cylinder 
8 also has a discharge hole 172 defined therein closely to the motor 
plungers 10 and communicating with the chamber 31. Lubricating oil from 
the chamber 31 can be poured via the discharge holes 171 over the sliding 
surfaces of the motor swash plate 63 and the motor shoe 66 to lubricate 
them, and also via the discharge hole 172 over the sliding surfaces of the 
motor plungers 10 and the cylinder holes 9 to lubricate them. The 
discharge holes 171, 172 should be of such a diameter as to retain a 
sufficient amount of lubricating oil in the chamber 31. 
FIG. 8 illustrates a hydraulically operated continuously variable 
transmission according to a further embodiment of the present invention. 
In this embodiment, a relief valve 150' is disposed between the oil 
passages 151, 152 in the distribution member 46. The relief valve 150' 
comprises a spherical valve body 173 disposed in a valve chamber 174 
defined in the distribution member 46 and normally urged in a closing 
direction by means of a spring 175. The valve chamber 174 comprises a 
bottomed hole 176 defined in the distribution member 46 and closed by a 
support member 177 threaded in the bottomed hole 176. The spring 175 is 
disposed between the valve body 173 and the support member 177. 
FIG. 9 schematically shows a hydraulically operated continuously variable 
transmission according to a still further embodiment of the present 
invention. As shown in FIG. 9, the relief valve 150 is connected between 
the replenishing oil passage 137 and the lubricating chamber 75 of the 
hydraulic motor M for supplying oil released from the relief valve 150 to 
the lubricating chamber 75. The pressure control valve 50 is connected 
between the oil tank T and a junction between the relief valve 150 and the 
lubricating chamber 75. The pressure control valve 50 is openable at a 
pressure level lower than the pressure level set for opening the relief 
valve 150. In operation, excess oil from the replenishing oil passage 137 
is supplied through the relief valve 150 to the lubricating chamber 75. 
Therefore, even if the amount of oil leaked from between the sliding 
surfaces of the motor shoe 66 and the motor swash plate 63 into the 
lubricating chamber 75 is small, the lubricating chamber 75 can be filled 
with lubricating oil from the relief valve 150. When the oil pressure in 
the lubricating chamber 75 is increased beyond a prescribed pressure 
level, the pressure control valve 50 is opened to release oil from the 
lubricating chamber 75 for keeping the oil pressure in the lubricating 
chamber 75 at a lever lower than the oil pressure in the replenishing oil 
passage 137. 
Although certain preferred embodiments have been shown and described, it 
should be understood that many changes and modifications may be made 
therein without departing from the scope of the appended claims.