Variable displacement hydraulic motor

A variable displacement hydraulic motor is easily mounted on a power shovel without interfering with a truck frame of the power shovel and without projecting outward therefrom. The hydraulic motor is easily assembled and machined in its manufacturing. In the hydraulic motor (M'), there is provided an end cover (57) in which is slidably mounted a piston lever (69) which is oppositely disposed from a drive shaft (44) of the hydraulic motor (M') to extend in a direction perpendicular to an axis of the drive shaft (44). Since the hydraulic motor (M') is provided with a valve plate swinging unit having a pin (71) through which the piston lever is connected with a valve plate (59) fixedly mounted on a cylinder block (60), it is possible to directly mount the end cover (57) on a main casing (50) of the hydraulic motor (M') so as to be perpendicular to the axis of the drive shaft (44).

FIELD OF THE INVENTION 
The present invention relates to a variable displacement hydraulic motor 
serving as a hydraulic drive motor mounted in a power shovel. 
BACKGROUND OF THE INVENTION 
As one of variable displacement hydraulic motors, there is a bent-axis type 
axial-piston motor such as one disclosed, for example in U.S. Pat. No. 
3,961,563. 
In FIG. 1, the reference character M denotes such bent-axis type 
axial-piston motor provided with a motor housing which is constructed of a 
main casing 1, a motor casing 2 and an end cover 3, as shown in FIG. 1. In 
the motor housing is obliquely mounted a cylinder block 6 so that an axis 
of the cylinder block 6 forms a tilt angle with an axis of a drive shaft 
7, which tilt angle is variable within a range of from 7.5.degree. to 
30.degree. while controlled by moving a convex portion of a valve plate 8 
relative to an inner concave portion 9 of the end cover 3 in a swinging 
manner. 
As the tilt angle is controlled, the stroke of each of a plurality of 
pistons 4 is so controlled as to make it possible to change a rotational 
speed of the drive shaft 7 in a condition in which an output horsepower of 
the drive shaft 7 is kept constant, provided that an amount of hydraulic 
oil supplied to the hydraulic motor M is kept constant. 
On the other hand, in a power shovel, as shown in FIG. 1, a sleeve-like 
housing 12 is fixedly mounted in a bore 11 of a truck frame 10. A hub 14 
fixed to a sprocket 13 is rotatably mounted on an outer peripheral portion 
of the housing 12 in which the hydraulic drive motor M is housed. The 
drive shaft 7 of the drive motor M is connected to the hub 14 through a 
reduction-gear mechanism 15 so that the sprocket 13 is driven by the 
hydraulic drive motor M. 
As shown in FIG. 1, in the hydraulic drive motor M which is one of the 
conventional variable displacement hydraulic motors, since a slider 
element 3a for moving the valve plate 8 in a swinging manner is engaged 
with a central portion of the valve plate 8, it is impossible for the 
slider element 3a to smoothly swing the valve plate 8 in a direction 
perpendicular to an axis of the drive shaft 7. Consequently, as is clear 
from FIG. 1, the valve plate 8 is moved in a swinging manner by the slider 
element 3a in a direction slightly obliquing from the former direction 
perpendicular to the axis of the drive shaft 7. 
The above arrangement of the slider element 3a PG,4 requires the end cover 
3 to be mounted in a tilting condition, which increases the entire length 
of the end cover 3 and causes the motor casing 2 to be mounted in a 
tilting condition too to make its machining operation difficult in 
manufacturing. 
On the other hand, in case that the abovementioned variable displacement 
hydraulic motor is employed as the hydraulic drive motor M, since the 
overall length of the drive motor M is large, a part of the drive motor M 
projects outward from the truck frame 10 to often interfere with obstacles 
such as rock and the like. In addition, in this case, since the end cover 
3 is obliquely mounted, the end cover 3 tends to interfere with the truck 
frame 10, which makes it difficult to mount the hydraulic drive motor M in 
the truck frame 10, and, therefore requires a complicated mounting 
construction for mounting the drive motor M in the truck frame 10. 
SUMMARY OF THE INVENTION 
Under such circumstances, the present invention is made so that it is an 
object of the present invention to provide a variable displacement 
hydraulic motor which does not interfere with a truck frame, nor does it 
project outward from the truck frame to make it possible to easily mount 
the hydraulic motor in the truck frame and to easily assemble and machine 
the hydraulic motor in manufacturing. 
It is another object of the present invention to provide a variable 
displacement hydraulic motor in which a valve plate is smoothly moved in a 
swinging manner, and an end cover is so mounted as to be perpendicular to 
an axis of a drive shaft of the hydraulic motor. 
In order to accomplish the above objects of the present invention, 
according to the present invention, there is provided: 
A variable displacement hydraulic motor comprising: an end cover fixedly 
mounted on an end surface of a substantially cylindrical main casing; a 
drive shaft rotatably mounted in said main casing; a center shaft and a 
plurality of pistons, an end portion of each of which shaft and pistons is 
swingably engaged with a flange portion of said drive shaft, the flange 
portion being formed in a rear-end portion of said drive shaft; a cylinder 
block for slidably receiving the other end portion of each of said pistons 
therein, said cylinder block being provided with a through-hole through 
which said center shaft passes, the through-hole being formed in a central 
portion of said cylinder block; a valve plate fixedly mounted on a 
base-end portion of said cylinder block, said valve plate being provided 
with a central portion in which the other end portion of said center shaft 
is rotatably mounted; guide means for swingably guiding said valve plate, 
said guide means being provided in opposite sides of an inner portion of 
said end cover; a swinging means for moving said valve plate in a swinging 
manner, said swinging means being provided with a piston lever slidably 
mounted in a substantially central portion of said end cover to extend in 
a direction perpendicular to an axis of said drive shaft; and a pin for 
connecting said swinging means with said valve plate. 
It is possible for anyone skilled in the art to understand the above 
objects, other objects, advantages and preferred embodiments of the 
present invention which will be clarified hereinafter with reference to 
the following description and the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now, with reference to FIGS. 2 to 5 of the accompanying drawings, the 
present invention will be described hereinbelow in detail. 
FIG. 2 is a schematical longitudinal sectional view of a motor-mounting 
portion of a power shovel, in which portion a variable displacement 
hydraulic drive motor M' is mounted. In the motor-mounting portion of the 
power shovel shown in FIG. 2, a sleeve-like housing 32 is fixedly mounted 
in a hole 31 of a track frame 30 of the power shovel. A hub 33 is 
rotatably mounted on an outer peripheral portion of the housing 32. 
Fixedly mounted on the hub 33 is a sprocket 35 for driving a caterpillar 
34 of the power shovel. Also fixedly mounted on the hub 33 is a first ring 
gear 37 which is a component of a reduction-gear mechanism 36. 
The first ring gear 37 is meshed with a planet gear 39 which is rotatably 
mounted on a planet carrier 38. The planet gear 39 is meshed with a second 
ring gear 40 which is meshed with a gear 41 fixedly mounted on the housing 
32. On the other hand, a sun gear 42 is connected to a drive shaft 44 of 
the variable displacement hydraulic motor M' through a coupling 43. 
Consequently, when the drive shaft 44 rotates, the sun gear 42 is 
rotatably driven by the drive shaft 44 so that the planet gear 39 is so 
driven that it not only rotates about its own axis but at the same time 
its axis rotates about an axis of the second ring gear 40. At the same 
time, the first ring gear 37 is rotatably driven by the planet gear 39 to 
drive the hub 33 together with the sprocket 35. 
The variable displacement hydraulic motor M' has a construction shown in 
FIGS. 3 to 5. 
Namely, in the interior of a cylindrical main casing 50 of the hydraulic 
motor M', the drive shaft 44 is rotatably mounted on an end portion of the 
main casing 50 through a bearing 51. Brake disks 53 are alternately 
splined to both of an outer peripheral surface of a base-end flange 
portion 52 of the drive shaft 44 and an inner peripheral surface of an 
intermediate portion of the main casing 50 to make it possible to rotate 
the former and the latter together when the brake disks 53 are pressed to 
each other by actuating a piston 54 slidably mounted in the other end 
portion in the interior of the main casing 50. The piston 54 is normally 
pressed against the brake disks 53, while actuated under the influence of 
a pressurized oil contained in a pressure chamber 56 to release the brake 
disks 53 from a pressure applied thereto. A brake mechanism of the 
reduction-gear mechanism 36 has the above construction. 
An end cover 57 is fixedly mounted on an end surface 50a of the main casing 
50, which end surface 50a is disposed in a position near the base-end 
portion of the drive shaft 44 as shown in FIG. 3. In an inner lower 
portion of the end cover 57, there is provided a concave guide portion 58 
which is symmetrical with respect to the axis of the drive shaft 44 and 
extends in parallel therewith. The concave guide portion 58 is constructed 
of: a pair of guiding side surfaces 58a extending in parallel with each 
other; and an arc-shaped curved guiding bottom surface 58b formed between 
the pair of the guiding side surfaces 58a. A valve plate 59 is swingable 
along the concave guide portion 58. Opposite side surfaces 59a of the 
valve plate 59 are brought into contact with the guiding side surfaces 58a 
of the concave guide portion 58, while an arc-shaped bottom surface 59b of 
the valve plate 59 is brought into contact with the guiding bottom surface 
58b of the concave guide portion 58. 
An end portion of a center shaft 61 rotatably mounted in a cylinder block 
is rotatably mounted in the valve plate 59. Both of a ball-like portion 
61a of the center shaft 61 and a ball-like portion 63a of each of the 
pistons 63 slidably inserted into cylinder bores 62 of the cylinder block 
60 are swingably mounted in ball-like concave portions 64 of the end 
surface 52a of the base-end flange portion 52 of the drive shaft 44 
through a holding plate 65. On the other hand, the cylinder block 60 is 
pressed against a front surface 59c of the valve plate 59 by a spring 66. 
A bore 67 is so formed in the end cover 57 as to extend in a direction 
perpendicular to the axis of the drive shaft 44, whereby the bore 67 is 
oppositely disposed from the drive shaft 44. An axial central portion of 
the bore 67 opens into the guide portion 58 in a notch portion 68 of the 
end cover 57. On the other hand, a base portion 71a of a pin 71 is fixedly 
mounted in a small bore 70 formed in an axial central portion of a piston 
lever 69 slidably mounted in the bore 67, which pin 71 is fixed to the 
small bore 70 by means of a plate 72 and a screw 73 as shown in FIG. 3. A 
front-end portion of the pin 71 assumes a ball-like form and extends 
forward from the notch portion 68 of the end cover 57 so as to be slidably 
mounted in a cylindrical bore 74 which is formed in an end portion of the 
valve plate 59, the end portion being disposed in a position near the axis 
of the drive shaft 44. 
A blank plug 75 is threadably engaged with opposite end portions of the 
bore 67 to form a first chamber 76 and a second chamber 77 which are 
communicated with the above opposite end portions of the bore 67 at 
opposite end surfaces 69a and 69b, respectively. When the pressurized oil 
is supplied to one of these chambers 76 and 77, the piston lever 69 is 
slidably moved upward or downward in FIG. 3 to move the pin 71 vertically, 
so that the valve plate 59 is moved along the concave guide portion 58 in 
a swinging manner, whereby the axis of the cylinder block 60 forms a tilt 
angle with the axis of the drive shaft 44, which tilt angle is variable. 
When the piston lever 69 is slidably moved in the bore 67, the front-end 
portion 71b of the pin 71 is slightly moved in a sliding manner in a 
direction parallel to the axis of the drive shaft 44 in the bore 74 of the 
valve plate 59. 
FIG. 5 is a diagram of a hydraulic circuit for the hydraulic drive motor 
M'. A pressurized oil is supplied from a port 80 to the pressure chamber 
56 of the above-mentioned brake mechanism. On the other hand, each of a 
first oil passage 81 and a second oil passage 82 is communicated with the 
variable displacement hydraulic motor M' while communicated with a by-pass 
passage 84 which is provided with a pair of check valves 83. The by-pass 
passage 84 is so controlled through a pilot valve 85 as to be communicated 
with a first 86 and a second 87 oil ports. The first oil port 86 is 
communicated with the first chamber 76 of the piston lever 69, while the 
second oil port 87 is communicated with the second chamber 77 of the 
piston lever 69. The pilot valve 85 is normally held in its first position 
"I" by means of a spring 88. When a pressurized oil is supplied to a 
pressure portion 85a of the pilot valve 85 through a pilot channel 89, the 
pilot valve 85 is moved to its second position "I". When the pressurized 
oil is not supplied to the pressure portion 85a of the pilot valve 85, the 
pilot valve 85 returns to its first position "I". When the pressurized oil 
contained in one of the oil passages 81 and 82 is supplied to the first 
chamber 76 of the piston lever 69, the piston lever 69 is moved downward 
in FIG. 3, to make the tilt angle of the valve plate 59 maximum. When the 
pressurized oil is supplied to the pressure portion 85a of the pilot valve 
85 through a pilot channel 89, the pilot valve 85 is moved to its second 
position "I" so that the pressurized oil contained in one of the first 81 
and the second 82 oil passages are supplied to the second chamber 77, 
whereby the piston lever 69 is slidably moved upward in the bore 67 in 
FIG. 3 so as to make the tilt angle of the valve plate minimum. 
Incidentally, the port 80, the first 81 and the second 82 oil passages, the 
by-pass passage, the first 86 and the second 87 oil channels and the pilot 
channel 89 are formed in the main casing 50 and the end plate 57. On the 
other hand, both of the check valves 83 and the pilot valve 85 are 
disposed between the main casing 50 and the end cover 57. 
As is clear from the above description, in the variable displacement 
hydraulic motor of the present invention, in contrast with the 
conventional hydraulic motor, there is no need to mount the end cover 
obliquely on the main casing through the motor casing, and it is possible 
to directly mount the end cover 57 on the main casing 50 so as to be 
perpendicular to the axis of the drive shaft 44, which makes it possible 
to decrease the overall length of the hydraulic motor M'. Consequently, in 
case that the hydraulic motor M' is mounted on a sprocket-drive portion of 
the power shovel, there is no fear that the end cover 57 projects outward 
from the truck frame and interfers with the truck frame itself. 
Consequently, there is no need to introduce a special machining operations 
in manufacturing of the hydraulic motor M' of the present invention to 
make it possible to easily mount the hydraulic motor M' of the present 
invention on the power shovel. 
In addition, in the hydraulic motor M' of the present invention, since the 
end cover 57 is so arranged as to be perpendicular to the axis of the 
drive shaft 44, it is possible to mount the end cover 57 on the main 
casing in an easy manner. Further, it is also possible to form the main 
casing 50 into a simple cylindrical form having no oblique portion, which 
makes it possible to easily assemble and machine the hydraulic motor M' of 
the present invention in its manufacturing.