Power plants – Pressure fluid source and motor – Input pump and rotary output motor system having...
Reexamination Certificate
1998-05-27
2001-11-13
Lopez, F. Daniel (Department: 3745)
Power plants
Pressure fluid source and motor
Input pump and rotary output motor system having...
C092S012200
Reexamination Certificate
active
06314730
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an axle driving apparatus which is housed in a common housing with a hydrostatic transmission (hereinafter referred to as an “HST”).
BACKGROUND OF THE INVENTION
RELATED ART
U.S. Pat. Nos. 4,903,545 and 4,914,907, for example, disclose an axle driving apparatus which includes an HST, a differential gear unit and axles interlocked with each other housed in a common housing. The HST comprises a hydraulic pump disposed on a horizontal portion of a center section which is L-like-shaped and has a horizontal portion and a vertical portion. A hydraulic motor is disposed on the vertical portion of the center section. The hydraulic pump and hydraulic motor are fluidly connected by a closed fluid circuit provided in the center section. The hydraulic pump is driven by an external prime mover so as to drive the hydraulic motor to thereby drive the axles. U.S. Pat. No. 5,201,692, for example, discloses providing a check valve at the negative pressure side of the closed fluid circuit of the center section and at the lower portion of the center section through which oil stored in the housing is automatically sucked into the closed fluid circuit.
U.S. Pat. No 4,903,545 discloses that in order for a pair of oil passages constituting the closed fluid circuit to communicate simply with a pair of arcuate ports formed on a pump mounting surface on the upper surface of the horizontal portion of the center section, each arcuate port is disposed in parallel to the extending direction of the oil passage overlapping a substantially longitudinal center portion of each arcuate port with each oil passage to communicate therewith. The substantially longitudinal center portion of each port, which is overlapped by each port, is formed to directly downwardly communicate with each oil passage.
When the arcuate ports are formed as mentioned above, a movable swash plate of the hydraulic pump is not able to slantingly rotate around its axis at a right angle to the axles. Hence, a control shaft for controlling the slanting rotation direction of the movable swash plate, when disposed at a right angle to the axis of rotation of the hydraulic pump, must be disposed perpendicular to the axles. However, a control rod connected to a speed changing member provided on the vehicle for changing the vehicle speed extends towards the axle driving apparatus and may be pushed or pulled longitudinally of the vehicle body, whereby the control rod cannot be directly connected to the control shaft for the movable swash plate. Hence, a link mechanism is required to convert the longitudinal direction of operation to a lateral direction of operation.
In U.S. Pat. No. 5,094,077, the control shaft for the movable swash plate is disposed in parallel to the axis of rotation of the hydraulic pump so that such a link mechanism is not required. However, in order to convert the horizontal movement of the swinging arm provided at the operating shaft into a lateral movement of the movable swash plate, the utmost end of the control arm is made spherical. A pair of shaft guide members, each having a hemispherical recess, are provided for receiving each spherical end of the control arm so that the control arm must be connected to the movable swash plate through the shaft guide member, resulting in that the number of necessary parts is increased as is the manufacturing cost.
In the above-mentioned U.S. Pat. No. 4,914,907, the arcuate ports at the pump side of the center section are disposed perpendicularly to the extending direction of the oil passages respectively. As such, the operating shaft of the movable swash plate can be disposed at a night angle with respect to the axis of rotation of the hydraulic pump and in parallel to the axles so that the aforesaid link mechanism is unnecessary. However. since the arcuate ports and oil passages communicate with each other through separate oil passages formed perpendicularly with respect to said passages, the construction of the passages is more complicated than is preferable.
Also, in U.S. Pat. No. 5,201,692, at the lower surface of the center section are open two oil holes communicating with the closed fluid circuit. A ball is inserted into each oil hole. A plate is mounted to the lower surface of the center section by a plurality of bolts. The plate is provided with openings which enable oil in the housing to flow into the closed fluid circuit while preventing the balls from escaping from the holes. This check valve arrangement requires a large number of parts, more man-power to construct and is high in manufacturing cost.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improvement in a center section on which a hydraulic pump is mounted so that a movable swash plate of the hydraulic pump housed in a housing can be efficiently operated. In particular, the HST comprises a hydraulic pump and a hydraulic motor, which are individually mounted on mounting surfaces of the center section. The center section has a horizontal portion and a vertical portion and is substantially L-like-shaped. The horizontal portion of the center section is provided with a pair of linear oil passages which extend in parallel to each other. One end of each oil passage communicates with one of a pair of arcuate ports provided on the motor mounting surface formed on the vertical portion of the center section. An intermediate portion of each of the oil passages communicates with one of a pair of arcuate ports disposed on the pump mounting surface formed on the horizontal portion of the center section. Whereby, two pair of arcuate ports are connected with each other forming a closed fluid circuit.
The arcuate ports on the pump mounting surface are disposed substantially vertically with respect to the direction in which the oil passages extend and overlap at both ends with the respective oil passages. One of the arcuate ports is deeper at one end so as to communicate with one of the oil passages. The other arcuate port is deeper so as to communicate with the other oil passage, whereby the construction of the oil passages and arcuate ports is simple for communicating with each other so as to reduce manufacturing cost.
Since the arcuate ports are open at the pump mounting surface and extend in parallel to the direction of downward movement the vehicle body, the axis of slanting movement of the movable swash plate for changing the discharge direction and a discharge amount of oil from the hydraulic pump extends laterally of the vehicle body. A control shaft for slantingly operating the movable swash plate can be disposed at a right angle to the axis of rotation of the hydraulic pump and parallel to the axles. The rotating direction of an arm provided at the control shaft and the operating direction of a control rod connected to a speed changing member are coincident with each other. Whereby the control rod can be directly connected at one end thereof with a control arm for the movable swash plate so as to simplify the link mechanism.
In the case where the movable swash plate is of a cradle type such that the upper surface thereof is made convex to be slidable along a concave portion formed on the inner surface of the housing, the axis of the control shaft rotatably supported by the side wall of the housing is made coincident with the center of curvature of the convex portion of the movable swash plate. An engaging portion of the swinging arm provided on the control shaft can be directly connected with respect to a groove in the side surface of the movable swash plate. Thereby enabling the above-mentioned shaft guide member to be omitted, so as to reduce the number of parts required. Also, the relative sliding movement of the groove in the movable swash plate to the engaging portion of the swinging arm is scarcely formed. Whereby the movable swash plate can be operated smoothly without the need to apply excessive force.
Vertical oil holes are branched from a pair of oil passages for fluidly coupling the hydraulic pump with the hydraulic motor and then ar
Kanzaki Kokyukoki Mfg. Co. Ltd.
Lopez F. Daniel
Sterne Kessler Goldstein & Fox P.L.L.C.
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