Power plants – Pressure fluid source and motor – Input pump and rotary output motor system having...
Reexamination Certificate
2000-02-07
2001-10-16
Ryznic, John E. (Department: 3745)
Power plants
Pressure fluid source and motor
Input pump and rotary output motor system having...
Reexamination Certificate
active
06301885
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to hydrostatic transaxles intended primarily for use in the lawn and garden industry on riding lawnmowers, lawn and garden tractors and the like, but may also be applied to larger implements and vehicles.
Hydrostatic transmissions transmit rotary mechanical motion, typically from an internal combustion engine, to fluid motion, typically oil, and then back to rotary mechanical motion to rotate a pair of drive axles in order to drive the vehicle. The hydrostatic transmission controls the output rotary mechanical motion such that varying output speeds in the forward and reverse directions are possible with a single speed input rotary mechanical motion. Such transmissions have utilized radial piston pumps and motors, axial piston pumps and motors and hybrid transmissions wherein the pump may be of the radial piston design, for example, and the motor formed as a gear pump. The speed of the output of the transmission is typically controlled by varying the eccentricity of the pump track ring or swash plate.
A typical construction of the hydrostatic transmission component of the transaxle includes a block common to both the pump and motor units, often referred to as a “center section.” The center section facilitates an external mounting surface for a motor cylinder barrel and a pump cylinder barrel, and additionally, internal passages body for providing hydraulic communication between the pump and motor cylinder barrels. Conventionally, the pump and motor cylinder barrel axes of rotation are 90 degrees relative to one another. Center section machining is difficult because the center section is substantial in size and machined surfaces are substantially perpendicular, often requiring multi-axis machining capabilities. This corresponds to a significant cost associated with this design type.
Moreover, many HSTs heretofore require that the pump and motor mechanism unit be matched to a fixed swash plate prior to mounting the mechanism into the casing. Typically, assembly requires positioning the fixed swash plate in the casing, mounting the pump and motor mechanism into the casing then taking measures to ensure the fixed swash plate is suitably aligned with the pump and motor mechanism. Arranging the fixed swash plate and pump and motor mechanism, in the manner described above, poses a significant step in the assembly process which represents additional cost.
SUMMARY OF THE INVENTION
The present invention provides a variable displacement hydraulic pump including a pump cylinder barrel having a plurality of axially arranged cylinder chambers disposed therein and each cylinder chamber includes a reciprocating piston therein. The pump is rotatably supported by the pump block and a motor block is separable from and connected to the pump block. A hydraulic motor is rotatably supported by the motor block and hydraulically connected to the pump through a pair of continuous passages formed in the pump and motor blocks. The motor includes an axis of rotation substantially perpendicular to an axis of rotation of the pump.
The present invention further provides a hydrostatic transmission including a variable displacement hydraulic pump having a pump cylinder barrel with a plurality of axially arranged cylinder chambers disposed therein. Each cylinder chamber includes a reciprocating piston therein. The pump is rotatably supported by a pump and motor block. A motor, which is hydraulically connected with the pump, includes a cylinder barrel having a plurality of axially arranged cylinder chambers disposed therein and each cylinder chamber has a reciprocating piston therein. The motor includes an axis of rotation substantially perpendicular to an axis of rotation of the pump. A thrust bearing is supported by a portion of the pump and motor block and is engaged with the pistons extended from the cylinder barrel of the motor. A stop member is attached to the portion of the pump and motor block and retains the thrust bearing wherein relative movement of the thrust member is restrained by the stop member.
REFERENCES:
patent: 2503530 (1950-04-01), Weber
patent: 4893524 (1990-01-01), Ohashi et al.
patent: 5339631 (1994-08-01), Ohashi
patent: 5473964 (1995-12-01), Okada et al.
patent: 5768892 (1998-06-01), Hauser et al.
Johnson Kevin J.
Jolliff Norman E.
Baker & Daniels
Ryznic John E.
Tecumseh Products Company
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