ELECTRIC SHIFTING OF A VARIABLE
CROSS-REFERENCE TO RELATED
This application is related to and claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent application Ser. No. 60/138,483, filed Jun. 10, 1999.
BACKGROUND OF THE INVENTION 10
The present invention relates to hydrostatic transmissions and transaxies having fluid pumps of adjustable displacement, and particularly to means for adjusting the pump displacement to control the output speed and direction 15 of an output shaft or axle; the present invention also relates to fluid controlled mechanically-driven transmissions and transaxies having epicyclic gearing, the speed of rotation of the gears varied in response to resistance to a fluid flow through a pump coupled thereto, and particularly to means 20 for adjusting the resistance to the fluid flow through the pump to control the output speed of an output shaft or axle.
Typically, hydrostatic transmissions transmit rotary mechanical motion, typically from an internal combustion engine, to fluid motion, typically oil, and then back to rotary 25 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 30 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 motor formed as a gear pump. The speed of the output of the transmission is typically controlled by varying 35 the eccentricity of the pump track ring or swash plate, thereby varying the displacement of the pump.
U.S. Pat. No. 5,177,967, issued Jan. 12, 1993; U.S. Pat. No. 5,182,966, issued Feb. 2,1993; U.S. Pat. No. 5,373,697, issued Dec. 20, 1994; U.S. Pat. No. 5,701,738, issued Dec. 40 30,1997; U.S. Pat. No. 5,974,798, issued Nov. 2, 1999; and U.S. Pat. No. 5,992,150, issued Nov. 30, 1999; and U.S. patent application Ser. No. 09/302,312, filed Apr. 29, 1999, the disclosures of which are all expressly incorporated ^ herein by reference, disclose hydrostatic transmissions comprising radial piston pumps and motors.
U.S. patent application Ser. No. 09/498,692, filed Feb. 7, 2000, the disclosure of which is expressly incorporated herein by reference, discloses a hydrostatic transmission 50 comprising an axial piston pump and motor of the swashplate or wobbleplate type.
Some types of mechanically-driven transmissions couple an input shaft to an output shaft or axle through an epicyclic gear train. The input-to-output speed of the epicyclic gear 55 train may be varied by restricting the rotation of a ring gear which is intermeshed with a plurality of planet gears, which are in turn meshed with a sun gear. If the ring gear is free to rotate, the planet gears will not tend to revolve about the rotating sun gear. If the ring gear's rotation is partly or fully go restricted, the planet gears will tend to revolve about the sun gear at a speed inversely corresponding to the ring gear's rotation.
U.S. Pat. No. 5,860,884, issued Jan. 19, 1999; U.S. Pat. No. 5,971,881, issued Oct. 26, 1999; and U.S. Pat. No. 65 6,010,423, issued Jan. 4, 2000, the disclosures of which are all expressly incorporated herein by reference, disclose fluid
controlled mechanically-driven transmissions having epicyclic gearing comprising a ring gear, the outer periphery of which forms an inner member of a gerotor pump. The inner gerotor pump member is meshed with a rotatable outer gerotor pump member. Fluid flow from the gerotor pump is regulated by a linearly traveling valve. The speed of rotation of the output shaft coupled to the epicyclic gearing corresponds to the amount of resistance to a fluid flow through the gerotor pump. Those skilled in the art will recognize that a gear pump may be used in lieu of a gerotor pump. The valve may be of the type which is manually operated.
A problem associated with hydrostatic transmissions or fluid pump-controlled mechanically-driven transmissions described above and disclosed in the above-mentioned, expressly incorporated references, is that the mechanical linkages used for varying the displacement of the pump in a hydrostatic pump, or for varying the fluid flow restriction from the gerotor pump of the fluid controlled mechanicallydriven transmission, are imprecise and may require actuation force levels which are undesirably high for some operators. A means of more precisely setting the transmission speed, with less required effort, is highly desirable.
SUMMARY OF THE INVENTION
The present invention provides a variable speed transmission including a rotatable input member, a fluid pump operatively engaged with the input member, a fluid in the pump being pumped in response to rotation of the input member, and a fluid motor in fluid communication with the fluid pump, fluid pumped by the pump being received by the fluid motor, the fluid motor being driven by fluid received by the fluid motor and having a variable output speed. Means are provided for selectively varying the displacement of the fluid pump or the fluid motor, whereby the output speed of the fluid motor is varied. A rotatable output member is operatively engaged with the fluid motor, and a reversible electric motor having an output shaft is provided, the output shaft having varying angular positions. The output shaft is in mechanical engagement with the displacement varying means, and the displacement of the one of the fluid pump and the fluid motor being varied in response to changes in the output shaft angular position.
In certain embodiments of the present invention, a rotatably adjustable electric motor, such as a servomotor or stepper motor, is provided which has a gear attached to the motor shaft and is in meshed engagement with a gear attached to a pivoting swashplate of an axial piston fluid pump in a hydrostatic transmission, whereby the displacement of the pump is variably controlled by adjustment of the motor shaft, thereby controlling the speed and/or direction of an output shaft of the transmission.
In certain other embodiments of the present invention, a rotatably adjustable electric motor, such as a servomotor or stepper motor, is provided which has a gear attached to the motor shaft and is in meshed engagement with a gear attached to a pivoting track ring of a rotary piston fluid pump in a hydrostatic transmission, whereby the displacement of the pump is variably controlled by adjustment of the motor shaft, thereby controlling the speed and/or direction of an output shaft of the transmission.
The present invention also provides a variable speed transmission assembly including a rotatable input member connectable to a drive source, a rotatable output member, and a gear train operatively connected to the input member and the output member for transmitting rotational power of the input member to the output member, the gear train