Power plants – Pressure fluid source and motor – Servo-motor having externally operated control valve sets...
Reexamination Certificate
1999-06-08
2001-01-23
Ryznic, John E. (Department: 3745)
Power plants
Pressure fluid source and motor
Servo-motor having externally operated control valve sets...
C060S486000, C060S445000
Reexamination Certificate
active
06176085
ABSTRACT:
BACKGROUND
The present invention relates to hydraulic power transmission systems, and more particularly to a hydraulic drive incorporating a variable displacement pump for powering vehicles and the like.
Hydraulic vehicle drives including torque converters and hydraulicly shifted planetary gear trains are well known. Among the limitations of such drives is the requirement for mechanical shaft/housing continuity between an engine or other power source and driven wheels, which necessitates the use of universal joints and differential gearing, etc. Also, the range of torque multiplication is limited, useable ranges generally necessitating complex torque converter configurations and multiple ratio gear shifting systems that are expensive to provide, the efficiency of the combination being compromised by trade-offs relating to the complexity of the torque converter and the number of selectable gear ratios. For example, under a particular operating condition such as ascending a long grade, one selected ratio might provide insufficient drive wheel torque for maintaining a desired speed, whereas the next available ratio would result in undesirably high engine RPM. A further problem is that the braking systems of vehicles having automatic transmissions have greater wear and shorter life than those having manual transmissions that maintain a selected gear ratio during engine braking.
It is also known to use a positive displacement hydraulic pump that is driven, for example, by a battery powered electric motor, the pump being connected by suitable conduits to hydraulic motors that are coupled to wheels of a vehicle, one advantage being elimination of conventional drive shafts, universal joints, and differential gearing that are components of conventional vehicle drives. The use of electric motor power to the exclusion of internal combustion engines in such drives is dictated by the fixed turns ratio that exists between the positive displacement pump and the hydraulic motors. Actually, the use of such drives is substantially limited to special purpose vehicles such a fork-lifts and the like that operate within a very limited speed range, being preferably battery powered and having other justification for hydraulics, such as for the lift mechanism. Variable displacement hydraulic pumps are also known, but a principle disadvantage is that they are awkward to use in that adjusting the displacement is quite difficult, particularly under load.
Thus there is a need for a variable ratio drive system that overcomes the disadvantages of the prior art.
SUMMARY
The present invention meets this need by providing a continuously variable ratio hydraulic drive that us particularly effective in changing drive ratios under fully loaded conditions without requiring a complex actuator control system. In one aspect of the invention, a variable displacement hydraulic machine includes a main hydraulic pump having a rotary shaft input, and a control element being movable in a control path, the main pump having a displacement that is variable in response to positioning of the control element; a hydraulic actuator for moving the control element in the control path in response to fluid pressure; and a secondary pump for feeding the actuator, the secondary pump being rotatably coupled to the shaft input of the main pump for driving the secondary pump simultaneously with the main pump.
The main pump can include a main hydraulic cylinder, a piston sealingly slidable in the cylinder in response to rotation of the shaft input, and inlet and exhaust valves fluid coupled to the cylinder for admitting hydraulic fluid through the inlet valve and delivering the fluid through the exhaust valve under pressure when the piston reciprocates in the cylinder, the control element being coupled between the shaft input and the piston for adjusting an operating stroke of the piston. The inlet and exhaust valves can be one-way check valves. The main pump can further include a rotor member rotatably supported on a main rotor axis, the control element including a journal member movably supported on the rotor member at variable eccentricity relative to the main rotor axis in response to the hydraulic actuator, the stroke of the piston being related to the eccentricity of the journal member.
The journal member can move radially perpendicular to the main rotor axis, a counterweight preferaby being coupled to the journal member for radial movement oppositely to the journal member for balancing the rotor member notwithstanding the radial movement of the journal member. The coupling of the counterweight can utilize a journal rack fixedly supported relative to the journal member and a counterweight rack fixedly supported relative to the counterweight in facing relation to the journal rack, a pinion rotatably supported at a fixed location on the rotor member having geared engagement with the journal and counterweight racks for driving the counterweight oppositely from the movement of the journal member relative to the rotor member. The journal member is movable preferably from a first position being substantially concentric with the main rotor axis to a second position corresponding to a maximum stroke of the piston and a maximum displacement of the main pump, the first position producing substantially zero displacement of the main pump. The hydraulic actuator can include an actuator cylinder fixedly mounted to the main rotor, an actuator piston sealingly slidably engaging the actuator cylinder and being coupled to the journal member for movement thereof between first and second positions thereof. The actuator piston can move the journal member from the first position toward the second position in response to hydraulic pressure, the hydraulic actuator further comprising means for biasing the journal member toward the first position.
The main hydraulic cylinder can be one of a plurality of main hydraulic cylinders having counterparts of the piston and the inlet and exhaust valves, the main hydraulic cylinders being supported in circumferentially spaced relation about the control element, each of the pistons of the main pump being coupled to the control element for reciprocating movement thereby, the main pump having a main outlet in fluid communication with each of the exhaust valves. The control element can include a ring member having variable eccentric movement in response to rotation of the shaft input, each piston of the main pump being coupled to a follower member, each of the main hydraulic cylinders having means for biasing the corresponding piston toward the control element whereby the follower members maintain engagement with the ring member.
The main pump can be a positive displacement pump. The secondary pump can be a positive displacement pump. The secondary pump can include a secondary hydraulic cylinder having a secondary piston sealingly slidably movable therein on a piston axis and mounted for rotation on an axis transversely oriented relative to the piston axis in response to rotation of the shaft input; a track member having a track surface being non-concentric with the transversely oriented axis; a follower element for engaging the track surface and being coupled to the secondary piston for reciprocation thereof within the secondary cylinder during rotation during rotation thereof; and valve means for controllably feeding the hydraulic actuator in response to reciprocation of the secondary piston.
The valve means can include a secondary inlet valve having a first one-way check valve fluid connected between the secondary hydraulic cylinder and a reservoir of hydraulic fluid; an exhaust valve having a one-way check valve fluid connected between the secondary hydraulic cylinder and the hydraulic actuator; and a control member connected for controllably preventing closure of the one-way check valve of the exhaust valve. The secondary inlet valve can further include a control valve fluid connected in series with the first one-way check valve, the control valve being responsive to movement of the control member. The track surface c
Ryznic John E.
Sheldon & Mak
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