Partial-Stroke Fluidic Pump-Motor With Rolling Cam Followers
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Solution Overview
Problem
Existing piston pump-motors suffer from high mechanical inefficiencies due to frictional losses and side loading on pistons, which reduce their performance and service life.
Innovation Solution
The introduction of rolling cam followers between the cam and piston in a piston pump-motor architecture, eliminating sliding contact and reducing transverse frictional forces, combined with a hydraulic valving system for variable displacement, maintains high mechanical efficiency and extends service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sliding contact is used between cam and piston, then the structure is simple, but frictional losses are high
Solution Approach 1:
A cam follower is introduced as an intermediary component between the cam and piston. The cam follower contacts the cam surface and transmits motion to the piston through rolling contact, eliminating direct sliding contact between cam and piston. This intermediary element converts sliding friction into rolling friction, significantly reducing energy losses while maintaining the compact cam-driven structure.
Solution Approach 2:
The sliding mechanical contact between cam and piston is replaced with a rolling contact mechanism. The cam follower incorporates rolling elements that rotate as they contact the cam surface, substituting the sliding friction mechanism with a rolling friction mechanism. This mechanical substitution dramatically reduces frictional losses and improves mechanical efficiency.
2Ease of manufacture
If sliding contact is used between cam and piston, then manufacturing is easier, but side loading on pistons increases
Solution Approach 1:
The cam follower acts as a mediator that changes the direction and nature of force transmission. Instead of the cam directly pushing the piston with significant transverse side loads, the cam follower converts the cam's rotational motion into linear piston motion through rolling contact, greatly reducing side loading forces on the piston while maintaining manufacturing simplicity.
Solution Approach 2:
The cam follower incorporates curved or spherical rolling surfaces that contact the cam. This curvature allows the follower to roll smoothly along the cam profile, converting transverse forces into rotational motion of the follower itself. The spherical or curved contact surfaces naturally redirect forces, minimizing side loading on the piston while keeping the mechanism manufacturable.
3Loss of energy
If rolling cam followers are introduced, then mechanical efficiency increases, but device complexity increases
Solution Approach 1:
The cam follower, while adding a component, serves as a highly efficient intermediary that enables rolling contact. The follower's simple cup-shaped or block structure with internal rolling elements adds minimal complexity while delivering substantial mechanical efficiency improvements by eliminating sliding friction between cam and piston.
Solution Approach 2:
The cam follower performs multiple functions simultaneously: it converts rotational cam motion to linear piston motion, provides rolling contact to reduce friction, supports the piston load, and maintains proper timing through its geometric relationship with the cam. This multi-functionality justifies the added component by consolidating several critical functions into a single element.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly reduces frictional losses and side loading, enhancing mechanical efficiency and extending the service life of the pump-motor by nearly eliminating transverse forces and maintaining ideal fluid pressure timing across varying operating conditions.
Implementation Method 1
Two cam followers are attached to an end of the piston located between the flat face of the cam and the cylinder. The cam followers include rolling elements in contact with the flat face of the cam.
Implementation Method 2
A biasing element presses the cam followers against the flat surface.
Implementation Method 3
The pilot pressure supply has a pressure greater than the low pressure. A change from low pressure to pilot pressure or vice versa to the latch supply line maintains a bypass state of the latching check valve.
Data Source
AI summary
A partial stroke pump or motor includes a piston coupled to a rotating shaft to evacuate a fluid within a cylinder during an upstroke. A latching check valve includes an actuator piston that is displaceable within a center cavity to bypass a blocking member in a bypass state. The actuator piston is driven by a latch supply line. A spool of a rotary valve selectively couples one of the low and pilot pressure supplies to the latch supply line over different timing angle ranges of the rotating shaft. Coupling of the pilot pressure to the latch supply line causes the bypass state. When operating as a pump, the bypass state causes the pressure in the cylinder to fall below the high pressure during part of the upstroke. When operating as a motor, the bypass state allows the fluid to be evacuated from the cylinder during the upstroke.