Single Piston Pump Tappet Piloting Reduces Side Loads
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Solution Overview
Problem
Single piston, cam driven high pressure pumps experience pump piston seizures due to fluid film breakdown caused by side loads resulting from spring out-of-squareness, particularly in regions with poor fuel quality.
Innovation Solution
The piston return spring is piloted by the tappet, allowing the tappet to bear the spring side load by creating a radial clearance between the piston and spring seat greater than between the spring seat and tappet, thereby eliminating side loading on the piston.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If the spring is constrained by both spring seats to radially align the spring, then the spring can be positioned correctly, but significant side load is imparted to the pump piston
Solution Approach 1:
The tappet serves as an intermediary element that pilots the spring seat, allowing the spring to be properly aligned while bearing the side load instead of the piston. The tappet's radial clearance with the spring seat is controlled to be less than the piston's radial clearance, creating a hierarchical clearance system that directs side loads to the tappet.
Solution Approach 2:
The invention changes the clearance parameters between components. Specifically, the radial clearance between the tappet and spring seat is made smaller than the radial clearance between the piston and spring seat. This parameter change ensures that the tappet, not the piston, bears the spring side load while maintaining proper spring alignment.
2Shape
If the piston is closely attached to the spring seat, then spring alignment is maintained, but side loads are transferred to the piston causing seizures
Solution Approach 1:
The tappet acts as an intermediary that absorbs the spring side loads through controlled radial clearance. By positioning the tappet between the spring seat and piston with appropriate clearance relationships, the system maintains spring alignment while protecting the piston from damaging side loads that would cause seizures.
Solution Approach 2:
The harmful side load effect is extracted from the piston-spring seat interface and relocated to the tappet-spring seat interface. The tappet assumes the role of bearing side loads, while the piston is extracted from this harmful interaction through larger radial clearance.
3Shape
If radial clearance between piston and spring seat is reduced, then spring alignment improves, but side loads increase on the piston
Solution Approach 1:
The invention inverts the conventional approach by increasing the piston-spring seat radial clearance while decreasing the tappet-spring seat radial clearance. This reversed parameter relationship ensures that spring alignment is achieved through the tappet's tighter fit, not the piston's fit, thereby maintaining alignment while reducing piston side loads.
Solution Approach 2:
Instead of making the piston the primary alignment element with small clearance, the invention inverts the approach by making the tappet the primary alignment element with small clearance, and the piston with large clearance. This inversion transfers the alignment function and side load bearing to the tappet.
Data Source
AI summary
In a tappet-driven single piston pump, piston side loads caused by return spring out-of-squareness are eliminated by effectively piloting the piston return spring, preferably the associated spring seat, by the tappet, thereby allowing the tappet to bear the spring side load. The piston engages and is returned by the spring seat, but radial clearance between the piston and spring seat is greater than radial clearance between the spring seat and tappet, thus eliminating side loading imparted to the piston. The spring seat can be considered a piston retainer, in which the piston is not closely attached to the retainer but instead exhibits a predefined radial clearance greater than the piloting clearance between the retainer and the tappet.