Fuel Pump Return Spring Variable Stroke Mechanism
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Solution Overview
Problem
Existing fuel pump assemblies face challenges in maintaining contact between the plunger and the drive arrangement at high camshaft speeds, leading to increased stress on the return spring and reduced fatigue life.
Innovation Solution
A fuel pump assembly with a spring assembly that includes a return spring with a variable stroke length, achieved through a damper arrangement that dampens the movement of one end of the return spring relative to the other, allowing the spring to provide a variable return force dependent on engine speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the return spring is designed for the highest camshaft speeds to maintain contact force, then the contact force between plunger and drive arrangement is sufficient at high speeds, but the spring encounters unnecessarily high stress range at lower speeds reducing fatigue life
Solution Approach 1:
The patent applies the dynamics principle by making the return spring's stroke length variable rather than fixed. The spring stroke is dynamically adjusted based on camshaft speed through a speed-sensitive mechanism that allows the spring to operate with optimal stroke at different speeds, preventing excessive stress at low speeds while maintaining sufficient force at high speeds.
Solution Approach 2:
The patent changes the parameter of spring stroke length from a constant value to a variable value that depends on operating conditions. By varying the stroke length parameter according to camshaft speed, the system optimizes the spring's stress range and fatigue life while maintaining adequate return force when needed.
2Device complexity
If the return spring is designed with fixed stroke length, then the structure is simple, but the spring cannot adapt to varying engine speeds and operates with excessive stress at lower speeds
Solution Approach 1:
The patent transforms the static spring assembly into a dynamic system where the stroke length can vary. This is achieved through a mechanism that responds to camshaft speed, allowing the spring to adapt its operational parameters without requiring a completely complex assembly structure.
Solution Approach 2:
The patent introduces an intermediary mechanism that mediates between the fixed spring and the variable speed conditions. This intermediary component allows the spring to achieve variable effective stroke length through a relatively simple additional mechanism rather than redesigning the entire spring assembly.
3Force
If the return spring provides high return force at all speeds, then contact is maintained at high speeds, but unnecessary stress is applied at lower speeds
Solution Approach 1:
The patent changes the operational parameters of the spring by varying its stroke length according to camshaft speed. This parameter variation allows the spring to provide high force only when necessary at high speeds, while operating with reduced stress at lower speeds, optimizing both performance and durability.
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 variable stroke length of the return spring reduces unnecessary stress and improves fatigue life by providing a high return force only at high engine speeds, while maintaining contact between the plunger and the drive arrangement at lower speeds.
Implementation Method 1
a spring assembly including a return spring configured to apply a return force to the plunger to effect the return stroke
Implementation Method 2
a damper arrangement which acts on the second spring member to determine the damped speed of movement, with the extent of damping depending on the speed of rotation of the drive shaft
Data Source
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AI summary
A fuel pump assembly (110) for an internal combustion engine comprises a plunger (114) arranged to reciprocate within a plunger bore (132) under the influence of a drive arrangement (123) driven by means of a drive shaft (18), to perform a pumping cycle comprising a pumping stroke and a return stroke, the pumping stroke comprising movement of the plunger (114) from a bottom dead centre (BDC) position to a top dead centre (TDC) position to pressurise fuel within a pump chamber (36), and the return stroke comprising movement of the plunger (114) from the TDC position to the BDC position. The fuel pump assembly comprises a spring assembly including a return spring (154) configured to apply a return force to the plunger (114) to effect the return stroke, wherein the return spring (154) is cooperable, at a first end (62), with a first member (150) coupled to the plunger (114) and movable at a first speed dependent on the speed of rotation of the drive shaft (18) and, at a second end (64), with a second member (70) which is movable at a damped speed relative to the first speed so that the return spring has a variable stroke length depending on the speed of rotation of the drive shaft (18).