The design of valve spring is a complicated system design subject. Good spring design can minimize friction and wear of valve train. This paper summarizes an analytical method for valve spring design based on the construction parameter sensitivity design diagram as follows.

(1) The first step is to determine the design objective of the valve train's flying-off speed by analyzing the vehicle's downhill driving performance and engine braking, so as to determine the required valve spring pre-tightening force and spring stiffness.

(2) In the second step, the dynamic model of valve train is established in order to accurately predict the flight-off and evaluate the effect of in-cylinder re-compression pressure on the flight-off.

(3) In the third step, the parameters of the valve train dynamics are constructed by sweeping the values of spring preload and spring stiffness to check their influence on the vibration of the valve train. In order to show the design margin of flight, the curve of push rod force, acceleration of valve train and spring deceleration relative to crankshaft rotation angle should be drawn in the graph, so that the target values of spring preload and spring stiffness can be selected conveniently and wisely in step 4.

(4) Step 4 calculates the required spring preload based on static force balance of the exhaust valve head to prevent the valve from jumping. For engines with and without exhaust brakes, the pre-tightening force of exhaust valve spring is selected, and the matching spring stiffness is selected by using the design parameter diagram in step 3.

(5) Step 5 calculates the parameter sweep value of design parameters, and constructs the parameter sensitivity design diagram for spring design by using graphical design method. The average diameter of spring, the diameter of coil wire and the number of coils are selected, and the design constraints such as torsional stress, natural frequency and coil clearance are satisfied, or it can be solved directly by analytical optimization method.

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