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Research Papers

Mechanical Spring Replacement With Pneumatic Return Device in a Valve Train: Effects on Dynamics and Preload Tuning

[+] Author and Article Information
Pastorelli Stefano1

Department of Mechanics, Politecnico di Torino, C.so Duca degli Abruzzi, 24, 10129 Torino, Italystefano.pastorelli@polito.it

Almondo Andrea, Sorli Massimo

Department of Mechanics, Politecnico di Torino, C.so Duca degli Abruzzi, 24, 10129 Torino, Italy

1

Corresponding author.

J. Mech. Des 132(1), 011008 (Dec 30, 2009) (9 pages) doi:10.1115/1.4000640 History: Received November 19, 2008; Revised October 20, 2009; Published December 30, 2009; Online December 30, 2009

The paper presents a comparison of performance for a cam transmission of an engine valve train operating with a mechanical spring and with a return spring device that uses a pneumatic spring. Dynamic analysis of the cam mechanism is performed in the frequency and time domains employing a combined lumped-distributed parameter model capable of predicting the effects of the higher harmonics of the cam lift profile on system performance, in particular of the return spring device. Dynamic stiffness of the transmission in the frequency domain and time history of the contact force between cam and follower are evaluated. The limits of the traditional mechanical spring-closing system at high-speed camshaft operations are investigated, highlighting that they are mainly imposed by the internal resonances of the spring. The pneumatic spring is an improved replacement of the steel spring because of better dynamic behavior. Furthermore, the pneumatic return device allows preload tuning of the spring, which may increase transmission efficiency through proper control of the fluid pressure. Study of the pressure control circuit is also presented.

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Figures

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Figure 1

Cam-follower system (a) and follower equilibrium (b)

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Figure 2

Mechanical (a) and pneumatic (b) spring

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Figure 3

Cam lift profile (a) and its spectrum (b)

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Figure 4

Dynamic stiffness of the system with mechanical and pneumatic spring (a) and Campbell diagram (b)

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Figure 5

Pneumatic spring with pressure control circuit

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Figure 6

Influence of the orifice on the dynamic stiffness (a) and on the controllability (b)

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Figure 7

Nonlinear model of the cam-follower system with mechanical or pneumatic spring

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Figure 8

Exact dynamic stiffness of the mechanical spring and its rational approximation

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Figure 9

Follower displacement and contact forces for different rotating frequencies

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Figure 10

Required preloads for mechanical and pneumatic springs

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Figure 11

Performance of the pneumatic system with variable speed

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