Design Methodology of Camshaft Driven Charge Valves for Pneumatic Engine Starts

Michael M Moser,Christopher H Onder,Christoph Voser,Lino Guzzella

doi:10.2516/ogst/2013207

Abstract

Idling losses constitute a significant amount of the fuel consumption of internal combustion engines. Therefore, shutting down the engine during idling phases can improve its overall efficiency. For driver acceptance a fast restart of the engine must be guaranteed. A fast engine start can be performed using a powerful electric starter and an appropriate battery which are found in hybrid electric vehicles, for example. However, these devices involve additional cost and weight. An alternative method is to use a tank with pressurized air that can be injected directly into the cylinders to start the engine pneumatically. In this paper, pneumatic engine starts using camshaft driven charge valves are discussed. A general methodology for an air-optimal charge valve design is presented which can deal with various requirements. The proposed design methodology is based on a process model representing pneumatic engine operation. A design example for a two-cylinder engine is shown, and the resulting optimized pneumatic start is experimentally verified on a test bench engine. The engine’s idling speed of 1200 rpm can be reached within 350 ms for an initial pressure in the air tank of 10 bar. A detailed system analysis highlights the characteristics of the optimal design found.

Highlights

Air pressure tankAn inherent property of Internal Combustion Engines (ICE) is their limited operability below a minimum rotational speed
In contrast to [9], this paper focuses on camshaft driven Charge Valve (CV)
The bold 350 ms line indicates the boundary of the feasible set in the pt-dCV subspace

Summary

Introduction

An inherent property of Internal Combustion Engines (ICE) is their limited operability below a minimum rotational speed. Starting an engine involves accelerating it up to a specific minimal speed of operation. Due to its inertia and the low starter power, a conventional start of an ICE takes up to 1 second. An engine shutdown during idling phases implying such long start times is not accepted by the driver. Conventional ICE are typically not shut down during idling phases. During the New European Driving Cycle (NEDC), they amount to 4-8% depending on the engine type and size as shown in [1,2,3,4]. In order to exploit this fuel saving potential by eliminating the idling phases while still satisfying driver demands, the duration of an engine start needs to be reduced

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Conclusion