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Proportional valves key to BMW's hydrogen car

Edited by the Engineeringtalk editorial team Jun 28, 2001

BMW's 750hL, the first series-built hydrogen car in the world, has the control valves required to regulate the inlet pressure of the hydrogen injection valves supplied by Asco Joucomatic

The "clean-age" of the car came a step nearer in Berlin recently, when BMW unveiled the 750hL, the first series-built hydrogen car in the world.

The luxury limousines were rolled-out during EXPO 2000 to be used as shuttles during the exhibition.

The objective of the launch was to demonstrate to passengers that hydrogen powered cars could meet the most stringent requirements of comfort, dynamics and suitability for workaday use.

To account for the size and weight of the limousines they are fitted with twelve cylinder 150kW/204hp engines.

These are required to accelerate the vehicles to 100kmph in 9.6 seconds from a standing start, and to do it in such a way that their dynamic behaviour cannot be told apart from the equivalent petrol driven engine.

Satisfying these twin requirements is a demanding task.

Its success depends upon the performance of the control valves that are required to regulate the inlet pressure of the hydrogen injection valves.

This highly dynamic and precise operation is being performed by Asco Joucomatic's unique Sentronic proportional valves.

The Sentronic is well established for use with high performance pneumatic systems.

However, for hydrogen a modified version was produced.

In laboratory tests and under actual road test conditions the proportional valve demonstrated it could meet the BMW engineers' ambitious design requirements in every respect.

Sentronic is able to provide the dynamic performance required for the hydrogen inlet system because it is a direct acting, single-stage valve, which benefits from matched inlet and exhaust ports.

The latter feature ensures rapid response rates, with minimum hysteresis when both increasing or decreasing pressure/flow.

In addition, internal sealing between the valve servo chambers by a metal bellows (which doubles as a spring) avoids any elastomeric seal stiction, and this guarantees smooth, linear operation without any of the stepping problems experienced on other designs of proportional valves.

A further key feature of the Sentronic design is the balancing of all its internal components.

This ensures that the valve is not subject to internal forces and can control pressures across a wide range - up to 20 bar.

Sentronic can also accommodate large orifice sizes (20mm) - a feature that provides for excellent flow characteristics while, at the same time, allowing the valve to retain its direct method of operation.

The development of the modified Sentronic, including testing and production of subassemblies for Expo, took only four months.

This was made possible by Asco Joucomatic's extensive know-how of handling media such as hydrogen and the control engineering expertise, which the company has accumulated from numerous other Sentronic applications.

The Sentronic package supplied by Asco Joucomatic also included all the control electronics and a cut-off valve.

The control electronics are supplied direct from the 12 VDC power supply and regulate the proportional valve in accordance with a pre-set value and also the level of the engine rpm.

Sentronic is a direct-acting, self-contained device, which in its most compact form integrates a proportional solenoid valve, a control card, and a piezo-electric pressure sensor - the latter for closed loop control.

It is designed to control pressure, flow, force, temperature and angular and linear movement.