Reflections about Camshaft Adjusters

An overview of the patent applications for camshaft adjusters and the number of different systems in production engines clearly illustrates that, in the future, probably all modem spark-ignition engines will use camshaft adjusters.

We know of no series systems of production engines with only one camshaft in which the intake and exhaust cams can rotate in opposite directions. Perhaps it might make sense, however, to offset the entire camshaft via a camshaft adjuster, if only at narrow adjusting angles.

There are many reasons to use timing devices that allow the continuous variable offsetting of the camshaft. It is recommendable to also use these systems for multivalve engines with dual camshafts in which one system is affixed to a camshaft. In particular, the control of the internal exhaust gas recirculation with continuously variable systems can have a positive influence on the direct exhaust emissions.

To implement the functional principle, designers prefer timing devices with swing motors. The primary focus of these elements is on the development and use of light components and weight reduction. The swing motors can be economically and easily controlled by hydraulic direction control valves.

The harmonization of the valves with the timing device is one of the essential engineering tasks during development. Here as well, the aim is to lower costs. In contrast to the other known systems for changing the control times during operation, camshaft adjusters have a simple design and are correspondingly economical. These systems should be integrated in the cylinder head design early in the initial development of a cylinder head. The oil circulation required for regulating the system can then be more easily harmonized with the hydraulic directional control valves.

Because of the potentially attainable improvement, new engines will probably increasingly use continuously variable timing devices. The control of inner exhaust gas recirculation requires cylinder head designs with at least two camshafts. The continuously variable camshaft timing device works similarly in spark-ignition engines with direct injection. In this case as well, the internal exhaust gas recirculation can be controlled by this system. Camshaft adjustment will also be used for this still-new combustion process.

Camshaft adjusters can be combined with variable valve actuation that allows the valve stroke or opening period to be varied. Porsche has used this approach in a series six-cylinder engine. Numerous applications are possible for camshaft adjusters that offer substantial potential optimization of internal combustion engines. Infinitely variable valve actuation systems need to focus on the potential improvement that can be achieved with these measures.