Development of an electromagnetic valve actuation system for high efficiency engines

An actuator which incorporates a permanent magnet into the upper stator has been developed. The permanent magnet excitation offers scope for both enhancing efficiency during normal operation and providing fail-safe behaviour, specifically in terms of its ability to latch the valve into a closed position in the event of a loss of power or a fault in the winding and/or the power electronic converter. A detailed understating of the performance of this type of actuator and the various design trade-offs has been established by means of extensive finite element modelling. An experimental actuator, which embodies these findings, has been manufactured, and its dynamic performance and fail-safe capability has been demonstrated on a test-rig. One important consideration in terms of future exploitation is the different power electronic converter requirements, which may impact on its cost-effectiveness. Although originally conceived to operate in conjunction with a bi-polar current source, useful performance can be achieved with a unipolar source, albeit with some performance compromise. A patent has been granted on this technology and initial investigations suggest that it may be competitive if the market performance requirements begin to exceed the capabilities of more conventional variable reluctance actuators, notably in terms of fail-safe operation.

A sensor has been developed which allows the direct measurement of armature velocity. This offers the possibility of improving the dynamic performance of valve actuation system compared to existing sensors, which measure displacement. This sensor is based on a novel structure in which the armature stem includes a thin walled steel sleeve and the stationary element consists of two axially magnetised ring magnets, a pair of coils wound in series opposition and a simple magnetic circuit manufactured from 3 solid steel parts. This sensor is capable of directly providing an output voltage, which is proportional to velocity and requires neither amplification nor signal processing prior to A/D conversion. Considerable optimisation of this device has been performed during this project to obtain sensor designs, which combine high sensitivity and linearity. A fundamental understanding of the design issues in this type of sensor has been established by means of detailed modelling and experimental investigations. These studies have encompassed the influence of eddy currents, harmonic distortion caused by non- linearities and the various trade-offs between sensor compactness and performance. Two sensors design, which are very similar but with slightly different dimensions have been manufactured. One has undergone extensive bench testing in a dedicated experimental rig to fully validate its performance and the design methodology, while the other has been fully integrated into the bore of the spring in a demonstrator actuator unit for unit level testing. This sensor design has demonstrated considerable promise in terms of its applicability to high performance valve actuation systems, and its relatively simple structure amenable to volume manufacture. A patent has been granted on this technology, and its commercial potential is being benchmarked against competing technologies such as variable reluctance transformers / inductors and Hall effect / permanent magnet based sensors. It is worth noting that although this sensor has been developed within the specific context of valve actuation, it potentially has wider application in systems which require direct and low-cost measurements of velocity in the range 1-10 m. /s and stokes up to a few tens of millimetres.

As the armatures belong to the moving part of the EMVT, like the valves, their weight affects the Eigen frequency of the system, too. The aim is to reduce the overall moving mass as much as possible to achieve a high Eigen frequency. A high Eigen frequency means a short travelling time from the open to close position and vice versa. Such a fast system is necessary for proper operation of the engine at high rpm. The goal for the armatures is to reduce their weight from 0.77 kg down to 0.63 kg. In contrast to the valves a weight reduction by alternative materials is impossible, since only iron nickel and cobalt have the required magnetic properties. Weight reduction has to be achieved by an optimised design. A solid silicon-iron is used as the armature plate to reduce eddy current losses since a lamination seems to be to fragile. A stem of valve steel is attached to the plate by friction welding. This manufacturing process is more cost effective and has a better rigidity than brazing. All necessary processes were developed and are well understood. The transfer of the sample production to mass production is meanwhile only a smaller step as similar technologies are applied for the production of valves.

CETENASA has developed a new concept for the EMV actuation electronics. This new concept results in a mechatronic component for the EMVT, integrating power electronics and first control loop into the actuator. This integration of the electronic and mechanical parts can offer some improvements: - Reduction of volume and wiring over a centralized solution, related to this, its important to note that EMI can also be reduced as we reduce the number of connections delivering high power levels with high current slew rates. - Cost reduction over a centralized solution. As long as the actuator serves as a thermal union between the power electronics and the water-cooling loop of the cylinder head, using a dedicated cooling solution, is not needed. - Improved Dynamics and controllability. The short paths between the power electronics and the actuator could also improve the dynamics of the system and then the controllability. So the mechatronic concepts can give an important value to many actual actuators in the automotive industry. For a confident and reliable introduction new technology and components must be investigated. CETENASA have designed and manufactured a prototype of the power electronics with this guideline. Functional validation have proved good results but deeper investigation should be carried on about decoupling technology witch is responsible for the main limitations of temperature and guarantied full life operation.

Foundation CETENASA has applied in the framework of ELVAS the LCA methodology to compare new electromagnetic valve actuation system vs. traditional camshaft solution. Life Cycle Assessment (LCA) is an objective methodology to evaluate the environmental impact associated with a product, process or activity. LCA studies a product throughout its life cycle (from cradle to grave), from the extraction of raw materials to the production, use and disposal. The main steps carried out in this methodology are: - To identify and quantify the use of materials and energy. - To identify and quantify dumping to the environment. - To determine the impact of the use of resources (materials and energy) on the environment. - To determine the impact of dumping in the environment. - To evaluate and implement strategies of environmental improvement. One of the key aspects for the success in the LCA studies is related to the availability of qualified data for the materials and process involved in the life of a certain product. This point has been one of the major drawbacks for the LCA methodology. We have observed that data related to mechanical products and process are getting an important speed up in terms of quantity and quality, allowing to apply efficiently LCA in this framework. For electronics components and process environmental data quality is still some years behind mechanical data so its still quite difficult to evaluate environmental impact for them. As long as data bases for extensive electronic devices arises LCA will be an important methodology for generating specifications for new components and systems due to the high environmental repercussion of electronics. The experience developed in this project allows Foundation CETENASA evaluate environmental aspects in technical specifications for new products.

The result is a downsized actuator compared to state of the art electromechanical actuator, considered as reference. Iterative simulation work was performed to establish the best compromise for the definition of the spring mass oscillator system. This iterative process starts with valve lightweight design, which is then exploited to reduce spring rate and subsequently to reduce the mass of the actuator contributors to the mobile mass. Following magnetic design, mechanical design was performed, generating the full set of drawings. Corresponding prototype actuators were manufactured both for bench level evaluation and engine level validation. Performance of this actuator were validated by detailed experimental studies with the precise assessment of static force but also dynamic performance including transition time and electrical power consumption. The benefits of this downsized actuator for intake application are the following: compatibility with 34 mm valve pitch engines, 28% volume reduction, 25% mass reduction and up to 40% electrical power consumption reduction for equivalent transition times.

Engine electromagnetic valve actuation is a new technology based on electromagnetic actuators and control electronics instead of pure mechanical valve driving. The general objective of the ELVAS project was to develop an improved electromagnetic valve actuation system with lightweight valves and materials to reduce valve actuation power losses and be in a position to maximise fuel economy. The EU-funded ELVAS project has successfully designed, produced and tested an improved electromagnetic valve actuation system for car engines, delivering optimised fuel efficiency and reducing CO2 emissions. In a working engine, the new system delivers: - CO2 emissions reduced by up to 15 %; - car engine noise reduced by up to 10 dB at 3000 rpm; - fuel consumption reduced by up to 15 %; - materials 100 % recyclable; - weight savings of 25 %, compared with conventional system; - reduced electrical consumption. In addition, ELVAS partners have developed a new set of testing guidelines for valve actuation system components, as well as a number of new manufacturing processes.

A novel E-core actuator design has been developed which potentially offers scope for improving the performance of the valve actuators, specifically in terms of enhancing the force capability at large air gaps. Although being very similar to a standard actuator topology with an E-core stator and a plain rectangular armature, additional components of force are introduced by incorporating pole extensions to regions of the E-core stator and corresponding apertures in the armature. Extensive modelling studies were performed to optimise actuator performance, gain a fundamental understanding of the various design trade-offs and the scope for tailoring the nature of the force-displacement characteristics. An experimental actuator was manufactured and its static performance was assessed on a test-rig. Although this actuator demonstrated useful improvements in force capability at large air gaps, practical problems were encountered with armature rotation and the large consequent torques which are produced. It is recognised that the further exploitation of this technology is contingent on establishing a reliable and cost-effective means of limiting armature rotation to a greater degree than is currently required by actuators with plain armatures. A patent has been granted on this technology, and although the particular embodiment studied in this project is unlikely to be commercially viable as it stands, many of the underlying concepts for enhancing force characteristics by employing pole extensions are likely to be considered in future actuator designs.

To give evidence to the predicted advantages of a consequential lightweight design in an electromagnetic valve train system (EMVT), a demonstration and a standard 4-cylinder inline spark ignition engine has been conducted. The emphasis of the testing was lying on the endurance testing and to a lesser extent on the known advantages of an EMVT system like fuel efficiency or lower pollutant emissions. These points have already been proven in several publications. The engine was installed on a test bench and was equipped with 16 lightweight valves an 8 double actuators. The 4 actuators on the intake side were of the downsized actuator type. The control and power electronics were a commercially available system for EMVT test benches. Since the initially intended lightweight valves from outside the ELVAS project were not available, a coating for the Titanium-Aluminum (TiAl) alloy valves had to be developed within the ELVAS project. After a 200-hour endurance test at 2150 rpm and two load points, the guides and valve seats of the cylinder head as well as the valves and armatures themselves were subjected to an investigation concerning the mechanical wear. Except for the tip ends of valves and armatures, wear was almost not detectable. A solution for the tip end problem is under way. The engine level validation has shown the predicted advantages of a lightweight EMVT design and that a durable implementation of such a system is feasible.

Exploitable results

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