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Rudolf Seethaler and his team at the University of British Columbia have demonstrated that internal combustion engines can be built to be more efficient while cutting their harmful emissions.
The team’s concept is an innovative cogging-torque-assisted motor drive (CTAMD), which would replace conventional camshaft valvetrains with electromechanical valvetrains (EVA).
An EVA is a system for opening and closing valves that combines electrical and mechanical processes as opposed to a conventional fixed camshaft engine.
During analytic simulation carried out in a lab at the university’s Okanagan campus, the team determined that the CTAMD could change the way internal combustion engines are manufactured, making them cheaper and more efficient.
The basic structure of how gas exchange valves are controlled in petrol engines has changed relatively little over the past century. Typically, mechanical cam systems are used because they are accurate, fast and reliable.
However, cams can display limitations.
For example, when less than full engine power is required, a throttle is used
in the air intake system that chokes the air flow entering the combustion chamber. Considering that most vehicles require large amounts of engine power only during acceleration, fuel economy could be improved by 10-15% if the throttle were removed.
Carmakers use mechanical or hydraulic systems to reduce throttle losses and provide cylinder deactivation. Examples are BMW’s Valvetronic and Fiat’s Multiair systems. But such systems are not perfect. Cylinder deactivation using conventional cam systems results in cooling down of the deactivated cylinders. This process increases emissions when cylinders are switched on again.
Another combustion strategy, homogeneous charge compression ignition, requires that the valve timing be drastically changed during engine operation. This is not possible with conventional cam-based valvetrains.
For the CTAMD, when the throttle in the air intake system is removed, the engine valves need to take over the function of the throttle. This process requires the valves to open for shorter periods of time during low engine load and to open for longer at high engine loads. The idea is to control this valve motion with an electromagnetic actuation system. Unfortunately, achieving the required valve accelerations with conventional electric actuators is difficult, since engine valves require more than 10 times the acceleration that conventional electric motors can provide. The CTAMD system gets around this problem by using cogging torque as a magnetic spring to assist the acceleration and deceleration of the valves.
Cogging torque is generated when a permanent magnet in the electric motor gets attracted to one of the stator teeth. This phenomenon occurs in all electric motors with permanent magnets, but is usually not desired, since it leads to non-uniform motor speed. Therefore, conventional electric motors are designed to minimise cogging torque.
However, for the team’s application, graduate student Brad Reinholz designed the motor to maximise cogging torque, to help accelerate and decelerate the valve during opening and closing.
Seethaler’s previous role was working on electronic valve actuation technologies at BMW, where his team generated a lot of knowledge and patented several valve actuation technologies. These never made it to market as they were expensive and had reliability problems. But he believes the CTAMD overcomes these problems, because it is easy to manufacture, cost-effective, energy-efficient and robust.
He has been discussing tests of the technology with one of Canada’s leading automotive development companies. He hopes it will find its way into mainstream automotive engines, where it can provide the emission reductions needed to mitigate pollution until more viable energy storage technologies other than fossil fuels can be found to power transport needs.