While variable valve timing has been a hot topic over the last few weeks with the introduction of the updated GSX-R1000 featuring Suzuki's innovative mechanical VVT system, many companies are working toward the next step in this area: eliminating camshafts completely and controlling the valves directly using electromagnetic actuators. There are many stumbling blocks to electromagnetic valve actuation (EVA), but a research group in the Control and Automation Laboratory of the University of British Columbia has created a new type of actuator that may make EVA a very realistic option in the not-too-distant future.
There are many advantages to using a "camless" design with EVA as this gives complete freedom and control of valve lift and timing. Increased power and fuel economy along with reduced emissions are the main benefits, and many parts are eliminated - no camshaft or cam drive system, and no throttle butterfly as the intake can be controlled solely using the intake valve. While several versions of EVA have been shown in various prototype stages, there are several obstacles to its use in a production car or motorcycle just yet. Those obstacles include electrical power consumption, precise control at higher engine rpm, reliability and cost.
The system being developed at UBC is unique in that it addresses many of the drawbacks of traditional EVA used in an automotive application. Detailed in a paper submitted by engineering student Bradley Reinholz under the supervision of associate professor Rudolf Seethaler, the actuator utilizes a "cogging-torque-assisted motor drive" to control each valve. Cogging torque refers to the design of an electric motor that results in an interaction between the rotor and stator when there is no current applied - like how the motor in a radio-controlled car feels notchy when you turn the wheels.
Typically cogging torque is undesirable as it makes the motor less smooth at low speeds, but in this application it is put to use for energy recovery as the valve closes; traditional EVA systems retain mechanical springs for this purpose, but the UBC design eliminates the springs and improves efficiency even further over a typical EVA setup. According to the paper, the design potentially reduces losses by more than 40 percent compared with other electromechanical valve actuators, and more than 70 percent compared to a conventional camshaft drive. Other advantages of the system outlined in the paper are a compact size comparable to current mechanical camshaft operation, minimal impact on a vehicle's electrical system to power the actuators, and very little heat produced.
In the video shown here, Seethaler notes that electromagnetic systems are steadily replacing mechanical/hydraulic systems in automobile use, pointing to the use of electric-assist power steering in some vehicles as an example. Braking systems are likely next, with valve control also in the future. Seethaler's research additionally includes replacing traditional fuel injectors with a similar actuator, an application that requires smaller motions than for valve control but even higher speeds.
The cogging-torque-assisted motor drive valve control system is unique compared to other electromagnetic systems in that it is cost effective and reliable, overcoming two of the major hurdles to its use in a production setting. The cogging-motor EVA is in the simulation phase for now, and in that setting has shown improvements in efficiency and emissions. The next step is to properly test the system and present it to engine manufacturers for their consideration.
Read the paper "A Cogging-Torque-Assisted Motor Drive for Internal Combustion Engine Valves" here: https://open.library.ubc.ca/cIRcle/collections/ubctheses/24/items/1.0228784