Electronic valve control project

[jharvey]

wikipedia has a lot of stuff. Check out this

http://en.wikipedia.org/wiki/Variable_valve_timing

[GrowlingandBiffo]

http://www.camcontec.com/about_the_technology.htm



While the basic devices could undoubtedly move engine poppet valves very quickly, they could not do so very quietly. Engine manufacturers have been looking for years for an electric valve actuator technology that would combine low cost, fast response, small size, and variable movement with low seat landing speed. This has to be no more than 240mm/s, equivalent to 0.01mm/cam deg in a conventional valve train at an engine speed up to 8000 rpm. Other requirements include: a 50,000 mile reliability and the ability to move a 36g, 29mm diameter valve against 6 bar cylinder pressure over 1 to 10mm with a 2.5ms reaction time. Operating temperatures are -40 to +150 deg C while valve head temperature may be up to 700 deg C. A normal 12V power supply is preferred.

The resulting design has a four-pole permanent magnet rotor and eight coil windings arranged as four opposed pairs. It thus resembles a conventional stepper motor, but being based on Camcon's bistable technology, the device only requires input energy to change its position. This is in contrast to a conventional stepper motor, which exerts either no or only a very small position holding force when not energised.

A unique feature is the use of two camshafts. One, interacting with a leaf spring is used to effect the energy recycling. The other, which is of very different shape, moves the valve and is described as being 'desmodromic', in that it opens and closes the valve rather than the more usual practice of opening the valve against coil spring pressure which is then relied on to close the valve. The new device achieves two dynamically stable conditions. One, when the valve is closed, is based on mechanical equilibrium. The other, then when the valve is fully or partially open occurs when the permanent magnets in the rotor provide locking torque equal to the spring force. Only a very small electric pulse is needed to disturb the equilibrium.

Each actuator has its own positional sensor in the form of a reluctor ring on the rotor read by a Hall effect sensor, which inputs to the control system. One full rotation results in the valve opening and closing with a maximum lift of 10mm. Smaller valve openings are achieved by oscillatory movements. The actuator has a maximum speed of response of 7ms for a complete valve event. At 7000 rpm, this equates to a valve open period of 296 deg crank angle, whereas at 1000 rpm, 7ms equates to a valve open period of 42 deg crank angle. Where longer valve opening times are required, the rotor is dwelled for the necessary times.

The magnitude of the current pulses required to initiate and slow the motor have been reduced from those initially encountered during the development process by improved software and PWM (Pulse Width Modulated) control. The actuator has the capability for valve opening within 3.5ms, but this is not required under all operating conditions. Therefore, in the interests of energy management, it is favourable to slow the valve opening and closing time rather than having a fast opening event followed by a dwell period and a fast closing event.

When a braking pulse is used, the actuator effectively becomes a generator. This energy can then be fed back into the vehicle electrical system. The work done during one complete actuator cycle is 1.5J. A four cylinder valve train using 16 actuators operating at 67Hz (8040 rpm) would require 1.6kW of electrical power. This compares favourably with a direct operating mechanical valve train, which typically consumes 3kW.

The development work was conducted in conjunction with Powertrain Ltd, who prior to the demise of the MG Rover Group, successfully packaged it into a 'K' series engine with valve centres of 35mm and cylinder bore centres of 88mm. Under the intellectual property agreement, all IP has since reverted to Camcon which is thus now in a position to offer it to MG Rover's successors or other companies.

The mechanism design was undertaken using SolidWorks.

The original jet engine noise suppression project is still continuing in co-operation with Rolls Royce and leading laboratories with support from the DTI.

Other valve developments include a design to admit air to the top of helicopter blades to increase lift during the backwards part of their rotation and special purpose valves for the oil and gas industry. One of these is a Camcon "Roller" valve with key ring springs to apply sufficient force to allow the crushing of debris when the valve operates. Crushing/sealing force is 500N and magnetic locking force is 25N. Working pressure is 60bar and orifice size is 6mm. The specification requires reliable operation over 1 million cycles.

[Wiglaf]

http://en.wikipedia.org/wiki/Tucker_Torpedo
neat story

http://www.autoweek.com/apps/pbcs.dll/a ... feed=rss01
company Valeo is in this pretty far, possibly releasing engines for their french cars this year.

[Fred]

It's a good looking car except from the front isn't it.

Valeo seem to have it licked don't they!

SOHC can finally Rock again ;-)

Fred.

[shameem]

Electric cam phasing seems to be a hot research topic right now - maybe it is the next big step towards independent electric actuators.....

http://www.greencarcongress.com/2007/04 ... _grou.html
http://www.wipo.int/pctdb/en/wo.jsp?wo=2005095765
http://www.denso-europe.com/Electric-Va ... 00001.aspx