Intelligent Valve Actuation

A valve control system that operates in real time, adjusting individual valves according to the demands of each cylinder and power stroke seems like a dream come true for engine designers. 

It’s a step change in engine design and development that is probably even more important in the long run than the switch from points ignition to engine management systems or the move from carburettors to fuel injection. Such a significant move forward says Roger Stone, Camcon Automotive’s technical director unlocks an Aladdin’s cave of possibilities. Here he discusses some of them in an article originally published in Automotive Design magazine.

HCCI and 2 Stroke Operation

Equally applicable to petrol and diesel Stone believes that IVA could, amongst other things, unlock the difficulties that Homogenous Charge Compression Ignition (HCCI) is currently presenting to manufacturers, like Mercedes-Benz, trying to develop it: “Potentially it’s an enabler for HCCI, for example, at lower speeds, we are fast enough to get more than one valve cycle in during a 720° period so we could have the normal exhaust event followed by an additional, much smaller, event during the induction stroke to induce the volume of exhaust radicals required.” Whilst he is equally convinced that because the link between the valves and the crank is broken it would be possible to open the valves every stroke below 3000rpm to run the engine as a two-stroke for short periods of time, “Even the ability to run for short periods as a two-stroke is thrown in for free, although you get the breathing compromises that are inherent in a two-stroke.”

Miller cycle and optimisation

He talks enthusiastically about the ability to run Miller Cycle where the intake valve is left open longer than it would be in an Otto cycle engine, and sophisticated cylinder deactivation on demand which he dubs ‘roaming’ cylinder deactivation; “It varies with the engine configuration, but you can avoid individual cylinders cooling down and giving you a hydrocarbon spike when you restart, by running all cylinders but skipping cycles depending on power and torque demands.” Imagine, also, the potential of linking the Valve Control Unit (VCU) into a topographical navigation system so the power and torque demands to maintain a given vehicle speed can be predicted and precisely tailored for the local terrain and traffic conditions, to the extent that cylinders would be deactivated on a real time basis.

Fuel savings up to 15% in the real world

But one of the obvious and immediate fuel saving benefits – 3.5 to 6% for this feature alone according to Stone – would be the elimination of the throttle and its associated pumping losses. “The other great thing is that whatever the engine load speed condition is you don’t have a significant number of timing and lift events based on a compromise; you have the valve timing, period and lift optimised for each particular event. Our research suggests this will result in an overall FE improvement of more than 15% - both on the statutory cycle and in a real world driving environment.”“In the 70s, before cam phasers started to become more common, the valve timing you had at idle was the same as at maximum revs, whereas at idle you want almost no overlap and at full engine speed you might want 50, 60, 70 degrees of overlap. We can do that and, of course, at idle if only 0.2mm of inlet lift is needed we can deliver that too.”

Innovative actuators drive design

The key enabler to Camcon’s IVA is a development of its proprietary Binary Actuation Technology (BAT) invented in the late 90s by Wladyslaw Wygnanski as Stone explains: “Although the IVA employs a Desmodromic valve system, that in itself wasn’t the starting point although the fact that it employs a positive opening and closing mechanism lends itself to our application by maximising control system authority. It also helps minimise the actuator size and power demand . “The starting point for us was the Camcon bi-stable actuator, a very low energy and fast actuator. Unlike a solenoid, it has two zero-power stable states whereas a conventional solenoid has only one, requiring power all the time and an extra latching mechanism at the extreme of movement. The Camcon Binary system is fired from one end to the other with no separate latching and no power except during the switching operation.” This feature, says Stone, makes it equally applicable to park brake systems, thereby eliminating a potential noise path into the cabin via any cabling. Adding, “The inspirational leap was ‘Could we make this architecture multi-stable by rolling it into a multi-pole rather than two pole device with a rotating permanent magnet arrangement, to drive a poppet valve?

Camcon's 1st generation IVA mechanism (shown ) was designed for a single cylinder. This has been replaced with a 3rd generation, fully integrated 4 cylinder module with bespoke electronics and control

The key enabler to Camcon’s IVA is a development of its proprietary Binary Actuation Technology (BAT) invented in the late 90s by Wladyslaw Wygnanski as Stone explains: “Although the IVA employs a Desmodromic valve system, that in itself wasn’t the starting point although the fact that it employs a positive opening and closing mechanism lends itself to our application by maximising control system authority. It also helps minimise the actuator size and power demand . “The starting point for us was the Camcon bi-stable actuator, a very low energy and fast actuator. Unlike a solenoid, it has two zero-power stable states whereas a conventional solenoid has only one, requiring power all the time and an extra latching mechanism at the extreme of movement. The Camcon Binary system is fired from one end to the other with no separate latching and no power except during the switching operation.” This feature, says Stone, makes it equally applicable to park brake systems, thereby eliminating a potential noise path into the cabin via any cabling. Adding, “The inspirational leap was ‘Could we make this architecture multi-stable by rolling it into a multi-pole rather than two pole device with a rotating permanent magnet arrangement, to drive a poppet valve?

Cost

Cost, as ever, is an issue and as in so many instances is dependent on numbers being manufactured. However, Stone is confident that the IVA will come in at “around the marginal cost of a diesel injection system compared with one for gasoline” of which the VCU represents “a big chunk.” What this means to the OEM, says Stone is that they can mix’n match the valve train according to an engines’ individual requirements: “You could have one per valve or just run IVA on the inlets only with a conventional exhaust camshaft. Alternatively you could use a tandem arrangement so there’s one IVA actuator shared between a pair of inlet valves. Or, maybe go the whole hog on the inlets with individual valve actuation and use a tandem arrangement on the exhausts. If you have independent control on every valve you have more capability than if you compromise. for a four cylinder engine

Flexible system architecture

Further savings can be made depending on the engine’s architecture, claims Stone: “It’s a new head, obviously. In terms of the bottom end it’s delete really as we don’t need the timing drive any more unless you retain the conventional exhaust cam drive , in which case it’s even simpler–but you lose the potential engine length advantage. It depends on the individual design of the engine, for example, if the water pump is driven by the timing chain it’s a bit more complicated than just deleting the timing drive, but it should not be too difficult to engineer IVA onto an existing engine or even run it as a derivative alongside other more conventional variations of the same engine family..” The beauty of the system is that the OEM can tune the system to meet their own specific balance between bmep, emissions and fuel consumption at every engine speed:load condition and there is also potential to minimise knock by better control of residuals and of the effective compression ratio.. To achieve this, says Stone, the VCU has to be significantly faster than any other controller currently in use on an engine: “It’s extremely important to get the controlling algorithms right. The system power consumption depends on the quality of that algorithm, and that’s an area we’re particularly active in at the moment. By automotive standards the VCU needs to be significantly faster than an ignition or fuelling ECU because we’ve got to be looking at where valve position maybe 100, times per event, whereas a fuel/ignition ECU only has to do its sums once every other revolution for each cylinder. We’ve got a lot of computing to do; we’re talking about a 100 microsecond computing cycle.”

Way forward

Now working towards their third generation of development rig, Camcon is seriously courting interest from the industry, “We do engagement with OEMs, because we need a very serious level of interest from an engine producer in order to encourage a tier one that there will be a market for it . Ultimately any OEM will be looking for a tier one to take on the industrialisation.. “It would be nice to think that we could move it forward quickly enough to be in service, with some reasonable experience, before the 2020 regulations come in, maybe 2018. It all depends on what goes on from here.”