Valve events are one of the few remaining major constraints on internal-combustion engine optimization. Eliminating those constraints is the aim of a new technology called Intelligent Valve Actuation (VCA), developed by U.K.-based Camcon. According to the company's Technical Director, Roger Stone, IVA will play a major role in allowing OEMs to meet 2020 requirements for fuel consumption and emissions.
The basis of the system involves control technology that eliminates the mechanical connection between valve operation and crankshaft rotation, allowing valve events (lift, timing, and period) to be optimized for every speed and load combination and even varied from one cycle to the next, said Stone, a former Ricardo technical director for design.
IVA is claimed to overcome the limitations of previous variable valve control systems via the combination of high-speed digital control with continuous, high-precision mechanical operation of the valve at every point in its movement. In effect, it is the creation of valve-by-wire technology.
Stone explained: “Engine designers have become conditioned to working within the restrictions of engine-driven camshafts. So a new mind-set is needed, whereby the designer considers what the engine requires at a particular load and speed condition, then specifies the appropriate valve events without having to work within the limitations of a traditional system.”
He sees two distinct groups of possibilities for IVA application: “The immediate benefits from optimizing valve lift, timing, and duration across the load-speed map are improvements in torque, fuel economy, and emissions," he said. Additionally, IVA is a potential enabler for advanced combustion concepts such as homogeneous-charge compression ignition (HCCI), switchable Miller cycle operation, and seamless switching between two- and four-stroke cycles.
Enabling advanced combustion strategies
Camcon's development work has demonstrated that even a “relatively straightforward” application to an existing engine would provide increased low-speed torque to allow higher gearing, deletion of the throttle to reduce pumping losses, and greater control of EGR (exhaust gas recirculation). Putting a figure on this, based on simulation and extensive rig testing, Stone estimates that such a level of implementation could provide at least 15% improvement in fuel economy and CO2.
However, Stone is confident that applications of IVA offer far more and believes it could act as the enabler to facilitate alternative combustion concepts.
“Extending the inlet valve opening period to give Miller cycle operation would be straightforward," he noted. "IVA could also potentially overcome some of the challenges of HCCI implementation because at lower engine speeds we can accommodate multiple valve events during a 720° period. This allows us to follow the normal exhaust event with a separate, much smaller event during the induction stroke, which would induce the required volume of exhaust radicals.”
In view of recent trends within the auto industry, IVA would also allow a more sophisticated cylinder deactivation strategy than conventional methods. This would be by continually varying the cylinders that are shut down to avoid cooling of the inactive cylinders and emissions peaks at reactivation.
Because of its high response speed, the system would also permit two-stroke operation at an engine speed of less than 3000 rpm.
Despite the cutting-edge potential, Stone stresses that IVA is not based on unproven technology but a combination of compact mechanical desmodromic valve gear and Camcon’s multi-stable actuator.
The system is controlled via a Valve Control Unit (VCU) that operates considerably faster than conventional engine controllers used for ignition or fueling. Typically, a fuel or ignition ECU only has to calculate an output once every other revolution for each cylinder; IVA monitors the valve position up to 100 times per event, requiring a 100 ms computing cycle.
Low power consumption
At the heart of IVA technology is a mechanical actuator patented by Camcon and based on its Binary Actuation Technology (BAT). The company’s present low energy actuator has two stable zero-power states, unlike a conventional solenoid which has only one, so it locks passively at both extremes of movement and only consumes power during the switching operation.
Stone noted that for the IVA application, engineers made the device multi-stable "by using a rotating permanent magnet to create a multi-pole rather than a two-pole arrangement, like a compact ultra-responsive electric motor.” He explained that to convert the rotary motion into high-precision linear valve operation, the system uses a desmodromic cam pair and rockers for each valve. A third cam lobe operates an energy recovery spring, improving system efficiency by recycling energy from one valve event to the next.
Combined with the high efficiency rotary actuators, this makes the IVA system highly energy efficient and therefore capable of operating within a conventional 12-V electrical architecture, the company claims.
IVA has a low power consumption at low speed and low engine load, regarded as being critically important to its operation.
“Even at the other end of the range, power consumption will be of the same order of magnitude as a conventional system,” added Stone. He reported testing has shown that refinement is “excellent” with “significantly lower noise than a conventional camshaft and valvetrain.” When idling, fuel injection systems may become the dominant noise source on engines with IVA.
“It really is about time we brought engine valve control into the digital age and freed ourselves from the restrictions of the last remaining mechanical system in the control of the combustion process,” Stone remarked.
Camcon is in discussion with several OEMs and one (unnamed) in particular, with which it has an established business relationship. At the point when sufficient interest in the system has been achieved, Camcon will seek a Tier 1 supplier to take the technology through to series production, said Chief Executive Danny Chapchal. “Engines with IVA could be in production comfortably to meet the demanding 2020 requirements for vehicle fuel economy and emissions.”