| Throttle response: a term often used to describe the immediacy with which the engine delivers go when the driver pushes the accelerator pedal into the carpet. Using valve lift instead of the butterfly valve as a means of load control, INA’s Uniair system improves engine responsiveness, but the old description is now redundant. A cam-actuated electro-hydraulic valvetrain, Uniair also offers improved power and torque, especially in the lower rpm range, reduced emissions and improved fuel economy.
Uniair was one the power/ drivetrain technologies demonstrated by INA, part of the Schaeffler Group, at last month’s SMMT test day in the UK. INA already supplies components to BMW for Valvetronic, Porsche’s complete Variocam system and switchable tappets to Subaru and Volvo.
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| Uniair: electrohydraulic control of variable valve lift |
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Uniair was originally developed and patented by Fiat, but Schaeffler has the exclusive licence and is developing component design and control software. The principal aim of the system is optimisation of cylinder charging. This is achieved by infinitely variable lift of each inlet valve, independently, between 0 and 9.5mm. In so doing, valve lift can be matched precisely to engine load across the entire operating range, ensuring each cylinder receives the correct charge without the pumping losses induced via throttle based load control.
Continuously variable valve lift offers better control than systems that switch to a different cam profile at a specified rpm.
BMW’s Valvetronic was the first production gasoline engine to use variable lift to control engine load, using a stepper motor acting on intermediate rocker arms of a non-constant profile to provide a direct mechanical actuation of the inlet valves.
Uniair uses engine oil under high pressure for valve actuation, with no mechanical contact between valves and the camshaft, which helps to lower friction losses in the valvetrain. Basic architecture is of the roller finger follower type (RFF).
Both systems retain a throttle butterfly but it is normally fully open: it is retained as a system failsafe and to purge the evaporative emission control canister.As on all diesel engines, the reduced depression in the inlet manifold means that vacuum pumps are required for brake servo functionality.
Oil at standard operating pressure is admitted by a solenoid valve into the actuator body where it becomes further pressurised via a piston pump driven directly by the cam lobe. This oil opens the inlet valves according to signals sent by the Uniair ECU. Valve closure is via springs but return is controlled by a hydraulic damper and therefore independent of the cam profile. Thus, valves are normally closed.
Prototypes use a dedicated ECU to control the Uniair actuators, linked to the engine ECU via Canbus, and with input from an extra oil temperature sensor: oil viscosity is key to the performance of the system, especially from cold starts. The system has performed as well as the base engine from -30°C.
Production versions could ee the functionality consolidated into a single ECU, offering cost savings and reduced packaging requirements.
An additional benefit of the system is greater control of valve overlap so not only can idle quality be improved but internal exhaust gas recirculation (EGR) can be optimised.
Based on the 2.2 litre four-cylinder Opel Vectra, the unit required few changes to incorporate the valvetrain, save for an increase in compression ratio from 10:1 to 10.5:1 and a 4:2:1 exhaust system. The Uniair system gives these improvements:
Power increased from 108KW (147PS) @ 5800rpm to 118KW (160PS) @ 6000rpm
Torque increased from 203Nm @ 4000rpm to 218Nm @ 4000rpm
Increased output throughout entire rpm range
More immediate engine response
Fuel consumption reduced by 10 per cent
Reduced CO2 and CO emissions; Euro IV compliant.
Further improvements would be expected if Uniair was integrated into engine design instead of bolting it on to an existing powerplant, as per the test car: revisions to inlet manifold, combustion chamber and cam profiles would raise thermodynamic efficiency.
Peak electrical power consumption of the system is 130W; the prototype car has an oil cooler fitted but INA says this will not to be required for production.
The test car did not feature variable valve timing. It might be a further enhancement as INA already produces cam phasing systems, including those used by Porsche and BMW.
INA says OEMs are interested in the technology, and it is scheduled for series production in Europe in 2009 in a gasoline engine application, using port fuel injection.
Also on display was INA’s switchable roller finger follower (SRFF) valvetrain, again fitted to a modified 2.2 litre Vectra. The aims of the system are the same as Uniair but conventional throttle body fuel injection is retained; valve lift does not control engine load. SRFF is an evolution of the widely used RFF layout, and may be retrofitted to existing engines. Advantages are reduced cost and simpler control requirements.
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Switchable roller finger follower: switches between two valve lifts |
The followers permit switching between inlet valve lift of 9 or 11mm, at engine speeds up to 4500rpm. Exhaust valve operation is by standard RFF. A camshaft phaser has been added, giving variable valve timing for both inlet and exhaust valves. The demonstrator offers:
Power increased from 108KW (147PS) @ 5800rpm to 125KW (170PS) @ 6250rpm
Maximum torque increased from 203Nm @ 4000rpm to 220Nm @ 4000rpm
Fuel consumption reduced by up to 7 per cent
Optimised low-end torque
Improved engine response
Reduced emissions
The test car, aside from the SRFF system, was modified to include revised manifolds and a prototype engine ECU.
The followers operate on the lost motion concept and feature two arms on a common roller pivot, one working against a lost motion spring during lower valve lift operation. When switching over to higher lift, a solenoid supplies oil at high pressure to a locking pin between the followers. With the pin displaced, the two move together, allowing actuation of the valve by a different cam lobe. At a maximum switching speed of 6.67ms, alternating between the two modes is said to be undetectable to the driver.
The limits of switching operation are set at 4500rpm because of valve train kinematics, packaging of the lost motion spring and base circle duration of the cam.
On multi-cylinder engines, the SRFF system can be used for cylinder deactivation, further improving fuel economy. INA says that the system would be available for around the same cost as its switchable bucket tappets, given equal production volumes.
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