Question To All The Gearheads?

[Jambe]

It seems I am lacking one critical bit of information on this variable cam configuration. I don't understand how the cam "lifter" can be changed to allow a different duration/higher lift (whatever it is that happens). I do understand how a regular cam shaft works. What is the mechanical change that takes place and how is it actuated?

 

[goofyone]

It seems I am lacking one critical bit of information on this variable cam configuration. I don't understand how the cam "lifter" can be changed to allow a different duration/higher lift (whatever it is that happens). I do understand how a regular cam shaft works. What is the mechanical change that takes place and how is it actuated?

These diagrams are from a Porsche system however Elio Motors will be using essentially the same setup on each of the three intake valves. The computer uses a valve to allow oil pressure either lock or unlock the center pin so the valve is either activated by the dual outer cam lobes or the inner cam lobe which allows the intake valve to have two different lift/timing configurations depending on the load.

"One of the potential technology features of the Elio engine is the two-step valve lift system (VVA) which uses switching tappets. The two-mode tappets allow switching between two different valve lift profiles which allows the engine to change its airflow capacity. One mode increases airflow capacity for more torque/power in city driving. The other mode decreases airflow to reduce pumping work during light load operation such as highway driving.

The switching tappet consists of two nested housings, the inner and outer housing. The inner housing is actuated by the center cam lobe while the outer housing is actuated by lobes on either side of the center lobe. The outer housing presses against a lost motion spring when the hydraulic actuation circuit is at low pressure. In this mode the center lobe determines the valve lift. Both housing parts can be linked by means of a coupling mechanism, a high pressure hydraulic chamber. In the locked condition, the high lift is transmitted via the outer housing to the valve. As in the standard tappet, valve lash adjustment can be by hydraulic or mechanical means.

The Elio engine uses a cooled Exhaust Gas Recirculation (EGR) system. The EGR system will be used to improve fuel consumption of the engine by reducing pumping losses and lowering peak cylinder temperatures which reduces NOx emissions. When the EGR is cooled it further reduces combustion temperatures and reduces engine knocking. This enables the engine to have a high mechanical compression ratio which helps improve fuel economy and performance. The EGR system is controlled by the ECU and will allow a specific amount of EGR into the intake manifold to be distributed into the combustion chamber."

 

[BlioKart]

It seems I am lacking one critical bit of information on this variable cam configuration. I don't understand how the cam "lifter" can be changed to allow a different duration/higher lift (whatever it is that happens). I do understand how a regular cam shaft works. What is the mechanical change that takes place and how is it actuated?

 

[Johnapool]

Great valve train pictures. An important thing not being shown, for non-gearheads, is that the entire valve train, from the camshaft bearings to those cams actually spinning on the valve set, are running in a constantly pressurized oil bath. This is good illustration of the importance of having very clean oil in your engine.