This animation shows two IVA capabilities:
1. MOP shift represents the ability to distort the basic valve lift curve shape so that the valve either opens fast, reaching its maximum lift early and then closes more slowly – or vice versa. iVT can achieve quite severe lift curve modifications of this kind. This can be used for the purpose of tuning manifold pressure waves or adjusting the available flow area relative to piston velocity during the event. MOP shift is available for both full lift and part lift events
2, Differential lift is an iVT feature permitting each valve to be operated through completely different events. The valves can be driven to provide different lifts, different valve opening timings and different periods – they are completely independent of each other. This may be useful under conditions where single valve operation might cause combustion velocities to become excessive causing harshness or other undesirable combustion phenomena. Admitting part of the charge through the second valve can be used to reduce the mean velocity of the macro-motion of the charge in-cylinder and “tune” the rate of combustion.
As load and speed increase the trapped mass required increases but, by employing appropriate valve timings with iVT it proves advantageous to maintain single valve operation.
This increased flow requirement can be met by increasing lift on the single valve until it reaches its maximum value as shown here. Results to date suggest that the required charge mass flow to achieve full torque can be maintained through a single inlet valve right up to around 4000 RPM (at the same boost level). The advantage of enhanced in-cylinder charge motion is, of course maintained.
Using the individual valve control inherent to iVT enables many novel strategies, such as roaming cylinder de-activiation through running a 4 cylinder engine in a 12 stroke cycle. This animation shows this - here depicting exhaust and inlet valves as in a single row. The advantage of this method is to allow deactivation without the usual HC spike on resumption of 4 cylinder operation because roaming deactivation maintains even cylinder temperature
iVT can provide stable idle at reduced engine revs, providing a range of benefits. This can be achieved by the accuracy and repeatability of the valve opening event and its positioning relative to TDC
The trapped mass of charge required to maintain low load operation can be very modest and at low engine speed, piston speeds are low too. This means that the gas velocity into the chamber can be slow and the subsequent in-cylinder charge motion sluggish with conventional valvetrains– which results in burn rates slower than would be ideal.
With iVT, by limiting the admission of the charge to a single inlet valve and reducing the lift on that valve, the charge entry velocity can be substantially increased – and charge motion dramatically enhanced. Results to date have demonstrated that, even in a port/chamber arrangement designed for tumble, the resulting energetic swumble provides substantially accelerated combustion and corresponding FE benefits. These possibilities could be enhanced by the use of asymmetric ports and valve sizes.
IVA is capable of delivering an infinite variety of valve events through changing timing, lift and shape as it is independent of crankshaft. We are currently exploring the benefits of this space through dynamometer testing. What we have learned so far is that the work done on the valve is so small that, even allowing for electrical losses the overall parasitic losses are less than a conventional valvetrain in the majority of operating conditions
We have prepared animations of a range of example events at different engine conditions and these are shown below. Many more event shapes can be programmed however - pretty much at will.