Well documented is the energy wasted when throttling-back a petrol engine for idling or lower speeds, as we do all the time. This throttling causes a partial vacuum in the inlet system, against which each piston must be pulled on its induction-stroke, known as pumping-losses. This increases the energy (and therefor fuel) needed for each throttled power-stroke. The diesel needs no such throttling, as its power is controlled by adjusting the fuel quantity injected – which is not possible with petrol (spark ignition) engines. This is one reason for the diesel’s superior economy. CITS for the first time, eliminates the throttle on a petrol engine with its patented By-Pass valve.
To reduce this throttling penalty of pumping-losses, new four-stroke engines now come with cylinder-deactivation. This means when an engine is throttled, and when less cylinders are adequate for the reduced power demanded, one or more cylinders are deactivated – usually by means of exhaust valves being kept open and ignition and of course fuel is shut-down. This achieves two things:
- The de-activated cylinder no longer burns any fuel, but still reciprocates as before, so there is no friction saving, but now without compression or induction pumping losses,
- The other cylinders now need more open-throttle to maintain the desired output – which reduces the throttling pumping-losses, for improved overall fuel economy.
This technology undoubtedly helps fuel efficiency, but is incredibly complex and costly.
Ford and others see the continued market for internal combustion engines and hence continue research on such developments as cylinder deactivation on the 3 cylinder Focus. There are benefits of course, but the shutting down of 1 cylinder when there are only 3 cylinders in total, whilst under power, causes rough and uneven firing – unbalancing the engine.
The CITS engine technology is a much more effective solution than those possible by existing systems to reduce pumping losses as illustrated here:
By using the patented Pivot Valve and By Pass technology all cylinders can be progressively deactivated as needed without having to completely shut down one of the cylinders. This is a gradual, smooth process with better fuel efficiency gains.
It has the added benefit in being smaller and more cost-effective to produce.