Originally Posted by korax123
I know there are other topics on this, but here is my idea. How come V8's and V6's have cylinder deactivation when cruising but no 4cyl car do. They can easily cruise off of 2cyl. I think it would save a descent amount of fuel on the freeway.
Since gas prices are getting higher some car companies should look into this.
I think it's a wonderful idea. I don't know if it could be implemented as seamless as the 6- and 8-cylinder cases, though. IIRC, for a V6 with variable displacement, it operates with no less then 3 cylinder. For an I4, if there are only 2 cylinder working, the vibration might be an issue, and the driver may notice when half the cylinders are deactivated. I'm not an expert on engines, so I'm not sure if my concern is valid or not. But I agree, the manufacturers should look into this if they are not doing so. On the other hand, they probably would rather put more effort on pushing the hybrid vehicles, which most likely has a higher profit margin than plane-Jane 4-cylinder compact cars.
In fact, we could even take your idea a step further, so that all 4 cylinders can be deactivated. This could make coasting an ultimate fuel-saving technique. At present, when we coasting down in gear, we are using engine brake, although the engine is not using fuel, it is converting kinetic energy into thermal energy, which means that the fuel we used to accelerate is wasted. If we coast in neutral, the engine uses fuel to maintain idle speed. To save the most fuel, we could shut the engine off. However, this could be dangerous because power steering, power brake, ABS, airbags and other safety features may be deactivated. But if all 4 cylinders are deactivated, when we coast, no fuel is injected into the engine, we are not using engine braking, and all the safety features are still active. This is a win-win-win situation. One caveat is that either the car has to recognize when we want to employ engine brake (long steep downhill), and when we want to deactivate all the cylinders (coasting), or provide the driver a button so he can control the deactivation of the cylinders himself. Either way, it's more cost and liability for the car manufacturer with a benefit that only sensible drivers can reap. Seeing how most people drive on the road, I doubt engines with completely deactivateable cylinders will appear in passenger cars in the near future.