The industry is in a state of flux at the moment – the media loves the idea of electric cars, although no one talks about where the electricity to recharge the vehicles is coming from. Honda and several other manufacturers are still developing fuel cells and Motoring Weekly recently wrote about the Nikola truck that uses this technology. There have also been articles about several manufacturers who have been breathing more life into petrol powered engines to get more power or fuel economy.
Delphi, a parts manufacturer and supplier to pretty much every car company, has been hard at work in also trying to revamp the petrol powered engine. The issue that many manufacturers have, is fuel economy. In the US, the CAFE standards dictate the fleet average economy figures, although these are being challenged by the Trump Administration to reduce the figures simply because they think that more gas guzzlers will mean more sales of American built cars. In Europe, there are similar standards that the manufacturers have to meet.
Last week Motoring Weekly wrote about Nissan’s variable compression engine to try and keep the petrol powered engine young and efficient. Diesel motors are very fuel efficient, however they have a problem with emissions. This came to a head after the diesel emissions scandal where the VW Group and others including Mitsubishi were found to have ensured that Government test results were exactly what was required, although not in the way that the Governments wanted!
Delphi, like Nissan, have been looking at how to combine existing technologies to improve the fuel efficiency of the motor whilst keeping below the CO2 regulations. The company reckons they can get an additional 19% efficiency and get low-end torque which is a feature of diesel motors and means better power delivery.
Delphi have developed a 48-volt hybrid system. Several manufacturers have already moved to 48-volts and this is more an evolution of battery systems than a great leap forward. The concept of hybrid systems has already proven itself as a way of saving fuel, especially with a kinetic energy recovery system. Delphi’s system however, doesn’t save a massive amount of fuel on its own.
The other technology that Delphi has developed is a new cylinder deactivation system they call “Dynamic Skip Fire”. Again, this isn’t a new idea, many cars – especially V8s have had cylinder deactivation where four cylinders can be “switched off” under light loads. This needs to be carefully managed because if the system is not balanced, it will cause excessive noise and more importantly, excessive vibration. That is why, typically, half the cylinders in the engine are deactivated at the same time.
Dynamic Skip Fire goes further – they even call it a “continuously variable-sized engine!” They have worked out how to deactivate cylinders down to a single cylinder powering the vehicle. They can do this by figuring out how to avoid known resonance patterns within the target engine to keep the motor running smoothly. The heart of the system is a roller finger follower with a deactivation arm which is in between the cam lobe and the top of the valve stem. It is managed by oil pressure.
The idea is simple. When power is needed, the deactivation arm is locked in place by oil pressure that keeps the follower in place. The cam is then able to open and close its associated valve(s). When the oil pressure drops, the follower moves back and the cam moves the deactivation arm only which means that the valve(s) stay shut. The system controls both the input and output valves.
The ECU controls the flow of oil to the roller finger follower via data inputs from the throttle and it also controls the ignition to stop the spark as well as the fuel injection system to manage the delivery of fuel to the cylinders that need it. With no air input, no fuel and no spark, there is no power stroke, however the cycle is kept complete. This means that the engine can run with one or more cylinders based on power requirements and smoothness.
Dynamic Skip Fire enables a much improved fuel economy and reduced emissions. Combined with the hybrid system gives the economy improvements reported above. General Motors will replace their older deactivation system with Dynamic Skip Fire on some of their 2020 model SUVs. Delphi hope that the European manufacturers will consider the combined system on petrol engines to reduce their reliance on diesel to meet future economy and emission regulations.
The Featured Image is the Temple of Delphi in ancient Greece – where the oracle would make important decisions, rather like this system that makes decisions inside your engine. The Greeks considered Delphi to be the centre of the world – in some ways the ECU is the centre of your engine’s world!