| Next summer Mahle Powertrain will unveil a novel three-cylinder 1.2-litre downsizing technology demonstrator engine, to be followed some six months later by an equally efficient 2.4-litre V6 demonstrator. The engines have been designed at Northampton in the UK and at the Novi operations in the US, but the engines will embrace technology and components from all Mahle’s divisions.
Plans call for a total of five engines to be built, the first of which will undergo testing in summer 2007 for the engine to be unveiled at the Frankfurt show in September. Early development testing will focus on combustion, fuel injection and boosting systems to prove out the already completed concept work.
Among parameters set for the privately funded project is a power density of 150bhp/litre and a 25 to 30 per cent fuel economy gain over a 1,600kg C-class car (such as Mondeo or Passat) equipped with a port fuel-injected engine. The engine will use a compression ratio of 9.75 to 1.
The aim is a brake mean effective pressure (BMEP) of 30 bar between 2,000 and 4,000 rev/min – 16bar at 1,000rev/min full load. This leaves open the door to progress to 35bar in due course. Other targets include a minimum brake specific fuel consumption of 230g/kWh and Euro V compliance.
 |
Mahle's aggressively downsized gasoline engine
(click on image for BMEP plots) |
The twin sequential turbocharged, twin overhead camshaft engine has four-valves-per-cylinder, central direct injection, air-water-air inlet intercooling and EGR to offset detonation and reduce charge temperatures.
Mahle Powertrain engineers stress they are not attempting to encroach into any OEM’s bespoke engine manufacturing territory. Rather, by building their own engine they hope to demonstrate Mahle’s products in the context of downsizing, evaluate various boosting technologies suitable for downsizing and, finally, provide an independent and robust R&D engine platform open for inspection. A number of suppliers are co-operating with Mahle in the design and development.
Mahle itself is keen to show it has the engine components essential for the next generation of downsized engines. It also wants to have the tools at its fingertips that can demonstrate future directions.
In selecting a swept volume of 1.2 litres, engineers were aware of the constraints imposed at the cylinder head to accommodate the four-valves per cylinder, an M10 spark plug and a central piezo fuel injector, while achieving optimum combustion shape.
Bore diameter becomes a limiting factor of downsized engines. Mahle engineers selected a bore of 83mm and a stroke of 73.9mm.
With this in mind, the result is a head with central spray guided gasoline direct injection and a combustion chamber with high-tumble turbo ports. A feature of the head will be injector tip cooling to protect from the very high heat rejection rates and prevent coking.
Packaging of valves, spark plug and injector, compact as it is, still produces an engine with a wide cylinder head to accommodate the DOHC roller finger follower layout with its dual independent cam phasers, lightweight valves and assembled camshafts. The cylinder head is the most complex part of the engine, demonstrating Mahle’s modular capability.
Mahle supplies assembled camshafts for the three-cylinder Smart engine. The two engine designs, of course, bear no similarity other than cylinder numbers. The assembled camshafts, however, will be unique to the downsized engine.
New construction techniques
The cylinder block design uses novel construction and bolting techniques. Besides making use of the Coscast process – both heads and blocks will be made at Mahle’s Worcester foundry – the block will use Nikasil surface protection. The aim is to demonstrate the technology of aggressively downsized gasoline engines. Particularly important aspects of the engine include transient and low-speed response. To assist this, Mahle’s approach to twin turbocharging plus additional technologies under consideration, such as two-stage valve lift and compressor map enhancers will help.
 |
| Twin sequential turbocharger layout |
Equally challenging is the turbocharging and exhaust system, both of which will be required to meet 1050°C operating conditions. To achieve this the manifold will be cast from austenitic stainless steel. The final design and choice of turbocharging system – and suppliers – have yet to be finalised, but the low-speed turbo ideally will be the smallest available. The second turbo will handle roughly twice the airflow for high performance duty.
The demonstrator’s machined four counterweight lightweight crankshaft, primary balancer and forged/cracked connecting rods are from high quality steel. The piston pins will be in diamond-like coated (DLC) high quality nitrided steel.
The partly plastic intake manifold has been designed to incorporate the modular air filter, the air-water-air intercooler, and the throttle body.
At this juncture, engineers side-step questions about details of sump design – but with such a small engine core, a structural sump looks almost certain to accommodate the loads imposed by various ancillaries such as air conditioning drive. Engine weight has yet to be disclosed.
The engine is targeted to be a cost-competitive unit when measured against future alternative gasoline technologies such as stratified direct fuel injection and fully variable valve trains.
|
[BACK TO TOP]
|
