Engine supplier Mahle becomes its own customer by developing its own 3-cylinder power plant.
|On the test stand Mahle’s first complete engine delivers vital data and findings on the interplay of the company’s components and subsystems.|
If an engine component specialist has a program which covers all but two major parts of the whole, how strong is the temptation to develop a complete engine?
In the case of Stuttgart-based Mahle Group, the answer was “irresistible,” and the result was on show at last year’s IAA — the first “Mahle Motor.”
During a press conference at the Mahle Motorsport works in Fellbach, Germany, the company recently revealed full details of the engine and, more importantly, its rationale — it is to serve as a combination of “technology demonstrator,” racing engine and a research and development project designed to release a broad array of synergies within Mahle among its various product groups.
“The racing aspect centers on ‘Formula SAE’ an international competition run by America’s Society of Automotive Engineers,” notes Mahle CEO, Prof. Heinz Junker. “Also known as ‘Formula Student’ the competition is open to academic institutions in all parts of the world, who build and race their own single-seater as a ‘hands-on’ learning project.
“On the R&D side, we had long wanted to try our hand at developing a complete engine, both to demonstrate our existing overall know-how and to add to this fund of knowledge, especially regarding the interplay of the components and subsystems we produce. At our product groups pistons and piston assemblies, cylinder components, valve train, air and liquid filtration, we develop world-leading technologies for the world’s best engines. Developing a complete engine was a logical next step.”
|Cross-section of the “Mahle Motor” showing its stiff tunnel crankcase and broad based oil pan. Both contribute to structural strength. Inlet and exhaust valves are angled at 13 and 12.5 degrees to the vertical and actuated via drag arms from twin, contra-rotating camshafts and lightweight gears.|
A happy combination of circumstances made possible this “quantum leap” to engine developer status, noted Mahle Motor project leader Dr. Adolf W?nsche. “Our involvement in Formula SAE arose from our close contacts with the Technische Hochschule Aachen, with whom we cooperate closely in R&D projects. Aachen has an excellent reputation in engines and vehicle dynamics, and when we heard of their plans to participate in Formula SAE we felt well placed to assist.
“First, no engine component manufacturers is better equipped — in principle, the crankshaft and the cylinder head casting are the only major engine components not in our range. Second, we enjoy a leading position as a supplier of components for racing engines, notably in Formula One and endurance racing, and Aachen’s Formula SAE project revolves around a race. We also see our support as a contribution to developing the next generation of engineers at a time when technical professions have lost some of their popularity.”
Dr. Uwe Mohr, head of Research & Development detailed Formula SAE’s specifications and stressed that the Mahle Motor is a completely new design in both architecture and features. “While leaving free the configuration and number of cylinders, the SAE Formula prescribes natural aspiration, a four-stroke cycle, a maximum 610 cm³ displacement and a maximum 20 mm diameter inlet restrictor on the basic engine. To this the students may add the options of turbocharger or supercharger, carburetor or fuel injection with electronic engine management. The intake system might consist of filter, carburetor /throttle body, air restrictor, charger and engine.
Mahle went for a 3-cylinder, in line configuration with swept volume of 609 cm³. Rated output is around 60 kW (80.4 hp) at 9,500 rpm and maximum torque 65 Nm (48 lb. ft.) at 7,000 rpm. The 3-cylinder inline design gives short inlet tracts in view of the 20 mm restrictor rule, and keeps down overall engine length.
This minimized costs and with bore and stroke dimensions of 70.8 x 51.5 mm, cylinder dimensions are close to those of commercial engines, making acquired data and findings widely applicable. The requirement for the engine to form part of the vehicle structure necessitated a balance shaft to compensate the ‘rocking couple’ inherent to an inline three.”
With its role as technology demonstrator Mahle has clearly taken pride in developing innovative solutions on its engine. With its deep involvement in competition engines, a number of solutions borrow straight from current motorsport practice. “Solutions to which, in many cases, Mahle has made a vital contribution,” Junker says.
|The complete Mahle, 3-cylinder Formula SAE engine, showing the side mounted water pump, broad, flat sump, and steep inlet tracts with indirect fuel injection.|
For example, the engine block is an interesting light alloy design using Mahle’s NIKASIL coating on parent bores. “The block is a two-piece structure and its halves locate the crankshaft and form a stiff “tunnel” capable of withstanding thermal and mechanical distortion,” Mohr says. “This prevents cylinder distortion and gives additional structural strength. The main bearing caps are in ferrous material to maintain tight clearances and are integral to the lower half of the crankcase. A broad based, integral oil sump lends additional stiffness and a low center of gravity. To minimize hydraulic losses, it is connected to the crankcase by a series of windows and oil strainers.”
The cylinder head is a also two-piece structure, allowing the camshaft covers to form its bearing caps. “It features four valves per cylinder with a central spark plug,” notes Dr. Martin Lechner, Mahle’s head of pre-development.
“For favorable gas exchange we use steep, straight inlet and outlet ports. The valves are actuated via drag arms from twin, contra-rotating camshafts. Inlet and exhaust valves are angled at 13 and 12.5 degrees to the vertical. The exhaust ports are cooled on both sides.”
Intake air flows through the filter, air mass flowmeter and via the throttle body to the 20 mm diameter air restrictor specified by Formula SAE. “To optimize engine performance under this constraint, the students located an air box after the restrictor to equalize flows to the cylinders. Air reaches the inlet manifold via an expanding conical inlet pipe,” Lechner says.
Timing gears were chosen instead of belts or chains for their better mechanical stiffness and lower weight. They are located on the flywheel side and drive the oil and water pumps as well as the camshafts and balancer.Borrowed from Motorsport
Taken straight from Formula One practice is the Mahle Motor’s lightweight running gear, designed to allow rapid accelerations and decelerations, W?nsche notes. “The piston is a squat, two ring design with extensive internal ribbing for high stiffness at low weight. It is cooled by oil sprays.
We use an ‘I’ section connecting rod, designed for high resistance to axial forces at high engine speeds. It features a chamfered small end eye and, as in many racing engines, to reduce friction the con-rod is axially restrained by the piston instead of the crankpins.”
Also derived from current motorsport practice is axial lube oil feed to the main bearings. “Lubricant is fed into a longitudinal bore at the front end of the crankshaft via a rotating seal. This gives better lubrication at lower oil pressures, since in contrast to radial feed, the lubricant does not have to overcome the centrifugal force of an object rotating at up to 9,500 r/min.”Home Made
Among innovative features designed to demonstrate Mahle’s know-how by targeting rigorous system efficiency are the lubrication and cooling systems. “All oil and waterways are integral to the block,” W?nsche explaines. “The cooling system features a rear mounted pump feeding coolant direct into a manifold on the side of the block, ensuring equal flows to all cylinders. All water jackets are completely circumferential and in a cross-flow system, coolant transfers from the block to the cylinder head at the hotter exhaust side, where it cools the exhaust ports on both sides. From there it passes to the inlet side and a coolant collector leading to the radiator.”
|The running gear of Mahle’s 3-cylinder, Formula SAE engine draws heavily on current Formula One practice. Squat, two ring pistons have extensive internal ribbing for high stiffness at low weight. An ‘I’ section connecting rod gives high resistance to axial forces at high speeds. To combat friction, the con-rod is axially restrained by the piston.|
Likewise, the lubrication system is designed to give even, efficient fluid paths. “The oil pump feeds upper and lower main pressure lines via the relief valve and full flow filter. The lower line feeds the big end bearings and the upper line the main bearings and piston cooling jets. A riser in the rear of the block from the upper line delivers oil to the cylinder head for lubrication of the camshafts, drag arms and timing gears. Oil return to the sump is via generously dimensioned, directly connected vertical ducts.”
Outside suppliers involved in the Mahle Motor project are Robert Bosch GmbH, supplying fuel injection and ignition equipment, and French specialist Chambon SA of St. Etienne, which cut the lightweight crankshaft from a single piece of metal. The major external contributor, however, was rapid prototyping and prototype specialist Becker CAD-CAMCAST, which provided molds and cores for all castings using the laser sintering and resin tooling methods.
Although the engine has yet to race, Mahle already feels vindicated by the internal synergies released by its racing engine project and the knowledge gained. “We organised the project to involve as many levels as possible in our research and development departments,” W?nsche says. “This led to exchanges of ideas and information on an unprecedented scale and ‘across the board’ amongst our product groups piston and piston assemblies, cylinder components, valve train, air filtration and liquid filtration. The quality of our findings, especially in terms of understanding the interaction of subsystems, and hence the total system ‘engine,’ has been outstanding.
“Simultaneously — and equally important — for the first time we assumed the role of our customers and became engine developers. Confronted with the design and manufacture of a complete engine, we gained a deep appreciation of their problems and considerations.
That this has made us an even better development partner has already been recognised and appreciated by our counterparts.”
And the project is ongoing. “Mahle Motor Mark II is already under development and among several improvements will be variable length inlet pipes to optimize the torque curve and a larger bore to gain higher engine speeds,” W?nsche concludes.