Lotus has recently completed its involvement in the development of Proton’s first forced induction engine.
The programme was born out of Proton’s desire for a more powerful derivative of their new MPV that was in the latter stages of validation ahead of its early 2009 launch with a 1.6 litre engine. After much discussion and investigation, it was decided to use a turbocharged variant of the Campro engine family as a downsized alternative to a bought in 2.0 litre normally aspirated engine.
The first application is in the Proton Exora Bold newly launched in the Malaysian market, with further engine rollout into Euro 5 markets later in several platform variants. The engine is manufactured and assembled at Proton’s Shah Alam facility outside Kuala Lumpur.
The new 103 kW 1.6 litre gasoline port fuel injection (PFI) engine, designated Charged Fuel Efficiency (CFE), is based on the existing Proton Campro 76 mm bore normally aspirated engine family, developed by Proton and Lotus which has been in mass production at Proton since 2004 in 70 kW (1.3 litre), 82 kW (1.6 litre) and 93 kW (1.6 litre PFI) variants.
As well as the increase in performance over the existing engines, the engineering programme permitted the introduction of numerous improvements in quality and serviceability.
Taking the decision to develop their own engine provided Proton with a solution that was a lower overall cost and also gave them more flexibility for the future by owning the IPR of the engine. This was a bold step by Proton because at the time, downsizing was seen as popular in Europe but not in Japan which drives a lot of the direction of the Malaysian market. However, since the start of the project, using a smaller forced-induction engine is becoming more common in Malaysia with VW and PSA entering the market with their downsized engines. Gasoline direct injection (GDI) would seem an obvious choice for such an engine but this was ruled out due to durability concerns relating to fuel quality standards in some of their key export markets.
The overall objectives for the engine were clear, the performance and fuel economy were to match or better a state of the art 2.0 litre NA engine. Because of the nature of the target vehicle (the Exora has a gross vehicle weight of over 1,900 kg), there was to be a particular focus on good low speed torque rather than outright power.
The engineering team comprising Proton and Lotus engineers started the design work at Lotus’ UK Technical Centre outside Norwich, before migration of the project to the Proton technical center in Shah Alam, Malaysia.
This allowed for good continuity within the engineering team, as well as building strong interpersonal links. This method also allowed inexperienced engineers an unparalleled opportunity to be introduced onto a live project, being mentored by Lotus and Proton senior engineers. In total, around 30 Proton engineers spent time at the engineering centre at Lotus.
Web conferencing packages were used extensively to efficiently communicate between Lotus and Proton, as well as with vendor engineering teams in Asia and Europe. As well as utilizing Proton’s existing supply base, many new technology suppliers were used for the CFE engine. Lotus Engineering Malaysia worked closely with the Proton supplier quality assurance (SQA) team through the advanced product quality planning (APQP) process.
Lotus manufacturing engineers worked with Proton manufacturing engineers to define and plan out the changes needed to the existing manufacturing facility in terms of equipment and processes to accommodate the changes of the Campro CFE engine.
Engine dynamometer testing was carried out at both the Lotus UK and Proton Malaysian test facilities. Additionally engines and electrically driven rigs were run at vendor sites to validate key components.
The first prototype engines were available for test 7 months after kick-off, with the initial design verification (DV) phase engines built at Lotus using prototype suppliers. Later DV phase engines would be built offline at Proton using soft tooled parts from production suppliers, before final process validation engine built on a new final assembly line in the Shah Alam facility.
The engineering programme included application of a new torque based engine management system (EMS) as well as the base engine changes required for the higher performance of the force induction system’s application. The new system would allow for seamless integration with a new continuously variable transmission, as well as permitting the vehicle to be upgraded to the latest levels of electronic stability program (ESP).
Calibration of the EMS was carried out by Lotus and Proton engineers, working closely with the transmission supplier (Punch Powertrain) and also the EMS software and hardware supplier (Continental SA).
In line with the product plan, the engine management calibration was proven at low temperature in Sweden, as well as high temperature/high altitude in Spain and Malaysia.
Although based on the existing engine family, retaining many of the key features like bore size, block height, cam positions etc, the vast majority of the components were replaced or modified in some way.
One fundamental change was a reduction in stroke from 88 mm to 86 mm. With the retained 76 mm bore, the swept volume reduced from 1,597 cc to 1,561 cc. This was brought about by the very compact height of the existing iron cylinder block which did not provide enough space to increase the required piston strength or lower the piston crown to achieve the desired compression ratio
The compression ratio was set at 8.9:1, which although relatively low for a modern downsized engine, allows the same hardware to be used for all the target markets including those with 88 RON fuel and very hot climates without excessive retardation.
The cylinder block was based on the original Campro cast iron block. Extensive finite element analysis (FEA) showed no requirement to strengthen the casting to withstand the increased cylinder pressures. Small changes to the block were made to incorporate piston cooling jets into the oil gallery, and computational fluid dynamics (CFD) driven flow improvements into the water jacket to improve the engine cooling required for the performance increase.
A forged steel crankshaft replaced the original cast iron unit in the engine. FEA indicated that it would be possible to maintain the existing main bearing and rod bearing dimensions; however it was necessary to improve the bearing material to withstand the projected loadings.
A new piston design with a 19 mm floating piston pin to withstand the higher cylinder pressures was implemented. The cast piston incorporated an anodised top ring groove to prevent micro-welding damage with the expected high temperatures, and a scuff resistant coating applied to the piston skirts.
The changes to the piston and the increased gas pressure loading necessitated a change in connecting rod and connecting rod length. A new forged steel fracture cap design replaced the original powder metal design.
The aluminium 4 valve per cylinder DOHC Campro cylinder head was re-engineered to accept an intake cam phaser for the CFE application. This was achieved maintaining the existing cambelt location and now permits 40 crank degrees of intake cam phasing for improved performance, fuel economy and emissions. An improved cambelt material was implemented along with an
auto-tensioner for improved serviceability.
During the cylinder head redesign, the spark plug was changed to a narrow thread, long reach design so that the spark plug boss would allow better cooling as well as a lower coolant back pressure in the cylinder head water jacket. In the same way as the cylinder block, the water jacket design actions were led by extensive up-front CFD analysis. Through the reductions in coolant restriction developed through CFD, only a modest increase in water pump flow rate was required.
A new multiple layers steel (MLS) cylinder head gasket was developed to withstand the higher cylinder pressures.
To withstand the expected higher exhaust gas temperatures, sodium filled exhaust valves maintaining the original 5 mm stem diameter were selected.
An upgraded oil pump was also implemented to compensate for the higher demand of piston cooling jets, turbocharger bearing oil supply, and to maintain good oil pressure at low engine speed so that the intake variable valve timing (VVT) system could be operated. A water-cooled oil cooler is fitted as standard.
A Borg Warner turbocharger’s compressor and turbine were selected for maximum low speed performance. It uses a pressure regulated wastegate to control plenum pressure, and incorporated an electric integrated compressor bypass. Air from the compressor is ducted to an air to air charge-cooler mounted in the front left hand side bumper aperture. An electrical pump which is actuated on key-off to provide coolant to the turbocharger bearing housing after engine shutdown. This pump also circulates coolant around the rest of the coolant circuit to prevent boiling, an important feature in the high ambient temperature of Malaysia and Proton’s export markets.
In line with the original Campro philosophy, the CFE engine uses a single close-coupled catalyst as sole exhaust gas after-treatment as a cost effective fast light off package. Variations in platinum group metals (PGM) loading and substrate density will cover Euro III to Euro V emissions markets.
The existing two-mode variable length plastic manifold was replaced with a compact fixed length plastic manifold for the CFE. The fuel rail was re-engineered to a return-less design to reduce fuel heating effects, and higher flow fuel injectors fitted to satisfy the increased performance level.
As well as improvements to produce and withstand the increased performance, several other changes were made to reduce the friction of the base engine.
These changes included replacing the original engine’s direct acting hydraulic tappets with lower friction mechanical graded tappets that are machine selected on the engine assembly line.
Piston ring heights were reduced allowing lower tangential loads and the piston skirts now include a low friction coating.
A windage tray was also added to the oil pan that has been shown to reduce parasitic losses by up to 1.5 kW. A higher specification lower viscosity mineral oil was specified to allow extended service intervals along with reduced friction.
The main focus for the CFE engine was as a downsized engine to power a large MPV, instead of a potential 2.0–2.2 litre NA engine. It was specified to deliver better full load performance and part load fuel economy than a 2.0 litre NA.
The resulting torque curve, shown as Figure 3, peaks at 205 Nm from 2,000-4,000 rpm to stay within the limits of the CVT transmission, this is achieved with a boost pressure of between 0.6 and 0.8 bar. Sufficient boost is achieved by 1500 rpm to exceed the torque of a 2.0 litre NA engine and to produce more than the peak torque of the Campro 1.6 CPS engine currently used in the Exora. The engine achieved a part load BSFC over 4% better than the state of the art 2.0-litre NA engine benchmarked at the start of the project.
The 1.6 litre CFE engine represents Proton’s first mass production downsized engine technology, with initial launch in the 2012 Proton Exora Bold vehicle.
The engineering programme from clean sheet to mass production was achieved inside 3 years with a relatively small team of Lotus and Proton engineers, and continues the track record of successful joint engineering programmes carried out over the last 15 years and demonstrates Lotus’ continuing powertrain capability from concept through to production.
Authors: John Birkmyre, Richard Jackson and Lee Jeffcoat