Powering the Rover 75
“Rover 75 has the most comprehensive range of engines and transmissions ever launched with a brand new Rover - and they are all world class.”
Mohinder Singh, Power Train Team Leader
As part of the customer choice philosophy behind the Rover 75, buyers have the freedom to choose their own engine and transmission, independently of the vehicle trim level. Four outstanding engines are available; each can be specified (subject only to individual world market variations) with new custom-designed 5 speed automatic or manual transmissions. The power train line up for Rover 75 establishes several firsts:
- The first 2-litre version of the KV6 engine.
- The first common-rail direct injection diesel engine to be available in a UK-built car.
- The first Rover diesel car available with automatic transmission.
- One of the first mainstream front drive, transverse engine car with 5 speed automatic transmission.
- The first manual gearbox in a Rover car with synchromesh on reverse.
In summary, the engine choice for Rover 75 is:
1.8 litre K Series petrol, 120Ps - the classic all aluminium twin cam 16 valve engine, upgraded in many details to suit the new installation.
2.0 litre KV6 petrol, 150Ps - a new short stroke version of the quad-cam, 24 valve KV6 design, specially developed for the Rover 75.
2.5 litre KV6 petrol, 177Ps - a substantially re-engineered, high volume production version of the ‘pilot production’ KV6 introduced for the Rover 825.
2.0 litre M47R CTD diesel, 116Ps - a version of BMW’s latest twin cam, 16 valve 4 cylinder turbo diesel, equipped with advanced common rail direct injection and developed jointly by BMW and Rover engineers to the Rover 75 brief.
Each of the above engines is available with either a new 5 speed Getrag manual gearbox, or a new 5 speed JATCO electronically controlled automatic transmission.
POWER TRAIN IN DETAIL - ENGINES
All Rover 75 power units have been engineered to be one step ahead of current European emissions standards, with tailpipe emissions already reduced below the ECD3 standards that do not become mandatory until January 2001 (the on-board diagnostics requirement for ECD3 will be incorporated earlier). Many of the changes made to the K Series petrol units are associated with meeting these very low emission levels; other changes are to suit the physical installation requirements of the Rover 75, and to reduce servicing costs. Features such as dual-mass flywheels, fitted to all Rover 75 engines, help to achieve exceptional standards of refinement across the range. New high-grade starter motors and alternators are specified on all these engines for efficiency and reliability.
1.8 LITRE K SERIES
This engine is upgraded to full sequential fuel injection, controlled by a new MEMS 3 electronic control unit. Revised sensors are used for the ECU inputs, and a camshaft position sensor has been added, along with revised camshaft seals. The direct ignition is provided by two twin-output, plug top coils, which provide higher spark voltage than the previous remote coils. Platinum tips extend spark plug life from 24,000 to 100,000 miles. Idle control is now more precisely carried out by a bi-polar stepper motor which controls the air by-pass around the throttle body. For optimum emissions performance from cold start, an additional starter catalyst has been incorporated directly into the exhaust manifold.
For quieter running and longer camshaft drive belt life (up from 60,000 to 90,000 miles), a new automatic tensioner is fitted; similarly, where air conditioning is fitted, the compressor drive belt now has an automatic tensioner.
2.0 AND 2.5 LITRE KV6 ENGINES
When the KV6 engine was launched in 1996 for the Rover 825 models, it was initially designed for what was essentially a pilot production facility. The engine was built to meet the limited requirement for six cylinder models of the 800 Series. For the Rover 75, which uses both 2.5 litre and 2.0 litre versions of the KV6, production has been moved onto a new, high technology, volume assembly line. In order to adapt the engine to a normal production rate, many components have been given uprated specifications, with changes of design, materials and manufacturing techniques.
Other changes have been made to suit the new installation - for example the general structure of the engine has been stiffened to meet the requirements of the torque-axis mounting system. As a result, nearly 90% of the engine components are new for these derivatives of the KV6 family. The 2.5 litre is now more powerful than the previous version, with maximum power up from 175 Ps to 177 Ps, while the new 2.0 litre produces 150 Ps, a healthy figure for a naturally aspirated engine with fixed valve timing. The only major difference between the 2.0 and 2.5 litre versions is the stroke, so the following information covers both versions.
A completely new Siemens fuel injection and engine management system is fitted, including all-new sensors for all the control parameters. Two knock-sensors (one per cylinder bank) are now included in the ignition control circuits to inhibit detonation, and allow the engine to tolerate variations in fuel octane. The new injection configuration uses a simple ‘air-assisted’ principle which improves fuel atomisation. A small proportion of the intake air is separately channelled into the area surrounding each injector nozzle so that the air stream blends with the fuel spray. This works in an entirely passive manner, there is no pump or any other moving parts, and the channels are simply formed within the manifolding.
Further development has been carried out on the advanced variable induction system (VIS), following extensive computer analysis of its flow and charge resonance characteristics; the new version has a high precision plastic moulded upper manifold in place of the previous cast aluminium type. Where traction control is specified, the VIS incorporates a secondary throttle that is actuated when torque reduction is required. Optimum VIS control maps for each of the two engine sizes have been generated to the benefit of overall torque characteristics and fuel economy.
Cylinder head castings have been modified to suit the Rover 75 engine installation, and the cam covers given extra volume to enhance crankcase breathing. New exhaust valves have carbon breaks to prevent sticking, and all valve seats are machined in three planes for improved seating efficiency. Multi-layer steel head gaskets, which have proved exceptionally reliable on Rover and BMW diesel units, are now used for the KV6. New direct ignition coils giving improved spark quality have been fitted, along with 60,000 mile platinum tip sparking plugs.
Revised cam profiles have been developed for each of the two engine sizes, and torsional vibration dampers have been incorporated into the camshaft drive system to enhance durability and refinement, particularly at high engine speeds.
A new cast aluminium sump with internal baffle plate has been designed to accommodate a new standard fit oil cooler. Other detail improvements and modifications have been made to the water pump, oil pump and oil filter.
2.0 LITRE M47R DIESEL ENGINE
The M47R turbo diesel unit is a special derivative of the M47D engine first launched in the latest BMW 3 Series. It has been jointly developed by Rover and BMW engineers to suit the transverse installation in the front wheel drive Rover 75, with performance and refinement characteristics tuned specifically for this car. It uses Bosch common rail high pressure injection - the first application of this leading edge diesel technology to a car built in Britain. This high performance unit delivers power (116Ps) and torque (260Nm) figures that compare quite closely with those for the former 2.5 litre diesel in the Rover 825D models, yet offers economy even better than that of the Rover 620 diesel derivatives.
The key to the remarkable efficiency of the M47R engine is its advanced cylinder head design. It has an aluminium head with four valves per cylinder operated by twin chain-driven overhead camshafts. To generate high swirl of the air charge in the combustion chamber for good fuel/air mixing, two distinctly different inlet ports are provided for each cylinder; one is a conventional side port, the other a downdraught spiral port feeding in from the top of the head. The use of four valves allows the direct injector and the piston-bowl combustion chamber to be centralised on the cylinder axis. This gives a symmetrical and well controlled fuel spray pattern, contributing to low emission levels. Another benefit of centralising the combustion chamber in the piston is that it allows space for an efficient cooling port inside the piston (fed by oil spray jets in the lower crankcase). Good cooling of the area around the first piston ring is essential to the reliable achievement of high output.
The valve gear of the M47R has been designed for very low friction, with high rigidity and low maintenance. The cams operate the valves via roller rockers with static hydraulic lash adjusters. The simplex chain drive for the camshafts also drives the high pressure radial piston fuel injection pump and the engine oil pump.
COMMON RAIL BENEFITS
The common rail injection system works on the accumulator principle; the special high pressure (up to 1350 bar/19,000 psi) fuel rail is continuously maintained at pressure by the injection pump. The four injectors can ‘tap into’ this source of high pressure fuel at any point required by the fully electronic ‘drive by wire’ control system, regardless of the position on the engine cycle or engine speed. Very high pressures give excellent injection spray atomisation to help achieve low emissions and also permit the required amount of fuel to be injected very quickly, which aids torque output, especially at lower speeds.
The system also facilitates a pilot injection strategy, whereby a small amount of fuel is injected at a precisely timed point just before top dead centre on the compression stroke, and the main injection charge follows just after top dead centre. This initiates combustion more gently, with a smoother release of heat and a lower rate of pressure rise, thus reducing the noise levels normally associated with direct injection diesels. In addition to its performance, refinement and emission benefits, common rail is also essentially simpler and more reliable than conventional rotary pump injection systems.
Other notable features of the M47R unit include a cylinder block cast in grey iron, with hollow sections in the walls to achieve very high strength and stiffness with minimum weight. A multi-layer steel head gasket provides even distribution of sealing forces. The crankshaft is steel, forged for strength and nitrided for durability.
An oil cooler is fitted as standard, and is the water/oil heat exchanger type, integrated with the oil filter housing. This not only moderates oil temperatures when required, but also speeds warm-up from cold, as the engine coolant heats up first. Also assisting rapid warm up in cold climate situations, where cabin heat is needed quickly, is a standard-fit fuel-burning engine heater. The sheer thermodynamic efficiency of this advanced diesel means that relatively little heat is rejected to the cooling system; the auxiliary heater unit compensates for this during warm up.
MULTI-FUNCTION INDUCTION SYSTEM MOULDING
A complex glass-filled polyamide induction system moulding ingeniously integrates a number of functions. In addition to the induction manifolding, it incorporates the cam cover, the crankcase breather with its oil separator and pressure control valve, the EGR (exhaust gas recirculation) valve, plus the air filter / induction silencer system and air flow sensor. Further, it uses rubber isolator mounting and the sound-deadening effect of the air filter cartridge inside it to act as an stylish acoustic cover to the complete engine.
One of the significant new components developed for the Rover 75 version of this engine is a new cast aluminium sump, designed to carry the loads of the lower torque reaction rod mounting. The oil dipstick tube has been engineered to allow suction removal of old oil at an oil change, hence saving time and service costs.
THE NEW TRANSMISSIONS
The transmission design brief for the new Rover 75 was extremely demanding. Not only were the project engineers seeking class leading levels of transmission performance, reliability and refinement, but they also required gearboxes that added minimum width to the transverse power units.
It was therefore necessary to provide two brand new transmissions, manual and automatic, which would fit the package for all four engines. Full advantage was taken of this ‘clean sheet’ opportunity to invest in world-class technical excellence, with transmissions specifically designed and developed to meet the brief.
MANUAL GEARBOX - GETRAG 283
Getrag is BMW’s established supplier of manual transmissions, and has worked closely with Rover engineers to create a compact 5-speed gearbox for the Rover 75. Known as the 283, the new gearbox is made in a brand new, high technology factory in Bari, Italy. It achieves its minimal width by means of a novel 3-shaft design, and has a 14% higher torque capacity than Rover’s existing PG1 heavy duty car transmission. It features synchromesh on reverse gear to prevent unpleasant gear clashing if reverse is required quickly.
All the speed gears rotate on caged needle roller bearings. For refinement of running, all the 2nd to 5th gears and final drive have power-honed teeth. Lubrication is by internal splash effect, with a catch channel to feed a generous supply of oil down the centres of the input and output shafts to all gears, synchroniser hubs and bearings.
Clutch operation is hydraulic, with a concentric slave cylinder (rather than a lever type) acting directly on the clutch release for smoother and lighter control.
The gearbox is common to all manual Rover 75 models, with appropriate intermediate and final drive ratios to suit each power unit.
AUTOMATIC TRANSMISSION - JATCO FPO
Rover enjoyed excellent co-operation from the Japanese Automatic Transmission Company when developing its 4 speed automatic transmission for the original KV6-powered Rover 800. JATCO are exclusively designers and makers of automatic transmissions and have a strong reputation for mechanical excellence as well as for the sophistication of their electronic control systems. They became the natural choice to supply a brand new 5 speed automatic, tailored specifically for the Rover 75, and is one of the first uses of a 5-speed automatic with a transverse-mounted front drive engine.
The five gears provide a wider ratio spread than four speeds, which give benefits in terms of outright and mid-range acceleration, as well as enhanced responsiveness and economy.
The control system can engage fuel-saving torque converter lock-up in third, fourth and fifth gears.
The shift provides selection of P, R, N, D, 4, 3 and 2. There are also three driver selectable modes - normal, sport and winter. Normal mode also includes several additional modes, automatically selected by the advanced electronic control system. This system allows sophisticated shift control and adaptability. Sensors read vehicle speed, brakes, engine signals (such as speed, throttle demand and water temperature), transmission temperature and ambient temperature. The messages are transmitted via the car’s CAN-bus multiplex system to the gearbox control unit, and enable it to respond co-operatively and intelligently to a wide range of driving situations, as detailed below.
Normal mode is selected at start-up and is the default mode when either of the other two is de-selected.
Sport mode has unique shift maps which make the gearbox change down more readily and hold onto lower gears longer in order to aid acceleration and improve responsiveness.
Winter mode is calibrated to aid control of the vehicle by commanding 2nd gear for a standing start.
Self-selecting adaptive modes. These are enacted in ‘normal’ setting to respond to the following situations:
High coolant temperature mode. Under extreme loads, the engine and transmission can generate excessive heat. Rover 75 will engage a special cooling shift map at certain temperatures to aid vehicle cooling. The transmission has been designed to perform normally in high temperatures. It will only use the cooling strategy under exceptional circumstances.
Hill/trailer mode. This mode adapts the shift pattern to aid driveability on steep gradients or when pulling a trailer. It will be cancelled if Sport mode is selected by the driver.
Altitude mode. To aid driveability at high altitude, (detected by an air pressure sensor), the transmission will adapt shift pressures to compensate for the reduced engine torque caused by less dense air.
Cruise control mode. Linking cruise control to an automatic transmission can under some circumstances give rise to unwanted shifts, that are at odds with Rover’s concept of relaxed cruising. Where an automatic Rover 75 is specified with cruise control, a special communication link is provided between the cruise control unit and the transmission control. When cruise control is engaged, the transmission will switch to a ‘cruise strategy’ map which is far less sensitive to throttle changes.
ADDITIONAL FUNCTIONS OF THE JATCO CONTROL SYSTEM
Torque-down. This feature momentarily reduces engine torque during gear changes, for smoother acceleration. Rover 75’s advanced CAN-bus multiplex links between engine and transmission ECUs allow particularly rapid and precise mapping of torque-down, so that with all engines, automatic gearchanges are very smooth.
Downhill recognition. Automatics have a tendency to upshift going downhill as they recognise increase in speed with decrease in throttle angle. This is unhelpful if the driver has lifted off the throttle to slow down, and the resultant lack of engine braking may lead to otherwise unnecessary use of the brakes. The Rover 75 automatic system recognises an increase in speed with a decrease in throttle angle as a downhill, and inhibits the upchange accordingly until the throttle is re-applied. If the brakes are applied at the same time as the throttle angle is decreased, the transmission will change down to provide increased engine braking.
Cold start. In very cold conditions, fast warm-up helps reduce emissions and improve economy, driveability and comfort. The transmission ECU will hold on to lower gears for longer and inhibit torque converter lock-up in order to help increase heat generation. Once normal coolant temperature has been reached, the transmission reverts to the regular shift strategies.
Certain other facilities are available for market requirements, including interlock arrangements between gear selector and brakes or between selector and key removal.