Td5 - Taking the Diesel World by Storm
Land Rovers new 5 cylinder, electronic unit injection turbo diesel
A major factor in the success of the original Discovery was the Tdi direct injection turbo-diesel engine, which in 200 Tdi and then 300 Tdi forms provided excellent driveability on and off-road, and a class-leading blend of performance and economy. Now Land Rover has taken an even greater leap ahead in 4x4 diesel technology with the all-new Td5 engine making its debut in the New Discovery.
Impressive Power and Torque
Developed under the code name Storm, Td5 is a totally new, 5 cylinders, 2.5 litres, direct injection diesel engine that sets a new standard in the sector for its span of attributes: power, torque, and economy, refinement, low cost of ownership and low emissions. It has been designed, developed and manufactured within Land Rover. The Td5 develops a maximum power of 101.5 kW (136 bhp) and a maximum torque of 315 Nm (232 lb.ft.). Although Td5 has the expected Land Rover low-speed torque - the maximum is at 1950 rpm, with 90% available at a mere 1450 rpm - the torque spread is greatly extended, with at least 80% of maximum on tap from 1,300 to 3,900 rpm. The governed speed is high, at 4,850 rpm, with a progressive cut-off characteristic and excellent performance at high speeds.
Innovation in Engine Design
Td5 pioneers many significant innovations in 4x4 (and indeed passenger car) diesel engine design including a specially-developed version of the Electronic Unit Injector (EUI) technology from Lucas Diesel Systems, giving optimum performance, refinement and emissions control. Reflecting Land Rovers continuing leadership in 4x4 engineering, Td5 incorporates an array of new patents.
The original Storm diesel engine concept, approved in 1993, was for a modular family of 4, 5 and 6 cylinder units, capable of meeting all projected Rover Cars and Land Rover diesel engine requirements. The first application was the 5 cylinder version for the New Discovery and Defender; development of this was under way when BMW acquired Rover in 1994. BMW approved the continuation of the Td5 programme in 1995 for production as a dedicated Land Rover 4x4 engine, completely replacing the Tdi in UK-built Discovery and Defender ranges. Before designing Td5, Land Rover engineers undertook an intensive review of international best practice in power unit design and manufacture. Countless competitor engines from around the world were tested and minutely analysed; the lessons learnt were added to Rover Groups positive and extensive experience with the Tdi and L Series direct injection diesels.
Electronic Unit Injectors (EUI)
Central to the Td5 concept was the adoption of EUI technology. This has already proved very successful over many millions of miles in large diesels, such as those used in premium trucks, delivering enhanced driveability and economy as well as providing a high-confidence route to meeting increasingly tough emissions regulations. EUI uses an individual camshaft-driven plunger pump for each cylinders injector, with ultra-precise electronic control of the injection period and timing.
High Pressure Injection
One of the keys to good diesel emission control is high fuel injection pressure. EUI can readily and safely provide very high injection pressures - Td5 typically uses 1500 Bar (22,000 psi), compared with around 600 Bar for the high pressure system on the 300Tdi. If still higher pressures were to be needed for emission control in the future, an increase to 2000 Bar (29,000 psi) is already feasible with this system. Because the pressure is only created directly and briefly within the injector itself, there are no problems with containing the pressure within fuel rails, distribution pipes or connections, as on other high pressure injection systems.
A Powerful New Engine Management Computer
In parallel with the adoption of EUI came the need to develop a new Engine Control Module (ECM), more powerful than any previous Rover Group petrol or diesel ECU, and capable of handling the advanced fuelling strategies that Land Rover wanted for this engine. This major in-house ECM project followed the meteorological theme in being code-named Thunder.
Close Co-Operation with Suppliers
Land Rover engineers worked closely with their counterparts Lucas EUI colleagues in developing the Td5 installation, which in itself incorporates four new EUI patents. Their joint success can be measured by the fact that Td5 achieves significant advances in output, efficiency and refinement, while also being able to meet all emissions legislation in relevant world markets without the use of an exhaust catalyst. It also meets Land Rovers traditional and exceptionally stringent requirements for reliability and endurance under all-terrain, all-climate and all-purpose use.
Fast Throttle Control for the Best of Both Worlds
A pioneering feature of the Td5s drive-by-wire programming is a two-stage throttle response strategy. Traditionally, 4x4 vehicles have had to compromise between having a long-travel throttle for off road use (to facilitate gentle power application on low-traction surfaces and to reduce inadvertent throttle changes on bumpy terrain) and having normal road car throttle responsiveness on tarmac. The Td5 ECM gives the best of both worlds, with Fast Throttle Control (FTC) for road driving, where most of the engine power is accessible in the first 30% of pedal travel, and a more linear, long-travel setting which is automatically provided when low-range is selected.
Digital Inputs from other vehicle systems
Td5s ECM interfaces with other electronic control units on the vehicle:
On automatic models, the new electronically-controlled automatic transmission.
The new air conditioning system, with its automatic temperature control (ATC).
The ECU that controls both the new anti-lock braking system (with its associated electronic brake distribution, traction control and hill descent control functions) and the new self-levelling rear suspension where fitted.
The Body Control Unit (BCU) which deals with various body systems and in particular the security systems requirements for engine immobilisation/re-mobilisation functions.
Safety inertia switch - this feeds a signal to the ECM to cut engine and fuel pump operation if a sudden deceleration (i.e. impact) is detected.
Td5 in Detail
A major part of the Td5 design and development effort went into the cylinder head, which has to be uniquely tailored to the EUI technology. The head, designed for maximum stiffness and for high clamping loads, is cast in LM25 aluminium alloy. The porting shapes have been developed in conjunction with AVL, the diesel design consultancy which assisted with both Tdi and L Series, and represent the latest achievements in flow management and combustion technology. The overhead camshaft bearings are formed half in the head, half in the cam carrier. These bearings are line bored with the head clamped to reproduce the normal head bolt loads, ensuring correct bearing tolerances in operation. Two valves per cylinder are operated via roller-type finger followers. Each cylinder also has a unit injector, driven from its own lobe on the camshaft via a rocker with a roller cam follower. A fuel gallery system formed directly within the head feeds fuel to each injector and returns excess fuel for recirculation, via a unique patented cooling arrangement, to the tank. Glow plugs are fitted in the head for cylinders 1 to 4, number 5 being omitted to package the fuel connection block. The cylinder head is designed so that it can be sub-assembled and tested, complete with injectors, before being assembled to the rest of the engine.
Cyclone Oil Cleaning System
An innovative Rover-patented system for removing oil mist from the crankcase breather air is built into the top cover of the cam carrier. It comprises five sequential cyclone chambers; as the breather air is drawn through the cyclones, oil droplets are centrifuged onto the chamber walls, to drain back into the lubrication system. Cleaned air is fed through a hose to a breather valve on the induction system.
The cast iron Td5 cylinder block is closely related in construction and bore/stroke dimensions to that of the L Series, and in fact, the brand new block-machining facilities at Solihull have been designed to handle both. Td5 uses the same through-bolt fixings for the cylinder head, which ensures that the cylinder bores are subjected to symmetrical compression. This feature helps to provide excellent bore stability, allowing close tolerances to be used for piston rings, minimising emissions and oil consumption. These objectives are also assisted by diamond micro-honing of the cylinder bores, now a proven Rover practice. Other features in common with the L Series include the patented vertical box-section channels cast into the sides of the block which stiffen the block as well as allowing rapid oil return. Adding further stiffness and refinement to the power unit assembly is an aluminium crankcase ladder frame with integral oil pump and feed galleries, and a structural cast aluminium sump.
As on Tdi and L series, each piston incorporates a compact re-entrant shaped combustion chamber set into the centre of the top face. The carefully-developed shape provides an efficiency-promoting fuel/air mix at the beginning of combustion. Two compression rings and one oil control ring are fitted to each piston, and the skirt is graphite coated. The upper compression ring sits in a nimonic steel piston insert to withstand combustion forces. Piston cooling is assisted by internal oil galleries, fed by oil squirt jets on the crankcase wall.
Td5s con-rods use the modern manufacturing technique of fracture-splitting the big end bearing cap from the main rod but for the first time on a forged rod. This technique provides an extremely strong and accurate register between cap and rod. The small end of the con-rod is tapered in side elevation, to provide maximum bearing area combined with minimum intrusion into the piston head, to optimise its strength. Td5 con-rods are common with those of all the current L Series units. They have therefore been thoroughly proven in several vehicle test programmes as well as demonstrating perfect reliability in customer use.
Following established practice, the Td5 crankshaft is cast in spheroidal graphite (s.g.) iron, with cold-rolled fillets for strength and fatigue resistance. Five crankshaft balance weights enhance the smoothness of running.
Dual Mass Flywheel
As part of the brief to achieve class-leading refinement, Td5 in manual transmission form has a new dual-mass flywheel. Working in a similar manner to a crankshaft damper, this has two masses connected by internal spring elements. It helps to smooth out individual cylinder combustion pulses, particularly when driving at low speed or when the engine is idling. Where automatic transmission is fitted, the torque converter provides a similar damping effect.
Camshaft & Drive
The camshaft, made for Land Rover by BMW, is ground from a forged steel billet and case hardened. It has three lobes per cylinder, two to operate the valves, one to power the EUI. Because of the extra duty of driving the high pressure injectors, a duplex chain drive from the crankshaft is used, rather than the now conventional toothed belt drive. Two composite nylon chain guides are used, one fixed and the other is automatically tensioned by spring and an hydraulic cylinder which has direct engine oil feed for correct pressure/speed relationship for good chain control.
The oil pump, mounted at the front end of the crankcase stiffening ladder, has a short chain drive from the crankshaft. It lifts oil from the sump and feeds it, via galleries cast in the ladder, to the cylinder block galleries. The oil squirt jets that provide piston cooling and small end lubrication incorporate pressure valves which close them off whenever the oil pressure falls below a set figure at low engine speeds.
Centrifugal Filter Design allows 12,000 Miles Between Oil Changes
In order to reduce cost of ownership and beneficial environmental effects an innovative approach has been taken to oil filtration on Td5. In addition to a conventional full-flow paper element primary filter, it also has a secondary centrifugal filter. Although this type of filter is well respected in such applications as large marine engines, this is the first time it has been scaled down for use in a vehicle of this size. It is mounted in a small pot by the exhaust manifold, and the centre canister is spun up to as much as 15,000 rpm by two fine oil jets. Particles down to 3 microns or less are retained on the inner wall of the canister, which is replaced every 20,000 km (12,000 miles). So effective is this device that the oil change intervals are also 20,000 km (12,000 miles) and the primary filter element lasts for 60,000 km (36,000 miles). This makes a major contribution to long engine life, customer convenience, reduced cost of ownership and significant benefits to environmental impact. The housing between the two oil filters contains a thermostatically-controlled oil cooler, which transfers heat to the cylinder block water jacket.
Td5 uses a new bottom hose-mounted radiator thermostat design that has two Rover patents. One concerns the positioning of the thermostat bulb to achieve ambient temperate sensing and system control. The other patent relates to the pressure relief arrangement which prevents premature opening of the thermostat or open/shut cycling by balancing water pump pressure against itself. The arrangement is designed to encourage fast warm-up, and in particular to provide cabin heat as soon as possible after a cold start. A new lightweight cross-flow radiator with aluminium matrix and plastic end tanks incorporates a separate cooling section for the fuel cooler and there is a new moulded polymer 460 mm (18 in.) one-piece cooling fan, with an integral, moulded-in viscous drive. Induction System Air is taken into the air filter via an under-wing nozzle, positioned to draw cool, dry air and to optimise the vehicles deep water wading capability. There is cyclone type intake system to give maximum dust extraction and longer life for the filter element. A thick-film type air flow meter provides the ECM with intake air mass data. The new Garrett GT20 turbocharger, developed specifically for Td5, is based on the highly successful GT15 concept used for the L Series diesel, with its new generation bearing system and improved aerodynamic characteristics. A new system of electronic waste gate modulation is used and there is a new lightweight air-to-air intercooler with aluminium matrix and plastic end tanks. The aluminium log-type inlet manifold has long curving intake pipes to enhance torque.
The entire fuel system is new for the EUI-equipped Td5 New Discovery. It begins with a new moulded plastic fuel tank, increased in capacity from 88.6 litres (19.5 gallons) to 95.5 litres (21 gallons) for even greater range. A two-stage electric pump is submerged in the tank, with a swirl pot to ensure continuity of supply on steep or rough terrain. The first low-pressure stage of the pump feeds the fuel to a canister-type replaceable-element filter mounted on the chassis. The Importance of Clean Fuel Because the high-precision EUI system requires very clean fuel, this filter is ultra-fine, able to retain particles in the 3-5 micron range, compared with conventional 15-20 micron diesel fuel filters. A water sensor at the base of this filter illuminates a facia warning light if excessive fuel contamination is detected.
A Patented System for Fuel Cooling
Even the return system plays a very important role in the efficiency of the Td5s EUI installation. It incorporates a fuel cooler unit, mounted on the side of the inlet manifold, which has its own dedicated coolant circulation to a separate, small diameter cooling tube mounted on the main engine radiator. The cooler has a thermostat which opens when the coolant inside it reaches around 70°C (158°F). Because the radiator tube is narrow, it constrains the flow, and super-cools the coolant. Land Rover has patented the fuel cooler and the partitioned radiator concept. Maintaining a steady fuel temperature is essential to achieving the remarkable performance and clean running of Td5. Without this provision, the bulk fuel temperature in the tank would steadily rise in use. Under high pressure injection conditions, overheated fuel would markedly reduce the fuel delivery from the injectors. While the ECM can compensate for reasonable fuel temperature variations by adjusting the fuel mapping, cool fuel gives the best results.
Land Rover Borrows from Medical Science
Return fuel from the cooler goes to the rear filter unit, where it passes through a special restrictor device. The principle of this restrictor has been borrowed from medical science - it is a micro-porous item similar to that used in blood drips, and allows air to pass but not fuel. This de-bubbles the fuel before it passes through the filter again and then returns to the fuel tank. Any air or vapour extracted from the fuel is also vented to the tank.
All Td5 engines in New Discovery are equipped with a combined 120 amp alternator and vacuum pump, driven off a single pulley. The vacuum pump supplies the brake servo and the EGR modulating valve. Likewise, the power steering pump and water pump are also mounted in tandem. According to vehicle specification, there may be up to two other ancillary machines - the air conditioning compressor and the pump for the Active Cornering Enhancement (ACE) system - to be driven by the auto-tensioned serpentine poly-vee belt drive on the front of the engine. There are four different lengths of belt to suit all permutations. The crankshaft drive pulley for the ancillaries has a triple-mass, dual spring configuration so that it not only provides torsional vibration damping of the crankshaft, but also protects the ancillaries from drive pulses.
A styled acoustic cover is fitted over the top of the engine as part of the New Discovery installation, which reduces noise levels by 8 to 10 dBA. There is also an under tray to reduce drive-by noise.
Information reproduced from Land Rover Press release