D5 – Volvo’s Own Diesel Engine

D5 – Volvo’s Own Diesel Engine

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During the 1980s, Volvo had a secret project known as ‘X-100’ which would eventually lead to the 850 – the company’s ‘first’ front-wheel drive sedan – in 1991. It was the most expensive project ever undertaken by the Swedish company but was vital for its future.

Part of the X-100 project included the development of an all-new all-aluminium engine which would serve as the basis for a new engine family in the 1990s and beyond. The X-100 engine evolved into the B5xxx engine family which has since been produced in a various forms and used in virtually all current models.

The original X-100 engine project also examined the possibility of using other fuels besides petrol and a diesel prototype was studied but never built. Now, some 14 years later, the diesel version finally appears and is Volvo’s first in-house diesel powerplant (previous Volvo diesels have used engines supplied by other companies).

Coded ‘D5’, the new engine is said to ‘turn a new leaf in Volvo Cars’ engine history’. It is evidence of just how important it is for the company, a unit in the Ford Premier Automotive Group, to be able to offer a modern diesel engine in the premium segment.

In the development brief for the D5, one obvious parameter was to utilise one of the most compact and strongest engine blocks on the market: Volvo’s own 5-cylinder aluminium block, which was originally launched in the Volvo 850 in 1991. This block was designed and dimensioned from the very outset to be able to accommodate diesel power. Since the cylinder head too is made of aluminium, the D5 weighs just 163 kgs without the gearbox – a major benefit since low weight plays a major role in ensuring high performance and low fuel consumption.

The D5 produces higher torque than the most powerful 5-cylinder petrol engine in the Volvo range. What is more, this high torque is available at even lower revs. Besides having 120 kW/163 bhp, it pumps out no less than 340 Nm at just 1750 rpm, compared with the 330 Nm at 2400 rpm produced by the T5 petrol engine that also develops 184 kW/250 bhp.

This means there is plenty of power on tap, irrespective of engine speed and driving style, providing a high degree of flexibility and hence driving enjoyment. Used in the coming XC70 all-wheel drive model, it is claimed to provide the car with a capability to get from standstill to 100 km/h in 11.5 seconds and reach a top speed of 195 km/h with a 5-speed automatic transmission.

Low fuel consumption is one of the strongest reasons for the customer to buy a car with a diesel engine. And with the XC70 D5, Volvo’s factory testing has returned around 11.85 kms/litre (approximately 33.2 mpg), giving the car a range of up to 810 kms.

This low fuel consumption has been achieved with a range of well-integrated factors, including low internal engine friction owing to simple engine architecture and a single cam belt-drive system for camshafts and injection pump; roller finger followers in the valve and cam systems, for the lowest possible friction in the cylinder head, particularly at low revs and in urban operation; lightweight moving parts, particularly pistons and connecting rods, resulting in less vibration, lower loads on bearings and crankshaft and thus lower friction.

There’s also an efficient combustion system with four valves for each cylinder and injection with a centrally-positioned vertical injector, plus the relatively (for a diesel engine) modest compression ratio of 18:1 which is beneficial as regards combustion pressure, reducing mechanical loads and friction.

The major source of this engine’s enormous reserves of torque is the turbocharger, which is of the VNT or Variable Nozzle Turbine type. With this system, the turbine on the intake side has movable guide vanes that change position to provide optimum flow conditions and a high turbine efficiency rating, throughout the engine speed range. This permits high boost pressure from low engine speeds, and thus a flatter torque curve and higher power output.
The movable guide vanes are controlled by the engine management system, adjusting gas flow to the turbine to ensure optimum efficiency. The result is that the engine responds instantly to the throttle, providing excellent drivability.

Common-rail technology plays a vital role in modern diesel engines. The common-rail system adopted in the D5 is a second-generation development, featuring a higher pressure and load-responsive volume and pressure control. Volvo claims that this makes it one of the most modern and advanced systems in the automobile industry today.

The amount of fuel and the injection timing are controlled electronically by fast-acting solenoid valves. Fuel is injected directly into the cylinders under exceptionally high pressure, up to 1600 bar. The result is extremely finely atomised fuel, ensuring that combustion is as efficient as possible, while at the same time minimising emissions of nitrogen oxides (NOx) and particulates.
In order to further reduce exhaust emissions, the D5 is equipped with the very latest advances in EGR (exhaust gas recirculation) technology. With this system, some of the exhaust gases are returned to the combustion system, further reducing emissions of NOx.

Increased efficiency and precision are achieved with the fast-acting EGR valve, which is directly electrically operated. The recirculated exhaust gases are cooled in a special EGR cooler before being mixed with the intake air.
This advanced EGR system sharply reduces NOx emissions, while retaining high fuel efficiency. The EGR cooler itself provides a further 7% reduction in nitrogen oxides compared with a system without cooling.

Hydrocarbons (HCs) and carbon monoxide (CO) – the main components of the remaining exhaust gases – and some of the particulate emissions are cleaned with the help of an oxidising catalytic converter. The D5 is said to easily exceed the Euro 3 standards, halving exhaust gas emissions compared with Volvo’s previous passenger-car diesel engines.

The X-100 project
The late 1970s were a critical period for Volvo: as a result of economic recession, the company finances were in dire straits and sales were significantly down. The 240/260 models had always been the revenue-earners, especially from the giant US market which took the bulk of production, but with the energy crisis, the big Volvos began to lose their appeal not only because of their age.

Hakan Frisinger, then president of Volvo Car Corporation, called a meeting in mid-1978 to chart the company’s course for the next decade, with a view of developing competitive models for the next century. A project team was formed for the crucial assignment that would decide Volvo’s market position in the distant and somewhat uncertain future.

To underline the need for a technical generation shift in its products, the project was given the codename ‘Galaxy’. It would consume more than 250 billion Swedish kronor (at 1991 values) and become Volvo largest industrial project ever.

The Galaxy project, initiated in the aftermath of the energy crisis, was to develop Volvo’s future models. However, Project Galaxy was more than just developing new cars; it was also a major industrial venture which was to bring forth new technologies, new working methods and even new plants. It had many sub-projects which enabled Volvo to develop several different alternatives from the same basic concept, using common components, for the flexibility required to match market requirements – a capability vital for a small manufacturer.

The first years of the project were spent developing the X-100, a prototype aluminium 1.8-litre 4-cylinder engine with 4-valve technology and a modular concept that allowed various cylinder numbers. In theory, from having 5 cylinders displacing 2.5 litres, it was possible to go right down to a 2-cylinder 1.0-litre engine.

It could run on petrol or diesel and was intended for a car weighing 1,000 kgs upwards. Significantly, it was designed for use with front-wheel drive… a clear sign that Volvo – while expressing loyalty to the rear-wheel drive layout – had, during the 1980s, been seriously looking at FWD.

The X-100 engine went through a fairly smooth R&D phase and Volvo’s engineers were to develop a 5-cylinder version while Porsche would develop a 6-cylinder version. But one engineer in Volvo did not like the idea of Porsche’s involvement and “designed” a six in his spare time. His commitment impressed the management and the 6-cylinder project was retained by Volvo with Porsche asked to do fine-tuning and optimisation.

Actually, the X-100 had started off as a powerplant for a small car in an energy-oriented society and with many interesting technical solutions, it became the basis of Volvo’s new engine family and powertrain programme for the 1990s. Among the technical requirements laid down were a service life of more than 20 years and an operating life of 200,000 kms without needing dismantling.

The first car that was powered by the new engine family was the 850, introduced in 1991. Although Volvo had been producing small FWD models like the 360 and 480, these were never considered ‘true’ Volvos and the 850 was regarded as the company’s ‘first’ FWD.

The advanced thinking that went into the design of the original X-100 engine is now evident when, more than 10 years after the concept was conceived, it is still possible to develop the D5 engine from it.


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