The first car to benefit from the "Common Rail" diesel engine technology, the 406 ST HDi (High-pressure Direct injection) makes its Australian debut in sedan version.

Launched at the 1998 Geneva Motor Show the HDI design boasts dramatically reduced fuel consumption, improved performance, low noise levels and extremely low exhaust emissions.

Based on a cast iron cylinder block with alloy cylinder head and single overhead camshaft the turbocharged, intercooled, 2.0-litre four cylinder (DW10 ATED) engine, develops 82 kW and peak torque of 255 Nm at just 1750 rpm.

Developed in close co-operation with Bosch the HDI "Common Rail" injection system produces a super-fine fuel mixture which ensures immediate atomisation and optimal fuel/air mixture quality.

A combination of high fuel feed pressure (1350 bar), very small fuel-injector holes (less than 200 Microns) and computer management of each system component adds up to extremely accurate and efficient engine operation.

The HDI Common Rail engine's combustion chamber has been developed using CAD three-dimensional simulation of the combustion/injection process as well as aerodynamic modelling.

The overall result is precise fuel injection and timing, more complete combustion, greater efficiency, reduced fuel economy and lower exhaust emissions.

On the open road the 406 ST HDi (using just 4.6 L/100 km) has a theoretical range in the order of 1500 km.

The efficiency of the HDI engine's high-pressure direct-injection process makes it one of the most environmentally-friendly diesel engines in the world.
It boasts:

• a 20 percent decrease in CO2 emissions
• a 40 percent decrease in carbon monoxide (CO) emissions
• a 50 percent decrease in unburned hydrocarbons
• a 60 percent decrease in diesel particulate emissions

The HDI engine is also highly effective in terms of smoke emissions, releasing virtually no smoke over 95 percent of its operating range.

As well a sophisticated deNOx catalytic converter which reduces NOx emissions by 12 percent is being developed as part of the HDI program.

Noise and vibration have been reduced in the HDI engine through an emphasis on reduction at the source, optimising the engine's structure and the addition of an acoustic engine shield.

Vibration is reduced thanks to the HDI's pre-injection process in which the engine's computer sends a control pulse to the injector (lasting ten micro-seconds).

This small pulse of fuel (less than one milligram) gradually increases the temperature of the combustion chamber before the primary injection for smoother and more gradual combustion.

This process lowers engine noise at idle by over three decibels (dBa), reducing the HDI engine's noise levels to those of a similarly sized petrol engine.

Optimisation of the overall engine structure, paying particular attention to the cylinder casing walls, has reduced vibration and noise by a further three dBa and an acoustic shield covering the engine's upper structure lowers noise by a further two dBa for an overall eight dBa gain.

Maximum power and torque figures for the HDI are similar to Peugeot's current 2.1-litre turbo-diesel engine however maximum power of 82 kW is developed 300 rpm lower (4000 rpm) and peak torque of 255 Nm comes at just 1750 rpm (250 rpm lower).

The systematic lightening and friction-reduction of all HDI engine moving parts has resulted in a six percent decrease in friction and a weight advantage of 22 kg (12 percent), compared with the current 2.1-litre turbo-diesel.

The result is strong pulling power at very low engine revs, excellent throttle response over a wide range of engine speeds, even greater reliability and improved fuel economy.

The most immediate and obvious advantage is increased driving pleasure, the result of higher acoustic and vibration comfort, as well as much higher torque from the lowest engine speeds (230 Nm from 1500 rpm).

This degree of torque adds the benefits of better acceleration and safety, enabling the 406 HDi to motor at low rpm and significantly reduce (by 20 percent, or 1.6 L /100 km) the average fuel consumption, compared with the 2.1 litre turbo diesel (XUD 11 BTE) it replaces.

Peugeot diesel customers have three key expectations:

• Economy in operation
• Driving pleasure, in particular through the flexibility available at low rpm, and
• Robust build and longevity, especially for those covering long distances

The HDi technology exceeds these requirements and dispels the "conventional wisdom" which says the diesel customer is buying a compromise.

The first surprise comes at start up, without any pre-heating required in ambient temperatures above 0o C. As well, low noise and vibration levels deliver a degree of comfort in the 406 HDi noticeably superior to its predecessor, particularly at low rpm.

These are more than straight numerical improvements. The tangible benefits have the potential to transform customer expectations concerning diesel engines.

Forty years ago, at the 1959 Paris Motor Show, Peugeot launched the 403 diesel and since then has retained its enthusiasm for the technology.

Peugeot launched the world's (then) smallest diesel engine in the 204 in 1967, and again with the first European turbo-diesel in the 604 of 1979.

Unrivalled in the diesel domain, Peugeot will have equipped more than eight million vehicles with its XUD engines over the last 20 years of this century.

And the 406 becomes the marque's first model to be equipped with the HDi (High Pressure Direct Injection) Common Rail diesel engine.

It is the first in an eventual family of HDI engines planned for the future, in 2.0 and 2.4-litre versions with turbo and turbo-intercooled variants as well as two and four-valves per cylinder configurations available.

Developed over 36 months the HDi engine represents an investment of AUD$750 Million, one third devoted to research.

The Common Rail high pressure injection system consists of feeding, via an electronically controlled high pressure pump, a rail (or common conduit) functioning as an accumulator of fuel under pressure.

This rail is connected to injectors with five injection nozzles of very small diameter in an electro-hydraulically controlled head, ensuring a very finely atomised spray directly into the combustion chamber.

The combustion chamber recessed into the piston crown is specially shaped to result in a thoroughly blended air/fuel mixture.

A particular feature of the system is electronic control of the duration of injection, according to the quantities of fuel and the pressure in the rail.

Mapping is worked out so that the system observes this balance in line with the way the car is driven.

This feature is especially used to ensure that in advance of the main injection there is a pre- or pilot-injection, regulated for flow and duration. A more gentle and progressive combustion reduces the levels of noise and pollutant emissions, and gives better performance at low rpm.

HDi, a Common Rail system, combines the following elements:

• A pump unit immersed in the tank with a total flow capacity of 140 litres/hr,
• An engine-driven high pressure pump with regulator at between 150 and 1350 bars,
• A "rail" or common conduit which supplies the injectors and regulates variations in pressure,
• A rail pressure sensor with input to a computer,
• Electro-hydraulically controlled injector ports,
• A camshaft position sensor to synchronise injection with engine speed,
• An electronic control system comprising a computer, sensors for water temperature and turbocharger pressure, an accelerator pedal sensor, and an rpm and actuators sensor ( in particular for the electro valves for the turbine and exhaust gas recirculator).

Adaption of HDi specifically for the 406 comprises:

• A fuel circuit with a low pressure pump. The return line to the tank has a cooler to reduce the temperature which has been raised by high pressure injection,
• Snap-on connectors for better safety and easier fitting,
• A classic air intake with an air/air exchanger,
• A flowmeter which, via the computer and an electrol-pneumatic system, regulates the turbine and depollution circuit as well as limiting smoke emission,
• An electronic accelerator control and potentiometer regulating fuel flow,
• Special engine support components adapted to the engine's movement (support shims and anti-torque rods).

Overall consumption is down by over 20 percent compared with the already excellent fuel economy returned by the indirect injection turbo diesel being replaced (XUD11BTE).

In urban use the gain is almost 25 precent and out on the open road, with the HDi using just 4.6 L/100 km the theoretical range is of the order of 1500 km.

The 406 HDi is not only frugal but also less pollutant, since the greenhouse gas emissions are reduced by 18.5% compared with the previous engine.

The objective in designing the HDi engine was to save weight, principally in the moving parts, so as to aggregate the benefits from reduced weight and lower friction.

Overall, the weight-saving on the engine is 22 kg or 12 percent relative to the engine being replaced. In particular, weight-saving effort concentrated on the valves (-50 percent), the conrods (-15 percent) and the pistons.

These weight savings directly influence fuel economy and friction reduction compounds the effect. Note in particular the softer valve springs, thanks to the valves being lighter.

Similarly, reduced piston clearances are possible because of a cylinder honing technique. The engine also employs a method of valve actuation by rocker arms with rollers, instead of the traditional camshaft friction on the rockers. This further improves fuel consumption, mainly at low rpm, by some two percent.

The relative turbo pressure of +1 bar is controlled by the engine computer. At a steady speed between 2500 and 3000 rpm and in all gears, the pressure can be cut to 0.7 bar.

Not noticeable on the move, this frees up a corresponding amount of energy resulting in a fuel economy of four percent. At other times, in transition phases during acceleration, a slight over-boost adds liveliness without affecting engine reliability.

Thanks to the engine torque available from the Common Rail system at low rpm, the usable torque curve becomes wider and can be exploited via a gearbox with wider ratios.

For example, the 6.5 percent wider spacing (46.99 km/h vs. 44.15 km/h in 5th gear with the XUD11 BTE) makes for a significant saving in fuel, because the engine's flexibility involves less changing down to regain speed.

Robust build and longevity
Reliability has been "designed in" to every aspect of the 406 HDi.

As for all Peugeot engines servicing intervals, previously set at 10,000 km, now go up to 20,000 km for the 406 HDi. That means lower maintenance costs and less time off the road for servicing over the life of the vehicle.

The Common Rail system (high pressure controlled injection) has endowed this engine with very high torque and the ability to deliver it across a wide rpm range.

With maximum torque of 255 Nm at 1750 rpm (vs 2000 rpm for the XUD 11 BTE), and 190 Nm even from 1250 rpm, the 406 HDi offers flexibility and virtually no "turbo lag" effect.

The net effect is better low rpm performance, less down-changing and therefore better economy, as well as strong acceleration for safer overtaking.

Great attention as paid to this prime objective, which is still a critical factor deterring the owners of petrol models from buying diesels. The progress made on this front springs from the three following aspects:

The sophistication of the system of injection includes a pre-injection phase and a progressive temperature rise ahead of the main injection. This slows down the spontaneous flame-spread as well as reducing the amount of fuel burned at the beginning of combustion.

This special feature, unique to Common Rail turbo diesel engines, greatly reduces the characteristic combustion noise of diesels, mainly on the over-run, and results in a improvement for the 406 HDi of the order of 3db compared with the previous engine.

The prominent ribbing which stiffens the walls of the engine crankcase, plus the reduction of friction and general weight-saving for moving parts, allows a low level of vibration to be achieved. The resultant acoustic improvement is again some 3db, or a 50% cut in the acoustic output.

To further reduce engine noise, a bi-material moulded blanket covers the whole of its upper section as well as the injection equipment.

This blanket also has a double layer of sound-absorbent material to deaden the noise level.

Because of certain technological choices, the 406 offers a degree of comfort which does not affect its dynamic qualities. E.g. the steering power-assistance which varies with engine speed makes parking more comfortable, while the valved front and rear shock absorbers give a smoother ride.

The hydraulically operated clutch is light, as is the electronic accelerator; and the ML5 T gearbox is smooth and positive.

As for the design of the HDi engine itself, the acoustic and vibration comfort is the outcome of extreme care over its installation in the 406.

• To minimise the transmission of engine noise into the body shell and to preserve acoustic comfort, in particular avoiding rumble, engine mountings,
  Hydraulic dampers (valved on the right hand side) are dynamically stiffer,
• Cast iron upper anti-torque struts now incorporate rubber buffers,
• A lower strut is stiffer and a counterweight at its connection prevents noise being transferred to the sub-frame.
• Additionally, the exhaust includes a flexible length which is better for accomodating clearances; its fastenings to the sub-frame, with two rubber components reduces potential vibration transfer to the body shell.

To improve comfort still further, the DW10 ATED is now fitted with a dual engine flywheel aimed at filtering the acyclic vibrations naturally found at low engine speeds.

A conventional crankshaft actually spins true, but brakes and accelerates at every revolution.

This phenomenon, which is most noticable at low engine speeds, is filtered on HDi by a flywheel made in two sections, between which a damper system has been introduced, absorbing the acyclic vibrations.

The thermal comfort of the 406 HDi was the subject of considerable attention, because the HDi engine gives off little heat compared with a conventional unit.

A 1000W electrical resistance, located in the air intake just ahead of the aerotherm, allows the incoming flow of air to be reheated before it enters the cabin.

The engine computer actuates the resistance when inlet air temperature is below 100C and switches it off when the water temperature reaches 800C.

In the event of a drop in battery voltage, a power reduction maintains the car's vital functions by only drawing a 650W or even 350W basic supply.

In spite of the Class 15 alternator (260W - 157 A) fitted to the 406 HDi, volts drop can occasionally be provoked by low speed driving with maximum equipment in use (heated rear screen, heated seats, headlamps, etc ...)