Overview: Peugeot 3008 Hybrid4
Peugeot has stated its intention to develop a range of hybrid vehicles of different shapes and sizes. Although the Company has not yet actually said that it will introduce a hybrid variant into every model range, there have been hints that this might be the case.
The modus operandi is to use a hybrid ‘architecture’ that allows the modular deployment of common hybrid components more-or-less off the shelf. The layout of the components — and, in many cases, the components themselves — must be the same irrespective of the shape and size of the vehicle to which they’re fitted. This makes the whole business much easier from an engineering point of view, and also much cheaper, both by reducing development costs and through the economies of scale.
At first glance, incorporating hybrid components into a drivetrain does not seem to be something that can be standardised, and it isn’t. Peugeot’s solution is not to incorporate the hybrid components into the drivetrain at all, but to fit an entirely separate, electric drivetrain to the rear of a car that would otherwise be driven solely by its front wheels.
An electric motor is incorporated into a multi-link rear suspension assembly along with a battery-pack and power-electronics; this complete module is then fitted to the car. The electric drivetrain is linked to the front of the car electrically and electronically, but not mechanically. The car’s front drivetrain — a two-litre diesel and automated six-speed manual gearbox, in the case of the 3008 — is coordinated with the rear electric drivetrain by the car’s Powertrain Management Unit to provide a full series-parallel hybrid. With four-wheel drive. Hence Peugeot’s name for its hybrid system: Hybrid4.
Power for the electric drive motor is provided by a 200V nickel hydride battery pack — not lithium ion, as Peugeot has decided that it would rather avoid the complicated battery-leasing arrangements that are presently the only way of making these more modern packs affordable for buyers. Given that you’ll pay €79 a month to lease a lithium-ion battery-pack for a Renault Fluence, we can understand Peugeot’s decision.
The Hybrid4 system is appealing in its conception. It can be applied to any floorpan that will accept the rear electric drivetrain module, which apparently includes most of PSA’s current range of platforms, and it offers ‘mild’ four-wheel drive without a propshaft. ‘Mild’ because the electric drive motor is not very powerful: 27PS and 100Nm continuous, 37PS and 200Nm peak.
The 3008 Hybrid4’s main power-unit is PSA’s 2.0 HDi FAP engine, rated here at 163PS. Aside from the hybrid, this unit is used in the 3008 range only with a six-speed automatic transmission; the hybrid uses an automated six-speed manual box, while manual transmission versions without the hybrid drivetrain use a derated 150PS version of the engine. Curiously, the quoted torque outputs of the 150PS and 163PS engines fitted to front-wheel drive 3008s are the same — 340Nm at 2000rpm — but the hybrid is rated at 300Nm at 1580rpm. We offer no explanation, and neither can Peugeot.
The engine complies with Euro 5 emissions standards and uses a combustion chamber architecture dubbed ECCS (for Extreme Conventional Combustion System). The turbocharger is a variable-geometry low-inertia unit with a maximum boost pressure of 170kPa, blowing through and air-to-air intercooler. Fuel is delivered by a common-rail system with a maximum injection pressure of 200MPa by way of eight-hole solenoid injectors. An octosquare particulate filter is fitted, working in conjunction with a fuel-borne rare-earth catalyst called Eolys; this allows the regeneration of the catalyst to take place at around 350° instead of 600°. It also accelerates the regeneration process. Eolys is a liquid, and each new car comes with a small tank of it, mounted near the main fuel tank. A built-in pump automatically adds the Eolys additive to the vehicle fuel. The material’s manufacturer, Rhodia, claims that new cars are currently being specified with enough additive for 250,000km of motoring — 1.7l of the stuff.
The snappily-named DW10DTED4 FAP engine has an alloy head and cast iron block. Double overhead camshafts are driven by a single timing belt; the valve timing is fixed. This 163PS engine is a development of the 136PS DW10B HDi unit. The cylinder head, internal engine components, intake, exhaust and timing have all been revised.
The Hybrid4’s gearbox is a six-speed electronically controlled sequential manual unit. Peugeot claims that, in automatic mode, the gearbox’s electronic management permits a significant reduction in fuel consumption compared with a conventional manual gearbox. In essence, the system mapping is better at judging gearchange points than a human driver. The BMP6 can be operated manually.
Electronic control over the entire drivetrain delivers an unusual benefit with the hybrid4: the rear electric drive activates during gearchanges, more or less maintaining drive torque to give the impression of seamless gearchanging.
The combination of the DW10 diesel driving the front wheels and the electric motor driving the rears can deliver up to 200PS: 163PS from the diesel, plus the electric motor’s peak output of 37PS. The duration for which the motor can maintain this output is not stated; its continuous power rating is 27PS. Peak and continuous torque outputs are 200Nm and 100Nm.
A selector control on the centre console allows the driver to choose between four different driving modes.
In ‘Auto’ mode, the electronics manage the entire hybrid system automatically, in particular the handover of power between the diesel engine and the electric motor.
‘ZEV’ mode (Zero Emission Vehicle) can be invoked when the nickel hydride battery pack had adequate charge. In this mode, the threshold at which the diesel engine would normally cut in is raised, allowing electric drive to b maintained until the driver demands sustained acceleration.
‘Four-wheel drive’ mode obviously sees the engine and electric motor working together. Clearly the car is also de facto operating in four-wheel drive mode when the motor boosts the diesel engine brief during periods of hard acceleration.
‘Sport’ mode delivers higher gear-change points; four-wheel drive is permanent in this mode.
The high-voltage stop-start system, with an output of 8kW, can power the electric motor if required in four-wheel drive mode.
The PTMU (Powertrain Management Unit) is an electronic control unit which manages the hybrid drivetrain’s operating modes in a way which is completely transparent to the driver. The system’s operation is biased towards low fuel consumption.
The power electronics are an inverter and converter. The inverter controls the torque of the electric motor by
regulating the current from the high voltage battery pack. This operates over a voltage range of between 150 and 270V. The converter converts the 200V from the NiMH battery pack to 12V to supply the on-board vehicle systems.
Manufacturers of power electronics, such as Bosch, are working to reduce the bulk of these ‘black boxes’ so that hybrid drivetrains can be applied to smaller vehicles.
The nickel metal hydride battery pack, developed by Sanyo, is fitted under the rear load area floor. A conventional 12V lead-acid battery is also fitted, in the engine bay.
Background: the 3008
Laser welding is used on the 3008’s bodyshell. This process involves welding in a continuous bead, in contrast to spot-welding, and holds out the prospect of an improved strength-to-mass ratio for a given structure: partly because the join is continuous, and partly because the required panel overlap is smaller. In the case of the 3008, laser welding is applied to the door frames and to parts of the rear structure. Peugeot modestly claims a mass-saving of 5kg for the 3008 structure as a result of this technique.
Another noteworthy feature of the 3008’s bodyshell is the Bogé impact absorber. This is a simple patented engineering trick to reduce the required length of impact-absorbing beam required to mop up a given amount of impact energy. Reducing the length of the impact-absorbing beams at the front of the car obviously reduces the front overhang.
A Bogé impact absorber uses two conical absorbers located between the impact absorption beam and the chassis leg. The assembly collpanses internally without affecting the chassis leg, maintaining the structural integrity of the engine compartment.
The engine compartment comprises three impact absorption structures, or channels, in a layout first seen on the 308. These structures are:
- A traditional upper structure formed by the chassis legs;
- A lower structure, which backs up the upper structure through the use of two sub-frame extensions — a feature derived from the 407;
- A third structure, consisting of reinforcements located above the front wheel arches and extending from the front windscreen pillars and door frame braces.
In the event of a frontal impact, 60 per cent. of the energy is distributed through the main structure, 20 per cent. through the lower channel and 20 per cent. through the top structure. This design is intended to transmit impact forces through the pre-established channels to areas specially designed to withstand and dissipate them: the bulkhead, the underbody, the sills and the front door braces spanning the A and B/C pillars.
In the event of an impact, the steering column retracts in a way similar to Audi’s ProConTen system in the 1980s.
Most of the 3008’s structure is steel; exceptions are the bonnet and front impact absorption beam, which are aluminium, and the front wings, which are produced from a composite material.
The most powerful versions of the 3008 are fitted with a system called dynamic roll control. This is a passive, engineered (that’s to say, non-electronic) means of achieving side-to-side damping of roll motions, and in our view should be standardised for all 3008s: models without dynamic roll control suffer from a severe side-to-side rocking motion during brisk cornering.
Dynamic roll control is a hydraulic system consisting of a central hydraulic module, built into the rear suspension cross-member, that connects the two rear dampers. This module is pressurised to 20 bar (2MPa) and consists of a floating piston and a hydraulic compensation reservoir; it acts like a third damper.
In corners, or when taking evasive action, the system links hydraulically the right and left rear dampers. The module’s internal piston does not move. This effectively increases the stiffness of the rear dampers, reducing the rate at which the body rolls (but not the ultimate roll angle that will be achieved at a given speed on a given curve). In a straight line — referred to as the ‘compression phase’ — the two rear dampers operate in a conventional fashion, independently, with the central module’ piston moving in response to the hydraulic forces created by the dampers.
The 3008 Hybrid4 will be produced in France — in Sochaux and Mulhouse — and marketed in the spring of 2011 in Europe. The RCZ Hybrid4, which has been shown recently, is not presently set for production; it uses the same platform and drivetrain as the 3008 Hybrid4.
|(1) Continuous / maximum.