The Alfa Romeo 159 Sportwagon: Ride And Handling | Part Two

Alfa Romeo 159 Sportwagon

Alfa Romeo 159 Sportwagon

Steering

All Alfa Romeos are renowned for their direct, lively and responsive steering feel. The Alfa 159 Sportwagon is no exception, and is fitted with hydraulically power assisted, speed sensitive steering which achieves an effective balance between low speed manoeuvrability and high speed accuracy and feel. With just 2.33 turns lock-to-lock and a ratio of 12.7 degrees of steer for every degree of steering wheel input, the new Alfa 159 Sportwagon offers the most direct steering in its class.

The telescopic steering column is divided into two sections for comfort and safety. The lower section is collapsible to ensure that steering wheel position is maintained relative to the driver during an impact. The upper section offers both reach and rake adjustment to the driver. A steel bracket and a rigid magnesium mounting prevent vibration.

Careful matching of the steering geometry to the wheel arch volume has facilitated high steering angles even with the largest tyres fitted, affording the new Alfa a turning circle of just 11.1 metres between kerbs.

Q4 four-wheel drive

The V6 3.2 JTS engined Alfa 159 Sportwagon, 159 saloon and Brera are all equipped, as standard, with Alfa Romeo’s Q4 permanent four-wheel drive system. Q4 employs three differentials, with a self-locking Torsen C unit at the centre of the system which divides drive torque by a ratio of 57% to the rear wheels and 43% to the front.

Torque split between front and rear axles is constantly modulated by the central Torsen differential on the basis of available grip, with a bias towards the rear axle promoting sporting handling appropriate to the marque. Modulation is mechanical and continuous to guarantee the smoothest possible power delivery, and the system is further enhanced by the full range of electronic stability controls to guarantee optimum traction and performance under all driving conditions.

Q4 in more detail

This all new system was specifically developed and tailor-made to fulfil the performance and packaging requirements of Alfa 159, 159 Sportwagon and Brera. It is an evolution of the Q4 System first seen in the Alfa Romeo Crosswagon Q4, and has been developed in conjunction with ZF Gmbh.

Designed with the aim of further improving Alfa Romeo’s widely appreciated handling and traction characteristics, the system is a permanent AWD, based on a three differential concept, with the centre unit being a Torsen C type. The system has a base split defined as 43:57 front:rear, but changes its behaviour according to road and dynamic conditions, the Torsen unit being finely tuned to deliver the desired characteristics.

The Torsen C central differential and the front differential are integrated in one compact unit, built into the gearbox. The system has been designed to accommodate several engines, and manual and automatic gearboxes, both featuring six speeds.

Thanks to this integration, the power take off unit (PTU) is both light in weight, and compact. The latter has a ‘drop down’ design, to suit the chassis characteristics of the car, and is developed for high efficiency. It features a pair of helical gears along with a bevel gear set. The given package contstraints required a special arrangement of the internal components as well as a new housing split concept. The housing is constructed using an aluminium pressure die-cast process, and consists of two main parts and a lateral support tube. In the interests of high strength and good NVH (noise, vibration, harshness) performance, the gears are machined by grinding, which guarantees a consistent high quality level. PTU lubrication is separate from the gearbox, thus avoiding compromises in the oil choice, and the unit is sealed for life, meaning that it does not need any servicing during the life of the vehicle.

The rear differential is also designed for compactness, high efficiency, low weight, and quiet operation. It includes an NVH-optimised finish-ground bevel gear set, in which the ring-gear is attached to the differential case by laser welding. The housing is in pressure die-cast aluminium and includes three integrated mounting arms to interface with the rubber bushings, which isolate the rear drive module (RDM) from the chassis. High-strength-finish forged gears provide the interface to the drive shafts. Main rotating parts are individually balanced and lubrication is for life.

The propshaft is in tubular steel, built in three sections for improved rigidity and low NVH. It is linked to the body by two very stiff brackets and highly sophisticated rubber bushings, to enhance vehicle NVH behaviour. The propshaft is carefully balanced in four planes.

Alfa Romeo’s engineers have paid particular attention to NVH containment. Special design and testing activity has been dedicated to this issue with the aim of cutting any possible transmission-borne source of disturbance for driver and passengers, as this class of car demands. This activity has proved very effective, and has resulted in fine-tuned design of gear microgeometry, PTU and RDM casing, PTU to engine connection, propshaft dimensions, propshaft brackets and all the rubber bushings that connect the transmission to the vehicle body.

The NVH effort also includes some special features in the vehicle production line, where exclusive aligning and balancing systems are available: each car is checked for the all-important angles that the transmission has in respect to the vehicle body, and for final system balancing. Each component comes already balanced, but inevitable tolerance-induced imbalance is addressed with a sophisticated on-vehicle end-of-line balancing process, that brings transmission balancing to very high tolerances.

The newly developed PTU and RDM are assembled on a new assembly line, which includes the latest state-of-the-art assembly technology and error-proof systems. Every unit has to pass an end-of-line test before it is shipped to the vehicle assembly plant. The gears for PTU and RDM are produced in ZF’s main gear plant, where huge investments in highly sophisticated manufacturing technology have been made recently.

Published 6 June 2006 Melanie Carter

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