Porsche Technical HighlightsPublished 25 October 2002
Ceramic Brake Discs
The revolutionary Porsche braking system
Dr. Ing. h.c. F. Porsche AG is the world’s first car maker to develop an internally ventilated ceramic composite brake disc for use on a road car. Fitted as standard on the 911 GT2, the Porsche Ceramic Composite Brake, or PCCB, represents cutting-edge braking technology that sets new standards for road cars, particularly in the crucial areas of brake response, fade resistance, weight and durability.
Weight reduced by 50 per cent
In common with the excellent Porsche conventional metal brake discs, the ceramic composite discs are cross-drilled and internally ventilated. They are also very similar in size to the grey-cast iron discs. But compare their weights and the two types of disc are poles apart - the PCCB disc is more than 50 per cent lighter. This cuts the overall weight of the car, on the GT2, for example, by 16.6kg, which not only saves fuel, but reduces the unsprung masses, resulting in a further improvement of damper response and behaviour.
Frictional values remain consistently high, even in extreme conditions
On the road, PCCB ensures exceptional results. In conjunction with all-new brake pads, the ceramic brake disc ensures very high and extremely consistent frictional values throughout the entire deceleration process. Brake temperature - a crucial governing factor in the stopping distances of metal brake discs - becomes a minor factor with the PCCB set-up, since both the brake pads and ceramic brake discs retain their high level of friction whether they are hot or cold. This spares the driver unpleasant surprises when, for instance, having to apply the brakes from very high speed. In such circumstances, conventional metal discs can initially appear to provide strong levels of retardation, but as they heat up they lose their frictional coefficient, forcing the driver to press down on the pedal even harder.
The new Porsche brake system also offers advantages during emergency braking at low speeds; because of the high friction levels of PCCB’s discs and pads, maximum braking force is applied from the first touch of the pedal without the need for substantial pedal force or electronic assistance. The system works supremely well in wet conditions, too, as the new generation brake pads do not absorb as much water as the conventional variety. Wet weather performance and response are also enhanced by the cross-drilling of the discs.
Even under the most severe of driving conditions, including track work or downhill runs on mountain passes, the PCCB system shrugs off high loads. Compared with metal discs, surface abrasion is very low thanks to the extremely hard surface of the ceramic composite material. As a consequence, the working life of the brake disc is greatly extended. A further contributory factor to the extraordinary durability of the PCCB discs is their total resistance to corrosion - they are unaffected by road salt used for winter gritting.
Two engine concepts in one
Porsche now offers VarioCam Plus on all 911 models. Camshaft adjustment on the intake side (VarioCam) is now supplemented by valve-lift control, also on the intake side (Plus). First featured on the 911 Turbo, this new system is able to optimise engine outputs and performance, while at the same time reducing fuel consumption and exhaust emissions, and improving smoothness and overall refinement.
The valve-lift adjustment system comprises switching cup tappets on the intake side of the engine operated by a 3/2-way switching valve. With two different cam lobe profiles on the intake camshaft, the engine always runs on the appropriate lift curve, with the cams switching from one to the other as required. The cup tappets are made up of two interacting tappet elements, locked one against the other with the aid of a bolt. This creates a direct link firstly between the inner tappet and the small cam, and secondly between the outer tappet and the large cam. A hydraulic compensation unit for valve play is integrated in the tappet’s force flow line.
Variable valve lift
The overall effect of VarioCam Plus is to create an engine with two opposing sets of characteristics; at one end of the scale is its prodigious power and torque outputs, at the other its low emissions and fuel consumption. While the engine is idling, valve-lift is controlled by the small cams to a maximum limit of 3.6mm and valve timing optimised to keep valve overlap to a minimum. The low valve lift serves to reduce friction, significantly increases the charge motion thanks to the very short opening times, and cuts emissions from the previous combustion cycle. This helps reduce fuel consumption and emissions by up to 10 per cent.
However, under part-load the engine runs more efficiently if the exhaust gases are recirculated internally, minimising any throttle effect and reducing fuel consumption. This is achieved by swapping over to a valve-lift strategy that provides a large overlap area to draw in exhaust gases. Finally, to ensure maximum power and torque under full-load, there is the need for a highly efficient gas charge cycle with minimum losses. This is achieved through an uncompromising cam lobe profile giving a maximum of 11mm valve-lift and suitably adjusted valve opening and closing times. VarioCam Plus also helps the engine’s cold-start characteristics, and reduces emissions during the engine’s warm-up cycle.
Both of VarioCam Plus’s two systems – (camshaft adjustment and valve-lift control) are masterminded by Motronic ME7.8 engine management, designed especially for this application and offering a high standard of operating and computing capacity. This ‘brain-power’ is vital, since there are many and various factors required for controlling VarioCam Plus, including engine speed, throttle pedal position, engine oil and coolant temperature, and current gear ratio. The driver’s commands in terms of engine power and torque are compared against control maps within the system, the Motronic control unit then deciding within milliseconds how VarioCam Plus should respond.
With Five and Six Gears
In addition to five-speed Tiptronic S on the 911 and Boxster, Porsche offers a six-speed Tiptronic transmission for the first time in the Cayenne. This is a brand-new development tailored specifically to the high torque and power of the Cayenne Turbo. Featuring appropriately modified shift units and a special torque converter, this new transmission is also available as an option on the Cayenne S.
As well as the larger number of gears providing a wider range of individual gear increments, the option to shift gears manually simply by touching the selector lever in addition to the existing toggles on the steering wheel is another new feature. All the driver has to do is press his thumb forward slightly to shift up, and pull it back to shift down. To avoid possible gearshift errors when driving offroad, the toggles on the steering wheel are deactivated when the offroad reduction gearbox is in mesh, meaning that the driver can only shift gears by moving the gear selector with Tiptronic, using gearshift control maps to ensure optimum dosage of power on rough terrain. A further feature of Tiptronic S in the Cayenne is the hill-holder function which prevents the car from rolling backwards when setting off in a forward gear even on a very steep gradient.
Automatic convenience, manual control
A distinctive advantage of Tiptronic S is the manual override facility, operated by a toggle switch on the steering wheel. It allows the driver to change gears at will, even when the main gear selector is in automatic. When the manual mode is brought into play, it remains ‘active’ for at least 8 seconds, this minimum period being extended when the car is on overrun - for example on a downhill gradient - in order to capitalise on the braking effect of the engine, or under lateral acceleration in bends when the driver shifts down early for for even more sporty driving.
As long as this mode is active, the letter ‘M’ and the current gear choice appear in the right-hand instrument face. Meanwhile, the transmission retains its kickdown function enabling the driver to shift down spontaneously whenever required; road and engine speed permitting, the automatic transmission will shift down a maximum of three gears as soon as the driver stamps down hard on the throttle pedal.
Your right foot counts
In automatic mode Tiptronic S offers various programmes with different control maps, automatically activated as a direct function of the driver’s style of motoring and the route he is taking. The range of shift points extends from a particularly economical strategy - early up-shifts and that keep the revs low - activated when the car is being driven gently, through to a sporting protocol that hangs onto revs as long as possible under hard acceleration. The crucial factor in how and when the gearbox changes up and down is the driver’s foot on the throttle pedal. For example, if the pedal moves swiftly and through a long travel, as it would, say, on a winding road taken at speed, the gearshift points change to a dynamic strategy. Short, gentle movements activate a ‘lazy’ strategy. Over and above its ability to ‘recognise’ the driver’s style of motoring, Porsche Tiptronic S also features the following highlights:
• A warm-up programme preventing the transmission from shifting up early in order to increase the temperature of the catalytic convertor as quickly as possible (reducing emissions), at the same time allowing the engine to warm up smoothly and without strain.
• Active gearshift strategy that immediately moves the shift points to the most sporting and dynamic programme whenever the throttle pedal is pressed down fully and quickly.
• Suppression of upward gearshifts on the overrun when the throttle is suddenly released, for example before entering a bend.
• Downward shift to the next lowest gear when applying the brakes, in the interests of optimum engine braking.
• After an active downshift, the transmission changes up sequentially, rather than shifting immediately to the highest possible gear.
• Hill recognition that retains lower gears as long as possible in uphill or downhill gradients.
• Retention of gears in bends to prevent unsettling mid-bend upshifts.
Porsche Side Impact Protection
The POSIP (Porsche Side Impact Protection) side airbag system is standard on all Porsches. It comprises side airbags offering the driver and front passenger a broader scope of protection than conventional side airbags are able to provide. Another special feature of POSIP is that the side airbags give the same superior protection in an open convertible.
Housed in the door panel, the airbag modules differ from conventional units in their large volume and geometry. In a side collision this ensures not only the usual protection at chest level but at head level, too. The superior standard of all-round safety ensured by the POSIP system is maintained regardless of the position of the front seats.
When triggered, the side airbags are inflated by a hybrid gas generator. As a consequence, the system’s pyrotechnics are kept to an absolute minimum, serving primarily to open the valve that allows an argon-helium mix to escape from a pressure vessel into the gas-tight airbags. The airbags are triggered by sensors on the sills beneath the doors and a central actuator on the instrument panel.
Porsche Traction Management
A new generation in four-wheel drive
In the new Cayenne, Porsche has succeeded in combining outstanding power and torque, sporting and agile handling as well as excellent driving dynamics with superior performance on and offroad. Porsche Traction Management (PTM) featured as standard in the Cayenne, feeds 62 per cent of the engine's power to the rear and 38 per cent to the front wheels in the basic mode. Using a multi-plate clutch operated by an electric motor and controlled electronically, the driver is able to vary the power split as required, if necessary even feeding 100 per cent of the engine's torque to the front or rear wheels.
Porsche Traction Management is an all-new generation of four-wheel drive with a significant influence on the Cayenne's dynamic performance. The map-controlled front-to-rear lock and the optionally available rear axle differential lock not only respond to lack of traction on the front or rear wheels, but also incorporate sensors within the PTM system measuring the speed of the car, lateral acceleration, the steering angle and operation of the throttle pedal which provides data for PTM to determine the optimum lock on both axles and distributing the power actually required to the front and rear wheels. PTM may therefore be compared with an intelligently networked electronic system providing superior driving stability and safe lane change behaviour both at high speeds and when driving on snow and ice at moderate speeds.
This new technology offers a whole range of outstanding results:
• Excellent driving stability and traction in all situations, regardless of the frictional coefficient • Better steering provided by the front-to-rear differential lock which opens up to avoid any understeer effect • Better control when driving to the limit ensured by the front-to-rear differential • Enhanced directional stability and better road grip by operating the front-to-rear lock as required • Better traction by increasing locking action before the wheels start to spin
Porsche Stability Management (PSM) also featured as standard in the Cayenne remains constantly in touch with PTM but only intervenes when the vehicle reaches its limits. Masterminding essential systems such as ABS, ASR and the ABD Automatic Brake Differential, PSM cuts in immediately under critical over- or understeer conditions and tells PTM to open up the locks in order to restabilise the vehicle by applying the brakes specifically on individual wheels.
A champion off the beaten path
The Cayenne successfully combines outstanding performance on the road with equally impressive offroad abilities. It is already a genuine master off the beaten path in its standard configuration with intelligent four-wheel drive enabling the Cayenne to easily cross light terrain without any modification of the traction systems. On rough terrain the Porsche Traction System then uses the reduced-ratio gearbox featured as standard in the torque distribution unit.
With its reduction ratio of 2.7:1, the reduction gearbox is ideal for even the most extreme offroad manoeuvres, easily handling steep gradients and downhill passes. Activating the low-range mode by means of a toggle switch on the centre console, the driver can automatically prepare several control systems for offroad driving conditions: PTM switches over to the reduced ratio for offroad requirements and changes to a special offroad control map activating the differential locks, PSM responds by setting ABS and ABD to a special traction mode for offroad driving, and the air suspension - featured as standard in the Cayenne Turbo - automatically raises the entire vehicle to its offroad level. Porsche is the first manufacturer to offer this combination of systems all controlled by one central offroad switch and thus significantly facilitating operation of these systems when driving under extreme road conditions.
Porsche Communication Management
New PCM operating at the speed of light
New multi-media data exchange technology bearing the name MOST (Media-Oriented Systems Transport) is featured as of the 2003 model year in all Porsche models. The principle advantage of this data bus system is that the use of fibre optics ensures that data is exchanged between the various units without any loss of quality and at a very high speed. The radio, CD changer, amplifier units and the telephone module are all masterminded through MOST fibre optics, ensuring high quality audio transmissions. When choosing his car the customer decides the specific units to be integrated in the system. Networking Porsche Communication Management (PCM) with the instrument cluster via the CAN (Controller Area Network), the driver is able to view the radio station currently tuned in, music titles, incoming telephone calls and navigation pictograms in the instrument cluster display. Basic telephone functions such as receiving or ending telephone calls can be controlled straight from the on-board computer switch on the steering column or via the multifunction steering wheel on the Cayenne.
PCM: a new highlight in electronic management offering supreme comfort and convenience
Porsche Communication Management (PCM) comes in an all-new, user friendly design featuring a double tuner, a CD player, a trip computer and, as a further option, a GSM dual-band telephone. Main features include the 5.8-inch (Boxster, Carrera) and 6.5-inch (Cayenne) colour screen providing crystal-clear pictures in 16:9 aspect ratio and the 12-digit keyboard for entering telephone numbers or the frequency of a certain radio station directly with the utmost simplicity. A small drawer beneath the 12-digit keyboard accommodates the user's SIM card, dispensing with the need for an adapter when making telephone calls. The new PCM system also facilitates the process of inserting the small card, its exact position being shown on the display.
The buttons beneath the display provide direct access to the individual menus such as telephone operation (Tel button), trip computer (Trip button) or the navigation system (Navi button). Two new buttons provide direct access to the Set (Set button) and Return (button with a bent arrow) functions avoiding the need to “jump around” from one sub-menu to another.
Apart from interference-free radio reception ensured by a modern double tuner constantly seeking the best frequency, and significantly improved voice reception quality in telephone calls provided by full-duplex transmission, the navigation module in particular features the following outstanding highlights:
• Large choice of navigation configurations and great flexibility when displaying and selecting navigation functions: Points of interest can also be presented on the map in the display, informing the driver of, say, car parks, restaurants or service stations. • A considerably faster map refresh rate and on-demand road junction zoom which automatically enlarges road junctions in the active guidance mode, providing helpful support above all at dangerous points where a road junction is unclear. • Map scroll: with a wider range of map options, the user is now able to shift the map display, scroll and set the map with a cursor. • Tour planning: this function allows the user to enter and memorise tours with up to 8 destinations in a row. When setting out, the system will automatically guide the driver to the individual destinations, in precisely the order recorded in advance. Further processing options on such extended tours include adding information, removing destinations, changing the order of destinations on the way or skipping a certain point. • Music played by the navigation CD ROM drive: as well as the usual navigation function provided by a CD-ROM, the new PCM system also allows memory-based navigation. In this case the user can remove the navigation CD after calculating his route or recording the route corridor and subsequently insert an audio CD into the drive and enjoy music in first-class quality. And should it be necessary to reinsert the navigation CD, for example to calculate an all-new route, the system will automatically inform the driver by generating an optical and an acoustic signal.
New antenna systems
Apart from the radio antenna in the windscreen, the GPS antenna used for navigation purposes in the instrument panel and the telephone antenna hidden beneath the windscreen cover (between the bonnet and the windscreen), Porsche's new Communication Management also comes with an antenna diversity system. This system is made up of four antenna wires integrated in the windscreen and ensures that FM signals are always received by the best positioned antenna. The antenna diversity system is controlled by a special amplifier and serves to further reduce any interference in radio reception.