Running Gear
Running gear - overview
Front axle / steering
McPherson wheel suspension with offset spring. Twin-tube gas pressure shock absorbers in standard or sports model.
In order to obtain greater stiffness with reduced intrinsic weight as compared with steel, the following components have been made from aluminum: Control arms, diagonal brace, track rod, wheel carriers and cross members / side member.
Rack-and-pinion steering gear (i = 16.9 : 1) with hydraulic assistance.
Steering wheel longitudinally adjustable (40 mm).
Rear axle
McPherson wheel suspension with offset spring. Twin-tube gas-filled shock absorbers in standard or sports model.
In order to obtain greater stiffness with reduced intrinsic weight as compared with steel, the following components have been made from aluminum: Control arms, diagonal brace, track rod, wheel carriers and side members.
Wheels and tyres
Specifications
Brakes
Hydraulic dual-circuit brake system with front-axle / rear-axle brake-circuit distribution.
Vacuum brake booster, internally ventilated brake disks with four-piston fixed caliper at front and rear axles.
ABS 5.3 (3-channel system) standard.
ABS/TC 5.3 (4-channel system) on special request.
TC = Traction Control, consisting of ASR (anti-slip control) and ABD (Automatic Brake Differential).
Parking brake (handbrake):
Drum brake acting mechanically on both rear wheels.
Information on ABS 5.3 and ABS/TC 5.3
General
The Porsche Boxster is equipped as standard with an antilock braking system (ABS 5.3). "Traction Control (TC) is available on special request on the basis of ABS 5.3. Traction Control (TC) is a combination of Anti-Slip Control (ASR) and Automatic Brake Differential (ABD). TC is a further system for increasing driving safety.
Compared with the ABS 5 (ABS 5 in the 993), ABS 5.3 has been optimized with regard to installed volume and weight. Control unit (No. 1), hydraulic unit (No. 7), pump-motor relay and valve relay (No. 2) of ABS 5.3 and ABS/TC 5.3 form a unit that is located next to the brake master cylinder.
Diagnosis and system tests on both systems are carried out with the Porsche System Tester 2.
Differences between ABS 5.3 and ABS/TC 5.3
ABS 5.3 = 3-channel system (diagram: refer to Diagrams; Exploded Views).
ABS/TC 5.3 = 4-channel system (diagram: refer to Diagrams; Exploded Views).
The essential distinguishing features between ABS and ABS/TC are:
- Number of brake lines at intermediate piece (No. 8 / Figure above):
ABS 5.3 = 3 brake lines
ABS/TC 5.3 = 4 brake lines
- TC off switch for switching driving stability control on and off is not available on vehicles with Solo ABS (ABS 5.3)
- TC (ASR/ABD) warning light and TC (ASR/ABD) function light (information light) in vehicles with ABS/TC. These lights light up when the ignition is switched on (lamp check).
These lights are not allocated in the instrument cluster in vehicles with ABS 5.3 (Solo ABS).
A figure showing the warning lights and function light is shown under Locations; Components.
ABS 5.3 (3-channel system) system description
ABS operation
The ABS control unit receives a signal from the brake-light switch and the AC voltage signals from the four speed sensors. These signals are converted into digital wheel-speed signals independently of each other by two microprocessors. The wheel slip (approximately proportional to the computed vehicle reference speed) is formed from these wheel-speed signals.
If vehicle deceleration and excess slip are detected at a wheel, the pressure-holding phase is initiated, i.e. the inlet valve for the relevant wheel is closed to prevent a further increase in pressure. If in spite of the pressure being held constant the wheel tends to continue to lock up, the pressure in the wheel cylinder is reduced. For this purpose, the outlet valve is opened and the brake fluid is pumped back to the brake master cylinder via the return pump (pressure-reduction phase) until the wheel turns again. Then, depending on the control cycle, further appropriate cycles are initiated.
This function and the input signals are continuously monitored. If a fault is detected, the control unit switches the ABS function off, switches on the ABS warning light and stores the fault in a non-volatile memory in the control unit.
In addition, whenever a journey is begun and a speed of 6 km/h is exceeded, a test program is started. The solenoid valves and the pump motor are electrically actuated and checked. If a fault is detected, the control unit switches the ABS function off, the ABS warning light is switched on and the fault is stored.
Diagram: ABS 5.3 (3-channel system)
ABS / TC 5.3 (4-Channel system) system description
Note: Traction Control (TC) represents an extension of the ABS system and is a combination of Anti-Slip Control (ASR) and Automatic Brake Differential (ABD).
TC prevents the drive wheels from spinning when moving off and during acceleration. Driving stability and traction are improved over the entire speed range.
Traction Control (TC) is ready for operation whenever the engine is started.
The TC information light in the instrument panel lights up during a control process and warns that the driving style must be adapted to road conditions.
Operation
Driving stability control:
If Traction Control (TC) detects that a certain speed difference between the wheels has been exceeded (wheel spin), engine power is automatically reduced.
Brake control:
In addition to reducing the engine power (driving stability control), the TC (via the ABD) brakes the drive wheel that is spinning.
Since this control requires the drive wheels to be individually controlled, the ABS/TC system is a 4-channel system.
Diagram: ABS / TC 5.3 (4-channel system)
Component arrangement (ABS 5.3 and ABS/TC 5.3)