The Tyre Pressure Control (RDC) is a system for permanent monitoring of the tyre pressure. To achieve this, the tyre pressure and temperature in the tyres are measured at certain intervals and telemetrically transmitted across an HF transmission path to a central control unit. The control unit evaluates the received data and makes the corresponding information available to the driver. The driver is thus informed of a necessary correction of the tyre pressure or a puncture that might have occurred.
Control unit
The RDC control unit evaluated the transmitted pressure and temperature values from the individual tyres. If required, it informs the driver with a CC message. This signal may also be supported by supplementary information via the Man-Machine Interface (MMI).
4 reception aerials with wiring harness
The reception aerials are fitted in the individual wheelhouses and receive the pressure and temperature values of the associated tyre. This information is routed to the relevant wiring harness on the RDC control unit.
4 wheel electronic systems in the wheels (or 5 if the spare wheel is also fitted with one)
The wheel electronic systems are mounted in the wheel drop centre. Together with the filling valve, they form a compact unit and are fitted in the same way as a screw valve in the rim. The wheel electronic system contains a pressure and temperature sensor, a battery and a transmitter stage. The wheel electronic system is activated on initial fill of the tyre and it then transmits the measurement values in cycles. This cycle is temporarily shortened if a certain pressure change is detected. In the case of temperature values greater than 120°C inside the tyre, the wheel electronic system is switched off; if it cools down to less than 110°C, it is switched on again. Transmission rate normal: 55 sec; Transmission rate increased: 0.8 sec; Battery service life: approx. 7 years.
Button initialization
The button is integrated as a soft button in the controller and it is used to standardize the system.
The main function of RDC is permanent monitoring of the tyre pressure when the car is moving and stationary. The tyre pressure to be monitored is specified by the driver. The driver uses the control function in the MMI to instruct the system to adopt the current tyre pressure as the setpoint pressure (initialization). The plausibility of the setpoint pressure is check before the system adopts it (axle-wise comparison of the specified pressures, minimum pressures). An initialization of the system is only possible when the tyre pressure on all wheels is at least 1.7 bar. If the tyre pressure of one wheel falls below this limit, a warning is issued immediately. If the pressure difference between the tyres on one shaft > 0.4 bar, the initialization is rejected following a plausibility check. A warning is issued. Remedy: set tyre pressures to the correct values and then run the initialization once again. Process following triggered initialization:
1. Individual wheel recognition: identification of wheel electronic systems fitted 2. Wheel position assignment: identification of wheel electronic system position 3. Plausibility check: check of setpoint pressures 4. Adoption of setpoint pressures as specified pressures
On comparison of the current tyre pressure with the specified pressure, the tyre temperature is taken in to account. On the basis of the specified pressure and temperature during the standardization, the system calculates the pressure limit values for the current tyre temperature. The tyre pressure increases per 10°C temperature rise by 0.1 bar. If the temperature-evaluated values are not reached, the RDC control unit issues a message via the driver information system.
The RDC differentiates between the following statuses:
Range with correct pressure. No message to the driver.
Range in which the ”Reminder” status applies (”soft warning”).
This range is characterized a reduces tyre pressure at which driving safety is still ensured. With ”ignition onn”, the driver is requested to check the tyre pressure at the next possible opportunity. The reminder is displayed independently of the wheel position.
Temperature-evaluated tyre pressure 0.2 bar lower than the specified pressure. Tyre temperature 20°C lower than filling temperature for at least 14 days (autumn filter).
Range in which the ”hard warning” status applies.
In this range, driving safety is no longer ensured. The driver is requested to stop the vehicle and check the condition of the tyres. The driver must decide whether he or she can continue the journey with lower speed to the nearest repair area, or whether a repair or the spot is necessary. The message is issued immediately and is dependent on wheel position, insofar as the system has already learned the position. Otherwise, the message is issued independently of the wheel position.
Pressure drop compared to specified pressure of at least 0.4 bar (temperature-evaluated). Pressure drop of 16% of the inflated pressure (not temperature-evaluated). Pressure drop below 1.3 bar (not temperature-evaluated).
Fault range.
Occurs when the control unit is defective, there is external radio interference, there are too many wheel electronic systems in the vehicle, a wheel electronic system is defective, etc. In the case of a fault, a corresponding message is displayed.
CC message ”Check tyre pressure” with supplementary information in the MMI:
Temperature-evaluated tyre pressure 0.2 bar lower than the specified pressure. Tyre temperature 20°C lower than filling temperature for at least 14 days (autumn filter).
CC message ”Tyre Pressure Control without function” with supplementary information in the MMI:
External radio interference.
CC message ”Tyre Pressure Control without function” with supplementary information in the MMI:
Wheel fitted without wheel sensor.
CC message ”Tyre Pressure Control initialization” with supplementary information in the MMI:
Initialization running.
CC message ”Puncture! Immediately stop the vehicle carefully” with the relevant supplementary information in the MMI:
Pressure drop compared to specified pressure of at least 0.4 bar (temperature-evaluated). Pressure drop of 16% of the inflated pressure (not temperature-evaluated). Pressure drop below 1.3 bar (not temperature-evaluated).
CC message ”Puncture! Stop vehicle carefully”
Puncture report not related to wheel position. Message only comes in this way during the initialization phase.
Pressure drop compared to specified pressure of at least 0.4 bar (temperature-evaluated). Pressure drop of 16% of the inflated pressure (not temperature-evaluated). Pressure drop below 1.3 bar (not temperature-evaluated).
Important
An initialization of the system must be run in the following cases:
USA, Japan
Transmitting frequency of the system: 315 MHz
Other
Transmitting frequency of the system: 433 MHz