The Tire Pressure Control (RDC) is a system for permanent monitoring of the tire pressure. To achieve this, the tire pressure and temperature in the tires are measured at certain intervals and telemetrically transmitted across an HF transmission path to a central control module. The control module evaluates the received data and makes the corresponding information available to the driver. The driver is thus informed of a necessary correction of the tire pressure or a puncture that might have occurred.
Control module
The RDC control module evaluated the transmitted pressure and temperature values from the individual tires. 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 antennas with wiring harness
The reception antennas are fitted in the individual wheel housings and receive the pressure and temperature values of the associated tire. This information is routed to the relevant wiring harness on the RDC control module.
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 center. 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 tire 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 tire, 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 tire pressure when the car is moving and stationary. The tire 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 tire pressure as the setpoint pressure (initialization). The plausibility of the setpoint pressure is checked before the system adopts it (axle-wise comparison of the specified pressures, minimum pressures). An initialization of the system is only possible when the tire pressure on all wheels is at least 1.7 bar. If the tire pressure of one wheel falls below this limit, a warning is issued immediately. If the pressure difference between the tires on one shaft > 0.4 bar, the initialization is rejected following a plausibility check. A warning is issued. Remedy: set tire 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 tire pressure with the specified pressure, the tire 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 tire temperature. The tire pressure increases per 10°C temperature rise by 0.1 bar. If the temperature evaluated values are not reached, the RDC control module 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 by a reduced tire pressure at which driving safety is still ensured. With ”ignition on”, the driver is requested to check the tire pressure at the next possible opportunity. The reminder is displayed independently of the wheel position.
Temperature evaluated tire pressure 0.2 bar lower than the specified pressure. Tire 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 tires. The driver must decide whether he or she can continue the journey with lower speed to the nearest repair area, or whether a repair on 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 module 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 tire pressure” with supplementary information in the MMI:
Temperature evaluated tire pressure 0.2 bar lower than the specified pressure. Tire temperature 20°C lower than filling temperature for at least 14 days (autumn filter).
CC message ”Tire Pressure Control without function” with supplementary information in the MMI:
External radio interference.
CC message ”Tire Pressure Control without function” with supplementary information in the MMI:
Wheel fitted without wheel sensor.
CC message ”Tire 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