METHOD FOR MONITORING THE TIRE PRESSURE OF A VEHICLE

Description

[0001] The invention relates to a method for monitoring the tire pressure of a vehicle. A method having the features specified in the preamble of claim 1 is known from JP 2012 148646 A. Similar methods are known from DE102008004953 A1 and US2004046651 A1.

[0002] Tire pressure monitoring units, which contain a pressure sensor and usually also a temperature sensor, are mounted on vehicle wheels and can then provide information about the tire pressure wirelessly, i.e. send it to a central evaluation unit of the vehicle.

[0003] A constant challenge in the development of tire pressure monitoring units is the conflict between achieving the most energy-efficient operation possible and providing the most up-to-date and reliable pressure data possible. The more frequently tire pressure information is sent, the greater the energy consumption of a tire pressure monitoring unit.

[0004] One problem with optimizing tire pressure monitoring systems is that a driver of a vehicle should be informed as early as possible about a pressure loss that has occurred while parked and that impairs driving safety. In the method known from DE 10 2008 004 953 A1, the tire pressure is measured at predetermined intervals while the vehicle is parked and compared with a predetermined threshold value. If the pressure falls below the threshold value, the transmitter of the tire pressure monitoring system, which is otherwise deactivated while parking, is activated and begins transmitting pressure data at predetermined intervals of approximately 10 to 20 seconds. The receiver of a central evaluation unit is activated as soon as the vehicle's ignition is switched on, so that the driver can then be warned of a critical pressure loss within 10 to 20 seconds.

[0005] The object of the present invention is to show a way how tire pressure monitoring can be improved in an energy-efficient manner when the vehicle is parked.

[0006] This object is achieved by a method having the features specified in claim 1. Advantageous developments of the invention are the subject of subclaims.

[0007] In a method according to the invention, tire pressure is measured even when the vehicle is parked, and pressure data is transmitted at predetermined intervals. A receiver of an evaluation unit in the vehicle is activated at appropriate intervals. Advantageously, current tire pressure data is already available when the vehicle is started, allowing the driver to be immediately warned of a pressure loss that could impair driving safety.

[0008] An excessive load on the vehicle battery is avoided with a method according to the invention, since the receiver is not constantly ready to receive, but is activated at time intervals that match the time intervals at which the tire pressure monitoring devices of the vehicle send pressure data.

[0009] The tire pressure monitoring devices preferably transmit at time intervals that are constant or vary around a constant target value to avoid reception being disrupted by simultaneous transmissions from different tire pressure monitoring units. The variations around the target value are preferably no more than twenty times, preferably no more than ten times, the duration of a transmission, and no more than one thousandth of the target value, preferably less than one ten-thousandth.

[0010] However, it is also possible to significantly change the time intervals, especially by increasing them with increasing parking time, for example, by doubling them. Such changes can be communicated to the evaluation unit in a data telegram containing tire pressure data or can be implemented according to a predefined pattern known to the evaluation unit.

[0011] For a method according to the invention, it is not necessary for the receiver to be activated at the same time intervals at which a tire pressure monitoring device sends pressure data. In particular, if pressure data is sent at constant, predetermined time intervals, in order to protect the vehicle battery, the receiver can be activated only for every second or every third transmission, or even less frequently. During longer parking periods, the strain on the vehicle battery can be reduced in this way. For example, in the first twelve hours of a parking period, the receiver can be activated for every transmission, thereafter only for every second transmission or even less frequently, for example from the second to fifth day only for every fourth transmission and thereafter only for every tenth transmission.

[0012] Typically, vehicles have multiple wheels, each with a tire pressure monitoring device mounted on it. If a single receiver is used for all tire pressure monitoring devices, it will only be deactivated after receiving a transmission if no transmission from another tire pressure monitoring device is currently expected. For simplicity, the case of a single tire pressure monitoring device will often be considered below. Conditions for deactivating the receiver are cumulative, i.e., the receiver remains activated if a transmission is expected from any of the tire pressure monitoring units and will only be deactivated when the deactivation conditions for all tire pressure monitoring units are met.

[0013] An advantageous development of the invention provides that each tire pressure monitoring unit of the vehicle and also the evaluation unit contain a timer. The timer of the tire pressure monitoring unit determines the times at which pressure data is transmitted, and the timer of the evaluation unit correspondingly determines the times at which the receiver is activated. The timers thus measure the time and ensure activation. Since the timers, like any clock, have an inaccuracy, which can be exacerbated by strong temperature fluctuations, it is preferable that the timer of the evaluation unit be readjusted each time a transmission is received.For example, if a tire pressure monitoring unit is to send pressure data every 5 minutes, the timer of the evaluation unit can be reset each time pressure data is received from the tire pressure monitoring unit in question and thus synchronized with the timer of the tire pressure monitoring unit.

[0014] A further advantageous development of the invention provides that the tire pressure monitoring unit switches between a driving mode and a parking mode depending on signals from the acceleration sensor, wherein tire pressure data is transmitted in the parking mode at different time intervals, in particular longer time intervals, than in the driving mode. While driving, the receiver can be constantly ready to receive, so that pressure data can be received at short time intervals.

[0015] The receiver preferably remains activated for a follow-up time after the vehicle's engine has been switched off. The purpose of this follow-up time is to receive a (first) transmission while the vehicle is parked. From the time of receipt of the first transmission, the evaluation unit can then determine the time at which the next transmission from the relevant tire pressure monitoring device is expected. The individual tire pressure monitoring devices use signals from their acceleration sensors to determine when the vehicle has come to a standstill. Typically, each tire pressure monitoring unit determines a slightly different time due to noise and interference. The follow-up time should preferably be no more than twice the time intervals at which the receiver is initially activated when the vehicle is parked. These time intervals can be increased for longer parking periods to save energy.With regard to the follow-up time, this refers to the shortest time intervals in which the receiver is activated when the vehicle is parked, i.e. the time intervals before they are extended due to longer parking times.

[0016] The run-on time can be terminated if a transmission containing pressure data has been received from each tire pressure monitoring device after the engine has been switched off. Since it may happen that no transmissions can be received from a tire pressure monitoring unit due to unfavorable reception or transmission conditions or as a result of a defect, it is preferable to deactivate the receiver after a maximum time, even if not all tire pressure monitoring units have received a transmission by then. The maximum time can be, for example, 5 to 10 minutes.

[0017] If the receiver has been activated, it can be deactivated as soon as the expected transmission has been received, or as soon as the expected transmission has been received from each tire pressure monitoring device. If an expected transmission was not received, this may be because the receiver was activated too late, for example due to a timer inaccuracy, or because the tire pressure monitoring device is not (or no longer) transmitting due to a defect. In this case, the receiver can simply remain activated for an extended period, for example until the next transmission from this tire pressure monitoring device is expected. If no transmission is received even then, it can be assumed that transmissions from the tire pressure monitoring device in question cannot be received and the receiver can be deactivated (provided that no transmissions from other tire pressure monitoring units are expected).Alternatively, a time window can be specified for each activation, after which the receiver is deactivated, regardless of whether a transmission was received from the tire pressure monitoring device in question. If no transmission was received within such a time window, the time window can be gradually extended for subsequent activations up to the expected interval between transmissions.

[0018] If a time window is specified for each activation, after which the receiver is deactivated, this time period is preferably significantly shorter than the time intervals between transmissions from a tire pressure monitoring device. For example, the time window can be as short as 1 second or less, preferably no more than 100 milliseconds.

[0019] Further details and advantages of the invention are explained using an embodiment with reference to the accompanying drawing: Fig. 1 shows a schematic representation of a tire pressure monitoring system of a vehicle; Fig. 2 shows a flowchart for the central evaluation unit of a tire monitoring system; and Fig. 3 shows another embodiment of a flowchart for the central evaluation unit of a tire monitoring system.

[0020] A tire pressure monitoring system, as used in Fig. 1shown schematically, consists of tire pressure monitoring devices 1, each mounted on one of the wheels of a vehicle, and a central evaluation unit 2. Each tire pressure monitoring device 1 contains a pressure sensor 1a for measuring the tire pressure, an acceleration sensor 1b, a temperature sensor 1c, a power source 1d, e.g. a battery, and a transmitter 1e for wirelessly transmitting tire pressure data. Pressure data is transmitted in the form of data telegrams, each of which contains a characteristic identifier of the transmitting tire pressure monitoring unit as well as pressure and temperature data. The central evaluation unit 2 has a receiver 3 for receiving data telegrams from the tire pressure monitoring units 1.

[0021] While driving, receiver 3 is constantly activated so that data about a sudden pressure loss, for example due to a tire burst, which is immediately transmitted by tire pressure monitoring units 1, is available as quickly as possible. For example, the evaluation unit can communicate via a bus, such as a CAN bus (Controller Area Network), with vehicle stabilization systems that can intervene to stabilize the vehicle in the event of a tire burst.

[0022] The tire pressure monitoring devices 1 can operate in a driving mode and a parking mode. In driving mode, pressure data is measured at regular intervals and transmitted at longer intervals. For example, a pressure measurement can be taken at intervals of 0.1 to 5 seconds, and a transmission can be made at intervals of 1 minute to 3 minutes. If a critical pressure drop is detected while driving, the measurement and transmission activity can be intensified. For example, a critical pressure drop can be transmitted immediately, followed by a transmission at intervals of a few seconds, for example, 1 second to 10 seconds.

[0023] In parking mode, pressure data is measured and transmitted at specified intervals, for example, at intervals of 3 minutes to 10 minutes. Data telegrams transmitted in parking mode can differ from data telegrams transmitted in driving mode in their format or by corresponding information. The tire pressure monitoring units 1 switch between parking mode and driving mode depending on signals from their acceleration sensors 1b.

[0024] In Fig. 2A flowchart for the central evaluation unit of such a tire pressure monitoring system is shown. This flowchart begins with the vehicle being parked, i.e., the ignition is turned off (terminal 15 off). The evaluation unit then deactivates the connection to the vehicle bus in step 10 to reduce the load on the vehicle battery. However, receiver 3 remains active and thus ready to receive transmissions from tire pressure monitoring units 1.

[0025] The receiver 3 remains ready to receive until either a data telegram sent in parking mode has been received by all tire pressure monitoring devices 1 or a predetermined period of time has elapsed (step 11). This period of time is referred to as the follow-up phase and is selected such that, upon expiration, each tire pressure monitoring unit in parking mode has sent at least one data telegram. If no data telegram has been received from a tire pressure monitoring unit, it can be assumed that reception is not possible, e.g., due to a defect. The duration of the follow-up phase can, for example, be more than the time interval between transmissions from a tire pressure monitoring unit in parking mode and twice the time interval between transmissions from a tire pressure monitoring unit in parking mode. Follow-up phases lasting between 3 minutes and 10 minutes are particularly suitable.

[0026] If a transmission is received from a tire pressure monitoring device during the follow-up phase (step 12), the evaluation unit starts a timer (ie a timer) for the tire pressure monitoring unit in question, which results in Figure 1 symbolized by box 13. As long as no transmissions have been received from all tire pressure monitoring devices 1, a check is performed repeatedly as per step 11 to determine whether any transmissions have been received or whether the run-on phase has expired. Once all tire pressure monitoring devices have received transmissions or the run-on phase has expired, the evaluation unit is shut down (step 14). In the shut-down state, the receiver is no longer ready to receive, but the timers started in step 12, each assigned to one of the tire pressure monitoring units, are still running.

[0027] Fig. 3shows a flow chart for the central evaluation unit 2 of the tire pressure monitoring system, which describes the procedure according to Fig. 2explained follow-up phase. The process begins in step 20 with one of the timers having expired, for example a timer x. A transmission from the relevant tire pressure monitoring device x is therefore expected and therefore in step 21 the receiver 3 is activated and a further timer x1 is started, which monitors the period of time in which a transmission from the tire pressure monitoring unit x is waited. In step 22 a check is then made as to whether a transmission from the tire pressure monitoring unit x has been received. If this is the case, the timer x is restarted in step 23. If this is not the case, a check is made in step 24 as to whether the timer x1 has expired, i.e. whether the time window in which a transmission from the tire pressure monitoring device x is waited for has elapsed.If so, in a step 25 this time window is increased for a later activation, so that when the receiver 3 is activated later the timer x1 allows a correspondingly larger time window to elapse, so that the chance of receiving a transmission from the tire pressure monitoring device x is improved. From step 25 the evaluation unit goes to step 23, i.e. starts the timer x.

[0028] After starting timer x in step 23, a check is performed in step 26 to determine whether transmissions are currently awaited from other tire pressure monitoring devices y. This check determines whether another timer y assigned to a tire pressure monitoring device y has expired and whether its associated time window, monitored by a timer y1, has not yet expired. If a transmission from another tire pressure monitoring device y is still awaited, the method continues with step 22; otherwise, the receiver is deactivated in step 27.

[0029] As already mentioned, each tire pressure monitoring device of the vehicle transmits pressure data in parking mode at predetermined time intervals t1, for example, every 3 to 10 minutes. Accordingly, the timers activate the receiver at time intervals t1-Δ, where Δ is negligibly small compared to the time interval t1 and is preferably less than 1 second, more preferably less than 1 millisecond, for example, less than 5 microseconds. The receiver must be activated a (relatively short) time before a transmission so that the transmission can be reliably received.

[0030] The time window for receiving a transmission can be very short, for example, less than 1 second or less than 100 milliseconds. For example, the time window for receiving a transmission can be less than 100 times or less than 20 times the duration of a transmission. The strain on the vehicle battery for such short receiver activation times is advantageously low.

[0031] Receiving transmissions from tire pressure monitoring units can be difficult if multiple tire pressure monitoring units transmit simultaneously or if their transmissions overlap in time. This is inherently unlikely, since the individual tire pressure monitoring devices are prompted to transition to parking mode by signals from their respective acceleration sensors, and the different wheels of a vehicle are normally subject to slightly different accelerations. To further prevent problems caused by overlapping transmissions from different tire pressure monitoring devices, it can be provided that the time intervals t1 at which the tire pressure monitoring units transmit in parking mode are varied by a target value from transmission to transmission, in particular randomly or quasi-randomly.To vary the time interval, a small value ε is added, which is determined randomly or generated according to a more or less complex rule that makes synchronous changes in multiple tire pressure monitoring units unlikely. The value of ε can, for example, be between twice and five times the duration of a transmission, e.g., between 10 milliseconds and 50 milliseconds. In this case, only a target value is specified for the time intervals t1 between transmissions, which is then varied slightly.

[0032] In order to reduce energy consumption during longer parking periods, the timers of evaluation unit 2 can be set to increasingly larger values ​​as the parking period increases, so that not every transmission from a tire pressure monitoring device can be received. For example, for the second to fifth day of parking, it can be specified that only every fourth data telegram from a tire pressure monitoring unit is received. If a tire pressure monitoring unit transmits data telegrams with pressure data at time intervals t1 while parked, the receiver will be activated accordingly at time intervals four times t1 on the second to fifth day of parking. After five days, reception can be reduced to every tenth data telegram, and after an even longer time, for example from the 21st day onwards, activation of receiver 3 can be stopped entirely to protect the vehicle battery.

Claims

1. Method for monitoring the tyre pressure of a vehicle by means of a tyre pressure monitoring device (1), which comprises a pressure sensor (1a) for measuring the tyre pressure, an acceleration sensor (1b) and a transmitter (1e) for wireless trans-mission of tyre pressure data, and a central evaluation unit (2) of the vehicle, which comprises a receiver (3), wherein when the vehicle is parked, the tyre pressure is regularly measured by the pressure sensor (1a) of the tyre pressure monitoring device (1), and when the vehicle is parked, pressure data are sent by the tyre pressure monitoring device (1) at preset time intervals, characterised in that the receiver (3) is actuated at matching preset intervals to receive the pressure data.

2. Method according to claim 1, characterised in that the tyre pressure monitoring device (1) comprises a timer which is used to determine the times at which the transmitter (3) is activated, and the central evaluation unit (1) comprises a timer which determines the time of activation of the receiver (3) and is readjusted each time a transmission from the tyre pressure monitoring device (1) is received.

3. Method according to any one of the preceding claims, characterised in that the central evaluation unit (2) comprises a timer which activates the receiver (3) to receive the next transmission and is reset each time a transmission is received.

4. Method according to any one of the preceding claims, characterised in that the tyre pressure monitoring unit (1) switches between a driving mode and a parking mode as a function of signals from the acceleration sensor (1b), tyre pressure data being transmitted in the parking mode at different time intervals than in the driving mode.

5. Method according to any one of the preceding claims, characterised in that the receiver (3) remains activated for a cooling-down time after the engine of the vehicle has been switched off.

6. Method according to claim 5, characterised in that the stopping time is at least as long as the predetermined time intervals between transmissions when the vehicle is parked.

7. Method according to claim 5 or 6, characterised in that the cooling-down time is not more than twice as long as the predetermined time intervals at which the receiver (3) is activated at the beginning of a parking period.

8. Method according to any one of the preceding claims, characterised in that the time intervals at which the receiver (3) is activated when the vehicle is parked are increased after a predetermined period of time, preferably doubled.

9. Method according to any one of the preceding claims, characterised in that, when the vehicle is parked, the receiver (3) is deactivated after a transmission has been received or a period of time has elapsed which is less than the predetermined time interval between transmissions when the vehicle is parked.

10. Method according to any one of the preceding claims, characterised in that the predetermined time intervals at which pressure data are transmitted by the tyre pressure monitoring device (1) when the vehicle is parked are varied around a set-point value in order to avoid overlapping with transmissions from other tyre pressure monitoring units (1) of the vehicle.

11. Method according to claim 10, characterised in that the variations around the setpoint value are no more than ten times the duration of a transmission.