Method for the automatic operation of a tire inflation device for motor vehicles

The invention relates to a device for the automatic actuation of a tire inflation system for motor vehicles, with control electronics that use sensors to determine the driving condition and the tire pressure of all tires and control pneumatic valves and a compressor to adjust the tire pressure to the respective conditions, such as driving speed, load , 5 road condition, terrain, etc. adapt, the compressor being arranged between the tires and a pressure reservoir in a system which is closed in the normal operating state with respect to the atmosphere.

A device for the automatic actuation of a tire inflation system for motor vehicles is described in AT 408 867 B, for example. Essentially, the driving speed of the io vehicle and the current tire pressure are measured and the target value of the tire pressure is determined, and if the actual value deviates from the target value, the filling or emptying valves are activated until the target value for the tire pressure is reached.

The air required for filling is sucked in from the atmospheric environment by a compressor and compressed; the air is also released into the open when the pressure is reduced.

The critical operating state of an automatic tire pressure control is the infestation, since a tire pressure which is too low for the respective driving speed represents a safety-critical driving state. A sufficient design of a storage tank guarantees the automatic in principle, but with several short-term alternating control processes 20 this stock can be quickly exhausted, which would have to involve an intervention in the engine management in order not to endanger driving safety.

In order to avoid this critical operating condition as far as possible, it has already been proposed that the compressor be arranged in a normally closed system between the tires and a pressure reservoir. A 3/2-way solenoid valve was arranged between the pressure reservoir designed as a spare wheel and the compressor. This solenoid valve had to be specially controlled, which made the construction and operation of the device more complicated.

The invention has set itself the goal of simplifying a device of the type mentioned at the beginning, which is achieved in that the compressor is connected to the pressure reservoir via a direct connection line without switching elements.

In a closed system according to the invention, the filling capacity is significantly increased while the compressor capacity remains the same, since the compressor capacity only serves to shift the amount of gas between two closed reservoirs at different pressure levels, and to maintain the enthalpy of the gas to be taken from the tire when the pressure is released in the system remains and does not have to be supplied again by the compressor. In this case, no control of a switching element arranged between the compressor and the pressure reservoir is required.

The closed system, in which an existing, closed volume of gas is shifted between the tire and the storage container by means of a compressor, also has several significant advantages over an open system in which fresh air is sucked in for filling and the tire air is released into the atmosphere when the pressure is reduced will: a. Due to the closed system, any gases other than air can also be used; special tire gases can be used to support the technological and comfort properties of the tire.

b. Due to the closed system, the otherwise required air dryer can be omitted, which causes additional costs and takes up additional installation space.

c. The valve arrangement can be significantly simplified, since the closed system means that no valve combination is required to delimit the system from the outside.

d. The noisy process of venting the tire air into the open is no longer necessary, which significantly improves the comfort function of the system.

On the other hand, the closed system has a disadvantage that needs to be compensated accordingly. Minor leaks are unavoidable in a pneumatic system with numerous connections, valves, and seals. The closed system does not have the inherent property of compensating for leaks caused by fresh air drawn in from outside.

AT 41 1 664 B

According to the invention, however, leakage avoided can be compensated for by an easily exchangeable additional cartridge, which is filled with liquefied tire gas, for example, which automatically brings the filling level back to the target level when a critical filling level is exceeded.

Furthermore, in a closed system, a gradual loss of pressure caused by a defective tire cannot be compensated for, since the design criteria mean there is no potential for an additional pressure supply. In order to make full use of this additional safety potential that an automatic tire pressure control can provide, the device is to be switched over to a fresh air supply in the event of a recognized emergency in this regard. This function can also come into effect if the previously described 10 print cartridge has been exhausted and not replaced in time. The valve, which switches to the fresh air supply, can also be used to vent the line system and, above all, the rotary feedthroughs to the wheels or tires.

This venting of the line system can also be done by an additional variable air volume, which is enlarged for venting so that the pneumatic lines are largely relaxed, and when the tires are inflated or pressure-reduced, this volume is again compressed to a minimum volume by external energy input to feed the gas volume of the lines back into the system. This variable volume can be driven electrically, for example.

The invention is described in more detail with reference to an embodiment example shown in the drawings, without being limited to this example. The circuit diagram of a device according to the invention is shown in which the pressure information for the tire pressure control system electronics is provided by sensor electronics inside the tire. The tire pressure information can also be provided in other ways, and the sensor system for detecting the driving state and for assigning the corresponding target tire pressure is not limited to the tire pressure information.

The drawing shows the pneumatic circuit diagram behind the tire pressure control system as an example for axle-by-axle control of the wheels, but the system can also be used for any other control, e.g. all four wheels individually or depending on the axle, for each wheel or axle.

The control is carried out by the central control electronics 1. This electronics 1 is with a

Connected sensor system, which monitors, among other things, the load condition, tire pressure, driving speed, brakes and driving condition and communicates it to the central control electronics. A preferably driving speed and driving condition monitoring is in detail ζ. B. in AT 408 867 B, or in AT 5548 U1. Tire pressure monitoring is state of the art.

If, on the basis of a logic command that is linked to an incoming sensor signal, the need for a control process is recognized, the electronics 1 switch the pneumatic elements as follows:

If a switching command is issued because the switching values ​​specified in the control maps for increasing pressure in one or more tires or control circuits are exceeded, the preferably electromagnetically actuated control valves 3 are opened via the electrical control lines 2. The compressed gas flows via the control gas lines 11 and the control gas feedthrough of the sealing package 4 to the wheel valves 5 and opens the valves for filling. At the same time, the 3-way valve 6 is switched through and the filling valves 7 of the respective wheels or control loops are opened, via which the compressor 8 or if there is a corresponding pressure increase in the storage container 9, which is reported to the control electronics via the pressure sensor 25 and the data line 26, the gas for increasing the tire pressure from the pressure reservoir 9 via the bypass 23 and the bypass valve 22 through the filling lines 10 and the filling gas duct of the sealing package 4 the wheel valve 5 flows into the respective tires 13.

The purpose of the 3-way valve 6 in this arrangement is to provide a switch for the tire inflation system so that the compressor 8 and the gas supply in the pressure vessel 9 can also be used for other purposes, such as a gas spring.

Since the volume of the tires 13 is very large compared to the internal volume of the filling lines 10, and the pressure change in the tire is relatively slow, the tire internal pressure 55 can be seen as quasi-static in terms of measurement technology, and only by measuring the static pressure3

AT 411 664 B proportion of the gas a sufficiently accurate value can be determined. The wheel electronics 12 with the associated pressure sensor of the tire pressure control system inside the wheel continuously determines the respective pressure value and forwards it via the electrical control line 14 to the central control electronics 1, which interrupts the filling process when the setpoint is reached by controlling the control valves 3, the filling valves 7 and the three-way valve 6 is terminated. The pneumatically operated wheel valve 5 thus also closes. B. an externally actuated variable volume, vented.

If a shift command is issued because the shift values ​​specified in the control maps for pressure reduction in one or more tires are exceeded, the same process as described above is carried out in the opposite direction. The tire gas flows or is conveyed by the compressor 8 in the opposite direction from the tire 13 via the wheel valve 5, the filling lines 10, the filling valves 7, the valve 6 and into the pressure reservoir 9. The switch-off command is also sent by the corresponding sensor signal from the wheel electronics 12 to the central

Control electronics 1 given when the target pressure is reached.

The driver can be informed about the respective condition of the tires via a corresponding display 18. This driver information system can also be used to issue a defect warning, or to provide information about the respective maximum vehicle speed associated with the load and pressure state of the tires.

Leakage losses can be compensated for by an easy-to-change additional cartridge 20, which is filled with the same medium as the closed system, e.g. with air or a special tire gas in a liquefied state Brings the filling level back to the target level.

In order to compensate for a gradual loss of pressure due to a defective tire, a valve 21 can be used to switch to a fresh air supply. This function can also come into effect if the print cartridge 20 has been exhausted and has not been replaced in time.