GB1580240A

GB1580240A - Tyre pressure control system

Info

Publication number: GB1580240A
Application number: GB28293/77A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1976-07-07
Filing date: 1977-07-06
Publication date: 1980-11-26
Also published as: FR2357388B1; SE434369B; FR2357388A1; DE2630511A1; IT1116620B; SE7707349L; JPS537011A; DE2630511C2

Description

(54) TYRE PRESSURE CONTROL SYSTEM (71) We, WABCO FAHRZEUG BREMSEN G.M.B.H. formerly Wabco Westinghouse G.m.b.H, a German Company of, Am Lindener Hafen 213000 Hannover 91, Germany, do hereby declare the invention, -for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a control system for changing the air pressure in the tyres of vehicles, especially of motor vehicles as they are being driven.

Control systems of this kind are chiefly used for lorries in which, because of the 'conditions under which they are used, the pressure in the tyres has to be adapted as they are being driven, that is to say, without the journey being interrupted, to the particular ground or road conditions.

A tyre pressure control system is known in which the driver, after establishing the desired tyre pressure-without having to pay attention to special instruments-is informed of the end of the tyre pressure changing process by a buzzer or by a control light.

However, a disadvantage of this known system is that it is time-controlled, that is, the end of the tyre pressure changing process is automatically indicated, in an acoustic or optical manner, after a certain period of time which under normal conditions is sufficient for the pressure of the tyres to be changed. This automatic indication, however, also operates even if, for some reason-for example because of a leak in the compressed air system of the vehicles desired increase in the tyre pressure has not yet been completed.

The present invention provides a control system for changing the air pressure in a tyre of a vehicle, especially of a motor vehicle as it is being driven, the system including a switching valve having a compressed air inlet connection and an outlet connection, the outlet connection being joined by way of a control line to a control valve operable to control communication between the control line and the interior of the tyre, a pressuremeasuring unit in compressed air connection with the control line and operable to measure the pressure therein, and a control device operable to actuate the switching valve for a predetermined time period for the purpose of inflating or deflating the tyre, the measuring unit being connected to the control device to deliver a pressure-measurement signal thereto following an inflation or deflation of the tyre, said signal causing the control device to actuate the switching valve automatically for a further predetermined time period if the desired pressure has not been reached.

The system may include a valve in compressed air connection with the control line and actuable, by the control device, when the desired pressure has been reached, to vent air from the control line and cause closure of the control valve. The switching valve may have a pressure release connection joined to a pressure limiting valve and serving to vent air from the tyre during deflation of the latter.

The control valve may include a switching piston arrangement exposed to the pressure of compressed air coming from the control line, and a sealing element engageable with the piston arrangement to form a pressure-tight seal and thereby close the control valve, the piston arrangement having a portion of reduced cross-section which, when aligned with the sealing element, releases the pressure-tight seal, thereby opening the control valve.

An embodiment of the invention is explained in greater detail in the following text with reference to the accompanying drawings, in which: Figure I shows the circuit diagram of a tyre pressure control system according to the invention, and Figure 2 shows the cross-section of a control valve used in the system of Fig. 1.

The tyre pressure control system shown in Fig. I consists of a compressed air part and an electronic control part.

A container 1, associated with the compressed air part, is filled directly with compressed air by way of a line 2 from the air compressor 3 of the compressed air brake system, or by way of a line 4 and a non-return valve 5 from the brake system of the vehicle. The container 1 is connected by way of a line 6 and the inlet and outlet ports 8, 9 of a 5/3-way double solenoid valve 7, and then by way of a line 10 to each of the rotors 11 assigned to the wheels. From each rotor 11 there is a connection to the tyres by way of the connections 12a and 12b of a control valve 12.

A pressure-measuring unit 14 and a 2/2 solenoid valve 15 are connected to the line 10. In addition, the 5/3-way double solenoid valve 7 has an air release connection 16 connected by way of a line 17 to a pressurelimiting valve 18.

The electronic control part of the control system consists of an electronic control block 19 and a pulse generator 20, the control block 19 being connected to a switch key board 21 in the driver's cab.

Lines 22 and 23 form a pulse connection between the pulse generator 20 and the 5/3way double solenoid valve 7. There is a control connection by way of line 24 between the electronic control block 19 and the pressure-measuring unit 14 and a control line 25 joins the electronic control block 19 to the 2/2-way solenoid valve 15.

The control valve 12 is shown in greater detail in Fig. 2 and consists of a housing 26 in which there is located a switching piston arrangement comprising a piston 27 and a piston tube 28, the upper and the lower end of the piston tube 28 being guided in sealing rings 29 and 30.

Connections 1 2a and 1 2b are interconnected, by way of a reduced section 31 of the piston tube 28, when the switching piston arrangement 27/28 is in the position shown in Figure 2. A sealing element 32 interrupts this interconnection when the switching piston arrangement 27/28 is forced to move, under the tension of a spring 34 located in the interior 33 of the piston tube, into the position defined by engagement between a stop 35 secured to the housing and a piston stop 36. Channels 37 and 38 join the connection 12a to a pressure chamber 39 located above the piston 27. By way of the interior 33 of the piston tube a ventilation bore 40 connects a chamber 41, formed beneath the piston 27 when it is in its uppermost position, to the atmosphere by way of a bore 42.

Before the description of the operation of the system shown in Fig. I, the manner in which the control valve 12 functions will first be described.

When the valve 12 is in use in the system of Fig. 1, the line 10 of the system is joined to the connection 12a of the valve and the connection 12b of the valve is joined to the tyre. When line 10 of the system is pressurized as described below, compressed air flows through the channels 37 and 38 into the chamber 39 and the pressure which builds up in this chamber pushes the switching piston arrangement 27/28 downwards, against the force of the spring 34, into the position shown. As a result, the reduced section 31 of the piston tube 28 comes into the region of the sealing element 32 and compressed air is able to flow from connection 12a to the connection 12b and thence into the tyre.

When air is vented from the line 10 of the system, air is simultaneously vented from the chamber 39 of the control valve, by way of the channels 37 and 38, and the force of the spring 34 pushes the switching piston arrangement 27/28, with its stop 36, upwards and against the stop 35 secured to the housing. In this process, the sealing element 32 engages with the surface 28a of the piston tube 28 to form a seal, so that the connection between the connections 12a and 12b is interrupted and the pressure which has built up in the tyre is maintained or cannot flow back.

In the following description of the pressure control system shown in Fig. lit is assumed that the system has three control stages, the pressure level for control stage I being set at 0.7 bar, for control stage II at 1.2 bar and for control stage III at 2.3 bar.

When the system is not actuated, the input connection 8 of the 5/3-way double solenoid valve 7 (which is in the position shown in Fig. 1) is acted upon by the entire supply pressure.

If the vehicle is being driven with a tyre pressure of 1.2 bar and a higher tyre pressure is necessary because of the ground or road conditions, the driver pushes button III for 2.3 bar and thus initiates an inflation process in the tyre pressure control system.

With the push on the button III, the pulse generator 20 is put into operation and an inflation pulse emitted from it opens the passage 8/9 of the 5/3-way double solenoid valve 7, and the tyres are inflated by way of .the line 10, the rotors 11 and the control valves 12 which open as described above.

After a predetermined period of time, a stop pulse controlled by the electronic control block 19 and passed via the pulse generator 20 to the 5/3-way double solenoid valve 7 interrupts the inflation process by blocking the passage 8/9 of the solenoid valve. The pressure in the line 10 equalises with the pressure in the tyres by way of the open control valves 12, and the pressuremeasuring unit 14 measures this pressure and passes the result, by way of line 24, to the electronic control block 19 which in turn undertakes a comparison of the "desired" and "actual" values of the pressure. If the preselected level of pressure in the tyres has still not been reached, the inflation process is repeated automatically until the comparison of "desired" and "actual" values is positive: the 2/2-way double solenoid valve 15 then receives an opening pulse from the electronic control block 19 by way of the line 25, so that air is vented from the line 10 and the rotors 11 in a sudden burst, and the control valves 12 close as described above and block off the pressure introduced into the tyres. The line 10 between the 5/3-way double solenoid valve and the control valves 12, and thus also the rotors 11, are without pressure when the tyre pressure control system is not actuated.

If, conversely, it is necessary to reduce the pressure in the tyres, for example from stage III to stage II, the driver initiates a deflation process in the tyre pressure control system by pressing the button II.

With the push on button II, the 5/3-way double solenoid valve 7 first of all receives an inflation pulse from the pulse generator 20 influenced by the electronic control block 19, so that the specific pressure necessary to open the control valves 12 builds up in the line 10. Then the 5/3-way double solenoid valve 7 receives a deflation pulse to open the passage 9, 16, and the tyres are deflated by way of the rotor 11, the line 10, the deflation connection 16 of the valve 7, the line 17 and the pressurelimiting valve 18. After a pre-determined period of time, a stop pulse emitted from the electronic control block 19 and passed by way of the pulse generator 20 to the valve 7 interrupts the deflation process, the pressure in line 10 equalises with that in the tyres and the pressure-measuring unit 14 delivers the measured value of this pressure to the electronic control block 19. The control block in turn effects the comparison of "desired" and "actual" values and the pulse process is repeated in the manner described until the lower pressure level of stage II is reached. The valve 7 then receives a stop pulse again and the 2/2-way solenoid valve removes air, as described previously, from the line 10 and the rotor 11, as a result of which the control valves 12 are closed to block and thereby safeguard the pressure level in the tyres.

It is worth mentioning also that the pressure-limiting valve 18 always retains a residual pressure of 0.6 bar during the deflation process, so that the control valve 12 does not close when a deliberate deflation process is effected, that is to say, this pressure of 0.6 bar is required to overcome the force of the spring 34 in the control valve.

However. on the other hand, this means that if, for any reason, for example as a result of errors in the system, the deflation process has still not ended when the lowest pressure of 0.7 bar of the lowest switching stage I is reached, the control valve 12 closes automatically under the force of the spring 34 when a pressure of 0.5 bar is reached and hence a residual pressure is kept in the tyres.

In a pressure control system as described above, an adequate tyre pressure can be maintained in the working line 10 during the processes of inflation and deflation and, because of the pressure-controlled measurement techniques employed, hystereses can be reduced and the tyres can be inflated and deflated comparatively rapidly. After the desired tyre pressure has been reached, the system as far as the control valves 12 is driven without pressure, which means that the rotor system is relieved and also guarantees that the tyre pressure is safeguarded if there is damage to the lines.

Owing to the comparatively short duration inflation and deflation of the tyres which are made possible by the system described above, vehicles are enabled to move forward relatively rapidly in an area having varying ground or roadway conditions. Thus, vehicles that, for example, are moving over sandy terrain can continue driving on firm tracks or finished roads without stopping for the purpose of inflating the tyres.

WHAT WE CLAIM IS: 1. A control system for changing the air pressure in a tyre of a vehicle, especially of a motor vehicle as it is being driven, the system including a switching valve having a compressed air inlet connection and an outlet connection, the outlet connection being joined by way of a control line to a control valve operable to control communication between the control line and the interior of the tyre, a pressuremeasuring unit in compressed air connection with the control line and operable to measure the pressure therein, and a control device operable to actuate the switching valve for a predetermined time period for the purpose of inflating or deflating the tyre, the measuring unit being connected to the control device to deliver a pressure-measurement signal thereto following an inflation or deflation of the tyre, said signal causing the control device to actuate the switching valve automatically for a further predetermined time period if the desired pressure has not been reached.

2. A system as claimed in claim 1, including a valve in compressed air connection with the control line and

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. turn undertakes a comparison of the "desired" and "actual" values of the pressure. If the preselected level of pressure in the tyres has still not been reached, the inflation process is repeated automatically until the comparison of "desired" and "actual" values is positive: the 2/2-way double solenoid valve 15 then receives an opening pulse from the electronic control block 19 by way of the line 25, so that air is vented from the line 10 and the rotors 11 in a sudden burst, and the control valves 12 close as described above and block off the pressure introduced into the tyres. The line 10 between the 5/3-way double solenoid valve and the control valves 12, and thus also the rotors 11, are without pressure when the tyre pressure control system is not actuated. If, conversely, it is necessary to reduce the pressure in the tyres, for example from stage III to stage II, the driver initiates a deflation process in the tyre pressure control system by pressing the button II. With the push on button II, the 5/3-way double solenoid valve 7 first of all receives an inflation pulse from the pulse generator 20 influenced by the electronic control block 19, so that the specific pressure necessary to open the control valves 12 builds up in the line 10. Then the 5/3-way double solenoid valve 7 receives a deflation pulse to open the passage 9, 16, and the tyres are deflated by way of the rotor 11, the line 10, the deflation connection 16 of the valve 7, the line 17 and the pressurelimiting valve 18. After a pre-determined period of time, a stop pulse emitted from the electronic control block 19 and passed by way of the pulse generator 20 to the valve 7 interrupts the deflation process, the pressure in line 10 equalises with that in the tyres and the pressure-measuring unit 14 delivers the measured value of this pressure to the electronic control block 19. The control block in turn effects the comparison of "desired" and "actual" values and the pulse process is repeated in the manner described until the lower pressure level of stage II is reached. The valve 7 then receives a stop pulse again and the 2/2-way solenoid valve removes air, as described previously, from the line 10 and the rotor 11, as a result of which the control valves 12 are closed to block and thereby safeguard the pressure level in the tyres. It is worth mentioning also that the pressure-limiting valve 18 always retains a residual pressure of 0.6 bar during the deflation process, so that the control valve 12 does not close when a deliberate deflation process is effected, that is to say, this pressure of 0.6 bar is required to overcome the force of the spring 34 in the control valve. However. on the other hand, this means that if, for any reason, for example as a result of errors in the system, the deflation process has still not ended when the lowest pressure of 0.7 bar of the lowest switching stage I is reached, the control valve 12 closes automatically under the force of the spring 34 when a pressure of 0.5 bar is reached and hence a residual pressure is kept in the tyres. In a pressure control system as described above, an adequate tyre pressure can be maintained in the working line 10 during the processes of inflation and deflation and, because of the pressure-controlled measurement techniques employed, hystereses can be reduced and the tyres can be inflated and deflated comparatively rapidly. After the desired tyre pressure has been reached, the system as far as the control valves 12 is driven without pressure, which means that the rotor system is relieved and also guarantees that the tyre pressure is safeguarded if there is damage to the lines. Owing to the comparatively short duration inflation and deflation of the tyres which are made possible by the system described above, vehicles are enabled to move forward relatively rapidly in an area having varying ground or roadway conditions. Thus, vehicles that, for example, are moving over sandy terrain can continue driving on firm tracks or finished roads without stopping for the purpose of inflating the tyres. WHAT WE CLAIM IS:

1. A control system for changing the air pressure in a tyre of a vehicle, especially of a motor vehicle as it is being driven, the system including a switching valve having a compressed air inlet connection and an outlet connection, the outlet connection being joined by way of a control line to a control valve operable to control communication between the control line and the interior of the tyre, a pressuremeasuring unit in compressed air connection with the control line and operable to measure the pressure therein, and a control device operable to actuate the switching valve for a predetermined time period for the purpose of inflating or deflating the tyre, the measuring unit being connected to the control device to deliver a pressure-measurement signal thereto following an inflation or deflation of the tyre, said signal causing the control device to actuate the switching valve automatically for a further predetermined time period if the desired pressure has not been reached.

actuable by the control device when the desired pressure has been reached, to vent air from the control line and cause closure of the control valve.

3. A system as claimed in claim 1 or claim 2, in which the switching valve has a pressure release connection joined to a pressure limiting valve and serving to vent air from the tyre during deflation of the latter.

4. A system as claimed in any one of the preceding claims, in which the control device is an electronic device including an electrical pulse generator connected to actuate the switching valve.

5. A system as claimed in claim 4, in which the electronic control device is operable from a control panel located in the driving cab of the vehicle.

6. A system as claimed in any one of the preceding claims in which the switching valve is a multi-way double solenoid valve.

7. A system as claimed in any one of the preceding claims, in which the control valve includes a switching piston arrangement exposed to the pressure of compressed air coming from the control line, and a sealing element engageable with the piston arrangement to form a pressuretight seal and thereby close the control valve, the piston arrangement having a portion of reduced cross-section which, when aligned with the sealing element, releases the pressure-tight seal, thereby opening the control valve.

8. A system as claimed in claim 7, in which the piston arrangement is resiliently biased against the action of compressed air pressure from the control line.

9. A system as claimed in claim 7 or claim 8, in which the piston arrangement is exposed to compressed air pressure in the control line through bores in the control valve housing.

10. A control system for changing the air pressure in the tyres of a vehicle, substantially as described herein with reference to, and as illustrated by, the accompanying drawings.