Fluid-pressure and analogous brake systems – Multiple fluid-receiving devices – Multiple motors
Reexamination Certificate
1999-10-21
2001-08-21
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Multiple fluid-receiving devices
Multiple motors
C303S127000, C303S008000, C303S009660
Reexamination Certificate
active
06276761
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention concerns a vehicle braking system, and particularly an air braking system of the kind used on commercial vehicles.
Light vehicles such as cars and vans use dual circuit hydraulic braking systems, often with servo assistance. Heavier vehicles such as trucks and buses often use air braking systems in which air under pressure is the working medium.
A typical air braking system will include an air compressor, an air reservoir, a distribution valve, two service brake circuits and a handbrake circuit. Other components such as an air dryer and oil filter may be provided to ensure that the air supplied is at a desired quality. In addition to the usual three braking circuits air may also be supplied to a low pressure auxiliaries circuit where it is used for example for gear shift assistance or drivers seat adjustment. A high pressure auxiliary circuit may be provided, for example for vehicle air suspension control.
The distribution of air under pressure between the respective circuits is highly complex. As a priority air must be supplied to the brake circuits, but for example it is undesirable for a handbrake circuit to permit release of the handbrake whilst air pressure in the service brake circuits is low. The braking system must have carefully designed distribution arrangements to ensure that an air leak in one circuit does not result in loss of air pressure in all circuits; these arrangements may be very complex in order to give effective braking under all likely failure conditions. The air compressor must be large enough to meet all reasonable needs, but not to be so large that power consumption is unnecessarily high. The components of the braking system are preferably designed to meet the alternative legislative requirements which may be in force in different countries. For example legislation may limit the maximum usable pressure in some circuits but not in others. Finally the cost of the braking system must be maintained at a reasonable level for competitive reasons.
A conventional air braking system usually includes a rather complicated valve block which houses numerous valves, restrictors and other fluid components, the purpose of which is to direct air from the compressor to the air consumer circuits in the desired manner. Each valve block is designed for a particular vehicle installation and, once manufactured, is not susceptible of modification or adaptation. The danger of contamination is such that tampering or repair is discouraged. The manufacturing tolerances of a valve block must be very precisely controlled in order to ensure that the braking system operates correctly. The requirement for close tolerances leads to a consequential increase in manufacturing cost, and the potential for a high scrap cost if a mistake is made in the manufacturing process.
In order to reduce costs it would be desirable to reduce the number of different valve blocks. Furthermore it would be desirable to be able to adapt a valve block to generally different circumstances of use without requiring a re-design of the fluid components therein. It would also be useful to be able to tune a valve block to the precise circumstances of a particular vehicle application.
BRIEF SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided an air braking system of a vehicle comprising a compressor, an air consumer circuit, a first electrically actuable valve between said compressor and said consumer circuit, an auxiliary air circuit, and a second electrically actuable valve between said compressor and said auxiliary circuit, wherein said auxiliary circuit is connected to said consumer circuit via a non-return valve.
In use said first and second valves are normally maintained closed and said first valve is opened according to the demand of said consumer circuit. In the event of an electrical failure of said first valve, the auxiliary circuit can be arranged to supply said consumer circuit via the second valve and the non-return valve. The non-return valve ensures that the consumer circuit does not feed the auxiliary circuit.
The system preferably includes a plurality of consumer circuits each supplied via a respective electrically actuable valve, and each having a connection to the auxiliary circuit via a respective non-return valve. Thus a failure of any of the electrically actuable valves supplying a consumer circuit can be overcome, as least partly by supplying air under pressure from the auxiliary circuit.
In a preferred embodiment the consumer circuit is supplied by a valve normally biased closed by resilient means, whereas the valve supplying the auxiliary circuit is normally biased open by resilient means. Thus an electrical failure ensures that fluid pressure is available to the consumer circuit via the auxiliary circuit. In normal operation however the valve supplying the auxiliary circuit is energized, and thus closed.
The auxiliary circuit may include a pressure relief valve.
According to a second aspect, the invention provides a method of operating the air braking system according to the first aspect of the invention, the method comprising the steps of
1) maintaining said first and second valves closed,
2) opening said first valve on demand to supply said consumer circuit, and
3) in the event of an electrical failure, causing said second valve to open, thereby to supply air under pressure to said consumer circuit via said auxiliary circuit.
According to a third aspect of the invention there is provided an air braking system of a vehicle, the system comprising a compressor, a distribution manifold, a non-return valve between said manifold and said compressor, a first air circuit, a second air circuit, a first electrically actuable valve between said manifold and said first air circuit, a second electrically actuable valve between said manifold and said second air circuit, sensor means to determine the condition of said first and second air circuits and logic means responsive to said sensor means to open and close said solenoid valves to permit charging of said circuits from said compressor and connection of said circuits via said manifold.
Such a braking system can eliminate the usual valve block and admit air to a respective air circuit according to pre-programmed logic. A standard distribution valve may include two or more full flow electrically actuable valves, and be suitable for use on many kinds of vehicle according to programming of the logic means. An alternative logic means can change the operating characteristics of the system without requiring modification of the distribution valves themselves. Lengthy re-design and testing for different vehicle specifications is obviated. Cost is substantially reduced due to standardization, and the individual valves may be replaceable as discrete units without compromising overall system safety.
The logic means may include a programmable element to permit the logic to be changed or tuned to meet specific needs of an air braking system. The electrically operable valve may be a solenoid valve.
The non-return valve between the compressor and the consumer circuits permits air under pressure in one circuit to be fed to another circuit independently of the compressor. In this way air under pressure in an auxiliaries circuit could be directed to a service brake circuit so as to give a greater safety reservoir in the event of compressor failure, or to permit more efficient use of the compressor in normal operation.
Thus there is the possibility that the usual service brake reservoir can be reduced in size because a reservoir of an auxiliaries circuit can be made available to supplement the service brake reservoir. Alternatively the compressor itself may have a reduced output during normal vehicle operation owing to the reservoirs of all of the independent circuits being available to supplement the reservoir of one or two circuits. Numerous possibilities for diverting air between air circuits exist, leading to the possibility of a reduction in compressor size and/or greater efficie
Kramer Devon
Oberleitner Robert J.
Stroock & Stroock & Lavan LLP
WABCO Automotive (UK) Limited
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