Air supply system with reduced oil passing in compressor

Abstract

An air supply system includes a compressor having a compression chamber, an inlet port through which air flows into the compression chamber and an outlet port through which air exits the compression chamber, an unloader which causes the compressor to be in an unloaded state when a desired system air pressure is maintained, an isolation valve preventing inlet air from flowing into the inlet port of the compressor when the compressor is in the unloaded state, and a source of pressurized air supplying pressurized air to the inlet port of the compressor at least when the isolation valve prevents inlet air from flowing into the inlet port of the compressor.

Description

FIELD OF THE INVENTION[0001]The present invention relates generally to air supply systems using reciprocating type air compressors and, more particularly, to compressor unloading systems usable in such air supply systems, such as might be found in air supply systems for truck air brakes and the like.BACKGROUND OF THE INVENTION[0002]It is well known in the art that in air supply systems, such as might be found in air supply systems for truck air brakes and the like, the air compressor operates in its pumping mode for only a relatively short period of time, and that it is operated in what is known as an unloaded mode for as much as approximately 70-90 percent of the time. How to unload the air compressor to save horsepower when the compressor is not pumping, without having other problems occur, has been a long standing problem in the art.[0003]Air compressors used in medium and heavy duty vehicle air supply systems, such as those found in transport trucks, passenger buses, and the lik...

AI Technical Summary

Benefits of technology

[0013]Accordingly, it is an object of the present invention to provide an air supply system which is efficient in operation and economical to manufacture.

[0014]Another object of the present invention is to provide an air supply system having the above characteristics and which reduces the horsepower used by air compressors in their unloaded mode as compared to traditional systems.

[0016]Still another object of the present invention is to provide an air supply system having the above characteristics and which causes relatively equalized pressure to be maintained on both sides of the compressor pistons.

[0017]Yet a further object of the present invention is to provide an air supply system having the above characteristics and which results in reduced levels of oil passing around the compressor piston rings when the compressor is in its unloading mode.

[0021]In some embodiments, the isolation valve comprises a valve body moveable, in response to the pneumatic signal received at the signal port of the isolation valve, between an open position in which the isolation valve allows air to flow from the inlet port of the isolation valve to the outlet port of the isolation valve, and thereby allows air to flow from the source of inlet air to the inlet port of the compressor, and a closed position in which the isolation valve prevents air from flowing from the inlet port of the isolation valve to the outlet port of the isolation valve, and thereby prevents air from flowing from the source of inlet air to the inlet port of the compressor. In certain of these embodiments, the valve body is biased toward the open position, and is moveable against the bias to the closed position when the pneumatic signal is received at the signal port of the isolation valve.

Problems solved by technology

How to unload the air compressor to save horsepower when the compressor is not pumping, without having other problems occur, has been a long standing problem in the art.

This method of unloading is now generally viewed as unsatisfactory because of the noise produced, and the horsepower losses incurred.

In many cases, when the intake valve was held open on a single cylinder air compressor and the compressor was supplied with naturally aspirated air, which was common at the time, since the compressor intake was supplied with a separate air cleaner, pumping back and forth through the air cleaner in many cases destroyed the air cleaner, or reduced its efficiency so it would not perform for the purpose for which it was intended.

This caused some truck manufacturers to switch to a system supplied with turbocharged inlet air from the engine turbocharger to avoid the air cleaner problems and assure a clean inlet air supply, but it was then found that when unloading in the conventional way, by holding the intake valve open, the faster the engine was running, the denser the air, and the more horsepower was lost due to the unloading.

A clutched compressor was developed, but was not felt to be the answer to the horsepower loss problem because the compressor shaft normally runs through the compressor and often drives other accessories, such as the power steering, or engine fuel pump, and it was not satisfactory to have the power steering and other items nonfunctional for the time the compressor was unloaded.

Also, the clutched compressor would substantially increase the cost of the air supply system, and this was not satisfactory.

Thus, not much progress was made in developing a more efficient compressor unloading system, and simply holding the intake valve open to allow unloading either to atmosphere, or the engine turbocharger, was the accepted way of unloading the air compressor for some time.

However, while the system disclosed in U.S. Pat. No. 4,993,992 does provide advantages over previously known systems, it suffers from disadvantages of its own.

One such disadvantage was that, while the system employs elevated pressure at the exhaust side of the compressor in order to prevent the exhaust valve from operating, the pressure at the intake side remains relatively low.

This pressure differential, in turn, leads to increased levels of oil passing, which, as is known, leads to further complications within the system.

Images