Title of Invention

A CYLINDER HEAD FOR AN AIR COMPRESSOR OF A MOTOR VEHICLE

Abstract

A cylinder head for an air compressor of a motor vehicle, comprising a body and a cover joined together, the said body containing separate chambers for Intake and delivery air and hOMSing separate inlet valve and delivery valve discs, the said valve discs working with valve seats and valve springs aiding closure of the said valve discs, the said springs being made of multiple finger shaped limbs, the shape of the fingers providing a low force and spring rate in the closed position of the valves and a significantly higher force and spring rate in the open position of the valves.

Full Text

This invention relates to the cylinder head of the air compressor of a motor vehicle, more particularly to the valve assembly in the cylinder head of a compressor used in the air brake system of commercial vehicles. The cylinder head of the compressor consists of an arinular ring shaped intake valve, which opens during the suction stroke of the piston, filling the cylinder with air from the atmosphere. During the delivery stroke of the compressor, the said inlet valve is forced to close by a backing spring. When the pressure in the cylinder exceeds the pressure at the delivery of the compressor, an annular ring shaped delivery valve opens and delivers the compressed air to the delivery. During the next downward stoke of the piston, another backing spring behind the said delivery valve forces the valve to close. The compressors known to the art mostly employ circular disc type valves with helical coil springs or reed type valves, whose closing force Is provided by their own stiffness. Annular ring type valves are also known to the art, whose closing force is again provided by helical coil springs. The cylinder heads are also constructed such that inlet air coming into the cylinder head, compressed air leaving the cylinder head, and compressed air in the cylinder above the piston contact common walls of the cylinder head, allowing heating up of the inlet air by the hotter air in other parts of the cylinder. The valve system like a circular disc valve or annular ring shaped valve backed by helical coil springs with uniform stiffness for opening and cipeing positions of the valve, do not provide optimum volumatric efficiency for the compressor. Ideally, the valves should close instantly at the end of the respective suction and delivery strokes of the piston, such that cross flow across the valves do not take place at any part of the stroke of the piston. Such cross flow causes the inlet air to partially escape back to the inlet port during the compression stroke of the piston and the compressed air to flow past the delivery valve Into the cylinder during the suction stroke of the piston. To close the valves quickly, sufficiently high return spring force is required at the backing spring. However a higher spring force would also cause a delayed opening of the valves, causing lesser amount of air to be charged into the cylinder per cycle. Hence the valve spring forces should be optimised to achieve the objective of reducing the delay of opening and closing of the valves. The compressor for the air brake system of a motor vehicle is driven by the engine and speed of the engine varies form idling speed to the maximum speed. The compressor is expected to deliver compressed air with a high volumetric efficiency throughout the speed range. However, at different speeds of the compressor, the velocity of the piston and also the time available to fill the cylinder changes. Hence valve spring forces optimised for low speed operation will exhibit lower volumetric efficiency at higher speeds. Similarly spring forces optimised for high speed operation will have poor volumetric efficiency at lower speeds. In reed valve systems also, the stiffness of the reed is fixed and volumetric efficjipncy can be maximised only for a narrow range of speeds. This variation In volumetric efficiency with speed is one of the deficiencies of the known compressor. Another deficiency of the known compressor is heating up of the intake air by the hotter delivery air chamber and also by heat from the air compressed in the cylinder portion. This increases the delivery air temperature of the compressor. Longer metal pipes will be required to connect the delivery of the compressor to downstream coniponents like the air processing unit to bring down the teniperature of the air to acceptable limits. The higher delivery air temperatures will further result In more heat generation within the cylinder, which in turn results in burning up of the lubricating oil to form carbon deposits. This will result in frequent servicing of the compressor. The main fegiture of the present invention Is annular ring type Inlet and delivery valves whose opening and closing speeds are optimised for high volumetric efficiency throughout the speed range, the optimised opening and closing speeds being achieved by optimised force and rate of the return springs at the closed and open position! of the valves respectively. Yet another feature of the present invention is that the intake air and delivery air cavities in the cylinder head are separated by air pockets In the qylinder head. The intake and delivery cavities are also sepgifated tp a substantial extent by the said air pockets from the cylinder bora. These pockets also help atmospheric air to cool the hottest areas of the cylinder head. This feature reduces the delivery air temperature. This invention will now be described with reference to the accompanying drawings which illustrate, by way of example, and not by way of limitation, one of possible embodiments of this invention, wherein Figure 1 shows the partial view of a reciprocating air compressor with the cylinder head assembly. Figure 2 shows the section of the cylinder head assembly with the valve components Figure 3 shows the inlet valve in the closed condition Figure 4 shows the inlet valve in the open condition Figure 5 shows the delivery valve in the closed condition Figure 6 shows the delivery valve in the open condition Figure 7 shows an enlarged view of the valve disc and the valve return spring Illustrating how the spring load varies with the valve travel Figure 8 shows the cylinder head casting with the cavities to separate the Inlet and delivery chambers and also to separate the cylinder bore area. Referring to figure 1, the reciprocating air compressor known to the ^rt, qonsjits of a cylinder A, piston B moving within the bore of the said cylinder with the cylinder head assembly C fixed to the said cylinder. Referring to flggre 2, the cylinder head assembly consists of a body D and g cover E assembled through fixing screws F. The inlet air cavity Q from which air flows through the inlet valve during the suction stroke and the delivery cavity H to which compressed air flows through the delivery valve during the delivery stroke are indicated in figure 2. The inlet valve assembly consists of a valve seat M with holes for the passage of inlet air, an annular shaped valve disc O made of spring steel, a valve spring P made of spring steel and a valve stop N fixed to the valve seat M. The inlet valve assembly is attached to the body through threads on the inlet valve seat. The valve spring P is assembled such that it urges the valve disc to close over the valve seat holes when the compressor is at rest. The delivery vglve assembly consists of a valve seat I with holes for the passage of compressed delivery air, an annular shaped valve disc K made of spring steel, a valve spring L made of spring steel and a valve stop J fixed to the valve seat I. The delivery valve assembly Is attached to the body through threads on the delivery valve seat. The valve spring L is assembled such that it urges the valve disc K to close over the valve seat holes when the compressor is at rest. When the piston B moves on its downward stroke, which is normally referred to as suction stroke, the volume of air available in the cylinder expands. As both the inlet and delivery valves are closed against their respective valve seats, vacuum is created inside the cylinder. This causes the inlet valve disc O to move away from Its seat M, compressing the valve spring P. Figure 3 shows the Inlet ya've in the closed position and figure 4 shows the same valve |n the open condition with the valve disc stopping against the stop N- Air from the atmosphere enters through passages in the seat, the direction of air flow indicated by the arrow R. At the end of the suction stroke, the piston reverses direction and starts the delivery stroke. This causes the pressure in the cylinder to change from vacuum to atmospheric. Since the vacuum is no longer exerted on the inlet valve disc P, the spring urges the disc to close over the seat, shutting off air flow into the cylinder from inlet cavity H. Further movement of the piston In the delivery stroke causes the air to get compressed. The delivery valve experiences the air pressure in the delivery cavity G on one side and the air pressure from the cylinder on the other side. When the pressure Inside the cylinder exceeds the pressure In the cavity G, the delivery valve disc K compresses the valve spring L and moves away from the seat I. Figure 5 shows the delivery valve in the closed condition and figure 6 shows the same valve in the open condition with the valve disc stopping against the valve stop J. The air passage from the cylinder to the cavity G is marked by the arrow S. During the next suction stroke of the piston, the valve spring urges the delivery valve disc to close over the seat I, thMS preventing air flow from delivery cavity G to the cylinder. For the compressor to work with optimum volumetric efficiency, the inlet and delivery valve movement need to be optimised as described hereafter. The inlet valve should open early enough during the suction stroke. Hence this requires the force of the spring P in the valve closed condition to be low. During the delivery stoke, the inlet valve should close quickly. To achieve this quick closure of the valve, the spring force should be high enough. During the delivery stroke, similarly the delivery valve has to open even with a small positive differential pressure between the cylinder and the delivery cavity G. During the suction stroke, the delivery valve should close quickly to prevent compressed air from flowing from the delivery cavity G to the cylinder. Hence the force of the delivery spring P should also be low in the valve closed condition and high In the fully open condition. Referring to flgiire 7, the individual fingers of the valve spring act as a cantilever beam in the valve closed condition. The fingers of the spring undergo deflection when the valve disc starts opening compressing the spring. The fingers continue to act as a cantilever till the tips of the fingers touch the valve stop. During this stage of cjeflection corresponding to the initial opening of the valves, the spring force opposing the valve movement is low and the rate of the spring is also low. When the valve moves through the distance T1, the tip of the cantilever fingers touch the stop and the fingers act as propped cantilevers, thus increasing the rate of the spring sharply. Hence when the valve disc moves through an retentional distance T2 to the full open position, the opposing spring force is high. This feature of the spring with a low spring rate during travel T1 enables the valves to open early during the stroke of the piston. The high spring rate during the travel T2 ensures that adequate spring force is available to close the valves quickly so that the air does not flow In the reverse direction, causing a loss of volumetric efficiency. As already described the cylinder head contains an inlet air cavity G and a delivery air cavity H. The inlet air cavity is heated by the delivery air cavity, which contains hot compressed air, through the common ponnecting wall. Heat is also transferred to the inlet air cavity from the hot compressed air above the piston through the cylinder heac^ wall. When inlet air gets heated up due to such heat transfer, the temperature of the air at the end of compression also increases. Hence air delivered to downstream components in the brake system is also hotter. This increases the tendency for the lubricating oil of the compressor to form carbon deposits within the cylinder head, which further hampers heat transfer and Inpreases the delivery air temperature further. More length of metal pipe is required at the compressor delivery to cool down the delivery air before it reaches downstream components. Referring to figure 8, the cylinder head consists of air pockets U which separate the delivery and inlet air cavities and also the inlet air cavity from the cylinder area to a large extent. This reduces the heating up of the inlet air and henq^ rpclMCe$ the temperature of the compressed air. The pockets also facilitate the surrounding air to contact the hottest parts of the cylinder head and cool them. It will be appreciated from the foregoing description that various other embodiments of this invention are possible without departing from the scope and ambit thereof. We claim 1. A cylinder head for an air compressor of a motor vehicle, comprising a body and a cover joined together, the said body containing separate chambers for Intake and delivery air and hOMSing separate inlet valve and delivery valve discs, the said valve discs working with valve seats and valve springs aiding closure of the said valve discs, the said springs being made of multiple finger shaped limbs, the shape of the fingers providing a low force and spring rate in the closed position of the valves and a significantly higher force and spring rate in the open position of the valves. 2. A cylinder head for an air compressor of a motor vehicle, £)>5 a\ wherein the said valve discs are shaped in the form of annular rings made of spring steel. 3. A cylinder head for an air compressor of a motor vehicle, as claimed In pjaim 1 or Claim 2 wherein the said valve springs are made from spring steel sheet. 4. A cylinder head for an air compressor of a motor vehicle, as claimed In any one of the Claims 1 to 3 wherein the said body contains air pockets which separate the inlet and delivery valve chambers, the said Inlet and delivery air valve chambers be|ng similarly separated from the cylinder bore. 5. A cyllncjer head for an air compre^^or of a motor vehicle, substantially as herein described and illustrated with reference to the accompanying drawings.

Documents:

2614-CHE-2007 AMENDED CLAIMS 20-07-2012.pdf

2614-CHE-2007 AMENDED PAGES OF SPECIFICATION 20-07-2012.pdf

2614-CHE-2007 CORRESPONDENCE OTHERS 20-07-2012.pdf

2614-che-2007 form-6 16-06-2008.pdf

2614-CHE-2007 POWER OF ATTORNEY 20-07-2012.pdf

2614-che-2007-claims.pdf

2614-che-2007-correspondnece-others.pdf

2614-che-2007-description(complete).pdf

2614-che-2007-drawings.pdf

2614-che-2007-form 1.pdf

2614-che-2007-form 18.pdf

2614-che-2007-form 26.pdf