GB2165893A - Unloading twin cylinder compressor - Google Patents

Abstract

A twin-cylinder compressor includes a housing (12) defining the cylinder bores pistons reciprocable in the bores, and pressure responsive inlet and outlet valves for each cylinder bore. A pair of apertures (90, 92) communicate each of the bores into a common cavity (52) having a disc-shaped relief valve (94) normally urged into sealing engagement with both of the apertures and having a pressure responsive piston (100) responsive to a pressure signal produced when the compressor is to be unloaded. The signal causes the valve (94) to move away from the apertures, so that the compressor pumps air back and forth between the cylinder bores, <IMAGE>

Description

SPECIFICATION Gas compressor This invention relates to a gas compressor with an unloading valve especially a twin cylinder feed valve compressor for automotive applications.

Air compressors are commonly used on heavy duty trucks to compress air for use in the air brake systems. These air compressors are normally driven continuously by the vehicle engine, but the air usage of this type of vehicle is such that the air compressor must compress air only a relatively small percentage of the time that the air compressor is operated, as little as 5% or less in the case of long haul trucks used on open highways. Accordingly, a mechanism must be provided for disabling or "unloading" the compressor when the storage reservoirs on the vehicle have been charged to the correct level.

Prior art unloading mechanisms commonly respond to a pressure signal generated by a conventional governor to cause the inlet valves of the compressor to be held open, thereby disabling the compressor so that, while the compressor is still being operated, it will not compress air. Whereas air compressors have subsequently been designed with reed valves to more efficiently control the communication into and out of the cylinders of the air compressors reed valves are very difficult to hold open during unloading.

According to the present invention there is provided a gas compressor having two cylinders with respective reciprocating compression members arranged such that when one said member is compressing air the volume of a respective compression chamber the other is expanding and vice versa, each cylinder being provided with an inlet valve and each cylinder having a delivery valve via which compressed gas is fed to a receiver and further valve means responsive to a predetermined pressure being attained in said receiver for interconnecting said compression chambers to unload the compressor.

The present invention will now be further described by way of example with reference to the accompanying drawings, in which Figure 1 is a side elevational view, partly in cross section, of an air compressor made pursuant to the teachings of the present invention: Figure 2 is a fragmentary partial cross-sectional view taken substantially along lines 2-2 of Figure 3.

Figure 3 is a view taken substantially along lines 3-3 of Figure 1: Figure 4 is a view taken substantially along lines 4-4 of Figure 1; and Figure 5 is a view taken substantially along lines 505 of Figure 1.

Referring now to the drawings, an air compressor generally indicated by the numeral 10 includes a cylinder block or housing 12 in which a pair of substantially parallel cylindrical bores 14, 16 are machined. One end of the bores opens into a crankcase generally indicated by the numeral 20 which is defined within the lower portion 22 of the cylinder block or housing 12. A pair of roller bearings, only one of which is shown as at 24, rotatably mount a crankshaft 26 for rotation within the crankcase 20. If the air compressor 10 is used to supply compressed air into a vehicle air brake system, the crankshaft 26 is connected for rotation by the vehicle engine. A pair of pistons 28, 30 are slideably mounted in the bores 14, 16 respectively.

A pair of connecting rods 32, 34 connect corresponding pistons 28, 30 to the crankshaft 26 through crank pins 36, 38 in a manner well known to those skilled in the art. Accordingly, since the connecting rods 32, 34 are mounted on corresponding articulations in the crankshaft 26, the rotation of the crankshaft 26 will cause the pistons 28, 30 to move within their corresponding bores 14, 16 in sequential timed relationship with one another, such that when one piston (piston 28 viewing the drawing) is at the top of its stroke, the other piston (piston 30 in the drawing) is at the bottom of its stroke. The pistons 28, 30 cooperate with the corresponding upper ends of their bores to define pressure chambers 40, 42 therebetween, where air communicated into the pressure chambers 40, 42 is compressed to provide compressed air.

The upper ends (viewing Figure 1) of the bores 14, 16 are closed by a valve plate 44 which is clamped between a head assembly 48 and the cylinder block 12. An inlet 50 on one side of block 12 communicates air into an inlet cavity 52 defined within the head assembly 48. Coolant inlets 54 communicate coolant into a water jacket, a portion of which is illustrated at 56, to cool the head assembly 48 in a manner well known to those skilled in the art.

The head assembly 48 includes the inlet cavity 52 and an outlet cavity 58 which is separated from the inlet cavity or chamber 52 by a wall 60. Compressed air is communicated from the outlet chamber or cavity 58 to appropriate fluid storage devices (not shown) through an outlet port 62. The inlet chamber or cavity 52 communicates with the pressure chambers 40, 42 through openings 64, 66 respectively in the valve plate 44 which communicate with the corresponding bores 14, 16. A pair of reed valves 68, 70 control communication through the corresponding openings 64, 66. The reed valves are manufactured from a resilient metallic material such as spring steel.As most clearly seen in Figure 5, each of the reed valves 68, 70 include tabs 67 which are mounted in recesses 69 provided in the upper surface of the block 12 (which the valve plate 44 engages), and an elongated aperture 71 near the centre of each valve 68, 70. When the pressure level in the pressure chambers 40 or 42 drops below the pressure level in the inlet chamber 52, which would be caused by the corresponding piston 28 or 30 moving downwardly in the bore, the reed valves 68, 70 are deflected off of their corresponding valve seats to permit air to communicate from the inlet chamber 52 into the corresponding pressure chamber 40 or 42 through the openings 64 or 66, the aperture 71, and around the periphery of the valves.

Communication between the pressure chambers 40, 42 and the outlet cavity 58 is controlled by delivery valves generally indicated by the numerals 76, 78. The delivery valves 76, 78 are also manufactured from a resilient metallic material, are mounted on the upper surface of plate 44 viewing the Figures, and are provided with backup members generally indicated at 80, 82. Openings 77, 79 are provided in the plate 44 which are in registry with the apertures 71 of the inlet valves. When the pressure level in either of the pressure chambers 40, 42 exceeds the pressure level in the outlet cavity 58, as would occur when the pistons 27, 30 approach the top of their stroke viewing Figure 1, the delivery valves 76, 78 are deflected away from openings 77, 79 to permit communication from the pressure chambers 40 or 42 into the outlet cavity 58.Delivery valve back up members 80, 82 are provided to limit the deflection of the reed valves 76, 78. The backup members 80, 82 are installed on the valve plate 44 by threaded bolts which extend through the valve plate 44.

The portion of the head assembly 48 straddling the dividing wall 18 is provided with a generally circular cavity 88 which overlies a smail portion of each of the bores 14, 16. Apertures 90,92 extend through the valve plate 44 to communicate each of the pressure chambers 40, 42 with the cavity 88. A substantially circular relief valve member 94 is mounted for substantially vertical movement in the cavity 88 viewing Figure 2 and is adopted to sealingly engage the plate 44 to prevent communication through the apertures 90, 92 or to move away from the apertures 90, 92 to permit communication between the pressure chambers 40, 42 by way of the cavity 88. The cavity 88 is defined by a wall 96 within the head assembly 48, which cooperates with the other portions of the head assembly 48 to define a bore 98 therewithin.A pressure responsive piston 100 is slideably mounted in the bore 98 and is provided with an extension 102 which is engaged with the relief valve member 94. A spring 104 yieldably urges the piston 100 downwardly viewing the drawing, thereby yieldably maintaining the relief valve member 94 at a position covering the apertures 90, 92. A passage 106 communicates a pressure signal from the aforementioned governor (not shown) when it is necessary to unload the compressor.

In operation, the crankshaft 26 is connected for rotation by the vehicle engine. Rotation of the crankshaft 26 causes the pistons 28, 30 to move upwardly and downwardly in their corresponding bores 14 or 16 in a manner well known to those skilled in the art.

Downward movement of the pistons 28 or 30 draws air into the corresponding pressure chambers 40 or 42 by deflecting the corresponding inlet valves 68, 70 to draw air into the corresponding chambers 40 or 42, and upward movement of either of the pistons 28, 30 compresses air in corresponding pressure chamber 40, 42. When the air is compressed to a sufficient degree, the delivery valves 76, 78 moves away from their corresponding openings 77, 79 to permit communication of compressed air into the outlet chamber 58. The compressed air is communicated from outlet chamber or cavity 58 to a fluid receiving reservoir (now shown) through the outlet 62.

As described hereinabove, the spring 104 normally loads the piston 100 downwardly viewing Figure 2, thereby maintaining the relief valve member 94 in a position sealingly engaging the apertures 90, 92, to prevent compressed air from escaping from either of the pressure chambers 40, 42 through the apetures 90 or 92.

However, when it becomes necessary to unload the compressor due to the fact that the aforementioned pressure reservoir is at the predetermined pressure level, the aforementioned governor (now shown) produces a pressure signal which is communicated to the bore 98 through the passage 106 where it acts upon the face 108 of the piston 100 to urge the latter upwardly viewing Figure 2, thereby compressing the spring 104. As the piston 100 is lifted upwardly, the higher pressure air in the chamber 40 or 42 urges the relief valve member 94 away from the apertures 90, 92 permitting air to communicate from the pressure chamber 40 or 42 at the higher pressure level to the pressure chamber at the lower pressure level. Since the pistons 28, 30 are moving up and down in the bores 14, 16, the pressure levels in the compression chambers 40, 42 will always be alternately increasing and decreasing, so that air is continually pumped from one of the pressure chambers 40 or 42 to the other pressure chambers as long as the compressor is unloaded.

It will also be noted that the relief valve member 94 may be urged off of its sealing engagement with the apertures 90, 92 if the pressure level in one of the chambers should increase above a safe level due, for example, to a blockage or freeze-up of a delivery passage. The higher pressure level in the apertures acting against the relief valve 94 will urge the latter in opposition to the spring 104 even in the absence of a pressure signal, to thereby relieve the pressure in the pressure chamber at the exceedingly high pressure level.

Claims (6)

1. A gas compressor having two cylinders with respective reciprocating compression members arranged such that when one said member is compressing air the volume of a respective compression chamber of the other is expanding and vice versa, each cylinder being provided with an inlet valve and each cylinder having a delivery valve via which compressed gas is fed to a receiver and further valve means responsive to a predetermined pressure being attained in said receiver for intercommunicating said compression chambers to unload the compressor.

2. A gas compressor comprising a housing defining a pair of parallel bores therewithin separated by a dividing wall, each of said bores having a piston reciprocally mounted therein, a crankshaft rotatably mounted in said housing at a corresponding end of each of said bores and oper ably connected to said pistons for movement of the pistons in response to rotation of the crankshaft, the other ends of said bores being closed by a cylinder head assembly, an inlet port for commu nicating compressed gas from the housing, inlet valve means for controlling communication from said inlet port into said bores, delivery valve means for controlling communication from said bores to said outlet port, means for receiving a pressure signal generated in response to a predetermined pressure level in a storage vessel communicated to the outlet port, and communication initiating means independent of said inlet valve means CANNOT READ LAST LINE! between said bores in response to said pressure signal, said head assembly including a plate covering said other ends of said bores, said communication initiating means includes a cavity in said head, a pair of apertures in said plate communicating with said cavity, one of said apertures communicating with one of said bores, the other aperture communicating with the other bore, a single relief valve member slidably mounted in said cavity and movable toward and away from positions opening both of said apertures and closing both of said apertures, and a pressure responsive piston responsive to said pressure signal for normally holding said relief valve member in a position closing said apertures in the-absence of said pressure signal but responding to said pressure signal to open said apertures to permit communication between said bores by way of said apertures, said apertures being located in said plate adjacent and on opposite sides of said dividing wall, and relief valve member being disposed in said cavity to extend across said dividing wall to simultaneously cover both of said apertures.

3. A gas compressor as claimed in claim 1, wherein said inlet and delivery valves are reed valves mounted on said plate and cooperating with the latter to control communication to and from said bores.

4. A gas compressor as claimed in claim 1, wherein said inlet and delivery valves are reed valves mounted on said plate and cooperating with the latter to control communication to and from said bores, wherein said inlet valves and said delivery valves are separated from said apertures by portions of said plate.

5. A gas compressor comprising a housing defining a pair of parallel bores therewithin separated by a dividing wall, each of said bores having a piston reciprocally mounted therein, a crankshaft rotatably mounted in said housing at a corresponding end of each of said bores and operably connected to said pistons for movement of the pistons in response to rotation of the crankshaft, the other ends of said bores being closed by a cylinder head assembly, an inlet port for communicating compressed gas from the housing, inlet valve means for controlling communication from said inlet port into said bores, delivery valve means for controlling communication from said bores to said outlet port, means for receiving a pressure signal generated in response to a predetermined pressure level in a storage vessel communicated to the outlet port, and communication initiating means independent of said inlet valve means and said delivery valve means for initiating communication between said bores in response to said pressure signal, said head assembly including a plate covering said other ends of said bores, said communication initiating means including a cavity in said head, a pair of apertures in said plate communicating with said cavity, one of said apertures communicating with one of said bores, the other aperture communicating with the other bore, a single relief valve member slidably mounted in said cavity and movable toward and away from positions opening both of said apertures and closing both of said apertures, and a pressure responsive piston responsive to said pressure signal for normally holding said relief valve member in a position closing said apertures in the absence of said pressure signal but responding to said pressure signal to open said apertures to permit communication between said bores by way of said apertures, a spring yieldably maintaining said piston against said relief valve member and said relief valve member in sealing engagement with said apertures, said piston moving in opposition to said spring in response to said pressure signal to permit said relief valve member to move away from said apertures, said relief valve member being responsive to pressures at either of said apertures in excess of a predetermined level necessary to overcome said spring to move away from said apertures to permit communication between said bores, said apertures being located in said plate adjacent and on opposite sides of said dividing wall, said relief valve member being disposed in said cavity to extend across said diving wall to simultaneously cover both of said apertures.

6. A gas compressor substantially as described herein with reference to the accompanying drawings.