Piston assembly for an unloader valve of an air compressor

Abstract

A piston assembly is provided for an unloader valve of an air compressor. The assembly comprises an unloader piston having a first bore of a first diameter, and a second bore of a second diameter which is smaller than the diameter of the first bore. The assembly also comprises a coil spring having a central opening, one end portion disposed in the second bore, and an opposite end portion extending into the first bore. The assembly further comprises a balance piston including a head portion sized to be disposed in the first bore, a first stem portion extending from the head portion and having a diameter smaller than the first and second bores, and a second stem portion extending from the first stem portion and extending into the central opening of the coil spring and having a diameter smaller than the first stem portion.

What is claimed is: 
     
         1 . A piston assembly for an unloader valve of an air compressor, the piston assembly comprising:
 an unloader piston having (i) a first bore of a first diameter, and (ii) a second bore of a second diameter which is smaller than the diameter of the first bore;   a coil spring having a central opening, one end portion disposed in the second bore of the unloader piston, and an opposite end portion extending into the first bore of the unloader piston; and   a balance piston including (i) a head portion having a diameter sized to be disposed in the first bore of the unloader piston, (ii) a first stem portion extending from the head portion and having a diameter smaller than the diameter of the first and second bores of the unloader piston, and (iii) a second stem portion extending from the first stem portion and extending into the central opening of the coil spring and having a diameter smaller than the diameter of the first stem portion.   
     
     
         2 . A piston assembly according to  claim 1 , wherein the balance piston includes a tapered stem portion interconnecting the first and second stem portions. 
     
     
         3 . A piston assembly according to  claim 2 , wherein the tapered stem portion comprises a spline form from the first and second stem portions. 
     
     
         4 . A piston assembly according to  claim 1 , wherein the unloader piston has a third bore having a third diameter which is smaller than the diameter of the second bore, wherein the second bore is disposed between the first bore and the third bore. 
     
     
         5 . A piston assembly according to  claim 1 , further comprising:
 a first seal disposed in a first seal cavity disposed in an inner diameter bearing surface of the unloader piston to provide an air-tight seal between an outer diameter bearing surface of the head portion of the balance piston and an inner diameter bearing surface within the first bore of the unloader piston.   
     
     
         6 . A piston assembly according to  claim 5 , further comprising:
 a second seal disposed in a second seal cavity disposed in a first outer diameter bearing surface of the unloader piston to provide an air-tight seal between the first outer diameter bearing surface of the unloader piston and a first inner diameter bearing surface of a cylinder head of the compressor.   
     
     
         7 . A piston assembly according to  claim 6 , further comprising:
 a third seal disposed in a third seal cavity disposed in a second outer diameter bearing surface of the unloader piston to provide an air-tight seal between the second outer diameter bearing surface of the unloader piston and a second inner diameter bearing surface of the cylinder head of the compressor.   
     
     
         8 . A piston assembly according to  claim 1 , wherein the unloader piston is responsive to a control signal pressure to move the unloader piston against bias of the coil spring and thereby to move the unloader piston from the loaded position to the unloaded position. 
     
     
         9 . A piston assembly according to  claim 1 , wherein the one end portion of the coil spring abuts a surface of the unloader piston and the opposite end portion of the coil spring abuts a surface of the balance piston. 
     
     
         10 . An unloader valve apparatus for an air compressor, the unloader valve apparatus comprising:
 an unloader piston having a longitudinal central axis and movable along the longitudinal central axis between a loaded position and an unloaded position;   a coil spring having a central opening and disposed in the unloader piston; and   a balance piston including (i) a head for supporting movement of the unloader piston between the loaded position in which the unloader piston blocks an associated unloading passage and the unloaded position in which the unloader piston is not blocking the unloader passage, and (ii) a stem extending from the head and including means for reducing wear of the stem as the coil spring vibrates when the unloader piston is in the loaded position.   
     
     
         11 . An unloader valve apparatus according to  claim 10 , wherein the means comprises a tapered stem portion. 
     
     
         12 . An unloader valve apparatus according to  claim 10 , wherein the means comprises first and second stem portions and a tapered stem portion interconnecting the first and second stem portions. 
     
     
         13 . An unloader valve apparatus according to  claim 10 , wherein the means comprises first and second stem portions each stem portion having a different diameter. 
     
     
         14 . An unloader valve apparatus according to  claim 13 , wherein the means comprises a tapered stem portion interconnecting the first and second stem portions. 
     
     
         15 . An unloader valve apparatus according to  claim 14 , wherein the tapered stem portion comprises a spline form from the first and second stem portions. 
     
     
         16 . A vehicle air compressor apparatus for a heavy vehicle braking system, the vehicle air compressor apparatus comprising:
 a compressor crankcase assembly;   a compressor cylinder head assembly disposed on the crankcase assembly and co-operating with the crankcase assembly to generate compressed air, wherein the cylinder head assembly includes (i) an air inlet port through which air can be received for compression within the crankcase and cylinder head assemblies, (ii) a discharge port through which compressed air can be delivered from the cylinder head assembly; and (iii) an unloading passage; and   an unloader valve assembly connected internally of the crankcase and cylinder head assemblies and including (i) a coil spring including opposite end portions and a central opening extending between the opposite end portions, (ii) an unloader piston having a bore in which one of the opposite end portions of the coil spring is disposed, and (iii) a balance piston including a first stem portion having a first diameter and a second stem portion having a diameter which is different from the diameter of the first stem portion, wherein the first and second stem portions are disposed in the central opening at one of the opposite end portions of the coil spring.   
     
     
         17 . A vehicle air compressor apparatus according to  claim 16 , wherein the unloader piston is movable against biasing force of the coil spring between a blocking position in which compressed air is blocked from leaving the unloading passage as compressed air is being delivered through the discharge port and an unloaded position in which compressed air is allowed to be unloaded from the crankcase and cylinder head assemblies. 
     
     
         18 . A vehicle air compressor apparatus according to  claim 16 , wherein the balance piston includes a tapered stem portion interconnecting the first and second stem portions. 
     
     
         19 . A vehicle air compressor apparatus according to  claim 18 , wherein the tapered stem portion comprises a spline form from the first and second stem portions. 
     
     
         20 . A vehicle air compressor apparatus according to  claim 16 , wherein the balance piston includes a head portion extending from the first stem portion and having a diameter larger than each of the diameters of the first and second stem portions.