阅读说明：本技术 用于空气压缩机的卸载器阀的活塞组件 (Piston assembly for unloader valve of air compressor ) 是由 J·迈拉尔 J-B·马雷斯科 B·希罗 A·沙泽勒 J-L·梅扎 于 2020-04-02 设计创作，主要内容包括：本申请涉及一种用于空气压缩机(2)的卸载器阀(16)的活塞组件(26),该活塞组件包括：卸载器活塞(28),该卸载器活塞具有包括具有第一孔径的第一孔(36)的一个端部、包括具有第二孔径的第二孔(40)的居间部分和包括具有第三孔径的第三孔(44)的相反端部；螺旋弹簧(30),其具有中心开口(52)、布置在卸载器活塞(28)的第二孔中的一个端部以及延伸到卸载器活塞(28)的第一孔(26)中的相反端部；以及包括头部(48)和杆部(50)的平衡活塞(32),其头部具有布置在卸载器活塞(28)的第一孔(36)中的直径,其杆部从头部(48)延伸到螺旋弹簧(30)的中心开口(52)中并且杆部的直径小于头部(48)的直径。其中,杆部(50)在背离头部(48)的端部(82)处的直径基本上对应于螺旋弹簧(30)的中心开口(52)的内径。平衡活塞(32)包括热保护机构(82；84；86；88；92)。本申请还涉及一种用于空气压缩机(2)的包括根据本发明的活塞组件(26)的卸载器阀组件(16),以及一种用于重型车辆的空气制动系统的根据本发明的包括压缩机曲轴箱组件(6)、压缩机气缸盖组件(4)和卸载器阀组件(16)的空气压缩机。(The present application relates to a piston assembly (26) for an unloader valve (16) of an air compressor (2), the piston assembly comprising: an unloader piston (28) having one end including a first bore (36) having a first bore diameter, an intermediate portion including a second bore (40) having a second bore diameter, and an opposite end including a third bore (44) having a third bore diameter; a coil spring (30) having a central opening (52), one end disposed in the second bore of the unloader piston (28), and an opposite end extending into the first bore (26) of the unloader piston (28); and a balance piston (32) including a head (48) having a diameter disposed in the first bore (36) of the unloader piston (28) and a shaft (50) extending from the head (48) into a central opening (52) of the coil spring (30) and having a diameter less than the diameter of the head (48). Wherein the diameter of the shank (50) at the end (82) facing away from the head (48) substantially corresponds to the inner diameter of the central opening (52) of the helical spring (30). The balance piston (32) includes a thermal protection mechanism (82; 84; 86; 88; 92). The application also relates to an unloader valve assembly (16) for an air compressor (2) comprising a piston assembly (26) according to the invention, and an air compressor according to the invention for an air brake system of a heavy vehicle comprising a compressor crankcase assembly (6), a compressor cylinder head assembly (4) and an unloader valve assembly (16).)

1. A piston assembly (26) for an unloader valve (16) of an air compressor (2), comprising:

An unloader piston (28) having one end including a first bore (36) having a first bore diameter, an intermediate portion including a second bore (40) having a second bore diameter, and an opposite end including a third bore (44) having a third bore diameter, wherein the first bore diameter is larger than the second bore diameter, which in turn is larger than the third bore diameter;

a coil spring (30) having a central opening (52), one end disposed in the second bore (40) of the unloader piston (28), and an opposite end extending into the first bore (36) of the unloader piston (28);

a balance piston (32) comprising a head (48) having a diameter to be disposed in the first bore (36) of the unloader piston (28) and a shaft (50) extending from the head (48) into a central opening (52) of the coil spring (30) and having a diameter less than a diameter of the head (48); and

the diameter of the shank (50) at the end (82) facing away from the head (48) corresponds substantially to the inner diameter of the central opening of the helical spring (30),

the method is characterized in that:

the balance piston (32) includes a thermal protection mechanism (82; 84; 86; 88; 92).

2. The piston assembly (26) of claim 1, wherein the thermal protection mechanism includes a groove section (84) between an end (78) extending from the head (48) and an end (82) facing away from the head (48) and a thermal shield formed by the end (82) facing away from the head (48).

3. The piston assembly (26) of claim 2, wherein the stem (50) further includes an intermediate portion (80) interconnecting an end (78) extending from the head (48) and an end (82) facing away from the head (48), both ends (78, 82) having a first diameter and the intermediate portion (80) having a second diameter less than the first diameter.

4. A piston assembly (26) according to any of claims 1 to 3, wherein the thermal protection means comprise a cap (86) of high temperature resistant material at the end (82) facing away from the head (48) and/or a disc (88) of high temperature resistant material at the head (48) of the balancing piston (32).

5. The piston assembly (26) of claim 4, wherein the high temperature resistant material is a high temperature resistant plastic.

6. The piston assembly (26) of any of claims 3-5, wherein the length of the intermediate portion (80) is at least half and up to 80% of the length of the stem portion (50).

7. The piston assembly (26) of claim 1 wherein the thermal protection mechanism includes a cooling line (92) integrated into the balance piston (32).

8. The piston assembly (26) of claim 7, wherein the cooling line (92) is filled with a cooling fluid.

9. The piston assembly (26) of any of claims 1-8, wherein the rod portion (50) has a length that is at least 50% of the length of the coil spring (30) and at most 95% of the length of the coil spring (30).

10. The piston assembly (26) of any of claims 1-9, wherein the piston assembly (26) further comprises:

a first seal (58) configured to provide a gas-tight seal between an outer diameter bearing surface (60) of a head (48) of the balance piston (32) and an inner diameter bearing surface (62) within a first bore (36) of the unloader piston (28);

a second seal configured to be capable of providing a hermetic seal between a first outer diameter bearing surface (66) of the unloader piston (28) and a first inner diameter bearing surface (68) of a cylinder head of the compressor (2); and

a third seal configured to provide a hermetic seal between a second outer diameter bearing surface (72) of the unloader piston (28) and a second inner diameter bearing surface (74) of a cylinder head of the compressor (2).

11. The piston assembly (26) of any of claims 1-10, wherein a diameter of the central opening (52) of the coil spring (30) and a diameter of the stem (50) are such that a clearance fit is formed between the central opening (52) and the stem (50).

12. A piston assembly (26) according to any of claims 1 to 11, wherein one end of the helical spring (30) abuts a surface (54) of the unloader piston (28) and an opposite end of the helical spring (30) abuts a surface (56) of the balance piston (32).

13. The piston assembly (26) of any of claims 1-12, wherein the piston assembly (26) further comprises a cover plate (22), the cover plate (22) disposed on an opposite side of the head portion (48) from the stem portion (50), wherein the cover plate (22) is separate from the head portion (48) or is integrally formed with the head portion (48).

14. An unloader valve assembly (16) for an air compressor (2), the unloader valve assembly (16) comprising:

a piston assembly (26) according to any one of claims 1 to 13, wherein the unloader piston (28) is responsive to a control signal pressure to move the unloader piston (28) against the biasing force of the coil spring (30) to move the unloader piston (28) along its longitudinal center axis (34) from a loaded position in which the unloader piston (28) blocks an associated unloading passage (76) to an unloaded position in which the unloader piston (28) does not block the unloading passage (76).

15. A vehicle air compressor (2) for a heavy vehicle braking system, the vehicle air compressor (2) comprising:

a compressor crankcase assembly (6);

a compressor cylinder head assembly (4) disposed on the crankcase assembly (6) and cooperating with the crankcase assembly (6) to produce compressed air,

wherein the cylinder head assembly (4) comprises:

(i) an air inlet (8) through which air can be received for compression within the crankcase assembly and the cylinder head assembly (6, 4);

(ii) an outlet opening (10), through which compressed air can be conveyed out of the cylinder head assembly (4) via the outlet opening (10); and

(iii) an unloading channel (76); and

the unloader valve assembly (16) of claim 14, connected within a crankcase assembly and a cylinder head assembly (6, 4),

wherein the unloader piston (28) is movable against the biasing force of the coil spring (30) between a loaded position in which compressed air is prevented from exiting the unloading passage (76) when compressed air is delivered out through the exhaust port (10), and an unloaded position in which compressed air is allowed to be unloaded from the crankcase assembly and the cylinder head assembly (6, 4).

Technical Field

The present application relates to a piston assembly for an unloader valve of an air compressor, the piston assembly comprising: an unloader piston having an end including a first bore having a first bore diameter, an intermediate portion including a second bore having a second bore diameter, and an opposite end including a third bore having a third bore diameter, wherein the first bore diameter is larger than the second bore diameter, which in turn is larger than the third bore diameter; a coil spring having a central opening, one end disposed in the second bore of the unloader piston, and an opposite end extending into the first bore of the unloader piston; and a balance piston including a head having a diameter disposed in the first bore of the unloader piston and a shaft extending from the head into the central opening of the coil spring and having a diameter smaller than the diameter of the head. The application also relates to an unloader valve assembly for an air compressor comprising such a piston assembly, and an air compressor, for example a vehicle air compressor for use in an air brake system of a heavy vehicle such as a truck.

Background

An air brake system for use in a truck includes a vehicle air compressor that establishes an air pressure for the air brake system. A pressure control system, such as an air handling device or regulator, controls the system air pressure between preset maximum and minimum pressure levels by monitoring the air pressure in the supply reservoir. When the air pressure in the supply reservoir becomes higher than the preset "cut-off" set pressure of the regulator, the regulator controls the compressor to stop the compressor from compressing air. The regulator returns the compressor to continue compressing air as the air pressure in the supply reservoir drops to the preset "on" set pressure of the regulator.

The vehicle air compressor is typically a reciprocating air compressor and is continuously operated. The compressor is operated in a load mode or an idle mode. When the compressor is operating in a load mode, compressed air is delivered to the air brake system. When the compressor is operating in an unloaded mode, compressed air is directed to an alternate location other than the air brake system. Further, when the compressor is operating in the unloaded mode, an unloader valve included in the compressor releases pressurized air accumulated within the compressor to reduce the pressurized air in the compressor, which in turn reduces the load on the device driving the compressor. This reduces power consumption during operation of the compressor in the unloaded mode.

WO 2016/164400 a1 discloses an unloader valve that includes a balance piston having a stem that extends into a central opening of a coil spring that in turn extends into a bore of the unloader piston. Disadvantageously, in such systems, premature wear of, in particular, the balance piston, as well as compressor overheating and compressor seizure, can occur.

Disclosure of Invention

It is therefore an object of the present invention to provide a piston assembly for an unloader valve in an air compressor, an unloader valve including such a piston assembly, and an air compressor including such an unloader valve to improve the performance of such a compressor, particularly in terms of energy saving efficiency, and to avoid problems of overheating, premature wear and seizure.

The object of the invention is solved by the subject matter of the independent claims. Advantageous embodiments are defined in the dependent claims.

According to one aspect of the invention, the shaft of the compensation piston of the piston assembly has a diameter at the end facing away from the head which substantially corresponds to the inner diameter of the central opening of the helical spring, and the compensation piston comprises a thermal protection means.

The helical spring is stabilized by the diameter of the end facing away from the head, so that vibrations of the helical spring, in particular vibrations caused by pressure differences along the length of the helical spring, are reduced. By reducing such vibrations, wear between the coil spring and the rod portion of the balance piston is reduced. The thermal protection mechanism reduces heat transfer to the head. Thereby, overheating of the compressor and jamming of the compressor are avoided without affecting the energy efficiency in a negative way. Furthermore, other heat sensitive components arranged in the head, such as seals, are protected from overheating.

According to another aspect of the invention, the unloader valve includes a piston assembly according to the first aspect, wherein the unloader piston moves the unloader piston against the biasing force of the coil spring in response to the control signal pressure to move the unloader piston from a loaded position, in which the unloader piston blocks the associated unloading passage, to an unloaded position, in which the unloader piston does not block the unloading passage, along its longitudinal center axis.

According to still another aspect of the present invention, a vehicle air compressor includes: a compressor crankcase assembly; a compressor cylinder head assembly disposed on and cooperating with the crankcase assembly to produce compressed air; and an unloader valve assembly according to another aspect of the present invention, the unloader valve assembly being connected within the crankcase and cylinder head assembly. The cylinder head assembly includes: an air intake through which air may be received for compression within the crankcase and cylinder head assembly; an exhaust port through which compressed air may be delivered from the cylinder head assembly; and an unloading channel. An unloader piston of the unloader valve assembly is movable against the biasing force of the coil spring between a loaded position in which compressed air is prevented from exiting the unloader passage when the compressed air is delivered out through the exhaust port, and an unloaded position in which the compressed air is allowed to be unloaded from the crankcase assembly and the cylinder head assembly.

As the compressor piston operates back and forth during the load mode, air flows back and forth between the two chambers of the unloader valve. The movement of the air flow back and forth into and out of the bore of the unloader piston requires a finite amount of time to pass up and down through the various coils of the spring, which results in a pressure differential along the length of the spring. The pressure differential along the length of the spring may cause the spring to vibrate. The diameter of the end facing away from the head stabilizes the helical spring so that vibrations of the helical spring are reduced. By reducing this vibration, wear between the coil spring and the stem of the balance piston and at the valve seat in the valve plate of the unloader piston is reduced. The thermal protection mechanism reduces heat transfer to the head to avoid overheating and jamming of the compressor without adversely affecting energy efficiency.

Further exemplary embodiments are defined in the dependent claims and are further explained below.

In one embodiment, the thermal protection mechanism may comprise a groove section between an end extending from the head and an end facing away from the head and a thermal shield formed by the end facing away from the head. The groove section has a reduced diameter that reduces heat transfer through the stem towards the head of the balancing piston. The end (of the shank) facing away from the head has a larger diameter than the groove section, preferably the same size as the diameter of the end extending from the head. In such a piston assembly, two heat transfers from the compressed air to the unloader section can be distinguished: convection, which is configured to heat a portion of the assembly due to contact with hot air; and thermal radiation that is configured to radiate electromagnetic radiation from the object in relation to its temperature. The end facing away from the head acts as a heat shield, in particular against heat radiation. The groove section reduces the third heat transfer, i.e. the heat conduction in the part of the unloader valve, in particular the stem towards the head. Thereby, the heat transfer towards the head of the balancing piston is further reduced.

The stem of this embodiment may also include an intermediate portion interconnecting the end extending from the head with the end facing away from the head, both ends having a first diameter, e.g., 9.0mm, and the intermediate portion having a second diameter, e.g., 7.8mm, smaller than the first diameter. This cross-sectional reduction in the diameter of the shank increases the radial clearance for the coil spring, for example from 2.75mm to 3.75mm, thereby reducing, preferably eliminating, spring wear.

The thermal protection means may also comprise a cap made of a refractory material arranged at the end facing away from the head, and/or a disc made of a refractory material having a low thermal conductivity arranged at the head of the balancing piston. The cap at the end facing away from the head may similarly act as a heat shield and heat conduction limiter as described above.

The cap may be attached, e.g. clamped, screwed, glued, pressed in, etc., to the end facing away from the head, or may also be integrally formed with this end. The disc may similarly serve as a heat shield, wherein the disc is arranged between seals provided in the head and the stem. For example, the disc may be disposed between one end face of the head portion and the end of the stem portion extending from the head portion.

As the high temperature resistant material, a high temperature resistant plastic, preferably Polyetheretherketone (PEEK), may be used. Plastic is a lightweight material and is therefore particularly suitable for reducing the weight of the piston assembly.

In another embodiment, the thermal protection mechanism may include cooling lines or cooling channels integrated into the balance piston for internally cooling the balance piston. For example, the cooling line is arranged coaxially with the balancing piston and extends through the head into the shank. The cooling line may have a first bore having a first diameter in the head region and a second bore having a second diameter extending from the first bore into the shank portion along a central axis of the cooling line, wherein the second diameter is smaller than the first diameter.

The cooling line may be filled with a cooling fluid, such as a coolant or water. For example, the cooling fluid may be supplied from and returned to the cooling fluid circuit.

In all the embodiments described above, the length of the stem may be at least 50% and up to 95%, preferably 60% to 90%, more preferably 70% to 80% of the length of the helical spring. The stem thus provides sufficient support to the coil spring to avoid buckling of the spring.

If present, the intermediate portion may be at least half the length of the shaft and up to 80%, preferably 55% to 75%, more preferably 60% to 70% of the length of the shaft. The intervening portion increases the spring clearance, which reduces or eliminates wear between the spring and the stem, but may also increase the risk of buckling of the spring. Therefore, for setting the length of the intervening portion, both a reduction in wear of the spring and sufficient support of the spring (to avoid buckling) should be considered.

The balance piston may also be stationary. The balancing piston is thus the part of the piston assembly relative to which all other parts are arranged to be movable. The term "stationary" means that the balance piston does not move in the axial direction, but radial movement is possible.

The piston assembly according to the invention may further comprise a first seal, for example arranged in a first seal chamber arranged in the outer diameter bearing surface of the head of the balance piston, the first seal being configured to be able to provide a gas tight seal between the outer diameter bearing surface of the head of the balance piston and the inner diameter bearing surface in the first bore of the unloader piston. A first seal, such as an O-ring, provides a gas-tight seal to support the up-and-down movement of the unloader piston relative to the (stationary) balance piston.

Further, the piston assembly may include a second seal disposed, for example, in a second seal cavity disposed in the first outer diameter bearing surface of the unloader piston, the second seal configured to provide a hermetic seal between the first outer diameter bearing surface of the unloader piston and the first inner diameter bearing surface of the cylinder head of the compressor.

Further, the piston assembly may include a third seal disposed, for example, in a third seal cavity disposed in the second outer radial bearing surface of the unloader piston, the third seal configured to provide a hermetic seal between the second outer radial bearing surface of the unloader piston and the second inner radial bearing surface of the cylinder head of the compressor.

The second and third seals may each be designed as O-rings and provide an air tight seal to support the up and down movement of the unloader piston relative to the body of the cylinder head assembly.

In the above embodiments, the diameter of the central opening of the coil spring and the diameter of the shank may form a clearance fit therebetween. This ensures that the stem portion fits into the central opening of the helical spring. The clearance fit must be set such that the support of the coil spring by the rod is sufficient.

The coil spring may be arranged such that one end of the coil spring abuts a surface of the unloader piston and an opposite end of the coil spring abuts a surface of the balance piston. Thus, the coil spring may be biased such that the biasing force urges or holds the unloader piston in a loaded position in which the unloader piston blocks the associated unloading passage.

The piston assembly may further comprise a cover plate disposed on an opposite side of the head from the stem, wherein the cover plate may be separate from the head or integrally formed with the head. The cover plate serves as a seat for positioning the piston assembly in the cylinder head. The cover plate may provide a fastening means for securing the piston assembly at the cylinder head assembly. Further, the cover plate may be a metal plate. The heat dissipation from the compensation piston to the outside is improved by the contact between the head of the compensation piston and the cover plate.

Drawings

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view of a vehicle air compressor including an unloader valve assembly according to an exemplary embodiment of the present invention;

FIG. 2 is a cross-sectional view taken generally along the line II-II shown in FIG. 1 and illustrating a first embodiment of a piston assembly for the unloader valve assembly;

FIG. 3 is an exploded view of an unloader valve assembly according to a first embodiment;

FIG. 4 is a perspective view of a piston assembly according to a first embodiment;

FIG. 5 is a perspective view of a balance piston of the piston assembly according to the first embodiment;

FIG. 6 is a cross-sectional view taken generally along the line II-II shown in FIG. 1 and illustrating a second embodiment of a piston assembly for the unloader valve assembly;

FIG. 7 is a cross-sectional view taken generally along the line II-II shown in FIG. 1 and illustrating a third embodiment of a piston assembly for the unloader valve assembly;

FIG. 8 is a cross-sectional view taken generally along the line II-II shown in FIG. 1 and illustrating a fourth embodiment of a piston assembly for the unloader valve assembly;

fig. 9 is an exemplary view illustrating different states of the air compressor in the no-load mode.

Detailed Description

Referring to FIG. 1, an air compressor 2 includes a cylinder head assembly 4 disposed on a compressor crankcase assembly 6 in a known manner. The components of the crankcase assembly 6 and the components of the cylinder head assembly 4 cooperate together to produce compressed air.

The cylinder head assembly 4 includes an intake port 8 through which air may be received for compression within the crankcase assembly 6 and the cylinder head assembly 4. The cylinder head assembly 4 includes a discharge port 10, i.e., an exhaust port, through which compressed air may be delivered from the cylinder head assembly 4. A pair of coolant ports 12 (only one cooling port 12 is shown in fig. 1) are provided through which coolant can cool the cylinder head assembly 4 when compressed air is generated. The cylinder head assembly 4 also includes a relief valve port 14 and a regulator port (not shown) connectable to a regulator (also not shown) via a pneumatic control line (not shown).

The compressor 2 also includes an unloader valve assembly 16 disposed between the crankcase assembly 6 and the cylinder head assembly 4. The unloader valve assembly 16 abuts a valve plate 18, which in turn abuts the crankcase assembly 6, and a cooling plate 20, which abuts the cylinder head assembly 4 and is on the valve plate 18. The cover plate 22 is secured to the cylinder head assembly 4 by a pair of fasteners, such as screws 24.

Referring to fig. 2 and 6-8, cross-sectional views are taken generally along the line II-II shown in fig. 1, and each figure shows a component of the unloader valve assembly 16. The unloader valve assembly 16 includes a piston assembly 26, the piston assembly 26 including an unloader piston 28, a coil spring 30, and a balance piston 32.

The unloader piston 28 is generally cylindrical and movable along its longitudinal center axis 34 between a seated position (contacting the valve plate 18) and an unseated position (not shown) shown in fig. 2 and 6-8. The seated position corresponds to the compressor 2 operating in the load mode and the unseated position corresponds to the compressor 2 operating in the unloaded mode.

The unloader piston 28 has: an end having a first bore 36 defining a chamber 38; an intermediate portion having a second aperture 40 defining a chamber 42; and an opposite end having a third aperture 44 defining a chamber 46. The first bore 36 has a larger diameter than the second bore 40, and the second bore 40 has a larger diameter than the third bore 44.

The balance piston 32 includes a head 48 and a stem 50 extending from the head 48. The diameter of the head 48 is greater than the diameter of the shaft 50. The diameter of the head 48 is disposed in the first bore 36 of the unloader piston 28, and the stem 50 extends into a central opening 52 of the coil spring 30. The coil spring 30 is disposed in the unloader piston 28 such that one end of the coil spring 30 abuts a surface 54 of the unloader piston 28 in the chamber 42 of the second bore 40 and an opposite end of the coil spring 30 extends into the chamber 38 of the first bore 36 of the unloader piston 28 and abuts a surface 56 of the balance piston 32.

A first seal 58, illustratively shown as a first O-ring, is disposed in a first seal cavity (illustratively formed as a groove) disposed in an outer diameter bearing surface 60 of the head 48 of the balance piston 32. The first seal 58 provides an air-tight seal between an outer diameter bearing surface 60 of the head 48 of the balance piston 32 and an inner diameter bearing surface 62 within the chamber 38 defined by the first bore 36 of the unloader piston 28. Thus, the first seal 58 provides an air tight seal to support the up and down movement of the unloader piston 28 relative to the balance piston 32.

A second seal 64 (illustratively shown as a second O-ring) is disposed in a second seal cavity disposed in a first outer diameter bearing surface 66 of the unloader piston 28. The second seal 64 provides a hermetic seal between a first outer diameter bearing surface 66 of the unloader piston 28 and a first inner diameter bearing surface 68 of a cylinder head of the cylinder head assembly 4 of the compressor 2.

A third seal 70, illustratively a third O-ring, is disposed in a third seal cavity disposed in a second outer diameter bearing surface 72 of the unloader piston 28. The third seal 70 provides a hermetic seal between the second outer radial bearing surface 72 of the unloader piston 28 and the second inner radial bearing surface 74 of the cylinder head assembly 4 of the compressor 2.

The second and third seals 64, 70 provide a gas-tight seal to support the up and down movement of the unloader piston 28 relative to the body of the cylinder head assembly 4.

The balance piston 32 serves to provide a volume into which air flows to generate sufficient air pressure to push the unloader piston 28 downward from the unseated position (i.e., the unloaded mode of the compressor 2) toward the seated position (i.e., the loaded mode of the compressor 2). The volume needs to be maintained at a minimum otherwise it will affect the flow rate of the compressor 2.

When the compressor 2 is operating in the loaded mode, the unloader piston 28 is in the seated position shown in fig. 2 and 6-8. When the compressor 2 is operating in the unloaded mode, the unloader piston 28 is in an unseated position (not shown). The seated position of the unloader piston 28 will also be referred to as a loaded position, a loaded mode, or a blocked position. The unseated position of the unloader piston 28 will also be referred to as an unloaded position, an unloaded mode, or an unblocked position.

During operation of the unloader valve assembly 16, the unloader piston 28 is responsive to a control signal pressure from a regulator (not shown). The unloader piston 28 moves to an unseated position in response to the control signal pressure and the compressor 2 is in an unloaded mode. The unloader piston 28 returns to the seated position when the control signal pressure is removed and the compressor 2 is in the load mode. Compressed air from the unloader passage 76 in the valve plate 18 flows into the chambers 46, 42, 38 of the unloader piston 28. Air pressure from the unloader passage 76 helps to urge the unloader piston 28 from an unseated position (not shown) to a seated position (shown in fig. 2, 6-8), thereby supporting the bias of the coil spring.

In order to increase the energy-saving efficiency of the compressor 2, in particular in the unloaded mode, the diameter of the unloading channel 76 is, for example, 16mm to 20mm, and the diameter of the head 48 substantially corresponds to the diameter of the unloading channel 76.

Fig. 2-5 illustrate a first embodiment of the unloader valve assembly 16, wherein fig. 2 is a cross-sectional view of the unloader valve assembly 30 taken along line II-II shown in fig. 1, the unloader valve assembly including a piston assembly 26, the piston assembly 26 including a balance piston 32 according to a first embodiment, fig. 3 is an exploded view of the unloader valve assembly 16 as shown in fig. 2, fig. 4 is a perspective view of the piston assembly 26 according to the first embodiment, and fig. 5 is a perspective view of the balance piston 32 according to the first embodiment.

The unloader valve assembly 16 according to the first embodiment includes a balance piston 32 including a stem portion 50 having an end 78 extending from the head portion 48, an intermediate portion 80, and an end 82 facing away from the head portion 48. The two end portions 78, 82 have a first diameter and the intermediate portion 80 has a second diameter that is less than the first diameter. In addition, the intermediate portion 80 includes a recessed section 84 formed immediately adjacent an end 82 facing away from the head portion 48.

The ends 78, 82 support the coil spring 30 such that the coil spring 30 cannot flex, i.e., the coil spring 30 contacts the ends 78, 82 of the shaft 50. The diameter of the intermediate portion 80 is set small enough so that the intermediate portion 80 does not contact the coil spring 30, but is also set large enough so that the coil spring 30 still cannot flex. This avoids premature wear of the rod portion 50 of the balance piston 32 and the spring 30 caused by too little spring clearance. For example, the two end portions 78, 82 have a diameter of 9.0mm and the intermediate portion 80 has a diameter of 7.8 mm. In other words, by providing the intermediate portion 80, the spring gap is increased section by section, for example from 2.75mm to 3.75 mm.

When the distance between the end 82 facing away from the head 48 and the heat source, e.g., the unloader passage 76, becomes too small, the balance piston 32 heats up too much and causes overheating and burning of the first seal 58, resulting in premature wear and/or seizure of the unloader valve assembly 16. The groove section 84 has a smaller diameter than the diameter of the intermediate portion 80. Such a cross-sectional contraction acts as a thermal barrier reducing heat conduction towards the head 48 of the balance piston 32 and allows the rod portion 50 to be longer than would be the case without the recessed section 84. Furthermore, the end 82 facing away from the head 48 serves as a heat shield, in particular against heat radiation and also against convection. By providing the groove section 84, the thermal insulation effect is enhanced.

The length of the stem 50 is significant for the support of the coil spring 30, with the greater the distance between the two ends 78, 82 of the stem relative to the (defined) length of the coil spring 30 (i.e., the longer the intermediate portion 80 extends between the two ends 78, 82), the better the support of the coil spring 30. This reduces the risk of buckling of the helical spring 30 and thus prevents premature wear between the stem 50 and the helical spring 30.

To avoid wear between unloader piston 28 and valve plate 18 (which may also be referred to as valve seat wear), third bore 44 is made larger in diameter relative to known piston assemblies, for example increasing in diameter from 5.0mm to 6.5 mm. By increasing the diameter of the third bore 44 of the unloader piston 28, air flows in more easily, which results in less flow resistance, which in turn reduces vibration of the unloader piston 28 and thus eliminates premature valve seat wear.

Fig. 6 is a sectional view taken generally along the line II-II shown in fig. 1 and illustrates an unloader valve assembly 16 according to a second embodiment. Hereinafter, only the differences between the first and second embodiments will be described. Components having similar or identical configurations or functions have the same reference numerals, and detailed description thereof is omitted.

The main difference between the second embodiment and the first embodiment is the stem portion 50. The stem portion 50 according to the second embodiment comprises a cap 86 made of a high temperature resistant material, such as a high temperature resistant plastic, preferably Polyetheretherketone (PEEK). The cap 86 is arranged at the end 82 facing away from the head 48 and serves as a heat shield in a similar or analogous manner to the end 82 facing away from the head 48 according to the first embodiment. The cap 86 may be formed separately and may be attached to the end 82 facing away from the head 48, for example by pinning, clamping, screwing, pressing, etc., or may be formed integrally with the stem 50, for example by molding, injection molding, etc.

Although the stem 50 shown in fig. 6 includes neither a recessed section nor an intermediate portion, a cap 86 may be attached to the stem 50 including the intermediate portion 80 and/or the recessed section 84.

Fig. 7 is a sectional view taken generally along the line II-II shown in fig. 1 and illustrates an unloader valve assembly 16 according to a third embodiment. Hereinafter, only the differences between the second embodiment and the third embodiment will be described. Components having similar or identical configurations or functions have the same reference numerals, and detailed description thereof is omitted.

The third embodiment corresponds to the second embodiment further comprising a disc 88 made of a high temperature resistant material, such as a high temperature resistant plastic, preferably Polyetheretherketone (PEEK). The disc 88 is arranged at the head 48, i.e. between an end face 90 of the head 48 and the end 78 of the shaft 50 extending from the head 48. Disc 88 similarly acts as a heat shield and may be otherwise disposed so long as disc 88 is disposed between first seal 58 and stem portion 50.

Alternatively, the balance piston 32 of the unloader valve assembly 16 can also include only the cap 86 or the disc 88. Furthermore, it is possible to provide only the disc 88 in combination with the balancing piston 32 with the intermediate portion 80 and/or the groove section 84 as shown in the first embodiment.

Fig. 8 is a sectional view taken generally along the line II-II shown in fig. 1 and illustrates an unloader valve assembly 16 according to a fourth embodiment. Hereinafter, only the difference between the first embodiment and the fourth embodiment will be described. Components having similar or identical configurations or functions have the same reference numerals, and detailed description thereof is omitted.

The fourth embodiment of the unloader valve assembly 16 includes a balance piston 32 having a cooling line 92. The cooling line 92 is substantially cylindrical and extends from the head 48 of the balance piston 32 along the longitudinal center axis 34 into the shank 50 of the balance piston 32. As shown in FIG. 8, the cooling line 92 has a first bore 94 of a first diameter and a second bore 96 of a second diameter, wherein the second diameter is smaller than the first diameter. The cooling line 92 is filled with a cooling fluid, such as coolant or water, and may be connected to a cooling fluid circuit, such as the cooling port 12 (shown in fig. 1). The cooling line 92 cools the balance piston 32 from the inside and thus prevents overheating of the balance piston 32, in particular of the first seal 58.

As shown in fig. 8, the rod portion 50 of the balance piston 32 according to the fourth embodiment includes neither an intermediate portion nor a groove section. According to an alternative embodiment, the stem 50 may include an intermediate portion 80.

Fig. 9 shows different stages of an exemplary process of the air compressor 2 in the unloaded mode. In the unloaded mode, the unloader piston 28 (shown simplified) is lifted off the valve seat by the control signal pressure against the biasing force of the coil spring 30 and thus does not block the unloader passage 76. Fig. 9(a) shows a state during an intake phase during which the compressor piston 98 draws air to be compressed into the associated compression chamber 100 through an inlet, such as the intake port 8 (shown in fig. 1), by moving downward (i.e., increasing the volume of the compression chamber 100).

Referring to fig. 9(b), the unload passage 76 connects the compression chamber 100 with the additional clearance volume 102 into which air is compressed as the compressor piston 98 moves upward (i.e., reduces the volume of the compression chamber 100). By connecting the compression chamber 100 with the additional interstitial volume 102, the pressure in the compression chamber 100 is kept below the pressure level required to open the gas outlet, e.g. the discharge port 10 (also shown in fig. 1).

Referring to fig. 9(c), when the compressor piston 98 moves downward again (i.e., increases the volume of the compression chamber 100), compressed air flows back into the compression chamber 100 from the additional clearance volume 102, so no fresh air is drawn through the inlet.

The system shown in fig. 9 may also be referred to as a "closed room system". The closed chamber system connects the compression chamber 100 to an enclosed space in the cylinder head, called "closed chamber", which corresponds to the additional clearance volume 102. Thereby, the same air volume is maintained.

Fig. 9(b) and 9(c) may be summarized as so-called "ESS phases", wherein ESS stands for "energy saving system". During the ESS phase, a significant amount of energy is saved compared to the idle phase of a conventional compressor without such ESS (i.e. the unloaded mode of the compressor 2).

Designs using so-called "open transfer lines" are feasible, but have reduced efficiency compared to so-called "closed transfer lines". Compatibility is best for closed transfer lines.

List of reference numerals

2 air compressor

4 compressor cylinder cover assembly

6 compressor crankcase assembly

8 air inlet

10 discharge port

12 coolant port

14 safety valve port

16 unloader valve assembly

18 valve plate

20 cooling plate

22 cover plate

24 screw member

26 piston assembly

28 unloader piston

30 helical spring

32 balance piston

34 longitudinal central axis

36 first hole

38 chamber

40 second hole

42 Chamber

44 third hole

46 chamber

48 head

50 rod part

52 central opening

54 (of the unloader piston) surface

56 (of the balance piston)

58 first seal

60 outer diameter bearing surface

62 inner diameter bearing surface

64 second seal

66 first outside diameter bearing surface

68 first inner diameter bearing surface

70 third seal

72 second outer diameter bearing surface

74 second inner diameter bearing surface

76 unloading channel

78 end of the pipe

80 intermediate part

82 end portion

84 groove section

86 cap

88 dish

90 end face

92 cooling line

94 first hole

96 second well

98 compressor piston

100 compression chamber

102 additional clearance volume