US20090155106A1

US20090155106A1 - Extended compressor operation for auxiliary air supply

Info

Publication number: US20090155106A1
Application number: US11/954,699
Authority: US
Inventors: Ronald P. Maloney; Steven R. Coleman
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2007-12-12
Filing date: 2007-12-12
Publication date: 2009-06-18

Abstract

A machine air supply system includes a primary air circuit and a secondary air circuit and a single compressor for supplying compressed air to both circuits. In an embodiment, the compressor is a reciprocating piston compressor having a primary air circuit including a compression chamber of the compressor and a secondary air circuit including a crankcase chamber of the compressor. In an aspect, the compressor may be a multi-cylinder compressor.

Description

TECHNICAL FIELD

This patent disclosure relates generally to vehicle air systems and, more particularly to a compressor for supplying a primary vehicle air supply via a pump chamber and for supplying a secondary vehicle air supply via a secondary chamber associated with the pump chamber.

BACKGROUND

Large on-highway machines typically require pressurized air to operate properly. For example, the braking systems for such machines are typically air driven, using a source of pressurized air to drive a piston in a regulated maimer, providing the necessary force for braking the machine. The air driven systems, e.g., pistons, are often mechanically sensitive high tolerance devices, requiring that the pressurized air be essentially free of debris and contaminants. For this reason, the air delivery system for the machine may include an oil filter, desiccant filter, e.g., dryer, and/or other air cleaning device between the compressor and the air driven system.
Because the drag imposed by the compressor on the machine engine is related to the compressor size, it is typical to use a small compressor without significant additional capacity beyond that required by the braking system. Moreover, because of the packing requirements in and around the engine of such machines, a larger compressor is not suitable in most such machines.
However, there are increasingly other auxiliary machine systems, especially related to engine and emissions operations, that are air driven or that utilize pressurized air to perform a function. Because the main compressor of the machine is operating near capacity, it is not practical in most cases to bleed air from the main compressor to supply the auxiliary functions. Moreover, these functions often require clean air, and the compressor filter system may be located on the chassis, remote from the engine compartment.
There have been attempts to solve the problem of compressor capacity by using separate pumps. For example, U.S. Pat. No. 7,226,273 entitled “Method of Generating Compressed Air and Compressor Arrangement for Implementing the Method” describes a two-stage system for generating compressed air of sufficient flow rate and pressure for commercial vehicles. The system uses a compressor unit driven by an internal-combustion engine to generate low-pressure compressed air. The low-pressure compressed air is then used to generate higher-pressure compressed air via a separate auxiliary compressor unit. The compressor and auxiliary compressor unit are triggered based on the instantaneous pressure demand of the machine systems. However, the foregoing system is complex and cumbersome to operate, and requires an additional auxiliary compressor, thus complicating installation and maintenance as well.
This background section is presented as a convenience to the reader who may not be of skill in this art. However, it will be appreciated that this section is too brief to attempt to accurately and completely survey the prior art. The preceding background description is a simplified narrative and is not intended to replace the reference being discussed. Therefore, interested readers should refer directly to the U.S. Pat. No. 7,226,273 patent instead of relying upon the foregoing simplified narrative. Moreover, the resolution of deficiencies, noted or otherwise, of the prior art is not a critical or essential limitation of the disclosed principles.

SUMMARY

In one aspect, the disclosure relates to a machine having a plurality of air-operated systems including at least one primary system and at least one secondary system. In this aspect, the machine comprises at least one air tank for containing a supply of compressed air for providing compressed air to the primary system and the secondary system. The machine includes a compressor for supplying compressed air to the air tank. The compressor is a reciprocating piston compressor having a primary air circuit including a compression chamber of the compressor and a secondary air circuit including a crankcase chamber of the compressor.
In a further aspect, the disclosure relates to a machine air supply system for providing compressed air to two or more air-operated features of a machine. In this aspect, the air supply system includes a primary air circuit for providing compressed air to one of the air-operated features of the machine and a secondary air circuit for providing compressed air to another of the air-operated features of the machine. In this aspect, the primary air circuit and the secondary air circuit share a single compressor while operating at different air pressures.
In another aspect, the disclosure relates to a method for managing an air supply in a machine having a high-pressure air circuit and a secondary air circuit, the secondary air circuit having a lower pressure than the high-pressure air circuit. In this aspect, the high-pressure air circuit and a secondary air circuit are driven by a single compressor. The method comprises sensing a pressure in the high-pressure air circuit to establish a first sensed pressure and holding open a first intake valve on the compressor if the sensed pressure exceeds a first deactivation threshold, and releasing the first intake valve if the sensed pressure is less than a first activation threshold. The method also comprises sensing a pressure in the secondary air circuit to establish a second sensed pressure, and holding open a second intake valve on the compressor if the sensed pressure exceeds a second deactivation threshold, and releasing the second intake valve if the sensed pressure is less than a second activation threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic view of a machine and associated air supply system according to an aspect of the disclosed principles;

FIG. 2 is a partial cross-sectional side view of a single-piston compressor according to an aspect of the disclosed principles;

FIG. 3 is a partial cross-sectional side view of a multi-piston compressor according to a further aspect of the disclosed principles; and

FIG. 4 is a flow chart illustrating a process of controlling primary and secondary air circuits in a machine such as illustrated in connection with FIG. 1.

DETAILED DESCRIPTION

This disclosure relates to a machine air supply system having a primary air circuit and a secondary air circuit with a single compressor for supplying compressed air to both circuits. In an embodiment, the compressor is a reciprocating piston compressor having a primary air circuit including a compression chamber of the compressor and a secondary air circuit including a crankcase chamber of the compressor. In a further embodiment, the compressor may be a multi-cylinder compressor.
FIG. 1 is a schematic view of a power and air delivery system for a machine 1 such as an on-highway machine. The air delivery system comprises an engine 2 or other power source of the machine 1. Generally, the engine 2 supplies power through a drive train 4 for movement of the machine 1. A compressor 3 is linked to the engine 2 via a gear drive, pulley, or other transmission means so that as the engine 2 shaft rotates, the compressor 3 is driven at a speed that is generally at or proportional to the speed of the engine 2.
The compressor 3 supplies compressed air at an outlet 6. The compressed air is supplied to an air tank 7 via a filter system 8. The filter system 8 typically comprises one or more filters, typically including filters to remove water, debris, and oil from the compressed air. These contaminants may arise from the operation of the compressor 3 itself or from contaminants in the air compressed by the compressor 3.
An air pressure in the tank 7 is maintained within a desired range, such as 110-150 PSI in the United States and 250-280 PSI is Europe. The air pressure in the tank 7 is affected by the supply of air to the tank 7 as well as the release of air from the tank 7 via tank outlet 9. In particular, air from the tank 7 is released from tank outlet 9 to various machine 1 systems such as an air brake system 10. It will be appreciated that the disclosed principles apply in various machine systems regardless of whether such machines include an air brake system or instead include some other type of air-driven system.
A regulator module 11 senses the air pressure in the tank 7 via a sensor 12 and modifies the operation of the compressor 3 in response to the sensed pressure. In particular, if the sensed pressure falls below a specified range, the regulator module 11 causes the compressor 3 to supply compressed air to the tank 7. If, on the other hand the sensed pressure exceeds the specified range, then the regulator module 11 causes the compressor 3 to cease supplying compressed air. It will be appreciated that the regulator module 11 may apply hysteresis to the control of the compressor 3 to avoid rapid on-off cycling when the air from the tank 7 is being released from tank outlet 9 to the air brake system 10 of other machine 1 system.
As noted above, the drag imposed by the compressor 3 on the engine 2 is related to the size of the compressor 3. Moreover, the space constraints in and around the engine 2 limit the area available for the compressor 3. Thus, it is generally desirable to use the smallest compressor 3 able to supply the requirements of the braking system 10 without significant additional capacity.
However, there are other auxiliary air systems 13, especially related to engine and emissions operations, which are air driven or which utilize pressurized air to perform a function. For example, pressurized air may be used to supply a regeneration purge system, a selective catalytic reduction (SCR) air-assisted urea injector, a crankcase purge system, etc. Because the compressor 3 of the machine 1 is operating near capacity, it is not practical in most cases to bleed air from the compressor 3 to supply the auxiliary air systems 13. Moreover, these auxiliary air systems 13 often require clean air, and the compressor filter system 8 may be located on the machine 1 chassis, remote from the engine 2.
Although the foregoing discussion illustrates a tank 14 and filter 15 associated with the secondary circuit, it is not critical that the secondary circuit have such components, nor are they required for the primary circuit in every implementation. Moreover, although the above example describes each circuit as being regulatable at the compressor 3, this need not be true of one or both circuits. For example, for simplicity or other reasons, it may be desirable in a particular implementation to control circuit pressure and/or flow in the secondary and/or primary air circuit via one or more throttling orifices or pressure relief valves.
In an embodiment, the compressor 3 is modified to supply additional air via a secondary pump circuit and secondary tank 14 and filter 15 without increasing the size of the compressor 3, without bleeding air from the primary circuit or tank 7 used to supply the air brake system 10, and without requiring an additional pump or compressor. In particular, in this embodiment, the compressor 3 is piston-operated, with a piston 20 slidably fitting within a cylinder 21 so that the cylinder 21 and piston 20 form a compression chamber 22 as shown in FIG. 2.
A one-way intake valve 23 allows air into the compression chamber 22 on an intake stroke but does not allow air egress during a compression stroke. A one-way outlet valve 24 allows air egress from the compression chamber 22 during the compression stroke, but does not allow air entry during the intake stroke. In this manner, as the piston 20 reciprocates within the cylinder 21, air is drawn into the compression chamber 22 through the intake valve 23 and is forced out of the compression chamber 22 through the outlet valve 24, thus supplying compressed air, i.e. to the tank 7. The intake valve 23 and the outlet valve 24 may be of any suitable types and configuration. However, in an embodiment, the intake valve 23 and the outlet valve 24 are reed valves. In another embodiment, the intake valve 23 and the outlet valve 24 are disk valves or ball valves. It will be appreciated that the compressor 3 may be an oil-less compressor in order to avoid oil contamination of the air provided by the secondary air circuit.
The piston 20 is reciprocally driven by a connecting rod 25 driven by a crankshaft 26. The crankshaft 26 is driven from the engine 2 via a gearing or pulley system, not shown. The crankshaft 26 rotates within a chamber 28 formed by the crankcase 27. The crankshaft 26 is rotatably supported within the crankcase 27 by one or more bearings 29 or bushings.
To provide an auxiliary flow path for supplying compressed air, the crankcase 27 is formed with a secondary intake 30 controlled by a secondary intake valve 32 and a secondary outlet 31 controlled by a secondary outlet valve 33. The crankcase is substantially sealed against the ambient atmosphere via a rotary seal 34, e.g., a U-cup or other suitable seal as will be appreciated by those of skill in the art.
In operation, as the piston 20 rises in the chamber 22, the volume of the crankcase chamber 28 increases, causing a drop in pressure therein. This causes an influx of air into the crankcase chamber 28 through the secondary intake 30 via the secondary intake valve 32. Once the piston 20 passes top dead center and begins to descend, the volume of the crankcase chamber 28 decreases, causing a rise in pressure therein. This causes an egress of air out of the crankcase chamber 28 through the secondary outlet 31 via the secondary outlet valve 33.
In this manner, as the piston 20 reciprocates within the cylinder 21, a primary air circuit including the intake valve 23, outlet valve 24, and compression chamber 22 provides a first source of compressed air. At the same time, a secondary air circuit including the secondary intake 30, secondary intake valve 32 and a secondary outlet 31 controlled by a secondary outlet valve 33 provides a first source of compressed air. Because the compression ratio (the ratio of largest to smallest volume) of the compression chamber 22 is greater than that of the crankcase chamber 28, the primary air circuit provides air at a higher pressure than the secondary air circuit. Thus, while the first air circuit is a suitable source of high-pressure air for an air brake system 10 or the like, the secondary air circuit is suitable for auxiliary functions that operate on a lower pressure supply, e.g., a regeneration purge system, an SCR air-assisted urea injector, a crankcase purge system, etc.
In an embodiment, a multi-cylinder compressor 40 is adapted as shown in FIG. 3 to provide a secondary air circuit. Typically, a multi-cylinder compressor uses cylinders that rise and fall at different times for purposes of reducing vibration, although it will be appreciated that the disclosed adaptation may be used with multi-cylinder compressors regardless of the number of cylinders and the manner in which the cylinders are coordinated.
A first primary intake valve 56 allows air into the first compression chamber 57 on an intake stroke and a first primary outlet valve 58 allows air egress from the first compression chamber 57 during the compression stroke. Similarly, a second primary intake valve 59 allows air into the second compression chamber 60 on an intake stroke and a second primary outlet valve 61 allows air egress from the second compression chamber 60 during the compression stroke. In this manner, a primary air circuit is provided.
In an embodiment however, the crankcase pressure of the compressor 40 is used to provide a secondary air circuit. To ensure that the pressure rise and fall potentially caused by one of the first piston 41 and second piston 42 is not negated by an opposite movement of the other of the first piston 41 and second piston 42, the pistons do not share a common crankcase chamber. Rather, the first piston 41 has associated with it a first crankcase chamber 43 and the second piston 42 has associated with it a second crankcase chamber 44. The first crankcase chamber 43 and the second crankcase chamber 44 are sealed against one another via one or more rotary seals 45. Similarly, the second crankcase chamber 44 is sealed against the ambient atmosphere where the crankshaft 46 exits by another rotary seal 47.
To provide the secondary air circuit, the first crankcase chamber 43 has associated therewith a first secondary intake 48 controlled by a first secondary intake valve 49 and a first secondary outlet 50 controlled by a first secondary outlet valve 51. Similarly, the second crankcase chamber 44 has associated therewith a second secondary intake 52 controlled by a second secondary intake valve 53 and a second secondary outlet 54 controlled by a second secondary outlet valve 55. It will be appreciated that the compressor 40 may be an oil-less compressor in order to avoid oil contamination of the air provided by the secondary air circuit. The compressor 40 may include a sealed shaft 62 passing between the crankcase chambers 43, 44.
A compressor such as the compressor 3 or the compressor 40 imposes a drag on the machine engine 2 when operating. In order to impose this drag only when the compressor is providing useful work, the compressor may be disengaged when not needed. Because disengagement may require the mechanical complexities required by disengagement of gears or pulleys, in an embodiment the compressor is allowed to turn when inactive, but the associated drag is reduced by deactivation of one or both of the primary and secondary air circuits.
Referring to the compressor 3 of FIG. 2, with the understanding that the same principles apply to the compressor 40 of FIG. 3, the primary air circuit may be deactivated by holding open the one-way intake valve 23. Thus, when the piston 20 causes the volume of the compression chamber 22 to rise and fall, air is allowed both into and out of the one-way intake valve 23. In this manner, the primary air circuit is deactivated and does not supply compressed air. Similarly, the secondary air circuit may be deactivated by holding open the secondary intake valve 32. Thus, when the piston 20 causes the volume of the crankcase chamber 28 to rise and fall, air is allowed both into and out of the secondary intake valve 32. In this manner, the secondary air circuit is deactivated and does not supply compressed air.
The flow chart of FIG. 4 illustrates a process 70 for controlling a compressor to provide compressed air from a primary and secondary air circuit of a compressor to machine systems as needed. It will be assumed in this example that the compressor is as illustrated in FIG. 2, although it will be appreciated that the compressor may instead be a multi-cylinder compressor as shown in FIG. 3. At stage 71 of the process 70 the machine 1 is started, i.e., the engine 2 is started, which also starts the rotation of the compressor 3. At this point, the air tanks of the machine 1 are not pressurized and the primary and secondary air circuits are not deactivated. At stage 72, the regulator module 11 checks the air pressure in the primary tank 7 and if the air pressure in the primary tank 7 falls below a predetermined activation threshold, e.g., 110 PSI then the regulator module 11 ensures that the primary air circuit is active, i.e., that none of the primary circuit valves are held open at stage 73. At stage 74, the regulator module 11 checks the air pressure in the primary tank 7 and if the air pressure in the primary tank 7 is greater than a predetermined deactivation threshold, e.g., 140 PSI, then the regulator module 11 deactivates the primary air circuit at stage 75, e.g., by holding an intake valve open. In an embodiment, the activation threshold is different from and greater than the deactivation threshold. In this manner, the regulator module 11 will not cause rapid on/off cycling of the primary air circuit when the pressure is near a threshold. As the machine 1 operates and air is released from the tank 7, e.g., to operate the air brake system 10, the regulator module 11 continues to loop through stages 72-75 to maintain the air pressure in the tank 7 at an appropriate level.
Similarly, at stages 76-79, the regulator module 11 maintains the pressure in the secondary tank 14 at an appropriate level via the secondary air circuit of the compressor 3. Although the stages of regulation are similar, it should be noted that the secondary air circuit will typically operate at a lower pressure and will supply air to devices different from those supplied by the primary air circuit. Therefore, the secondary activation threshold may be different from the activation threshold of the primary circuit and the secondary deactivation threshold may be different from the deactivation threshold of the primary circuit. In an embodiment, the secondary activation threshold is lower than the activation threshold of the primary circuit and the secondary deactivation threshold is lower than the deactivation threshold of the primary circuit. In a further embodiment, the secondary activation threshold is lower than the secondary deactivation threshold. When the machine 1 is turned off, the regulator module 11 may cause tank 7 and tank 14 to be vented or may allow the tanks 7, 14 to remain pressurized.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to machines that utilize compressed air from a single compressor for multiple machine functions. A primary air circuit including the compressor's compression chamber is used to supply high-pressure air to machine systems that require high-pressure air. Examples of such systems include air brake systems and other critical or non-critical systems.
In addition, a secondary air circuit that includes the compressor crankcase chamber provides a secondary supply of compressed air to auxiliary machine systems. For example, pressurized air may be used to supply a regeneration purge system, a selective catalytic reduction air-assisted urea injector, a crankcase purge system, etc. Because machine compressors typically operate near capacity and because the space available to place an additional compressor is limited, the compressor according to the disclosed principles supplies the secondary supply of compressed air without substantially increasing the size of the compressor, without bleeding air from the primary circuit, and without requiring an additional pump or compressor.
It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely unless otherwise indicated.
Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.
Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

1. A machine having a plurality of air-operated systems including at least one primary system and at least one secondary system, the machine comprising:

at least one air tank for containing a supply of compressed air for providing compressed air to the at least one primary system; and

a compressor for supplying compressed air to the at least one air tank, the compressor being a reciprocating piston compressor having a primary air circuit including a compression chamber of the compressor and a secondary air circuit including a crankcase chamber of the compressor.

2. The machine according to claim 1, further including a secondary air tank, separate from the primary tank, for providing compressed air to the at least one secondary system.

3. The machine according to claim 2, wherein the primary tank operates at a higher air pressure than the secondary tank.

4. The machine according to claim 1, wherein the compressor is an oil-less compressor.

5. The machine according to claim 1, wherein the compressor includes multiple reciprocating pistons associated with respective separate compression chambers and respective separate crankcase chambers, wherein the primary air circuit includes the respective separate compression chambers and the secondary air circuit includes the respective separate crankcase chambers.

6. The machine according to claim 5, further including at least one sealed shaft passing between the respective separate crankcase chambers.

7. The machine according to claim 1, further including at least one filter in the primary air circuit and at least one filter in the secondary air circuit.

8. The machine according to claim 1, wherein the at least one primary system includes an air brake system and the at least one secondary system includes one of a regeneration purge system, a selective catalytic reduction air-assisted urea injector, and a crankcase purge system.

9. The machine according to claim 1, further including a regulator module for controlling the primary air circuit and the secondary air circuit separately by controlling the operation of the compressor.

10. The machine according to claim 9, wherein the primary air circuit and the secondary air circuit each include an air intake valve, wherein the regulator module separately controls the primary air circuit and the secondary air circuit by independently controlling the air intake valves.

11. A machine air supply system for providing compressed air to two or more air-operated features of a machine, the air supply system including:

a primary air circuit for providing compressed air to one of the two or more air-operated features of the machine; and

a secondary air circuit for providing compressed air to another of the two or more air-operated features of the machine, wherein the primary air circuit and the secondary air circuit share a single compressor while operating at different air pressures.

12. The machine air supply system according to claim 11, wherein the primary air circuit includes a primary tank and the secondary air circuit includes a secondary tank separate from the primary tank.

13. The machine air supply system according to claim 12, wherein the primary tank operates at a higher air pressure than the secondary tank.

14. The machine air supply system according to claim 11, wherein the single compressor includes multiple reciprocating pistons associated with respective separate compression chambers and respective separate crankcase chambers, wherein the primary air circuit includes the respective separate compression chambers and the secondary air circuit includes the respective separate crankcase chambers.

15. The machine air supply system according to claim 11, further including at least one filter in the primary air circuit and at least one filter in the secondary air circuit.

16. The machine air supply system according to claim 11, wherein the two or more air-operated features of the machine include an air brake system and at least one of a regeneration purge system, a selective catalytic reduction air-assisted urea injector, and a crankcase purge system.

17. The machine air supply system according to claim 11, further including a regulator module for controlling the primary air circuit and the secondary air circuit separately by controlling the operation of the single compressor.

18. The machine air supply system according to claim 17, wherein the primary air circuit and the secondary air circuit each include an air intake valve, wherein the regulator module separately controls the primary air circuit and the secondary air circuit by controlling the air intake valve of the primary air circuit and the secondary air circuit.

19. A method for managing an air supply in a machine having a high-pressure air circuit and a secondary air circuit having a lower pressure than the high-pressure air circuit, the high-pressure air circuit and the secondary air circuit being driven by a single compressor, the method comprising:

sensing a pressure in the high-pressure air circuit to establish a first sensed pressure;

holding open a first intake valve on the compressor if the sensed pressure exceeds a first deactivation threshold, and releasing the first intake valve if the sensed pressure is less than a first activation threshold;

sensing a pressure in the secondary air circuit to establish a second sensed pressure; and

holding open a second intake valve on the compressor if the sensed pressure exceeds a second deactivation threshold, and releasing the second intake valve if the sensed pressure is less than a second activation threshold.

20. The method according to claim 19, wherein the compressor includes a reciprocating piston, and wherein the high-pressure air circuit includes a compression chamber associated with the reciprocating piston and the secondary air circuit includes a crankcase chamber associated with the reciprocating piston.