Hydraulic Power System for HVAC Compressor

A modular HVAC unit may incorporate a hydraulically powered refrigerant compressor to more efficiently provide air conditioning to an operator cab of a work machine. The refrigerant compressor may be fluidly powered by a hydraulic fluid motor fluidly coupled to and driven by a variable displacement pump. An electronic controller may be configured to vary hydraulic pump flow rates to the motor via use of a proportioning control valve to maintain a desired evaporator performance temperature. The control valve may be configured to stop the HVAC unit whenever a backup system may be used, when a discharge is to be prevented, and/or when operator air-conditioning is not desired. The controller may monitor evaporator performance via a fin temperature sensor, and may send appropriate signals to the control valve for modulating hydraulic flows through the motor. The arrangement may provide a significant increase in the life and performance of the compressor.

DETAILED DESCRIPTION

Referring initially toFIG. 1, a work machine in the form of a mining shovel machine2, used for digging and removing coal, rock and/or soil, as examples only, from a worksite, is displayed in a perspective view. The mining shovel machine2may include a translatable and rotatable main body4, which may contain an engine, and hydraulic and electrical systems (not shown). The mining shovel machine2may also include a work tool such as, for example, a mining shovel6as depicted. An operator cab8may be situated atop of the main body4; the operator cab may include an operator control station (not shown) of the type in which air-conditioning by way of an HVAC unit may be desirable.

Referring now toFIG. 2, a first embodiment of a hydraulically powered HVAC system10that may be configured in accordance with this disclosure is shown schematically. The HVAC system10may include an electronic control module (ECM)12adapted to control a hydraulic proportioning valve14adapted to receive electronic signals from the ECM12. The ECM12may also be configured to control all aspects of the HVAC system10, including a hydraulic circuit16and all hydraulic components associated therewith, as well as related electrical control functions to be further described herein.

Continuing reference toFIG. 2, the HVAC system10may further include a variable displacement pump18configured to drive a fixed displacement motor20. The fixed displacement motor20may be coupled directly to a refrigerant compressor30, and the ECM12may be adapted to control the proportioning valve14to ultimately control the speed of the compressor30in accordance with a desired fin temperature of an evaporator40. To the extent that the motor20is of fixed displacement, any modulation of the proportioning valve14as directed by the ECM12may cause the variable displacement pump18to react to the corresponding change in demand, resulting in a direct change in compressor speed as a function of desired evaporator performance.

For this purpose, the variable displacement pump18may be adapted to incorporate a hydraulic load sensing capability. Thus, a load sensing line24may be configured to read actual pressure on a high pressure side of the HVAC system10, per the schematic ofFIG. 2. The load sensing line24, as part of the hydraulic circuit16, may enable the pump18to be directly responsive to HVAC demand, as manifested via a modulation of the proportioning valve14upon command as signaled by the ECM12.

As part of the hydraulic circuit16, a one way check valve26may be situated between the high and low pressure sides of the circuit16as will be appreciated by those skilled in the art, and a relief valve28may be situated on the high pressure side of the hydraulic circuit16to potentially avoid damage due to any overpressuring of the circuit16.

A combination hydraulic trickle flow and stop valve22may be situated in the hydraulic circuit16between a high-pressure discharge outlet19of the pump18and the proportioning valve14for reasons to be explained below.

Apart from being driven by a fixed displacement hydraulic motor20for controlling its speed, the compressor30is otherwise part of a separate refrigeration circuit36, to be distinguished from the hydraulic circuit16. The refrigeration circuit36utilizes a refrigerant fluid such as a type of Freon, and includes the compressor30, as well as a condenser32, a refrigerant expansion valve34, and an evaporator40, components that are generally adapted to work in concert to produce HVAC cooling, as will be appreciated by those skilled in the art.

Several additional features of the hydraulic circuit16of the HVAC system10may include a hydraulic fluid reservoir50for containing and supplying hydraulic fluid as may be used in the various components of the hydraulic circuit16, including the proportioning valve14, the pump18, and the motor20. Among other things, the pump18has a suction or low pressure inlet17in communication with the reservoir50. The hydraulic motor20receives hydraulic fluid directly from the portioning valve14, which then enters the motor20through a motor inlet25, and after hydraulically driving the motor is discharged through a motor fluid outlet21and back into the reservoir50. A case drain23allows a lesser amount of hydraulic fluid to return to the reservoir50from the motor20, as part of a standby feature. However, whenever the motor20becomes operative the case drain23flow is reduced, as the bulk of the flow then becomes diverted to and through the motor fluid outlet21.

Finally, any high-pressure hydraulic fluid which may escape through the relief valve28also passes back into the reservoir50. Detailed operation of the HVAC system10is provided below.

Referring now toFIG. 3, an alternate embodiment100offering a dual HVAC system capability, as shown schematically. A diesel engine or electric motor110provides a motive source for driving a hydraulic pump118via a connection media such as a gear, belt, chain, or other coupling device (not shown). The hydraulic pump118is part of a unitary hydraulic circuit116, and includes a hydraulic fluid reservoir150. In the disclosed embodiment, an ECM112, the circuit116, and the reservoir150are not redundant or duplicated, though they could be if desired.

The ECM112is configured to control a pair of HVAC refrigeration subsystem units A and B, in accordance with at least one control algorithm described below.

Although only a single variable displacement pump118is utilized, the HVAC subsystem units, including evaporators (not shown), primary and secondary compressors130,230, and primary and secondary condensers132,232are redundant, and may provide separate primary and backup HVAC systems for greater field reliability. With respect to the unitary hydraulic circuit116, the proportioning valves114,214are duplicated to permit switching from one subsystem system to the other by means of a reversible sensing shuttle valve126. Although the valve126appears to be part of HVAC subsystem A, it may not be. Instead, the valve126may be a unitary component physically situated between the subsystems A and B. In addition and/or separately, there may be valves in each subsystem adapted to divert the fluid flows from respective case drains23to respective motor fluid outlets21, so as to accommodate the full operation of either motor120,220.

The shuttle valve126may also provide a hydraulic fluid load sensing function for assuring that the pump is in communication with the appropriate system; i.e., with the primary proportioning valve114of subsystem A, or to the backup proportioning valve214of subsystem B. Primary and backup fixed displacement motors120,220, respectively, may be operative to drive primary and backup compressors130,230, respectively. Finally, primary and backup condensers132,232, as well as main and backup evaporators (not shown) are also included in the dual or redundant HVAC embodiment100, as disclosed herein.

INDUSTRIAL APPLICABILITY

Operation of the HVAC system10may be explained with reference toFIG. 2, which schematically displays the single HVAC system10. The dual HVAC system100ofFIG. 3includes redundant refrigeration units; as such, operation of the system100may be functionally similar to that of system10.

Starting with the air-conditioning refrigeration circuit36turned off and otherwise inactive, and/or air-conditioning may not be desired, the combination hydraulic trickle flow and stop valve22may be in a closed position to generally prevent normal hydraulic fluid flow to the motor20. However, the trickle flow (also called a motor flush) aspect of the stop valve22may allow the pump22to receive a small amount of hydraulic fluid flow to assure that the motor20remains in a standby condition; i.e. warmed up and ready for operation on demand. During the standby state, the variable displacement pump18is configured to provide a minimal displacement of fluid, which lowers horsepower requirements, and provides greater overall work machine fuel efficiency at a level that could not otherwise be achieved with a fixed displacement pump.

Upon a demand for air-conditioning, the ECM12will command the opening of the valve22. Once the valve is opened, the proportioning valve14will be continuously adjusted, or modulated, as required to achieve desired compressor speed via commands from the ECM12based upon sensed evaporator fin temperature. The latter temperature information is made available to the ECM12via an evaporator temperature sensing line37. For control purposes, the ECM12may be programmed to execute a specific algorithm designed for the particular size and operating parameters of the HVAC system10. As such, a given compressor speed may be correlated closely with a given control position of the proportioning valve14.

With respect to hydraulic system pressure changes resulting from modulation of the proportioning valve14, the hydraulic circuit16has both a high-pressure side, with highest system pressure being reflected at the high-pressure discharge outlet19of the pump18, and a low-pressure side, with the lowest pressure being reflected at the pump inlet17while the pump is operating, or at atmosphere pressure reflective of the hydraulic reservoir50, as part of the open loop circuit16, whenever the pump is off or in a standby state.

The variable displacement pump18is adapted to read the pressure on the high-pressure side of the hydraulic circuit16through the load sensing line24, as previously described. The load sensing feature may enable the pump24to either increase or decrease its rate of hydraulic fluid displacement in response to system demand changes resulting from modulation of the proportioning valve14, as commanded by the ECM12.

To the extent that the proportioning valve14may be adjusted strictly as a function of a desired evaporator temperature, the HVAC system10is able to accommodate air-conditioning loads without shutting off, thus allowing the evaporator to maintain a greatly improved temperature distribution over systems that cycle on and off, particularly during periods of decreased air-conditioning demands. This improves the efficiency of the evaporator40, and permits the compressor30to operate more slowly whenever higher or maximum air-conditioning levels are not required. To the extent that the pump18may be configured, via its load sensing capability, to lower the amount fluid displacement during periods of low air-conditioning demand, the system may require considerably less horsepower, and thus overall machine efficiency may be improved.

A principal advantage of utilizing a hydraulic power system for HVAC compressor control relates to how the hydraulic pump18may automatically adjust for significant or large changes in the pump demand. To the extent that the load sensing circuitry may be configured to automatically change the fluid displacement rate of the pump18to accommodate any desired compressor speed, the use of the hydraulic circuit16instead of the typical electrical control system to make large or significant valve adjustments or modulations may be avoided. Moreover, since the compressor30may be configured to run at higher speeds, even during periods of work machine engine idle, the HVAC system10may inherently have more capacity to meet cooling needs over other available systems.

As suggested above, the HVAC system10disclosed herein may also be configured to employ an open loop hydraulic circuit, which may facilitate the use of multiple air-conditioning units, as for example in the embodiment ofFIG. 3. Such accommodation may be made with relatively inexpensive fixed displacement motors20. Moreover, the dual air-conditioning subsystems A and B disclosed in the HVAC system100may be configured to run independently, although alternative embodiments envisioned hereunder may permit simultaneous subsystem operability.

The HVAC systems10,100may be packaged in modular form for ease of handling and providing for easier field replacements. Referring now toFIG. 5, the physical HVAC systems may be contained in a simple modular housing package Y. The housing package Y may offer the convenience of not having to discharge any refrigerant; i.e. the refrigerant lines do not need to be disturbed for removal or for replacement. For such purpose, only three sets of connections are required, including two heater hoses which are adapted to provide inlet and outlet connections for engine coolant, two electrical connectors, and a few hydraulic connectors, as shown. The back of the unit as indicated provides the mechanical structural connectors for attachment of the HVAC system10,100to the backside of the cab8.

In the modular package Y, a blower for the evaporator and heater cores, as well as a heater/evaporator subunit is provided at one end, while the electrical, heater, and hydraulic connectors are shown at the other. Intermediate of the ends are situated the condenser, condenser fans, refrigerant expansion valve, along with the compressor/hydraulic motor subassembly.

Thus, those skilled in the art will appreciate that the modular housing package Y may facilitate simpler replacements of defective units in remote field locations where the machines2are often utilized.

Either of the HVAC systems10and100may be utilized in large work machines, particularly hydraulic powered work machines such as mining shovels, mining trucks, excavators, and the like. The systems10and100may offer greater compressor reliability due to avoidance of the on-off compressor cycling involved in many existing HVAC system configurations. The higher compressor reliability may result in fewer downtime periods for maintenance and/or replacement of various HVAC system parts.

Finally, to the extent that higher compressor speeds can be maintained even during engine idle, greater operating efficiencies and lower noise levels may result. To the extent that evaporator temperature may directly be correlated to a given compressor speed, the HVAC systems10and100may offer systems subject to less temperature variations of the air-conditioned environments within the cab8.

One control algorithm for use with the hydraulic HVAC system100ofFIG. 3, which utilizes primary and secondary refrigeration subsystems A and B, respectively, wherein subsystem B refrigeration components have 200-series references, e.g., the hydraulic motor220and compressor230, may be described as follows.

Assuming that subsystem A will act as a primary refrigeration subsystem by default, an initial HVAC systems check may be connected by the ECM112. The systems check may include confirmation of whether the primary or secondary subsystem A or B is to be activated, and if so, whether the reversible shuttle valve126is properly oriented. For example, if the primary subsystem A is to be activated, the shuttle valve126should be configured to pressurize hydraulic fluid associated with the proportioning valve114. In some embodiments, both A and B may be activated. Once confirmation is received that the shuttle valve126is in proper orientation, the variable displacement pump118may be fully activated; i.e., the stop valve22(not shown, but as earlier shown and described) may then be switched from trickle flow status through drain line23(FIG. 2) to fully open status to permit hydraulic fluid flows at normal operating volumes through drain line21(FIG. 2).

At this point the ECM112may initiate its modulation commands to the proportional valve114, based upon real time fin temperature readings of the evaporator (not shown, but as earlier shown and described). For this purpose, the pump118may utilize its load sensing capability to meet appropriate hydraulic system pressure demands necessary to ultimately control the speed of the fixed motor120, and hence to directly control the speed of the compressor130to which the motor120is coupled.

Operation of the secondary refrigeration subsystem B is similar, except for operation of the sensing shuttle valve126. The orientation of the latter becomes changed so as to sense pressurization of the side of the hydraulic circuit116associated with the proportioning valve214, wherein the ECM112may then control the respective motor and compressor components,220and230, respectively. Although for brevity, the respective evaporators are not shown inFIG. 3, the respective primary and secondary refrigerant condensers132and232are in fact displayed. Once subsystem A, B or both are engaged, the hydraulic control aspects of the ECM112will apply as already described for the HVAC system10ofFIG. 2.

The above describes a self-contained unit with an automatic control module that allows an improved level stability in control matching the capacity requirements of the cab and the increased stability increases compressor life and performance.