Patent Application
20140172269
The present disclosure generally relates to pumps and, more particularly, relates to liquid natural gas (LNG) cryogenic pumps.
It has become increasingly common for many work machines used in agricultural, construction and mining operations to be powered by alternative fuels. Such machines, which may be provided in many forms such as front-end loaders, track-type tractors, excavators, pipe layers, graders and the like, have traditionally been powered by diesel fuel, which to this day is still the most common fuel source. However, due to environmental concerns, cost and availability, other fuels such as, but not limited to, natural gas, have been utilized. Such natural gas can be provided in many forms including methane.
In order to provide the natural gas to the engine in a portable, efficient manner, the natural gas is cooled to a liquid state and stored on-board the machine in a cryogenic tank. Such tanks are typically double-hulled with insulation between the hulls in order to maintain the natural gas at temperatures at least as low as −160° C., and at pressures of at least as high as 300 psi. A pump is then used to deliver the LNG to the engine of the machine. Such pumps are typically provided as piston pumps which not only deliver the LNG to the engine but also pressurize same to convert the LNG to compressed natural gas (CNG). For example, whereas LNG is typically at the aforementioned pressure of about 300 psi, CNG is typically ten times that, or about 3000 psi.
Such a piston pump, also referred to as a cryogenic pump, often consists of a single piston reciprocatingly mounted in a cylinder. In order to move the piston back and forth in the cylinder, and thus draw in (suction stroke) and then compress (compression stroke) the natural gas, hydraulic fluid is utilized. More specifically, hydraulic fluid is directed to a retraction port in the piston pump, while hydraulic fluid is expelled from an extension port when the suction stroke is conducted. Conversely, when the compression stroke is conducted, hydraulic fluid is directed to the extension port, while hydraulic fluid is released from the retraction port. An example of this technology is disclosed in Canadian Patent No. 2,523,732.
In order to provide the hydraulic fluid, one or more hydraulic pumps are typically provided on the machine and driven by the engine of the machine. Such pumps can be provided in a number of different forms, with variable displacement piston pumps being one common example. With a variable displacement piston pump, a central barrel or block is rotatably driven by the engine. The barrel includes a plurality of cylinders each of which is adapted to receive a reciprocating piston. At a driven end, each of the pistons is pivotally and slidably engaged with a swashplate angularly positioned relative to the cylinder barrel. At a work end of each cylinder, a valve plate is provided having two or more kidney-shaped inlets and outlets. During the inlet phase of operation, hydraulic fluid is drawn in through the inlet of the valve plate, and into the cylinders of the rotating barrel. This drawing in or filling of the cylinders occurs as the barrel rotates, and the pistons of the barrel proximate to the inlet move from a top dead center position to bottom dead center position. The rotation of the barrel and size of the inlets are such that once the piston reaches its bottom dead center position, the cylinders rotate out of communication with the inlet of the valve plate. Further rotation of the barrel causes the cylinders, now completely filled with hydraulic fluid, to create fluid flow as the pistons move from the bottom dead center position to the top dead center position. During travel from the bottom dead center to the top dead center position, the cylinders are placed into communication with the outlet of the valve plate such that the hydraulic fluid can be delivered from the pump to provide for useful work such as the aforementioned driving of implements and work arms provided on various earth moving equipment.
While effective, in certain situations this may be inefficient. For example, with current liquefied natural gas (LNG) cryogenic piston pumps, regardless of whether the engine employing the pump is idling, current controls provide a quick compression stroke and relatively long suction stroke. As such quick compression stroke require significant hydraulic fluid flow from the hydraulic pump, this burdens the engine even when at idle. This results in higher torque at idle than is needed, higher load on the engine at idle than is needed, a larger overall pump size than is needed, and lower fuel economy.
In accordance with one aspect of the disclosure, a method of operating a cryogenic piston pump for use in supplying fuel to an engine is disclosed. The method may comprise determining the actual speed of the engine, operating the cryogenic piston pump under a first control strategy when the engine is at an idle speed, and operating the variable displacement piston pump under a second control strategy when the engine is at a rated speed, with the second control strategy being different from the first control strategy.
In accordance with another aspect of the disclosure, a liquefied natural gas pump control system is disclosed which may comprise a source of liquefied natural gas, a cryogenic piston pump operatively connected to the source of liquefied natural gas, an engine receiving compressed natural gas from the cryogenic piston pump, and an electronic control module commanding the cryogenic piston pump to operate in at least two different modes depending on the speed at which the engine is operating.
In accordance with another aspect of the disclosure, a machine is disclosed which may comprise a chassis, an engine supported by the chassis, a locomotion device supporting the chassis, a hydraulic cylinder operatively associated with the machine, a fuel source supported by the chassis, a fuel pump interconnecting the fuel source and the engine, and an electronic control module operatively connected to the engine and the fuel pump and commanding the fuel pump to operate in at least two different modes depending on an operating parameter of the engine.
These and other aspects and features of the present disclosure will become more readily apparent upon reading the following detailed description when read in light of the accompanying drawings.
Referring now to the drawings, and with specific reference to
As shown therein, the machine 10 may include a chassis 12 supported by a locomotion device 14. While the locomotion device 14 depicted in
Extending from the chassis 12, the machine may include one or more work implements 22 adapted for movement relative to the chassis 12 by a plurality of hydraulic cylinders 24. While the work implement 22 is depicted as a bucket in
Referring now to
As noted above, the LNG pump 30 may be called upon to deliver a variable volume of LNG depending upon the speed at which the engine 18 is operating. For example, if the machine 10 is engaged in digging, loading, or in otherwise using its work implement, the engine 18 will be operating at a rated speed, whereas if the machine 10 is not performing useful work and is simply idling, the engine 18 will be working at a lower idle speed. Of course at the higher rated speed, the engine will be requiring more fuel and at the lower idle speed, the engine will be requiring less fuel. This, in turn, requires that the variable displacement fuel pump 30 provide more or less fuel as dictated by the speed of the engine 18. Other engine parameters can certainly be used to dictate the amount of fuel being supplied by the fuel pump.
In order to supply the LNG, the pump 30 may be provided as a piston pump such as shown in
In order to provide that hydraulic fluid, a hydraulic pump 100 such as that depicted in
In order to reciprocate the pistons 120 through the cylinders 116, a driven end 122 of each piston is rotatably and slideably engaged with a swashplate 124 by way of a shoe 125. As will be noted, the swashplate 124 can be provided at a transverse angle relative to the cylinder barrel 110 such as that as the barrel 110 and pistons 120 rotate about longitudinal axis 126 under the influence of hydraulic fluid entering and exiting the cylinders 116, the pistons 120 are caused to reciprocate back and forth therein. Moreover, the angle at which the swashplate 124 is positioned necessarily dictates the resulting volume of fluid flow from the pump 100. For example, if the swashplate 124 is parallel to the valve plate 112, then there would be no flow of fluid at all. However, with each degree the swashplate 124 is pivoted away from parallel, the resulting flow of the expelled fluid is increased.
Opposite to the driven end 122, each piston 120 includes a working end 127. Also shown in
With prior art devices, the LNG pump 30 is simply operated in one manner regardless of the mode in which the machine 10 is operating. By necessity, this required the pump 30 to operate at its higher speed so as to be able to provide the necessary fuel when the machine 10 was performing useful work. This in turn meant that the LNG pump 30 and overall machine 10 were operating inefficiently when at idle speed.
In light of this, the present disclosure significantly improves upon the teachings of the prior art and allows for the LNG pump 30 to be operated in a bifurcated fashion. More specifically, the present disclosure sets forth the LNG and diesel fuel delivery system 60 of
A significance of the two modes of operation manifests itself in enabling the engine 18 to operate at a much lesser load at idle in that, when idling, it is not necessary to have the cryogenic pump 30 provide a quick compression cycle which necessarily uses more hydraulic oil flow from the hydraulic fluid pump 100. At idle, a significantly lesser amount or even no torque is required than at rated speed. A second benefit is reduced hydraulic pump size. By altering the control strategy, the cryogenic pump 30 can be used to its fullest and most efficient capacity at both idle and rated speeds. If the control strategies were the same, as is the case with the prior art, the hydraulic pump 100 would necessarily have to be oversized so as to accommodate the idle condition, or conversely, underutilized in the rated condition. These two benefits also result in a reduced component cost and fuel savings.
As this applies to one specific embodiment of the actual operation of the machine 10, in the rated speed mode, i.e. when the sensors 132 determine that the engine 18 is operating at a rated speed or within the rated speed range, the electronic control module 76 will command the hydraulic fluid pump 100 to operate in a manner wherein some percentage (for example 25%) of the LNG cryogenic piston pump 30 cycle time is spent in compression strokes, and some other percentage (for example 75%) of the LNG cryogenic piston pump 30 operation cycle is spent in a suction stroke. Of course, 25% and 75% are but one example, and the teachings of this disclosure allow for an infinitely variable range between 0 and 100% for either stroke/cycle. This allows for the LNG cryogenic piston pump 30 to more easily keep pace with the fuel demands of the engine when it is performing useful work. In other words, when the engine 18 is being called upon by the work implements 22 to perform useful work, a larger volume of fuel is required, and thus more time is spent by the LNG pump 30 in drawing fuel from the tank 26 and directing same to the engine 18, as opposed to compressing same.
Conversely, when the sensors 132 determine that the engine 18 is working at an idle speed, the idle speed mode of the LNG pump 30 allows the electronic control module 76 to operate the LNG pump 30 but with more time in compression strokes, and less time in suction strokes. For example, at idle speed, the electronic control module may dictate that the LNG cryogenic pistonpump 30 split time evenly, i.e. with 50% of the fuel pump operating cycle being in compression strokes, and 50% being in suction strokes. Again, while the 50/50 split is indicated herein for such an idle condition, it is to be understood that any number of other different percentages may be employed and still fall within the range of equivalents the present disclosure. What is of importance is that some form of a bifurcated control strategy is used to more efficiently operate the LNG pump 30 depending on the needs of the engine 18. In so doing, idle torque can be reduced and pump utilization can be tailored to its most efficient extent in both idle and rated speeds. Moreover, in so doing, the overall size of the hydraulic pump 100 can be reduced, and thus component cost can be reduced and fuel economy of the machine 10 can be increased.
Referring now to
From the foregoing, it can be seen that the technology disclosed herein has industrial applicability in a variety of settings such as, but not limited to, engine control strategies. Such engines may be diesel engines or hybrid engines employing both diesel fuel and liquefied natural gas and used on earth-moving equipment, or highway trucks, or the like. By providing dual modes of operation, significant gains in efficiency and cost reduction can be achieved.
More specifically, a first benefit is reduced engine load at idle. When idling, it is not necessary to provide a quick compression cycle, which uses more hydraulic oil flow. If a single control strategy were to be employed, the torque required at idle would be significantly higher than that required at rated speed. A second benefit is reduced hydraulic pump size. By altering the control strategy, the pump can be utilized to its fullest at both idle and rated speeds. If the control strategies were the same, the pump would be under-utilized in the rated condition. These two benefits result in reduced component costs and fuel savings.
