Patent Description:
Internal combustion engines require fuel to be injected at high pressure. It is known to provide a high pressure pump to increase fuel pressure for this purpose. It is also known to provide a pump lubricant circuit to facilitate efficient operation of such high pressure pumps.

High pressure pumps, such as reciprocating pumps with pistons or plungers, can facilitate migration of fuel between, for example, the piston and the piston bore. In this way, fuel may contaminate the pump lubricant. Depending on the fuel being used, contamination of the lubricant with fuel may reduce the lubricating qualities of the lubricant.

In the case of diesel fuel, the impact of a modest quantity of diesel contaminating the lubricant may be relatively minor because diesel itself has reasonable lubricating qualities.

Methanol is an alternative fuel to diesel that is of interest for use with combustion engines, for example in marine propulsion. For example, ship engines that are around <NUM>-<NUM> MW and that conventionally use diesel could be adapted to use methanol. Methanol has around half the heating value of diesel, and so double the injection volume is needed. It is convenient for such industries to use engines similar to existing diesel engines or to modify diesel engines such that they can use methanol (or alternative low flash point fuels), particularly given that the same air system can be used. Barriers to using methanol include its very low viscosity and the fact that it is a polar liquid, leading to risks of fuel migration and of corrosion. It is preferable to avoid mixing of methanol with lubricant in a high pressure fuel pump and to prevent any leakage of diluted lubricant to the engine's lubrication circuit.

The requirement for a larger volume of Methanol than diesel means that a higher pressure may be required, meaning that the fuel pump needs to operate at higher pressures. A higher pressure may increase the risk of fuel migrating into the pump lubricant. Furthermore, since the lubricating qualities of Methanol are poor, the impact of such contamination may be significantly more severe.

In short, relative to diesel, the risk and consequences of fuel migration are increased for fuels such as Methanol (and other low flash point fuels) which have very low viscosity and no lubricating qualities.

<CIT> describes a fuel system and method for reducing fuel leakage from a fuel system. The fuel system is for supplying pressurised fuel, in particular dimethyl ether (DME) or a blend thereof, to an internal combustion engine, said fuel system comprising a fuel pump, which has a pumping mechanism arranged partly in a housing containing lube oil, a drain line connected to said housing and suitable for draining at least fuel vapour from an interior of said housing, a lube oil supply line connected to said housing, a lube oil supply valve installed in said lube oil supply line ,a seal installed between said pumping mechanism and said housing for preventing at least lube oil leakage to the outside of said housing, and a drain valve installed in said drain line, wherein both said drain valve and lube oil supply valve are controlled to be closed during an engine non-running state for preventing fuel vapour leakage from said housing.

Against this background, there is provided a lubricated high pressure fuel pump assembly comprising:.

such that the lubricant is retained within the lubricated high pressure fuel pump assembly.

In this way the high pressure fuel pump may be lubricated with lubrication oil with minimal risk of lubricant mixing with the fuel or leaking to the engine lubricant supply.

A lubricated high pressure fuel pump assembly comprising a fuel pump and a lubrication circuit, wherein the fuel pump comprises:.

and wherein the lubrication circuit comprises:.

such that the lubricant is retained within the lubricated high pressure fuel pump assembly.

A specific embodiment of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which:.

According to an embodiment of this disclosure, there is a lubricated high pressure fuel pump assembly <NUM>. There is a pump lubrication circuit <NUM> for lubricating the drive shaft and plunger drive mechanism of the high pressure fuel pump <NUM> that is configured to prevent lubricant from reaching an engine or mixing with engine lubricant. The fuel may be a low flash point fuel. In an embodiment, the fuel may be methanol. In alternative embodiments the fuel may be dimethyl ether, ethane, ethanol or ammonia.

With reference to <FIG>, there is a high pressure fuel pump <NUM> that is configured to increase the pressure of fuel prior to injection into an engine's combustion chamber. Low pressure fuel enters the fuel pump <NUM> via a low pressure fuel inlet <NUM>, and fuel pumping section <NUM> increases the pressure of the fuel such that high pressure fuel leaves the fuel pump <NUM> via a high pressure fuel outlet <NUM>. The fuel pumping section <NUM> is configured to be mechanically driven via a pump drive shaft <NUM>. The fuel pump <NUM> may be a reciprocal pump, in which a plunger drive mechanism converts the rotation of the pump drive shaft <NUM> to translational motion of plungers in the fuel pumping section <NUM>.

The pump drive shaft <NUM> requires lubrication, and is sensitive to the detrimental effects of diluted lubricant. The pump drive shaft <NUM> is lubricated via a pump lubrication circuit <NUM> that is configured to prevent the lubricant and fuel mixing, and to prevent lubricant from leaking to the engine. The pump lubrication circuit <NUM> comprises a lubricant reservoir <NUM>, from which lubricant pump <NUM> receives lubricant (as indicated by arrow <NUM>). The lubricant pump <NUM> pumps lubricant to the pump drive shaft <NUM> (as indicated by arrow <NUM>). The lubricant is collected and returned to the lubricant reservoir <NUM> via lubricant outlet <NUM> (as indicated by arrow <NUM>).

A first portion <NUM> of the pump drive shaft <NUM> that is exterior to the fuel pump <NUM> is enclosed by a sealed enclosure <NUM>. The sealed enclosure <NUM> is configured to prevent lubricant from leaking from the fuel pump <NUM> and associated pump lubrication circuit <NUM> via the pump drive shaft <NUM> to the environment. In an embodiment, the sealed enclosure <NUM> may be dry. In another embodiment, with reference to <FIG>, the sealed enclosure <NUM> may comprise a drain that is configured to transfer any fluid in the sealed enclosure <NUM> to the lubricant reservoir <NUM> (arrow <NUM>). The sealed enclosure <NUM> may be further configured to monitor fluid within it. Entry of liquid into the sealed enclosure <NUM> may be monitored by an appropriate sensor, such as a liquid sensor or a pressure sensor, as a measure of leakage detection. In the case of leakage, a failure mode may be triggered.

With reference to <FIG>, the pump drive shaft <NUM> is configured such that in use, it may be mechanically driven by an engine <NUM>. The sealed enclosure <NUM> thus prevents lubricant passing from the fuel pump <NUM> to the engine <NUM>. The engine <NUM> may comprise an engine lubrication circuit <NUM>.

With reference to <FIG>, in an embodiment the pump lubrication circuit <NUM> may further comprise a fluid separator <NUM> that is configured to isolate lubricant from a contaminated mixture of lubricant and fuel, to facilitate removal of fuel that may be present in the pump lubrication circuit. The lubricant reservoir <NUM> may receive lubricant from the lubricant outlet <NUM> of the fuel pump <NUM> and from the sealed enclosure <NUM>. There is a risk that this lubricant may have been mixed with some fuel. It is preferable that the pump drive shaft <NUM> is lubricated by lubricant only, rather than lubricant that is diluted by fuel, and so the fluid separator <NUM> may be used to purify the lubricant that is output from the lubricant reservoir <NUM>. The fluid separator <NUM> may receive fluid from the lubricant reservoir <NUM> (arrow <NUM>), and separate said fluid into lubricant and contaminates such as fuel. The lubricant is transferred (via arrow <NUM>) to the lubricant pump <NUM> and any contaminates are collected (arrow <NUM>). In an embodiment, the fuel may be methanol. Methanol has low viscosity and is polar, whereas the lubricant may have high viscosity and be non-polar. The fluid separator <NUM> may separate the methanol and lubricant based on these properties or via density.

In another embodiment, with reference to <FIG>, the lubricant reservoir <NUM> may additionally receive lubricant from an engine lubricant supply. This may occur in accordance with a schedule or on demand, for example in the event that lubricant levels in the lubricant reservoir <NUM> drop below a threshold. The lubricant from the engine lubricant supply may pass through a valve assembly <NUM> that is configured to allow fluid flow only in the direction from the engine lubricant supply to the lubricant reservoir <NUM>, and not in the direction from the lubricant reservoir <NUM> to the engine lubricant supply. The valve assembly <NUM> may comprise two or more one way valves in series, each configured to allow fluid flow only in the direction from the engine lubricant supply to the lubricant reservoir <NUM>, and not in the direction from the lubricant reservoir <NUM> to the engine lubricant supply. This may provide redundancy; in the event that one of the one way valves fails, the other one way valve will still prevent backflow. The valve assembly <NUM> may comprise any feature or features that prevent backflow.

In an embodiment, the pump drive shaft <NUM> may be an end of an engine shaft, such as a power take-off shaft. With reference to <FIG>, in another embodiment the pump drive shaft <NUM> may be mechanically coupled to an engine shaft <NUM>, such as a power take-off shaft, such that the engine <NUM> mechanically drives the pump drive shaft <NUM>. The first portion <NUM> of the pump drive shaft <NUM> may comprise a first end of the pump drive shaft <NUM> that is mechanically coupled to a first end <NUM> of an engine shaft <NUM>, such as a power take-off shaft, via a mechanical coupling <NUM>. The first end of the pump drive shaft <NUM> and the first end <NUM> of the engine shaft <NUM> protrude into the sealed enclosure <NUM>. The sealed enclosure <NUM> and the mechanical coupling <NUM> may be configured to prevent fluid transfer from the first end of the pump drive shaft <NUM> to the engine shaft <NUM>, such that said fluid is prevented from reaching the engine <NUM>.

In an embodiment the lubricant pump <NUM> may be an electrically driven pump. In another embodiment, with reference to <FIG>, the lubricant pump <NUM> may be mechanically driven by a second end of the pump drive shaft <NUM> wherein the second end of the pump drive shaft <NUM> is the free end of the pump drive shaft <NUM>.

The fuel pump <NUM>, pump lubrication circuit <NUM> and engine shaft <NUM> may further comprise one or more shaft seals. With reference to <FIG>, there may be first and second shaft seals <NUM> and <NUM> around the pump drive shaft <NUM> and the engine shaft <NUM> respectively, exterior to the sealed enclosure <NUM>. There may also be a third shaft seal <NUM> around the pump drive shaft <NUM> within the fuel pump <NUM>. The fuel pump <NUM> may further comprise a drain from one or more bearings of the pump drive shaft <NUM>, configured to drain fluid from the pump drive shaft <NUM> to the lubricant reservoir <NUM>.

In exemplary embodiments, the fuel pump <NUM> may be a positive displacement pump. The pump drive shaft <NUM> may comprise a camshaft or a plunger drive mechanical system. The fuel pumping section <NUM> may comprise a piston or plunger pump that may be inline, radial or axial. The engine shaft <NUM> may be a power take-off (PTO) shaft. Alternatively, an engine crankshaft may indirectly drive the pump drive shaft <NUM>. For example, the engine crankshaft may engage drive lines, belt drives or gears.

In use, lubricant reservoir <NUM> contains lubricant for lubrication of the fuel pump <NUM>. The lubricant pump <NUM> receives lubricant from the lubricant reservoir <NUM>, and pumps lubricant to the pump drive shaft <NUM> of the fuel pump <NUM>. The lubricant lubricates the pump drive shaft <NUM> and the plunger drive mechanical system, and is then drained via lubricant outlet <NUM> to the lubricant reservoir <NUM>. The pump drive shaft <NUM> is configured to be mechanically driven. Lubricant may seep past plane bearings in the fuel pump <NUM> from a section of the pump drive shaft <NUM> within the fuel pump <NUM> to a section of the pump drive shaft <NUM> exterior to the fuel pump <NUM>. A sealed enclosure <NUM> surrounds a first portion <NUM> of the pump drive shaft <NUM>, and is configured to prevent or contain leakage of lubricant from the fuel pump <NUM> via the pump drive shaft <NUM>. In an embodiment, the fuel pump <NUM> is mechanically driven by an engine <NUM> and the sealed enclosure <NUM> is configured to prevent transfer of lubricant from the fuel pump <NUM> to the engine <NUM> along the pump drive shaft <NUM>. The sealed enclosure <NUM> may comprise a drain via which any lubricant that enters the sealed enclosure <NUM> is drained and returned to the lubricant reservoir <NUM>. The sealed enclosure <NUM> may be monitored as a leak detection measure.

Claim 1:
A lubricated high pressure fuel pump assembly (<NUM>) comprising:
a fuel pump (<NUM>) including a pump drive shaft (<NUM>) via which the fuel pump (<NUM>) is configured to be mechanically driven;
a sealed enclosure (<NUM>) configured to surround a first portion (<NUM>) of the pump drive shaft (<NUM>), wherein the first portion (<NUM>) is exterior to the fuel pump (<NUM>); and
a pump lubrication circuit (<NUM>) comprising:
a lubricant reservoir (<NUM>); and
a lubricant pump (<NUM>) configured to pump lubricant from the lubricant reservoir (<NUM>) to the pump drive shaft (<NUM>);
wherein:
the sealed enclosure (<NUM>) is configured to prevent fluid leakage from the fuel pump (<NUM>) via the first portion (<NUM>) of the pump drive shaft (<NUM>); and
the lubricant reservoir (<NUM>) is configured to collect the lubricant from the pump drive shaft (<NUM>);
such that the lubricant is retained within the lubricated high pressure fuel pump assembly (<NUM>).