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Variable capacity oil pump

Variable capacity oil pump description/claims

The invention relates to a fluid displacement pump having a drive shaft, and where said pump is provided with a coupling arrangement between at least a first pumping member and at least a second pumping member. The invention also relates to a fluid supply system comprising a fluid inlet and a fluid outlet of the first pump and a fluid inlet and a fluid outlet of the second pump. Furthermore, the invention relates to a wind turbine with a fluid supply system comprising a fluid displacement pump. The invention also relates to a method of controlling a fluid pressure in a fluid supply system of a wind turbine.

Lubrication and cooling of mechanical equipment such as gearboxes, bearings or combustion engines is typically obtained by either of the following principles:

An oil pump with constant geometric volume is driven by a constant or variable speed electric motor, more recently also by frequency controlled motors allowing a continuous variation of the pump speed and thereby the oil flow. This arrangement allows continuous adjustment of the flow to the momentary needs by an external controller as long as electrical power is available. In case of loss of this external source of energy, the oil flow ceases, and a safe run-down of the equipment cannot be granted.

An oil pump with constant geometric volume is driven by a shaft of the equipment, for example a power-take-off (PTO) from a gearbox. The oil flow is hence directly dependent on the speed of the drive shaft, and cannot be adjusted to the momentary needs. This becomes a particular disadvantage in applications where the speed of the PTO-shaft varies. Obtaining sufficient oil supply at the lowest operating speeds may require selection of quite large pumps, which will then supply too much oil in the upper speed range. The surplus oil needs to be wasted through bypasses, which increases the system's complexity.

Additionally, excessive circulation deteriorates the oil, causes premature ageing, and will typically require increased oil volumes. Compared to electrical driven pumps, such shaft driven pumps allow a safe run-down also in case the external power supply collapses. The efficiency will typically be higher, as no additional power transformation is required.

A common solution combining the advantages of shaft-driven and electrical pumps is installing two independent systems where the shaft-driven pump cares for sufficient supply when no external power is available, and where the electrical pump or both. i.e., also the shaft-driven pumps in parallel provide the oil supply in regular operation. Two independent systems are more costly and more complex systems

Shaft driven pumps, where the geometric volume of the oil pump is varied, is a third possibility of obtaining variable oil flow independent of the speed of the equipment. This technology is typically used in automotive systems and hydraulic applications, but has technical limitations for large oil flow, or for fluids with high viscosity as typically used in industrial applications, due to the limited suction capacity of those pump designs.

It is one object according to one aspect of the present invention to combine the advantages of a shaft driven fluid pump such as an oil pump in respect to safe run-down with the variable flow characteristics of electrically driven pumps for lubrication systems for large fluid flow and high viscosity.

It is another object according to a second aspect of the present invention to combine the advantages of a shaft driven fuel pump such as an oil pump in respect to safe run-up with the variable flow characteristics of electrically driven pumps for lubrication systems for large fluid flow and high viscosity.

The object of the invention according to the first aspect of the invention may be obtained by a pump being provided with a coupling arrangement between at least a first pumping member and at least a second pumping member, said at least first and second pumping members in total exhibiting a certain increased pumping capacity at a certain reduced rotational speed of the drive shaft.

By providing an increased pumping capacity at a certain reduced rotational speed of the drive shaft, chosen mechanical parts such as the gearbox of a wind turbine, said parts still being in limited motion during idling of the wind turbine, will be provided a much better lubrication despite the often very limited rotational speed of the rotor.

The object of the invention according to the second aspect of the invention may be obtained by a pump having a drive shaft, said pump being provided with a coupling arrangement between at least a first pumping member and at least a second pumping member, said at least first and second pumping members in total exhibiting a certain increased pumping capacity at a certain increased rotational speed of the drive shaft.

By providing an increased pumping capacity at a certain increased rotational speed of the drive shaft, a wind turbine, when in an emergency situation, will be provided a much better lubrication of the different mechanical parts, such as gears of a gear box, being in very fast motion during an emergency situation.

According to a possible embodiment of the invention, said drive shaft constitutes a common drive shaft intended for driving at least a first rotating pumping member and at least a second rotating pumping member by a driving means driving the drive shaft, and said pump further being provided with a mechanical coupling arrangement between the at least first pumping member and the at least second pumping member.

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