Patent Description:
A conventional wind turbine comprises a rotor with rotor blades. The rotor is mounted rotatable to a nacelle of the wind turbine by means of a main bearing. The rotor is thus rotatable about a rotation axis. Some oil is usually leaking from the main bearing. There may be very long periods without wind flow, where the main bearing can be completely dried, but the wind turbine must still be functional even after months or years after a leakage begins to appear.

The main bearing is usually a single fluid film bearing (SFFB) which comprises a cavity which needs completely to be filled by the lubrication oil. To compensate for thermal expansion and contraction of the oil and for possible leakage from shaft seals, a small oil flow is continuously pumped from an oil tank into the main bearing. Thereby, there will be excess oil in the main bearing. <CIT> discloses an example of a device for controlling the lubricating oil flow through a generator bearing. It is difficult to monitor the presence of such oil flow, as there is only small oil pressure by gravity. Conventional oil flow meters take a greater oil pressure than what is available here. Oil levels are usually measured with level gauges, however, since the lubrication oil in the main bearing is not a level but simply fills the cavity, a conventional level gauge can hardly be used in a top part of the main bearing.

It is the object of the present invention to provide a device and a method of determining a lubrication condition of a main bearing of a wind turbine. This object is achieved by the subject matters according to the independent claims. The present invention is further developed as set forth in the dependent claims.

According to a first aspect of the invention, a device for determining a lubrication condition of a main bearing of a wind turbine is provided. The device comprises a container which is configured to collect a leakage lubrication oil from the main bearing; an outlet which is configured to discharge the collected oil from the container with a predetermined flow rate; an overflow passage which is configured to discharge on overflow of the collected oil from the container; a detecting device which is configured to detect an overflow of the collected oil through the overflow passage; and a determining device which is configured to determine that the lubrication condition of a main bearing is sufficient if the detecting device detects the overflow of the collected oil through the overflow passage.

In the context of the present patent application, the "sufficient lubrication condition of a main bearing" may refer to a condition where the cavity of the main bearing is substantially completely filled by the lubrication oil.

The present invention uses a kind of difference measurement, i.e., if a total leakage lubrication oil flow amount is higher than the flow amount through the outlet, the excessive leakage lubrication oil escapes through the overflow passage. Such flow amount is then detected by the detecting device which eventually results in the determination that the lubrication condition of a main bearing is sufficient.

According to an embodiment, the overflow passage is connected to the container at a location which is higher than a location of the outlet. It is ensured that the flow through the overflow passage starts after a flow through the outlet.

According to an embodiment, the detecting device comprises a level detecting device which is configured to detect a predetermined oil level in the container. Preferably, the predetermined oil level is arranged substantially at the same level where the overflow passage is connected to the container. If the level detecting device detects the predetermined oil level in the container, the overflow of the collected oil through the overflow passage is detected.

According to an embodiment, the predetermined flow rate of the outlet is adjustable or controllable. If the outlet is fully closed, the oil flow therethrough can be even zero.

According to the invention, the device for determining a lubrication condition further comprises an oil tank which is configured to receive the discharged oil from the outlet and the discharged oil from the overflow passage. According to an embodiment, the device for determining a lubrication condition further comprises a feedback passage which is configured to feed back the oil from the oil tank to the main bearing.

According to the invention, the device for determining a lubrication condition further comprises at least one funnel which is configured to collect the leakage lubrication oil from the main bearing and to lead the leakage oil to the container. According to an embodiment, the leakage oil is collected by means of gravitation.

According to an embodiment, the leakage lubrication oil is collected by means of gravitation.

The present invention monitors that there is a leakage oil flow in overflow passage, which indicates that the lubrication condition is sufficient. The leakage oil flows by gravity alone, and the overflow is led to the container with the outlet at the bottom which allows a limited oil flow. Close to the top of the container, there is the overflow passage where oil will flow out if more oil flows into to the container than out of the container through the outlet. The detecting device detects the oil flow in the overflow passage. If there is a flow in the overflow passage, then it is determined there is a sufficient lubrication condition of the bearing because it can be ascertained that the cavity in the main bearing is sufficiently filled by the lubrication oil. Instead of a conventional level measurement, the present invention uses an overflow detection which can be monitored in a simple and reliable manner with only one sensor. A sophisticated sensor in the cavity of the main bearing is not required. Since the oil flows by gravity alone, no additional pressure source is necessary.

It has to be noted that embodiments of the invention have been described with reference to different subject matters.

In particular, some embodiments have been described with reference to apparatus type claims whereas other embodiments have been described with reference to method type claims. However, a person skilled in the art will gather from the above and the following description that, unless other notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters, in particular between features of the apparatus type claims and features of the method type claims is considered as to be disclosed with this application.

<FIG> shows a wind turbine <NUM>. The wind turbine <NUM> comprises a nacelle <NUM> and a tower <NUM>. The nacelle <NUM> is mounted at the top of the tower <NUM>. The nacelle <NUM> is mounted rotatable with regard to the tower <NUM> by means of a yaw bearing. The axis of rotation of the nacelle <NUM> with regard to the tower <NUM> is referred to as the yaw axis.

The wind turbine <NUM> also comprises a hub <NUM> with three rotor blades <NUM> (of which two rotor blades <NUM> are depicted in <FIG>). The hub <NUM> is mounted rotatable with regard to the nacelle <NUM> by means of a main bearing <NUM>. The hub <NUM> is mounted rotatable about a rotor axis of rotation <NUM>.

The wind turbine <NUM> furthermore comprises a generator <NUM>. The generator <NUM> in turn comprises a rotor connecting the generator <NUM> with the hub <NUM>. If the hub <NUM> is connected directly to the generator <NUM>, the wind turbine <NUM> is referred to as a gear-less, direct-driven wind turbine. Such a generator <NUM> is referred as direct drive generator <NUM>. As an alternative, the hub <NUM> may also be connected to the generator <NUM> via a gear box. This type of wind turbine <NUM> is referred to as a geared wind turbine. The present invention is suitable for both types of wind turbines <NUM>.

The generator <NUM> is accommodated within the nacelle <NUM>. The generator <NUM> is arranged and prepared for converting the rotational energy from the hub <NUM> into electrical energy in the shape of an AC power.

<FIG> shows a block diagram of a device for determining a lubrication condition of the main bearing <NUM> of the wind turbine <NUM> according to an embodiment. The device for determining a lubrication condition of the main bearing <NUM> of the wind turbine <NUM> comprises a container <NUM> which is configured to collect a leakage lubrication oil from the main bearing <NUM>. The leakage lubrication oil can be supplied to the container <NUM> via an inlet pipe <NUM>. A a funnel <NUM> is provided which collects the leakage lubrication oil and supplies the same to the container <NUM>. Preferably, the leakage oil is collected by means of gravitation so that no pressurizing or feeding means is necessary.

The device for determining a lubrication condition further comprises an outlet <NUM>, such as a small hole/orifice, at the bottom of the container <NUM>, wherein the outlet <NUM> is configured to discharge the collected oil from the container <NUM> with a predetermined flow rate. Preferably, the predetermined flow rate of the outlet <NUM> is adjustable or controllable. If the outlet <NUM> is closed, the predetermined flow rate is zero.

The device for determining a lubrication condition further comprises an overflow passage <NUM> which is configured to discharge on overflow of the collected oil from the container <NUM>. Preferably, the overflow passage <NUM> is connected to the container <NUM> at a location which is higher than a location of the outlet <NUM>. The device for determining a lubrication condition further comprises a detecting device <NUM> which is configured to detect an overflow of the collected oil from the container <NUM> through the overflow passage <NUM>.

The device for determining a lubrication condition further comprises a determining device <NUM> which is configured to determine that the lubrication condition of a main bearing <NUM> is sufficient if the detecting device <NUM> detects the overflow of the collected oil through the overflow passage <NUM>. For example, the determining device <NUM> receives a signal from the detecting device <NUM> which indicates that there is an oil flow in the overflow passage <NUM>. The determining device <NUM>, which can comprise a processor and the like, then determines that the lubrication condition of the main bearing <NUM> is sufficient.

The detecting device <NUM> can comprise a level detecting device which is configured to detect a predetermined oil level in the container <NUM>. The predetermined oil level is arranged substantially at the same level where the overflow passage <NUM> is connected to the container <NUM>. If the level detecting device <NUM> detects the predetermined oil level in the container <NUM>, the overflow of the collected oil through the overflow passage <NUM> occurs and is detected thereby.

When the overflow from the main bearing <NUM> is higher than the limited amount drained from the bottom outlet <NUM> of the container <NUM>, the container <NUM> will be filled up and the detecting device <NUM> in the shape of the level detecting device located at the predetermined level in the container <NUM> will detect that there is oil at this predetermined level in the container <NUM>. In short, it can be said that as long as the level detecting device detects that there is the predetermined oil level in the container <NUM>, then the amount of overflow of excess oil from the main bearing <NUM> is higher than the limited amount that is drained out of the outlet <NUM> of the container <NUM>.

The present invention uses a kind of difference measurement, i.e., if a total leakage lubrication oil flow amount is higher than the flow amount through the outlet <NUM>, the excessive leakage lubrication oil escapes through the overflow passage <NUM>. Such flow amount is then detected by the detecting device <NUM> which eventually results in the determination by the determining device <NUM> that the lubrication condition of the main bearing <NUM> is sufficient.

The device for determining a lubrication condition further comprises an oil tank <NUM> which is configured to receive the discharged oil from the outlet <NUM> and the discharged oil from the overflow passage <NUM>, and a feedback passage <NUM> which is configured to feed back the oil from the oil tank <NUM> to the main bearing <NUM> so that an oil circulation passage is realized. The feedback passage <NUM> preferably comprises a pump <NUM>.

Claim 1:
A wind turbine (<NUM>) comprising a device for determining a lubrication condition of a main bearing (<NUM>) of the wind turbine (<NUM>), the device comprising:
a container (<NUM>) which is configured to collect a leakage lubrication oil from the main bearing (<NUM>);
an outlet (<NUM>) which is configured to discharge the collected oil from the container (<NUM>) with a predetermined flow rate;
an overflow passage (<NUM>) which is configured to discharge on overflow of the collected oil from the container (<NUM>);
a detecting device (<NUM>) which detects an overflow of the collected oil through the overflow passage (<NUM>);
a determining device (<NUM>) which determines that the lubrication condition of a main bearing (<NUM>) is sufficient if the detecting device (<NUM>) detects the overflow of the collected oil through the overflow passage (<NUM>); and
at least one funnel (<NUM>) which is configured to collect the leakage lubrication oil from the main bearing (<NUM>) and to lead the leakage oil to the container (<NUM>).