Abstract:
A method involves directing lubricant to different consumers which are to be monitored via their lubricant. The lubricant is drained through drain lines connected to the consumers and directed to a tank. At least some the lubricant in the drain lines or the consumers is extracted into extraction lines. Flow from the extraction lines is selectively directed to a measurement device, which then measures a characteristic of the lubricant. A system for carrying out such a method is also provided, wherein the system includes a multiplexer for selectively directing flow from the extraction lines.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to lubrication systems and methods where consumers are monitored via their lubricant. The systems and methods are especially relevant to wind turbines. 
       BACKGROUND 
       [0002]    A wind turbine (also referred to as a “wind turbine generator” or WTG) includes many moving parts that facilitate converting the kinetic energy of the wind into electrical energy. This is particularly evident in the power transmission system of a wind turbine, which often includes one or more main bearings, a gearbox, and a generator for processing rotational mechanical energy from a rotor of the wind turbine. The components of the power transmission system typically require some form of lubrication to help reduce friction and wear. Thus, wind turbines typically include one or more lubrication systems for these and other components. 
         [0003]    It is advantageous to monitor the condition of lubricant in a lubrication system for a variety of reasons. For example, the presence of large particles (greater than approximately 70 μm) in lubricant drained from a component often means the component has become worn or damaged beyond acceptable levels. Lubrication systems sometimes include particle counters to detect the presence and quantity of such particles so that appropriate action can be taken to minimize further wear or damage. 
         [0004]    Typically a particle counter or other measurement device is placed in the drain lines of each component whose condition is being monitored via the lubricant. This increases the cost and complexity of the lubrication system. 
       SUMMARY 
       [0005]    The present invention provides a method of lubrication that allows the health or other aspects of multiple consumers to be monitored via their lubricant. The term “consumer” refers to a component having one or more rotating parts to be lubricated. According to the method, lubricant is directed to different consumers whose lubricant is to be analyzed. The lubricant is later drained through drain lines connected to the consumers and directed to a tank. At least some the lubricant in the drain lines or the consumers is extracted into extraction lines. The method further involves selectively directing flow from the extraction lines to a measurement device. As used herein, the term “selectively directing” refers to selecting an output from multiple inputs and changing the selection based on observed activity and/or predetermined time periods; the output may correspond to one of the inputs or a subset of the inputs. 
         [0006]    The measurement device to which lubricant is directed measures a property of the lubricant. The property may be any characteristic of the lubricant, such as pressure, temperature, viscosity, oxidation, water content, flow rate, etc. In one particular embodiment, the measurement device is a particle counter such that measuring a characteristic of the lubricant comprises counting particles in the lubricant. This may be for monitoring oil cleanliness or for detecting wear in one or more of the consumers beyond an acceptable level (health monitoring). Either way, the method may further involve collecting particles greater than a predetermined minimum size in a particle collector downstream from the particle counter. 
         [0007]    A lubrication system for carrying out the above-mentioned method is also provided. The lubrication system includes the tank, the drain lines configured to receive lubricant from the different consumers, the extraction lines connected to the drain lines or the consumers, and the measurement device. A multiplexer connected to the extraction lines selectively directs flow to the output line. Thus, as used herein, the term “multiplexer” refers to the device or arrangement of components that selectively directs flow from the extraction lines to the output line. The measurement device connected to the output line is configured to measure a characteristic of the lubricant, as mentioned above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view of one example of a wind turbine. 
           [0009]      FIG. 2  is a perspective view of a power transmission system for the wind turbine of  FIG. 1 . 
           [0010]      FIG. 3  is a cross-sectional view of the power transmission system of  FIG. 2 . 
           [0011]      FIG. 4  is a schematic view of a lubrication system for the power transmission system of  FIGS. 2 and 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIG. 1  shows one example of a wind turbine  2 . Although an offshore wind turbine is shown, it should be noted that the description below may be applicable to other types of wind turbines. Indeed, the description below relates to a system and method of lubrication that may be applicable to a wide range of industrial products or systems, including those in other industries. A wind turbine is shown and described simply to facilitate discussion. 
         [0013]    With this in mind, the wind turbine  2  includes rotor blades  4  mounted to a hub  6 , which is supported by a nacelle  8  on a tower  12 . Wind causes the rotor blades  4  and hub  6  to rotate about a main axis  14  ( FIG. 2 ). This rotational energy is delivered to a power transmission system (or “power train”)  10  housed within the nacelle  8 . In the representative embodiment shown in  FIGS. 2 and 3 , the power transmission system  10  includes a main shaft  16  coupled to the hub  6  ( FIG. 1 ). The power transmission system  10  also includes first and second main bearings  18 ,  20  supporting the main shaft  16 , a bearing housing  22  surrounding the first and second main bearings  18 ,  20 , and a gearbox  24  having a gearbox input member connected to the main shaft  16  by a coupling  30 . The gearbox  24  increases the rotational speed of the main shaft  16  to drive a generator  28 . 
         [0014]    Other arrangements for the power transmission system  10  are possible. Accordingly, the components of the power transmission system  10  and their operation need not be described in further detail. Only aspects pertaining to their lubrication are described below. Indeed, as schematically shown in  FIG. 3 , the first and second main bearings  18 ,  20 , gearbox  24 , and generator  28  are “consumers” of lubricant in a lubrication system  40 . Each contains moving parts to be lubricated and are supplied with lubricant from a tank (i.e., reservoir) via one or more feed lines  42 . Drain lines  44  allow lubricant to return to the tank after passing through the consumers. There may be a single or multiple drain lines per consumer depending on the design of the lubrication system. The gearbox in the figures is an example of the latter (e.g., the drain lines  44  of the gearbox  24  may be associated with different gear stages). The coupling  30  is not shown as having a feed line or drain line, but could have such lines in alternative embodiments. 
         [0015]      FIG. 4  illustrates one possible embodiment of the lubrication system  40  in further detail. The lubrication system  40  includes a fluid circuit between tank  46  and feed lines  42 . Because the fluid circuit may be arranged in ways other than what is shown, it will not be described in detail. Standard features/components, such as a pump  50  for delivering lubricant from the tank  46 , an inline filtration system  52 , an offline filtration system  54 , and a heat exchanging system  56 , may be provided. 
         [0016]    The drain lines  44  connected to the consumers are eventually combined and run to the tank  46 . Extraction lines  58  (“probe lines”) are connected to the drain lines  44  before they converge. The extraction lines  58  direct at least some lubricant from the drain lines  44  to a multiplexer  60 . Probe points  62  for the extraction lines  58  are located in the drain lines  44  so that extraction lines  58   a  are each associated with a respective consumer (note: an exception in the embodiment shown is a common extraction line  58   a  for the first and second main bearings  18 ,  20 ). A common extraction line  58   b  may also be provided downstream from where the drain lines  44  converge so as to be associated with a combined flow from the consumers. 
         [0017]    The multiplexer  60  in  FIG. 4  is an arrangement of valves  62  that are controlled to selectively direct flow from the extraction lines  58  to an output line  64 . In other words, the multiplexer  60  selects which of the extraction lines  58  communicate with the output line  64 . This selection is alternated between the extraction lines  58 , as will be described below. 
         [0018]    The lubrication system  40  further includes a measurement device  66  connected to the output line  64  downstream of the multiplexer  60 . The measurement device  66  is configured to measure at least one characteristic of the lubricant in the output line  64 . In the embodiment shown, the measurement device  66  is a particle counter configured to detect particles in the lubricant received from the multiplexer  60 . The particle counter normally allows the lubricant to return to the tank  46 , but directs particles greater than a predetermined minimum size to a particle collector  68 . The predetermined minimum size may be 70 μm, for example. Particles of such size in wind turbine lubrication systems are often indicators of wear or damage in the consumer beyond an acceptable level. A pump  70  may be connected to the output line  64  of the multiplexer  60  to ensure lubricant is drawn from the extraction lines  58  to the measurement device  66 . The multiplexer  60  may alternatively or additionally be arranged so that gravity ensures flow from the extraction lines  58 . 
         [0019]    In use, lubricant is directed to the different consumers  18 ,  20 ,  24 ,  28  via the feed lines  42 . After passing through the consumers, the lubricant enters the drain lines  44  so as to be directed toward the tank  46 . At least some the lubricant is extracted into the extraction lines  58 . Under normal operating conditions the multiplexer  60  directs a combined flow from the consumers to the output line  64 . This may be achieved by closing the valves  62  of the extraction lines  58   a  and opening the valve of the common extraction line  58   b . In other embodiments not shown, the combine flow may be the result of all extraction lines  58   a  being open to the output line  64  such that the common extraction line  58   b  is not necessary. If the measurement device  66  detects particles greater than 70 μm, the multiplexer  60  selects one of the extraction lines  58   a  to direct to the output line  64  while blocking the remaining extraction lines  58 . This selection is alternated if particles greater than 70 μm are not detected after a predetermined time interval. Thus, the multiplexer  60  switches between the individual extraction lines  58   a  to identify the source of the large particles so that appropriate action may be taken. The particles registered and counted by the particle counter (i.e., those exceeding 70 μm) are gathered by the particle collector  68 . This may be achieved by physical entrapment, magnetic attraction, or other known methods. 
         [0020]    As can be appreciated, on a broad level the lubrication system  40  provides the following functionalities: 1) measuring a characteristic (e.g., counting particles) of a combined flow of lubricant from all consumers, and 2) measuring a characteristic of the flow of lubricant from individual consumers. The first functionality may be achieved as described above, namely by connecting a common extraction line  58   b  to a point in the lubrication system  40  downstream from where the drain lines  44  converge, or by combining flow from various extraction lines  58   a . The second functionality includes switching between the extraction lines to search for which consumer is the source of an observed characteristic, which is particularly advantageous when the lubrication system  40  is used to monitor health. The additional functionality of particle collection may be provided when the characteristic of the lubricant being measured is particle size. 
         [0021]    It should be noted that the lubrication system  40  also offers advantages in terms of oil sampling capabilities. The ability to switch between the extraction lines  58  means that oil samples can be taken from the different consumers during different stages of the wind turbine&#39;s operation. For example, at a first time period after startup, the multiplexer  60  may switch between the extraction lines  58  so that lubricant from the different consumers can be analyzed by the measuring device  60  or otherwise. The sampling can then be repeated at a different time after startup to observe characteristics during a different stage of operation. 
         [0022]    It should also be kept in mind that the embodiments described above are merely examples of the invention defined by the claims that appear below. Additional advantages, examples, and modifications will be appreciated. For example, the extraction lines  58  may be connected to the consumers themselves rather than to the drain lines  44 . Moreover, the multiplexer  60  may be a different arrangement of valves or other mechanical components (e.g., actuators) capable of switching between different flow lines. Finally, although there are advantages to switching between combined and individual flows, lubrication systems and methods where there is only measurement of individual flows are possible. 
         [0023]    With this in mind, the details of any particular embodiment should not be seen to necessarily limit the scope of the claims below. In addition to appreciating other modifications and variations, skilled persons will understand how features of various embodiments may be combined in different ways.