COMPRISING A MICROFLUIDIC CHIP

FIELD OF THE INVENTION

The present invention relates to a lubricated system provided with an assembly that samples and analyzes a lubricant within the system.

BACKGROUND

A gearbox is one example of a lubricated system where the quality of the lubricant plays a vital role in ensuring proper functioning and a long service life of the components within the system. In gearboxes, special oils are generally used, which contain high-pressure additives and/or anti-wear additives. These additives ensure that under high application loads, an adequate lubrication film is formed that prevents metal-to-metal contact between meshing gear teeth and between rolling contact surfaces of bearings that support the gears. Contaminants in the oil impair its function and thus, for gearboxes, oil analysis has been deemed the best early indicator of problems.

For example, ASTM D6624 "Standard practice for in-service monitoring of lubricating oil for auxiliary power plant equipment" prescribes a number of tests to be performed on a regular basis. These tests include: viscosity, water content, and cleanliness. Generally, an oil sample is taken and each of the prescribed tests/analyses is performed separately. Thus, the owner of the lubricated system must either have access to specialized equipment, or has to send the oil sample to a laboratory for testing. Often, however, there is a need for real-time or almost real-time data.

Oil analysis can also be performed directly online. For example, an apparatus for fluid analysis is disclosed in US 6561010, where the apparatus is connectable to an engine or a machine. A sample line leads from a pressurized machine fluid line and at least one meter is placed in contact with the fluid for measuring a standard laboratory analysis parameter. In one embodiment, the sample line comprises two branches. The first branch leads through a viscometer and the second branch leads through a spectrometer and then through an optical meter. Such an apparatus is dependent on the machine having a pressurized fluid line and requires a modification of the fluid line. In US 7275420, a system is disclosed which comprises a casing that is immersed in a fluid inside a machine, whereby the casing has apertures that are opened to permit the fluid to enter the casing and are closed to confine a sample of the fluid within the casing. The casing also houses a multi-element sensing device (MEMS device) for measuring one or more properties of the fluid. In some embodiments, a flushing mechanism is provided within the casing for forcing a portion of tested fluid out of the casing and for forcing a portion of untested fluid into the casing and into contact with the sensing device. The fluid can be a lubrication oil.

A drawback of this system is that the sensing elements of the sensing device may become contaminated, because it is only after an oil change that the sensing elements can be flushed clean with fresh oil. Otherwise, the flushing mechanism replaces tested oil with untested oil that becomes increasingly contaminated over time. This can lead to a build up of residue on the sensing elements, thereby affecting the accuracy of the measurements. In some embodiments of the system disclosed in US 7275420, a screen is provided to prevent particulate contaminants coming into contact with the sensing elements.

Consequently, there is room for improvement. DISCLOSURE OF THE INVENTION

The present invention resides in a lubricated system comprising a lubricant and at least one lubricated component, the system being provided with an analysis device for analyzing at least one property of the lubricant and further provided with a micropump for extracting a sample of the lubricant and for supplying the sample to the analysis device. According to the invention, the analysis device is a microfluidic chip which is arranged in connection with the micropump, externally to the lubricated system. The microfluidic chip comprises a substrate in which one or more micro-channels are provided, and further comprises means for measuring a property of the lubricant. For example, electrodes may be provided at either side of a micro- channel in order to measure the conductivity of the lubricant flowing therethrough. The one or more micro-channels have a cross-section or diameter of less than 1 mm and typically have a length of less than 2 cm. When the lubricant in the system is a grease, the one or more micro-channels suitably have a diameter greater than 0.3 mm. When the lubricant is oil, the micro-channels may have a diameter of between 0.01 and 0.1 mm.

Consequently only a small volume of lubricant needs to be extracted for analysis purposes. The removal of a small volume of lubricant from the system has no effect on the lubrication performance of the system. A further benefit of the invention is that because the microfluidic chip is arranged outside of the lubricated system, it does not interfere with the flow or migration of lubricant within the system. In addition, the chip can easily be detached from the micropump. This is advantageous because if contaminants in the lubricant sample get deposited in the one or more micro-channels, the chip can simply be flushed out with a suitable cleaning fluid. Thereafter, the chip is quickly ready for re-use with unimpaired measurement accuracy.

In a particularly preferred embodiment, the micropump is an electro-osmotic pump comprising a suction chamber and a discharge chamber separated by an electro- osmotic member. A first connection line extends from a first opening in the suction chamber into a lubricant reservoir within the lubricated system. A second connection line extends from a second opening in the suction chamber to the microfluidic chip. Suitably, the first and second connection lines have a diameter of between 0.3 and 1 mm when the lubricant in the system is grease, and have a diameter of between 0.01 and 0.1 mm when the lubricant is an oil.

The micropump further comprises a drive fluid that exhibits electro-osmosis, e.g. water, whereby at least some of the drive fluid is contained within the suction chamber, at a level above the second opening. Further, the micropump is configured such that when a voltage of predetermined polarity is placed across the electro-osmotic member, the drive fluid is transported from the suction chamber, through the electro-osmotic member, to the discharge chamber. This creates an underpressure in the suction chamber, meaning that lubricant is drawn into the suction chamber, via the first connection line. To prevent contact with the drive fluid and contamination of the lubricant sample, the drive fluid in the suction chamber is preferably separated from the entering lubricant by a deformable membrane. As the transport of drive fluid continues, the suction chamber fills with lubricant, and the lubricant is caused to flow through the second connection line to the microfluidic chip, and then through the one or more micro-channels in the chip.

An advantage of using an electro-osmotic micropump is that simply by reversing the polarity of the voltage across the electro-osmotic member, the pumping direction is reversed, since the drive fluid is made to flow in the opposite direction. The drive fluid presses on the deformable membrane, and the lubricant is pumped out via the first and second openings in the suction chamber. Thus, after analysis of a lubricant sample is complete, any lubricant that remains in the suction chamber and in the first connection line can be pumped back into the lubricant reservoir. Alternatively, the second connection line may comprise e.g. a T-junction, whereby a first branch of the line is connected to the microfluidic chip and a second branch is a discharge outlet. Suitably, the second branch comprises means that enable this branch to be closed off when analysis is being performed and to be opened when remaining lubricant is to be discharged. Preferably, the second branch has a larger diameter than the first branch, which will speed up the emptying process. The advantage of discharging the remaining lubricant is that, when the next sample is extracted for analysis, it is not "contaminated" with lubricant from the previous sample.

A further advantage of an electro-osmotic pump is that only low voltages are needed to operate the pump, e.g. 2 - 5 Volts, and the flow rate of the drive liquid displays an excellent linear response to the applied voltage, even at very small flow rates. Consequently, the flow of the drive fluid can be controlled with great precision, meaning that the flow of the lubricant can be controlled with equal precision. A still further advantage of an electro-osmotic micropump is that such a pump can generate the relatively higher suction pressures that are necessary to cause grease to flow. Thus, in one embodiment, the lubricated system comprises a grease lubricated bearing having an inner ring and outer ring with rolling elements disposed in between. The bearing may be mounted on a shaft within a housing that is partially filled with grease, or the grease may be sealed within a cavity of the bearing by means of radial seals at each axial side of the bearing. In the former case, the first connection line from the suction chamber may extend through the housing, to extract a grease sample from a grease reservoir within the housing. In the latter case, the first connection line may extend through one of the radial seals, into the bearing cavity, to extract a grease same from e.g. a reservoir of grease adhering to a radially inner surface of the bearing outer ring.

The at least one lubricated component of a system according to the invention may also comprise a plain bearing.

In a further embodiment, the lubricated system comprises a gearbox lubricated with oil, whereby the oil sample is extracted from an oil sump. In a still further example, the lubricated system comprises a spindle and a bearing arrangement for high speed operation. Lubrication quality is also essential in such applications. The system may be provided with active oil lubrication, whereby a minimal quantity of oil is supplied directly to a zone of rolling contact in the bearing arrangement. During operation, the high centrifugal forces associated with the high speed operation cause much of the oil to be flung out of the bearing cavity. This oil collects in a reservoir, from where a sample can be extracted and analyzed using the micropump and the microfluidic chip of the invention. The microfluidic chip used in the present invention can be adapted to measure a variety of parameters. As mentioned, conductivity is measurable by providing electrodes at either side of a micro-channel, such that contact is made with the lubricant sample. This measurement provides an indication of water content in the lubricant. Water can exist in three phases in a lubricant: dissolved, emulsified and free. For lubrication purposes, free water causes the most problems, and this may readily be detected on a micro-fluidic chip. When water is dissolved or emulsified in a lubricant, the resulting mixture has a constant conductivity. When, however, a globule of water suspended in the lubricant passes by the electrodes, a distinct change in conductivity is measurable. Suitably, the microfluidic chip is connected to processing means which receives the measurement signal and may be configured to detect and record changes in conductivity. The processing means may also be configured to determine an overall water content percentage from the measured conductivity. In addition, or alternatively, the processing means may be configured to determine an acidity level from the measured conductivity.

In a further embodiment, the microfluidic chip comprises an array of nanoholes for optical detection of e.g. particles. Suitably, the one or more micro-channels are provided in a layer of the substrate that is made of a transparent material. The array of nanoholes may be provided on an opaque metallic layer that is patterned onto the floor of the micro-channel. Further, a photodiode array is arranged below the nanohole array, whereby changes in an amount of detected light are caused by e.g. particles in the fluid flowing through the micro-channel. The optical detection may be based on enhancement, in which case a fluorescent substance is added to the fluid sample. Particles in the fluid become fluorescent, meaning that an increase in light intensity is detected when a particle passes over a nanohole. The optical detection may also be based on absorption. In this case, a decrease in light intensity is detected when a particle obturates a nanohole.

Consequently, a microfluidic chip comprising an array of nanoholes and a corresponding array of photodiodes can be used to determine a degree of particulate contamination in the lubricant sample. In a further development, the microfluidic chip comprises filtering means for separating different particles into different micro-channels or branches of a micro-channel. This technique can be used to determine the degradation of lubricant additives such as zinc and sulphur. It may also be used to detect the presence of long-chain hydrocarbons in the lubricant, which is a symptom of aging. Furthermore, when the lubricant is an oil, its viscosity can be determined by adding a fluorescent droplet into the oil and calculating how long the droplet takes to travel between two detection points. The same principle may be applied when the lubricant is a grease, in order to measure grease consistency.

As will be understood, the microchip used in the invention may comprise a photo- detection array, as described above, in addition to electrodes for measuring e.g. lubricant conductivity. Furthermore, the photo-detection array may be configured for measuring several lubricant parameters of interest. The microfluidic chip may thus be adapted to perform all the lubricant tests as prescribed by ASTM D6624, and more.

Other advantages of the present invention will become apparent from the detailed description and accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1a is a cross-sectional view of an example lubricated system according to the invention;

Figure 1 b is a top sectional view of a microfluidic chip for use in the invention; Figure 1c is a cross-sectional view of a micropump for use in the invention.

DETAILED DESCRIPTION

An example of lubricated system according to the invention is depicted in Figure 1a. The system 100 comprises a rolling element bearing 105 which supports a shaft 110 relatively to a housing 115. Further, the system comprises an oil for lubricating the bearing 105 during use. This oil gathers in a lower part of the housing 115, which is hereafter referred to as an oil reservoir 120. Typically, the oil reservoir is filled to a level that covers a radially lower half of the rolling elements of the bearing. In addition, the system 100 comprises a first seal 125 and second seal 27 at first and second axial ends of the housing, for sealing an annular gap between the shaft 110 and a bore of the housing. The seals 125, 127 retain the oil within the housing 115, and prevent the ingress of contaminants. In extremely moist or humid environments, however, the entry of moisture cannot be entirely excluded. Initially, the moisture dissolves in the oil; then it becomes emulsified. It has been found that when oil contains water in a dissolved and emulsified phase, there is little damaging affect on lubrication performance. However, if moisture continues to contaminate the oil, a saturation point is reached at which the moisture exists in the oil as free water. Especially in high load applications, the presence of free water in the oil can seriously affect the formation of an adequate lubrication film to separate rolling contact surfaces in the bearing. It may therefore be advisable to test the oil for the presence of water on a regular basis.

According to the invention, the system 100 is provided with a micropump 130 for extracting an oil sample from the oil reservoir 120, and is further provided with a microfluidic chip 180, which in this example is configured to measure conductivity. For extracting the oil sample, a first connection line 155 is provided between a suction chamber 135 of the pump 130 and the oil reservoir 120. The first connection line 155 may have a diameter of between 0.01 and 0.1 mm. A greater diameter is also possible, depending on the viscosity of the oil. In this example, the first connection line 155 extends through an outer casing of the second seal 127 and then into the lower part of the housing 115, such that an orifice of the first connection line 155 opens in the oil reservoir 120. A second connection line 157, which may have the same diameter as the first connection line 155, is provided between the suction chamber 35 of the pump 130 and the microfluidic chip 180. Suitably the suction chamber is provided with first and second outlets for receiving the first and second connection lines 155, 157. During sampling, the pump 130 is configured such that oil is sucked into the suction chamber 135 via the fist connection line. Suitably, the first connection line 155 is then closed off and the action of the pump 130 is reversed, such that an amount of oil is pumped to the microfluidic chip 180 via the second connection line 157. A particularly preferred pump for use in the invention is an electro-osmotic pump. An example of such a pump is shown in more detail in Figure 1b.

Figure 1 b illustrates a pump 130 comprising a pump housing 132 containing a pump drive mechanism 140 that partitions the housing into a suction chamber 135 and a discharge chamber 137. The suction chamber comprises the first outlet 150 to which the first connection line 155 is connected and comprises the second outlet 152 to which the second connection line 157 is connected. Suitably, the first and second outlets are arranged in the suction chamber 135 towards an end opposite from the drive mechanism 145. The drive mechanism 140 comprises an electro-osmotic member 142 and first and second electrodes 145, 147 for generating an electric field across the electro- osmotic member 142. Further, at least part of the suction chamber 135 is filled with a drive fluid 160 that exhibits electro-osmosis, such as de-ionized water or methanol. When a DC voltage is placed on the electrodes 145, 147, the drive fluid is transported through the electro-osmotic member 142, from the suction chamber 135 to the discharge chamber 137. This creates an underpressure in the suction chamber 135, causing oil to be sucked from the oil reservoir 120, through the first connection line 155, and into the suction chamber 135.

The drive fluid 160 is contained in the suction chamber 135 within a deformable membrane 162, in order to separate the drive fluid from the oil that is sucked in. As drive fluid is transported from a suction chamber side of the electro-osmotic member to a discharge chamber side, the deformable membrane 162 contracts until all of the drive fluid 160 which was present in the suction chamber 135 has been transported to the discharge chamber 137. A corresponding amount of oil is sucked into the suction chamber via the first outlet 152. By closing off the first outlet 152 or the first connection line 155, a sample of oil can be pumped to the microfluidic chip 180, via the second outlet 155. Pumping is achieved by reversing the polarity of the voltage across the electro-osmotic member 142. This causes the drive fluid 160 to be transported from the discharge chamber 137 to the suction chamber 135. As a result, the drive fluid 160 expands the deformable membrane 162, causing oil to be pressed out of the suction chamber 135 via the second outlet 152, to the microfluidic chip 180.

An example of a chip suitable for use in the invention is show in a top sectional view in Figure 1c. The chip 180 comprises a substrate 182 in which a micro- channel 185 is provided. The micro-channel 185 may have a diameter of approximately 0.01 mm. In this example, a single micro-channel is shown, but the chip 180 may of course comprise more than one micro-channel 185. The substrate further comprises first and second mounting holes 187, 190 that enable the chip 180 to be mounted in a holding device (not shown), whereby the micro-channel 185 is provided between an inlet 192 in the first mounting hole 187 and an outlet 195 in the second mounting hole 190. Typically, the second connection line from the micropump is connected to the holding device, which device is also provided with a channel that leads to the aforementioned inlet 192. The outlet 195 in the second mounting hole 190 may simply be a discharge outlet or may, for example, be connected via a further connection line that extends back into the bearing housing.

During operation of the electro-osmotic pump 130, an oil sample is supplied to the microchip 180 and flows through the micro-channel 185. In order to measure conductivity of the sample, the chip 180 is provided with first and second electrodes 197, 199. The electrodes are arranged at opposite diametrical sides of the micro-channel 185 such that each electrode 197, 199 makes contact with the sample as it flows through the micro-channel. Suitably, the electrodes are connected to a voltage source, so that an electrical circuit is created when a conductive medium flows through the micro-channel. Conductivity of the sample is therefore measurable, and the chip 180 may be connected to e.g. a current meter and processing means for performing the measurement and analyzing the results.

Oil is a poor conductor, but its conductivity increases as water content increases. As mentioned previously, water can exist in oil in three phases: dissolved, emulsified and free. With regard to dissolved and emulsified water, an essentially stable conductivity reading is likely to be obtained as the oil sample flows past the electrodes. Thus, it is possible to correlate an average value of the conductivity measurements to a percentage content of water. Now let assume that the oil sample contains free water. Water is an excellent conductor, and when a droplet of water passes the first and second electrodes, 197, 199, a substantial increase in the conductivity reading will occur, followed by a significant drop as the water droplet is replaced by poorly conductive oil. Consequently, the presence of free water in a lubricant is quickly and easily detectible in a system according to the invention.

As will be understood, the presence of conductive particles in a lubricant sample may be detected in a similar fashion. Furthermore, oil conductivity increases as the oil ages, due to the presence of long-chain hydrocarbons. The chip may additionally be provided with means for particle filtering in order to detect e.g. the degradation of additives in the lubricant sample. Thus, a microfluidic chip for measuring the conductivity of an extracted lubricant sample can be configured for a variety of purposes. A further advantage of a lubricated system according to the invention is that due to the fast, straightforward extraction and measurement process, analysis of the lubricant in the system can be performed as regularly as needed. For example, once every day.

In other embodiments, the microfluidic chip 180 is additionally or alternatively provided with an array of nanoholes and means for optical detection. Suitably, the substrate 182 is made of a transparent material and the array of nanoholes may be provided on an opaque metallic layer that is patterned onto the floor of the micro-channel 185. Further, a photodiode array is arranged below the nanohole array, whereby changes in an amount of detected light are caused by e.g. particles in the lubricant flowing through the micro-channel. The optical detection may be based on enhancement, in which case a fluorescent substance is added to the fluid sample. Particles in the fluid become fluorescent, meaning that an increase in light intensity is detected when a particle passes over a nanohole. The optical detection may also be based on absorption. In this case, a decrease in light intensity is detected when a particle obturates a nanohole. Detecting the presence of free water is also possible, since a water droplet will allow more light to reach the photodiodes than an oil sample.

A chip provided with an array of nanoholes and photodiodes as described above may also be configured to perform a variety of measurements, including viscosity measurement and the quantification of particulate contamination and additive degradation.

After a sample has been analyzed, the chip 180 may simply be detached from its holding device and the micro-channel can be flushed through with a suitable cleaning fluid. The channel in the holding device can also be flushed through. This removes any particles which would otherwise pollute the next lubricant sample that is extracted using the electro-osmotic pump. With reference again to Figure 1a and 1 b, oil that remains in the suction chamber 135 of the pump 130, after analysis of the sample is complete, can be pumped back into the oil reservoir 120 in the bearing housing 115. As mentioned, this is achieved simply be reversing the polarity of the voltage across the electro-osmotic member 142. The drive fluid 160 is then transported from the discharge chamber 137 back into the suction chamber 135. This in turn causes the deformable membrane 162 to expand and press out remaining oil via the outlets 150, 152 in the suction chamber 135. Consequently, the system can be quickly and easily made ready for extracting the next oil sample, whereby the measurement accuracy of the next analysis is ensured.

In an alternative embodiment, the microfluidic chip 180 is arranged in series between the bearing housing 115 and the micropump 130. Suitably, the suction chamber 135 of the pump comprises only a first outlet 150, which is connected to the lubricant reservoir 120 by the first connection line 155 such that the at least one micro-channel 185 of the microfluidic chip 180 forms part of the first connection line. The suction chamber 135 suitably contains an amount of clean lubricant, such as oil. Initially, the suction chamber is only partly filled with clean lubricant, which enables a contaminated sample of lubricant to be sucked up from the lubricant reservoir 120 and through the microfluidic chip 180. When an analysis is finished, the contaminated lubricant is then pumped back to the reservoir 120, by reversing the action of the pump 130. Thus, the contaminated lubricant is pushed back into the reservoir 120 by the clean lubricant. Preferably, an amount of clean lubricant is pushed back that is at least sufficient to fill the microfluidic chip 180, thereby flushing the micro-channel 185 clean of contaminated lubricant. More preferably, all of the contaminated lubricant is pumped back to the reservoir 120. As will be understood, the chip and pump assembly may be provided with one or more flow sensors to ensure that when a next analysis is performed, it begins only when all of the clean lubricant has passed back through the microfluidic chip towards the suction chamber of the pump. The advantage of this embodiment is that the microfluidic chip can be prepared for re-use without disconnecting it from the micropump.

A number of aspects/embodiments of the invention have been described. It is to be understood that each aspect/embodiment may be combined with any other aspect/embodiment. The invention may thus be varied within the scope of the accompanying patent claims.

Reference numerals

100 Lubricated system (bearing in housing)

105 Rolling element bearing

110 Shaft

115 Housing

120 Lubricant reservoir in housing

125, 127 Radial seal

130 Electro-osmotic pump

132 Pump housing

135 Suction chamber of pump

137 Discharge chamber of pump

140 Pump drive mechanism

142 Electro-osmotic member

145, 147 Electrodes of pump drive

150 First outlet in suction chamber

152 Second outlet in suction chamber

155 First connection line to lubricant reservoir

157 Second connection line to microfluidic chip 160 Drive fluid

162 Deformable membrane

180 Microfluidic chip

182 Chip substrate

185 Micro-channel

187, 190 First and second mounting holes

192 Inlet in first mounting hole

195 Outlet in second mounting hole

197, 199 Electrodes of microfluidic chip