BE1025611B1 - Oil circuit, oil-free compressor provided with such oil circuit and method for controlling lubrication and / or cooling of such oil-free compressor via such oil circuit - Google Patents

Abstract

Oil circuit for an oil-free compressor (1) comprising an engine (4) and a compressor element (2), - wherein this oil circuit (5) comprises an oil reservoir (10) with oil (11) and an oil rotor pump (13) around oil ( 11) to be sent to the compressor element (2) and / or the motor (4) via an oil line (12); - wherein this oil rotor pump (13) is driven by the aforementioned engine (4); - wherein the oil circuit (5) comprises a return line (19) for passing oil (11) from the compressor element (2) and / or the motor (4) back to the oil reservoir (10); - wherein the oil circuit (5) comprises a bypass line (15) and a bypass valve (14) around a part of the oil (11) between the oil rotor pump (13) on the one hand and the compressor element (2) and / or the motor (4) on the other hand returning it to the oil reservoir (10) without it passing oil (11) along or through the compressor element (2) and / or the engine (4); and - wherein the oil circuit (5) is provided with an oil cooler (16), the oil cooler (16) being placed in the bypass line (15) and the bypass valve (14) being placed in the oil line (12).

Description

Oil circuit, oil-free compressor provided with such oil circuit and method for controlling lubrication and / or cooling of such oil-free compressor via such oil circuit.

The present invention relates to an oil circuit, an oil-free compressor provided with such an oil circuit and a method for controlling lubrication and / or cooling of such an oil-free compressor via such an oil circuit.

More specifically, the invention is intended to provide an improved oil circuit and an improved method for controlling lubrication and / or cooling via this improved oil circuit of an oil-free compressor comprising a variable speed or speed motor, i.e. with a VSD scheme.

It is known that an oil circuit is used to lubricate and cool components in such an engine.

These components are, for example, but not limited to, bearings and gears of the engine.

At high speeds, these bearings and gears require precisely dosed oil lubrication: not too much oil, which leads to hydraulic losses and even overheating, but also not too little oil, which causes poor lubrication and overheating.

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That is why oil jet lubrication is used, whereby nozzles with a very accurate opening are used which are directed to the exact location where lubrication is needed.

This location is the bearing surface of the bearings and where the teeth of the gears turn together.

The oil in the oil circuit must be cooled to prevent overheating of the oil in the oil circuit and related changes in oil lubrication properties.

The oil circuit that supplies the nozzles with filtered and cooled oil at a predetermined pressure level typically comprises an oil reservoir, an oil rotor pump, an oil cooler, an oil filter, and connection lines which may or may not be integrated into other parts of the oil-free compressor. Furthermore, minimum pressure valves, bridging lines, oil pressure sensors and temperature sensors are often also provided.

Traditionally, an oil circuit for such an oil-free compressor is arranged as follows.

Oil is pumped from an oil reservoir using an oil rotor pump, after which the oil is led to an oil cooler. The cooler will cool the oil before it is brought to the parts of the oil-free compressor to be lubricated and possibly cooled.

The temperature of the oil will rise during lubrication and cooling.

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After the oil has passed through the components to be lubricated and / or cooled, the oil-free compressor will be led back to the oil reservoir via a return line. The hot oil will be led through the oil rotor pump from the oil reservoir to the oil cooler, where the oil will be cooled before it is returned to the components of the oil-free compressor.

The aforementioned oil rotor pump plays an important role: if insufficient oil is delivered to the nozzles in time, poor lubrication can result in damage or failure of the bearings and / or gears.

It is possible to use an oil rotor pump that is driven by a separate motor.

This has the advantage that the oil rotor pump can be checked, but has the disadvantage that a separate engine and control or control unit are required. As a result, the oil-free compressor will not only be more expensive, but also more bulky, and will additionally include additional components that must be maintained and may fail.

It is therefore interesting to drive the oil rotor pump with the same motor as a compressor element of the oil-free compressor. This ensures that the oil rotor pump will always run when the compressor element is running. This also means that at a higher speed or speed of the engine and the compressor element of the oil-free compressor, when more oil is required for the lubrication and cooling of the oil-free compressor, more oil is pumped up and sent to the

B E2018 / 5237 oil cooler and then the engine and / or the compressor element.

However, the oil pressure must not increase too much and at higher speeds or speeds of the engine and the compressor element, the oil rotor pump will pump up so much oil that the pressure becomes too high. Too high an oil pressure is not allowed, among other things, because too much oil is used for the bearing lubrication, causing the losses in the bearings to increase.

Therefore, a bypass line with a valve is fitted in the oil circuit downstream of the oil cooler, which will pump a part of the pumped oil back to the oil reservoir from a certain speed.

The higher the speed of the engine and therefore the oil rotor pump, the more oil the valve will send back to the oil reservoir via the bypass line.

In this way the oil pressure in the oil circuit will not rise too high.

According to a traditional oil circuit, all oil sent to the engine and / or the compressor element will pass through the oil cooler.

Such known oil circuits therefore have the disadvantage that at low engine speeds the oil is cooled too much, since the oil cooler is designed to cool the oil at the maximum engine speed when

B E2018 / 5237 the oil warms up the most due to losses in the rotating parts.

As a result, the oil will have a high viscosity at these low speeds, which will lead to oil losses in the bearings.

Moreover, there will be a large temperature difference in the oil at low and high speeds.

These large temperature differences are detrimental to the engine of the oil-free compressor.

As a result, an oil cooler will often be chosen for which the cooling capacity is adjustable, which is of course more expensive and more complex.

In addition, it will be necessary to use a large cooler designed for the full oil flow rate at maximum speed.

Suitable oil rotor pumps for the oil circuit are centrifugal pumps with impeller, gear pumps, internal gear pumps, such as rotor pumps and vane pumps.

A gerotor pump is described in US 3,995,978.

Such pumps can be designed to pump up the correct amount of oil when they are driven at the same speed as the compressor element motor, through an appropriate choice of pump width and / or the number of teeth or baffles, which will allow the

B E2018 / 5237 oil rotor pump to be mounted directly on the shaft of the engine, resulting in a very compact, robust, efficient and inexpensive machine.

However, a disadvantage of such an arrangement in which the oil rotor pump is mounted directly on the axis of the compressor element motor is the fact that the oil rotor pump then has to be mounted reasonably high in the oil-free compressor, and is therefore relatively high relative to the oil reservoir.

This means that when the oil-free compressor is started up, the oil rotor pump must first suck in the air from the suction pipe, which is connected to the oil reservoir through liquid, and then suck in and pump up oil from the oil reservoir.

This start-up will be easier if some oil is already present in the oil rotor pump, so that when the oil rotor pump starts, this oil is circulated and can provide a seal in the oil rotor pump, so that the suction power of the oil rotor pump is immediately optimal.

Therefore, during mounting of the oil rotor pump, a small amount of oil is often applied to the oil rotor pump, i.e., an amount that is small in relation to the total volume of oil in the oil circuit.

However, when the pump is started up for a long time after assembly, this initial amount of oil has already partially or completely evaporated and is therefore no longer sufficient to properly start the oil rotor pump.

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US 3,859,013 describes an oil rotor pump, wherein a kind of siphon-like structure is provided in the inlet line between the oil pump and the oil reservoir, which ensures that a small amount of oil is retained in the inlet line near the oil reservoir. However, when the oil-free compressor is started up, the oil rotor pump must still draw in a large amount of air before the oil can be sucked up from the siphon-like structure.

The present invention has for its object to provide a solution to at least one of the aforementioned and / or other disadvantages.

The present invention has an oil circuit as the object for lubrication and cooling of an oil-free compressor that comprises a motor and a compressor element driven by this motor,

- wherein this oil circuit is provided with an oil reservoir with oil and with an oil rotor pump configured to send oil from the oil reservoir through an inlet channel upstream of the oil rotor pump to the compressor element and / or the engine via an oil line;

- wherein this oil rotor pump is provided with a rotor mounted on a rotation axis, said oil rotor pump having a stroke volume, and wherein this oil rotor pump is driven by the motor of the compressor element;

wherein the oil circuit is further provided with a return line configured to direct oil from the compressor element and / or the engine back to the oil reservoir;

wherein the oil circuit is further provided with a bypass line and a pressure-controlled bypass valve which

BE2018 / 5237 are configured to direct part of the oil between the oil rotor pump on the one hand and the compressor element and / or the motor directly back to the oil reservoir on the other hand without this part of the oil on its way to the oil reservoir along or through the compressor element and / or the motor passes; and wherein the oil circuit is further provided with an oil cooler, characterized in that the oil cooler is placed in the bypass line 10 and that the bypass valve is placed in the oil line.

An advantage is that at low speeds of the compressor element, when little cooling is required, a small part of the oil in the oil circuit will be controlled via the bypass line and thus be cooled;

while at high speeds, when more cooling is required, a relatively larger part of the oil in the oil circuit will be sent via the bypass line and therefore more will be cooled.

By cooling less at low speeds and cooling more at high speeds, the temperature of the oil will be more constant and therefore the temperature differences smaller, compared to the known oil circuits.

Moreover, the average oil temperature will also be higher, so that the oil will have a lower viscosity, which will lead to fewer oil losses in the bearings and other locations in the oil-free compressor where the oil is used for lubrication.

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Another advantage is that at low speeds the oil will not be cooled as no oil will be sent via the bypass line and the oil cooler. In this way the oil will not have too high a viscosity at low speeds.

Moreover, the oil will not get too hot at higher engine speeds, because more oil will be sent through the cooler.

Yet another advantage is that the oil cooler can be sized smaller, i.e. a smaller oil cooler can be chosen for a smaller oil flow in the bypass line compared to the known oil circuits where the oil cooler is located in the oil line upstream of the bypass valve.

In a preferred embodiment of the invention, the inlet channel is provided with a dam with a height that is higher than the height of the center line of the rotation axis of the oil rotor pump minus the smallest diameter of the rotor of the oil rotor pump divided by two.

An advantage of this preferred embodiment is that after stopping the oil-free compressor, it is guaranteed that a large amount of oil remains in the oil rotor pump and in the inlet channel between the oil rotor pump and the dam so that the oil rotor pump is completely moistened internally with oil at the (re) start-up of the oil-free compressor and so that suction power of the oil rotor pump will immediately be very high.

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In this way, oil flow into the oil circuit will be quick and smooth

be started up Bee ( re) boot up from the oil-free compressor. Preferably the height from the dam smaller then the height from the center line of the axis of rotation of the oil rotor pump

reduced by the diameter of the oil rotor pump divided by two. the axis of rotation from the This will prevent oil through the axis of rotation from the

oil rotor pump can leak and / or will avoid the need for additional seals for the aforementioned

The invention also relates to an oil-free compressor provided with an oil circuit for its lubrication and cooling, wherein this oil-free compressor comprises a motor and a compressor element driven by this motor;

- wherein this oil circuit is provided with an oil reservoir with oil and with an oil rotor pump configured to send oil from the oil reservoir through an inlet channel upstream of the oil rotor pump to the compressor element and / or the engine via an oil line;

- wherein this oil rotor pump is provided with a rotor mounted on a rotation axis, said oil rotor pump having a stroke volume, and wherein this oil rotor pump is driven by the motor of the compressor element;

wherein the oil circuit is further provided with a return conduit configured to direct oil from the compressor element and / or the engine back to the oil reservoir;

BE2018 / 5237 wherein the oil circuit is further provided with a bypass line and a pressure-controlled bypass valve which are configured to direct part of the oil between the oil rotor pump on the one hand and the compressor element and / or the engine directly back to the oil reservoir on the other without this part of the oil passes through or through the compressor element and / or the engine on its way to the oil reservoir; and wherein the oil circuit is further provided with an oil cooler, characterized in that the oil-free compressor is configured such that the oil cooler is placed in the bypass line and that the bypass valve is placed in the oil line.

Finally, the invention relates to a method for controlling lubrication and / or cooling of an oil-free compressor via an oil circuit, wherein this oil-free compressor comprises a motor and a compressor element driven by this motor;

- wherein this oil circuit is provided with an oil reservoir and wherein oil is sent from the oil reservoir of the oil rotor pump to the compressor element and / or the engine via an oil pipe by means of an oil rotor pump;

- wherein this oil rotor pump is driven by the motor of the compressor element; and

- wherein part of the oil between, on the one hand, the oil rotor pump and, on the other hand, the compressor element and / or the engine is led directly back to the oil reservoir by means of a bypass line and a pressure-controlled bypass valve which are included in the oil circuit,

BE2018 / 5237 passes this part of the oil on its way to the oil reservoir along or through the compressor element and / or the engine;

characterized in that the method further comprises the steps of:

- the part of the oil that is led back through the bypass line and the bypass valve to the oil reservoir, by passing the oil cooler that is placed in the bypass line; and

- regulating the bypass valve such that a predetermined pressure is achieved in the oil line between the bypass valve on the one hand and the compressor element and / or the motor on the other.

The engine of the compressor element is preferably started only after oil or a lubricant with a higher volatility than the oil has been introduced into the oil circuit at a position downstream and higher than the oil rotor pump.

With the insight to better demonstrate the characteristics of the invention, a few preferred variants of an oil circuit according to the invention and an oil-free compressor provided with such an oil circuit are described below, with reference to the accompanying drawings, as an example without any limiting character. in which:

figure 1 schematically represents an oil-free compressor provided with an oil circuit according to the invention;

figure 2 schematically shows the course of the oil rotor pump flow rate as a function of the engine speed;

Figure 3 schematically shows the variation of the pressure in the oil line downstream of the bypass valve as a function of the speed of the engine;

figure 4 schematically shows the engine and the oil rotor pump of figure 1 in more detail;

figure 5 shows a view according to the arrow F3 in figure 4, with partial cut-away of the oil rotor pump housing;

Figure 6 shows in more detail the part which is indicated by F4 in Figure 5;

Figure 7 represents an alternative embodiment of Figure 6.

The oil-free compressor 1 shown in Figure 1 is in this case a screw compressor device with a screw compressor element 2, a transmission 3 (or "gearbox") and a variable speed motor 4, the oil-free compressor 1 being provided with an oil circuit according to the invention.

According to the invention, it is not necessary for the oil-free compressor 1 to be a screw compressor 1, since the compressor element 2 could equally well be of a different type, for example a tooth compressor element, a scroll compressor element, a vane compressor element, etc.

The compressor element 2 is provided with a housing 6 with an inlet 7 for sucking in a gas and an outlet 8 for compressed gas. Two cooperating screw rotors 9 are mounted in the housing 6.

BE2018 / 5237

The oil circuit 5 will provide the oil-free compressor 1 with oil 11 to lubricate and optionally cool the parts of the oil-free compressor 1.

These components are, for example, the gears in the transmission 3, the bearings with which the screw rotors 9 are mounted in the compressor element 2, etc.

The oil circuit 5 comprises an oil reservoir 10 with oil 11 and an oil line 12 for bringing the oil 11 to the parts to be lubricated and / or cooled of the oil-free compressor 1.

An oil rotor pump 13 is provided in the oil line 12 for pumping oil 11 out of the oil reservoir 10.

The oil rotor pump 13 is driven by the motor 4 of the compressor element 2.

The oil rotor pump 13 can be directly connected to the shaft of the engine 4 or connected to a drive shaft. This drive shaft is then connected to the motor 4 via a coupling. The gear is then mounted on the drive shaft and is driven by the gearbox. One or more compressor elements 2 can be driven via the gearbox.

Downstream of the oil rotor pump 13, a bypass valve 14 and a bypass line 15 are provided in the oil line 12 which leads from the oil line 12 back to the oil reservoir 10.

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Although in the example shown the bypass valve 14 is arranged in the oil line 12, it is not excluded that the bypass valve 14 is arranged in the bypass line 15. It is also not excluded that a three-way valve is used which is arranged at the location of the connection of the oil line 12 to the bypass line 15.

The bypass valve 14 will distribute the oil 11 that is being pumped up by the oil rotor pump 13: one part will be sent via the oil line 12 to the parts to be lubricated and / or cooled of the oil-free compressor 1, the remaining part will be returned via the bypass line 15 the oil reservoir 10 can be controlled.

The bypass valve 14 is, but not necessarily, a mechanical valve 14 in this case.

In a preferred embodiment, the valve 14 is a spring-controlled valve, that is, the valve 14 comprises a spring or spring element wherein the spring will open the valve 14 more or less depending on the pressure p upstream or downstream of the valve 14.

In this case, the valve will be a spring-controlled valve 14 that will close and open the bypass line 15 depending on the pressure p downstream of the valve 14. When a certain threshold value of the pressure p is exceeded, the valve 14 will open the bypass line 15 so that a portion of the pumped-up oil 11 will flow via the bypass line 15 to the oil reservoir 10.

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According to the invention, an oil cooler 16 is placed in the bypass line 15. This means that the oil 11 that flows via the bypass line 15 can be cooled, but that the oil 11 that flows via the oil line 12 to the parts to be lubricated and / or cooled will not be cooled.

In other words: cooled, cold oil 11 will be led to the oil reservoir 10 via the bypass line 15.

In this case, the aforementioned oil cooler 16 forms part of a heat exchanger 17. The oil cooler 16 could, for example, be a plate cooler, but any type of cooler suitable for cooling the oil 11 can be used in this invention.

In this case, the oil cooler 16 has a fixed or constant cooling capacity for a given oil flow rate and flow rate of a coolant. This means that the cooling capacity cannot be adjusted. By adjusting the flow rate of the coolant it would indeed be possible to adjust the cooling capacity. However, this is not necessary.

The oil line 12 runs from the bypass valve 14 to the parts of the oil-free compressor 1 to be lubricated and possibly cooled. The oil line 12 will then be split into sub-lines 18, which may optionally be partially integrated into the compressor element 2.

Furthermore, the oil circuit 5 is provided with a return line 19 for returning the oil 11, after it has lubricated and optionally cooled, from the compressor element 2 to the oil reservoir 10.

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This oil 11 will have a higher temperature.

In the oil reservoir 10 this hot oil 11 will be mixed with the cooled, cold oil 11 which is led via the bypass line 15 to the oil reservoir 10.

The operation of the oil-free compressor 1 with the oil circuit 5 is very simple and as follows.

When the compressor element 2 is driven by the motor 4, the cooperating, rotating screw rotors 9 will suck in and compress air.

During operation, various components of the compressor element 2, the transmission 3 and the motor 4 will be lubricated and cooled.

Since the oil rotor pump 13 is driven by the motor 4 of the compressor element 2, it will pump up oil 11 from the start-up of the oil-free compressor 1 and send it via the oil pipe 12 and sub-pipes 18 to the parts of the oil-free compressor 1 to be lubricated and cooled.

The course of the flow Q of the oil rotor pump 13 as a function of the speed n of the engine 4 is shown in Figure 2.

As can be deduced from this figure, at low speeds n the oil rotor pump 13 will pump up less oil 11 compared to high speeds n. This is advantageous since at low speeds n less lubrication and cooling will be required and at high speeds n more.

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At low speeds n all the oil 11 that is pumped up will be sent to the compressor element 2 and the motor 4, that is to say that the bypass valve 14 will close the bypass line 15, so that no oil 11 along the bypass line 15 and the oil cooler 16 will return to the oil reservoir 10 can flow. Since no cooling is required at low speeds n since the oil 11 will hardly heat up, this is not a problem and will ensure that the oil 11 does not become too cold.

The course of the pressure p in the oil line 12 downstream of the bypass valve 14 is shown in Figure 3.

The pressure p will increase systematically and proportionally to the speed n, until a specific pressure p 'is reached, corresponding to the speed n'.

From this speed n ', a pressure p' is achieved such that the bypass valve 14 will be partially opened towards the bypass line 15.

As a result, at higher speeds than n ', a portion of the pumped-up oil 11 will be controlled via the bypass line 15 through the bypass valve 14.

This is shown schematically in Figure 2, the curve splitting into two branches: part of the oil flow rate Q corresponding to zone I will be sent via the oil line 12 to the parts to be lubricated and cooled of the oil-free compressor 1, while the remaining part of the oil flow rate Q corresponding to zone II is sent back to the oil reservoir 10 via the bypass line 15.

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Because the bypass valve 14 will open, the pressure p from the speed n 'will no longer increase proportionally to the speed n of the motor 4, but the curve is smoothed, as shown in figure 3.

The higher the speed n, the more the bypass valve 15 will be pressed open by the higher pressure p downstream of the bypass valve 14 in the oil line 12. After all, at a higher speed n the flow Q of the oil rotor pump 13 will be higher, so that this pressure p will also increase, as a result of which the bypass valve 14 will open more and more.

The spring characteristics of the spring-controlled bypass valve 14 are selected such that the bypass valve 14 is controlled by the spring such that a predetermined pressure p is achieved in the oil line 12 between on the one hand the bypass valve 14 and on the other hand the compressor element 2 and / or the motor 4 according to the curve from figure 3.

The oil 11 that is sent via the bypass line 15 will pass through the oil cooler 16 and be cooled.

Because the cooled oil 11 that is sent via the bypass line 15 ends up in the oil reservoir 10, the temperature of the oil 11 in the oil reservoir 10 will drop. This cold (er) oil 11 is then pumped up by the oil rotor pump 13 and brought to the compressor element 2 and / or the motor 4.

Since at high speeds n more heat is generated in the oil-free compressor 1, there will now be more cooling

BE2018 / 5237 are needed, which is precisely taken care of in the above way.

At increasing speeds n the oil rotor pump 13 will pump more and more oil 11 out of the oil reservoir 10. Since the pressure p downstream of the bypass valve 14 would thereby become increasingly higher, this bypass valve 14 will respond to this by sending more and more oil 11 via the bypass line 15. so that the pressure p does not rise too high and the curve from Figure 3 continues to follow.

As a result, more and more oil 11 will be cooled at increasing speeds n, so that the rising temperature of the oil-free compressor 1 can be absorbed at these increasing speeds n.

This is shown in Figure 2, where zone II becomes increasingly larger at higher speeds n.

It is clear from the above that at low speeds n little or no oil 11 is cooled, while at increasing speeds n more and more oil 11 is cooled.

As a result, the oil temperature will be more constant and on average higher, which causes the viscosity of the oil 11 to be lower on average, so that there are fewer oil losses in the oil rotor pump 13 and in the lubrication locations.

As can be further deduced from Figure 2, at all engine speeds n, the oil flow rate Q passing through the bypass line 15 and the oil cooler 16 (zone II) will be smaller than the

B E2018 / 5237 oil flow rate Q that is sent to the compressor element 2 and / or the engine 4 (zone I).

This has the consequence that the oil cooler 16 can be dimensioned smaller in comparison with the known cooling circuits.

The oil 11 from the compressor element 2 and / or the motor 4 will be returned to the oil reservoir via the return line 19.

This oil 11 will have a higher temperature than the oil in the oil reservoir 10.

In addition to this hot oil 11, the cooled oil 11 also enters the oil reservoir 10 via the bypass line 15.

Both will be mixed in the oil reservoir 10, which will result in an oil 11 at a certain temperature, located between the temperature of the cooled oil 11 and the hot oil 11.

From the oil reservoir 10, the oil rotor pump 13 will pump up the oil 11 again and the method and control explained above will be followed.

Although in the example shown a bypass valve 14 is used that is a mechanical valve that is spring-controlled, it is possible to use an electronic bypass valve 14 that is controlled with a controller 20.

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In figure 1 this controller 20 is shown with a dotted line as an example. This controller 20 will control the bypass valve 14, for example on the basis of a signal from a pressure sensor 21 which is placed downstream of the bypass valve 14 in the oil line 12. The controller 20 will control the bypass valve 14 so that the pressure p as recorded by the pressure sensor 21 will follow the course of the curve from Figure 3. In other words: the bypass valve 14 is controlled such that a predetermined pressure p is achieved in the oil line 12 between on the one hand the bypass valve 14 and on the other hand the compressor element 2 and / or the motor 4.

Although in the examples shown and described the oil circuit 5 is shown separately from the compressor element 2 and the motor 4, it is of course not excluded that the oil circuit 5 is integrated into or forms a physical part of the compressor element 2 and / or the motor 4.

It is possible that in all embodiments shown and described above, the oil circuit 5 also comprises an oil filter. This oil filter may, for example, but not necessarily, be arranged in the oil line 12 downstream of the bypass valve 14. The oil filter will remove any contaminants from the oil 11 before sending them to the compressor element 2 and / or the motor 4.

The motor 4 will directly drive both the compressor element 2 and the oil rotor pump 13. Figure 4 shows that the axis of rotation 22 of the motor 4 directly drives the oil rotor pump 13.

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The oil circuit 5 will allow the oil rotor pump 13 to pump up oil 11 from the oil reservoir 10 through an inlet channel 23 upstream of the oil rotor pump 13, after which the oil 11 can be sent via the pipe 12 and the sub pipes 18 to nozzles which discharge at specific locations in the engine 4 and / or the compressor element 2 for the lubrication and / or cooling of one or more bearings and other components of the oil-free compressor 1.

Since the oil rotor pump 13 is driven by the motor 4 of the compressor element 2, it will be at a considerably higher level than the oil reservoir 10. This means that the inlet channel 23, which runs from the oil reservoir 10 to the oil rotor pump 13, is relatively long .

The oil rotor pump 13 comprises a housing 24 with a stator 25 and a rotor 26 disposed therein. The rotor 26 is mounted on a rotation shaft 27, which is driven by the rotation shaft 22 of the motor 4.

The oil rotor pump 13 is of the gerotor type, but this is not necessary for the invention.

The housing 24 is provided with an inlet port 28 for oil 11, to which an inlet channel 23 is connected, and with an outlet port 29 for the pumped-up oil 11.

In Figure 5, the inlet port 28 and the outlet port 29 are clearly visible.

As can be seen in figure 6, a dam 30 is provided in the inlet channel 23, near the oil rotor pump 13.

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By "dam 30" is meant here a structure that will ensure that, when the engine 4 is off, a certain amount of oil 11 will remain in a space 31 in the inlet channel 23 dammed by the dam 30.

By "near the oil rotor pump 13" it is meant here that the aforementioned residual amount of oil 11 will remain at a location such that the oil 11 can be immediately pumped up by the oil rotor pump 13 upon start-up of the oil rotor pump 13.

This means that the aforementioned residual amount of oil 11 will, for example, be located at least partially in the oil rotor pump 13 or that the aforementioned residual amount of oil 11 will be located in the inlet channel 23 right next to the inlet port 28 of the oil rotor pump 13.

Figure 6 also clearly shows that the dam 30 has a minimum height equal to the height A of the center line 32 of the axis of rotation 27 of the oil rotor pump 13 less half a smallest diameter B of the rotor 26 of the oil rotor pump 13 .

By making the dam 30 at least as high as this minimum height, indicated by the line C, enough oil 11 will remain in the space 31 dammed by dam 30 in the inlet channel 23 between the dam 30 and the oil rotor pump 13, whereby the oil rotor pump 13 is immediately fully wetted internally when the oil-free compressor 1 starts up.

Due to this immediate internal wetting of the oil rotor pump 13 with oil 11, the rotor 26 and the stator

BE2018 / 5237 be immediately sealed by this oil 11 so that the suction power of the oil rotor pump 13 is immediately maximum.

In this case, and preferably, the height D of the dam 30 is smaller than a maximum height equal to the height A of the center 32 of the rotation shaft 27 of the oil rotor pump 13 less half a diameter E of the rotation shaft 27 of the oil rotor pump 13.

If the dam 30 were to be higher than this maximum height, indicated by the line F, the level of the remaining oil 11 would be higher than a lowest point of the rotation shaft 27 of the oil rotor pump 13. This could cause oil 11 to leak out via the axis of rotation 27 of the oil rotor pump 13 and / or seals should be provided on the axis of rotation 27 of the oil rotor pump 13 to prevent this.

In addition to the minimum height C and the maximum height F of the dam 30, the shape of the dam 30 in this case, and preferably, is such that the volume of the oil 11 which can be found in the oil rotor pump 13 and the inlet channel 23 between the oil rotor pump 13 and the dam 30, is at least twice the stroke volume of the oil rotor pump 13.

This has the advantage that immediately enough oil 11 is present in the oil rotor pump 13 and the inlet channel 23 when the oil rotor pump 13 is started up, so that not only the oil rotor pump 13 can be immediately internally moistened, but also that an amount of oil 11 can be pumped up immediately. or be pumped through the outlet port 29 to the oil circuit 5 and so on to the parts to be lubricated and / or cooled of the oil-free compressor 1.

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In spite of the fact that the dam 30 in figures 5 and 6 is designed as a sloping slope towards the rotor 26 and the stator 25 of the oil rotor pump 13, it is not excluded that the dam 30 has a different shape.

Figure 7 shows an alternative form, wherein the dam 30 has a stepped form, wherein a step 33 is arranged, as it were, in the inlet channel 23.

Although this embodiment has the advantage that more oil 11 will remain in the space 31 between the dam 30 and the oil rotor pump 13, it does have the disadvantage that when the oil 11 is sucked in, the oil 11 as it were via the step 33 down, which could cause unwanted turbulences. In the embodiments of figures 5 and 6, the oil 11 will, as it were, flow down or flow down from the dam 30.

The operation of the oil-free compressor 1 is very simple and as follows.

The following steps are preferably followed to start the oil-free compressor 1:

- introducing oil 11 into the oil circuit 5 at a position downstream and higher than the oil rotor pump 13 until the space 31 is completely filled with oil 11; and

- then starting the engine 4.

The oil 11 introduced into the oil circuit 5 can drain to the oil rotor pump 13 and fill both the oil rotor pump 13 and the inlet channel 23 in the space 31 between

BE2018 / 5237 the dam 30 and the oil rotor pump 13 to a level equal to the height D of the dam 30.

When the engine 4 is then started, the compressor element 2 and the oil rotor pump 13 will be driven and the oil 11 introduced into the oil circuit 5 and now located in the oil rotor pump 13 and in the aforementioned space 31 will ensure that the oil rotor pump 13 can immediately pump up oil 11 and send it to the oil circuit 5, so that the compressor element 2 is immediately supplied with the necessary oil 11 from the start-up of the oil-free compressor 1.

Alternatively, a less volatile lubricant than the oil 11 is first introduced internally into the oil rotor pump 13 before the engine 4 is started.

Such a method is preferably used in the assembly of the oil-free compressor 1, so that at the very first start-up of the oil-free compressor 1 the less volatile lubricant is present in the oil rotor pump 13.

It is of course not inconceivable that both methods are combined, with a less volatile lubricant being introduced at the very first start-up and with the subsequent start-up of the oil-free compressor 1, oil 11 being introduced into the oil circuit 5.

B E2018 / 5237

As soon as the engine 4 has started, the oil rotor pump 13 will immediately be able to pump up oil 11 from the oil reservoir 10 via the inlet channel 23.

The pumped oil 11 will then leave the oil rotor pump 13 via the outlet port 29 and end up in the oil circuit 5 where it is sent to different nozzles with different parts of the compressor element 2 and / or the motor 4 to be lubricated and / or cooled.

The compressor element 2 and / or the motor 4 will therefore be supplied with oil 11 almost immediately from the start-up of the motor 4 of the oil-free compressor 1, so that its proper functioning can be guaranteed.

It is not excluded that the oil-free compressor 1 comprises a sensor which is configured to register whether oil 11 is present in the space 31 between the oil rotor pump 13 and the dam 30.

The aforementioned sensor can be any type of oil level sensor, but can also be an oil pressure sensor or oil temperature sensor according to the invention.

For starting an oil-free compressor 1 with such a sensor, the engine 4 is preferably started only after oil 11 has been detected in the inlet channel 23 between the oil rotor pump 13 and the dam 30.

If no oil 11 is detected, the oil-free compressor 1 is not started, but is switched on, for example

B E2018 / 5237 instead issued a warning signal to the user.

It is clear that the sensor and the aforementioned method for controlling the lubrication and / or cooling of the oil-free compressor 1 can be combined with the previously described methods. This method will incorporate an additional safety in order to prevent the oil-free compressor from being started without oil 11 being present in the inlet channel 23 between the oil rotor pump 13 and the dam 30.

It is also possible that the oil-free compressor 1 comprises a connection between the oil reservoir 10 and the space 31 between the oil rotor pump 13 and the dam 30, the connection being configured to move oil 11 from the oil reservoir 10 to the space 31 between the oil rotor pump 13 and the dam 30.

This can be achieved, for example, with the help of a small pump that can be operated manually or electrically.

When the oil-free compressor 1 is provided with such a connection, the following method can be followed for starting up the oil-free compressor 1:

- moving oil 11 from the oil reservoir 10 to the space 31 between the oil rotor pump 13 and the dam 30, until the space 31 is completely filled with oil 11;

- the subsequent starting of engine 4.

It is of course not excluded that the oil-free compressor 1 is also provided with a sensor that is configured to

BE2018 / 5237 register whether oil 11 is present in the inlet channel 23 between the dam 30 and the oil rotor pump 13.

In this case, if no oil 11 is detected at start-up, a signal will be given to the user to move oil 11 from the oil reservoir 10 to the space 31 between the oil rotor pump 13 and the dam 30 by operating the small pump or, if this small pump is electrically operated, the small pump will be started automatically by the oil-free compressor 1, to ensure that oil 11 is moved from the oil reservoir 10 to the space 31 between the oil rotor pump 13 and the dam 30, after which the engine 4 can be started without problems.

The present invention is by no means limited to the embodiments described by way of example and represented in the figures, but an oil circuit according to the invention and an oil-free compressor provided with such an oil circuit can be realized in all shapes and sizes without departing from the scope of the invention .

Claims (29)

Conclusions. Oil circuit for lubrication and cooling of an oil-free compressor (1) comprising an engine (4) and a compressor element (2) driven by this engine (4), said oil circuit (5) being provided with an oil reservoir (10) with oil (11) and from an oil rotor pump (13) configured to drain oil (11) from the oil reservoir (10) through an inlet channel (23) upstream of the oil rotor pump (13) to the compressor element (2) and / or the engine (4) to be controlled via an oil line (12); - wherein this oil rotor pump (13) is provided with a rotor (26) mounted on a rotation shaft (27), said oil rotor pump (13) having a stroke volume, and wherein this oil rotor pump (13) is driven by the motor (4) of the compressor element (2); - wherein the oil circuit (5) is further provided with a return line (19) that is configured to lead oil (11) from the compressor element (2) and / or the motor (4) back to the oil reservoir (10); - wherein the oil circuit (5) is further provided with a bypass line (15) and a pressure-controlled bypass valve (14) which are configured to provide a part of the oil (11) between the oil rotor pump (13) on the one hand and the compressor element (2) on the other hand / or direct the engine (4) back to the oil reservoir (10) without this part of the oil (11) on its way to the oil reservoir (10) along or through the compressor element (2) and / or the engine ( 4) passes; and - wherein the oil circuit (5) is further provided with an oil cooler (16), BE2018 / 5237 characterized in that the oil cooler (16) is placed in the bypass line (15) and that the bypass valve (14) is placed in the oil line (12). An oil circuit according to claim 1, characterized in that the oil circuit (5) is provided with only a single oil rotor pump (13). Oil circuit according to claim 1 or 2, characterized in that the oil cooler (16) has a fixed or constant cooling capacity. Oil circuit according to one of the preceding claims, characterized in that the bypass valve (14) is a mechanical valve, preferably a spring-controlled valve. Oil circuit according to one of the preceding claims, characterized in that the inlet channel (23) is provided with a dam (30) with a height (D) that is higher than a height (A) of a center line (32) of the rotation axis (27) of the oil rotor pump (13) reduced by a smallest diameter (B) of the rotor (26) of the oil rotor pump (13) divided by two. Oil circuit according to claim 5, characterized in that the height (D) of the dam (30) is smaller than the height (A) of the center line (32) of the axis of rotation (27) of the oil rotor pump (13) less a diameter (E) of the axis of rotation (27) of the oil rotor pump (13) divided by two. Oil circuit according to claim 5 or 6, characterized in that the dam (30) is configured such that the BE2018 / 5237 oil rotor pump (13) and the inlet channel (23) can contain a volume of oil (11) between the oil rotor pump (13) and the dam (30) that is at least twice the stroke volume of the oil rotor pump (13). Oil circuit according to one of the preceding claims 5 to 7, characterized in that the oil circuit (5) is provided with a sensor that is configured to record whether oil (11) is present between the oil rotor pump (13) and the dam ( 30). Oil circuit according to one of the preceding claims 5 to 8, characterized in that the oil circuit (5) is provided with a connection between the oil reservoir (10) and a space (31) in the inlet channel (23) between the oil rotor pump (13) ) and the dam (30), the connection being configured to move oil (11) from the oil reservoir (10) to the space (31) between the oil rotor pump (13) and the dam (30). 10. - Oil-free compressor provided with an oil circuit (5) for its lubrication and cooling, - wherein this oil-free compressor (1) comprises a motor (4) and a compressor element (2) driven by this motor (4); said oil circuit (5) comprising an oil reservoir (10) with oil (11) and an oil rotor pump (13) configured to drain oil (11) from the oil reservoir (10) through an inlet channel (23) upstream of the oil rotor pump (13) to be sent to the compressor element (2) and / or the motor (4) via an oil line (12); - wherein this oil rotor pump (13) is provided with a rotor (26) mounted on a rotation shaft (27), this B E2018 / 5237 oil rotor pump (13) has a stroke volume, and wherein this oil rotor pump (13) is driven by the motor (4) of the compressor element (2); - wherein the oil circuit (5) is further provided with a return line (19) that is configured to lead oil (11) from the compressor element (2) and / or the motor (4) back to the oil reservoir (10); - wherein the oil circuit (5) is further provided with a bypass line (15) and a pressure-controlled bypass valve (14) which are configured to provide a part of the oil (11) between the oil rotor pump (13) on the one hand and the compressor element (2) on the other hand / or direct the engine (4) back to the oil reservoir (10) without this part of the oil (11) on its way to the oil reservoir (10) along or through the compressor element (2) and / or the engine ( 4) passes; and - wherein the oil circuit (5) is further provided with an oil cooler (16), characterized in that the oil-free compressor (1) is configured such that the oil cooler (16) is placed in the bypass line (15) and that the bypass valve (14) is placed in the oil line (12). Oil-free compressor according to claim 10, characterized in that the oil circuit (5) is provided with only a single oil rotor pump (13). Oil-free compressor according to claim 10 or 11, characterized in that the oil cooler (16) has a fixed or constant cooling capacity. BE2018 / 5237 Oil-free compressor according to one of the preceding claims 10 to 12, characterized in that the bypass valve (14) is a mechanical valve, preferably a spring-controlled valve. Oil-free compressor according to one of the preceding claims 10 to 13, characterized in that the inlet channel (23) is provided with a dam (30) with a height (D) that is higher than a height (A) of a center line ( 32) of the axis of rotation (27) of the oil rotor pump (13) reduced by a smallest diameter (B) of the rotor (26) of the oil rotor pump (13) divided by two. Oil-free compressor according to claim 14, characterized in that the height (D) of the dam (30) is smaller than the height (A) of the center line (32) of the rotation axis (27) of the oil rotor pump (13) reduced with a diameter (E) of the axis of rotation (27) of the oil rotor pump (13) divided by two. An oil-free compressor according to claim 14 or 15, characterized in that the dam (30) is configured such that the oil rotor pump (13) and the inlet channel (23) a volume of oil (11) between the oil rotor pump (13) and the dam (30) may contain at least twice the stroke volume of the oil rotor pump (13). Oil-free compressor according to one of the preceding claims 14 to 16, characterized in that the oil circuit (5) is provided with a sensor that is configured to record whether oil (11) is present between the oil rotor pump (13) and the dam (30). B E2018 / 5237 Oil-free compressor according to one of the preceding claims 14 to 17, characterized in that the oil circuit (5) is provided with a connection between the oil reservoir (10) and a space (31) in the inlet channel (23) between the oil rotor pump ( 13) and the dam (30), the connection being configured to move oil (11) from the oil reservoir (10) to the space (31) between the oil rotor pump (13) and the dam (30). Oil-free compressor according to one of the preceding claims 10 to 18, characterized in that the oil-free compressor (1) is an oil-free screw compressor. 20.- Method of controlling lubrication and / or cooling of an oil-free compressor (1) via an oil circuit (5), - wherein this oil-free compressor (1) comprises a motor (4) and a compressor element (2) driven by this motor (4); said oil circuit (5) being provided with an oil reservoir (10) and wherein oil (11) is sent by means of an oil rotor pump (13) from the oil reservoir of a (10) to the compressor element (2) and / or the motor (4) via an oil line (12); - wherein this oil rotor pump (13) is driven by the motor (4) of the compressor element (2); and - wherein part of the oil (11) between, on the one hand, the oil rotor pump (13) and, on the other hand, the compressor element (2) and / or the motor (4), is led directly back to the oil reservoir (10) by means of a bypass line (15) and a pressure controlled bypass valve (14) included in the oil circuit (5), without this part of the oil (11) on its way to the oil reservoir (10) along or through the compressor element (2) and / or the motor (4) passes; B E2018 / 5237, characterized in that the method further comprises the steps of - the part of the oil (11) passing through the bypass line (15) and the bypass valve (14) back to it oil reservoir (10) is guided by an oil cooler (16) to lead that in the bypass line (15) is placed; and - the bypass valve (14) such to arrange that a preset pressure is reached in the oil pipe (12) between, on the one hand, the bypass valve ( : i4), and otherwise , it compressor element (2) and / or the motor (4). Method according to claim 20, characterized in that the oil (11) is controlled by the oil circuit (5) by only a single oil rotor pump (13). Method according to claim 20 or 21, characterized in that the oil (11) is cooled by an oil cooler (16) with a fixed or constant cooling capacity. Method according to one of the preceding claims 20 to 22, characterized in that the part of the pumped-up oil (11) that is sent back through the bypass line (15) to the oil reservoir (10) is controlled by means of a bypass valve (14) which is a mechanical valve, preferably a spring-controlled valve. Method according to any of the preceding claims 20 to 23, characterized in that oil (11) is retained in a space (31) between the oil rotor pump (13) and a dam (30). B E2018 / 5237 Method according to claim 24, characterized in that the dam (30) upstream of the oil rotor pump (13) is provided with an inlet channel (23) between the oil reservoir (10) and the oil rotor pump (13), the dam (30) has a height (D) that is higher than a height (A) of a center line (32) of the axis of rotation (27) of the oil rotor pump (13) reduced by a smallest diameter (B) of the rotor (26) of the oil rotor pump (13) divided by two and smaller than the height (A) of the center line (32) of the rotation axis (27) of the oil rotor pump (13) less a diameter (E) of the rotation axis (27) of the oil rotor pump (27) 13) divided by two. Method according to claim 24 or 25, characterized in that, when starting and / or restarting the engine (4) of the oil-free compressor (1), the method comprises the following steps: - introducing oil (11) into the oil circuit (5) at a position downstream and higher than the oil rotor pump (13) until the space (31) is completely filled with oil (11); and - then starting the engine (4). Method according to claim 24 or 25, characterized in that, when starting and / or restarting the engine (4) of the oil-free compressor (1), the method comprises the following steps: - introducing a less volatile lubricant than the oil (11) internally into the oil rotor pump (13) until the space (31) is completely filled with the lubricant; and - then starting the engine (4). BE2018 / 5237 Method according to one of the preceding claims 24 to 27, characterized in that, when starting and / or restarting the engine (4) of the oil-free compressor (1), the method further comprises the following steps: 5 - registering by means of a sensor of which the oil circuit (5) is provided, or the space (31) is completely filled; and - then, when it is registered that the space (31) is completely filled, starting the engine (4). The method according to any of the preceding claims 24 to 28, characterized in that, when starting and / or restarting the engine (4) of the oil-free compressor (1), the method further comprises the following steps: - moving oil (11) from the oil reservoir (10) to the space (31) through a connection provided with the oil circuit (5) until the space (31) is completely filled with oil (11); and - then starting the engine (4). BE2018 / 5237 B E2018 / 5237 BE2018 / 5237 B E2018 / 5237 B E2018 / 5237 Oil circuit, oil-free compressor provided with such oil circuit and method for controlling lubrication and / or cooling of such oil-free compressor via such oil circuit. Oil circuit for an oil-free compressor (1) comprising a motor (4) and a compressor element (2), - wherein this oil circuit (5) comprises an oil reservoir (10) with oil (11) and from an oil rotor pump (13) for sending oil (11) to the compressor element (2) and / or the motor (4) via an oil line ( 12); - wherein this oil rotor pump (13) is driven by the aforementioned engine (4); - wherein the oil circuit (5) comprises a return line (19) for passing oil (11) from the compressor element (2) and / or the motor (4) back to the oil reservoir (10); - wherein the oil circuit (5) comprises a bypass line (15) and a bypass valve (14) around a part of the oil (11) between the oil rotor pump (13) on the one hand and the compressor element (2) and / or the motor (4) on the other hand to return to the oil reservoir (10) without passing the oil (11) along or through the compressor element (2) and / or the engine (4); and - wherein the oil circuit (5) is provided with an oil cooler (16), wherein the oil cooler (16) is placed in the bypass line (15) and that the bypass valve (14) is placed in the oil line (12).