Oil circuit for supplying a compressor compressing in an oil-free manner, and method for controlling an oil parameter for the oil supply of a compressor of this type

Abstract

The invention relates to an oil circuit (200) for supplying an oil-free compressor (100), to a compressor (100) of this type, and to a method for controlling an oil parameter for the oil supply of an oil-free compressor (100). The oil supply is used to lubricate and cool at least one bearing (55a, 55b), a drive and / or a gearing of the compressor (100). The oil circuit (200) comprises: an oil reservoir (1); an oil pump (3) for pumping oil from the oil reservoir (1) to the compressor (100) through an oil supply line (4, 4a, 4b, 4c) which connects an oil pump outlet (42) to at least one oil inlet (19, 19a, 19b) of the compressor (100); an oil cooler (6) which is located downstream of the oil pump (3) in a section of the oil supply line (4, 4a, 4b, 4c); an oil recirculation line (14, 14a, 14b) which branches off from the oil supply line (4a) downstream of the oil pump (3) and upstream of the oil cooler (6) and leads to the oil reservoir (1); and a valve (20), preferably an overflow valve, for controlling an oil flow in the oil circulation line (14, 14a, 14b).

Description

[0001] Oil circuit for supplying an oil-free compressor and method for controlling an oil parameter for the oil supply of such a compressor

[0002] Description

[0003] The invention relates to an oil circuit for supplying oil to an oil-free compressor for generating compressed gas, preferably compressed air, for a consumer. Furthermore, the invention relates to an oil-free compressor and a method for controlling an oil parameter for the oil supply of such a compressor.

[0004] Oil-free compressors are sometimes also referred to as dry-compressing compressors or dry compressors. They are primarily used for applications requiring the provision of oil-free compressed process gas, particularly oil-free compressed air, such as in the food or pharmaceutical industries. Unlike oil-injected compressors, where the oil injected into the compressor elements serves not only to lubricate and cool the compressor elements but also to seal them, oil-free compressors are designed to prevent oil from entering the compression chamber and the compressed gas produced.

[0005] Oil-free compressors with rotating compressor elements are often used, such as oil-free screw compressors. Oil-free compressors often feature oil lubrication and cooling for the bearings of the compressor rotor shaft. Due to the high rotational speeds of rotating compressor elements (compressor rotors), the bearings require a sufficient oil flow for cooling, with heat generated in the bearings being dissipated by the oil supplied via an oil circuit.

[0006] In oil-free screw compressors, the compressor stages and the oil pump are often driven by a common drive motor. This results in the oil flow delivered by the oil pump being too high, depending on the compressor's operating point. Depending on the operating conditions, particularly the oil temperature, the oil flow delivered by the oil pump sometimes exceeds the compressor's cooling requirements by a greater or lesser amount. Furthermore, the oil flow required for sufficient cooling in variable-speed compressors depends on the drive speed.

[0007] Oil circuits for supplying the bearings of oil-free compressors are generally known from the state of the art. These circuits use an oil cooler to cool the oil and an oil filter to clean the oil that is fed to the compressor.

[0008] Solutions are also known that use overflow valves to return excessive oil flow to the oil tank.

[0009] EP 3 392 478 A1 describes an oil-free compressor with an oil circuit, wherein the oil circuit's oil pump is driven by the compressor element's motor. One of the problems described is that an oil cooler designed for maximum speed cools the oil too much at low machine speeds, resulting in large temperature differences during operation, which are detrimental. Furthermore, a large oil cooler is required, designed for the entire oil volume flow at maximum speed. It is therefore proposed to arrange an oil cooler and a bypass valve in a bypass line, which could also be referred to as an oil recirculation line. According to EP 3 392 478 A1, this allows a more constant oil temperature and a smaller oil cooler dimensioning.

[0010] Other known solutions, for example, have the disadvantage of increased construction complexity due to the use of several separate valves in the oil supply line. Furthermore, there is often a risk of an oil filter being damaged ("overrun"), particularly during cold starts, due to an excessive pressure difference. Correspondingly oversizing the oil filter requires increased pump power. Correspondingly undersizing the oil pump to avoid overloading the oil filter may not provide sufficient oil flow at other operating points of the oil circuit. State-of-the-art oil circuits often have the disadvantage of unnecessarily high power consumption by the oil pump, namely when an unnecessarily large amount of oil is pumped at an unnecessarily high pressure.

[0011] The present invention aims to provide an oil circuit for supplying an oil-free compressor with oil, a corresponding compressor, and a method for operating an oil circuit of the compressor that overcome at least one of the aforementioned disadvantages. In particular, the oil circuit should be operable with low energy consumption and be as simple as possible. Furthermore, high operational reliability and the lowest possible maintenance effort should be achieved.

[0012] This task is solved by a sophisticated oil circuit, a sophisticated oil-free compressor and a sophisticated process.

[0013] In particular, the object is achieved by an oil circuit for supplying an oil-free compressor, in particular at least one bearing, a drive and / or a gear of the compressor, with oil, wherein the oil circuit comprises:

[0014] - an oil reservoir;

[0015] - an oil pump for conveying oil from the oil reservoir to the compressor, in particular to the at least one bearing, a drive and / or a gear of the compressor, through an oil supply line connecting an oil pump outlet to at least one oil inlet of the compressor;

[0016] - an oil cooler arranged downstream of the oil pump in a section of the oil supply line;

[0017] - an oil recirculation line branching off from the oil supply line downstream of the oil pump and upstream of the oil cooler and leading to the oil reservoir;

[0018] - a valve, preferably an overflow valve, for regulating an oil flow in the oil recirculation line. Such an oil circuit has the advantage that an oil flow delivered by the oil pump (oil volume flow), which is not required to supply the compressor (under the current operating conditions), is returned (recirculated) through the oil recirculation line to the oil reservoir, without having to be pumped through the oil cooler and, if applicable, other downstream components of the oil circuit, such as an oil filter and / or an oil cooler valve. A (direct) return of the excess oil to the oil reservoir with the lowest possible pressure losses is possible, in particular by branching the oil recirculation line immediately (i.e. directly) downstream of the oil pump outlet.In particular, there is no oil circuit component (relevant to the total pressure loss in the oil supply line) between the oil pump and the oil cooler (except for a pipe section with unavoidable low pressure losses). This can reduce the power consumption of the oil pump. Under certain circumstances, the oil pump can be dimensioned smaller, and thus more cost-effectively.

[0019] In addition, by regulating the oil flow in the oil recirculation line (exclusively) by the valve (overflow valve), an oil parameter of the oil supplied to the compressor, such as the oil pressure or the oil flow (oil volume flow), can be influenced, preferably regulated, in particular if the tapped oil parameter (actual value) is tapped at the oil inlet to the compressor and used as a controlled variable for regulating the oil parameter, preferably for comparison with a predetermined oil parameter (setpoint) for deriving (calculating) a manipulated variable to the valve (overflow valve). Preferably, the oil circuit has only one (single) valve (overflow valve) for regulating the oil parameter at the oil inlet of the compressor. In particular, no pressure reducing valve is present, especially not downstream of the oil filter.

[0020] The supply of oil to the oil-free compressor serves in particular the purpose of lubricating and / or cooling components of the compressor, in particular the bearings, a drive (motor) and / or a gearbox, via which several compressor stages can be coupled to one another and / or a drive of the compressor can be coupled to a drive of the oil pump. The cooling of other components of the compressor, such as the compressor housing, e.g. by means of jacket cooling, is also conceivable. The compressor can comprise one or more compressor stages that can be coupled to one another. The oil-free compressor is preferably an oil-free screw compressor, in particular for generating compressed gas, such as a process gas (e.g. helium) or air (compressed air), for a consumer to use the compressed gas.

[0021] The oil circuit, in particular, has an oil return line that connects at least one oil outlet of the compressor to the oil reservoir. The oil circuit may include additional oil lines. The oil circuit may include several sub-oil circuits that supply additional components of the compressor (bearings of additional compressor stages, drive of the compressor and / or the oil pump, gearbox, etc.) with oil. The oil circuit may include additional oil coolers. The oil cooler may include a temperature control system, e.g., with a 3-way valve and bypass line.

[0022] The arrangement of the oil cooler "in" a section of the oil supply line can be understood such that a first (upstream) section of the oil supply line is connected to an inlet of the oil cooler and a second (downstream) section of the oil supply line is connected to an outlet of the oil cooler.

[0023] The valve (overflow valve) is preferably arranged in the oil recirculation line. The oil recirculation line comprises, in particular, a valve supply line section leading from the oil supply line to the valve, and, in particular, a valve return line section leading from the valve to the oil reservoir. The oil recirculation line (overflow line) can be designed (in sections) as a pipe, hose, or channel.

[0024] The oil supply line can comprise various line sections that connect the components of the oil circuit (oil cooler, oil filter, valves, etc.) to one another. The oil supply line can branch out and comprise parallel oil supply line sections. In particular, the oil supply line comprises bypass lines that bypass, in particular, the oil cooler or an oil filter. A bypass line (of the oil cooler) can be switchable by a control valve, preferably with an adjustable flow rate. To supply oil to the compressor, flow can occur (variably over time) through various (parallel) sections of the oil supply line from the oil pump outlet to at least one oil inlet of the compressor, depending on the operating state of the oil circuit (different valve positions).

[0025] The at least one (oil-lubricated and / or oil-cooled) bearing (radial and / or axial bearing) is preferably arranged in a bearing chamber of the compressor, which is sealed by non-contact seals. A bearing can be part of a bearing arrangement comprising several bearings that support one or more shaft sections of a compressor element (compressor rotor). The at least one bearing defines at least one movable compression element, preferably a compressor rotor (screw rotor). Several bearings can be supplied with oil via a common oil inlet of the compressor, preferably via oil channels in the compressor housing and / or oil lines.

[0026] An oil inlet can be an inlet opening (bore) in the compressor housing that opens into an oil channel to the bearing or into a bearing chamber in which the at least one bearing is arranged. The oil inlet in particular establishes a fluidic (hydraulic) connection to at least one bearing in order to ensure the inflow (injection) of oil and preferably opens towards a bearing or into a bearing chamber. An oil inlet (an oil inlet opening) can be understood as a cross-sectional constriction (passage opening with a reduced cross-section) of an oil supply (oil line and / or oil channel), in particular an injection nozzle (oil injection nozzle), which is preferably formed in an oil channel in the compressor housing.In this respect, a section (compressor-side end section) of the oil supply line can extend within the compressor (compressor housing), in particular as a section of an oil feed line (an oil channel), preferably as far as an oil injection nozzle. Several oil inlets (oil injection nozzles) can be provided, in particular due to a branching of the oil supply line outside and / or inside the compressor housing. Several oil inlets for several bearings or a common oil inlet for several bearings can be provided. An oil inlet (an oil inlet opening) can also be designed as a cross-sectional constriction (nozzle) through which oil is supplied to a gear chamber and / or motor chamber in which at least one gear element (e.g. gears) and / or a motor is arranged.One or more oil inlets can be arranged in a region, in particular a section of the oil supply line, in which (substantially) the same oil pressure (oil injection pressure) prevails. In this respect, the oil inlet can be arranged, in particular, between an oil outlet of an oil cooler and one or more bearings of the compressor.

[0027] The invention is based on the finding that the differential pressure across the oil filter generally depends on its degree of contamination. If - as in the prior art - too high an oil volume flow is pumped through the oil filter, the problem of the oil filter collapsing can arise. If a bypass is present for the oil filter, high oil pressure differences can allow unfiltered oil and possibly already separated dirt to reach the bearings of the compressor. It was also recognized that the differential pressure of the oil cooler and the oil filter are strongly dependent on the temperature of the oil, since the viscosity of the oil changes with temperature. For optimal distribution of the oil to various lubrication points of the compressor, a certain minimum oil pressure at the oil inlet of the compressor is also required.

[0028] If the oil recirculation line were to branch off from the oil supply line downstream of the oil filter and oil cooler—unlike in the present invention—the oil pump would require increased power. This is because the entire oil flow would always have to be pumped through the oil cooler and oil filter, resulting in a cumulative pressure loss between both components to pump the entire oil flow. This would result in a correspondingly increased power consumption of the oil pump. Furthermore, the oil filter would be subjected to greater stress and could be damaged. Particularly during a cold start, there is a risk of overloading the oil filter element. Therefore, the oil filter would have to be dimensioned larger, which would increase the construction cost.

[0029] If the oil pressure is regulated by an overflow valve downstream of the oil cooler and upstream of the oil filter, the overflow valve opens (partially) when the oil pressure becomes too high. However, this approach does not take into account different oil pressure differences at the oil filter (e.g., depending on oil filter contamination, etc.). This would lead to varying oil pressures at the compressor's oil inlet, particularly depending on the differential pressure of the oil filter. Furthermore, the entire oil flow would then always have to be pumped through the oil cooler. The required oil pump power would therefore be higher than with the solution of the invention.

[0030] In contrast to the solution according to the invention, two separate valves could be used in the compressor's oil supply line, through which the oil pump delivers the oil. Firstly, an overflow valve could be used downstream of the oil pump and upstream of the oil filter, which directs excess oil back into the oil reservoir. However, if it is not possible to regulate the oil flow in the oil recirculation line, the overflow valve would have to be set to a significantly higher pressure in order to accommodate all possible differential pressures that may occur at the oil filter and oil cooler during operation. At a minimum, the differential pressure of the oil filter, which changes due to operational contamination, would have to be maintained. The power consumption of the oil pump would therefore be unnecessarily high, especially with a new or uncontaminated filter. Secondly, a pressure reducing valve could also be used downstream of the oil filter to limit the injection pressure.Compared to the invention, such a solution would have the disadvantage of requiring more construction effort for two valves and a significantly higher oil pump output, namely approximately twice as high, as in the inventive solution. For example, the oil pump would have to deliver oil at the pump outlet to approximately 3 bar for bearing lubrication, instead of only approximately 1.5 bar, as in the invention.

[0031] In one embodiment, the oil circuit comprises an oil filter arranged in a section of the oil supply line upstream, preferably immediately upstream, of the compressor's oil inlet and preferably downstream of the oil cooler. The oil circuit preferably comprises a bypass line bypassing the oil filter and having a (spring-loaded) differential pressure relief valve (overflow valve). The oil circuit according to the invention reduces the oil flow conveyed through the oil filter in that only the oil flow actually supplied to the compressor's oil inlet must pass through the oil filter and thus the corresponding pressure differential across the filter element. Overloading or damage to the oil filter located downstream of the oil cooler can be avoided. This leads to lower maintenance requirements and enables smaller dimensions of the oil filter.In one embodiment, to regulate an oil flow in the oil recirculation line, at least one oil parameter, in particular an oil pressure, an oil temperature and / or an oil flow rate, of the oil can be tapped in the oil supply line downstream of the oil filter and / or in the oil supply line downstream of the oil cooler. An oil parameter can be tapped in the oil supply line downstream of the oil cooler and upstream of the oil filter, i.e., at a position between the oil cooler and the oil filter. The oil injection pressure can preferably be tapped at the oil inlet of the compressor. The oil volume flow (oil injection flow rate) is preferably (sensibly) tapped (measured) downstream of the branching point of the oil recirculation line, for example, upstream of the oil cooler.The oil parameter, preferably oil pressure or oil flow, can be tapped within the compressor, for example by arranging a pressure sensor such that an oil pressure in an oil line (an oil channel) within the compressor housing is detected, or by branching a control line (directly) at or in the compressor housing. Preferably, an oil injection pressure and / or an oil injection flow can be tapped in an end section of the oil supply line, preferably (immediately) upstream of the compressor's oil inlet.

[0032] An oil injection pressure refers, in particular, to the oil pressure at which oil is supplied to one or more oil inlets of the compressor, in particular injected into the bearings (compressor bearings). An oil injection flow refers, in particular, to the oil flow (oil volume flow) that is supplied to an oil inlet (common to several bearings) of the compressor. An oil injection temperature refers, in particular, to the oil temperature of the oil that is supplied to one or more oil inlets (oil injection nozzles) of the compressor, in particular injected into the bearings (compressor bearings).

[0033] A tapped oil parameter can be understood as an actual oil parameter, in particular as actual oil pressure or actual oil flow. A value of an oil parameter can be tapped (detected) as a measured value by a sensor. An (actual) oil pressure can be tapped hydraulically and / or by a sensor. The oil pressure can be tapped via a hydraulic control line or by a pressure sensor. The pressure sensor (pressure transducer) can generate an analog (electrical) or digital measurement signal and in particular comprise measuring electronics. An (actual) oil flow is preferably tapped by a sensor, in particular via a flow sensor (electronic, e.g. ultrasonic sensor, or impeller sensor).An oil flow can be tapped (measured) at various points in the (main) oil circuit, in particular in the oil supply line downstream or upstream of the branch point of the oil recirculation line, preferably upstream of the oil cooler (and downstream of the oil pump) or upstream of the oil filter (and downstream of the oil cooler), or in the oil return line. An oil temperature is preferably tapped by a sensor, in particular via a temperature sensor.

[0034] A tapped oil parameter (actual oil parameter: oil pressure or oil flow) can be used for control with the oil parameter as the controlled variable. By controlling the oil parameter, preferably the oil injection pressure, the compressor can be supplied with oil with a predetermined (desired) parameter value (target oil parameter), regardless of varying differential pressures of the oil cooler and any other components present, such as an oil filter and, if applicable, an oil temperature control valve. The oil flow is preferably controlled as a function of temperature, with a target oil flow being specified as a function of temperature, preferably as a function of a measured oil temperature. At low oil temperatures, a lower oil volume flow is specified, while at higher oil temperatures, a higher oil volume flow is specified.In addition to regulating the oil pressure or oil flow, the oil temperature can be regulated, preferably via an adjustable oil cooler, in particular by regulating the flow of the coolant in a coolant circuit or by regulating a fan (speed regulation).

[0035] Tapping the actual value of the oil parameter, in particular as control pressure for a hydraulically controlled overflow valve or as a controlled variable for an electrically (electronically) controlled overflow valve downstream of (all) components relevant for the pressure difference (i.e. pressure loss) in the oil supply line (e.g. oil cooler, oil temperature control valve, oil filter), has the advantage that the oil pressure control or oil flow control functions independently of the oil temperature (i.e. the temperature-dependent viscosity of the oil) and the drive speed of the compressor and the oil pump (with coupled or identical drives). The pressure differences between the components in the oil supply line that must be generated by the oil pump have no influence on the control quality of the oil parameter at the compressor's oil inlet. The dimensioning of the oil pump, oil filter, etc. can therefore be optimized independently of one another.

[0036] In one embodiment, (all) pressure-loss components of the oil circuit in the oil supply line between the oil pump and the oil inlet of the compressor, in particular the oil cooler, the oil filter and / or at least one control valve of the oil cooler, are flowed through by the same oil flow (oil volume flow) during operation of the oil circuit, ie by an oil volume flow of constant size along the (entire) length of the oil supply line.

[0037] In one embodiment, the valve, preferably an overflow valve, is designed to regulate the oil flow in the oil recirculation line based on an oil pressure tapped as a control pressure in the oil supply line, preferably downstream of the oil filter and / or downstream of the oil cooler, preferably in such a way that the tapped oil pressure approximates a predetermined, preferably variably adjustable, target oil pressure. In particular, a control connection of the valve is connected to the oil supply line via a hydraulic control line downstream of the oil filter and / or downstream of the oil cooler. Preferably, the oil pressure in the oil supply line is tapped and transmitted to the valve as a control pressure. As a result, the oil flow (oil flow) in the oil recirculation line can be (hydraulically) regulated as a function of the control pressure such that a (variably) adjustable target oil pressure is established at the oil inlet of the compressor.Such a hydraulic oil pressure control can be implemented with relatively simple components and is cost-effective.

[0038] In one embodiment, in particular a configuration of the previous embodiment, the valve is designed to variably specify the target oil pressure by adjusting a spring preload of a spring element of the valve. Preferably, a closure body for a flow opening of the valve is subjected to the set spring preload. The spring tension can be changed via an adjusting screw on the valve. The valve (overflow valve) can alternatively or additionally comprise a thermal expansion element (e.g. paraffin element) which, based on the temperature of the oil, changes a spring preload of the valve in a temperature-dependent manner such that the set target oil pressure or target oil flow is adjusted according to the oil temperature. The expansion element is preferably arranged in the oil volume flow (in contact with the oil).As the oil temperature rises, the volume of the expansion element increases and increases the spring preload, which increases the oil injection pressure and the oil volume flow to the lubrication points of the bearings, so that more heat can be dissipated, i.e. the bearings can be cooled better.

[0039] In one embodiment, in particular a configuration of the two previous embodiments, the control line is connected to a damping chamber of the valve and / or the control line has a throttle section, preferably upstream of the control connection. The damping chamber and / or the throttle section are designed in particular to dampen a movement of a closure body of the valve. A movement of the closure body can be caused by fluctuations in a control pressure in the control line. A damping chamber can be designed as a cavity in the housing of the valve (overflow valve) that can be filled with oil displaced during a valve movement via a cross-sectional constriction, preferably via an annular gap. The throttle section in particular has a flow cross-section that is reduced compared to the flow cross-section of the control line.A throttle section can be arranged at any point in the control line, in particular, it can be designed as a (local) constriction (cross-sectional constriction) of the control line. The throttle section can be designed as a separate component, in particular as a throttle piece that can be connected to one end of the control line and, when installed, is arranged between a control connection of the valve and an end piece of the control line, in particular, it is screwed into the control connection. Damping pressure fluctuations in the control line can prevent overshoot in the control system.

[0040] In one embodiment, in particular a configuration of the three previous embodiments, the valve, preferably an overflow valve, has a closure body for changing at least one flow opening of the valve, wherein the closure body is displaceably guided in a valve housing, preferably in a valve insert, such that the closure body is subjected to a closing force by a spring element with a preferably adjustable spring preload, wherein a control pressure applied to a control connection of the valve exerts an opening force on the closure body that counteracts the closing force. In particular, the closure body is guided axially displaceably in a valve insert and is pressed towards a stop surface of the valve insert by a spring element with a preferably adjustable spring preload.In particular, a control pressure acting on a control surface of the closure body in a control chamber generates a control force that counteracts the spring preload, in particular to effect an axial displacement of the closure body to change the flow opening, which corresponds in particular to the control pressure applied to a control connection of the valve. The control pressure is preferably transmitted via the control line to the control connection of the valve. The valve is preferably designed without seals subject to wear and friction, thereby further improving the control quality. The target oil pressure can be specified by adjusting the spring preload. An overflow valve with this functional principle is suitable for hydraulic control of the oil pressure (oil injection pressure) at the oil inlet of the compressor.

[0041] In one embodiment, in particular a configuration of the first three embodiments, a sensor for detecting an oil parameter of the oil in the oil supply line, preferably a pressure sensor for detecting oil pressure, a temperature sensor for detecting oil temperature, and / or a flow sensor for detecting oil flow, is provided downstream of the oil filter and / or downstream of the oil cooler, which sensor is preferably connected to a control unit in a signal-transmitting manner. The temperature sensor is preferably arranged upstream of the oil cooler (and downstream of the oil pump) to detect the oil temperature. The connection to the control unit can be wired (via cable) or wireless (via radio connection, e.g., WLAN, Bluetooth, etc.).Sensory detection of the oil parameter (oil pressure, oil flow) enables precise control of the oil pressure (oil injection pressure) at the oil inlet of the compressor and optionally the consideration of other recorded measured variables and / or operating parameters of the oil circuit and / or compressor by processing in the control unit.

[0042] In one embodiment, in particular a configuration of the previous embodiment, the valve comprises a control unit and / or is configured for connection to a control unit, preferably of the compressor, wherein the control unit is designed to control an actuator of the valve based on at least one detected oil parameter, preferably based on at least one detected oil pressure and / or oil flow, for regulating the oil flow in the oil recirculation line such that the detected oil parameter approximates a predetermined target oil parameter, preferably a target oil pressure and / or a target oil flow. In particular, the control unit is designed to generate a control signal for an actuator of the valve based on the detected oil parameter.The actuator is particularly designed to adjust a flow opening of the valve based on the control signal by displacing a closure body. The (electronic) control unit preferably comprises a processing unit (processor) and a memory. The connection to the control unit can be wired (via cable) or wireless (via radio connection, e.g., Wi-Fi, Bluetooth, etc.). The control unit can be part of an integrated control unit of the compressor, a separate control unit of the oil circuit, or a control unit of the valve (overflow valve).

[0043] In one embodiment, in particular an embodiment of the two previous embodiments, the target oil parameter, preferably target oil pressure and / or target oil flow, can be specified, preferably variably, depending on at least one of the following operating parameters, preferably automatically by a control unit:

[0044] - a determined, preferably measured, oil temperature of the oil in the oil circuit, in particular the oil temperature of the oil in the oil supply line downstream of the oil filter and / or in the oil supply line downstream of the oil cooler; - a temperature-dependent determined, preferably measured, viscosity of the oil, in particular in the oil supply line;

[0045] - a specific, preferably measured, bearing temperature of the at least one bearing;

[0046] - a specified or measured drive speed of a compressor drive and / or a specified or measured speed of the compressor;

[0047] - a predetermined or determined, preferably measured, final compression pressure of a compressing gas produced by the compressor, preferably a screw compressor, in particular the compressed air produced;

[0048] - an operating condition of the compressor, in particular idle or load operation.

[0049] The dependence of the target oil parameter on operating parameters can be taken into account in a calculation (formula) performed by the control unit. The target oil parameter can be specified by a user and, in particular, stored in (a memory) of the control unit.

[0050] The (variably adjustable) drive speed of the compressor is specified in particular as a (user-selected) target speed of the compressor, preferably as an (adjustable) input parameter of a compressor control unit, particularly in the case of electronic control of the oil pressure or the oil volume flow. The drive speed of the compressor can also be measured by sensors, particularly in the case of hydraulic control of the oil pressure. The speed of the compressor and the speed of the oil pump are linked to each other, in particular, by the gear ratio of a transmission.

[0051] The final compression pressure can be specified as a target final compression pressure (by a user) or measured by a pressure sensor.

[0052] Operating parameters can be stored (as operating parameter data) in the control unit and / or transmitted (from a server) to the control unit. The control unit can be connected to a server (computer) for data communication via a (wireless) network. Target oil parameter values ​​(target oil pressure values, target oil flow values), in particular temperature-dependent curves thereof, are stored on the server (in a database).depending on operating parameters, as well as stored measured value data (oil pressure data, oil flow data, oil temperature data, bearing temperature data), oil parameter data (oil viscosity data, in particular temperature-dependent), gas parameter data (process gas data, compressed air data, compression end pressure data) and / or operating parameter data (drive speed data, load running state data, idle running state data) can be transmitted (wirelessly) from the control unit to the server, or vice versa, for (partial) processing by at least one processor of the server or the control unit.

[0053] A temperature sensor for detecting the oil temperature of the oil in the oil supply line can be provided downstream of the oil filter, whereby a target oil injection temperature can be specified at the oil inlet of the compressor. Preferably, a temperature sensor is arranged upstream of the oil cooler and downstream of the oil pump, i.e., between the oil filter and the oil cooler. In principle, the temperature sensor can be arranged at any location in the (main) oil circuit, in particular at any location in the oil supply line or the oil return line. The (temperature-dependent) viscosity of the oil can be derived (determined) from the measured oil temperature. Alternatively or additionally, at least one temperature sensor can be provided for detecting a bearing temperature of at least one bearing. In an electrical (electronic) control system, the temperature measurement values ​​detected by one or more temperature sensors are processed by the control unit.The target oil parameter (target oil pressure, target oil flow) can be determined, in particular calculated, by the control unit.

[0054] Temperature-dependent adjustment of the target oil parameters (target oil pressure, target oil flow) has a positive effect on the lubrication of the compressor bearings. At high oil or bearing temperatures, a higher oil pressure may be required to inject a larger oil flow rate to cool the bearings. However, under favorable cooling conditions or low bearing loads, the oil flow rate should be lower to minimize viscosity losses and churning losses in the bearing. With hydraulic control, the temperature dependence of the target oil pressure can be achieved using an expansion element (see above).

[0055] To adjust the target oil parameters (target oil pressure, target oil flow) depending on the discharge pressure (pressure of the generated compressed air), the discharge pressure is preferably measured with a pressure sensor at the compressor outlet (compressed air outlet). At high discharge pressures, higher loads act on the bearings. Depending on the bearing load, a different optimal (temperature-dependent) operating viscosity of the oil and a different optimal oil flow for lubrication and cooling of the bearings result.

[0056] Adjusting the target oil parameters (target oil pressure, target oil flow) depending on the speed can be achieved using a centrifugal governor, which, for example, varies the spring preload in a hydraulic control system. The optimal (temperature-dependent) operating viscosity of the oil and the optimal oil flow rate depend on the compressor speed.

[0057] When the compressor is idling, it may be advisable to use a different oil volume flow for lubricating the bearings than when the compressor is under load in order to prevent the rolling elements from slipping. This is because, particularly at high speeds and low loads (idling), the rolling elements in the bearings may not roll properly but instead begin to slide, which can result in bearing damage. When idling, the oil volume flow supplying the bearings can therefore be adjusted compared to when the compressor is under load, i.e. reduced or increased depending on the design of the bearing. An operating parameter that indicates an operating state of "load running" or "idle running" can be transmitted as a (digital) data stream by a (central) control system of the compressor or a compressor system with several compressors to the control unit of the oil circuit or the overflow valve.

[0058] In one embodiment, in particular an embodiment of the previous three embodiments, the control unit is designed to regulate the oil flow in the oil recirculation line through the valve during a cold start of the oil circuit, in particular during a cold start of the compressor, in such a way that a predetermined maximum permissible oil filter differential pressure across the oil filter is not exceeded. Preferably, a (single) differential pressure sensor across the oil filter is provided for determining the oil filter differential pressure by the control unit. Alternatively or additionally, to determine the oil filter differential pressure, the control unit detects a first oil pressure downstream of the oil pump and upstream of the oil filter, preferably by a pressure sensor, and a second oil pressure downstream of the oil filter and upstream of an oil inlet, preferably by a pressure sensor.Before starting, especially during a cold start, the overflow valve can be opened sufficiently to avoid overshoot due to the differential pressure occurring at the oil filter, which is caused by the high viscosity of the oil due to the (still) low oil temperature.

[0059] In one embodiment, the valve, preferably an overflow valve, is designed as a proportional valve, wherein the closure body has a plurality of flow openings with an opening cross-section that varies in the axial direction of the closure body, which in particular define a defined flow characteristic of the valve, preferably a linear or equal-percentage flow characteristic. An optimized flow characteristic (opening characteristic) of the valve through coordinated flow openings is characterized by high control quality.

[0060] The stated object is also achieved in particular by an oil-free compressor, preferably a screw compressor, for generating compressed gas, preferably compressed air, for a consumer, comprising an oil circuit for supplying the compressor with oil. The compressor in particular comprises an oil circuit in one or more of the previously described embodiments. The compressor and the oil pump preferably have a coupled drive. Preferably, the compressor and the oil pump are driven by a common drive unit (motor). In particular, a rotational speed of the oil pump is coupled (via a gear) to the rotational speed of the compressor, wherein the compressor and the motor are preferably driven by the same drive unit and can, for example, have a common axis of rotation. The compressor has the same or similar advantages as those described in connection with the oil circuit.The stated object is also achieved in particular by a method for controlling an oil parameter, preferably oil pressure and / or oil flow, for the oil supply of an oil-free compressor, in particular at least one bearing, a drive and / or a gear of the compressor, comprising the following steps:.

[0061] - Pumping oil in an oil circuit with an oil pump from an oil reservoir to at least one oil inlet of the compressor through an oil supply line connecting an oil pump outlet to the at least one oil inlet of the compressor, wherein an oil cooler is arranged downstream of the oil pump in a section of the oil supply line;

[0062] - preferably tapping an oil parameter downstream of an oil filter and / or downstream of the oil cooler;

[0063] - Recirculating oil to the oil reservoir through an oil recirculation line branching off from the oil supply line downstream of the oil pump and upstream of the oil cooler and leading to the oil reservoir;

[0064] - Actuating a valve, preferably an overflow valve, in particular based on the tapped oil parameter, to regulate an oil flow in the oil recirculation line, preferably in such a way that the oil parameter approximates a predetermined target oil parameter.

[0065] The compressor is, in particular, a previously described oil-free compressor and, in particular, comprises an oil circuit in one or more of the previously described embodiments. The tapping of an oil parameter, in particular an oil pressure (or oil flow), can be carried out hydraulically (as a control pressure through a control line) and / or by sensor means, i.e., by a pressure sensor (or a flow sensor), preferably downstream of an oil filter and / or downstream of the oil cooler.

[0066] The method has the same or similar advantages as those already described in connection with the oil circuit and compressor according to the invention. The method for controlling an oil parameter (control method) can be implemented by a control unit described in connection with the oil circuit and the compressor.

[0067] In particular, the process can implement some or all of the process engineering features described in connection with the oil circuit and the compressor.

[0068] Some or all of the method steps can be carried out on the basis of control commands, in particular for controlling (a separate drive) the oil pump (electrical actuating signal for the pump drive), for recording measured values ​​by sensors and / or for controlling the valve, preferably the overflow valve (electrical actuating signal for the valve actuator), which are generated by the control unit. The oil pump, preferably the speed of the oil pump, can be coupled to the compressor, preferably the speed of the compressor, preferably via a gear, wherein a common drive (motor) is preferably provided for the compressor and the oil pump. The control unit can control the drive of the compressor, comprising one or more compressor stages. For an oil pump with a separate drive or an oil pump with an adjustable flow rate, a actuating signal can be used to control the (adjustable) oil pump.

[0069] In one embodiment, the target oil parameter, preferably target oil pressure and / or target oil flow, is predetermined depending on at least one of the following operating parameters, preferably variable, preferably by a control unit:

[0070] - a determined, preferably measured, oil temperature of the oil in the oil circuit, in particular oil temperature of the oil in the oil supply line downstream of the oil filter and / or in the oil supply line downstream of the oil cooler;

[0071] - a temperature-dependent determined, preferably measured, viscosity of the oil, in particular in the oil supply line;

[0072] - a specific, preferably measured, bearing temperature of the at least one bearing;

[0073] - a specified or measured drive speed of a compressor drive and / or a specified or measured speed of the compressor;

[0074] - a predetermined or determined, preferably measured, final compression pressure of a compressing gas produced by the compressor, preferably a screw compressor, in particular the compressed air produced;

[0075] - an operating condition of the compressor, in particular idle or load operation.

[0076] For the advantages of taking these operating parameters into account, reference is made to the previous explanation in connection with the control unit of the described oil circuit.

[0077] Some embodiments of the invention are explained below with reference to the drawings.

[0078] Figure 1 shows a representation of a first embodiment of an oil circuit according to the invention as a P&I diagram with a hydraulic control of the oil injection pressure;

[0079] Figure 2 shows a representation of a first embodiment of an oil-free compressor with an oil circuit according to the invention as a P&I diagram with electronic control of the oil injection pressure;

[0080] Figure 3 shows a representation of a second embodiment of an oil circuit according to the invention as a P&I diagram with electronic control of the oil injection pressure;

[0081] Figure 4 shows a representation of a third embodiment of an oil circuit according to the invention as a P&I diagram with a temperature-dependent electronic control of the oil injection pressure;

[0082] Figure 5 shows a representation of a second embodiment of an oil-free compressor with an oil circuit according to the invention as a P&I diagram with electronic control of the oil injection flow;

[0083] Figure 6 is a schematic sectional view of an embodiment of an overflow valve used in an oil circuit according to the invention for hydraulically regulating the oil injection pressure. In the following description, the same reference numerals are used for identical and similarly acting elements.

[0084] Figure 1 shows the P&I diagram of an oil circuit 200 for supplying a single-stage, oil-free compressor 100 with oil-lubricated bearings and gears (not shown in Figure 1) for generating compressed air for a consumer. The compressor 100 has an air inlet 51 and a compressed air outlet 52 for the generated compressed air. Via an oil inlet 19, the compressor 100 is supplied with oil for lubricating and cooling the bearings and gears. This oil is injected through the oil inlet 19 to the bearings 55a, 55b (see Figure 2). The oil inlet 19 can be designed as an inlet opening in a housing of the compressor 100, e.g., as a bore, or as an oil injection nozzle, e.g., as a passage opening in an oil channel with a cross-sectional constriction leading into a bearing chamber.

[0085] The oil pump 3 sucks oil from the oil reservoir 1 (oil sump) via the suction line 2. The oil passes from the oil pump 3 through the oil pump outlet 42 through several line sections of the oil supply line 4, 4a, 4b, 4c (pressure line) successively to the oil cooler 6, oil filter 7 and then through the oil inlet 19 to the compressor 100. The oil supply line 4, 4a, 4b, 4c comprises a first section 4a (divisible into two subsections downstream / upstream of the branching point 9) downstream of the oil pump 3 and upstream of the oil cooler 6, a second section 4b downstream of the oil cooler 6 and upstream of the oil filter 7 and a third section 4c downstream of the oil filter 7 and upstream of the at least one oil inlet 19. The oil cooler 6 is arranged downstream of the oil pump 3 in a section of the oil supply line 4, namely between the sections 4a and 4b.The oil recirculation line 14, 14a, 14b branches off from the oil supply line 4 downstream of the oil pump 3 and upstream of the oil cooler 6 (branch point 9) and leads to the oil reservoir 1. The valve 20 (overflow valve) is arranged to regulate the oil flow in the oil recirculation line 14, 14a, 14b. The proportional valve 16 with thermocouple directs the oil, or a partial flow thereof, via the bypass line 17 past the oil cooler 6. This prevents cooling of the oil if the oil has not yet reached the required operating temperature. After the lubrication and cooling process in the compressor 100, the oil returns to the oil reservoir 1 via the oil return line 10.

[0086] Within the operating range of the compressor 100, a constant oil injection pressure P2 should be maintained as far as possible in order to ensure a uniform oil volume flow for supplying the bearings, e.g., 20 l / min. A typical oil injection pressure is 1 to 2 bar. The drive of the compressor 100 is often coupled to the drive of the oil pump 3 (not shown), so that a higher speed of the compressor 100 necessarily means the delivery of a larger oil flow. The valve 20, designed as an overflow valve, directs the excess oil delivered by the oil pump 3 back into the oil reservoir 1 via the oil recirculation line 14 (overflow line), which comprises a valve supply line section 14a and a valve return line section 14b as subsections.In this way, only the oil flow actually supplied to the oil inlet 19 flows through the oil supply line 4, 4b, 4c (and in the section of 4a downstream of the branch point 9) and the components of the oil circuit 200 arranged therein, which are relevant for the total pressure loss and thus for the required delivery capacity of the oil pump 3, namely in this example the proportional valve 16, the oil cooler 6 and the oil filter 7. The oil pump 3 therefore only has to pump as much oil through the oil cooler 6 and oil filter 7 as is actually required to supply the compressor 100.

[0087] In the event of a sharp increase in the oil pressure PI detected by pressure sensor 5 downstream of oil pump 3, for example, during start-up processes with cold, viscous oil, the spring-loaded differential pressure relief valve 43 (check valve) in bypass line 15 opens in the event of high pressure differences across oil filter 7, which is an undesirable extreme case. This can prevent the oil filter 7, specifically a filter element contained therein, from collapsing due to an excessive pressure difference and possibly becoming permanently damaged. However, the opening of differential pressure relief valve 43 should always be prevented to prevent unfiltered oil and any already separated dirt from reaching the lubrication points of compressor 100, particularly in bearings 55a, 55b.

[0088] During operation of the oil circuit 200, the position, i.e., the opening cross-section of the flow opening 31, of the overflow valve 20 is determined by the oil pressure P2 and a preloaded spring element 22 (compression spring) installed in the overflow valve 20 (shown in Figure 6). The oil pressure P2 (actual value) is tapped as control pressure via the hydraulic control line 11 downstream of the oil filter 17. The preload of the spring element 22 is adjusted via the adjusting screw 24 so that it corresponds to a desired target oil pressure P2. S oii (setpoint). During operation, the oil pressure P2 (actual value) equals the specified target oil pressure P2 So n (setpoint) and ideally keeps the oil pressure P2 (approximately) constant even under changing operating conditions, such as oil temperatures. Thus, the oil pressure P2 is controlled hydraulically as a controlled variable.

[0089] The throttle section 12 in the control line 11 prevents the overflow valve 20 from swinging open, even under rapidly changing operating conditions, and consequently pressure fluctuations in the oil pressures P2 and PI. In Figure 6, the throttle section 12 is designed as a throttle piece inserted, e.g. screwed, into the control connection 30 at the end of the control line 11. Further design details of the overflow valve 20 are explained below with reference to Figure 6. By branching off the oil recirculation line 14 from the oil supply line 4 at the branching point 9 in the first section 4a immediately downstream of the oil pump outlet 42, the overflow valve 20 arranged in the oil recirculation line 14 and tapping the oil injection pressure P2 immediately upstream of the oil inlet 19 via the control line 11, the oil pressure P2 can be precisely regulated and the oil pressure PI can be kept to a minimum at the same time.

[0090] Figure 2 shows a schematic sectional view of an oil-free compressor 100, here a screw compressor, for generating compressed air with two intermeshing compressor elements 53, which are designed as screw rotors (the second compressor element 53 is not visible behind in the sectional view). Shaft sections of the rotor shaft 54, which rotates about the rotational axis 56, are each axially and / or radially fixed by the bearings 55a and 55b, respectively. Two oil inlets are provided in the compressor 1000, which are designed as oil injection nozzles 19a, 19b, formed by cross-sectional constrictions in oil channels. Oil channels can be designed as bores or recesses in the compressor housing 50 and each represent a section 4c of the oil supply line 4 downstream of the oil filter 7.The oil injection nozzles 19a, 19b are supplied with oil via the oil supply line 4, 4a, 4b, which branches into several sections 4c, through a common oil inlet opening in the compressor housing 50, and supply oil to the bearings 55a, 55b at an oil injection pressure P2 for lubrication and cooling. Corresponding oil outlets in the compressor housing 50 (shown on the underside in Figure 2) open into the oil return line 10. The compressor 100 symbolically represented in Figures 1 and 3-5 can be constructed identically to the compressor 100 shown in Figure 2, except for any deviations described in each case.

[0091] Figure 2 shows an alternative embodiment of the control of the oil pressure P2 shown in Figure 1, namely as an electronic control with an electronic control unit 40. The pressure sensor 8 detects the oil pressure P2 in an oil channel within the compressor housing 50 between the oil injection nozzles 19a, 19b, which represent a section 4c of the oil supply line 4 and form the oil inlet to the bearings 55a and 55b, respectively. The oil pressure P2 is essentially the same throughout the entire section 4c, which consists of various subsections inside and outside the compressor 100. The detected oil pressure P2 is transmitted to the control unit 40 via a cable or wirelessly (see dashed lines), which, based on a comparison of the detected oil pressure P2 with a stored target oil pressure P2 Son outputs a control signal to a motorized actuator 35 (symbolically shown in Figure 3) of the overflow valve 20. The overflow valve 20 is controlled in such a way that the oil pressure P2 measured during operation corresponds to the specified target oil pressure P2 Son or reaches it. The overflow valve 20 adjusts the free cross-section of the flow opening 31 to regulate the oil flow in the oil recirculation line 14 via the actuator 35. This allows electrical or electronic control of the oil pressure P2 as a controlled variable using sensor means. The oil temperature TI (oil injection temperature) in the third section 4c of the oil supply line 4 is detected by the temperature sensor 13. The oil temperature T2 is detected by the temperature sensor 44 in the second section 4b of the oil supply line 4 between the oil cooler 6 and the oil filter 7. The oil temperatures TI and / or T2 are transmitted to the control unit 40.Either the oil temperature TI or T2 can be used as the actual temperature to regulate the oil temperature in the oil circuit 200 to a predetermined target oil temperature, namely by means of an adjustable oil cooler 6, in particular if this, as shown in Figure 4, is designed with a controllable control valve 18 for regulating the coolant flow (e.g. water).

[0092] The problem of overloading the oil filter 7 due to an excessively high differential pressure at low operating temperature (viscous oil), in particular during a cold start, described with reference to Figure 1, can be achieved by specifying a target oil pressure difference between the two oil pressures PI and P2, ie P1-P2, for an oil pressure difference control that is suitable for the respective operating point, for example during a cold start, so that a maximum permissible pressure difference across the oil filter 7 is not exceeded.

[0093] Figure 3 shows an embodiment which essentially corresponds to the embodiment in Figure 2, wherein the compressor 100 is shown symbolically.

[0094] The oil pressure control according to Figure 4 includes, in addition to detecting the oil pressure P2 (oil injection pressure), also detecting an oil temperature using a temperature sensor, which transmits the detected oil temperature to the control unit 40. A temperature sensor for detecting the oil temperature can be provided at any point in the oil circuit 200, preferably upstream of the oil cooler 6, for example, the temperature sensor 44 for detecting the oil temperature T2. Alternatively or additionally, the oil temperature TI (oil injection temperature) can be detected using the temperature sensor 13. The coolant quantity (see the separate circuit for coolant shown, e.g., water) through the oil cooler 6 is regulated via the control valve 18. Alternatively, air cooling of the oil flow in the oil supply line 4 can be provided by means of an adjustable (variable speed) fan. The oil temperatures in the oil circuit 200, e.g.,TI, T2 can thus be changed using the control valve 18. The oil pressure control, in particular the control unit 40, can now use one or more detected oil temperatures TI, T2 for a temperature-dependent specification of the target oil pressure P2. So n into account. Furthermore, in addition to the oil injection pressure P2, a suitable oil injection temperature TI can be set depending on the operating point. With oil cooling via an oil-air cooler, temperature control can be implemented using a regulated cooling air or coolant quantity (see Figure 4). Likewise, temperature control can be implemented via a bypass line 17 (see Figure 1) switchable by a proportional valve 16, whereby the proportional valve 16 can be actuated electrically or mechanically.

[0095] The embodiment according to Figure 5 corresponds to the illustration in Figure 2, but instead of oil pressure control, oil flow control is implemented. The oil flow VI at the oil inlet 19, here designed as an inlet opening in the compressor housing 50, is detected by a flow sensor 41 and compared by the control unit 40 with a predetermined target oil flow V2. Son is compared in order to output a corresponding control signal to the overflow valve 20 based on the detected deviation, so that the oil flow VI (oil injection flow) in the oil supply line 4, 4b, 4c (and in the section of 4a downstream of the branch point 9) adjusts to or reaches the desired oil flow V2soii. The oil volume flow supplied via the common oil inlet 19 is divided between the oil injection nozzles 19a and 19b, which inject oil toward the bearings 55a and 55b, respectively. This allows the oil inlet 19 to be supplied with a total desired oil flow (oil volume flow) for the lubrication and cooling of the bearings 55a, 55b.

[0096] For the regulation of the oil flow in the oil recirculation line 14, a commercially available controllable valve 20 (overflow valve), e.g. with a servomotor 35 controllable by a control unit 40, can be used in the electronic oil pressure control described with reference to Figures 2 to 5 and the oil flow control described with reference to Figure 5.

[0097] Figure 6 shows an exemplary embodiment of the overflow valve 20 used in the oil circuit 200 according to Figure 1 in the closed position. The oil injection pressure P2 reaches the control chamber 26 as control pressure via the control line 11 and the throttle section 12. If the oil pressure P2 increases, the closure body 27 moves upwards and thus increases the opening cross-section of the flow openings 29, which then releases part of the flow opening 31 for flow. If the oil pressure P2 in the control chamber 26 decreases, the spring element 22 pushes the closure body 27 downwards and thus reduces the opening cross-section of the flow openings 29. The closure body 27 thus serves to change the flow openings 29, which, depending on the position, do not correspond, partially correspond or completely correspond to the flow opening 31 and thus regulate the oil flow, i.e. the flow rate, through the overflow valve 20.The overflow valve 20 is directly connected to the pressure side of the oil pump 3 or the oil pump outlet 42 via the valve supply line section 14a (and, if applicable, a line section 4a of the oil supply line 4). Excess oil flows back into the oil reservoir 1 via the flow openings 29 and the valve return line section 14b.

[0098] Alternatively or in addition to the throttle section 12, a damping chamber (not shown) can be provided, which is formed by a cavity in the valve housing 21 between the closure body 27 and the valve insert 28, which cavity can be filled with oil via a cross-sectional constriction, preferably an annular gap. During the movement of the closure body 27, displaced oil can flow into or out of the damping chamber via the constriction and thus act as a damper (vibration damper) for the overflow valve 20, in particular the closure body 27. Overshoot of the overflow valve 20 due to fluctuations in the oil pressure P2 can thus be prevented.

[0099] The valve housing 21 with the valve insert 28 (sleeve) ensures a uniform flow to the control chamber 26 and the flow openings 29, the contours of which influence the opening characteristics of the overflow valve 20. The closure body 27 has a plurality of flow openings 29 with an opening cross-section that changes in the axial direction of the closure body 27, which define a defined flow characteristic of the overflow valve 20, for example, a linear or equal-percentage flow characteristic.

[0100] The preload of the spring element 22 (compression spring) can be changed via the adjusting screw 24 and the piston 23 guided in the cover 25. This allows the target oil pressure P2 Soii is changed and variations in the cooling / lubricating oil requirement of the compressor 100 can be compensated for. The target oil pressure P2soii can be variably specified by adjusting the spring preload of the spring element 22, wherein the closure body 27 is subjected to the set spring preload to close the flow opening 31. The closure body is guided axially displaceably in the valve housing 21, specifically in the valve insert 28, in such a way that the closure body 27 is subjected to a closing force by the spring element 22, wherein a control pressure applied to a control connection 30 of the overflow valve 20 exerts an opening force (upward in Figure 6) on the closure body 27 that counteracts the closing force (downward in Figure 6). The closure body 27 is pressed by the spring element 22 in the direction of the stop surface 33 of the valve insert 28.The control pressure acting in the control chamber 26 on the control surface 34 of the closure body 27 generates an opening force counteracting the spring preload to cause an axial displacement of the closure body 27 to change the flow openings 29, which corresponds to the control pressure applied to the control connection 30. An overflow valve with such a functional principle is particularly suitable for hydraulic control of the oil pressure P2 (oil injection pressure) at the oil inlet 19 of the compressor 100, as described with reference to Figure 1.

[0101] The invention results in low construction costs for the oil circuit, since oil pressure control or oil flow control no longer requires multiple separate valves to regulate the oil pressure in the oil supply line 4, 4a, 4b, 4c, such as a pressure reducing valve. The problem of an overloaded oil filter 7 during a cold start can be avoided. Consequently, there is no need to oversize the oil filter 7 or undersize the oil pump 6 in order to avoid overloading the oil filter 7. An unnecessarily high power consumption of the oil pump 3 is avoided, since only the required amount of oil (oil volume flow) is pumped through the oil supply line 4, namely through the sections 4c, 4b and the part of the section 4a downstream of the branch point 9, in particular through the oil cooler 6 and the oil filter 7, and made available to supply the compressor 100.In this respect, the invention offers economic and energy-saving advantages due to its simple design and lower power consumption, leads to greater operational reliability due to fewer components and less stressed components, and requires less maintenance. An optimal oil supply to the oil-free compressor for cooling and lubricating the bearings, as well as any drive and / or gearbox, of the compressor can be achieved in all operating states of the compressor. It should be noted at this point that all of the features of the invention described above, both individually and in any technically feasible combination, particularly the details illustrated in the drawings, are part of the invention.

[0102] Reference list:

[0103] 1 oil reservoir

[0104] 2 Suction line oil pump

[0105] 3 Oil pump

[0106] 4 Oil supply line

[0107] 4a first section of the oil supply line

[0108] 4b second section of the oil supply line

[0109] 4c third section of the oil supply line

[0110] 5 Pressure sensor (PI)

[0111] 6 oil coolers

[0112] 7 oil filters

[0113] 8 Pressure sensor (P2)

[0114] 9 Junction point

[0115] 10 Oil return line

[0116] 11 Control line

[0117] 12 throttle section

[0118] 13 Temperature sensor

[0119] 14 Oil recirculation line

[0120] 14a Valve supply section

[0121] 14b Valve return section

[0122] 15 Bypass line (oil filter)

[0123] 16 Proportional valve with thermocouple

[0124] 17 Bypass line (oil cooler)

[0125] 18 Coolant control valve

[0126] 19 Oil inlet

[0127] 19a, b Oil injection nozzle

[0128] 20 Valve, preferably overflow valve

[0129] 21 Valve housing

[0130] 22 Spring element

[0131] 23 pistons

[0132] 24 Adjusting screw 25 Cover

[0133] 26 Control Chamber

[0134] 27 locking bodies

[0135] 28 valve insert

[0136] 29 Flow opening

[0137] 30 control connection

[0138] 31 Flow opening

[0139] 33 Stop surface

[0140] 34 Control surface

[0141] 35 Actuator

[0142] 40 Control unit

[0143] 41 Flow sensor

[0144] 42 Oil pump outlet

[0145] 43 Differential pressure relief valve

[0146] 44 Temperature sensor

[0147] 50 compressor housings

[0148] 51 Air intake

[0149] 52 Compressed air outlet

[0150] 53 Compressor element

[0151] 54 Rotor shaft 55a, b Bearing

[0152] 56 Rotation axis

[0153] 100 oil-free compressor

[0154] 200 Oil circuit Pl Oil pressure (oil injection pressure) P2 Oil pressure

[0155] P2soii Target oil pressure

[0156] T1 oil temperature

[0157] T2 oil temperature

[0158] VI Oil flow (oil injection flow) Vlsoll Target oil flow

Claims

Claims 1. Oil circuit (200) for supplying an oil-free compressor (100), in particular at least one bearing (55a, 55b), a drive and / or a gear of the compressor (100), with oil, wherein the oil circuit (200) comprises: - an oil reservoir (1); - an oil pump (3) for conveying oil from the oil reservoir (1) to the compressor (100), in particular to the at least one bearing (55a, 55b), a drive and / or a gear of the compressor (100), through an oil supply line (4, 4a, 4b, 4c) which connects an oil pump outlet (42) to at least one oil inlet (19, 19a, 19b) of the compressor (100); - an oil cooler (6) arranged downstream of the oil pump (3) in a section of the oil supply line (4, 4a, 4b, 4c); - an oil recirculation line (14, 14a, 14b) branching off from the oil supply line (4a) downstream of the oil pump (3) and upstream of the oil cooler (6) and leading to the oil reservoir (1); - a valve (20), preferably an overflow valve, for regulating an oil flow in the oil recirculation line (14, 14a, 14b).

2. Oil circuit (200) according to claim 1, wherein the oil circuit (200) comprises an oil filter (7) which is arranged in a section of the oil supply line (4, 4a, 4b, 4c) upstream, preferably immediately upstream, of the oil inlet (19, 19a, 19b) of the compressor (100) and preferably downstream of the oil cooler (6), wherein the oil circuit (200) preferably comprises a bypass line (15) bypassing the oil filter (7) and having a differential pressure relief valve (43).

3. Oil circuit (200) according to claim 1 or 2, wherein, for regulating an oil flow in the oil recirculation line (14, 14a, 14b), at least one oil parameter (P2, TI, T2, VI), in particular an oil pressure (P2), an oil temperature (TI, T2) and / or an oil flow (VI), of the oil in the oil supply line (4c) downstream of the oil filter (7) and / or in the oil supply line (4b) downstream of the oil cooler (6) can be tapped, wherein preferably an oil injection pressure at the oil inlet (19, 19a, 19b) of the compressor (100) and / or an oil injection flow downstream of the branching point (9) can be tapped.

4. Oil circuit (200) according to one of the preceding claims, wherein the valve (20), preferably an overflow valve, is designed to regulate the oil flow in the oil recirculation line (14, 14a, 14b) based on an oil pressure (P2) tapped as a control pressure in the oil supply line (4, 4a, 4b, 4c), preferably downstream of the oil filter (7) and / or downstream of the oil cooler (6), preferably in such a way that the tapped oil pressure (P2) corresponds to a preferably variably adjustable, predetermined target oil pressure (P2 So n), wherein in particular a control connection (30) of the valve (20) is connected to the oil supply line (4, 4a, 4b, 4c) via a hydraulic control line (11) downstream of the oil filter (7) and / or downstream of the oil cooler (6).

5. Oil circuit (200) according to one of the preceding claims, in particular according to claim 4, wherein the valve (20) is designed to variably predetermine the desired oil pressure (P2soii) by adjusting a spring preload of a spring element (22) of the valve (20), wherein preferably a closure body (27) for a flow opening (31) of the valve (20) is subjected to the adjusted spring preload.

6. Oil circuit (200) according to one of the preceding claims, in particular according to one of claims 4 or 5, wherein the control line (11) is connected to a damping chamber of the valve (20) and / or the control line (11), preferably upstream of the control connection (30), has a throttle section (12), wherein the damping chamber and / or the throttle section (12) are in particular for Damping a movement of a closure body (27) of the valve (20).

7. Oil circuit (200) according to one of the preceding claims, in particular according to one of claims 4 to 6, wherein the valve (20), preferably an overflow valve, has a closure body (27) for changing at least one flow opening (29) of the valve (20), wherein the closure body (27) is displaceably guided in a valve housing (21), preferably in a valve insert (28), such that the closure body (27) is subjected to a closing force by a spring element (22), with a preferably adjustable spring preload, wherein a control pressure applied to a control connection (30) of the valve (20) exerts an opening force on the closure body (27) which counteracts the closing force.

8. Oil circuit (200) according to one of the preceding claims, in particular according to one of claims 1 to 3, wherein a sensor (8, 13, 41, 44) for detecting an oil parameter (P2, TI, T2, VI) of the oil in the oil supply line (4, 4a, 4b, 4c), preferably a pressure sensor (8) for detecting an oil pressure (P2), a temperature sensor (13, 44) for detecting an oil temperature (TI, T2) and / or a flow sensor (41) for detecting an oil flow (VI), is provided downstream of the oil filter (7) and / or downstream of the oil cooler (6), which sensor is preferably connected to a control unit (40) in a signal-transmitting manner.

9. Oil circuit (200) according to one of the preceding claims, in particular according to claim 8, wherein the valve (20) comprises a control unit (40) and / or is designed for connection to a control unit (40), preferably of the compressor (100), wherein the control unit (40) is designed to control an actuator (35) of the valve (20) based on at least one detected oil parameter (P2, T1, T2, V1), preferably based on at least one detected oil pressure (P2) and / or oil flow (V1), for regulating the oil flow in the oil recirculation line (14, 14a, 14b) in such a way that the detected oil parameter (P2, V1) approaches a predetermined target oil parameter (P2 S oii, Vlsoii), preferably a target oil pressure (P2 So n) and / or a target oil flow (Vlsoii).

10. Oil circuit (200) according to one of the preceding claims, in particular according to one of claims 8 or 9, wherein the target oil parameter (P2SO II, Vlsoii), preferably target oil pressure (P2 So n) and / or desired oil flow (Vlsoii), depending on at least one of the following operating parameters, preferably variable, can be specified, preferably automatically by a control unit (40): - a determined, preferably measured, oil temperature of the oil in the oil circuit (200), in particular oil temperature (TI, T2) of the oil in the oil supply line (4, 4c) downstream of the oil filter (7) and / or in the oil supply line (4, 4b) downstream of the oil cooler (6); - a temperature-dependent determined, preferably measured, viscosity of the oil, in particular in the oil supply line (4, 4a, 4b, 4c); - a specific, preferably measured, bearing temperature of the at least one bearing (55a, 55b); - a predetermined or measured drive speed of a drive of the compressor (100) and / or a predetermined or measured speed of the compressor (100); - a predetermined or determined, preferably measured, final compression pressure of a compressing gas produced by the compressor (100), preferably a screw compressor, in particular the compressed air produced; - an operating state of the compressor (100), in particular idle or load operation.

11. Oil circuit (200) according to one of the preceding claims, in particular according to one of claims 8 to 10, wherein the control unit (40) is designed to regulate the oil flow in the oil recirculation line (14, 14a, 14b) through the valve (20) during a cold start of the oil circuit (200), in particular during a cold start of the compressor (100), such that a predetermined maximum permissible oil filter differential pressure across the oil filter (7) is not exceeded, wherein, preferably, for determining the oil filter differential pressure by the control unit (40), a differential pressure sensor is provided across the oil filter (7) and / or a first oil pressure (PI) is detected downstream of the oil pump (3) and upstream of the oil filter (7), preferably by a pressure sensor (5), and a second oil pressure (P2) is detected downstream of the oil filter (7) and upstream of an oil inlet (19, 19a, 19b), preferably by a pressure sensor (8).

12. Oil circuit (200) according to one of the preceding claims, wherein the valve (20), preferably an overflow valve, is designed as a proportional valve, wherein the closure body (27) has a plurality of flow openings (29) with an opening cross-section that changes in the axial direction of the closure body (27), which in particular define a defined flow characteristic of the valve (20), preferably a linear or equal-percentage flow characteristic.

13. Oil-free compressor (100), preferably a screw compressor, for generating compressed gas, preferably compressed air, for a consumer, comprising an oil circuit (200) for supplying the compressor (100) with oil according to one of claims 1 to 12, wherein the compressor (100) and the oil pump (3) preferably have a coupled drive, in particular are driven by a common drive unit.

14. Method for controlling an oil parameter, preferably oil pressure and / or oil flow, for the oil supply of an oil-free compressor, in particular a compressor (100) according to claim 13, in particular at least one bearing (55a, 55b), a drive and / or a transmission of the compressor (100), comprising the following steps: - Pumping oil in an oil circuit (200), in particular according to one of claims 1 to 12, with an oil pump (3) from an oil reservoir (1) to at least one oil inlet (19, 19a, 19b) of the compressor (100) through an oil supply line (4, 4a, 4b, 4c) which connects an oil pump outlet (42) to the at least one oil inlet (19, 19a, 19b) of the compressor (100), wherein downstream of the oil pump (3) in a an oil cooler (6) is arranged in a section of the oil supply line (4, 4a, 4b, 4c); - preferably tapping an oil parameter (P2, TI, T2, VI) downstream of an oil filter (7) and / or downstream of the oil cooler (6); - recirculating oil to the oil reservoir (1) through an oil recirculation line (14, 14a, 14b) which branches off from the oil supply line (4, 4a, 4b, 4c) downstream of the oil pump (3) and upstream of the oil cooler (6) and leads to the oil reservoir (1); - actuating a valve (20), preferably an overflow valve, in particular based on the tapped oil parameter (P2, TI, T2, VI), for regulating an oil flow in the oil recirculation line (14, 14a, 14b), preferably in such a way that the oil parameter (P2, VI) corresponds to a predetermined target oil parameter (P2 S oii, Vlsoii) is adjusted.

15. The method according to claim 14, wherein the target oil parameter (P2 S oii, Vlsoii), preferably target oil pressure (P2 So n) and / or desired oil flow (Vlsoii), depending on at least one of the following operating parameters, preferably variable, is predetermined, preferably by a control unit (40): - a determined, preferably measured, oil temperature of the oil in the oil circuit (200), in particular oil temperature (TI, T2) of the oil in the oil supply line (4, 4a, 4b, 4c) downstream of the oil filter (7) and / or in the oil supply line downstream of the oil cooler (6); - a temperature-dependent determined, preferably measured, viscosity of the oil, in particular in the oil supply line (4, 4a, 4b, 4c); - a specific, preferably measured, bearing temperature of the at least one bearing (55a, 55b); - a predetermined or measured drive speed of a drive of the compressor (100) and / or a predetermined or measured speed of the compressor (100); - a predetermined or determined, preferably measured, final compression pressure of a compressor (100), preferably screw compressor, generated compressing gas, in particular the generated compressed air; - an operating state of the compressor (100), in particular idle or load operation.

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