Abstract:
A lubricant circuit includes, but is not limited to a lubricant pump, which is connected on the suction side to a reservoir and on the pressure side to a distributor, at least one lubricating point, which is connected to the distributor and a return leading to the reservoir, and an electronic control unit, which is set up to regulate the output pressure of the lubricant pump by reference to the temperature of the lubricant.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to German Patent Application No. 102010019007.1, filed May 3, 2010, which is incorporated herein by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The technical field relates to a lubricant circuit, in particular for the lubrication of an internal combustion engine such as an Otto or diesel engine in an automobile. 
       BACKGROUND 
       [0003]    Since the lubricant requirement of such an internal combustion engine increases with its speed, the lubricant circuit usually comprises a lubricant pump firmly coupled to an output shaft of the internal combustion engine and driven by means of this. As a result of this coupling, the throughput of the lubricant pump increases with the speed of the internal combustion engine. Since the lubricant throughput of the engine is not exactly linearly proportional to the rotational speed, but depends on other factors, in particular the temperature of the internal combustion engine, the lubricant pump must be designed to provide a sufficient amount of lubricant under all operating conditions. If the amount of lubricant conveyed by the pump is greater than the throughput of the internal combustion engine, the pressure at the output of the lubricant pump and an oil gallery connected thereto, which leads to the individual lubricating points, and the proportion of the power of the internal combustion engine, which must be applied for driving the lubricant pump, increases. 
         [0004]    In order to prevent damage in the lubricant circuit due to too-high pressure at the output of the pump, it is usual to provide a pressure relief valve directly at the output of the lubricant pump, via which lubricant can flow back into a reservoir when the pressure at the output of the pump exceeds a limiting valve. Such exceeding of the limiting value usually occurs when cold starting an internal combustion engine since the pressure then increases substantially faster than in continuous mode and the pressure at the pump outlet can shoot above the limiting value before it has disseminated to a regulating device disposed downstream in the oil gallery and this is able to counteract it. For this reason the pressure relief valve is also designated as cold start valve. The cold start valve certainly offers effective protection from critically high pressures in the lubricant circuit but energy is lost uselessly every time that the cold start valve lets lubricant through. 
         [0005]    In order to be able to operate an internal combustion engine energy-efficiently, it would therefore be desirable to have a lubricant circuit which, on the one hand, is capable of supplying the internal combustion engine with sufficient lubricant, but which on the other hand can restrict to a minimum or even completely avoid unnecessarily high lubricant pressures, which make it necessary to trip a cold start valve. If the occurrence of such a critically high pressure in the lubricant circuit can be completely avoided, the cold start valve can also be omitted, which in turn leads to cost advantages. 
         [0006]    In view of the foregoing, objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background. 
       SUMMARY 
       [0007]    A lubricant circuit, in particular for an internal combustion engine, comprising a lubricant pump, which is connected on the suction side to a reservoir and on the pressure side to a distributor, at least one lubricating point, which is connected to the distributor and a return leading to the reservoir, and an electronic control unit for controlling the operation of the pump, the control unit being set up to regulate the output pressure of the lubricant pump by reference to the temperature of the lubricant. Since the temperature of the lubricant can be determined even before starting the internal combustion engine, it is possible to suitably predefine a desired output pressure of the lubricant pump at the starting time of the internal combustion engine, so that pressure peaks at the output of the pump, which must conventionally be intercepted via the cold start valve, can be avoided a priori. 
         [0008]    According to a first embodiment, the control unit can be set up to estimate the temperature of the lubricant by reference to a model. Such a model can, for example, estimate the lubricant temperature by using the behavior of the engine load in the past and optionally other parameters. Naturally, the control unit can alternatively be connected to a temperature sensor. Conventional automobile engines provide no sensors for detecting the oil temperature but measured values of a coolant water temperature sensor usually provided can readily be used to estimate the oil temperature. In order to be able to estimate the oil temperature at least occasionally after the internal combustion engine has been at a standstill for a fairly long time, an intake air temperature sensor can also be used, which is present in any case in many modern automobiles for controlling the mixture. 
         [0009]    Since, at high temperature of the internal combustion engine (and the lubricant), the lubricant throughput of the internal combustion engine is generally high and the viscosity of the lubricant is low, it is expedient to select the output pressure to be higher, the higher the detected temperature. In practice, a simple threshold value control is sufficient, at which the control unit sets a low or a high output pressure of the lubricant pump depending on whether the detected temperature is below or above a limiting temperature. 
         [0010]    Since the lubricant throughput of the internal combustion engine can also depend on influences other than the speed and the temperature or can be in a non-exactly linear relationship with the speed, it is expedient to use a pump having a variable conveying rate as lubricant pump. Particularly preferred is a vane pump comprising a housing and a rotor, whose eccentricity relative to one another can be varied under the influence of the pressure prevailing in the distributor to control the conveying rate. In practice, the axis of the rotor of such a vane pump is preferably fixed in relation to a holder of the pump and a change of the eccentricity is effected by adjusting the housing of the pump relative to the axis of rotation in the radial direction. 
         [0011]    A first actuator communicating with the distributor can expediently be provided to drive the adjustment of the eccentricity. The actuator can in particular act on the one hand on the housing and on the other hand on the rotor of the lubricant pump or on the holder. 
         [0012]    In order to make the output pressure of the vane pump temperature-dependent, the electronic control unit preferably controls a valve, which optionally connects to the distributor or separates from the distributor a second actuator, which is disposed to adjust the eccentricity of the lubricant pump. If both the first and the second actuator are provided on the lubricant circuit, they are then expediently disposed so that they adjust the eccentricity of the lubricant pump in the same direction. If both actuators mutually support each other in this manner, a lower pressure at the output of the pump is sufficient to achieve a given change of the eccentricity and therefore a given change of the conveying rate of the pump, than is the case if only a single actuator is effective. 
         [0013]    In order that the second actuator does not block the movement of housing and rotor toward one another when it is separated from the distributor by the valve, the valve is preferably designed as a directional valve, which in one position in which it separates the second actuator from the distributor, connects it to the reservoir. Whereas the first actuator is generally connected to a downstream portion of the distributor in order to ensure that a requisite pressure is reached there, the valve is preferably connected to an upstream portion of the distributor to enable a rapid response of the second actuator to pressure fluctuations at the output of the pump. This is particularly expedient if a throttle element, in particular a lubricant cooler and/or a lubricant filter, is disposed between the upstream and the downstream portion of the distributor, which effects a pressure drop from the upstream to the downstream portion and/or delays the dissemination of a high pressure from the output of the pump to the downstream portion. 
         [0014]    In order to ensure a sufficient lubricant supply with at the same time high safety from impermissible excess pressures under all operating conditions of the internal combustion engine, it is expedient that the control unit is set up to further regulate the output pressure of the lubricant pump by means of the speed of the internal combustion engine. For this purpose, it can be connected to a speed sensor on a shaft of the internal combustion engine. 
         [0015]    The above-mentioned limiting temperature is then expediently a function of the speed or, which amounts to the same thing, at every temperature there is a limiting speed below which the control unit sets the low output pressure and above which it sets the high output pressure. The limiting temperature is expediently lower, the higher the detected speed or the higher the temperature, the lower the limiting speed above which the control unit switches to the high output pressure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and: 
           [0017]      FIG. 1  shows a block diagram of a lubricant circuit according to an embodiment; and 
           [0018]      FIG. 2  shows switching characteristics of the control unit at different starting temperatures. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The following detailed description is merely exemplary in nature and is not intended to application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or summary or the following detailed description. 
         [0020]      FIG. 1  shows a schematic diagram of an oil circuit in an automobile engine. A vane pump  1  is connected via a suction line  2  to an oil sump  3 . A distributor connected to the vane pump  1  on the pressure side comprises a supply line  4 , on which an oil filter  5  and an oil cooler  6  are disposed in series, and a gallery  7  from which branch lines  8  branch off to various lubricating points  9  of the engine such as bearings of a crankshaft  10 . From the lubricating points  9  the oil runs back into the oil sump  3  unguided. 
         [0021]    The vane pump  1  has in a manner known per se a housing  11  having a cylindrical cavity, in which there is provided a rotor  12  having a plurality of vanes  13  held by positioning rings in contact with an inner surface of the housing  11 , which divide the cavity into a plurality of cells. The rotor  12  has a fixed axis of rotation, against which the housing  11  can be moved transversely to the axis of rotation under the influence of a spring  14  and two hydraulic actuators  15 ,  16 . In practice, this movement is usually a pivoting movement about an axis running parallel to the axis of rotation of the rotor, outside the housing  11 . The two actuators drive a displacement of the housing  11  in the same direction, opposite to the driving direction of a spring  14 , which can be envisaged as a compressive spring in the diagram in  FIG. 1 . The actuators  15 ,  16  are shown schematically in  FIG. 1 , in each case comprising a cylinder and a piston which is displaceable in the cylinder, the piston acting on the housing  11  and the cylinder being rigidly connected to a bearing of the axis of the rotor  12 . In practice, the actuators are usually implemented as pressure chambers, which are delimited on the one hand by a one-piece frame part not shown in  FIG. 1  and on the other hand, by outer surfaces of the housing  11 , on which the pressure of the oil in the pressure chambers acts directly. 
         [0022]    The spring  14  and the actuators  15 ,  16  are each disposed in such a manner that a force exerted by the spring  14  works toward an increase of the eccentricity of the rotor  12  in relation to the housing  11  and therefore an increase of the conveying rate of the pump  1 , pressure of the actuators  15 ,  16  on the other hand works toward a reduction of the eccentricity and the conveying rate. 
         [0023]    A control chamber of the actuator  15  is connected via a measuring line  17  to a downstream end of the gallery  7  so that the pressure prevailing in the gallery  7  also exists in the control chamber of the actuator  15  and exerts a force acting against the spring  14  on the housing  11 . The cross-sectional area of the control chamber of the actuator  15  and the strength of the spring  14  are matched to one another such that if the second actuator  16  is pressure less, an oil pressure of approximately 4 bars is reached in the gallery in stationary operation. 
         [0024]    When starting the engine, the gallery  7  is pressure less and the spring  14  holds the housing  11  in a position of maximum eccentricity. Consequently, the conveying rate of the pump  1  is maximal when starting the engine, which is also expedient per se on order to build up an effective oil supply at all lubricating points  9  in the shortest possible time. However, as a result of the low temperature of the engine, a high conveying rate of the pump  1  accompanied by high viscosity of the oil and a low volumetric flow requirement brings about a temporarily too-high pressure which can damage components and which must therefore be avoided. In order to achieve this, the actuator  16  is connected via a second measuring line  18  directly to the pressure output of the vane pump  1 . For this purpose the measuring line  18  is kept as short as possible and preferably runs completely inside a structural unit, in which the vane pump  1  and the two actuators  15 ,  16  are combined. Whereas in practice it can take several seconds before a high pressure at the output of the vane pump  1  has disseminated over the entire distributor as far as the actuator  15 , this pressure acts on the actuator  16  almost without delay. The cross-section of its control chamber is exactly the same size as that of the actuator  15  so that if both actuators  15 ,  16  are pressurized, a pressure of 2 bar is established on the gallery  7  in the stationary state. 
         [0025]    Even if on starting the engine, the pressure of the oil conveyed by the pump  1  has not yet propagated as far as the actuator  15 , the actuator  16  is effective to avoid critical pressure on the supply line  4 , which could damage the oil filter  5 . 
         [0026]    In order to ensure sufficient lubrication of the lubricating points  9  (e.g., bearings) at higher speeds, the gallery  7  should be able to reach a pressure of approximately 4 bars. For this purpose a directional valve  19  is disposed in the measuring line  18 , which is capable of interrupting the measuring line  18  and making the control chamber of the actuator  16  pressure less via a connecting line  20  leading to the oil sump  3 . If the actuator  16  is pressure less, merely the actuator  15  controls the conveying rate of the pump  1  or the pressure on the gallery  7 . 
         [0027]    The directional valve  19  is controlled by an electronic control unit  21 , which is connected to a temperature sensor  22  and a speed sensor  23 . The control unit  21  is preferably implemented in the form of an additional software module of a program-controlled engine control unit (ECU) known per se. Since such engine control units are conventionally usually connected to a temperature sensor to detect the cooling water temperature of the engine and a speed sensor, the control unit  21  can be achieved with minimal expenditure. The control unit  21  is programmed to initially switch the measuring line  18  to transmitting for a short time whenever the engine is started and thus apply pressure to the actuator  16  from the output of the pump  1 . The time of switching to the pressure less state of the actuator  16  depends on the speed of the crankshaft  10  and on the measured temperature, as is shown in  FIG. 2  by reference to several curves C 1  to C 8 . C 1  describes the behavior of the control unit  21  at a temperature approximately of −30° C.: the control unit  21  only switches the actuator  16  pressure less at an extremely high speed between approximately 5000 and approximately 6000 rpm in order to increase the oil pressure in the gallery  7  from approximately 2 to approximately 4 bars. The same switching threshold applies at a temperature of approximately −20° C. (C 2 ). At approximately −10° C. (C 3 ), the switching threshold is reduced to a value between approximately 4000 and approximately 5000 rpm. The same value also applies at a temperature of approximately 0° C. In the range of approximately 10 to approximately 20° C. (C 5 , C 6 ), the switching threshold is reduced to approximately 3000 to approximately 4000 rpm and at temperatures of approximately 60° C. and above which occur in continuous operation, the switching threshold is approximately 2000 to approximately 3000 rpm (C 7 , C 8 ). Since the pump  1  can therefore be operated at reduced output pressure at standstill temperatures of the engine, the energy requirement for conveying a given amount of oil at times when the oil requirement of the engine is low due to low speed, can be reduced, which allows additional energy savings when operating the oil circuit. 
         [0028]    While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.