Patent Publication Number: US-2019186303-A1

Title: Oil supply device for a vacuum pump of an internal combustion engine

Description:
FIELD 
     The invention relates to an oil supply device for a vacuum pump of an internal combustion engine, in particular of a car, comprising an oil feed line via which the vacuum pump can be supplied with oil for lubricating the vacuum pump. 
     BACKGROUND 
     Vacuum pumps are used to actuate pneumatic components of an internal combustion engine or of a car. Pneumatic components of this kind include, for example, what are referred to as vacuum boxes, which are used to actuate EGR valves (exhaust gas recirculation valves), for example. It is further known to actuate what are referred to as intake pipe connections of an internal combustion engine by means of at least one such vacuum box, for example. Vacuum pumps are additionally used to supply brake boosters of cars with negative pressure. In order to achieve a particularly trouble-free operation of vacuum pumps, said pumps are generally lubricated with oil. 
     DE 10 2016 106 165 A1 discloses an internal combustion engine comprising a vacuum pump in which an oil passage is formed. The oil passage is connected to a vacuum chamber in order to conduct oil to respective sliding portions, for example a blade and a rotor of the vacuum pump. 
     After the internal combustion engine is cut off, the vacuum pump may be disadvantageously filled with lubricating oil (oil) due to a negative pressure remaining in the vacuum pump. The vacuum pump can be filled owing to its installation position, i.e. the geodetic height in relation to a lubricating oil circuit supplying the vacuum pump with oil. In order to avoid damage to the vacuum pump, the oil located in the vacuum pump is pumped or displaced out of said pump during the first rotation for example of a blade element of the vacuum pump when the internal combustion engine is started. Since the vacuum pump is generally driven by a crankshaft of the internal combustion engine, prevailing oil pressures occurring in the vacuum pump when the internal combustion engine is started depend on a starting gradient of the internal combustion engine, i.e. in other words on an acceleration of the crankshaft when the internal combustion engine is started, and on the gear ratio between the vacuum pump and the crankshaft. The higher the starting gradient of the internal combustion engine, the higher the oil pressures occurring in the vacuum pump, it being possible for damage to the vacuum pump to occur at particularly high oil pressures. 
     For hybrid cars, which can be driven both by the internal combustion engine and by at least one electric motor, there is a particularly high starting gradient at what is known as a hybrid start of the internal combustion engine, i.e. when the internal combustion engine is started after previous electric drive, and therefore component failure can occur on the vacuum pump owing to the correspondingly high oil pressure. 
     SUMMARY 
     The problem addressed by the present invention is that of providing an oil supply device of the above-mentioned type, by means of which component failure of the vacuum pump can be particularly effectively prevented. 
     This problem is solved by an oil supply device having the features of claim  1 . Advantageous embodiments comprising expedient developments of the invention are specified in the remaining claims. 
     The invention relates to an oil supply device for a vacuum pump of an internal combustion engine, in particular of a car, comprising an oil feed line via which the vacuum pump can be supplied with oil for lubricating the vacuum pump. The internal combustion engine can preferably be used in a car designed as a hybrid car, i.e. in a car which can be driven both by means of the internal combustion engine and by means of at least one electric motor. The vacuum pump can be supplied with oil (lubricating oil) via the oil feed line, which can extend, for example, through a cylinder head or a camshaft of the internal combustion engine and which can be designed as an oil duct. 
     In order to particularly effectively prevent component failure of the vacuum pump, it is provided according to the invention that the oil feed line comprises a valve connected to the oil feed line in an oil-conducting manner, which valve has a piston that is accommodated in a valve interior of the valve and can move at least between a supply position in which it allows a supply of oil to the vacuum pump and a blocking position in which it prevents the supply of oil to the vacuum pump, and has a spring element, by means of which a spring force that holds the piston in the blocking position can be applied to the piston when the internal combustion engine is at rest. Owing to the piston and the spring element of the valve, which may also be referred to as an on-off valve, a supply of oil to the vacuum pump can be effectively prevented in the blocking position when the internal combustion engine is at rest. Overfilling with oil, which damages the vacuum pump, can thus be prevented irrespective of the starting gradient of the internal combustion engine and irrespective of an installation position of the vacuum pump. 
     In contrast to lift check valves known from the prior art (ball-spring valves), which can be integrated in respective lubricating oil lines of vacuum pumps and close, i.e. prevent, an oil flow, only after a negative pressure has built up within the vacuum pump, a particularly early prevention of the oil flow can be brought about by means of the present oil supply device or the valve by moving the piston into the blocking position. Significantly less oil thus reaches the vacuum pump than when using lift check valves known from the prior art. 
     As is likewise known from the prior art, providing ventilation holes for a feed chamber of the vacuum pump leads to a permanent air leakage and thus to an increased power input. Moreover, by means of ventilation holes of this kind, there is no protection against unfavorable filling of the vacuum pump with oil in an unfavorable installation position of the vacuum pump. In contrast, by means of the valve of the oil supply device, effective protection of the vacuum pump against an overfilling with oil can be achieved irrespective of the installation position of the vacuum pump. Moreover, an excessive power input of the vacuum pump can be effectively prevented by means of the valve. 
     In an advantageous development of the invention, the piston can be displaced from the blocking position into the supply position counter to the spring force by means of an oil pressure of the oil that is applied to the piston during operation of the internal combustion engine. This is advantageous since a separate actuation of the valve is not required to displace the piston from the blocking position into the supply position counter to the spring force. In other words, the valve and thus a piston-spring system of the valve can be switched depending on oil pressure applied to the piston during operation of the internal combustion engine. In this case, a corresponding switch point of the valve is designed such that a sufficient lubricating oil supply (oil supply) to the vacuum pump is achieved, but overfilling the vacuum pump with oil is avoided. 
     In another advantageous development of the invention, the valve has a ventilation aperture via which air can be exchanged between the valve interior and the surroundings of the valve when the piston moves between the blocking position and the supply position. This is advantageous since, as a result, air pressure can be prevented from occurring in the valve interior when the piston is moved. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Further advantages, features and details of the invention can be found in the following description of a preferred embodiment and with reference to the drawings. The features and combinations of features mentioned above in the description and the features and combinations of features mentioned below in the description of the figures and/or shown in the drawings alone can be used not only in the respectively given combination but also in other combinations or in isolation, without departing from the scope of the invention. 
       In the drawings: 
         FIG. 1  is a schematic view of a vacuum pump which can be supplied with oil via an oil supply device, a piston of a valve of the oil supply device being in a blocking position; 
         FIG. 2  is a sectional view of a portion of the oil supply device which shows the piston of the valve in the blocking position in which the piston prevents the supply of oil to the vacuum pump; and 
         FIG. 3  is another sectional view of the portion of the oil supply device, the piston being in a supply position in which it allows the supply of oil to the vacuum pump. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a vacuum pump  20  of an internal combustion engine (not further depicted here) comprising a blade element  22  which is rotatably accommodated in a working chamber  24  of the vacuum pump  20  in order to produce a negative pressure by rotating the blade element  22 . In order to supply the vacuum pump  20  with oil  12  for the lubrication thereof, an oil supply device  10  is provided which comprises an oil feed line  30  and a valve  40  connected to the oil feed line  30  in an oil-conducting manner. The valve  40  has a valve housing  44  which delimits a valve interior  42 . A piston  50  is accommodated in a valve interior  42  of the valve  40 , which piston can move between a supply position  52  in which it allows a supply of oil  12  to the vacuum pump  20  and a blocking position  54  in which it prevents the supply of oil  12  to the vacuum pump  20 .  FIG. 1  and  FIG. 2  show the piston  50  in the blocking position  54  thereof, whereas  FIG. 3  shows the piston  50  in the supply position  52  thereof. The oil feed line  10  further comprises a spring element  60 , by means of which a spring force F that holds the piston  50  in the blocking position  54  can be applied to the piston  50  when the internal combustion engine is at rest. 
     The piston  50  can be displaced from the blocking position  54  into the supply position  52  counter to the spring force F by means of an oil pressure p of the oil  12  that is applied to the piston  50  during operation of the internal combustion engine, as can be seen from looking at  FIG. 2  and  FIG. 3  together. 
     Moreover, the valve  40  has a ventilation aperture  70  via which air can be exchanged between the valve interior  42  and the surroundings of the valve  40  when the piston  50  moves between the blocking position  54  and the supply position  52 . 
     The valve  40  can also be referred to generally as a stop valve for supplying lubricating oil to the vacuum pump  20 , i.e. in other words as a stop valve for supplying oil  12  to the vacuum pump  20 .