Abstract:
The invention relates to an oil pump for an internal combustion engine with at least one pair of toothed wheels which are in mutual engagement, at least one intake port and at least one outlet port. An improved supply of oil at reduced driving power can be achieved with at least two pairs of toothed wheels; a first common shaft, which a first toothed wheel of each pair of toothed wheels is arranged, and means are provided to charge the individual pairs of toothed wheels with oil depending on the required quantity of conveyed oil.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an internal combustion engine with internal combustion with at least one pair of toothed wheels which are in mutual engagement, at least one intake port and at least one outlet port. 
     DESCRIPTION OF THE PRIOR ART 
     Oil pumps for internal combustion engines which are intended for motor vehicles in particular are usually arranged as gear pumps. They consist of a pair of toothed wheels which are in mutual engagement, with the conveyance of oil being caused by the displacement effect of the teeth. The conveying effect of such gear pumps substantially depends linearly on the speed of rotation with which these gear pumps are driven. As the drive is generally performed directly by way of the internal combustion engine, the pump output is therefore substantially proportional to the rotational speed of the internal combustion engine. The oil quantity required for the operation of the internal combustion engine, however, is not linearly dependent on the rotational speed. This means that in a number of speed ranges, namely particularly at low engine speeds, there is a danger of a lack of supply with oil, whereas in other engine speed ranges a relatively large quantity needs to be removed by way of pressure control valves. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to improve an oil pump of the kind mentioned above in such a way that these disadvantages are avoided. It is the object of the present invention in particular to reduce the energy requirements for the drive of an oil pump in order to increase the total efficiency of internal combustion engines. These objects are achieved in accordance with the invention with at least two pairs of toothed wheels, a first common shaft on which a first toothed wheel of each pair of toothed wheels is arranged and means are provided in order to charge with oil the individual pairs of toothed wheels depending on the required quantity of conveyed oil. 
     In the case of the solution in accordance with the invention it is possible to adjust the oil pump output in certain stages to the actual demand. Although the dependence of the conveying quantity on the rotational speed is principally still retained in the solution in accordance with the invention, the factor of proportionality can be changed. 
     The solution in accordance with the invention is arranged in such a way that in the case of a relatively low demand for oil only one pair of toothed wheels will assume the actual conveyance. In the case of maximum oil demand all pairs of toothed wheels are used in parallel with one another for the conveyance. 
     In order to prevent no-load losses to the highest possible extent, it is advantageous that each pair of toothed wheels is assigned an own intake port and an own outlet port and that a valve is provided in order to optionally connect at least one intake port with the associated outlet port. The idly running pair(s) of toothed wheels is/are operated in circulation and substantially pressureless, so that cooling and lubrication are ensured and that with the exception of frictional losses no driving torque is required for the movement of the toothed wheels. 
     In a particularly simple embodiment of the present invention it is provided that a control valve is provided in order to optionally supply the individual pairs of toothed wheels with oil and that the oil pressure in the outlet line is used as a control pressure for said control valve. As an alternative it may also be provided that an electronic control apparatus is provided in order to charge with oil the individual pairs of toothed wheels. The oil pump in accordance with the invention can be controlled in an intelligent manner by the engine management. In this way it is also possible to cover any additionally required oil demand which can result from an apparatus for changing the setting angle of a camshaft for example. 
     There is an increase in the number of possibilities for adjustment in that the individual pairs of toothed wheels have a different width. In an oil pump with two pairs of toothed wheels, for example, this allows achieving three different characteristic performance curves. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be explained in closer detail by reference to the embodiments shown in the figures, wherein: 
     FIG. 1 schematically shows an embodiment of the present invention; 
     FIG. 2 shows a sectional view through an oil pump in accordance with the invention; and 
     FIG. 3 shows a diagram in which the conveyed quantity is entered over the drive speed. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The oil pump in accordance with the invention consists of a housing  1  in which two chambers  2 ,  3  are provided which are separated from one another by a separating wall  4 . A pair of toothed wheels is disposed in the first chamber, which pair consists of the toothed wheels  5   a ,  5   b , whereas a pair of toothed wheels consisting of the toothed wheels  6   a ,  6   b  is provided in the second chamber  3 . The toothed wheels  5   a ,  6   a  are attached to a common shaft  7  which is also used for the drive of the pump. A first intake port  8   a  is in connection with chamber  2 , whereas a second intake port  9   a  is in connection with chamber  3 . A first outlet port  8   b  leads away from the chamber  2 , whereas a second outlet port  9   b  leads away from the second chamber  3 . A control valve  10  is provided to switch over to the different operating modes of the oil pump. 
     In a first position of the control valve  10 , which is arranged as a sliding valve, an intake line  11 , which leads to a reservoir  12  such as an oilpan of an internal combustion engine (not shown), is connected with the first intake port  8   a . The first outlet port  8   b  is placed in connection with an oil supply line  13  which leads to the components to be lubricated. Furthermore, the second intake port  9   a  and the second outlet port  9   b  are mutually connected in this position of the valve  10 , so that the pair of toothed wheels  6   a ,  6   b  is operated in short circuit. 
     In a second position of the valve  10  the switching of the first intake port  8   a  and the outlet port  8   b  and the second intake port  9   a  and the outlet port  9   b  is reversed. Therefore, the pair of toothed wheels  5   a ,  5   b  is operated in short circuit while the oil conveyance occurs by way of the pair of toothed wheels  6   a ,  6   b.    
     As the pair of toothed wheels  6   a ,  6   b  is provided with a wider arrangement than the pair of toothed wheels  5   a ,  5   b , the output of the oil pump is increased in this state. 
     In a third switching position of valve  10  the two intake ports  8   a ,  9   a  are connected with the intake line  11  and both outlet ports  8   b ,  9   b  are connected with the oil supply line  13 . The quantity of oil conveyed by the pump is the highest in this state. 
     The control of the valve  10  can occur in accordance with the invention in such a way that in the case of low oil pressure the control valve  10  will be in the third position in any case. When exceeding a first pressure threshold the changeover to the second state can occur. When this pressure is reached again, a changeover to the third state can occur. As an alternative to this, however, the changeover of valve  10  can also be effected by the engine management. This leads to the additional advantage that during cold starting for example or in any other operating state where a high quantity of conveyed oil is required, valve  10  can be brought to the third position. Even if additional oil consumer sources such as certain actuating apparatuses are triggered, the engine management can already make available, in an anticipatory manner, a higher oil pressure. 
     FIG. 2 shows a possible embodiment of an oil pump in accordance with the invention. An internal toothed wheel  15   a  and a toothed wheel  15   b  which is in engagement with said internal toothed wheel  15   a  are provided in a housing  1 . Toothed wheels  15   a  and  15   b  are arranged eccentrically with respect to one another in order to be in engagement. A guide element  16  is provided in the gap between the toothed wheels  15   a  and  15   b , which guide element separates the intake chamber  17  from the outlet chamber  18 . It is assumed that the toothed wheels  15   a ,  15   b  rotate in the direction of arrow  19 . 
     FIG. 3 shows the oil demand and the quantity of conveyed oil of an oil pump according to the state of the art and of an oil pump according to the present invention, entered over the rotational speed n of the internal combustion engine. Curve  20  corresponds to the under proportionally increasing oil demand of the internal combustion engine. The unbroken straight line  21  corresponds to the conveyed oil quantity of a known oil pump. The stepped line  22 , which is shown as a broken line, corresponds to the characteristic curve of an oil pump in accordance with the invention. FIG. 3 shows that the output of the known oil pump pursuant to the characteristic curve  21  increases substantially more rapidly than the oil demand (curve  20 ). Although there is a range  23  in the range of low speeds in which the conveyed oil quantity is too low with the known pump, the conveyed oil quantity at higher speeds is substantially higher than the actual demand. This means that a relatively large quantity of oil has to be removed by way of the pressure control valve and that consequently a relatively large amount of driving power of the oil pump is uselessly consumed in this speed range. In contrast to this, the characteristic curve  22  of the oil pump in accordance with the invention is above curve  22 , which indicates the oil demand, in all speed ranges. The oil supply of the engine is thus improved as compared with the state of the art. Nevertheless, the oil quantity to be removed in the upper speed range is considerably lower than than the one in the known oil pump. FIG. 3 shows that the switching times at which the output of the oil pump is reduced is chosen at 2000 revolutions and at 3500 revolutions. As has already been explained above, it is not necessary to make the switching times dependent on the engine speed. Instead, they can be chosen depending on a plurality of operational parameters. 
     The present invention allows providing an oil pump which, on the one hand, ensures a better supply of the engine with oil and, on the other hand, has a lower power requirement.