DEVICE FOR LIMITING THE OIL PRESSURE IN THE LUBRICATING OIL CIRCUIT OF AN INTERNAL COMBUSTION ENGINE

Abstract: A device for limiting the oil pressure in the lubricating oil circuit of an internal combustion engine comprises an oil pump and a pressure relief valve (1) for unblocking an opening to form a connection between the pressure side and the suction side of the oil pump or between the pressure side of the oil pump and a sump. The pressure relief valve (1) includes a blocking member (3) movable against a biasing force in a valve housing (2) to unblock the opening. The opening is divided into at least two partial openings (9, 10), thereby forming a two-stage pressure relief valve which makes possible a better adaptation to the required engine oil pressure compared with conventional single-stage pressure relief valves of engine lubricating oil pumps.

Description: TITLE OF THE INVENTION Device for limiting the oil pressure in the lubricating oil circuit of an internal combustion engine. FIELD OF THE INVENTION The invention relates to a device for limiting the oil pressure in the lubricating oil circuit of an internal combustion engine, comprising an oil pump and a pressure relief valve for unblocking an opening to form a connection between the pressure side and the suction side of the oil pump or between the pressure side of the oil pump and a sump, which includes a blocking member movable against a biasing force in a valve housing to unblock the opening. BACKGROUND OF THE INVENTION AND PRIOR ART In order to avoid overloading and malfunctioning of components of the internal combustion engine and to keep down the delivery power of the oil pump, it is necessary to limit the maximum oil pressure. For this purpose it is known to use expensive pressure regulated oil pumps or even oil pumps which are provided with two individual pumps one of which is switched off in the upper engine speed region. The publication EP 0 624 719 Al discloses a pressure relief valve of the kind described above which at a predetermined pressure unblocks an opening through which the excess oil flows from the pressure side of the pump either to the suction side or to the oil sump. Although such pressure relief valves are often used, they cannot completely meet the requirements placed on the oil pressure. When idling, an internal combustion engine requires a minimum oil pressure in order to ensure lubrication of engine components such as, for example, the hydraulic plungers. Furthermore, at the maximum engine speed an internal combustion engine requires a minimum oil pressure in order ensure an adequate oil supply to the connecting rod bearings. When a conventional pressure relief valve of the kind described above is used to limit the pressure the oil pressure is unnecessarily high over a wide range of engine speeds . OBJECT OF THE INVENTION The object of the invention is to provide an improved pressure relief valve of the kind mentioned above with which a better adaptation to the oil pressure requirements of the internal combustion engine is possible. SUMMARY OF THE INVENTION To this end, according to the present invention the opening of the pressure relief valve is divided into at least two partial openings spaced apart from one another in the direction of movement of the blocking member. An advantage of this is that in the case of an increase in engine speed and an associated increase in oil pressure the two partial openings are unblocked in succession, namely at a first (lower) oil pressure value the first opening is unblocked and at a higher pressure the next opening is unblocked. When two partial openings are provided, the pressure relief valve thus operates in two stages, thereby giving a better adaptation to the pressure requirements of the engine oil than in the case of a pressure relief valve of the known design with only a single stage. In the lower and upper engine speed regions there is, in contrast to the conventional pressure relief valves, no difference in oil pressure, since the minimum requirements on the engine oil pressure in these regions are met in the same manner. In the middle engine speed range, however, the oil pressure can be markedly reduced by the use of the pressure relief valve made in accordance with the invention. Since over a wide range of engine speeds, both with cold and with hot oil, the oil pump pressure and consequently the oil pump delivery power can be markedly reduced, this leads at little expense to a reduction in the fuel consumption of the internal combustion engine. In a further embodiment of the invention the partial openings are of different sizes, with a main opening being preceded by a smaller first opening, so that at a predetermined oil pressure first of all the first opening is unblocked and at a predetermined higher oil pressure the main opening is also unblocked. According to yet another embodiment of the invention the shape and/or distance apart of the partial openings may be different. A greater distance between the partial openings results in the first stage setting in at a lower oil pressure than when the distance apart is smaller. The larger the first opening is made, the greater is the engine speed region in which the first (low) pressure step is available. When it is shown graphically in a diagram in which the oil pressure is plotted as ordinate and the engine speed as abscissa the gradient of the first pressure step is flatter in the case of an opening which, regarded in the direction of movement of the blocking member, is short but wide, than in the case of a long and narrow first opening. Thus through the selection of the size, the shape and the distance apart of the partial openings influence can be exerted on the oil pressure, particularly in the middle range of engine speed. The first opening may for example take the form of a slit-shaped opening, a bore, a triangular opening, or an oval opening. The two partial openings can be located in the valve housing. The openings can then be unblocked by the edge of the blocking member, which is usually in the form of a piston. Alternatively, however, the openings may be located in the blocking member. The openings are then respectively unblocked on reaching the edge of a groove (a so-called undercut) running round the inside of the housing . Finally, one partial opening could be located in the valve housing and a further opening in the blocking member. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail, by way of example, with reference to the embodiments shown schematically in the drawing, in which: Fig. 1 shows a diagrammatic longitudinal section through a first embodiment of a two-stage pressure relief valve in accordance with the invention; Fig. 2 shows a diagrammatic longitudinal cross section through a second embodiment of a two-stage pressure relief valve in accordance with the invention; and Fig. 3 shows a diagrammatic longitudinal cross-section through a third embodiment of a two-stage pressure relief valve in accordance with the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVEN- TION A pressure relief valve indicated generally by 1 has in a housing 2 a piston 3 which is movable in a cylinder bore 5 in the direction of the arrow A against the preload of a pressure spring 4. The spring 4 is retained by a plug 6. A pressure duct 7 connected to the pressure side of an oil pump (not shown) leads to the side of the piston 3 remote from the pressure spring 4. The suction side of the oil pump is indicated by 8. In the side of the cylinder bore two partial openings are provided, namely a first opening 9 and a main opening 10. The two partial openings 9 and 10 are spaced apart from one another by a distance B, so that when the oil pressure on the pressure side of the piston 3 increases, resulting in a movement of the piston in the direction of the arrow A, first of all the first opening 9 is unblocked and then, on a further increase in pressure, the main opening 10 is unblocked. As will at once be clear, after the unblocking of the first partial opening 9 part of the pressure oil can flow out through the opening 9 to the suction side 8 of the oil pump, so that excess oil flows from the pressure side to the suction side of the oil pump. In an internal combustion engine having a lubricating oil circuit with an oil pump and a pressure relief valve in accordance with the invention, this results in a fall in the oil pressure in the middle speed range compared with the use of a single-stage pressure relief valve. Both the oil pump pressure and the reduced pressure on the suction side of the oil pump are markedly lower in the middle engine speed range than in the case of conventional single-stage pressure relief valves. The second stage is unblocked by reaching the main opening 10 when a predetermined higher oil pressure is reached. A vent bore is indicated by the numeral 11. In Figures 2 and 3 the parts corresponding to those in Fig. 1 are indicated by the superscripts ' and ' ' respectively. A pressure relief valve 1' has a housing 2' and a blocking element in the form of a piston 3 ' , which is arranged to move in a cylinder bore 5 ' against the spring loading of a spring ' . A duct connected to the pressure side of an oil pump (not shown) is indicated by 7'. A plug carries the reference numeral 6 ' and a vent bore the reference numeral 8 ' . While in the embodiment shown in Fig. 1 the two partial openings 9 and 10 are located in the valve housing 2, in the pressure relief valve shown in Fig. 2 the two partial openings, here numbered 9' and 10', are located in the piston forming the blocking member 3 ' . The first opening 9 ' is angular, shaped as a slit, and may be sub-divided into a plurality of smaller openings distributed round the circumference of the piston. Spaced therefrom (regarded counter to the direction of movement A of the blocking element 3'), is the rounded main opening 10', which may, as shown, likewise be subdivided into a plurality of individual main openings 10' distributed round the circumference. A groove 12 running round the inside of the valve housing 3 ' opens in the vicinity of the suction side of the oil pump. When the piston 3 ' moves in the direction of the arrow A under the influence of the oil pressure prevailing in the duct 7, the openings 9' and 10' are successively unblocked as the openings reach the edge 13 of the groove 12. A vent bore is here designated 11'. In the further embodiment shown in Fig. 3 a partial opening forming a first opening is designated 9 ' ' . The first opening 9 ' ' is located in the valve housing 2 ' ' . A second partial opening forming the main opening is designated 10'' and is provided in the piston 3 ' ' forming the blocking member. On movement of the piston 3' in the direction of the arrow A the first opening 9 ' ' is unblocked as soon as the rear end face 14 of the piston 3'' reaches the vicinity of the partial opening 9''. The main opening 10'' is unblocked by passing the edge 13' ' of the groove 12 ' ' .

Claims: WHAT IS CLAIMED IS 1. A device for limiting the oil pressure in the lubricating oil circuit of an internal combustion engine, comprising an oil pump and a pressure relief valve for unblocking an opening to form a connection between the pressure side and the suction side of the oil pump or the pressure side of the oil pump and a sump, which valve includes a blocking member movable against a biasing force in a valve housing to unblock the opening, characterised in that the opening of the pressure relief valve (1) is divided into at least two partial openings (9, 10) apart from one another in the direction of movement of the blocking member by a distance (B). 2. A device according to claim 1, characterised in that the partial openings are of different sizes, with a main opening (10, 10', 10"') being preceded by a smaller first opening (9, 9', 9''), so that at a predetermined oil pressure first of all the first opening is unblocked and at a predetermined higher oil pressure the main opening is also unblocked. 3. A device according to claim 1 or claim 2, characterised in that the partial openings (9, 10 ; 9'. 10''; and 9'', 10'' respectively) are of different shapes. 4. A device according to any of claims 1 to 3 , characterised in that the partial openings (9, 10) are provided in the valve housing (2). 5. A device as claimed in any of claims 1 to 3, characterised in that the partial openings (9', 10') are provided in the blocking member ( 3 ' ) . A device as claimed in any of claims 1 to 3, characterised in that the partial openings (9"', 10'') are respectively formed in the valve housing (2'') and in the blocking member ( 3 ' ' ) . AMENDED CLAIMS [received by the International Bureau on 6 January 1998 (06.01.98); original claim 1 amended; remaining claims unchanged ( 1 page )] 1. A device for limiting the oil pressure in the lubricating oil circuit of an internal combustion engine, comprising an oil pump and a pressure relief valve for unblocking an opening to form a connection between the pressure side and the suction side of the oil pump or the pressure side of the oil pump and a sump, which valve includes a blocking member movable against a biasing force in a valve housing to unblock the opening, the opening of the pressure relief valve (1) being divided into at least two partial openings (9, 10) apart from one another in the direction of movement of the blocking member by a distance (B), the at least two partial openings being unblocked in succession at respective predetermined oil pressures, characterised in that the partial openings remain unblocked as long as the respective predetermined oil pressures are exceeded. 2. A device according to claim 1, characterised in that the partial openings are of different sizes, with a main opening (10, 10', 10'') being preceded by a smaller first opening ( 9 , ' , 9 ' • ) , so that at a predetermined oil pressure first of all the first opening is unblocked and at a predetermined higher oil pressure the main opening is also unblocked. 3. A device according to claim 1 or claim _. , characterised in that the partial openings (9, 10 ; 9 . 10''; and 9' 1 , 10' ' respectively) are of different shapes. . A device according to any of claims 1 to I , characterised in that the partial openings (9, 10) are provided in the valve housing (2). 5. A device as claimed in any of claims 1 to 3, characterised in that the partial openings (9', 10') are provided in the blocking member ( 3 ' ) . A device as claimed in any of claims 1 to 3, characterised in that the partial openings (9'', 10'') AMENDED SHECiT (Af ϊTiCLE 19)

Inventors: TRZOSKA PETER REINHOLD, TRZOSKA, PETER, REINHOLD
Applicants: FORD GLOBAL TECH INC, TRZOSKA PETER REINHOLD, FORD GLOBAL TECHNOLOGIES, INC., TRZOSKA, PETER, REINHOLD
Application year: 1997
Main classification: F01M1
IPC codes: F01M1, F16K17