ARRANGEMENT IN CONNECTING A POSITION SENSING TRANSDUCER TO A MACHINE

Abstract: The invention relates to an arrangement for the purpose of enabling the connection of a position sensing transducer (10) to a machine such that the transducer is not subjected to high temperatures or dirt. In accordance with the invention the transducer (10) is mounted on the outside of a housing (2, 4) in which there is mounted a rotatable means Carrying outside the housing unrotatably a drive means (5) for driving auxiliary equipment. The invention is distinguished in that the position sensing transducer (10) includes a disc (22) unrotatbly attached to the drive means (5), said disc co-acting touchlessly with a transducer (14) mounted on the outside of the housing (2, 4) for indicating the angular positions of the disc, and in that the drive means (5) and housing (2, 4) are disposed for axially fitting into each other to form a labyrinth seal to a space (9) accommodating the position sensing transducer (10). The invention is intended for use in an Otto-type internal combustion engine to connect the transducer (10) which senses the angular oposition of the engine crankshaft (1), thus making possible control of the engine ignition timing with great accuracy.

Description: The present invention relates to an arrangement comprising an internal combustion engine and a position sensing transducer fitted thereto, said position sensing transducer being arranged outside of the cylinder block of said engine in which there is mounted the crankshaft, which outside the cylinder block carries a belt pulley for driving auxiliary equipment, said position sensing transducer including a disc non-rotatably attached to the pulley and a sensor mounted outside of said cylinder block and co-acting without contact with said disc for indicating the angular position of the disc. An arrangement of this kind is disclosed in GB-A-1 512 720. In multi-cylinder Otto-type I.C. engines it is known to control the ignition timing in the respective combustion chambers with the aid of a mechanically driven distributor. This is usually driven by gearing from the engine camshaft, which is in turn driven from the engine crankshaft via a belt drive. It is thus possible to control the engine ignition timing in response to angular positions of the crankshaft, and thus also in response to piston position in the different cylinders. Driving the distributor in the way described above results in a plurality of transmission transfers which, due to play between the components concerned, impairs the accuracy of controlling the ignition timing relative the angular positions of the crankshaft. The ignition instant in the respective combustion chamber is of great importance in optimalizing the combustion process. Incorrect or inaccurate timing causes drawbacks such as increased fuel consumption, reduced power and/or increased exhaust gas emission. It is known, for the purpose of better controlling ignition timing, to arrange electrical transducers that sense the camshaft angular positions directly, and in response thereto directly controlling the respective ignition instants. Although this means an improvement in relation to an entirely mechanically driven distributor, there remains the drawback that there may be play in the transmission between crankshaft and camshaft which impairs accuracy. To achieve the best possible accuracy in controlling ignition timing, it is necessary directly to sense the crankshaft angular position. The possibilities of placing an electric transducer on known engine structures is limited, however, and for this reason such transducers have not found any practical application. Placing a transducer in the engine crankcase causes the transducer to be subjected to a temperature that is too high for it to function in the intended manner. Placing the transducer outside the engine, e.g. on a belt pulley at one end of the crankshaft, results in the transducer being subjected to dirtying such as can endanger its function. An example of how to locate a transducer outside the engine is disclosed in said GB-A-1 512 720, where a pulley, on the side facing away from the cylinder block, carries a first support that is bolted to the crank shaft. Said first support, at the rim of the pulley, carries members intended to cooperate with a pickup head carried by a second, annular support, which via a bearing is carried by said first support. A stay secured to the cylinder block prevents the second, annular support from rotation. In this way a number of extra components are needed to locate the transducer outside of the pulley. This means that the solution is complicated and expensive and does not provide a good protection for the transducer. The present invention has the object of enabling the connection of a position sensing transducer to a machine such that the transducer is not subjected to high temperatures or dirtying. In accordance with the invention the pulley and the cylinder block are disposed for axially fitting into each other to form a labyrinth seal to a space accommodating the position sensing transducer. The invention thus enables that a transducer controlling the ignition instant may be located in a place where there are no injuriously high temperatures. Furthermore, the transducer is protected against dirt, since there is only a narrow gap between the pulley and the cylinder block, this gap being also formed as a labyrinth seal. Other distinguishing features of the invention will be understood from the following description of an inventive arrangement in a multi-cylinder, Otto-type I.C. engine. The description is performed with reference to the accompanying drawings, in which Figure 1 is a part of an end elevation of an I.C. engine without a belt pulley and Figure 2 is an axial section A-A according to Figure 1, of the engine with a belt pulley mounted on the engine crankshaft. Otto-type I.C. engines are well-known, and it is not necessary to know their construction in detail to understand the significance of the present invention, although a short description of such an engine will now be given by way of introduction. The exemplified engine includes a cylinder block accommodating four cylinders and their pistons. The respective pistons are connected to a crankshaft 1, rotatably mounted in the cylinder block. One end of the crankshaft carries a chainwheel included in the engine camshaft drive transmission. At its other end the crankshaft 1 is connected to a flywheel, and engine power is taken off from this end. The transmission between crankshaft 1 and camshaft is covered by a transmission casing 2 bolted to the cylinder block, the transmission casing being partially visible in the figures. Said casing 2 is made with a cut-out accommodating a lubrication pump, said cut-out being covered by an oil pump cover 4 secured by bolts 3 to the casing 2. The oil pump is driven by a gear unrotatably attached to the previously mentioned chainwheel on the crankshaft 1. Attached to the outmost end of the crankshaft there is a belt pulley 5 which is part of a belt transmission for driving auxiliary engine equipment such as a generator, servo steering pump and the like. The belt pulley 5 is made with a hub 6 rigidly attached to the crankshaft 1 by a bolt 7 at the end thereof. The oil pump cover 4 is made with a central hole 8, at least partially accommodating the hub 6 of the belt pulley. The figures have been restricted to illustrating the oil pump cover 4, belt pulley 5 and an annular space 9 therebetween including the inventive arrangement. On its outside the oil pump cover 4, fastened to the casing 2 by the bolts 3, carries a position sensing transducer 10. This transducer 10 is adapted for sensing the angular position of the crankshaft such as to control suitable ignition timing for the engine. The transducer 10 is of the touchless type, and includes a mounting plate 11 fastened by three bolts 12 to the oil pump cover 4 inwards of an annular flange 17 extending axially and substantially concentrically with the central hole 8 in the oil pump cover in. The transducer 10 also includes a permanent magnet 13 and a Hall effect sensor 14, which are separated from each other by a narrow gap 15. The sensor 14, magnet 13 and plate 11 are partially moulded into epoxy plastics, and in a fitted condition the sensor 14 is connected to the engine ignition system by an electric cable 16. The belt pulley 5 is conventionally formed with a plurality of Vee grooves 18 for Vee belts. Internally, on the side facing towards the oil pump cover 4, the pulley 5 is provided with a recess 19. In an assembled state on the crankshaft 1, the flange 17 fits into the recess 19 of the pulley 5 to form a labyrinth seal with only a small gap between the recess 19 and the flange 17. A metal disc 22, the periphery of which is folded into a cylindrical axially extending portion, is attached to the inside of the belt pulley 5 by bolts 21. The cylindrical wall of the disc 22 fits into the gap 15 between the magnet 13 and the sensor 14. Said cylindrical wall is provided with two opposing cut-outs. The wall of the disc 22 prevents the magnetic field surrounding the magnet 13 from affecting the sensor 14. Only when the cut-outs in the wall of the disc 22 are between the magnet 13 and the sensor 14 can the magnetic field affect the sensor 14, and when this happens the latter generates an output signal. The cut-outs in the cylindrical wall of the disc 22 are preferably arranged such as to provide output signals indicating when the respective pistons in the engine have assumed positions in the vicinity of their top dead centres. In this way the Hall effect sensor 14 will give a signal every time one of the pistons is at its top dead centre. Although there is no direct drawback from the combustion aspect for a four stroke engine in letting the spark plugs spark each time some piston is at its top dead centre, this causes unnecessarily great wear on the spark plugs. To avoid this the ignition system may be supplemented with a transducer, e.g. arranged on the engine camshaft, which is utilized together with the Hall effect sensor 14 for controlling the ignition times. The implementation of this is outside the scope of the present invention and is therefore not described further. The implementation of the Hall effect sensor 14 and the rotating disc 22 allow the angular position of the crankshaft 1 to be indicated with great accuracy, in turn signifying that the ignition timing in the engine cylinders may be controlled with great accuracy. The ignition timing may also be controlled conventionally by engine loading and running conditions, so that actual ignition occurs at a time other than that indicated by the signal from the Hall effect sensor for a given angular position of the crankshaft. When the engine is in operation, the belt pulley 5 will rotate, as well as the disc 22 attached to it. When the cut-outs on the cylindrical wall of the disc 22 pass through the magnetic field between the magnet 13 and the sensor 14 the latter sends a signal to the engine ignition system. Placing the transducer 10 radially inwards of the flange 17 results in that the transducer 10 and the disc 22 will be protected against dirt. However, should dirt come through the narrow gap between the recess 19 of the belt pulley 5 and the flange 17, this dirt will be cast out by centrifugal force when the belt pulley 5 rotates. This means that the space 9 may be regarded as self-cleaning. The location of the transducer 10 also results in that it is protected against the high temperatures which can be prevalent with I.C. engines.

Claims: An arrangement comprising an internal combustion engine and a position sensing transducer (10) fitted thereto, said position sensing transducer (10) being arranged outside of the cylinder block (2, 4) of said engine in which there is mounted the crankshaft (1), which outside the cylinder block (2, 4) carries a belt pulley (5) for driving auxiliary equipment, said position sensing transducer (10) including a disc (22) non-rotatably attached to the pulley (5) and a sensor (14) mounted outside of said cylinder block and co-acting without contact with said disc for indicating the angular position of the disc, characterized in that the pulley (5) and the cylinder block (2, 4) are disposed for axially fitting into each other to form a labyrinth seal to a space (9) accommodating the position sensing transducer (10). Arrangement as claimed in Claim 1, characterized in that the labyrinth seal is formed by an annular flange formed on the cylinder block (2, 4), extending axially and concentrically with the crankshaft (1), and a recess (19) made in the pulley. Arrangement as claimed in Claim 1 or 2, characterized in that the position sensing transducer (10) includes a permanent magnet (13) and a Hall effect sensor (14) co-acting with the disc (22) attached to the pulley (5), and that the disc is implemented with equidistant cut-outs. Arrangement as claimed in Claim 1 or 2, characterized in that the position sensing transducer (10) is attached on a cover (4) removably mounted on the cylinder block. Arrangement as claimed in Claim 4, characterized in that the position sensing transducer (10) is included in an electrical system for controlling the engine ignition in response to angular positions of the crankshaft.

Inventors: BERGSTEN, LARS
Applicants: SAAB AUTOMOBILE AKTIEBOLAG
Application year: 1985
Main classification: F02P7
IPC codes: F02P7, F02P15, F02B1