AN ARRANGEMENT IN INTERNAL COMBUSTION ENGINES

Abstract: In a multi-cylinder internal combustion engine (1) having at least one cam shaft (3) which is driven by a crankshaft (2) via a transmission, the latter having a driving toothed pulley (4) at the front end of the crankshaft (2), a driven toothed pulley (5) for each cam shaft (3), and a toothed belt (6) wrapped around said toothed pulleys (4, 5), at least one driven toothed pulley (5) has an oscillation damper (17) connected thereto, said damper comprising an annular, resilient element (21) which integrally secures the inertia body (19) to the driven toothed pulley (5).

Description: AN ARRANGEMENT IN INTERNAL COMBUSTION ENGINES The subject invention concerns an arrangement in a multi-cylinder internal combustion engine comprising at least one cam shaft which is driven by a crankshaft via a transmission, said transmission comprising at least one driving toothed pulley positioned at the front end of the crankshaft, one driven toothed pulley for each cam shaft, and at least one toothed belt which is wrapped about the driving and the driven toothed pulleys. In internal internal combustion engines comprising a transmission of the type defined above, rigid body oscillations give rise to moment variations in the cam shaft/shafts during the rotary movement as a result of the valve lifting movement, which moment variations expos the toothed belt/belts to stress depending on the angular position of the cam shaft/shafts. The frequency of such moment variations is at its peak at a value corresponding to three times the r.p.m. in the case of a sex-cylinder internal combustion engine and to twice the r.p.m. in the case of a four-cylinder engine. Consequently, the cam shaft/shafts expose(s) the toothed belt/belts to modulated (not statical) stress in the longitudinal belt direction, known as excitation. Considering that the toothed belt/belts possess(es) a certain rigidity, denominated "K", and that the cam shaft/shafts and their associated toothed pulleys possess(es) a predetermined moment of inertia "I", an oscillation system of the first order, having the following resonance frequency is obtained. In the case of excitations from the cam shaft/shafts which, with respect to frequency, correspond to the resonance frequency of the system defined above, large amplitudes of angular torsion will occur while at the same time the toothed belt/belts (is) are subject to heavy stress during engine operation at a predetermined r.p.m.-value, resulting in a limited life. The oscillating system also possesses a certain "damping" quality which in itself reduces the amplitude, but the curve also becomes wider, so that even if the "critical" r.p.m.-value is not maintained exactly, operation in the neighbourhood of this r.p.m.-value still is sufficient to shorten the life of the toothed belt/belts. In addition, the market requires that the belt life be increased. The main purpose of the invention therefore is to increase the life of the toothed belt/belts, and this purpose is achieved by means of providing at least one driven toothed pulley with an oscillation damper which is connected to the pulley. These oscillating damper/dampers dampen(s) or counteracts) angular deflection, primarily at the above-defined resonance frequency. The result is very small deflection amplitudes during operational r.p.m.- situations in which the excitation corresponds to the resonance frequency, and the load on the toothed belt/belts is (are) considerably smaller with a consequential considerably increased life. The invention will be described in the following with reference to the accompanying drawings illustrating an at the moment particularly preferred embodiment of an oscillation damper. In the drawings: Fig. 1 is a schematical front view of a internal combustion engine equipped with two cam shafts, each one of which is associated with a driven toothed pulley having an oscillating damper integrated therein in accordance with a first integration method, Fig. 2 shows one of the driven toothed pulleys of Fig. 1 in a view from behind and on an enlarged scale. Fig. 3 is a sectional view along line III-III of Fig 2, and Figs. 4 and 5 show alternative methods of integratin the oscillating damper with its associated driven toothed pulley. The internal internal combustion engine 1 illustrate in Fig. 1 in a schematical front view is, in accordance with the embodiment illustrated, an in-line six-cylinder Otto engine but also other engine varieties are possible, as long as they have at least one cam shaft 3 which is driven by a crankshaft 2 via a transmission, the latter comprising at least one driving toothed pulley 4 positioned at the front end of the crankshaft 2, one driven toothed pulley 5 for each cam shaft 3, and at leas one toothed belt 6 wrapped around the driving and driven toothed pulleys 4, 5. In addition, the engine 1 in accordance with Fig. 1 comprises a tightening device 7 including a tightening roller 8 designed to automatically tighten the toothed belt 6, a water pump (not shown) which is driven via a toothed pulley 9, and a free-running deflection roller 10 Components 7-10 do not form part of the subject invention and therefore will not be described herein further. The two driven toothed pulleys 5 illustrated in Fig. 1 have an identical construction, for which reason only one of them will be decribed in closer detail with reference to Figs. 2-5. This driven toothed pulley 5 preferably is made of metal or other rigid material and is formed with a toothe rim 11 the teeth 12 of which are arranged for positive engagement with the teeth 13 of the toothed belt 6. In addition, the toothed pulley 5 comprises a hub 14 by mean of which the driven toothed wheel is mounted on the associated cam shaft 3, and a web portion 15 extending between the toothed rim 11 and the hub 14. As is clearly apparent from Figs. 3 - 5, the web portion 15 has a considerably reduced thickness dimension compared with the toothed rim 11 and also compared with the hub 14. The web portion 15 thus is positioned adjacent the face of the driven toothed pulley 5 which, when the pulley 5 is mounted on its associated cam shaft 3, is turned towards the front as seen in Fig. 1. In this manner, an inwardly open and consequently protected, annular recess 16 is formed internally of the toothed rim 11, i.e. a recess defined by the rim, the web portion 15, and the hub 14. An oscillation damper, generally designated by numeral 17, is connected to the driven toothed pulley 5, said oscillation damper being dimensioned for the associated cam shaft 3 and arranged to dampen or counteract rigid-body oscillation upon occurrence of the resonance frequency of the system defined in the aforegoing, with the result that the amplitudes of the angular torsion will be very small when operating at r.p. .-values where the excitation corresponds to the resonance frequency of the system, and the load on the toothed belt 6 will be considerably smaller, resulting in longer life. In accordance with the embodiment illustrated, the oscillation damper 17 comprises an inertial mass 18 in the shape of an annular body 19, preferably of metal or other comparatively heavy material having a predetermined moment of inertia. The inertia body 19 is received in the recess 16 and is integrally connected to the driven toothed pulley 5 by way of a resilient material 20, the latter likewise being part of the oscillation damper 17. The resilient material 20 also is annular in shape and consists of an element 21 which preferably is made from rubber or other similar material possessing rigidity qualities making it suitable for its intended function (torsion). In accordance with the embodiment illustrated in Figs. 2 and 3, the resilient element 21 is positioned between the external envelope surface of the annular inertia body 19 and the internal, likewise annular envelope surface of the toothed rim 11. In accordance with the embodiment of Fig. 4, the resilient element 21 is positioned between the front face of the inertia body 19 and the internal face of the web portion 15 whereas in accordance with Fig. 5, the resilient element 21 is positioned between the internal envelope surface of the inertia body 19 and the external, annular envelope surface of the hub 14. Further embodiments based on the same fundamental idea obviously are possible. In all cases the resilient element 21 interconnects the inertia body 19 and the toothed pulley 5, preferably by means of vulcanizing, provided that the pulley material is of a vulcanizable nature. However, glueing or other bonding methods are conceivable, for instance a press fit engagement. In accordance with one embodiment not illustrated in the drawings, the inertia body 19 and/or the resilient element 21 may be divided into segments, the latter preferably being of equal size and being equally spaced circumferentially. As one of several possible alternatives to the use of the above oscillation damper 17 having an inertia body 19 and a resilient element 21 may be mentioned the use of a viscous damper, not illustrated in the drawings, which like the above damper is integrally connected to the driven toothed pulley 5. In this case, the viscous damper comprises an oscillating mass in a damping medium, such as oil or a similar viscous substance. One advantageous side-effect of the use of the oscillation damper 17 is the improvement of the timing of the cam shaft/shafts 5, i.e. the valves of the interna combustion engine 1 open in a more precise sequence, with resulting higher performance at the above resonance frequency of the system. The invention should not be considered limited to the shown and/or described embodiments but could be varied optionally within the scope of protection defined in the appended claims.

Claims: CLAIMS 1. An arrangement in a multi-cylinder internal combustion engine (1 ) comprising at least one cam shaft (3) which is driven by a crankshaft (2) via a trans¬ mission (4, 5, 6), said transmission comprising at least one driving toothed pulley (4) positioned at the front end of the crankshaft (2), one driven toothed pulley ( 5) for each cam shaft (3), and at least one toothed belt (6) which is wrapped about the driving and the driven toothed pulleys (4, 5), c h a r a c t e r i z e d in that an oscillation damper (17) is connected to at least one driven toothed pulley (5) in order to dampen stress to which the toothed belt/belts ( 6) are exposed in their longitudinal direction in dependence of the angular position of the cam shaft/shafts (3) as a consequence of the moment variations of the cam shaft/shafts (3) due to rigid body oscillation during its/their rotation as a result of the valve lifting movement, and thus to increase the life of said toothed belt/belts (6). 2. An arrangement as claimed in claim 1, c h a r ¬ a c t e r i z e d in that the oscillation damper (17) comprises an interial mass (18) which is integrally connected to the driven toothed pulley (5) by way of a resilient material (20). 3. An arrangement as claimed in claim 1 and 2, wherein the driven toothed pulley (5) is formed with a toothed rim (11) for engagement with the toothed belt (6), a hub (14) to mount the pulley on the cam shaft (3), and a web portion (15) intermediate the toothed rim (11) and the hub (14), the thickness of said web portion (15) being smaller than that of the toothed rim and of the hub, said web portion (15) being positioned adjacent one of the faces of the driven toothed pulley to ensure that an annular recess (16) is defined internally of said toothed rim (11), c h a r a c t e r ¬ i z e d in that the inertial mass (18) consists of an annular body (19) which is received in said recess (16), and in that the resilient material (20) is in the shape of an annular element (21) connecting said inertia body (19) to the driven toothed pulley (5). 4. An arrangement as claimed in claim 3, c h a r ¬ a c t e r i z e d in that the inertia body (19) is made from metal or an equivalent, comparatively heavy material, and in that the resilient element (21) is made from rubber or similar material and bonds said inertia body to the driven toothed pulley (5) by means of vulcanizaton. 5. An arrangement as claimed in claim 3 or 4, c h a r a c t e r i z e d in that the resilient element (21) connects the inertia body (19) to the toothed rim (11) and/or to the web portion (15) and/or to the hub (14) of the driven toothed pulley (5). 6. An arrangement as claimed in any one of claims 3 to 5, c h a r a c t e r i z e d in that the inertia body (19) and/or the resilient element (21) are divided into segments. 7. An arrangement as claimed in claim 1, c h a r ¬ a c t e r i z e d in that the oscillation damper (17) comprises a viscous damper which is integrally connected to the driven toothed pulley (5) and which has an oscillation mass in a damping medium, such as oil.

Inventors: JOHANNESSON HANS, JOHANNESSON, HANS
Applicants: VOLVO AB, AB VOLVO
Application year: 1992
Main classification: F01L1
IPC codes: F01L1, F02B1, F02B67, F02B77, F16F15