The present invention relates to a method, where shafts are driven via a transmission by a drive shaft, for setting the rotational position of the shafts in relation to that of the drive shaft. The method is particularly intended for applying to the setting of camshafts.

As is well understood, the coordination between piston and valve motions in an engine is of decisive importance for the performance of the engine in such respects as efficien¬ cy, fuel consumption and discharge of uncombusted gases. Consequently, an accurate setting of the rotational posi¬ tion of the camshaft in relation to that of the crankshaft is very important for reducing operational costs as well as the effect on environment.

In known setting methods, where the transmission between crankshaft and camshaft/shafts consists of a toothed belt or chain which co-acts with transmission wheels rigidly connected to the respective shaft, the belts are first taken off, and then the transmission wheels are rotated to the setting positions, which are defined by marks on the transmission wheels, e.g. in the form of keyways, coming opposite marks in adjacent parts of the cylinder block and crankcase. The belts are then put on and tensioned. How¬ ever, this method has the disadvantage that the setting is done by eye, which makes the setting accuracy less than what can be afforded by the error tolerances allowed in the production of the mentioned markings. A further disadvan¬ tage is that the belts which are mounted on the positioned drive wheels have relatively large intrinsic error toleran¬ ces, which affects the total error to a large degree so that an exact setting is difficult to achieve.

The object of the invention is to achieve a method of cam¬ shaft setting which does not have the mentioned disadvan¬ tages, and an apparatus for carrying out the method.

This object is achieved by a method having the distinguish¬ ing features disclosed in claim 1. Since the shafts can be released from the transmission wheels, the setting is car¬ ried out with a tensioned timing belt which, apart from reducing the number of operations compared with known methods where the belts are removed, also results in that the effect of the belt error tolerance is eliminated in the inventive method. By utilizing well-defined, machined sur¬ faces on the crank- and camshafts, the error tolerances can be reduced, compared with the use of keyways and the like on the transmission wheels and the co-acting markings on the cylinder block or crankcase, and the use of tools results in that errors due to working by eye are elimina¬ ted, thus permitting the setting accuracy to increase by more than what is involved in solely the decrease of manu¬ facturing tolerances.

The distinguishing features of the apparatus in accordance with the invention for carrying out the method according to claim 1 are disclosed in claim H .

The method in accordance with the invention will be more easily understood by perusal of the following detailed description of an application thereof in an embodiment of an apparatus in accordance with the invention, the descrip¬ tion being carried out with reference to the accompanying drawings, where:

Fig. 1 is a view from the front and partially in cross-sec¬ tion of an embodiment of the apparatus in accordance with the invention;

Fig. 2 is a view from the rear and partly in cross-section of the apparatus in Fig. 1; and

Figs. 3 and -4 illustrate a tool for the angular setting of camshafts in an engine having dual camshafts.

A conventional engine is illustrated in Fig. 1, as seen from the front. The crankshaft has a transmission wheel 1 which, when the engine is in operation, drives two cam¬ shafts via a toothed belt 2 by co-action with their trans¬ mission wheels 3 , ^" The belt 2 further runs over a jockey pulley 5 and over a hydraulic belt tightener 6, which auto¬ matically ensures that correct belt tension is maintained.

The transmission wheels 3 and i. are fixed to the camshafts by a suitable type of releasable frictional joint so that the wheels are readily made rotatable relative the respec¬ tive shaft. The basic concept of the invention is thus enabled, namely of utilizing machined surfaces on the shafts for achieving a more accurate setting. As will be seen from the sectioned portion of Fig. 1, there is accord¬ ingly utilized an abutment 7 on the rear counterweight 8 of the crankshaft for setting the angular position of the crankshaft. In Fig. 1 this abutment is illustrated as being in engagement with a tool 9, which is inserted in a bore in the crankcase. Of course, other surfaces of a crankshaft can be utilized together with a complemental tool for setting the crankshaft 1 in a welldefined angular position. However, the abutment on the rear counterweight of the crankshaft is a particularly suitable surface, since this also constitutes a reference surface in the production of the crankshaft.

As will be seen from the figures, the engine to which the invention is applied in the embodiment example has dual camshafts 10,11. Although the same principle can be used

for the camshafts as for the crankshafts, for their indivi¬ dual setting, e.g. by allowing a cam surface on the cam¬ shaft to co-act with a complemental tool inserted in an opening in the cylinder block, a combination tool 12 is preferably used for simultaneously setting the angular position of both camshafts 10, 11, as indicated in Fig. 2.

The combination tool 12 is shown to a larger scale in Figs. 3 and , and principally comprises two levers 13, 14 with rectangular cross-section, the opposing end portions of the levers being unrotatably connectable to the rear ends of the respective camshafts 8,11, the other end portions of these levers engaging flat against each other in the set position of the camshafts, whereby a well defined angular position of the latter is achieved. The un-rotatable connection between camshaft end and lever can be achieved by the camshaft end being provided with a transverse slot, which co-acts with a complemental transverse projection 16 arranged on the corresponding lever end portion and is screwed into a thread in the camshaft end for fixing the lever axially. As will be seen from Fig. 2, the camshafts can be locked in their set positions with the aid of a nut 18 screwed onto a bolt 17 projecting out from the lever 14 and accommodated in a hole in the lever 13.

The method in accordance with the invention for setting the angular position of the camshafts in relation to the posi- • tion of the crankshaft is extremely simple, and will now be described for the apparatus illustrated in the figures.

In the.initial position, the transmission wheels 3 and 4 are rigidly connected to their respective shafts and the belts are tensioned. The first step of the method is to loosen the respective friction joint on the camshafts so that these can be turned relative the transmission wheels. The angular positions of the camshafts are then set by the

levers 13 _» 1*4 being taken into engagement against each other as illustrated in Fig. 2 by full lines, and the levers are locked in this position with the aid of the nut 18. The crankshaft is then turned to the position illustrated in Fig. 1 with the abutment 7 in engagement against the tool 9. While maintaining the set position of the crankshaft the friction joints between transmission wheels and shafts are then tightened, and the tools 9 and 12 are removed. The camshaft setting is thus completed.

In the described method, the crankshaft transmission wheel 1 does not need to be rotatable relative the crankshaft, since the rotation of wheels 3, -4 caused by this wheel do not affect the setting of the camshafts. Of course, it is also possible to let one of the camshaft wheels remain fixed and release the crankshaft wheel, or release all the wheels in the first step of the method. Since the shafts can be turned relative the transmission wheels during the setting, the large toothed belt tolerance will no longer affect the setting accuracy. In addition, setting by eye is completely avoided in the inventive method, and the accura¬ cy will be solely dependent on the manufacturing tolerances for the machined setting surfaces on the shafts and for the tools, and it is therefore possible to achieve very high setting accuracy.

By the invention there is thus achieved with simple means a method permitting very accurate setting of the angular positions of the crank- and camshafts, and which is very simple to carry out. By utilizing the surface which is a reference surface in the manufacture of the crankshaft, there is further obtained an extremely well defined setting surface for the crankshaft.

The described embodiment solely constitutes an illustrative example not restricting the invention, which can thus be modified in many different ways, and is therefore solely restricted by the disclosures in the accompanying claims.