CAMSHAFT WITH DETACHABLE BEARING JOURNALS

Abstract

The invention relates to a camshaft for a small internal combustion engine used in for example cars or motorbikes, it is characterized by being divided into two or more components, preferably it is the camshaft bearing journals (3) on the camshaft that are separate components.

Description

TECHNICAL FIELD

The invention relates to a camshaft according to FIG. 1 for an internal combustion engine with a camshaft design requiring the camshaft to be assembled into the engine through the camshaft support bearings (2).

BACKGROUND

A common design for built in camshafts in internal combustion engines is to allow the camshaft to rest on fixed bearings (2), either in the engine block or in the cylinder head. When the camshaft is assembled into the engine it is inserted through the fixed camshafts bearings (2), which have the same diameter as the camshaft bearing journals (3). This is foremost a very common design on engines with a push rod valve train, but can be found on other types of valve trains, for instance side valve engines.

Designs following the guidelines as mentioned above will result in limitations on how the camshafts lobes (4) on the camshaft can be designed when located close to the camshaft bearing journals (3). The largest radius on the camshaft lobe (4) cannot be allowed to be larger than the radius of the camshaft bearing journal (3), since it then would be impossible to insert the camshaft through the camshaft bearings (2)

By designing the camshaft bearing journals (3) as detachable details assembled on the camshaft at the same time or after the camshaft is assembled into the engine, it becomes possible to radially displace the camshaft during assembly into the engine, which hence makes it possible do design camshaft lobes (4) with a larger radius than the camshaft bearing journals (3).

There are earlier examples of camshafts designed in several separate sections. In DE 2706021 A1, aimed at large internal combustion engines where it by handling and assembly reasons is an advantage to split the camshaft in several smaller parts. To be able to apply this type of design on smaller engines with corresponding smaller camshafts, new solutions for assembling the parts of the camshaft together are needed, otherwise these details will strongly limit the earlier described advantages.

In U.S. Pat. No. 2,552,754A another divided camshaft design is described. This is however a design that still limits the design of the camshaft lobes according to the camshaft bearing journals. Hence this design does not solve the problem referred to in this patent

When designing a completely new engine with the purpose of a simple and low cost solution a design with fixed camshaft bearings (2) is very attractive. The dimensions of the camshaft bearings (2) are then adapted after the intended design of the camshaft lobes (4). A design with detachable camshaft bearing journals would then most likely be contra productive since it complicates the design and makes it all but simple. If the designer would need larger camshaft lobes he would instead make the camshaft bearings (2) larger, or choose a design with detachable camshaft bearing caps, which means the camshaft does not have to be inserted through the camshaft bearings during assembly, and the problem is avoided.

This invention is therefore best suited when the radius of the camshaft lobes (3) needs to be increased on an existing engine, usually for performance reasons. The skilled professional presented with this problem today solves it by modifying the engine by increasing the camshaft bearings (2) and corresponding increasing the camshaft bearing journals (3). This solution is limited by the available space in the existing design and is complicating other qualities of the engine. Another solution used is to machine an axial notch in the camshaft bearings (2), where the tip of the camshaft lobes (4) can be inserted. Also this design has negative impact on other engine properties.

These are solutions that allow for only minor increase of the radius of the camshaft lobes (4), in addition modification to camshaft bearings and other parts are required.

The invention distinguish itself from the described designs of divided camshafts by the fact that it has to be assembled together at the same time it is inserted into the engine, one must already when designing the camshaft have in mind in which order the parts should be assembled, to take advantage of the design. The main purpose of the earlier designs has been to divide large camshafts into smaller and more manageable details to ease manufacturing and assembly into the engine.

The main purpose of this invention is to enable camshaft lobes (4) with larger radius than the radius of the camshaft bearing journals (3) to be designed. To achieve this purpose in the best way, it demands the details of the design to differ from already available solutions.

PURPOSE OF THE INVENTION

The purpose of this invention is to make it possible to insert a camshaft with camshaft lobes (4) that has a larger radius than the camshaft bearing journals (3) through the fixed camshaft support bearings (2) in the engine. This is made possible by making the camshaft bearing journals (3) detachable, and/or the camshaft divided in a way so it is not assembled together until it is inserted into the engine.

This design makes it possible to use camshaft lobes (3) larger than what would normally be possible for a given engine model with a camshaft designed in one piece.

DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic view of a camshaft (1) with two camshaft bearing journals (3) and two camshaft lobes (4), resting on two fixed camshaft bearings (2), with lifters (5) resting on the camshaft lobes (4)

FIG. 2 shows a camshaft lobe (4), the camshaft bearing journal (3) and the geometrical relationship which limits the radius of the camshaft lobe (4) to not being larger than the radius of the camshaft bearing journal (3), when the camshaft is inserted through the fixed camshaft bearing (2)

FIG. 3 shows two camshaft lobes (4) with different radius base circle and the same lobe lift.

FIG. 4 shows a schematic comparison between how large camshaft lobe (4) that can be inserted through a given camshaft bearing, on one hand when the camshaft lobe base circle is in center of the camshaft bearing and on the other hand when it is possible to displace the base circle from the center and use all of the space of the camshaft bearing (2).

FIG. 5 shows a camshaft manufactured in one piece, or permanently assembled by several pieces when manufactured

FIG. 6 shows a camshaft with 3 detachable camshaft bearing journals, the 2 outer bearing journals (3) as sleeves, and the one in the middle (6) radially divided into two parts.

FIG. 7 shows a camshaft with 3 detachable bearing journals, all of them designed as sleeves (3). The camshaft is divided in the middle to make it possible to assemble.

FIG. 8 a-e show how to assemble a divided camshaft with two detachable bearing journals (3) and two camshaft lobes (4)

FIG. 9 a-c shows an alternative way of assemble a divided camshaft with two bearing journals (3)

FIG. 10 a-e shows the design and how to assemble a radially divided bearing journal (6). The view to the left shows the design in axial, the one to the left from the side.

FIG. 11 a-c shows an alternative way of assemble a radial divided camshaft bearing journal (6)

The same numbers on the different drawings refer to the same corresponding parts.

DETAILED DESCRIPTION

FIG. 1 shows a camshaft in its most basic design with two bearing journals (3) and corresponding camshaft bearings (2) in the engine. The camshaft also consists of two camshaft lobes (4). The camshaft is manufactured in one piece and when assembled into the engine is inserted through the camshaft bearing (2), which has the same inner diameter as the camshaft bearing journals (3) outer diameter D₁

FIG. 2 explains the limitation in camshaft lobe (4) design when the lobe is placed close to the bearing journal (3). The maximum radius of the camshaft lobe can then not be allowed to exceed the radius of the bearing journal (3), hence it would be impossible to insert the camshaft lobe (4) through the support bearings (2) of the engine.

A camshaft lobe can be explained according to the nomenclature in FIG. 3 with a base circle with radius R₁ and a lobe with a given height H. The top radius of the lobe in most cases corresponding to the smallest radius, are described as R₂. The axial centerline through the base circle of the camshaft lobe is corresponding to the axial centerline through the camshaft bearing journal (3).

To allow for a camshaft to be inserted through a camshaft support bearing (2) with inner diameter D₁, the following criteria need to be fulfilled:

2×R₁+2×H≦D₁   (1)

When designing an engine it is of weight and space reasons desirable to keep D₁ as small as possible. This limits the degree of freedom in the design of the camshaft lobe (4). When increasing H within a given D₁, R₁ must be reduced correspondingly to fulfill the criteria described in formula 1.

If the reduction of the base circle is large the diameter of the camshaft D₂, need to be reduced between lobes and bearing journals. Since the base circle of the camshaft lobe has to be larger than the surrounding diameter the following criteria are given:

D ₂≦2×R₁   (2)

A thinner camshaft will have negative impact on camshaft stiffness, which in turn will affect the dynamic function of the valve train.

A reduced base circle will also deteriorate the geometry of the camshaft lobe as described in FIG. 3, where two camshaft lobes can be seen with identical H, and hence will produce the same valve lift regardless of the fact that (b) has a larger base circle than (a). In the comparison between these lobes there is a major difference in the top radius R₂.

If the radius R₁ is increased, R₂ will also increase with the same amount which in turn will result in a larger contact area between the camshaft lobe and the follower (5), resulting in reduced surface stress and improved durability.

When an existing camshaft design are about to be modified, commonly with the purpose to increase H in order to increase the achievable valve lift, D₁ strongly limits the design of the camshaft lobe. One solution is to increase D₁, but that would also mean that the diameter of the camshaft support bearings (2) in the engine have to be increased, which most often is complicated or even impossible.

Designing a completely new engine will allow for a larger degree of freedom, but the drawbacks with increased weight and need of space still remains if the camshaft is designed with larger camshaft bearing journals (2).

The invention refers to making the camshaft bearing journals detachable and assembled with the camshaft at the same time, or after the camshaft has been inserted into its position in the engine. The advantage is, that when the camshaft is inserted through the camshaft support bearings (2) without the camshaft bearing journals (3) in place the camshaft can be radially displaced. FIG. 4a shows the traditional way of assembly, when the centerline of the camshaft lobe base circle has to be maintained in the center of the camshaft support bearing (2). FIG. 4b shows how much larger the camshaft lobe can be made if the centerline of the camshaft lobe base circle can be displaced and all the space in D₁ can be utilized. This improves the criteria described in formula 1 as follows

2×R₁+H≦D₁   (3)

Compared to criteria (1) there is an extra H in space that can be utilized to increase H or/and R₁. With the corresponding advantages described earlier.

To be able to utilize the advantages with detachable bearing journals to its full potential, it is important that the assembly of the included components is designed in such a way that the means of attachment do not expand on the outside of the camshaft, since that will limit the amount it can be radially displaced during assembly.

The solution suggested is to utilize a simple joint in the axial center of the camshaft. Since such a joint would eliminate details on the outer surfaces of the camshaft, it will maximize the amount the camshaft can be radially displaced when inserted through the camshaft support bearings (2). Hence also maximize the achievable radius of the camshaft lobe (4) with respect to the diameter of the camshaft support bearing (2).

With this solution it is possible that the fastening joint becomes the largest or longest component of the camshaft. This would not have been desirable if the purpose of the design would have been to design the camshaft divided to achieve smaller and more hand able components. This is of small relevance though in the applications this invention aims at, namely when the size of the camshaft is not the problem, instead it is the design of the camshaft lobe that is.

If only a central fastening joint is used, it becomes necessary that the components of the camshaft are fixed angularly towards each other. This is easiest done by feather keys, splines, or some kind of pin.

The centrally place joint also makes the design simple, with as few details as possible.

In FIG. 8a is an example of how to assemble a basic one piece camshaft into the engine, FIG. 8b shows it is not possible to insert the camshaft into the engine if the camshaft lobes (4) where to have a larger radius than the camshaft bearing journals (3), since the camshaft lobe (4) then would hit the camshaft support bearing (2).

If the camshaft bearing journals (3) is made detachable it becomes possible as shown in FIG. 8c-e to radially displace the camshaft when it is inserted through the camshaft support bearings (2), this makes it possible to insert a camshaft where the radius of the camshaft lobes (4) are larger than the radius of the camshaft bearing journals (3). The camshaft bearing journals (3) are then joined to the camshaft when it is in its position in the engine, in this case from each end as in FIG. 8e. The right camshaft bearing journal (3) is joined in its position with a bolt (7), central in the bearing journal (3) while the left bearing journal which in this case also should act as the driving flange of the camshaft is angular fixed to the camshaft with a feather key, but it could also be designed with splines, a pin or a similar fastening element.

In some engine designs one side towards the camshaft is open, if the camshaft has detachable bearing journals it then becomes possible to insert the camshaft in the engine through the open side as shown in FIG. 9a-c, instead of insert it through the camshaft support bearing (2). One side of the camshaft is then first inserted in an angle into one camshaft support bearing FIG. 9a-b, then placed in its supposed position and finally pushed into the second support bearing. The camshaft bearing journals (3) can be assembled in a similar way as earlier described and shown if FIG. 8e.

This assembly method might be needed for example when the camshaft lobes (4) are close to each other and in different angular position on the camshaft, they can then impose a similar problem as in between the bearing journals (3) and the camshaft lobe (4) and limit the possibility to radially displace the camshaft when it is inserted through the camshaft support bearings (2).

In these types of designs the joints between the components might have to be designed with tapered holes and shafts. Then the components do not have to be in the exact right angular position towards each other during assembly, until they are positioned in its final position. It is sometimes necessary to be able to insert the components into each slightly angled at the start of the assembly.

The designs described up to now only have two camshaft bearing journals (3) and two camshaft lobes (4), in its simplest form a camshaft can be made up of two bearing journals (3) and only one camshaft lobe (4). If the bearing journals (3) are placed close enough to each other, the same problem can occur in such a design as well.

More common though is that camshafts are made up of more than two bearing journals (3) and more than two camshaft lobes (4). In those cases different combinations of the designs described might need to be used and the camshaft might need to be divided into several components to make it possible to assemble after it has been inserted into the engine.

The following examples relate to a camshaft with 3 bearing journals, but the principles used relates to all camshaft designs with 2 or more bearing journals.

FIG. 5 show the standard camshaft design of today in one piece, which shall be replaced.

FIG. 7 show a design where the middle bearing journal (3) has been designed as a tubular sleeve and the camshaft is parted into two components, the components are fixed to each other in the sleeve at the same time the camshaft is assembled into the engine. In this design the last bearing journal, to the right can be made in one piece together with the camshaft component, since it will be possible to assemble anyway. All the components in this design can be joined together by a long bolt as joint if one of the axles is gun drilled and the other one is designed with a treaded hole.

If the camshaft in FIG. 7 would have had more than 3 bearing journals (3) it would have to be divided at each bearing journal (3). For example a camshaft with 5 bearing journals (3) will be divided into 4 axle components.

A design solution shown in FIG. 6, demonstrates that it is not always necessary to divide the camshaft even if the design has 3 or more bearing journals (3), in some designs it might instead be suitable to design the middle bearing journal (6) detachable. This is only possible if the bearing journal (6) is divided radially in two or more components, since it would otherwise be impossible to get the bearing journal over the camshaft lobes. This technique becomes suitable mostly on the middle bearing journals (6) on camshafts with 3 or more bearing journals (3).

The divided bearing journal components (6) can be fixed towards the camshaft with bolt joints, riveting joints or some form of clamp joint. The outer bearing journals (3) are designed as sleeves and not divided radially. This is possible since they do not have to be assembled over any camshaft lobe when assembled, they can be fixed to the camshaft with for example a feather key or splines.

The assembly of the divided bearing journal (6) onto a camshaft designed as described in FIG. 6, can be done as in FIG. 10a-e. One of the half bearing journal components (6) is axially inserted into its position according to FIG. 10b, which is possible on the opposite side to the camshaft lobe (4). When in place the divided bearing journal component (6) can be turned 180 degrees and positioned right beside the camshaft lobe (4) according to FIG. 10d. It then becomes possible to insert number 2 of the divided bearing journal components (6) in the same way as the first. When in its position the components can be fixes to the camshaft or towards the camshaft support bearing (2).

Depending on how the bearing journal components (6) are fixed, the bearing surface becomes either on the outside or the inside of the divided bearing journal components (6). Another solution would also be to not fixate the angular movement of the bearing journal components and both the outside and the inside become bearing surfaces.

In some cases it might be possible to assemble all components of the radially divided bearing journal (6) at the same time as described in FIG. 11a-c. One situation where that is possible is when the camshaft lobe (4) is positioned so far away from the bearing journal (6) that it is possible to insert the components in between the camshaft lobe (4) and the camshaft support bearing (2). In this case though there is no reason to make the bearing journal (3) detachable in the first place since it do not interfere when the camshaft is inserted though the camshaft support bearings (2).

Another case is when it is possible to position the radially divided bearing journal components (6) before the camshaft has reached its final position, there is then extra space for the bearing journal (6) between the camshaft lobe (4) and the camshaft support bearing (2). When in place the camshaft can be inserted into its final position according to FIG. 11c where the camshaft lobe (4) is closer to the camshaft support bearing (2).

Claims

1. A camshaft consisting of one or several camshaft lobes (4) and two or more camshaft bearing journals (3). Each bearing journal relates to a camshaft support bearing (2) in the engine which supports the camshaft. The camshaft is divided into two or more components designed to be assembled together at the same time as the camshaft is inserted into the engine. At least one of the bearing journals (3) is a detachable part. The camshaft lobes maximum radius is larger than the radius of the camshaft bearing journals (3). The camshaft is characterized by being joined together completely or in some part with a central bolt joint, extending in the center of the camshaft and through the center of at least one of the camshafts compromising components.

2. Camshaft according to claim 1 characterized by one or several of the bearing journals being sleeves.

3. Camshaft according to claim 1 characterized by one or several of the detachable bearing journals being radially divided into two or more parts. The bearing surface can be on the outside or the inside, alternative both surfaces of the detachable bearing journals.

4. Camshaft according to claim 1 characterized by the compromising components being fixed to each other with feather keys, splines or a combination of them.

5. Camshaft according to claim 1 characterized by its compromising components being joined together with tapered holes and corresponding tapers on the axle parts.