GB2299624A

GB2299624A - I.c.engine balancer shaft

Info

Publication number: GB2299624A
Application number: GB9507156A
Authority: GB
Inventors: Laurence John Albon
Original assignee: Albon Engineering & Manufactur
Current assignee: Albon Engineering & Manufactur
Priority date: 1995-04-06
Filing date: 1995-04-06
Publication date: 1996-10-09
Also published as: GB9507156D0

Abstract

The balancer shaft 20 is formed with an axially extending eccentric bore 22 or bores or a semi-circular insert (42, Fig. 4) is welded inside the shaft axial bore to provide the desired imbalance.

Description

Balancer Shaft for an Engine Field of the invention The present invention relates to a balancer shaft for an internal combustion engine that may be a spark ignition or a diesel engine.

Background of the invention The crankshaft and pistons of some engines cannot be perfectly balanced and to allow the engine to run more smoothly it is known to provide a balancer shaft that has the same imbalance as the crankshaft assembly and that rotates with it at the same speed (or a multiple of its speed) but usually in the opposite sense.

The known balancer shafts are cast with an external eccentric weight and it has been found with such shafts that they have a tendency to bend when rotating at high speed.

For this reason, the number of bearings on which the shafts are supported must be increased if one is to avoid excessive wear on the bearings.

Object of the invention The present invention seeks to provide a balancer shaft that has improved resistance to bending moments, and that can therefore be supported safely using fewer bearings than a balancer shaft of conventional design.

Sugary of the invention According to the present invention, there is provided a balancer shaft for an internal combustion engine, the shaft having a regular cross section and being formed with an axially extending eccentric bore.

The term 'bore' is not restricted herein to a hollow formed by drilling. While it is indeed preferred to form the bore by drilling into one axial end face of the shaft, it is alternatively possible to form a bore of other than circular cross section by mounting a separately formed insert eccentrically with the inner diameter of a hollow shaft.

The insert may for example be D-shaped in cross section and held in position within the hollow shaft by welding or any other suitable technique such as heat shrinking.

Because the imbalance in the shaft is created in the present invention by omitting or removing mass from within the body of the shaft rather than adding mass to its outer surface, the rigidity of the shaft and its ability to withstand bending moments is increased. Such a shaft can readily be supported using only two bearings, one near the driven end of the shaft and one midway along the length the eccentric bore.

If the bore is formed by drilling into an axial end face of the shaft, the extent of the imbalance can be changed readily by modifying the depth or diameter of the eccentric bore without the need to make changes to a casting mould.

If the shaft is to be located in a wet sump, the bore may be plugged to prevent oil from entering into it.

As an alternative to a single bore, one may provide two or more bores in parallel with one another but a single bore is preferred.

The end of the shaft remote from the eccentric bore may be formed with a drive sprocket or with a fixing to allow the shaft to be connected to a drive pulley or cog. This end of the shaft may be provided with a concentric bore that does not affect the shaft imbalance but reduces the weight of the shaft.

Brief description of the drawings The invention will now be described further, by way: of example, with reference to the accompanying drawings, in which: Figure 1 is a section through a known balancer shaft, Figure 2 is a section similar to that of Figure 1 through a balancer shaft of the invention, the section being taken along the line II-II in Figure 3, Figure 3 is a side view of the shaft shown in section in Figure 2, and Figure 4 is a view similar to that of Figure 2 showing an alternative embodiment of the invention.

Detailed description of the preferred embodiment The balancer shaft shown in section in Figure 1 is typical of balancer shafts to be found in the prior art. The shaft is cast with a central section 10 and a eccentric bob weight 12. The imbalance of the shaft cannot readily be modified without changing the casting and because mass is removed from the outer surface of the shaft (to form the bob weight 12) the structural rigidity is impaired and the shaft has a tendency to bend.

Imbalance is created in the balancer shaft 20 of Figures 2 and 3 by an eccentric bore 22 drilled into one end of the shaft. The other end of the shaft is formed with a drive sprocket 30 and has a central bore 24 that extends axially through the shaft until it meets the eccentric bore 22. The shaft is formed with two bearing races 26 and 28 for support bearings, the race 26 being formed at the driven end of the shaft 20 and the race 28 mid-way along the length of the eccentric bore 22. The end of the bore 22 is also shown as being blocked off by a plug 32 to prevent the ingress of oil, if the shaft is to be mounted inside a wet sump.

Because the outer surface of the shaft 20 is not intersected by the bore 22, the shaft has the rigidity of a tube. As is known, a tube has significantly greater resistance to bending than the solid cross section of a prior art balancer shaft as shown in Figure 1. Because of this increased rigidity, the end of the shaft projecting beyond the race 28 can safely remain unsupported without and the life of the bearings is not unacceptably reduced.

While the eccentric bore 22 creates the desired imbalance, the bore 24 in the other end of the shaft 20 does not affect the balance and merely reduces the weight of the shaft 20.

Any axial overlap between the two bores reduces the imbalance created by the eccentric bore 22 and it is desirable therefore that the two bores 22 and 24 should only just meet one another, if at all. It is not essential that the bores meet and if they should fail to meet then the need to cap the right hand end of the shaft, as viewed, is avoided.

The preferred embodiment illustrated in Figures 2 and 3 has only one eccentric bore 22 but it is possible to provide two (or more) eccentric bores, provided they remain on the same side of the shaft axis.

In the alternative embodiment of the invention shown in Figure 4, the balancer shaft is formed as a hollow shaft 40 and an insert 42 of D-shaped cross section is welded inside the shaft 40, leaving a 'bore' of semicircular cross section.

A shaft of the invention has particular advantage when used in a wet sump because it can rotate with minimum friction when immersed in oil. This is to be contrasted with the prior art shaft shown in Figure 1 where the shoulders of the bob weight 12 would act as paddles and would thus meet considerable resistance when the shaft is rotated while immersed in oil.

Claims

1. A balancer shaft for an internal combustion engine, the shaft having a regular cross section and being formed with an axially extending eccentric bore.

2. A balancer shaft as claimed in claim 1, the eccentric bore is formed by drilling into an axial end face of a solid shaft.

3. A balancer shaft as claimed in claim 1, wherein the eccentric bore is formed by eccentrically mounting an insert within the outer diameter of a hollow shaft.

4. A balancer shaft as claimed in claim 3, wherein the insert is of D-shaped cross section.

5. A balancer shaft as claimed in claim 3 or 4, wherein the insert is held in position within the hollow shaft by welding.

6. A balancer shaft as claimed in any preceding claim, wherein the end of the eccentric bore is plugged to prevent the ingress of oil.

7. A balancer shaft as claimed in any preceding claim, formed with only two races for support bearings, one race being located near the driven end of the shaft and the other substantially mid-way along the length of the eccentric bore.

8. A balancer shaft as claimed in any preceding claim, having two or more axially extending eccentric bores.

9. A balancer shaft as claimed in any preceding claim, wherein the driven end of the shaft is formed with a concentric bore that does not affect the shaft imbalance but reduces the weight of the shaft.

10. A balancer shaft as claimed in any preceding claim, wherein the driven end of the shafts is formed with a drive sprocket or with a fixing to allow the shaft to be connected to a drive pulley or cog.

11. A balancer shaft for an internal combustion engine constructed arranged and adapted to operate substantially as herein described with reference to and as illustrated in Figures 2 and 3 or Figure 4 of the accompanying drawings.