Claims:We claim:

1. A balancer shaft assembly with reduced stress concentration in critical areas thereof, wherein the balancer shaft assembly comprises:

• a balancer shaft having at least one stepped diameter for secured mounting of a gear thereon;

• a balancer mass tightened with the gear for balancing the same on the balancer shaft;

• a bolt for assembly of the above balancer shaft; and

wherein the balancer shaft is configured with stepped outer diameter having a step for supporting and retaining the inner race of the bearing thereof.

2. Balancer shaft assembly as claimed in claim 1, wherein the balancer shaft is configured with bolt threads extending deeper inside thereof and the thread end is configured substantially away from the fillet of the stepped small diameter provided for retaining the inner race of the balancer shaft bearing.

3. Balancer shaft assembly as claimed in claim 1, wherein the balancer shaft is configured with threads extending long and ending deep inside the balancer shaft to shift the load path and thereby reducing stress amplitude on stress concentration zone of the stepped diameter thereof.

4. Balancer shaft assembly as claimed in claim 1, wherein the bolt threads are configured to extend long and deep inside the bolt engagement region of the balancer shaft to effectively decouple the bolt engagement region from the fillet of the smaller diameter located in the stress concentration zone thereof.

5. Balancer shaft assembly as claimed in claim 1, wherein the bolt threads extending long and deep inside the balancer shaft eliminates the stretching of the small diameter of the balancer shaft.
6. Balancer shaft assembly as claimed in claim 1, wherein the bolt threads extending long and deep inside the balancer shaft relieves the smaller diameter step portion of the balancer shaft from the axial bolt load acting thereon.

7. Balancer shaft assembly as claimed in anyone of the claims 1 to 7, wherein the threads are placed deep inside the balancer shaft such that the distance of the first engaged thread from the fillet is greater than thread engagement length.

Dated: this day of 06th May, 2016. SANJAY KESHARWANI
APPLICANT’S PATENT AGENT , Description:FIELD OF INVENTION

The present invention relates to balancer shaft assembly in automotive engines. In particular, the present invention relates to the means for reducing stress concentration in the balancer shaft assembly. More particularly, the present invention relates to reconfiguring load path of the bolt loads acting in the balancer shaft to divert stress concentration in the critical areas thereof.

BACKGROUND OF THE INVENTION

The balancer shafts or simply balance shafts are most very common in the engines. Asymmetrical vibrations are inherently developed, which cannot be completely eliminated irrespective of the fine-balancing of the internal components. This vibration is generated due to the movement of the connecting rods in engine, which is not symmetrical throughout the crankshaft rotation. Therefore, during a specified period of crankshaft rotation, the pistons moving between the top dead center and bottom dead center are not always completely opposed in their acceleration. In internal combustion engines, a balancer shaft is configured as an eccentric weight shaft which is adapted to offset the vibrations developed in the engines that are not inherently balanced.

DISADVANTAGES WITH THE PRIOR ART

In the conventional configuration of the balancer shaft assembly shown in Figures 1, 2 and 4, the engaged threads are exactly under the stress concentration zone. This region becomes a critical zone, because the smaller diameter region on the balancer shaft is stretched due to torque applied on the bolt, which induces high tensile stresses on the fillet near the step (as shown in Figure (3), in the major principal stress directions), which is already lying in a critical location.

This leads to crack initiation during balancer shaft assembly and often causes catastrophic failures within a very short service life thereof.
DESCRIPTION OF THE PRESENT INVENTION

The present invention relates to the balancer shaft assembly of the internal combustion engines. The balancer shaft is used for balancing the rotating unbalanced loads in the engine. Normally, the balancer shaft assembly consists of the following components:

• Balancer shaft.
• Balancer masses.
• Gear
• Bolts

The balancer shaft, balancer mass and gear are held together by tightening the bolt and applying a torque load as shown in Figure 1. Very high bolt load acts on the balancer shaft assembly to keep these components together by means of surface friction therebetween. In this configuration, a step is configured on the balancer shaft to house the inner race of the bearing, which is sandwiched along with gear and the balancer mass between the step on the balancer shaft and the bolt-head during the assembly thereof. The step on the shaft is loaded due to axial loads generated from the torque being directly applied on the bolt.

Therefore, the area around this step is a stress concentration zone which is critical due to the change in diameter of the balancer shaft in this region and because of a smaller fillet radius near inner race of the bearing disposed there.

OBJECTS OF THE INVENTION

Some of the objects of the present invention - satisfied by at least one embodiment of the present invention - are as follows:

An object of the present invention is to provide a balancer shaft assembly having reduced stress concentration in the critical areas thereof.

Another object of the present invention is to provide a balancer shaft assembly which eliminates the stretching of balancer shaft fillet near the bearing seat.
Still another object of the present invention is to provide a balancer shaft assembly to decouple the smaller diameter step on the balancer shaft from bolt load.

Yet another object of the present invention is to decouple the stress concentration zones near the shaft step-fillet.

A further object of the present invention is to decouple the step-fillet from the balancer shaft bending due to the centrifugal loads of the balancer mass during operation.

These and other objects and advantages of the present invention will become more apparent from the following description when read with the accompanying figures of drawing, which are, however, not intended to limit the scope of the present invention in any way.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a balancer shaft assembly with reduced stress concentration in critical areas thereof, wherein
The balancer shaft assembly comprises:

• a balancer shaft having at least one stepped diameter for secured mounting of a gear thereon;

• a balancer mass tightened with the gear for balancing the same on the balancer shaft;

• a bolt to assembly the above balancer shaft; and

• wherein the balancer shaft is configured with stepped outer diameter having a step for supporting and retaining the inner race of the bearing thereof.

Preferably, the balancer shaft is configured with bolt threads extending deeper inside thereof and the thread end is configured substantially away from the fillet of the stepped small diameter provided for retaining the inner race of the balancer shaft bearing.

Preferably, the balancer shaft is configured with threads extending long and ending deep inside the balancer shaft to shift the load path and thereby reducing stress amplitude on stress concentration zone of the stepped diameter thereof.

Preferably, the bolt threads are configured to extend long and deep inside the bolt engagement region of the balancer shaft to effectively decouple the bolt engagement region from the fillet of the smaller diameter located in the stress concentration zone thereof.

Preferably, the bolt threads extending long and deep inside the balancer shaft eliminates the stretching of the small diameter of the balancer shaft.

Preferably, the bolt threads extending long and deep inside the balancer shaft relieves the smaller diameter step portion of the balancer shaft from the axial bolt load acting thereon.

Preferably, threads are placed deep inside the balancer shaft such that the distance of the first engaged thread from the fillet is greater than thread engagement length.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will be briefly described with reference to the accompanying drawings, which include:

Figure 1 shows a sectional view of the conventional arrangement of the balancer shaft assembly;

Figure 2 shows the load path in a conventional configuration of the balancer shaft assembly;

Figure 3 shows the stress concentration in the conventional balancer shaft assembly;

Figure 4 shows the improved load path in the balancer shaft assembly configured in accordance of the present invention

Figure 5 shows a detailed view of the maximum principal stress under bolt load condition in the balancer shaft assembly configured in accordance with the present invention.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS

In the following, different embodiments of the present invention will be described in more details with reference to the accompanying drawings without limiting the scope and ambit of the present invention in any way.

Figure 1 shows a sectional view of the conventional arrangement of the balancer shaft assembly. The balancer shaft 10 includes a step 12 for laterally supporting the inner race 22 of a bearing 20 and an internally threaded end 14 for tightening a threaded bolt 30 having a flared head 32 at one end and threads 34 near the other end thereof. The threaded bolt 30 is used for first placing the inner race 22 of the bearing 20 on the step 12. After placing circlip 24 thereon, then a gear 40 is mounted on the balancer shaft to finally tighten a balancer mass 50 on the balancer shaft 10. A very high axial load ‘L’ acts in axial direction of the balancer shaft 10 for keeping the bearing 20, gear 40 and balancer mass 50 together by means of the surface friction of the threaded bolt 30 in the bolt thread engagement region 60 due to torque T applied thereon while tightening it on the balancer shaft 10. Therefore, there is a stress concentration in the region of the step 12 because of sudden change in diameter and smaller fillet provided for joining the two diameters d1 and d2 of the balancer shaft 10.
Figure 2 shows the load path 70 and the stress concentration zone 80 in a conventional configuration of the assembly of the balancer shaft 10. It clearly shows that the stress concentration zone 80 is formed around the step 12 as it lies in the load path 70. Here, the bolt engagement region 60 is disposed before the stress concentration zone 80 formed due to the bolt torque applied for tightening the gear 40 and the balancer mass 50 on the balancer shaft 10.

Figure 3 shows the detailed view of the stress developed in balancer shaft 10, which is depicted by red arrows under bolt load condition in the conventional configuration of the assembly of the balancer shaft 10. The maximum principal stress is concentrated around the fillet of step 12 between diameters d1 and d2 and in the balancer shaft 10 and balancer mass 50 under bolt head 32. The region marked SCZ is the stress concentration zone, which is also shown inset in an enlarged view for a clearer view thereof. This region is critical as this smaller diameter is stretched on applying torque, inducing tensile stresses on this fillet which already is a critical location and crack initiation occurs during the assembly which leads to catastrophic failure within very short working life.

Figure 4 shows the load path 170 and the stress concentration zone 180 in the assembly of the balancer shaft 110 configured in accordance of the present invention. Here, the bolt engagement region 160 is disposed after and away from the stress concentration zone 180. Therefore, the bolt engagement region 160 is effectively decoupled from the stress concentration zone 180. This is achieved by forming the threads of the bolt 130 much long and deeper in the balancer shaft 110 and thereby by shifting these threads far away from the critical fillet region of the step 112 formed between the two diameters d1 and d2 of the balancer shaft 110. This significantly diverts the bolt load path to eliminate the stretching of smaller diameter step d2 on the balancer shaft shown in Figure 4 and 5. This configuration also relieves the smaller diameter step d2 from the axial bolt load ‘L’ as was prevalent in the conventional balancer shaft configuration shown in Figure 1, 2 and 3.

Figure 5 shows a detailed view of the stress developed in the balancer shaft 110 and depicted by red arrows under bolt load condition in the assembly of the balancer shaft configured in accordance with the present invention. A minimum stress is concentrated around the fillet of the step 112 between the diameters D1 and D2 and in the balancer shaft 110 and the maximum stress is uniformly distributed throughout the balancer shaft 110, i.e. from the balancer mass 150 under the bolt head 132 right up to and beyond the fillet of the step 112 joining the diameters D1 and D2. The region marked SCZ is the stress concentration zone shown inset in an enlarged view. It is clear from this view that the stretching of the smaller diameter D2 on the balancer shaft 110 is eliminated due to minimum stresses Smin in this zone around the fillet on step 112. This balancer shaft 100 configuration completely relieves the smaller diameter step from the axial bolt load ‘L’ and the fillet is loaded only by local bending and stress concentration.

WORKING OF THE INVENTION:

In accordance with this invention, the bolt threads are moved deep inside the balancer shaft, i.e. far away from the critical fillet region. The deeper placement of the threads diverts the bolt load path such that it eliminates stretching of smaller diameter step on the balancer shaft as shown in Figure 2 and 3. This relieves completely the smaller diameter step on the shaft from axial bolt load and the fillet is loaded only due to local bending and stress concentration.

TECHNICAL ADVANTAGES AND ECONOMIC SIGNIFICANCE

The balancer shaft assembly configured in accordance with the present invention has the following advantages:

1. Deeper bolt thread engagement into the balancer shaft by a longer bolt,

2. Load path is diverted to eliminate stretching of the balancer shaft step-fillet near the bearing,

3. Smaller diameter step on the balancer shaft is decoupled and relieved completely from any torque loads,

4. Stress concentration zones near the thread fillets and near the balancer shaft step-fillet are decoupled,

5. Step fillet also decoupled from the balancer shaft bending due to balancer mass centrifugal loads during operation,

6. Significantly reduces the stresses on the balancer shaft step-fillet,

7. Avoids the surface heat treatment process of the balancer shaft in critical regions, thereby reduces the manufacturing cost thereof,

8. Presents a very robust design, and

9. Facilitates in increasing the bolt load for achieving a more robust joint by eliminating the load complexities.

Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, shall be understood to implies including a described element, integer or method step, or group of elements, integers or method steps, however, does not imply excluding any other element, integer or step, or group of elements, integers or method steps. In the claims and the description, the terms “containing” and “having” are used as linguistically neutral terminologies for the corresponding terms “comprising”.

The use of the expression “a”, “at least” or “at least one” shall imply using one or more elements or ingredients or quantities, as used in the embodiment of the disclosure in order to achieve one or more of the intended objects or results of the present invention. Furthermore, the use of the term “one” shall not exclude the plurality of such features and components described.

The description provided herein is purely by way of example and illustration. The various features and advantageous details are explained with reference to this non-limiting embodiment in the above description in accordance with the present invention. The descriptions of well-known components and manufacturing and processing techniques are consciously omitted in this specification, so as not to unnecessarily obscure the specification.
In the previously detailed description, different features have been summarized for improving the conclusiveness of the representation in one or more examples. However, it should be understood that the above description is merely illustrative, but not limiting under any circumstances. It helps in covering all alternatives, modifications and equivalents of the different features and exemplary embodiments.

Therefore, innumerable changes, variations, modifications, alterations may be made and/or integrations in terms of materials and method used may be devised to configure, manufacture and assemble various constituents, components, subassemblies and assemblies according to their size, shapes, orientations and interrelationships.

While considerable emphasis has been placed on the specific features of the preferred embodiment described here, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiments without departing from the principles of the invention. These and other changes in the preferred embodiment of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

The exemplary embodiments were selected and described in order to be able to best represent the principles and their possible practical application underlying the invention. Many other examples are directly and immediately clear to the skilled person because of his/her professional knowledge in view of the above description. Thereby, the skilled persons can optimally modify and use the invention and its different exemplary embodiments with reference to the intended use.