FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patent Rules, 2003
Provisional Specification
(See section 10 and rule 13)
Robust And Sturdy Clutch Housing
Mahindra and Mahindra Ltd.
An Indian company registered under the Indian Companies Act, 1956.
F: 31, MIDC, Satpur, Nashik - 422 007, Maharashtra State, India

The following specification describes the invention:


Robust And Sturdy Clutch Housing
Field of invention:
Present invention relates to wet clutches used in automobiles. In particular this invention relates to increasing the strength of clutch housing to withstand high burst.
Background of Invention:
In the automotive industry, the use of wet clutch is predominant in manual transaxles where radial space is a constraint. This is commonly seen in 3 wheelers and 2 wheelers with the wet clutch mounted on Transmission Secondary shaft. This makes gearbox design complex. To make gearbox design simple we have mounted wet clutch on crankshaft of the engine. The clutch housing is having a gear, meshing with transmission cluster gear.
While down shifting from 4th to 2nd gear at vehicle max speed, of 60 kmph, the clutch rotational speed can go as high as 14000 rpm, instantaneously. The high instantaneous increase in rotational speed of the clutch housing is due to the following facts:
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- Rotational speed of the clutch housing is governed by vehicle speed and the driveline ratios.
- There is no braking of the engine, as the clutch is disengaged.
The high stresses generated due to centrifugal force in the housing in turn lead to bursting of the housing.
There are various possible designs whereby die wet clutches can withstand the high burst speeds generated during vehicle coast-down situations as well as during the down shifting conditions. Some of these designs incorporate housing made completely out of steel instead of Aluminum, the drawback of which is that it increases the overall weight and inertia of clutch assembly. The higher inertia also leads to harder gear shifting and increases the possibility of gear clashing.
Alternatively, the clutch gear is installed on the clutch hub and not on the clutch housing (see Figure 1). In the disengaged condition of the clutch, the clutch housing, along with the engine, is disconnected from the rest of the Drive Line. Although in this arrangement the clutch housing never rotates at a high speed, as the clutch housing is left floating, the clutch plates are not sufficiently guided in the housing, which leads to field complaints of poor clutch life.
In yet another method, the clutch is mounted on the secondary shaft of the
transmission whereby the clutch is situated between the Gear Box output shaft and
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final drive. Here the clutch housing speed is dependent on the final drive ratio, but independent of the transmission ratio. Hence high burst speeds are never achieved. However, this arrangement leads to a complex transmission design.
All such arrangements, including some which are not mentioned here, have other disadvantages with respect to packaging, clutch life and issues related to higher inertia. Moreover, adopting any of these arrangements into an already existing layout would also lead to higher development lead time and cost.
Objects and advantages of the invention:
The main objective of current invention is to provide a clutch housing design that brings the centrifugal stress levels (arising due to down shifting at vehicle max. speed, say, of 60 kmph)in the housing within the yield stress limit of the housing material,
Another objective of this invention is to provide a cost effective, low weight housing solution, which will withstand the high burst speed and be able to package the clutch components within the current driveline layout.
A major advantage of the invention over the currently used floating housing alternatives is that the clutch life is not compromised. A further advantage is that
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the invention supports use of light weight aluminium pressure die casting housing thus reducing inertia and weight.
This design can be implemented in place of some of the above solutions, to overcome the burst speed requirements with large direct or indirect cost saving.
Summary of Invention:
The present invention offers a simple and cost effective alternative of strengthened clutch housing to withstand high burst speeds. The invention discloses a moulded steel ring, preferably at the periphery of the housing, to protect the housing from bursting out under the stresses generated from the centrifugal forces developed inside the housing. The cross section thickness and vent hole shapes are also optimized to eliminate stress concentration.
Brief description of the figures:
Figure 1 shows a clutch housing of prior art
Figure 2 shows a layout explaining the powerflow
Figure 3 shows the clutch housing of the invention with its integrated peripheral
ring.
Figure 3 A shows the of the proposed model -1
Figure 4 shows the results of the CAE analysis of the base model
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Figure 5 shows the results of the CAE analysis of the Proposed model -1 Figure 6 shows the results of the CAE analysis of the Final model
Description of the invention:
Figure 2 explains the power flow from the engine to wheels when engine is driving the wheels and when wheels are driving the power train. We first seek to explain why under certain conditions there is a generation of high stresses.
Transmission ratios for the various gears are denoted as Yl, Y2, Y3, and Y4 respectively for the 1st, 2nd, 3rd, and the 4th gears. The final drive ratio is denoted asY5.
If the rotational speed of the engine is denoted as X, the following two states hold true:
1. The rotational speed of the wheel of the vehicle, Z = ((X/Y)/Y5), where Y is one of Yl, Y2, Y3, or Y4 - depending upon the gear engaged.
2. The rotational speed of the clutch is the same as the rotational speed of the engine, X, as clutch is in engaged condition.
In the coast-down condition the vehicle wheels drive the clutch, which is
disengaged from the engine and whereupon its speed becomes equal to X which in
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turn is equal to Z*Y5*Y, where Y is one of the Yl, Y2, Y3 or Y4 depending upon which gear has been engaged.
It is this clear that the clutch housing, which is engaged with transmission cluster gear, can attain a high rotational speed due to the driveline ratios multiplication factor. The resulting high centrifugal force is sufficient to burst an inadequately designed housing.
While down shifting at vehicle speed of 60 kmph, from 4th to 2nd gear, the rotational speed of the clutch housing is calculated to be 14000 rpm, which results in the bursting of the housing due to high centrifugal stresses.
As shown in Figure 3, the present invention provides a novel housing that incorporates a moulded steel ring at the periphery of the housing. The steel ring helps the overall housing withstand the stresses generated by the high centrifugal forces. Furthermore, a novel arrangement of vents and oil scoop openings accompanied by the optimum design of the thickness of the housing wall at critical stress sections results in an overall robust and sturdy clutch housing design.
Stress analyses were carried out under several conditions. Final design was such as to bring down the stress level to below the safe yield point of Aluminum.
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In the clutch housing without the steel ring of the present invention, the maximum stress experienced at any point along the clutch housing was 343 MPa. This is more than the max yield stress (120MPa) of Aluminum (LM6, used in the initial housing). This was resulting in the bursting of housing.
As the first attempt to reduce the stress levels in the housing, the thickness along the entire periphery of the housing was increased by 1mm (see figure 3A). In this case (denoted as Model 1), the maximum stress in the housing was seen to reduce from the existing 343 MPa to 253 MPa. However, the same is still more than the safe limit of LM6.
Further attempts to reduce the stress level by optimizing the housing design led to a reduction in stress level from 253 to 230 MPa, yet not meeting the design acceptance criteria. These attempts included reduction in thickness of the housing at the points where the housing radial displacement is outward and increase in the thickness where this displacement is inward. Optimization of oil scoop profile further reduced the stress level to 143MPa. It was therefore obvious that the optimization of design of the parts of the clutch housing would not reduce the stress level to within the required level.
Figures 4, 5 and 6 respectively show results of stress analyses for base model, proposed model - 1 and the final model.
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The inventors found that incorporation of a steel ring situates at the location of the high stress, namely the periphery of the housing, along with the 1mm increase in the thickness and the optimized design of other parts such as the oil scoop and vents, arrests the bursting by bringing down the stresses to a level of 109MPa, which is within the safe limit of LM6, with yield strength of 120 MPa.
Design Verification:
1. The clutch housing is tested on the test rig at 14000 and found in intact condition.
2. The clutch was tested on vehicle and coast down tests from 4 to 2 gear, at vehicle speed of 60 kmph was carried out for 1000 cycles successfully.

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Dated This 13th Day of April, 2009