A HYBRID CLUTCH PLATE

FIELD OF INVENTION

The invention relates to a clutch plate, especially to a hybrid clutch plate formed
with a combination of alloyed grade and conventional grade material.

BACKGROUND OF THE INVENTION

A clutch is a mechanical device, which provides for the transmission of power from a driving member to a driven member. Heavy-duty commercial vehicles working in arduous conditions, such as rugged terrain or over loaded conditions, normally face heavy abuse of clutch disc and clutch pressure plate. They normally undergo severe wear and thermal distortion during service. Clutch pressure plate butts with the friction facing surface of the clutch disc. The clutch transmits power through frictional force generated between the clutch disc and the pressure plate. The pressure plate frictional area comes in contact with the clutch disc friction material only on its surface. The remaining thickness of the pressure plate is designed to provide adequate pressure for clutching the system. The clutch has a number of clutch springs on the other side for clutching and de-clutching operations. Thus, normally, the wear and tear of the material happens only on the surface of the pressure plate. It is therefore needed to provide a higher wear and thermal distortion resistance for the pressure plate that is in contact with the clutch disc friction material.

There have been attempts to increase the overall mass of the pressure plate or of the pressure plate assembly, in order to be able to absorb heat and to reduce wear and tear. However, this entails increasing the size of the individual components, resulting in construction space problems and increased cost.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a clutch plate with high wear and thermal distortion resistance thereby increasing the service life of the clutch for a typical heavy duty commercial vehicle.

It is also an object of the present invention to provide a method of manufacturing a clutch plate with two layers made of different grades of cast iron without any manufacturing defect.

SUMMARY OF THE INVENTION

In order to achieve the above objects, the present invention provides a hybrid clutch pressure plate that is contactable with the friction surface of a clutch disc. The hybrid clutch pressure plate comprises a first layer formed from a conventional grade material and a second layer formed from an alloyed grade material. Further, the present invention also provides a hybrid clutch face plate that is contactable with the friction surface of a clutch disc toward the flywheel side of the clutch assembly.

The conventional grade material is preferably cast iron alloyed with suitable quantity of Carbon, Silicon, Manganese, Chromium, Sulphur, Phosphorus and Copper. The alloyed grade material is formed by adding suitable quantity of Nickel and Molybdenum with the conventional grade cast material.

According to a specific embodiment of the present invention, the alloyed grade material is formed by adding approximately 0.6-0.8 (wt.%) of Nickel and approximately 0.3-0.4 (wt. %) of Molybdenum to the conventional grade cast iron. In order to reduce overall cost of the component, only the surface of the clutch pressure plate and the face plate that is in contact with the friction material of the clutch disc is formed with the alloyed grade material.

According to a preferred modification, further to the addition of Nickel and Molybdenum to the conventional grade material, the weight percentage of chromium and copper in the conventional grade material is increased by at least 25% and 85% respectively to form the alloyed grade material.

In a further preferred embodiment, the heat transport capacity of the cast iron can be improved by introducing more graphite into the conventional grade composition. This is achieved by adding more carbon and controlling the silicon content in the composition. In this case, the layer of the clutch pressure plate and face plate having the conventional grade cast iron has a higher ratio of graphite than the layer having alloyed grade cast iron to effectively remove heat and maintain the overall stiffness of the clutch plate.

The invention further relates to a method of manufacturing a hybrid clutch plate. The conventional grade and the alloyed grade cast iron compositions are simuhaneously and separately melted in induction furnaces. A small batch of melt from each of the conventional grade melt and the alloyed grade melt are taken in 20 separate ladles. A sand mold for casting is first partially filled with the alloyed grade material from the ladle, which makes up the surface of the clutch pressure plate that would be in contact with the frictional surface of the clutch disc. After a predetermined time period of about 5 to 20 seconds, the batch of melt from the conventional grade melt is poured over the alloyed grade melt. The conventional 25 grade melt will butt and solidify with the already solidified alloyed grade melt present in the sand mold. After the solidified cast is taken out of the mold, the runner and risers are removed and machining is performed to obtain the final hybrid clutch plate.

In a preferred embodiment the conventional and/or alloyed grade material is poured into the sand mold at a temperature of about 1450 to 1500°C.

In a further preferred embodiment, equivalent amount of alloyed grade and conventional grade material is poured sequentially into the sand mold. By way of an example of the invention, a small batch of 12.5 kilograms of alloyed grade melt is poured into the sand mold followed by 12.5 kilograms of conventional grade melt, after a time interval of about 5 to 20 seconds.

STATEMENT OF INVENTION

Accordingly, the invention discloses a hybrid clutch plate comprising: a frictional region contactable with a clutch disc frictional lining unit; characterized in that said hybrid clutch plate comprises a first layer (14a) formed from a conventional grade material and a second layer (14b) forming the frictional region is formed from an alloyed grade material including, in addition to the conventional grade material, approximately 0.6-0.8 (wt.%) Nickel and approximately 0.3-0.4 (wt.%) Molybdenum.

The invention also discloses a method of manufacturing a hybrid clutch plate comprising the steps of: simultaneously melting and optimizing a conventional grade cast iron and an alloyed grade cast iron; filling a sand mold partially with the alloyed grade cast iron melt; pouring the conventional grade cast iron melt over the alloyed grade cast iron melt after a predetermined time interval, such that the conventional grade cast iron melt butts and solidifies with the alloyed grade cast iron in the sand mold; removing component formed in the sand mold after solidification; and machining the component to form the hybrid clutch plate.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings wherein the showings are for the purpose of
illustrating a preferred embodiment of the invention only, and not for the purpose
of limiting the same,

Figure 1 shows a normal conventional clutch assembly;

Figure 2a shows the clutch assembly with a hybrid clutch pressure plate according to the instant invention;

Figure 2b shows the clutch assembly with a hybrid clutch pressure plate and face plate according to an embodiment of the instant invention;

Figure 3a shows the friction surface of the hybrid clutch pressure plate according to the instant invention;

Figure 3b shows the rear surface of the hybrid clutch pressure plate according to the instant invention; and

Figure 4 shows the layers of the hybrid clutch plate, according to an embodiment of the instant invention.

DETAILED DESCRIPTION OF THE INVENTION

The basic structure of a clutch assembly is described with reference to figure 1.
The friction clutch shown by way of example is designated overall by the number
100. As can be seen in figure 1, the clutch (100) comprises a flywheel (12), which,
0 in its radially inner portion is rotationally connected to an engine take-off shaft or a crankshaft (not shown) either directly or by means of a torque-transmitter arrangement. Appropriate screw holes are designated by (S) in the figure 1. The flywheel (12) may be designed with a web-like support section (30), which is made as an integral part of the flywheel (12). A plate arrangement is formed by a pressure plate (14) and a face plate (16) located in the volume formed between the flywheel (12) and a cover (26). The clutch pressure plate (14) is formed radially on the outside of the flywheel (12) and is held in a housing in a rotationally fixed manner and such that it can be axially displaced. The clutch face plate (16) is located in the volume formed between the flywheel (12) and the pressure plate (14). Between the pressure plate (14) and the face plate (16) there is a friction- lining unit (18) of a clutch disc arrangement (20). A further friction-lining unit (28 in fig. 3) may also be provided between the face plate (16) and the flywheel (12). Suitable bolting arrangement is provided in the face plate (16) to fit to the internal area of the flywheel (12). Springs (22) is provided to act on the pressure plate (14) in such a way that the pressure plate (14) is pushed toward the flywheel. The friction-lining unit (18) is then clamped between the pressure plate (14) and the face plate (16) thereby engaging the clutch. The springs (22) also help in isolating the transmission from the shock of the clutch engaging. A releasing spring arrangement (not shown) is provided to pull the pressure plate (14) so that the engagement of the plate with the friction-lining unit is released and the clutch is disengaged accordingly.

As it can be observed from figure I, a frictional region of the clutch plate (14, 16) engages with the friction-lining unit (18) of the clutch disc when the clutch is engaged. This frictional region, especially in a heavy-duty vehicle such as trucks etc., undergoes enormous load, thereby resulting in the wear and thermal distortion of the clutch plates (14 & 16).

An embodiment of the invention is illustrated in figure 2a. A hybrid clutch pressure plate refers to a clutch pressure plate formed of both conventional and alloyed grade material. Thus, only the area that would be in contact with the friction-lining unit (18) of the clutch disc (20) would be formed by an alloyed grade material, rather than the whole thickness of the clutch pressure plate, to reduce the overall cost of the component.

The hybrid clutch pressure plate of the present invention has a first layer (14a) formed from a conventional grade material, usually cast iron with conventional alloying elements. The Table I below shows the percentage by weight of the conventional alloys used in the conventional grade cast iron forming the first layer (14a):

TABLE I

The clutch pressure plate of the present invention further comprises a second layer
(14b) formed from an alloyed grade material, i.e., cast iron mixed with additional
alloying elements, including elements used for the conventional alloys. The Table
II below shows the percentage by weight of the alloys used in the alloyed grade cast iron forming the second layer (14b) according to a preferred embodiment of the invention:

TABLE II

The second layer (14b) forms the frictional region of the hybrid clutch pressure plate, which comes in direct contact with the clutch disc friction-lining unit. As can be observed from Table II, Ni and Mo are alloying elements added to the conventional alloy to make it an alloy grade cast iron. Further, the content of Cr is increased by at least a 25% and the content of Cu is increased by at least 85% in the alloy grade material, compared to their respective content in the conventional grade alloy. The addition of Ni and Mo and the increase in the content of Cr and Cu improve the strength, toughness and wear resistance of the material. Ni and Cu increase the strength, toughness and wear resistance and Cr and Mo forms hard wear resistant phase called alloy carbides to provide additional wear resistance to the material. The above mentioned alloyed grade material also produces a refined microstructure that is responsible for improving the above said properties. The overall strength and hardness increases marginally compared to the conventional grade material, but the wear resistance, thermal cracking and distortion properties improve significantly with these additional alloying elements.

As illustrated in figure 2b, in a preferred variation, the hybrid concept can also be extended to the face plate (16). As illustrated in figure 2b, the clutch face plate (16) has a first surface (16a) formed from a conventional grade material, usually cast iron mixed with conventional alloys as shown in table 1 and a second surface (16b) formed from an alloyed grade material, i.e., cast iron mixed with additional alloying elements, including elements used for the conventional alloys as shown in table 2. Thus, the second surface (16b) of the face plate (16) forms the frictional region, which comes in direct contact with the friction-lining unit (18). It could be envisaged to extend this concept to a clutch plate assembly where a further frictional lining unit is provided between the face plate and the flywheel. Similar to the hybrid clutch pressure plate, the alloyed grade material produces a refined microstructure that is responsible for improving the strength, toughness and wear resistance of the material in the hybrid clutch face plate. The strength and hardness increases marginally compared to the conventional grade material, but the wear resistance, thermal cracking and distortion properties improve significantly with these additional alloying elements.

The alloyed grade clutch pressure plate and face plate was tested for its performance in a typical heavy duty commercial vehicle with excess payloads. Upon testing the performance of the alloyed grade material throughout the thickness of the clutch plate it was noted that the life of the clutch plate increased up to 2.0 - 3.0 times compared to conventional grade. It is obvious that the hybrid concept also would show similar improvement in the performance and life since the conventional material behind the alloyed grade layer in the hybrid concept does not take part in the friction contact, but rather acts only as a load support providing the required thickness on the other side for clutching action.

A manufactured hybrid clutch plate component is shown in figures 3a and 3b.
Figure 3 a shows the surface of the hybrid clutch pressure plate that would be in contact with the friction-lining unit of the clutch disc. Figure 3b shows the bottom I surface of the hybrid clutch pressure plate having projections (24) for seating of the clutch springs. The thickness of the manufactured hybrid clutch pressure plate is about 1 inch. However, the thickness may vary depending on the application.

A method of manufacturing the hybrid clutch pressure plate according to this invention requires a modification in the casting process. The conventional grade I cast iron and the alloyed grade cast iron are melted simultaneously and the composition is optimized in separate induction furnaces. The pouring sequence has to be set before filling the sand mold. The hybrid clutch pressure plate total mold volume is divided into two parts. Equal amounts of conventional and the alloyed grade melt are then taken in two separate ladles. Equal volume/weight of I conventional and alloyed grade melt are preferred to avoid composition changes at the friction face. In a preferred example, when the total weight of the pressure plate as-cast casting is 25 kilograms, 12.5 kilograms of conventional grade melt is taken in one ladle and about 12.5 kilograms of alloyed grade melt is taken in another ladle. A sand mold will first be filled with the alloy grade melt from the ladle, which would eventually make up the face of the clutch pressure plate wherever strength and wear resistance is required. The pouring temperature of the alloyed grade material is around 1450 to 1500. After a specific time period of about 5 to 20 seconds, preferably 10 to 20 seconds, and most preferably between 5 to 10 seconds, the conventional grade melt from the ladle will then be poured over the already poured alloyed grade melt. This time gap is very important, else the final component would have manufacturing defects. A little delay in the pouring would not allow the two grades of melts to butt with each other and solidify uniformly. On the contrary, if the pouring of the conventional grade melt occurs too early, it may mix with and dilute the alloyed grade melt. The pouring temperature of the conventional grade material is around 1450 to 1500˚C.

The conventional grade will butt and solidify with the already solidifying alloyed grade cast iron, which is present in the bottom of the sand mold. Figure 4 shows the conventional grade and alloyed grade layers of the hybrid clutch pressure plate formed in the sand mold, according to the instant invention. After the cast is taken out of the mold, the runner and risers are removed and the cast is machined to obtain the final component. The machining can be done similar to conventional methods.

Clutching action normally generates high temperature on the surface, which should be effectively vented out of the system or by providing higher thickness. The heat transport capacity of cast iron can be improved by introducing more graphite into the composition. The volume of graphite is controlled by the Silicon content of the melt. The heat transport capacity of the cast iron can be increased by adding more carbon and controlling the silicon content in the melt. In this case, the top half of the component with conventional grade cast iron can afford to have higher graphite to remove the heat while maintaining the overall stiffness of the clutch pressure plate. This also improves both the wear and heat transport capacity of the component. There would be a small difference between the alloy and conventional grade in the graphite content. This is because the alloy elements slightly thin down the graphite size. Currently, the graphite content is about 10% of the volume. Preferably, if the graphite content is slightly increased to, say, 15% volume, the heat transport capacity of the clutch pressure plate would increase. This, however, does not compromise the overall strength of the pressure plate since the conventional grade is butted to the alloy grade having higher strength and toughness.

While the above paragraphs explain the various embodiments of the invention, it is apparent that numerous modifications and variations can be made without departing from the scope and spirit of this invention. It is therefore intended that this invention be limited only as indicated in the appended claims.

WE CLAIM

1. A hybrid clutch plate comprising:

a frictional region contactable with a clutch disc frictional lining unit; characterized in that said hybrid clutch plate comprises a first layer (14a) formed from a conventional grade material and a second layer (14b) forming the frictional region is formed from an alloyed grade material including, in addition to the conventional grade material, approximately 0.6-0.8 (wt.%) Nickel and approximately 0.3-0.4 (wt.%) Molybdenum.

2. The hybrid clutch plate as claimed in claim 1, wherein the alloyed grade material comprises approximately 0.3-0.5% of chromium by weight and approximately 0.5-0.7% of copper by weight.

3. The hybrid clutch plate as claimed in claim 1, wherein graphite content of said conventional grade material is increased to approximately 15% (by volume).

4. A method of manufacturing a hybrid clutch plate comprising the steps of: simultaneously melting and optimizing a conventional grade cast iron and
an alloyed grade cast iron;

filling a sand mold partially with the alloyed grade cast iron melt;

pouring the conventional grade cast iron melt over the alloyed grade cast iron melt after a predetermined time interval, such that the conventional grade cast iron melt butts and solidifies with the alloyed grade cast iron in the sand mold;

removing component formed in the sand mold after solidification; and

machining the component to form the hybrid clutch plate.

5. The method as claimed in claim 4, wherein equal volume of alloyed grade cast iron and conventional grade cast iron are poured in the sand mold.

6. The method as claimed in claim 4, wherein the alloyed grade cast iron is poured into the sand mold at a pouring temperature of about 1450 to 1500°C.

7. The method as claimed in claim 4, wherein the conventional grade cast iron is poured over the alloyed grade cast iron at a pouring temperature of about 1450 to 1500°C.

8. The method as claimed in claim 4, wherein the predetermined time interval is about 5 to 10 seconds.

9. The method as claimed in claim 4, wherein the predetermined time interval is about 10 to 20 seconds.