DESC:FORM 2
THE PATENT ACT, 1970,
(39 OF 1970)
&
THE PATENTS RULE, 2003
COMPLETE SPECIFICATION
(SEE SECTION 10; RULE 13)

“CRANK BUSH PRESSING TECHNIQUE WITH AUTO CIRCULATION OF LIQUID NITROGEN THROUGH PRESSING DOLLY”

MAHINDRA & MAHINDRA LIMITED
A COMPANY REGISTERED UNDER THE PROVISIONS OF COMPANIES ACT, 1956 HAVING ADDRESS AT R & D CENTER, AUTOMOTIVE SECTOR, 89, M.I.D.C., SATPUR, NASHIK – 422 007, MAHARASHTRA, INDIA

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE NATURE OF THE INVENTION AND MANNER IN WHICH IT IS TO BE PERFORMED

FIELD OF INVENTION:-

The present invention is related to engine assembly method. More particularly, the invention is related to crank bush pressing with auto circulation of liquid nitrogen through pressing dolly during the engine assembly.

BACKGROUND OF THE INVENTION:-

In Single Cylinder Engine, the Crankcase is made of two valves fitted together. The material of crankcase is Aluminum, which is very soft and ductile. Prone to scratches and deformation in handling and under pressures. A Bush pressing operation is involved in process to fit a bi-metallic material bush with shrink fit. Thus Liquid Nitrogen chilling is defined for this application. For this instead of chilling the bushes in a container and then withdrawing them manually one by one in manufacturing a different concept has been derived.

The single cylinder engines wherein the Crank case is required to be fitted with crank bush, following difficulties were anticipated as the Crankcase material is Aluminium and Bush is of bi-metallic having outer cover of steel.
- Interference of 124 µm interference (Max. Material condition) will shear parent material while pressing.
- Pressing force of above 1000 kgf required, whereas, as per CAE analysis Crankcase cannot be subjected to force above 1000 kgf (Being hollow and will lead to permanent deformation).
- If crank case two valves opened for bush pressing in which case the bush has to be pressed in both valves separately, then one torqueing machine will be additionally required – cost 65 lacs.
- If bush is to be immersed in liquid nitrogen then operator faces risk of cold burns.
- If operator presses bush without chilling or long time is elapsed between bush removed from container & actual fitting, then there is a risk of process failure.

To press bush in Aluminum crank case without rupturing is a big challenge. To avoid rupturing, chilling of bush for shrink fitting is must, shrinkingof bush is essential to prevent tear of parent bore while bush pressing. Damaged parent bore will reduce interference in pressed bush and may get dislocated in Engine running condition.

OBJECTIVES OF THE PRESENT INVENTION:-

The main object of the present invention is to provide an innovative technique of crank bush pressing by using pressing dolly during assembly of an engine.

Another object of the present invention is to provide technique of crank bush pressing by using pressing dolly wherein liquid nitrogen is auto circulated through pressing dolly.

Still another object of the present invention is to address drawback occurring in the conventional system of crank bush pressing as mentioned above.

BRIEF DESCRIPTION OF THE FIGURES:-

Figure 1 shows crankcase (front and rear view) with the bush fitted therein.
Figure 2 shows the pressing Dolly and Hydraulic Press concept which is crux of the system of the present invention.
Figure 3 shows the auto circulation Nitrogen System circuit/ flow diagram in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION:-

Referring to Figure 1, the particular crank case is hollow. Bush is required to be pressed from both sides in assembled condition. Being hollow, the load sustainability was checked through CAE analysis. It can withstand up-to 1000 kgf.

To overcome the difficulties mentioned above, a different concept of Auto circulation of Liquid nitrogen through pressing dolly worked out. Conventional method of chilling is to dip bush in liquid nitrogen container and mount chilled bush on pressing adaptor and start the cycle of pressing.To avoid operator dependence of chilling, a system in which operator is not required to remove chilled bush from container was developed. This bush will then get chilled due to contact with chilled adaptor. After certain pre-determined time, bush will get pressed.

The system is designed such that the liquid nitrogen will get circulated within the bush pressing dolly. When operator places bush on dolly, bush shrinks by more than 80 to 90 µm in just 30 to 40 sec as presented in the following table.

Briefly, the chilling of bush takes place while it is mounted on pressing dolly. Liquid nitrogen is circulated through the pressing dolly due to internally crafted grooves. Since liquid nitrogen is having boiling temperature of -196°C, dolly and bush gets chilled because of its circulation.Switching ON & OFF of liquid nitrogen circulation is controlled by solenoid valve which is integrated with the machine pressing cycle. The Solenoid valve is kept in-between liquid nitrogen cylinder and pressing dolly and integrated with pressing cycle.This solution will ensure chilled bush being pressed, operator safety, less consumption of liquid nitrogen. The Load cells are taken in circuit to prevent load exceeding 1000 kgf. This fulfills the condition given by CAE analysis, allowable pressing load limit less than 1000 kgs.

The steps followed in the technique of crank bush pressing by using liquid nitrogen comprises of,
- Operator places Bush to be chilled on pressing dolly.
- Operator presses Auto cycle start push button.
- Electronic controller (PLC) gives signal and opens Nitrogen valve.
- Liquid nitrogen flows through pipe to pressing adaptor (Dolly).
- Electronic controller remains open for predetermined time (variable) to allow liquid Nitrogen to flow.
- Liquid Nitrogen circulates in Dolly and chills.
- Since bush is mounted on Dolly, bush also chills along with Dolly.
- This happens for both dollies (Top & Bottom) at the same time.
- After predetermined time, controller sends signal to press for pressing this chilled bush.

The technical advantages achieved are as under:

- This eliminates all quality related issues that would have come otherwise.
- Secondly, operator is kept at a distance from chilled bush handling, thus the safety is addressed eliminating possibility of cold burns.
- Capital expense Reduction of Rs. 70.5 Lacs is achieved.
If crank case is to be opened – we require one torqueing machine of 65 lacs + space and additional work content of 4 mins. per crank case (for opening and re-torqueing for final machining in assembled condition). If not opened then load has to be restricted to 1000 kgf.
- Optimum Utilization of Liquid Nitrogen thereby eliminating the wastage. (Annually estimated wastage Rs. 1.8 Lacs for Project peak volumes of 1, 33,000 nos.)
- This concept will lead to elimination of engine failure field complaints.

The Variable timer is to decide the delay time for bush chilling(Start of shift, during pressing cycle, after tea time, after lunch time etc….). The Cryogenic Solenoid valve switches the flow of nitrogen ON/OFF to minimize consumption of Nitrogen. The Internal expandable support is given to prevent crankcase deformation.Bush orientation to align Crankcase and bush oil hole. The Load cells are integrated to ensure pressing force below 1000 kgf. The process is robust and reliable as Liquid Nitrogen internal circulation through pressing dolly.

If bush is pressed without chilling then, while pressing, high interference will tear the surface of Aluminum parent bore where bush is being pressed. This will reduce the interference force between bush and Aluminum Crankcase and may lead to failure of bush rotation in crank parent bore while the engine is running (hot condition) and may cause seizure of Engine in field.
,CLAIMS:1. Crank bush pressing technique with auto circulation of liquid nitrogen through pressing dolly comprises the steps in a sequential manner
- Operator places Bush to be chilled on pressing dolly;
- Operator presses Auto cycle start push button;
- Electronic controller (PLC) gives signal and opens Nitrogen valve;
- Liquid nitrogen flows through pipe to pressing adaptor (Dolly);
- Electronic controller remains open for predetermined time (variable) to allow liquid Nitrogen to flow;
- Liquid Nitrogen circulates in Dolly and chills;
- Since bush is mounted on Dolly, bush also chills along with Dolly;
- This happens for both dollies (Top & Bottom) at the same time;
- After predetermined time, controller sends signal to press for pressing this chilled bush.

2. Crank bush pressing technique with auto circulation of liquid nitrogen through pressing dolly as claimed in claim 1, wherein the liquid nitrogen is circulated through the bush pressing dolly.

3. Crank bush pressing technique with auto circulation of liquid nitrogen through pressing dollyas claimed in claim 1, wherein the said dolly have internally crafted grooves for the circulation of liquid nitrogen.

4. Crank bush pressing technique with auto circulation of liquid nitrogen through pressing dolly as claimed in claim 3, wherein the Solenoid valve is kept in between liquid nitrogen cylinder and pressing dolly and integrated with pressing cycle; and the said cryogenic Solenoid valve controls the flow of nitrogen to minimize consumption of Nitrogen.