42621504 Design and Analysis of Camshafts DOHC

National University of Sciences and Technology

College of Electrical & Mechanical Engineering

Rawalpindi

8. Study the designs of DOHC used in various automobiles. Analyze the designs of intake and exhaust camshafts used in Toyota Corolla twin-cam engine. Use pro–e software for analysis.

A Project Report

De-30 Me (A)

Submitted By:

TC Uzair Ali

NS Esaam Jamil

TC Hassan Warriach

Bachelors

In

Mechanical Engineering

Year

2012

Project Supervisor

Col. Ikhlaq Khattak

Dated: June 14, 2010

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Acknowledgements:

First of all thanks to Allah Almighty who has given human beings brilliant minds and made us the crown of the creation.

Secondly, we would like to honor our respected Sir Col. Ikhlaq Khattak for his advice and encouragement in making this project. We would also like to thank him for always being available for our guidance and help inside and outside the class.

Finally, we would like to thank our parents for their love. We would also like to acknowledge with appreciation of their support in our studies.

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Abstract:

A camshaft translates the rotary motion of the engine to the reciprocating or oscillating motion that is used to operate (open or close) the intake and exhaust valves. It is usually made by chilled iron casting and billet steel. Camshafts can be classified into three types namely OHV, SOHC and DOHC.

Our basic objective is to study designs of twin overhead camshafts used in various automobiles; design and analyze the intake and exhaust camshafts of Toyota corolla twin-cam engine using pro engineer software. Therefore, we studied the designs of intake and exhaust camshafts after making the designs in pro-e. Furthermore, we have done stress analysis to get into the depth of the very topic which concludes our project report.

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Table of Contents:

Acknowledgements 2

Abstract 3

Table of Contents 4

List of figures 5

1. Introduction 62. Material and manufacturing of camshaft 62.1. Chilled iron casting2.2. Billet steel3. Types of camshafts 73.1. OHV or push rod 73.1.1. Merits3.1.2. Demerits3.2. SOHC 73.2.1. Merits3.2.2. Demerits3.3. DOHC or twin OHC 93.3.1. Merits3.3.2. Demerits4. History of DOHC 105. Design of DOHC used in various automobiles 116. Engine specifications of Toyota corolla used 127. Designs of intake camshaft of Toyota Corolla twin-cam engine

using pro-e 138. Designs of exhaust camshaft of Toyota Corolla twin-cam engine

using pro-e 159. Study of designs of intake and exhaust camshafts 1610. Stress analysis of exhaust camshaft of Toyota Corolla twin-

cam engine using pro-e 1811. Stress analysis of intake camshaft of Toyota Corolla twin-

cam engine using pro-e 1912. Conclusions from the stress analysis of intake and exhaust

camshafts of Toyota corolla twin-cam engine 2013. Bibliography 22

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Table of Figures:

Fig 3.1a: 4-cylinder 8 valves OHV engine

Fig 3.2a: 4-cylinder 8 valves SOHC engine

Fig 3.2b: SOHC

Fig 3.3a: 4-cylinder 16 valves DOHC engine

Fig 3.3b: DOHC

Fig 5a: Harley Davidson bike (left) and its DOHC design (right)

Fig 5a: Harley Davidson bike (left) and its DOHC design (right)

Fig 5c: Toyota Corolla (left) and its DOHC design (right)

Fig 6a: Toyota Corolla (right) of above specificationsFig 7a: Intake camshaft (3D view)

Fig 7b: Cam lobe and holes for lubrication of intake camshaft

Fig 7c: Gear attached to intake camshaft (3D view)Fig 7d: Side view of intake camshaftFig 8a: 3D view of exhaust camshaft

Fig 8b: Cam lobe and holes for lubrication of exhaust camshaft

Fig 8c: Side view of exhaust camshaft

Fig 9a: A typical cam and its distinct regions

Fig 10a: Stress on exhaust camshaft

Fig 10b: Displacement on exhaust camshaft

Fig 10c: P-level on exhaust camshaft

Fig 11a: Stress on intake camshaft

Fig 11b: Displacement on intake camshaft

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1. Introduction:

A camshaft translates the rotary motion of the engine to the reciprocating or oscillating motion that is used to operate (open or close) the intake and exhaust valves. It has cam lobes on the shaft. The camshafts are driven from the crankshaft by camshaft drivers which may be gear, belt or chain. The camshaft pushes the valves. The valves pushed back by the reactive force of the valve spring.

2. Material and manufacturing of camshaft:

2.1 Chilled iron casting:

This is a good choice for high volume production. A chilled iron camshaft has a resistance against wear because the camshaft lobes have been chilled, which makes them harder. When making chilled iron castings, other elements are added to the iron before casting to make the material more suitable for its application.

2.2 Billet Steel:

When a high quality camshaft is required, engine builders and camshaft manufacturers choose to make the camshaft from steel billet. This method is also used for low volume production. This is a much more time consuming process, and is generally more expensive than other methods. However the finished product is far superior.

When making the camshaft, CNC lathes, CNC milling machines and CNC camshaft grinders will be used. Different types of steel bar can be used. One example is EN40b. When manufacturing a camshaft from EN40b, the camshaft will also be heat treated. The method of heat treatment is gas nitriding, which changes the micro-structure of the material. It gives a surface hardness of 55-60 on the HRC. These types of camshafts can be used in high performance engines.

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3. Types of Camshaft:

3.1 Pushrod or OHV:

In over head valve engine design, the camshaft is installed inside the engine block and valves are operated through lifters, pushrods and rocker arms.

Fig 3.1a: 4-cylinder 8 valves OHV engine

3.1.1 Merits:

An OHV engine is very simple and it has more compact size and is proven to be durable.

3.1.2 Demerits:

It is difficult to precisely control the valve timing at high rpm due to higher inertia caused by larger amount of valve train components (lifter-pushrod-rocker arm). Also it is very difficult to install more than two valves per cylinder or implement some latest technologies such as Variable Valve Timing

3.2 SOHC or OHC:

In the SOHC engine, the camshaft is installed in the cylinder head and inlet and exhaust valves are operated either by the rocker arms or directly through the lifters.

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Fig 3.2a: 4-cylinder 8 valves SOHC engine

Fig 3.2b: SOHC

3.2.1 Merits:

Valves are operated almost directly by the camshaft - easy to achieve the perfect timing at high rpm. It is possible to install three or four valves per cylinder. The SOHC design has less reciprocating mass than a comparable pushrod design. This allows for higher engine speeds, which in turn will increase power output for a given torque.

3.2.2 Demerits:

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An OHC engine requires a timing belt or chain with related components - more complex and more expensive design.

3.3 DOHC or Twin OHC:

It use two camshafts, the inlet camshaft drives the inlet valves while the exhaust drives exhaust valves through the valve lifters. The Cam lobe makes contact with the head of the valve lifter directly or via a thin round plate (pador shim) which is positioned on the valve lifter head.

Fig 3.3a: 4-cylinder 16 valves DOHC engine

It is possible to install multiple valves per cylinder and place intake valves on the opposite side from exhaust vales. The main reason to use double overhead cams is to allow for more intake and exhaust valves. More valves mean that intake and exhaust gases can flow more freely because there are more openings for them to flow through. This increases the power of the engine.

Thus, it can produce more horse powers with smaller engine volume. For comparison: The 3.5-liter V6 DOHC engine of 2003 Nissan Pathfinder has 240 hp, similar to 245 hp of the 5.9-liter V8 OHV engine of 2003 Dodge Durango.

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Fig 3.3b: DOHC

3.3.1 Merits:

It is most widely used in cars now-a-days. It has high efficiency. It possible to install multiple valves per cylinder and it can adopt variable timing.

3.3.2 Demerits:

More complex and more expensive design.

4. History of DOHC:

Among the early pioneers of DOHC were Isotta Fraschini's Giustino Cattaneo, Austro-Daimler's Ferdinand Porsche Stephen Tomczak (in the Prinz Heinrich), and W. O. Bentley (in 1919). Sunbeam built small numbers between 1921 and 1923.

The first DOHC engines were either two- or four-valve per cylinder racing car designs from companies like Fiat (1912), Peugeot Grand Prix (1913, 4 valve), Alfa Romeo Grand Prix (1914, 4 valve) and 6C (1928), Maserati Tipo 26 (1926), Bugatti Type 51 (1931).

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When DOHC technology was introduced in mainstream vehicles, it was common for it to be heavily advertised. While used at first in limited production and sports cars, Alfa Romeo is one of the twin cam's greatest proponents, 6C Sport the first Alfa Romeo road car using DOHC engine was introduced in 1928, ever since this has been trademark of all Alfa Romeo engines.

Fiat was one of the first car companies to use a belt-driven DOHC engines across their complete product line, in the mid-1960s., Jaguar's XK6 DOHC engine was displayed in the Jaguar XK120 at the London Motor Show in 1948 and used across the entire Jaguar range through the late 1940s, 1950 and 1960s. By the late 1970s, Toyota was the best seller of DOHC engines.

5. Designs of DOHC used in various automobiles:

Fig 5a: Harley Davidson bike (left) and its DOHC design (right)

Fig 5b: Mitsubishi Galant (left) and its DOHC design (right)

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Fig 5c: Toyota Corolla (left) and its DOHC design (right)

6. Engine specifications of Toyota Corolla used:

Model: 2006Engine: 1.8 liter four cylinders, double overhead cam, four valves per cylinderHorsepower: 126 @ 6,000 rpmTorque: 122 lb.-ft. @ 4,200 rpmTransmission: 5-speed manual

Fig 6a: Toyota Corolla (right) of above specifications

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7. Designs of intake camshaft of Toyota Corolla twin- cam engine, using Pro-e:

Fig 7a: Intake camshaft (3D view)

Fig 7b: Cam lobe and holes for lubrication of intake camshaft

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Fig 7c: Gear attached to intake camshaft (3D view)

Fig 7d: Side view of intake camshaft

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8. Designs of exhaust camshaft of Toyota Corolla twin-cam engine, using Pro-e:

Fig 8a: 3D view of exhaust camshaft

Fig 8b: Cam lobe and holes for lubrication of exhaust camshaft

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Fig 8c: Side view of exhaust camshaft

9. Study of designs of intake and exhaust camshafts:

The camshaft’s function in an engine is to open and close the valves. Its design results in valves being opened and closed at controlled rate of speed as well as at a precise time in relation to piston position. DOHC have four lobes per cylinder, two to drive the intake valve and two to drive the exhaust valve. Camshaft has a shaft, cam lobes on it and the bearing journals.

The cam lobes convert the rotator motion of the camshaft to the reciprocating motion of the valve train and valves. The design of the cam lobe contour has a major effect on the engine performance. The amount of valve opening, how long the valve remains open, when the valves open and close and the speed at which valves open and close are all determined by the cam lobe design.

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Fig 9a: A typical cam and its distinct regions

The camshaft rotates in a clock wise direction. Four regions are identified starting from the bottom in a counter clock wise direction: base circle, opening ramp, nose, and closing ramp. Each region is identified by degree locations, starting at 0 degree at the nose, 60 at the closing ramp, 180 at the base circle and 300 at the opening ramp.

Camshaft lobe wear is caused by friction between the cam lobe and the cam follower. Insufficient, excessive valve spring tension, excessive valve lash, hydraulic lifter failure and dirty oil will contribute to early and rapid wear. Worn cam lobes retard valve timing which is detrimental to engine power and performance.

To avoid such damage, there are holes on the camshaft which provide way to oil for lubrication.

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10. Stress analysis of exhaust camshaft of Toyota Corolla twin-cam engine, using Pro-e:

Fig 10a: Stress on exhaust camshaft

Fig 10b: Displacement on exhaust camshaft

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Fig 10c: P-level on exhaust camshaft

11. Stress analysis of intake camshaft of Toyota Corolla twin-cam engine, using Pro-e:

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Fig 11a: Stress on intake camshaft

Fig 11b: Displacement on intake camshaft

12. Conclusions from the stress analysis of intake and exhaust camshafts of Toyota corolla twin-cam

engine:

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If we observe the working of camshafts, we see that only one pair of the rotating cam lobe pair touch the valve pair (intake or exhaust) at one time while the remaining are oriented at different angles. The ends of the cam lobes exert force on the valve to move downward causing it to open. Due to this action there is equal and opposite reaction by the valve spring.

Now to do analysis we have considered one end (the shaft in bearing side) to be fixed and the other end (the shaft attached to the gear and gear to the timing chain) to be free. We also have considered that the forces are acting on the cam lobe pair nearest to the gear.

According to the analysis, the camshaft acts as a cantilever. Stresses are more near the bearing side. The analysis also shows that stresses are maximum around the holes due to stress concentration. Also the stress is more at the region where the shaft changes diameter.

We also see that the displacement is maximum near the gear end which gradually decreases as we move away from it.

The p level diagram shows the potential level. It has maximum values between the pair of cam lobe (which are applying forces on the valves at the very instant). The bar at the top right of the stress analysis window shows different values from minimum (deep blue) to maximum (red).

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13. Bibliography:

www.howautowork.com

www.auto.howstuffworks.com

www.autotropolis.com

www.samarins.com

www.autospectator.com

www.sunrisejapanese.com

www.baggermag.com

www.wikipedia.com

www.wikimedia.com

www.wikicars.com

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www.engr.colostate.edu

www.cardictionary.com

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