CAMSHAFT DESIGN FOR OPTIMISING ENGINE PERFORMANCE

CONTENTS

Abstract______________________________________2

Introduction___________________________________3

Progress of work_______________________________6

Results and discussion__________________________13

References___________________________________14

ABSTRACTThe objective of the project is to study the working of camshaft on various cylinder to optimise the speed (rpm). This project really depend on camshaft designing include Lift, duration, lobe centre, overlap, and much more confer just how the camshaft will or will not alter an (often theoretical) engine's performance personality. To allow more airflow into engine, a camshaft is designed with a profile (or curve) that provides a specific amount lift to the valve. Ti-VCT (twin independent variable camshaft technology) allows extremely precise, variable control of valve overlap, or the window of time in which both the intake and exhaust valves in an engine are open at the same time. By adjusting overlap continuously, an engine can operate at optimum settings for peak fuel economy or power output as conditions demand. Engine performance is major consideration in this project. As engine using this technology deliver high rpm with efficient fuel consumption. For fulfilling the demand of designing various calculation, software, and a practical knowledge is implemented. Our work in building a cam which operate both intake and exhaust simultaneously with the accurate precision helps to understand how the calculations work out with software. It gives the simple understanding to design camshaft which provide optimal speed. INTRODUCTION

Cam is a mechanical member for transmitting a desired motion to a follower by direct contact. The driver is called cam and driven is called follower. Cam mechanism is a case of a higher pair with line contact. Camshaft is the Brain of the engine must include cam lobes, bearing journals, and a thrust face to prevent fore and after motion of the camshaft. In addition camshaft can include a gear to drive the distributor and an eccentric to drive a fuel pump. Camshaft is controlling the valve train operation. Camshaft is along with the crankshaft it determines firing order. Camshaft is along with the suction and exhaust systems it determines the useful rpm range of the engine.

Figure 1. Cam 1. Max lift or nose 2. Flank Opening clearance ramp 3. Closing clearance ramp 4. Base circle 5. Exhaust opening timing figure 6. Exhaust closing timing figure 7. Intake opening timing figure 8. Intake closing timing figure 9. Intake to exhaust lobe separation

Cam measurement2.1. Lift The valve should be lifted fully to its maximum as soon as the valve starts opening and should be closed in the same fashion difference in measurement between the nose of the lobe and the base circle of the lobe. Increasing the lift opens the valve further. This reduces the restriction to airflow at the valve and allows air to flow more freely into the cylinder. 2.2. Duration Duration is the length of time (measured in degrees of crankshaft rotation) that the valve remains open. At higher engine speeds the valve opens and shuts in a shorter amount of time. This limits how completely the cylinder can be filled. 2.3. Lobe Separation Angle Lobe separation angle (LSA) is the number of degrees separating the point of peak exhaust lift and peak intake lift. Lobe separation angle directly impacts the amount of valve overlap. Because of this, production vehicles usually employ a wide LSA to reduce valve overlap and increase idle quality. Because of this, production vehicles usually employ a wide LSA to reduce valve overlap and increase idle quality. 2.4. Valve Overlap Valve overlap is the time in which both the intake and exhaust valves are open. Valve overlap is affected by Lobe separation angle and duration. Valve overlap is used because of the principle of exhaust scavenging (the exiting exhaust gases help pull in the fresh intake charge, especially at higher rpm when fill time is limited). At low RPM when intake port speed is low, a long valve overlap period will cause reversion into the intake port (the cylinder pressure exceeds the force of the air in the intake port and exhaust gasses are forced into the intake port). This causes the lumpy idle associated with big camshafts. 2.5. Intake Valve Closing It is most critical valve opening/closing point. It is too early of an intake valve closing and the cylinder may not have time to fill completely. Intake Valve Closing is too late of an intake valve closing and the cylinder pressure will overcome the inertia of incoming airflow and revert flow back into the intake port. This causes a serious disruption to flow and destroys any pressure waving tuning. 2.6. Exhaust Valve Opening Exhaust Valve Opening is second most critical valve opening/closing event. It determines the balance between power event efficiency and exhaust pumping losses. It is too early of an exhaust valve opening will reduce the amount of energy converted from cylinder pressure to mechanical force on the piston

PROGRESS OF WORK

1. CALCULATIONS FOR CAM:Factors to consider:1. The longer the duration, the more time the engine will have to let the burnt gases out. The more burnt gases let out, the more space will have for fresh fuel and air from the intake system. This means more power.2. If the duration is too long, the exhaust valve will be open during combustion or when the piston is traveling down on the intake stroke. Either condition means less power.3. Duration is limited to 0 - 330 degrees.4. Exhaust valve size + intake valve size must be less than the size of the bore. If the exhaust valve diameter + intake valve diameter is bigger than the bore, one of those valves is hitting the deck of the block and not opening at all.5. Exhaust valve lift does not have air separation problems, so the lift can be higher, allowing smaller exhaust valve size. Exhaust valve lift can be 20% of the bore without losing effectiveness. After 20%, there are no gains in air flow.6. It is easier to push air out of an engine than it is to draw air in, so the average open exhaust valve area need only be 57.82% of the average open intake valve area. The lobes on the cam are the egg shaped bumps. These lobes have lift and duration specifications that we dictate. The lift is how high the lobe on the cam will lift the valve. The duration is how long, in crank degrees, the valve will be open.It is easier to push air out of an engine than it is to draw air in, so the average open exhaust valve area need only be 57.82% of the average open intake valve area. To design a cam and exhaust valve combination with an average open exhaust valve area that is 57.82% of the average open intake valve area, we could estimate it by using an exhaust valve duration or an exhaust valve size or an exhaust valve lift that is 57.82% of the same intake values. However, this will leave us short of the maximum benefit of a designed cam. So, if to find exact and maximize power, we uses the equation below. Exhaust valve duration is determined by the exhaust lobe on the cam. Exhaust valve duration is measured in crank degrees . When we set the duration in crank degrees, we are determining the point on the cam at which the lobe begins pushing the lifter up and where it lets the lifter back down. Since the cam rotates 1 time for every 2 times the crank rotates, an exhaust valve duration of 300 degrees means the exhaust valve is open for 150 degrees of a single revolution of the engine. Exhaust valve duration, exhaust valve diameter and exhaust valve lift factor in together to determine air velocity in the exhaust system. Parameters for designIntakeExhaust

Bore dia = 80mmBore dia = 80mm

Valve lift = .48in = 12mmValve lift = .48in = 12mm

Opening duration = 248oDelay period = 121o

Dwell period = 112oOpening duration = 248o

Stroke length = 12mmDwell period = 112o

Base circle dia = 46.9mmBase circle dia = 46.9mm

Valve dia = 35.77mm (20% area of bore)Valve dia = 28.47mm(intake valve area is 57.82% more than exhaust)

OBJECTIVES:1. Equation of cam profile Cam rotates 1 time for every 2 times the crank rotates and cam duration is measured in crank degrees, the equation for exhaust cam degrees is:1) exhaust cam degrees = exhaust valve duration 2Next, we calculate the angle from the x-axis to the point at which lift begins. We call this angle "theta".Theta = 90 - exhaust cam degrees/2=90-62 =28Next, we calculate the x and y values of the point at which lift begins, using the angle we just calculated:x = 0.5 cos (3.14159/ (180 / theta))x =0.5 cos (3.14159/ (180 / 28))x=0.4414.y = 0.5 sin (3.14159/ (180 / theta)) y = 0.5 sin (3.14159/ (180 / 28))y = 0.2344

Next, we calculate the b-value for the equation y = ax2 + b, which is the equation for a parabola. We use a parabola because it closely represents the shape of a cam lobe:b = exhaust valve lift + radius of base circleb = 12 mm + 23.45 (exhaust valve lift = stroke length )b = 35.45a = -(y-b)/x2a = 79.78The final equation for cam profile with constants a & bY = b ax2Y = 35.45 79.78x2The 0.5 in the equation above is the radius of what is called the cam base circle. The cam base circle is the minimum radius the lifter will rest on.

Displacement Diagram

DESIGN USING SOFTWARE1. Cam analyser for valve timing analysis.

This software help us to understand at what rocker ratio and lash ratio with total no of working cylinder at various intake and exhaust valve lift the cam can be determined. Like the company like ford use the rocker arm 1.5-1.8 and we use 1.5 as standard with .026-.028 lash ratio.

2. Solid works full model view (camshaft & cam).

We have prepared the solidwork model on the basis of the calculations performed. This model is based on two working cams on the basis of the intake valve lift and exhaust valve lift with total lift of the cam.

Results & DiscussionsA cam-shaft was designed using the standard parameters but using non-conventional technique of Ti VCT (Twin independent variable cam timing). The engine performance is optimised by improving the breathing capacity at different rpms by using 2 different cams for intake and exhaust valves controlled separately by ECU. A standard cam profile was drawn using pre-existing techniques for both intake and exhaust cams i.e. Y= 35.45 79.78x2The following optimisation of the cams gives better engine performance.1. 7% improvement in peak performance.2. 4.5% improvement in fuel economy.3. Reduced NOx and Hydrocarbon emissions without compromising idle quality.4. 5% improvement in low-speed torque for better acceleration.5. Optimised cold-start operation and minimizing cold-start emissions.

REFERENCES:1. High Performance Math by Doug Reisgen and Craig Reisgen | (2009)2. Ford.com/engine specification 2014 F-1503. EngineBasics.com: Engine Basics. Camshaft Basics from the February, 2009 issue of Chevy High Performance by Bob Mehlhoff.

4. Modelling, Design and Finite Element Analysis of Cam Shaft byVivekanandan.Pa, Kumar

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