MBD Simulation on IC Engine Valve Train

AIM: TO PERFORM MOTION ANALYSIS OF IC ENGINE VALVE TRAIN

THEORY: A valve train is a mechanical system that controls operation of intake and exhaust valve in an I.C. engine.

CAM LIFT PROFILE: The cam lift is actually an abbreviation of the follower lift at the cam side. The term is usually only meaningful for the pushrod valve train where the follower lift has a simple one-dimensional translational motion driven by the cam. Note that the cam lift is not equivalent to the contour shape of the cam lobe for the case of a roller follower. The cam contour shape refers to the radial distance beyond the cam base circle from the cam centre to any point on the cam lobe profile. The cam lift is not equal to the radial distance because the radius of the roller follower is not equal to zero. For the pushrod and the direct-acting OHC valvetrains, cam lift or essentially the follower lift is usually used to describe the intended cam profile design, and the actual contour shape of the cam lobe can be calculated once the cam lift profile and the roller size are specified. On the other hand, for some OHC valvetrains (e.g., with a finger follower), it is often more convenient to directly use the actual contour shape of the cam lobe to define the cam profile design.

COMPONENTS OF VALVE TRAIN:

CAM

The cams on a camshaft achieve this displacement by the rotation of a radial pattern, and a follower which moves perpendicular to the rotational axis. The cam pattern on a camshaft is non-circular with a single lobe. The follower matches the displacement of the cam as it rotates. This displacement is then translated to the stem of the valve, allowing head to rise as the lobes of the cam pass through the follower.

ROCKER ARM:

It is an oscillating lever that conveys radial movement from the cam lobe into linear movement at the poppet valve to open it. One end is raised and lowered by a rotating lobe of the while the other end acts on the valve stem. When the camshaft lobe raises the outside of the arm, the inside presses down on the valve stem, opening the valve. When the outside of the arm is permitted to return due to the camshaft's rotation, the inside rises, allowing the valve spring to close the valve.

PUSH ROD:

Pushrods are long, slender metal rods that are used to transfer motion from the camshaft to the valves. The bottom end of a pushrod is fitted with a lifter, upon which the camshaft makes contact. The camshaft lobe moves the lifter upwards, which moves the pushrod. The top end of the lifter pushes on the rocker arm, which opens the valve. At the bottom end, lifters are fitted upon which the CAM makes the contact. It pushes on the lifters, which pushes the pushrod, further pushing the rocker arm that rotates and applies a downward force on the valves.

VALVE AND VALVE MOUNT:

A poppet valve, also called mushroom valve is a valve typically used to control the timing and quantity of gas or vapor flow into an engine.

It consists of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. The portion of the hole where the plug meets with it is called the valve seat. The shaft guides the plug portion by sliding through a valve guide. In exhaust applications a pressure differential helps to seal the valve and in intake valves a pressure differential helps open it.

ASSEMBLY:

All the components mentioned above are assembled together. The cam is given the rotary motion which gets converted into the reciprocating motion of the pushrod and eventually the poppet valve. Springs are used at the valves to push back the rocker arm. The spring is initially compressed and of suitable stiffness. For this analysis, the material for every component is selected as cast carbon steel.

OBJECTIVE:

The objective here is to design IC engine valve train and perform its motion analysis for different cam lifts which are given in the problem.

Sl.No	CAM Lift (mm)	Speed (RPM)	Material
1	3.5	1500	Cast Carbon Steel
2	6	1500	Cast Carbon Steel

CAM Lift Formula

CAM Lift can be derived from the sketch
● The diameter of lower circle (D1)- 35 mm
● The diameter of upper circle (D2)- 20 mm

● The distance between two centres (L)- 30 mm
CAM Lift = (L-R1)+R2

IN OUR CASE

D1 = 25MM R1 = 12.5MM

D2 = 10MM R2 = 5MM

LIFT	DISTANCE BETWEEN CENTRES
3.5	11mm
6.0	13.5mm

Knowing the dimensions, all the components are designed and assembly is done. A motor rotating at 1500 RPM is applied to the axis of the cam and the soild body contacts are defined.

In order to capture all the degrees of rotation of the cam, the frame rate is set to 9000 fps because 1500 RPM = `1500*360/60`= 9000 deg/sec. precise contact is enabled and analysis is done.

RESULTS:

FOR 3.5mm LIFT

VALVE LIFT

CONTACT FORCES BETWEEN :

1. Cam and Push Rod

2. Pushrod and Rocker Arm

3.Rocker Arm and Valve

FOR 6mm LIFT:

VALVE LIFT:

CONTACT FORCES BETWEEN :

1. Cam and Push Rod

2. PUSH ROD AND ROCKER ARM

3. ROCKER ARM AND VALVE

ANIMATION VIDEO : THE OUTPUT OF THE MOTION ANALYSIS

CONCLUSION:

• The valve displacement is higher in case of cam lift of 6mm than cam lift of 3.5mm. This shows that the cam geometry affects the valve opening through which air fuel mixture enters.
• The contact forces are at their peak when the cam lobe is at its topmost position.
• In case of the contact force between rocker arm and the valve, the magnitude is different from the X-component of the force because the rocker arm swivels in both the direction, that is forward and backward which accounts for the negative value of force while measuring the X-component. The magnitude denotes the net force between the components whereas the X-component denotes only the frictional force.Hence the rocker arm moves in both forward and backward direction due to which the friction acts in both the direction ,accounting for negative value of the force.