MBD Simulation on IC Engine Valve Train

Aim: Motion analysis of Piston Valve Train using Solidworks Multi Body Dynamics.

Theory: A valve train is a mechanical system that controls operation of the valves in an internal combustion engine, whereby a sequence of components transmits motion throughout the assembly. A conventional reciprocating internal combustion engine uses valves to control the flow of the air/fuel admix into and out of the combustion chamber. A typical valve-train consists of valves, rocker arms, pushrods, lifters, and camshaft(s). Valve-train opening/closing and duration, as well as the geometry of the valve-train, controls the amount of air and fuel entering the combustion chamber at any given point in time. Timing for open/close/duration is controlled by the camshaft that is synchronized to the crankshaft by a chain, belt, or gear. Valve-trains are built in several configurations, each of which varies slightly in layout but still performs the task of opening and closing the valves at the time necessary for proper operation of the engine.

It consists of five components:

1. Cam
2. Push Rod
3. Rocker Arm
4. Valve
5. Valve Mount

Cam: A cam is a device to convert rotational motion into reciprocating motion. which actuate the intake and exhaust valves of the cylinders. The cams and the camshaft are usually formed as a unit, with the cams set at angles so as to open and close the valves in a prescribed sequence as the cams rotate. A separate camshaft for each row of cylinders is driven by gears or chains from the crankshaft.. One of the most widely used applications of camshafts is the opening and closing of fuel valves in virtually all piston-driven internal combustion engines.

Push Rod: Pushrod helps to transfer the rotation of the cam to linear motion. The rod is placed on the side face of the cam and the motion of the rod occurs in the vertical direction occurs when the bulge part of the cam makes contact with the pushrod. the end face of the push can be sharp, flat or even with a roller depending upon the application. Pushrods are one of the few components in gasoline combustion engines that are not curved or offset in some way. A push rod is a straight stem with a rollerball at each end. Manufacturers produce these from high-tempered steel or chrome "molly," which is an alloy.

Rocker Arm: Rocker arm 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 camshaft while the other end acts on the valve. 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 rotation of the camshaft, the inside rises, allowing the valve spring to close the valve. Some overhead cam engines employ short rocker arms in which the cam lobe pushes down on the rocker arm to open the valve. On this type of rocker arm, the fulcrum is at the end rather than the middle, while the cam acts on the middle of the arm. The opposite end opens the valve. A rocker arm (in the context of an internal combustion engine of automotive, marine, motorcycle, and reciprocating aviation types) is an oscillating lever that conveys radial movement from the cam lobe into linear movement at the poppet valve to open it.

Valve: Valves are usually of the poppet type, although many others have been developed such as sleeve, slide, and rotary valves.

Poppet valves typically require small coil springs, appropriately named valve springs, to keep them closed when not actuated by the camshaft. They are attached to the valve stem ends, seating within spring retainers. Other mechanisms can be used in place of valve springs to keep the valves closed.

Depending on the design used, the valves are actuated directly by a rocker arm, finger, or bucket tappet. Overhead camshaft engines use fingers or bucket tappets, upon which the cam lobes contact, while pushrod engines use rocker arms. Rocker arms are actuated by a pushrod, and pivot on a shaft or individual ball studs to actuate the valves.

Valves form an integral component of an internal combustion engine and every cylinder in an engine at least has two of them, i.e. an intake (intake of the fuel-air mixture) and an exhaust valve (exhaust gases). A multi-valve engine can have three, four and sometimes five valves.

Valve Mount: Valve Mount use to support the valve to move incorrect direction and spring is attached to the valve mount.

Assembly of the Piston Valve Train

Animated Vedio

youtube link

Drawing of Cam for case 1 and case 2

Case 1

Case 2

Design Specification

CAM: CAM Lift Formula: Cam lift = (L –R1) + R2

L = Distance between two centers.

R1 = Radius of the lower circle.

R2 = radius of the upper circle.

1. For CAM lift = 3.5mm, we assume R1 = 20mm & R2 = 10mm

From the cam lift formula, we get L = 13.5mm

2. For CAM lift = 6mm, we assume R1 = 20mm & R2 = 10mm

From the cam lift formula, we get L = 16mm

Material Specification:

‘Cast Carbon Steel’ material is used for all the components of a valve-train.

Poppet Valve Spring:

Spring Stiffness: 10N/mm^2

NOTE: If the spring constant of the spring is very less, the force produced by the rotation of the cam easily compresses the spring and the rocker arm will move beyond it and there won’t be any motion transfer thereafter.

1. For CAM Lift = 3.5mm

Free Length = 25mm

2. For CAM Lift = 6mm

Free Length = 35mm

The formula for calculation of the distance(L) is:

L=R1−R2+(cl)L=R1-R2+(cl)

where cl is cam lift

all units are in mm

Procedure:

• Creating required 3D model for IC Engine Valve Train.
• Creating 2 seperate cam's with 3.5mm lift and 6mm lift.
• Assembiling the 3D model by using constraints.
• In this input motor is fixed to cam and it rotes at the constant speed of 1500rpm in two cases.
• Linear spring is added between surface of valve and valve mount with spring constant of 10 N/mm and free length of 45mm.
• In this we are using motion study properties, 7200 frames per second and using Precise contact
• Fixing the contact type as solid bodies for IC Engine valve Train and assigning material as Cast Carbon Steel, and calculat the motion analysis.

Results and Plots:

Case 1)

Case 2)

CONCLUSIONS:

• We can observe thatt more the CAM-lift, more is the linear displacement of the valve lift.
• The contact force between different components also increases with increase in CAM-lift.
• In CAM-lift = 3.5mm3.5mm, there is a difference in the total magnitude of the contact force between rocker-arm and valves and the contact force in the x-direction because in the x-direction, the frictional force acts which helps in sliding of the rocker-arm on the valves. Hence, it is both in positive and negative direction. But, the total magnitude only pushes the rocker-arm downwards.