MBD Simulation on IC Engine Valve Train (SOLIDWORKS)
MBD Simulation on IC Engine Valve Train
1. OBJECTIVES
Model the parts and assemble them in SolidWorks. Run the simulation using the below parameters
| Sl.No | CAM Lift (mm) | Speed (RPM) | Material |
| 1 | 3.5 | 1500 | Cast Carbon Steel |
| 2 | 6 | 1500 |
Cast Carbon Steel |
a) To Plot
- Valve Lift.
- The contact force between
- Cam and Push Rod
- Pushrod and Rocker Arm
- Rocker Arm and Valve
B) Explain why the contact force between the Rocker arm and valve varies while measuring with respect to the X direction and measuring with respect to magnitude.
2. INTRODUCTION
Multi-Body Dynamics
A Multi Body Dynamic (MBD) system is one that consists of solid bodies, or links, that are connected to each other by joints that restrict their relative motion. The study of MBD is the analysis of how mechanism systems move under the influence of forces, also known as forward dynamics. A study of the inverse problem, i.e. what forces are necessary to make the mechanical system move in a specific manner is known as inverse dynamics.
A Cam and follower mechanism is a profiled shape mounted on a shaft that causes a lever or follower to move. Cams are used to convert rotary to linear (reciprocating) motion. As the cam rotates, the follower rises and falls in a process known as reciprocating motion.
The motion of the follower is restricted to a pre-determined pattern by a guide. The follower maintains contact with the cam through the force of gravity or by a spring. The total range of movement produced by the cam is called the stroke. The range of movement of the follower will depend on the distance from the shaft supporting the
cam to the upper and lower points of the rotation circle. Cams are commonly used in engines to control valves (in which the valve is the follower), sewing machines,
children's toys and many other mechanical applications.
Cams come in a variety of shapes and sizes - the most common types (from left to right): snail shaped, pear shaped and a circular with an off-centre hole. As the cams
rotate, the followers reciprocate motion according to the profile of each cam.
For example, cams that have a pear shape will cause the follower to lift, to fall and then to pause before repeating the action. The cams that have a circular shape, sometimes referred to as eccentric cams, will cause a smooth rise and fall movement with no pause. This is known as harmonic action.
Components
The valvetrain consists of all the components responsible for transferring the rotational movement of the camshaft into the opening and closing of the intake and exhaust valves. Typical components are listed below in order from the crankshaft to the valves.
Camshaft
The timing and lift profile of the valve opening events are controlled by the camshaft, through use of a carefully shaped lobe on a rotating shaft. The camshaft is driven by the crankshaft and— in the case of a four-stroke engine— rotates at half the speed of the crankshaft.
Motion is transferred from the crankshaft to the camshaft most commonly by a rubber timing belt, a metallic timing chain or a set of gears.
Pushrod
Pushrods are long, slender metal rods that are used in overhead valve engines to transfer motion from the camshaft (located in the engine block) to the valves (located in the cylinder head). 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.
Rocker arm
Depending on the design used, the valves are actuated by a rocker arm, finger or bucket tappet. Overhead camshaft engines use fingers or bucket tappets, upon which the cam lobes contact. Overhead valve engines use rocker arms, which are actuated by a pushrod and pivot on a shaft or individual ball studs in order to actuate the valves.
Valves
Most modern engines use poppet valves type, although sleevs valves, slider valves and rotary valves have also been used at times. Poppet valves are typically opened by the camshaft lobe or rocker arm, and closed by a coiled spring called a valve spring.
3. GEOMETRIC PARTS DESIGN
-
Rocker Arm : This is part which is connected to push rod in one end and valve on the other end.
- Valve : This allows the air-fuel mixture to enter the cylinder or exhaust the gases out from the cylinder by opening and closing of the inlet/exhaust port.
- Valve Mount : This acts as the stoppage for the valve and limits the movement of the valve.
- Push Road : This is the part to which the lift is provided, which is transmitted to the rocker arm.
- Cams : A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion. It is often a part of a rotating wheel or shaft that strikes a lever at one or more points on its circular path.
Case 1: cam lift of 3.5mm:
To calculate the distance between the two centres(L)
Given: R1 = 12.5; R2 = 5; Cam lift = 3.5mm
Cam lift = (L-R1)+R2
L = (12.5+3.5) - 5
L = 11mm
Case 2: cam lift of 6mm:
To calculate the distance between the two centres(L)
Given: R1 = 12.5; R2 = 5; Cam lift = 3.5mm
Cam lift = (L-R1)+R2
L = (12.5+6) - 5
L = 13.5mm
- Assembly : Assembly is made using the assembly mate option by properly aligning them as shown. Physical dynamics is used here for making contact between valve, rocker arm, push rod and cam which locks them in position and motion analysis is performed.
Case 1: cam lift of 3.5mm:
Case 2: cam lift of 6mm:
4. PROCEDURE
- To run the motion analysis first go to motion study and establish contact between Cam and push rod, push rod and rocker arm, rocker arm and valve.
- Next, give the rotation to the cam with 1500 RPM.
- Set up a linear spring between a valve and the valve mount with the spring stiffness of 10 N/mm and free length 45 mm.
- Change the frames to 7200 frames per sec and use precise contact.
- select the entire assembly and assign the material as follows, go to Material-Edit material and select Cast Carbon Steel and click apply.
- There will be an indication of the material assigned with a change in color of the entire assembly.
- Now click the calculation button.
- Run the analysis for the required time.
There are two cases to follow to get the desired motion analysis and the plots. They are as follows,
5. RESULTS & PLOTS
Case 1: cam lift of 3.5mm:
Animation:
- Linear displacement of valve = 2.5 mm
- Contact force between Cam and Pushrod
- Contact force between Pushrod and Rockerarm
- Contact force between Rockerarm and Valve
- Contact force between the Rocker arm and valve varies with respect to x direction
Case 2: cam lift of 6mm:
- Linear displacement of valve = 6mm
- Contact force between Cam and Pushrod
- Contact force between Pushrod and Rockerarm
- Contact force between Rockerarm and Valve
- Contact force between the Rocker arm and valve varies with respect to x direction
6. CONCLUSION
- For the 1st case as we give cam lift 3.5 mm, the valve displacement is around 2.5 mm but when we increases the cam lift to 6 mm, we got valve displacement of around 6 mm.
- From both the case 1&2 contact force between Push rod and Cam, and Push rod and Rocker Arm are approximately same.
- When comparing the contact forces between case 1&2 the contact forces is much more in case 2 then case 1. It's because the cam lift is more in case 2 so the force required compress the spring is more.
Q) Why the contact force between the Rocker arm and valve varies while measuring with respect to the X direction and measuring with respect to magnitude.
Explanation: The Magnitude represents net contact force between the parts, while the contact force along the X direction is the frictional force between the bodies that arise due to the rocker arm sliding over the surface of the valve head.
The change in direction of the force is because the rocker arm first slides towards origin giving a positive friction force (opposing the motion) and then slides away from the origin giving rise to friction in the negative x-direction. Therefore the plots are opposite to each other.
The explanation is same for the cam lift of 6 mm, only it differs in magnitude of contact forces. The movement in this case is quite smoother compared to the cam lift of 3.5 mm as observed. As the cam lift increases more air-fuel mixture can enter into the cylinder of IC engine.
Google Drive Link - https://drive.google.com/drive/folders/1s5Bto5eDcPGxL3KNv8-Rhxn_wYYUNajN?usp=sharing
A Cam and follower mechanism is a profiled shape mounted on a shaft that causes a lever or follower to move. Cams are used to convert rotary to linear (reciprocating) motion. As the cam rotates, the follower rises and falls in a process known as reciprocating motion.
The motion of the follower is restricted to a pre-determined pattern by a guide. The follower maintains contact with the cam through the force of gravity or by a spring. The total range of movement produced by the cam is called the stroke. The range of movement of the follower will depend on the distance from the shaft supporting the
cam to the upper and lower points of the rotation circle. Cams are commonly used in engines to control valves (in which the valve is the follower), sewing machines,
children's toys and many other mechanical applications.
Cams come in a variety of shapes and sizes - the most common types (from left to right): snail shaped, pear shaped and a circular with an off-centre hole. As the cams
rotate, the followers reciprocate motion according to the profile of each cam.
For example, cams that have a pear shape will cause the follower to lift, to fall and then to pause before repeating the action. The cams that have a circular shape, sometimes referred to as eccentric cams, will cause a smooth rise and fall movement with no pause. This is known as harmonic action.
Components
The valvetrain consists of all the components responsible for transferring the rotational movement of the camshaft into the opening and closing of the intake and exhaust valves. Typical components are listed below in order from the crankshaft to the valves.
Camshaft
The timing and lift profile of the valve opening events are controlled by the camshaft, through use of a carefully shaped lobe on a rotating shaft. The camshaft is driven by the crankshaft and— in the case of a four-stroke engine— rotates at half the speed of the crankshaft.
Motion is transferred from the crankshaft to the camshaft most commonly by a rubber timing belt, a metallic timing chain or a set of gears.
Pushrod
Pushrods are long, slender metal rods that are used in overhead valve engines to transfer motion from the camshaft (located in the engine block) to the valves (located in the cylinder head). 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.
Rocker arm
Depending on the design used, the valves are actuated by a rocker arm, finger or bucket tappet. Overhead camshaft engines use fingers or bucket tappets, upon which the cam lobes contact. Overhead valve engines use rocker arms, which are actuated by a pushrod and pivot on a shaft or individual ball studs in order to actuate the valves.
Valves
Most modern engines use poppet valves type, although sleevs valves, slider valves and rotary valves have also been used at times. Poppet valves are typically opened by the camshaft lobe or rocker arm, and closed by a coiled spring called a valve spring.
3. GEOMETRIC PARTS DESIGN
-
Rocker Arm : This is part which is connected to push rod in one end and valve on the other end.
- Valve : This allows the air-fuel mixture to enter the cylinder or exhaust the gases out from the cylinder by opening and closing of the inlet/exhaust port.
- Valve Mount : This acts as the stoppage for the valve and limits the movement of the valve.
- Push Road : This is the part to which the lift is provided, which is transmitted to the rocker arm.
- Cams : A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion. It is often a part of a rotating wheel or shaft that strikes a lever at one or more points on its circular path.
Case 1: cam lift of 3.5mm:
To calculate the distance between the two centres(L)
Given: R1 = 12.5; R2 = 5; Cam lift = 3.5mm
Cam lift = (L-R1)+R2
L = (12.5+3.5) - 5
L = 11mm
Case 2: cam lift of 6mm:
To calculate the distance between the two centres(L)
Given: R1 = 12.5; R2 = 5; Cam lift = 3.5mm
Cam lift = (L-R1)+R2
L = (12.5+6) - 5
L = 13.5mm
- Assembly : Assembly is made using the assembly mate option by properly aligning them as shown. Physical dynamics is used here for making contact between valve, rocker arm, push rod and cam which locks them in position and motion analysis is performed.
Case 1: cam lift of 3.5mm:
Case 2: cam lift of 6mm:
4. PROCEDURE
- To run the motion analysis first go to motion study and establish contact between Cam and push rod, push rod and rocker arm, rocker arm and valve.
- Next, give the rotation to the cam with 1500 RPM.
- Set up a linear spring between a valve and the valve mount with the spring stiffness of 10 N/mm and free length 45 mm.
- Change the frames to 7200 frames per sec and use precise contact.
- select the entire assembly and assign the material as follows, go to Material-Edit material and select Cast Carbon Steel and click apply.
- There will be an indication of the material assigned with a change in color of the entire assembly.
- Now click the calculation button.
- Run the analysis for the required time.
There are two cases to follow to get the desired motion analysis and the plots. They are as follows,
5. RESULTS & PLOTS
Case 1: cam lift of 3.5mm:
Animation:
- Linear displacement of valve
- Contact force between Cam and Pushrod
- Contact force between Pushrod and Rockerarm
- Contact force between Rockerarm and Valve
- Contact force between the Rocker arm and valve varies with respect to x direction
Case 2: cam lift of 6mm:
- Linear displacement of valve
- Contact force between Cam and Pushrod
- Contact force between Pushrod and Rockerarm