MBD Simulation on IC Engine Valve Train
Project Title: MBD simulation of IC engine valve train
Objective:
1. Study the valve displacement
2. Study the contact force between different parts in the valve train
3. Design the cam for different lift
4. Design the parts of the IC engine valve train
5. Make the assembly of the valve train
Theory
Cam
A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion. Often a part of a rotating wheel (e.g. an eccentric wheel) or shaft (e.g. a cylinder with an irregular shape) strikes a lever at one or more points on its circular path. The cam can be a simple tooth, as is used to deliver pulses of power to a steam hammer, for example, or an eccentric disc or other shapes that produces a smooth reciprocating (back and forth) motion in the follower, which is a lever making contact with the cam. A cam timer is similar and was widely used for electric machine control (an electromechanical timer in a washing machine being a common example) before the advent of inexpensive electronics, microcontrollers, integrated circuits, programmable logic controllers and digital control.
Fig 1 Cam
Type od followers
Fig 2 Types of followers
IC engine valve mechanism
Internal combustion engine valves are precision engine components. The valve train system is one of the major parts of the internal combustion engine, which controls the amount of air-fuel mixture to be drawn into the cylinder and exhaust gas to be discharged. The fresh charge (air-fuel mixture in Spark Ignition Engines and air alone in Compression Ignition Engines) is induced through inlet valves and the products of combustion get discharged to atmosphere through exhaust valves. This seals the working space inside the cylinder against the manifolds. So the design of valve lift profiles and valve train components is most important for the engine performance, valve train durability, and NVH. Therefore valve train system should be optimally designed so as to avoid an abnormal valve movement, such as valve jumping or bounce up to the maximum engine speed. There are different types of valves used by the manufactures; some common types of valves being poppet valves, slide valves, rotary valves and sleeve valve. The basic nomenclature used for valves is as shown in Fig. 3.
Fig 3 IC engine valve mechanisum
Parts
1. Cam
(3.5 mm lift)
(6 mm lift)
2. Pushrod
3. Rocker arm
4. Valve
5. Valve seat
Assembly
cam is connected to the push-rod.
push-rod connected to the rocker arm.
a rocker arm is connected to the valve body
To assemble the different parts some mates are created between parts
Motion Study
1. Motor
The motor is connected to the cam with 1500 rpm.
2. Contacts
Contact between cam and push rod
Contact between push rod and rocker arm
Contact between rocker arm and valve
3. Spring
Spring stiffness is provided 20n/mm2
Results
Case 1
3.5 mm lift
Animation
Valve Displacement
Valve displacement is 3.5 mm
The contact force between crank and push rod
the highest contact force between crank and push rod is 1899 newton
The contact force between the pushrod and rocker arm
the highest contact force between rocker arm and pushrod is 2099 newton
The contact force between rocker arm and valve
the highest contact force between the rocker arm and valve is 545 newton
Case 2
6 mm lift
Animation
Valve Displacement
Valve displacement is 6 mm
The contact force between crank and push rod
the highest contact force between crank and push rod is 2322 newton
The contact force between the pushrod and rocker arm
the highest contact force between rocker arm and pushrod is 1517 newton
The contact force between rocker arm and valve
the highest contact force between the rocker arm and valve is 545 newton