MBD Simulation on IC Engine Valve Train
Aim : Motion analysis of Piston Valve Train using Solidsworks Multi Body Dynamics.
Introduction : Internal combustion engine valves are precision engine components. The valve train system is one of the major parts of 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. Timing for open/close/duration is controlled by the camshaft that is synchronized to the camshaft by a chain, belt, or gear.
It consists of five components :
- Cam
- Push Rod
- Rocker Arm
- Valve
- 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 camshafts usually formed as a unit, with the cam set at angle so as to open and close the valves in a prescribed sequence as the cam rotates.
Push Rod : 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 : Rocker arm is an oscillating lever that conveys radial movement from the cam lobe into linear movement at the poppet valve to open it.
Valve : Valves form an integral component of an combustion engine and every cylinder in an engine at least has two of them, i.e. an intake (intake of 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 :
Procedure :
- At first make part modeling of all the 5 parts in solidsworks.
- Then assemble all 5 parts in solidsworks with proper constraints.
- Cast Carbon Steel is selected for the material of the valve train.
- Now go for the motion analysis.
- Define motor at cam axis as 1500 rpm speed.
- Then define contact between cam and push rod then push rod and rocker arm and then rocker arm and valve.
- Apply spring between valve and valve mount with stiffness 10N/mm
- Next give 7200 frames per sec and precise contact to the assembly.
- Finally hit on the calculate and go for the results and plots.
Design specification :
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
| Sl. No | CAM Lift(mm) | Speed(RPM) | Material |
| 1 | 3.5 | 1500 | Cast Carbon Steel |
| 2 | 6 | 1500 | Cast Carbon Steel |
Case 1 :
L = 11mm , R1 = 12.5mm , R2 = 5mm
Cam lift = (L-R1)+R2 = (11-12.5)+5 = 3.5mm
Case 2 :
L = 11mm , R1 = 15mm , R2 = 10mm
Cam lift = (L-R1)+R2 = (11-15)+10 = 6mm
Results and Plots :
Case 1 :
Animation of the valve train (3.5mm cam lift)
Linear displacement of the valve
Contact force between Cam and Push Rod
Contact force between Push Rod and Rocker Arm
Contact force between Rocker arm and Valve (w.r.t magnitude)
Contact force between Rocker Arm and Valve (w.r.t X direction)
Case 2 :
Animation of the valve train (6mm cam lift)
Linear displacement of the valve
Contact force between Cam and Push Rod
Contact force between Push Rod and Rocker Arm
Contact force between Rocker Arm and Valve (w.r.t magnitude)
Contact force between Rocker Arm and Valve ( w.r.t X direction)
Conclusion :
- With increase in cam lift, linear displacement if the valve also increased. Thus valve lift depends on design of cam.
- There is a in contact force between rocker arm and valve measuring with respect to X direction and measuring with respect to magnitude. Because in X direction frictional force acts. Hence it has both positive and negative direction. But the total magnitude only pushes the rocker arm downwards.