MBD SIMULATION ON IC ENGINE VALVE TRAIN USING SOLIDWORKS
AIM: To Simulate the Valve mechanism & analysis of motion for different different conditions.
OBJECTIVES:
1) Model parts in Solidworks & Assemble it.
2) Run Motion Analysis for below conditions:
| Sr. No. | CAM Lift (mm) | Speed (RPM) | Material |
| 1. | 3.5 | 1500 | Cast Carbon Steel |
| 2. | 6 | 1500 | Cast Carbon Steel |
3) Obtain Following Plots for each condition:
I) Valve Lift (Linear Displacement of Valve)
II) The contact force between
i) Cam and Push Rod
ii) Pushrod and Rocker Arm
iii) Rocker Arm and Valve [for X-direction & Magnitude both]
4) Explain the variation for contact force in X-direction & for Magnitude in last case[iii].
VALVE MECHANISM:
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.
CAM OR 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 camshaft 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.
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:
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.
VALVE:
Most modern engines use poppet valve type, although sleeve valves, slide valves and rotary valve 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. Valve float occurs when the valve spring is unable to control the inertia of the valvetrain at high engine speeds (RPM).
CAM LIFT CONDITION:
> In this project the cam lift is varied for two different values 3.5 & 6 mm respectively. The formula for the cam lift given in following image:
> From the above formula, for applying the cam lift I can only vary the value of distance between two circles (L) because the diameters are constant for the all conditions.
> Therefore from above formula the values of L is found and they are 11 & 13.5 mm for both cam's respectively. Using that values the analysis is carried out for two mechanisms having different cam's.
MOTION ANALYSIS PARAMETERS:
1) Motor Speed = 1500 RPM (Center of bigger circle is considered as center of rotation for cam)
2) Material for all parts = Cast Carbon Steel
3) Frames per second = 7200
4) Time period of simulation = 0.2 second
5) The spring is used between the valve face and the valve mount upper face using following conditions:
6) Spring stifness = 10 N/mm (Linear Spring)
7) Gap between wounds = 45 mm
8) solid contact is given for each mating parts.
9) All parts are constrained for the unique motion.
10) Presice Contact is enabled for each condition.
CASE-1 [CAM LIFT = 3.5] RESULTS:
1) VALVE LIFT (LINEAR DISPLACEMENT OF VALVE):
> From the plot the valve lift ranges between 50 to 53 mm.
2) CONTACT FORCE (CAM & PUSH ROD):
3) CONTACT FORCE (PUSH ROD & ROCKER ARM):
4) CONTACT FORCE (ROCKER ARM & VALVE) [MAGNITUDE]
5) CONTACT FORCE (ROCKER ARM & VALVE) [X-direction]
CASE-2 [CAM LIFT = 6] RESULTS:
1) VALVE LIFT (LINEAR DISPLACEMENT OF VALVE):
> From the plot the valve lift ranges from 50 to 56 mm.
2) CONTACT FORCE (CAM & PUSH ROD):
3) CONTACT FORCE (PUSH ROD & ROCKER ARM):
4) CONTACT FORCE (ROCKER ARM & VALVE) [MAGNITUDE]
5) CONTACT FORCE (ROCKER ARM & VALVE) [X-direction]
WHY THE CONTACT FORCE FOR ROCKER ARM & VALVE VARIES FOR MAGNITUDE & X-DIRECTION CONDITIONS:
> From the plots it can be seen that the contact force between the rocker arm & valve for magnitude ranges only is first quadrant. that means all values for the force are positive.
> But at the same time for only X-direction component the force value ranges from first quadrant to fourth quadrant. That means the force values are ranging from positive to negative in the upward & downward direction of the valve.
> This variation is happening because the magnitude is the total resultant force & which is calculated equaivalently for all the directions in which X-direction is also included. While on other hand the X-direction component is ranging from positive to negative region of the top plane and motions.
> Therefore the variation in the Plots is occuring.