MBD Simulation on IC Engine Valve Train

Simulation on IC Engine Valve Train

Aim :

     To create and assemble the parts of the IC engine valve train. And then perform the motion study for valve linear motion and contact force for this assembly.

Objective :

• To create and assemble 3D model of the Cam, Push rod, Rocker arm, valve stem and valve.
• To perform motion analysis and simulation on the following cases,

                  

Theory :

IC Engine Valve Train :

       A Valve train is a mechanical system that controls the operation of the intake and exhaust valves in an IC Engine. The intake valves controls the flow of air/fuel mixture into the combustion chamber while the exhaust valve controls the flow of spent exhaust gasses out of the combustion chamber once combustion is completed.

               

      The valve train consist of all 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 controled 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.

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 camshft 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 engine 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 valve type, although sleeve, slide 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.

       Valve float occurs when the valve spring is unable to control the inertia of the valvetrain at high engine speeds(RPM).

Design of Cam :

Cam Lift formula :

              

For Case 1 :

     Cam lift = 3.5 mm

                                          cam lift = (L-R1)+R2

                                                3.5 = (L-17.5)+10

                                                3.5 = L -7.5

                                                   L = 11 mm

Cam 1 Data :

        Diameter of lower circle (D1)= 35mm

        Diameter of Upper circle (D2)= 20mm

        Distance between the centres (L) = 11 mm

For Case 2 :

   Cam lift = 6 mm

                                          cam lift = (L-R1)+R2

                                                   6 = (L-17.5)+10

                                                   6 = L -7.5

                                                   L = 6+7.5

                                                   L = 13.5 mm

Cam 2 Data :

        Diameter of lower circle (D1)= 35mm

        Diameter of Upper circle (D2)= 20mm

        Distance between the centres (L) = 13.5 mm

3D Modelling of all parts :

       This requaired parts are created in the solidworks part modeling environment. By using the sketch tools like line circle create the 2D drawings and the using the 3D features like Extrude and Revolve the required parts are created. And then the matrial applied as Cast Corbon steel.  

      Then next step is to assemble all parts by using the assembly workbench in solidworks software as shown in figure.

Cam Shaft :

                        

                                       Case 1                                                                 Case 2

Push Rod :

                 

Rocker arm:

                   

Valve stem :

                   

Valve:

                      

Assemble :

              

                     

Motion Analysis :

 case 1 : 

• Motor is assigned to cam at the RPM of 1500rpm.
• Contact is assigned between all the components and material (dry steel) is given.
• Apply spring between the top face of the stem and bottom face of valve head and then assign the following values.

                 Spring constant : 12 N/mm

                 Free Length : 34 mm

• In motion analysis setting, select precise contact option and 7200 frames per second.

Motion study Results and plots :

Valve lift :

                       

        This plot is for view linear displacement of the value lift with respect to time in sec. The minimum value is 100 and maximum distace is 109 so, total distance travel by the valve is 9mm. And this cycle is happen with the regular period of time repeatly. 

Contact force (Cam and Push rod) :

                      

         This plot is for view contact force between the cam and push rod with respect to time in sec. The maximum force attain by the push rod is 1200N. And the constantly the 270N force is acted on the cam by the spring reflection force. And this cycle is happen with the regular period of time repeatly. 

Contact force (Push rod and Rocker arm ) :

                     

          This plot is for view contact force between the push rod and rocker arm with respect to time in sec. The maximum force attain by the rocker arm is 1200N. And the constantly the 280N force is acted on the rocker arm by the spring reflection force. And this cycle is happen with the regular period of time repeatly.

Contact force (Rocker arm and valve ) :

                    

         This plot is for view contact force between the rocker arm and valve with respect to time in sec. The maximum force attain by the valve head is 260N. And the constantly the 100N force is acted on the valve head by the spring reflection force. And this cycle is happen with the regular period of time repeatly.

Rocker arm and valve X direction force : 

                    

        This plot is for view contact force between the rocker arm and valve in X direction with respect to time in sec. The maximum force attain by the valve head is 70N. And the constantly the -25N force is acted on the valve head by the spring reflection force. And this cycle is happen with the regular period of time repeatly. Hear the force is low when compare the the previous plot because of the force is splited into two direction namely X and Y direction hear we plot the X direction force alone. 

 case 2 : 

• Motor is assigned to cam at the RPM of 1500rpm.
• Contact is assigned between all the components and material (dry steel) is given.
• Apply spring between the top face of the stem and bottom face of valve head and then assign the following values.

                 Spring constant : 12 N/mm

                 Free Length : 38 mm

• In motion analysis setting, select precise contact option and 7200 frames per second.

Motion study Results and plots :

Valve lift :

                     

        This plot is for view linear displacement of the value lift with respect to time in sec. The minimum value is 96 and maximum distace is 110 so, total distance travel by the valve is 14mm. And this cycle is happen with the regular period of time repeatly. 

Contact force (Cam and Push rod) :

                    

          This plot is for view contact force between the cam and push rod with respect to time in sec. The maximum force attain by the push rod is 1820N. And the constantly the 320N force is acted on the cam by the spring reflection force. And this cycle is happen with the regular period of time repeatly. 

Contact force (Push rod and Rocker arm ) :

                    

          This plot is for view contact force between the push rod and rocker arm with respect to time in sec. The maximum force attain by the rocker arm is 1830N. And the constantly the 320N force is acted on the rocker arm by the spring reflection force. And this cycle is happen with the regular period of time repeatly.

Contact force (Rocker arm and valve ) :

                    

          This plot is for view contact force between the rocker arm and valve with respect to time in sec. The maximum force attain by the valve head is 460N. And the constantly the 120N force is acted on the valve head by the spring reflection force. And this cycle is happen with the regular period of time repeatly.

Rocker arm and valve X direction force : 

                   

         This plot is for view contact force between the rocker arm and valve in X direction with respect to time in sec. The maximum force attain by the valve head is 110N. And the constantly the -80N force is acted on the valve head by the spring reflection force. And this cycle is happen with the regular period of time repeatly. Hear the force is low when compare the the previous plot because of the force is splited into two direction namely X and Y direction hear we plot the X direction force alone.

Observation and Result :

         After comparing the two case study in the first case is has obtained less force (1200N) when compared to the case 2 (1800N). Its because the spring length is increased in the case 2 to get smooth flow in the cam follower.

         And the X direction this force is actually two directional. so, the common force obtained by the valve is high in both cases. But, in the X direction plot the force analysis and plot for force act on the valve in the X direction alone so it is less. And the negative force indicate that the rocker arm is moving front and back on the valve head.  

Attached Files :

           1) Valve part and assembly file.

           2) Valve assembly animation video.