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                      VALDYN SOFTWARE”

                 Author : Ashwinkumar S. Dhoble and R. P. Sharma
                     R&D Centre, Mahindra & Mahindra Ltd.,
                                 Nashik, India.

ABSTRACT                                        INTRODUCTION
The authors have made an attempt to             Valve train design and the valve timing
analyse the dynamic behaviour of a              directly affect the engine performance.
single pushrod type valve train                 Validation of existing valve train is
configuration using Ricardo’s VALDYN            carried out using Ricardo VALDYN
software. The valve train model was             software. The important objectives of
prepared using flexible mathematical            valve train are,
element approach. Within this approach,
each component of the valve train is            •   Engine performance: The main
modelled as a lumped mass system                    demands here are the exact timings
having stiffness and damping.                       (Valve opening and closing), a high
                                                    volumetric flow (fat valve lift), fast
The stiffness properties of the valve train         opening and in some cases a short
components were calculated using 3-D                overlap     period.    The      usual
finite element model of the components              considerations       for      design
prepared and analysed using IDEAS                   optimisation are WOT (wide open
software.                                           throttle) performance characteristics
                                                    for gasoline engines and full load
The valve train was analysed for the                smoke for diesel engines.
rated speed and overspeed to find out the
dynamic forces acting on the                    •   Durability: The limits for the design
components. The results in the form of              are given by Hertz pressure, the oil
nodal     displacements      and     valve          film thickness at cam/follower,
acceleration were plotted to reveal the             velocity and force at the valve seat,
occurrence of the jump phenomenon at                prevention of contact loss and valve
the rated speed and or at overspeed.                bouncing.
The effect of variation in the cam profile      •   Vibration and Noise: Optimum
on dynamic forces acting on the valve               solutions are achievable with high
was also studied.                                   stiffness and high natural frequencies
                                                    of the valve train. The impacts and
The dynamic forces obtained from the
                                                    the inertia forces should be
analysis were used as input for finite
element model of the valve train
components for sustainability of the
valve train components at rated and

Conflicting demands in the design may         excitation to the model is provided by a
occur due to fast opening of valve, valve     rotating element. Then the equations of
train dynamics and its effects on the gas     motion are solved simultaneously for
exchange process. On the one hand big         subsequent elements in the model.
effective opening areas of the valve are
required to optimise the engine air flow      VALVE TRAIN MODELLING
and to minimise the pumping losses for a
given valve timing. This requirement          The modelling of the valve train
forces the designer to go close to the        components is done using the
limits of valve train durability. On the      representative mathematical elements in
other hand the resulting high forces in       the VALDYN object palette. The
the valve train may cause significant         detailed model of the valve train
differences between the geometric and         analysed is shown in Fig.1.
dynamic valve lift curves depending on        The geometric data and material data
the stiffness of the valve train. The gas     were taken from the component
exchange process of the engine,               engineering drawings. The stiffness data
however, is controlled by the dynamic
valve lift.
In view of this conflict the best
compromise can only be found if
accurate prediction of the system
performance can be made. This is
particularly important at high speeds.

The dynamic simulation of a single
valve train is done using Ricardo
VALDYN software, version 2.1. The
software consists of two modules; the
first is the VALDYN module, which
consists of the pre-processor and solver.
The second module is RPLOT, which is
the post processor. The current work was
carried out on the Windows NT based

VALDYN uses a flexible elemental
approach to model valve trains. Within
this approach individual parts of the
valve train are represented by modelling
elements, which can be linked together
to form the whole valve train model. The
software models each valve train              was collected by carrying out the CAE
component as a lumped mass system,            analysis of the valve train components.
having stiffness and damping. The             The 3-D models of the components were
                                              made in IDEAS. The discretization of

the model is also performed in IDEAS.                                                                This phenomenon has an adverse effect
The boundary conditions were specified                                                               on the effective flow area and
in accordance with actual loading of the                                                             consequently leads to reduction in the
component in valve train with unit load.                                                             volumetric efficiency of the engine.
The static displacement results were
used to calculate the individual                                                                     Breathing of the engine can be made
component stiffness value. The damping                                                               effective by increasing the dynamic
values for the component were assumed                                                                valve lift. The dynamic valve lift can be
to be 3-5% of critical damping. The                                                                  increased by reduction in the energy
mass data for the rocker arm was to be                                                               losses in the valve train or by increasing
calculated from the moment of Inertia                                                                the forces acting on the valve to the limit
around     the     axis    of    rotation                                                            of durability. For a given valve train the
(transformation of rotational motion into                                                            energy losses can not be reduced below
a transversal motion). The effect of                                                                 a certain limit constrained by material
temperature on the valve train                                                                       and friction. At this juncture it becomes
component can not been taken into                                                                    very important to check the valve train
consideration in the VALDYN model.                                                                   for the maximum dynamic forces.

                                                                                                     A lag in the valve displacement is
SIMULATION RESULTS                                                                                   observed with respect to the cam at the
The performance of the valve train                                                                   start of lift. This is due to the inertia
becomes critical at higher engine speeds,                                                            effect of tappet, pushrod, rocker, valve
particularly in relation to the dynamic                                                              and the spring pre-load.
valve lift, velocity and acceleration. The
displacement, velocity and acceleration                                                              The valve velocity plot shows a usual
curves for the valve are shown in Fig.2                                                              trend of reversal of velocity at the point
and Fig.3 at the rated speed and the                                                                 of maximum valve lift.
                                                                                                                                      ig .0 a e elo o p riso
                                                                                                                                     F . 3 Vlv V cityCma n
It can be observed from Fig.4 that the
dynamic valve lift is comparatively
lower than the kinematic lift. This can be                                                                                                               70 m
                                                                                                                                                        4 5 rp
                                                                                                                                                         80 m
                                                                                                                                                        3 0 rp
                                                                                                      Valve velocity in deg.

                                   Fig. 2.0 Displacement Comparison
                                                            Cam Lift                                                            0
                     10                                     Kinematic Valve Lift
                                                            Dynamic Valve Lift                                            -40        60        10
                                                                                                                                                6          20
                                                                                                                                                            6    6
 Displacement (mm)


                     6                                                                                                          -4
                                                                                                                                            a a g eg
                                                                                                                                           Cm n leind
                          0   50   100    150         200         250    300       350   400
                                                Cam Angle (deg)

attributed to the flexural rigidity of the
component and individual component

In valve train performance the valve
acceleration  at    overspeed  gives                                                                                                     ig.5.0 a e o o p riso
                                                                                                                                        F Vlv F rceCma n
information of the occurrence of the
shock phenomenon.                                                                                                            600
A steep acceleration curve signifies the                                                                                     400
probability of shock phenomenon, which

                                                                                                           Valve Force (N)
                                                                                                                             300                              3800 rpm
is one of the causes of valve breakage                                                                                       200
                                                                                                                                                              4750 rpm

and detrimental from the point of view                                                                                       100
of airflow into the cylinder. The                                                                                             0
acceleration curve for the simulated                                                                                    -100 0     50    100    150    200     250       300   350

valve train does not show any                                                                                           -200

probability of shock. It is observed that                                                                               -300
                                                                                                                                                   ngle eg)
                                                                                                                                               CamA (d
there is abrupt change in the acceleration
during valve closure. This leads to a
                                                                                                         durability limits has been established.
minor shock at the overspeed, but that is
                                                                                                         Based on the above results it can be said
not the case at the rated speed.
                                                                                                         that there is no valve jumping within the
                                                                                                         engine operation range. Also the
                                            Fig. 4.0 Valve Acceleration Comparison                       valvetrain is safe from strength point of
                                                                                                         This result matches with the durability
 Valve Acceleration (m/s2)

                             4000                                           3800 rpm
                                                                                                         testing done on engine dynamometer.
                             3000                                           4750 rpm
                             -1000 0   50         100      150      200      250       300   350         The authors would like to express
                             -2000                                                                       sincere thanks to Dr. P. K. Goenka, Vice
                                                                                                         President (R&D) , Mahindra and
                                                           CamAngle (deg)                                Mahindra     Ltd.,    Management      of
                                                                                                         Mahindra and Mahindra Limited for
                                                                                                         their support and guidance to publish
The dynamic forces on the valve follows
                                                                                                         this paper.
the same trend as that of valve
acceleration and the maximum value of                                                                    The result matches with the durability
the dynamic force acting encountered                                                                     tasking done on engine dynamometer.
during overspeed is well below the first
mode buckling load. The buckling load                                                                    References
value is established by carrying out finite
element analysis of the valve using                                                                      1. Akio Kinoshita, Hirofumi Aoki and
IDEAS.                                                                                                      Masao Ishihama, “An Effective
                                                                                                            Approach for Reducing Valve Train
CONCLUSION                                                                                                  noise”JSAE Review, December 1985
                                                                                                            p. 48.
An approach to quantify the dynamic
forces acting on the valve train                                                                         2. W. Hellinger, H. H. Priebsch, K.
components focusing on the valve train                                                                      Landfahrer and U. Mayerhofer,
performance within the frame of                                                                             “Valve Train Dynamics and Its

   Contribution      to      Engine
   Performance”, paper C389/129,
   FISITA’ 92 Congress London , 7-11
   June 1992
3. M. Colechin, C. R. Stone, and H. J.
   Leonard, “ Analysis of Roller –
   Follower Valve Gear”, SAE Paper
   930692 (1992)

4. Saied M. Baniasad and Michael R.
   Emes, “Design and Development
   Method of Valve- Train Fricton
   Measurement,” SAE Paper 980572



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