Bmw Transmission Problems

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INTEC GmbH, Argelsrieder Feld 13, 82234 Wessling, Germany

VOLUME 9, FIRST ISSUE                                                                     JULY 2005

                                                                                          » CUSTOMER APPLICATION ........01

                                                                                          Dr. Bencker, M. Nussbaumer, BMW
                                                                                          Group, Prof. B. Schlecht, TU Dresden

                                                                                          Gearshift-Comfort Oriented Trans-
                                                                                          mission and Drive Train Simulation
                                                                                          at BMW

                                                                                          » SOFTWARE ............................... 06

                                                                                          Dr. Wolfgang Trautenberg, INTEC

                                                                                          2-D-Plots in the New SIMPACK Plot

                                                                                          » SOFTWARE AND APPLICATION .. 08

                                                                                          Dr. Lutz Mauer, INTEC GmbH

                                                                                          Modelling and Simulation of Drive
                                                                                          Line Gears

                                                                                          » SIMPACK TIPS AND TRICKS ......11

Gearshift-Comfort Oriented                                                                Dr. Christoph Weidemann, Steve
                                                                                          Mulski, INTEC GmbH

Transmission and Drive Train                                                              Sensors and their Definition

Simulation at BMW
This report describes the way in which     larly negative influence in this respect.
the complete drivetrain was modelled       The continuously growing diversity of
with SIMPACK at BMW on the basis of        variants combined with increasing cost
experimental and theoretical system        pressure and shorter development pe-
analysis and how this model enabled        riods are leading to a situation in which   2 FUNDAMENTAL PRINCIPLES
analysis and evaluation of all param-      comfort objectives can no longer be         The manual gearboxes used at BMW
eters which affect gearshift comfort.      achieved by validating transmission         are inline countershaft transmissions,
                                           designs with testing alone. Therefore       Figure 1. With this gearbox construc-
1 INTRODUCTION                             a SIMPACK MBS simulation process            tion, the engine torque is transmitted
Apart from service life, gearshift com-    was enabled at BMW in order to assess       via the input shaft to the countershaft,
fort is one of the most important de-      effects of drivetrain modifications on       where the power flow branches via
sign criteria for manual transmissions     shiftability before test components are     the various gear stages to the drive
and makes a major contribution to-         manufactured.                               shaft according to the selected gear.
wards the driver’s general feeling of                                                  One exception to this is “direct drive”,
well-being. Irregularities in the shift-                                               whereby the gearbox input shaft is di-
ing sequence or faults exert a particu-                                                rectly linked to the output shaft when
» CUSTOMER APPLICATION                                                              2

Dr. Bencker, M. Nussbaumer, BMW
Group, Prof. B. Schlecht, TU Dresden

                                       the gear is selected. When changing              Phase IV.
                                       gear, the driver uses the gear lever to          The resulting impact, Figure 2, Phase
                                       activate the synchromesh mechanism               IV, is transmitted via the internal and
                                       with the clutch pedal pressed down.              external shift mechanisms to the driv-
                                       The gearshift effort is applied to the           er‘s hand and is shown as an impulse
                                       sliding sleeve of the synchroniser via           in the gearshift effort profile, also re-
                                       the external and internal shift mecha-           ferred to as the double bump, Figure
                                       nisms and the desired gear is selected.          3, Phase IV.
                                                                                        Phase V, in which the gear is engaged,
                                       2.1 SYNCHRONISER                                 begins when the bevels on the teeth
                                       The synchroniser, Figure 1, is used to           of the synchroniser hub have been
                                       accelerate or decelerate the gear set            overcome. The renewed increase in
                                       (with clutch disk) from the current              gearshift effort is due to the sliding
Figure 1: Inline Countershaft Trans-   gear level to the speed of the target            sleeve making contact with the end
missions and Synchroniser              gear, enabling gear selection. Positive          stop, Figure 3, Phase V.
                                       locking is then established during the
                                       subsequent phase and the gear is en-             3 PROBLEMS ENCOUNTERED IN THE
                                       gaged.                                           SHIFTING SEQUENCE
                                       The synchronisation sequence can be              Shifting Sequence Reference literature
                                       divided into 5 phases, which are re-             describes four known synchroniser re-
                                       flected in the gearshift effort profile            lated types of problem occurring in the
                                       at the gear lever, Figure 3.                     shifting sequence, which are perceived
                                       Joined to the fixed sleeve with a tor-            by the driver acoustically or in the
                                       sion resistant connection, the sliding           gearshift effort profile at the gear le-
                                       sleeve is in its neutral position during         ver. These phenomena are unblocking
                                       Phase I and the driver pushes it to-             inhibition, meshing inhibition, double
                                       wards the gear wheel to be selected,             bump and vibration grating. The first
                                       Figure 2, Phase I. Pre-synchronisation           three are static problems and can be
                                       is achieved by the thrust pieces which           influenced by geometric synchroniser
                                       move the synchroniser ring into the              variables (cone angle, sharpness of se-
                                       blocked position. This is perceived as a         lector teeth, etc.), for example. Unlike
                                       slight increase in gearshift effort, Fig-        these, vibration grating is essentially
Figure 2: Positive of the Synchroni-   ure 3, Phase I.                                  determined by the dynamic perform-
ser showing the five Phases of the      Phase II is referred to as the synchro-          ance of the entire drive train, as well
Synchronisation Sequence               nising phase. The sliding sleeve presses         as geometric transmission variables
                                       the synchroniser ring against the fric-          and the synchroniser. The reciprocal
                                       tion cone of the synchroniser hub, Fig-          influences of gearbox, drive train and
                                       ure 2, Phase II, while the rpm of the            vehicle on the shifting sequence lead
                                       gear set is matched to the speed of the          to numerous interactive effects and
                                       target gear by means of one or sev-              goal conflicts, which are very difficult
                                       eral friction surfaces. The gearshift ef-        to define in terms of testing, which is
                                       fort increases again rapidly during this         why simulation is used to examine this
                                       phase, Figure 3, Phase II.                       vibration phenomenon.
                                       Once synchronism is achieved, the
                                       torque between the mating surfaces                3.1 DESCRIPTION OF THE “VIBRATION
                                       tends towards zero and the synchronis-           GRATING” PHENOMENON
                                       er ring can rotate freely again, Figure          The continuous increase in engine
                                       2, Phase III. This eliminates the block-         torque is accompanied by an increas-
                                       ing effect and the free-flight phase              ing load on the drive train components
                                       (Phase III) begins. This process is evi-         (clutch, gearbox, etc.). The effects are
                                       dent as a noticeable dip in the effort           inevitably felt in their size and, above
                                       profile, Figure 3, Phase III. In Phase III,       all, in the inertia of their masses. In an
                                       the sliding sleeve again moves towards           effort to achieve short shifting times
                                       the gear wheel until it makes contact            with low gearshift effort, efficient
                                       with the synchroniser hub, initiating            multi-cone synchronisers are used, en-

                                       SIMPACK»News, July 2005
                                            3                                                 » CUSTOMER APPLICATION

                                                                                              Dr. Bencker, M. Nussbaumer, BMW
                                                                                              Group, Prof. B. Schlecht, TU Dresden

abling acceleration or deceleration of          perceived by the driver. The number of
the inert gear set to the level of the          force amplitudes n during the mesh-
target gear. The resulting high syn-            ing operation must also be known in
chronising torque – particularly when           order to distinguish between grating
changing down from 2nd to 1st gear              and faultless gear shifts. n = 1 indicates
– is supported by the drive train, which        a faultless gear shift, whereas n > 1 im-
is twisted as a result. In the free-flight       plies a grating gear shift, Figure 4.
phase, when the synchronising torque
drops to 0 Nm, the drive train settles          4 SIMPACK SIMULATION
back within its elasticity and backlash         Based on the results of experimental
limits. This leads to another difference        (test rigs, in vehicle tests) and theoreti-
between the speeds of the sliding               cal research the necessary modelling
sleeve linked to the output shaft in 1st        depth and the degree of detail was
gear and the synchroniser hub, which            determined in order to generate an            Figure 3: Five Phases of the Syn-
is linked to the gear set and rotates           appropriate simulation model. It was          chronisation Sequence
at virtually constant speed. When the           found out that it is essential to model
sliding sleeve makes contact with the           the complete drive train system with
synchroniser hub (Phase IV) during a            all of the relevant system characteris-
grating gear shift, the sleeve is locked        tics. This is the only way to ensure that
out and its teeth skip several times un-        the reciprocal effects of the individual
til the speeds are matched. The result-         subsystems are considered. The studies
ing axial motion of the sleeve is trans-        described below do not therefore sim-
mitted to the driver’s hand directly and        ply concentrate on the driver and the
is expressed in the form of the manual          influence exerted by variables inside
force profile shown in Figure 4.                 the transmission, but also allow for the
                                                vehicle as a whole.
An assessment of the unpleasant vi-             4.1.1 VEHICLE AS A WHOLE
bration grating subjectively perceived          The modular structure of the vehicle
by the driver’s hand on the gear lever          as a whole essentially comprises the
requires objectification of this process         body and its masses, with the transmis-
according to measured values. Meas-             sion, drive train and rear axle carrier       Figure 4: Manual Force Profile sho-
ured directly at the gear lever, the in-        sub models connected to its bearing           wing Synchronisation
terface to the driver, the gearshift ef-        points, Figure 6 and 8.
fort profile, Figure 4, is a particularly
suitable evaluation variable. The driv-         4.1.2 GEARBOX MODEL, INTERNAL
er regards a renewed increase in effort         AND EXTERNAL SHIFT MECHANISMS
after synchronisation as being very un-         The gearbox model comprises a hous-
pleasant as he does not instinctively           ing, which is connected to the body
anticipate any further resistance. This         and the engine, the synchroniser and
gives rise to the relationship between          one gear. Particular importance was
maximum synchronising force (Fmax,II)           attached to the model of the synchro-
and the double bump (Fmax,VI), Fig-             niser (sliding sleeve, synchroniser ring
ure 3, as an evaluation variable. The           and teeth of the synchroniser hub are
smaller the ratio Fmax,VI/ Fmax,II, the         mating components), Figure 7. The
more inconspicuous the double bump.             according SIMPACK library function-
The time dimension of the fault is ex-          ality (force element) was developed
pressed by integral IH for the manual           by INTEC within a project work. The
force from the time at which meshing            synchronising torque built up during
begins through to the time of posi-             the synchronising phase causes system
tive engagement, Figure 4. The more             excitation and it is stored in the model      Figure 5: Contact Situation of Syn-
time required for this operation and            as a measured function of gearshift           chronisation Phase IV
the higher the force amplitudes, the            effort and differential speed. The slid-
less easy the gearshift operation as            ing sleeve and synchroniser hub, which
» CUSTOMER APPLICATION                                                             4

Dr. Bencker, M. Nussbaumer, BMW
Group, Prof. B. Schlecht, TU Dresden

                                       make contact with one another during            4.2 MODEL VERIFICATION
                                       meshing, are represented by geometric           The model is verified according to vari-
                                       bodies. The forces exerted when these           ables measured in preliminary tests,
                                       bodies meet are therefore described             i.e. the torque at the prop shaft, the
                                       unambiguously. Furthermore, the flex-            rpm of the sliding sleeve, the rpm of
                                       ible internal and external shift mecha-         the gear wheel and the manual force
                                       nisms are modelled with the pertinent           profile. Apart from this, the model is
                                       bearing points on the body and gear-            calibrated with vibration measure-
                                       box. These bearing points constitute a          ments for the rear axle carrier and the
                                       very important variable determining             differential. Figure 10 and 11 shows
                                       gearshift comfort in transmission de-           an example of a comparison between
                                       velopment and therefore require in-             simulated and measured synchronis-
                                       depth examination.                              ing operations and unobstructed drive
Figure 6: Front View of the MBS                                                        train vibration.
Model                                  4.1.3 ROTARY DRIVE TRAIN MODEL
                                       The rotary drive train model comprises          5 MODEL ANALYSES
                                       flexible coupling, prop shaft, centre            With defined boundary conditions,
                                       bearing, differential, output shafts and        parameter variations or statistical ex-
                                       tyres. These components are also mod-           perimental design were performed
                                       elled in detail and are linked to the           with the according SIMPACK model.
                                       body at the relevant bearing points.            Conclusions regarding the sensitiv-
                                                                                       ity of components could be reached
                                       4.1.4 REAR AXLE CARRIER MODEL                   quickly and easily in order to enable
                                       The entire kinematics of the suspen-            definition of optimum design in a
                                       sion and all bearing points are stored          subsequent stage. Goal conflicts with
                                       in the rear axle carrier model. This ena-       other phenomena must be considered
                                       bles modelling of pitch and roll vibra-         in this respect, however. These include
                                       tion, as well as the translatory longitu-       longitudinal dynamics, stress reversal
                                       dinal vibration of the rear axle carrier,       behaviour (bucking) and acoustics
                                       which must also be considered when              (clacking, knocking noises during load
                                       examining vibration grating.                    reversal).

Figure 7: Synchroniser (Sliding Sle-   4.1.5 DRIVER MODEL                              5.1 BOUNDARY CONDITIONS
ve, Synchroniser Ring and Synchro-     Great importance is also attached to            Gearshift effort is varied within cer-
niser Hub)                             realistic modelling of the driver as his        tain limits during each simulation run,
                                       behaviour essentially determines the            which comprises numerous individual
                                       overall shifting operation, particularly        computations, to ensure that the sim-
                                       during the synchronising and meshing            ulation allows for the gear changing
                                       phases. A parameterised mass-spring-            behaviour of both sporty and comfort-
                                       damper system enables simulation of             oriented drivers. The forces taken as
                                       all relevant driver types (sporty, aver-        the basis for this are obtained from
                                       age and comfort oriented), which are            in-vehicles measurements and they
                                       represented by different gearshift ef-          represent the entire driver spectrum
                                       fort values and/or shifting times dur-          to be expected from customers. Apart
                                       ing the synchronising phase. The inter-         from this, it is essential to ensure that
                                       action with the internal and external           the meshing conditions between the
                                       shift mechanisms and the synchroniser           teeth of the sliding sleeve and the
                                       gives rise to the gearshift effort pro-         synchroniser hub are defined when
                                       file. A constant effort value is specified        they make contact for the first time to
                                       for the driver model during the mesh-           enable a comparison of the variants.
                                       ing phase, in which the driver per-             The starting conditions are therefore
Figure 8: Rear View of the MBS Mo-     ceives the response of the drive train          varied within the tooth pitch in the
del                                    at the gear lever. The interaction with         model. This method offers a means
                                       the vehicle gives rise to a correspond-         of examining a situation in which the
                                       ing double bump or grating.                     teeth of the sliding sleeve fit directly

                                       SIMPACK»News, July 2005
                                           5                                               » CUSTOMER APPLICATION

                                                                                           Dr. Bencker, M. Nussbaumer, BMW
                                                                                           Group, Prof. B. Schlecht, TU Dresden

into the gap between the teeth of the          ing all of the variables which affect
synchroniser hub or the bevels on the          vibration grating. This enables deter-
teeth collide with one another. Vehicle        mination of the sensitivity of each in-
speed is another important variable to         fluential parameter and identification
ensure comparability. This is also var-        of the contrary or reinforcing effects of
ied within certain limits during a simu-       a variation. To this end, a preliminary
lation run.                                    theoretical and experimental system
                                               analysis was carried out to identify the
5.2 OPTIMISATION VARIABLES                     parameters which influence vibration
There are interface variables between          grating and are found in the gearbox,
the driver, internal and external shift        the internal and external shift mecha-
mechanisms, gearbox, synchroniser              nisms and the rear drive train (includ-
and rear drive train subsystems. Op-           ing the rear axle bearing arrangement
timisation of the interface variables          and rear axle kinematics). Based on         Figure 9: Complete Vehicle Dyna-
between gearbox and drive train (re-           the knowledge acquired with respect         mics System
ducing differential speed and torque           to sequences, processes, sensitivity and
for meshing, maximum possible axial            system behaviour, the SIMPACK simu-
force) also brings about a reduction           lation model was produced which is
in the axial force acting on the slid-         capable of realistically simulating the
ing sleeve. This must be applied by the        aforementioned vibration phenome-
driver via the internal and external           non. The defined characteristic values
shift mechanisms or is transferred to          can be used to capture the driver’s sub-
the driver‘s hand and is expressed in          jective sense of comfort when chang-
the gearshift effort profile. Optimisa-         ing gear in objective measurements,
tion of the aforementioned variables           thereby describing vibration grating.
therefore also results in an improve-          These variables offer a means of ana-
ment in the characteristic values for          lysing and evaluating in vehicle meas-
gearshift comfort.                             urements and simulation results. Based
                                               on the acquired knowledge, various
5.3 PARAMETER VARIATION                        drive train variants can now be tested
Statistical Experimental Design and            cost-effectively and quickly according
Optimisation by systematically varying         to vehicle model and associated cus-
parameters (statistical experimental           tomer requirements (sporty or com-          Figure 10: Measured Synchronisati-
design) related to the gearbox, drive          fort-oriented), allowing for reciprocal     on Process
train and internal and external shift          effects and goal conflicts, beginning
mechanisms, it is possible to calculate        at the concept phase and going right
different variants and define one or            through to SOP. One result of this is a
more optimised designs on the basis            reduction in iterative loops, particular-
of the results. As the influence exerted        ly with respect to testing and trials, as
by the various components depends              only the promising variants need to be
on the vehicle configuration to a great         tested. Using statistical experimental
extent, and the evaluation criteria            design, the test engineer of the future
(gearshift comfort, longitudinal dy-           will be able to perform virtual optimi-
namics, stress reversal behaviour) are         sation and tuning calculations and use
determined by the design philosophy,           these as the basis for definition of test
no general conclusions can or should           variants.
be given here.

In an effort to counteract increasing
pressure on costs and shorter develop-
ment periods, the complete SIMPACK                                                         Figure 11: Simulated Synchronisati-
vehicle model presented in this article                                                    on Process
provides a tool that offers a means of
comprehensively studying and analys-

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