75 Jahre Sonceboz 75 years Sonceboz

75 Jahre Sonceboz
From DC brush motor to BLDC
motor
In a Valvetronic an eccentric shaft sets
the intake valve stroke. In the previous
layout of the Mini TVDI 1.6 l “Prince”
engine this eccentric shaft was driven
by a classic DC motor. A separate sensor
recorded the position of the shaft at the
shaft end. BMW’s specifications for this
small four-cylinder TVDI engine were:
compact installation with large torque
and high dynamics, long service life as
well as full integration of all the sensors.
The sensor was to be integrated into the
motor so that only a single 10-pin plug
was needed and the motor diameter
could be reduced from 61 to 42 mm. The
nominal peak torque was simultaneously
increased up to 0.8 Nm ❷ to achieve
additional functional reliability. The
mass moment of inertia also had to be
reduced to make cylinder-dependent
adjustments for greater actuator dynamics.
Under these general conditions, in
particular the significantly high ambient
temperatures and vibrations, it was
soon apparent that only a brushless DC
motor would be acceptable ➌. The high
tolerance for vibrations and the possibilities
for weight reduction through
minimisation of the space used were the
distinguishing features of this design.
This also facilitated mechanical integration.
A comparison of the classic VVT2
DC motor with the new VVT3 BLDC motor
is depicted in ❹.
Simulation versus prototype
construction
The project also faced an extremely
tight schedule. And so it was not possible
to approach the optimal design
through various experimental models.
The exact product definition as well as
the design had to be found through
purely numerical models ❺.
Due to challenging vibration requirements,
numerical simulation was
also used to determine mechanical
strength. This meant that optimisation
of, e. g. the motor flange, could begin
even before delivery of the B-sample
using purely numerical models.
Various simulations were performed
to define the optimal injection points
and also improve the mechanical characteristics
of the flow lines for the complex
injection moulding process, in
which the connector is formed and the
sensitive contacts of the three motor
pins on the coil windings are overmolded.
Quality in Design
Tools were also used to achieve the
high quality requirements. In close
cooperation with BMW, first FTA
analyses were performed, followed by
D-FMEA.
As soon as the first prototypes
were available, high accelerated lifetime
tests (HALT tests) ❻ and other
extreme tests were carried out to uncover
weaknesses within just a few
days. As a result, initial correction
processes were initiated as quickly as
possible so the official qualification
cycles could be started with a good basis
of confidence. Here, too, the time
specifications did not permit an iterative
development due to the successive
elimination of errors.
Challenge production
The fully automated production of
such a complex and highly stressed
electrical actuator was and is at least
just as challenging as its development
and qualification. The assembly concepts
were also developed simultaneously.
P-FMEAs were used as main tools here
to systematically verify the concepts.
For Sonceboz, it was the first project
in which fully automated assembly
immediately followed prototype construction.
Previously, the corresponding
experience was always gained first
on a manual assembly line. Process
stability is monitored using suitable
tools. Processes such as gluing and
welding can thus be checked for consistency
even before a delivery lot is
shipped.
Outlook for Euro 6
The TVDI technology, the various measures
for CO 2
reduction combined with a
simultaneous increase in performance,
was optimised toward achieving the
coming Euro 6 emission requirements.
Experience with VVT1 and VVT2 has
been gained with fully variable valve
control since 2001. For VVT3, more compact
and dynamic actuators can now be
used to drive the eccentric shaft. The
improved dynamics permit a finer and
faster adjustment to the optimal parameters
for every condition.
Thanks to this first high valuable
experience on “Prince” Engines, BMW
can consider the BLDC actuator as an
optimal solution for other internal
combustion engines. Whatever the cylinders.
The same actuator has already
been validated on the TwinPower Turbo
V8 cylinder 4.4l engines for instance
installed on BMW M5.
Innovation with future
Sonceboz and MMT engineers have designed
the next Brushless DC motor generation
in an even more compact design
while providing even improved motor
performances, accompanying the engine
downsizing need. Thanks to its compactness,
power and quality attributes,
Sonceboz foresees a bright future for
this technology concentrated piece in
other automotive applications, where
dynamic positioning and small installation
place are required like the Variable
Valve Timing and Camphasing.
References
[1] Liebl, J.; Klüting, M.; Poggel, J.; Missy, S.:
Der neue BMW Vierzylinder-Ottomotor mit Valvetronic.
In: MTZ 62 (2001) Nr. 7/8
[2] Unger, H.; Schwarz, C.; Schneider, J.; Koch,
K. F.: Die Valvetronic – Erfahrungen aus sieben
Jahren Großserie und Ausblick in die Zukunft.
In: MTZ 69 (2008) Nr. 7/8
| | ❶ Installation of the Valvetronic EC motor on the
cylinder head
| | ❷ Torque characteristics
24
| | ❸ Exploded view of the new BLDC motor
| | ❹ Comparison of DC motor VVT2 versus BLDC
motor VVT3
| | ❺ Rotor and magnet field modeling
| | ❻ HALT test conditions