Previous disclosures relating
to Torque VectoringTM (a
registered trademark of
Ricardo plc) devices have
described the operation of variants
in which actuation torque was
provided by a brushless
DC machine.
The system was shown to alter
dramatically the limit handling of
the vehicle from fwd to rwd to
improve both stability and the
responsiveness of the vehicle
under spirited driving.
Whilst suitable as a flexible
actuator for R&D purposes, an
e-machine is unsuited for nearfuture
production implementation
unless integrated as part of a
hybrid driveline.
As a practical alternative,
hydraulically operated wet multiplate
brakes were selected for
application to the rear axle of a
high performance compact-class
European vehicle to influence limit
and sub-limit handling and the
article describes the tool chain by
which the mechanical elements
were designed encompassing the
following disciplines:
?? Practical assessment of epicyclic
arrangement
?? Duty cycle definition from race
circuit data
?? Thermal simulation
?? Clutch calculations and
hydraulic circuit
?? Design of geared elements
and packaging.
Beyond the systematic design
of the rear axle using conventional
actuation, a description of R&D
effort around future actuation is
provided.Magneto-rheological
fluid brakes have been widely
described, but little relevant data
has been published for devices of
suitable torque capacity. A study
resulting in rig test data collection
has been undertaken and the
results are reported.
Variable torque bias axles
Comparison with alternatives
Controllable torque bias devices
fundamentally comprise an input
and two outputs between which
the input torque may be variably
distributed. Fig. 1 shows a stick
diagram of the Ricardo
arrangement applied to an axle.
So why pursue a design that
includes additional components
compared to alternatives, which
have apparently similar
functionality? The answer lies in
the load sharing and assembleability
of the sun/planet mesh sets
of the speed varying stage. Fig. 2
shows that assembly of the Ricardo
design has no constraints since
planets P2b and P2c can rotate on
the carrier to engage with sun S2
and annulus A2.
As a consequence each planet
carries the same load, allowing for
a smaller overall size, and low
precision (low cost) components.
Whereas, shown in Fig. 3 is a
generic design which uses joined
planets and assembly has two
constraints since the planets P2b
and P2c cannot rotate on the
carrier to engage with sun S2. As a
consequence, one planet carries
full load and assembly may be
impossible unless the planets
precise and are 'timed' relative to
one another.
.....CONTD
