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Asc, Cbc, Dsc-The Contribution of BmwS Wheel Slip Control Systems to the Improvement of Active Safety
Technical Paper
97A139
Sector:
Language:
English
Abstract
The standard installation of ABS in all model ranges of BMW
allowed more integrated designs for the traction and stability
controllers at BMW (Automatic Stability Control ASC). The
ABS-integration of the hydraulic and electronic hardware of t
results in compact and cost effective designs. To simplify the
application of the ASC to different cars and engine concepts a
torque interface was introduced. Different engine charge concepts
for diesel and petrol engines thus can easily be adapted to the
respective controllers.
The basic ABS normally operates within physical ranges where a
high risk of wheel locking or high wheel slip is given. Already
below the maximum longitudinal friction coefficient between tire
and road, tendencies to instability caused by brake actuation
during different dynamic maneuvers can occur. To achieve an active
correction of this unfavorable driving situation, the normal
operational range of ABS is extended. This new system, the
Cornering Brake Control CBC, is part of the ASC of the 5 and 7
series BMW.
ASC and ABS rely on the wheel speed information only. Certain
μ-slip characteristics of tires and road make it difficult to
distinguish exactly between low-μ and high-μ surfaces. To get a
better prediction of the driving situation simulation together with
additional sensor information proved successfully. Systems based on
a nominal/actual-comparison of the driving situation (Dynamic
Stability Control DSC) were used at BMW in different development
steps and are standard on the current 12-cylinder models.
Test results achieved with the different systems show the
improvements in traction, stability and a reduction in the work
load for the driver. The safety margins to the limits of physics
have become more precisely defined. DSC represents the actual
benchmark for stability control systems.
To extend the model ranges, where DSC can be considered as a
standard installation, requires further integration of the actual
hardware. The consideration of additional functions to be
controlled by the respective electronics and hydraulics of the DSC
assists the penetration in all model ranges.
Alternative design principles of the complete brake and wheel
slip control system must be considered if further extensions of the
brake control systems are foreseen. A system which manages the
complete interaction between the different controllers is the
Electronic Brake Management EBM. An outlook on development work
currently carried out on this field completes this overview on
BMW's wheel slip control systems