29-05-2012, 04:35 PM
Evolution of Electronic Control Systems for Improving the Vehicle Dynamic Behavior
[attachment=23396]
INTRODUCTION
The loss of yaw response of the vehicle to
steering inputs during full braking while the wheels
are locked has lead to very early investigations (in
the beginning of the 20th century) to prevent wheel
lock. ABS, which can prevent this can preserve a
high level of handling performance during full
braking [1]. Similarly, if the driven wheels spin due
to excess engine torque handling becomes difficult,
particularly if the driven and steered wheels are
identical. This has lead then to the introduction of
traction control systems which preserve also a high
level of handling performance during driving with
excess engine torque. Since neither the steering
angle nor the yaw moment on the car were available,
even a feed forward handling control by control
of the brake and engine was not possible. With
the introduction of ESP these important quantities
became available.
ANTILOCK BRAKE SYSTEM
Locked wheels generate forces on the car which
are in a direction opposite to the lineal wheel motion.
Changing the steering angle has virtually no
effect on the force vectors on the wheels. If the
brake pressure induced by the driver is such that
the wheels lock, then the brake pressure must be
reduced to regain steerability.
For this task ABS uses a hydraulic unit which
has electromagnetic valves to keep the pressure in
the wheel brakes below the level induced by the
driver
The main task of the control algorithm is to keep
a high level of braking force while at the same time
keeping a sufficient level of lateral force generation
by steering to preserve a high level of handling
performance.
TRACTION CONTROL SYSTEM
As a first approach to control the driving forces
on the driven wheels one may try to control the tire
slip to the value λk of the µ-slip curve (Fig. 5) by
the same concept chosen for ABS. This however
fails, since not only the rotating inertia of the driven
wheels is too large for a significant change in the
wheel acceleration (because of the engaged engine
and transmission) but also the engine torque
is nonlinearly dependent on the engine speed, and
thus also on the wheel speed.
ELECTRONIC STABILITY PROGRAM
Feedback control of the vehicle motion is possible
by extending the traction control system with
four additional sensors: steering wheel angle,
brake pressure, yaw rate and lateral acceleration.
Since the nominal trajectory desired by the driver
is unknown, the driver’s inputs are taken to obtain
nominal state variables that describe the intended
vehicle motion instead. These inputs are the
steering wheel angle, the engine drive torque as
derived from the accelerator pedal position and the
brake pressure.
ELECTROHYDRAULIC BRAKE SYSTEM
The Electro Hydraulic Brake System (EHB, also
called SBC: Sensotronic Brake Control) is a brake
by wire system, where the brake pressure in the
wheel brakes are controlled in accordance with the
brake master cylinder pressure using proportional
valves.
[attachment=23396]
INTRODUCTION
The loss of yaw response of the vehicle to
steering inputs during full braking while the wheels
are locked has lead to very early investigations (in
the beginning of the 20th century) to prevent wheel
lock. ABS, which can prevent this can preserve a
high level of handling performance during full
braking [1]. Similarly, if the driven wheels spin due
to excess engine torque handling becomes difficult,
particularly if the driven and steered wheels are
identical. This has lead then to the introduction of
traction control systems which preserve also a high
level of handling performance during driving with
excess engine torque. Since neither the steering
angle nor the yaw moment on the car were available,
even a feed forward handling control by control
of the brake and engine was not possible. With
the introduction of ESP these important quantities
became available.
ANTILOCK BRAKE SYSTEM
Locked wheels generate forces on the car which
are in a direction opposite to the lineal wheel motion.
Changing the steering angle has virtually no
effect on the force vectors on the wheels. If the
brake pressure induced by the driver is such that
the wheels lock, then the brake pressure must be
reduced to regain steerability.
For this task ABS uses a hydraulic unit which
has electromagnetic valves to keep the pressure in
the wheel brakes below the level induced by the
driver
The main task of the control algorithm is to keep
a high level of braking force while at the same time
keeping a sufficient level of lateral force generation
by steering to preserve a high level of handling
performance.
TRACTION CONTROL SYSTEM
As a first approach to control the driving forces
on the driven wheels one may try to control the tire
slip to the value λk of the µ-slip curve (Fig. 5) by
the same concept chosen for ABS. This however
fails, since not only the rotating inertia of the driven
wheels is too large for a significant change in the
wheel acceleration (because of the engaged engine
and transmission) but also the engine torque
is nonlinearly dependent on the engine speed, and
thus also on the wheel speed.
ELECTRONIC STABILITY PROGRAM
Feedback control of the vehicle motion is possible
by extending the traction control system with
four additional sensors: steering wheel angle,
brake pressure, yaw rate and lateral acceleration.
Since the nominal trajectory desired by the driver
is unknown, the driver’s inputs are taken to obtain
nominal state variables that describe the intended
vehicle motion instead. These inputs are the
steering wheel angle, the engine drive torque as
derived from the accelerator pedal position and the
brake pressure.
ELECTROHYDRAULIC BRAKE SYSTEM
The Electro Hydraulic Brake System (EHB, also
called SBC: Sensotronic Brake Control) is a brake
by wire system, where the brake pressure in the
wheel brakes are controlled in accordance with the
brake master cylinder pressure using proportional
valves.