26-06-2012, 05:29 PM
Adaptive Cruise Control System Overview
[attachment=25663]
Introduction
Adaptive Cruise Control (ACC) is an automotive feature that allows a vehicle's cruise control
system to adapt the vehicle's speed to the traffic environment. A radar system attached to the
front of the vehicle is used to detect whether slower moving vehicles are in the ACC vehicle's
path. If a slower moving vehicle is detected, the ACC system will slow the vehicle down and
control the clearance, or time gap, between the ACC vehicle and the forward vehicle. If the
system detects that the forward vehicle is no longer in the ACC vehicle's path, the ACC system
will accelerate the vehicle back to its set cruise control speed. This operation allows the ACC
vehicle to autonomously slow down and speed up with traffic without intervention from the
driver. The method by which the ACC vehicle's speed is controlled is via engine throttle control
and limited brake operation.
Definitions
Adaptive Cruise Control (ACC) – An enhancement to a conventional cruise control system
which allows the ACC vehicle to follow a forward vehicle at an appropriate distance.
ACC vehicle – the subject vehicle equipped with the ACC system.
active brake control – a function which causes application of the brakes without driver
application of the brake pedal.
clearance – distance from the forward vehicle's trailing surface to the ACC vehicle's leading
surface.
forward vehicle – any one of the vehicles in front of and moving in the same direction and
traveling on the same roadway as the ACC vehicle.
set speed – the desired cruise control travel speed set by the driver and is the maximum
desired speed of the vehicle while under ACC control.
Physical Layout
As shown in Figure 3, the ACC system consists of a series of interconnecting components and
systems. The method of communication between the different modules is via a serial
communication network known as the Controller Area Network (CAN).
ACC Module – The primary function of the ACC module is to process the radar information and
determine if a forward vehicle is present. When the ACC system is in 'time gap control', it sends
information to the Engine Control and Brake Control modules to control the clearance between
the ACC Vehicle and the Target Vehicle.
Engine Control Module – The primary function of the Engine Control Module is to receive
information from the ACC module and Instrument Cluster and control the vehicle's speed based
on this information. The Engine Control Module controls vehicle speed by controlling the
engine's throttle.
Brake Control Module – The primary function of the Brake Control Module is to determine
vehicle speed via each wheel and to decelerate the vehicle by applying the brakes when
requested by the ACC Module. The braking system is hydraulic with electronic enhancement,
such as an ABS brake system, and is not full authority brake by wire.
Operational Overview
The driver interface for the ACC system is very similar to a conventional cruise control system.
The driver operates the system via a set of switches on the steering wheel. The switches are
the same as for a conventional cruise control system except for the addition of two switches to
control the time gap between the ACC vehicle and the target vehicle. In addition there are a
series of text messages that can be displayed on the instrument cluster to inform the driver of
the state of the ACC system and to provide any necessary warnings. The driver engages the
ACC system by first pressing the ON switch which places the system into the 'ACC standby'
state. The driver then presses the Set switch to enter the 'ACC active' state at which point the
ACC system attempts to control the vehicle to the driver's set speed dependent upon the traffic
environment.
[attachment=25663]
Introduction
Adaptive Cruise Control (ACC) is an automotive feature that allows a vehicle's cruise control
system to adapt the vehicle's speed to the traffic environment. A radar system attached to the
front of the vehicle is used to detect whether slower moving vehicles are in the ACC vehicle's
path. If a slower moving vehicle is detected, the ACC system will slow the vehicle down and
control the clearance, or time gap, between the ACC vehicle and the forward vehicle. If the
system detects that the forward vehicle is no longer in the ACC vehicle's path, the ACC system
will accelerate the vehicle back to its set cruise control speed. This operation allows the ACC
vehicle to autonomously slow down and speed up with traffic without intervention from the
driver. The method by which the ACC vehicle's speed is controlled is via engine throttle control
and limited brake operation.
Definitions
Adaptive Cruise Control (ACC) – An enhancement to a conventional cruise control system
which allows the ACC vehicle to follow a forward vehicle at an appropriate distance.
ACC vehicle – the subject vehicle equipped with the ACC system.
active brake control – a function which causes application of the brakes without driver
application of the brake pedal.
clearance – distance from the forward vehicle's trailing surface to the ACC vehicle's leading
surface.
forward vehicle – any one of the vehicles in front of and moving in the same direction and
traveling on the same roadway as the ACC vehicle.
set speed – the desired cruise control travel speed set by the driver and is the maximum
desired speed of the vehicle while under ACC control.
Physical Layout
As shown in Figure 3, the ACC system consists of a series of interconnecting components and
systems. The method of communication between the different modules is via a serial
communication network known as the Controller Area Network (CAN).
ACC Module – The primary function of the ACC module is to process the radar information and
determine if a forward vehicle is present. When the ACC system is in 'time gap control', it sends
information to the Engine Control and Brake Control modules to control the clearance between
the ACC Vehicle and the Target Vehicle.
Engine Control Module – The primary function of the Engine Control Module is to receive
information from the ACC module and Instrument Cluster and control the vehicle's speed based
on this information. The Engine Control Module controls vehicle speed by controlling the
engine's throttle.
Brake Control Module – The primary function of the Brake Control Module is to determine
vehicle speed via each wheel and to decelerate the vehicle by applying the brakes when
requested by the ACC Module. The braking system is hydraulic with electronic enhancement,
such as an ABS brake system, and is not full authority brake by wire.
Operational Overview
The driver interface for the ACC system is very similar to a conventional cruise control system.
The driver operates the system via a set of switches on the steering wheel. The switches are
the same as for a conventional cruise control system except for the addition of two switches to
control the time gap between the ACC vehicle and the target vehicle. In addition there are a
series of text messages that can be displayed on the instrument cluster to inform the driver of
the state of the ACC system and to provide any necessary warnings. The driver engages the
ACC system by first pressing the ON switch which places the system into the 'ACC standby'
state. The driver then presses the Set switch to enter the 'ACC active' state at which point the
ACC system attempts to control the vehicle to the driver's set speed dependent upon the traffic
environment.