Truck Modeling for Longitudinal Control

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Truck Modeling for Longitudinal Control

• Xiao-Yun Lu J. Karl Hedrick
• Dan Empey, Project manager
• PATH, U. C. Berkeley

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• Characteristics of HDT Modeling for Longitudinal
  Control
• Vehicle Longitudinal Dynamics
• Engine Modeling
• Braking System
• Prominent Disturbances
• Implementation Experimental work
• Concluding Remarks

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Characteristics of HDT Modeling for Longitudinal
Control

• Complicatedness of overall system
• Mass dominant ?Road grade sensitive
• Low power/mass ratio ? actuator saturation ? lost
  controllability
• Large actuator delays ? to cause problems in
  driving stability and string stability
• Prominent external disturbances ? significant
  effect on string stability and robust performance
• Platooning requires high control performance ?
  requiring an exact model
• Simple enough for control design
• Complicated enough to capture vehicle intrinsic
  dynamics for large speed/acc ranges

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Vehicle Longitudinal Dynamics
Overall Longitudinal Dynamics power flow from
the engine to driving wheels
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(No Transcript)
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Overall Longitudinal Dynamics
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Overall Longitudinal Dynamics Engine Driving Mode
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Overall Longitudinal Dynamics Other Modes
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Engine

• Engine modeling for longitudinal control is
  different from the modeling for engine control
  itself. The former emphasizes on engine
  performance
• Turbocharger dynamics is separated from the
  engine dynamics under the assumption that the
  booster pressure (manifold pressure between
  turbocharger and the cylinders) is measured
• A static nonlinear engine mapping which gives a
  functional relation between engine speed, booster
  pressure, fuel rate and indicated torque is to be
  established
• Throttle control The built-in engine speed and
  torque PI control is used in the loop as the
  lower level actuator

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Internal Control
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Engine Mapping
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Braking System

• Pneumatic brake model
• Transmission retarder model
• A unified model for engine braking effect and
  Jake brake
• To build a coordinated/combined braking system
  which uses
• Jake (compression) brake
• Pneumatic brake
• Transmission retarder
• Distribution of braking torque among the three
• To be used in proper time for proper maneuvers

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Braking System - Pneumatic brake

• Large and continuous braking torque
• Slow response (time delay 600800ms )
• Braking torque applied to each wheel directly
• With and without EBS
• For modeling, two delays are involved pure time
  delays from actuation and release and pneumatic
  dynamic delay which is modeled as a time
  parameter. A variable structure second order
  brake model is established to count for the
  difference between activation and release delays

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Braking System - Pneumatic brake
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Braking System - Pneumatic brake
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Braking System - Pneumatic brake with EBS/ABS
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Braking System - Transmission Retarder

• Providing continuous and limited braking torque
• Slow response (time delay 1 s )
• Braking force go through drive-line and final
  gear to driving wheels only
• Braking torque depending on drive-line speed

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Braking System Jake Brake

• Providing discrete and limited braking torque for
  fixed engine speed
• Braking torque on driving wheels only, through
  tq-converter, transmission and drive-line
• Fast response (time delay 20ms )
• Braking torque depending on engine speed
• Working only for engine speed gt 800rpm

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Prominent Disturbances
Gear shifting The most prominent disturbance to
string stability Power Consumption of Accessories
Fan 42hp Generator 2.2hp Water pump
2.6hp Air Compressor 2.6hp Air Conditioner
5.2hp Road grade Mass dominant ? sensitive
due to the term
M g sin(q)
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Implementation Experimental Work

• Test bed Old Freightliner
• total weight (tractor trailer load)
  18200kg 40084 lb
• Jake brake air brake, no transmission retarder
• A virtual front vehicle is assumed
• Total test track length 2100m
• Msaximum peed tested 60 mph
• Thanks for the support from
• Paul Kretz
• David Nelson
• Scott Johnston

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45 mph
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45 mph
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50 mph
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50 mph
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55 mph
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55 mph
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60 mph
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60 mph
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Concluding Remarks

• A complicated vehicle longitudinal model is
  adopted
• Engine dynamics is separated from vehicle
  dynamics
• Engine braking effect is unified with Jake brake
  as a special case
• Braking system is composed of Jake Brake,
  Pneumatic Brake and Transmission Retarder WABCO
  EBS/ABS system for pneumatic brake will be in the
  loop for new trucks
• Model for disturbances are to be established
  Road grade needs precise estimation (road view or
  on-line estimation)
• Preliminary test results at CRO
• To improve braking system performance by using
  new WABCO EBS and transmission retarder
• More challenging tasks ahead for 2003 Demo
• Grading up and down slopes
• String stability for three trucks with different
  loads
• Merging maneuver for three trucks