U.S. ARMY TANK AUTOMOTIVE RESEARCH, DEVELOPMENT AND ENGINEERING CENTER ENERGY ANALYSIS OF A POWERTRAIN AND CHASSIS INTEGRATED SIMULATION ON A MILITARY DUTY CYCLE GT Suite User s Conference: 9 November 2015 Denise M. Rizzo US Army TARDEC, Warren, MI Periannan Kumaran Pratt & Miller Engineering, New Hudson, MI Jonathan Zeman Gamma Technologies, Westmont, IL 1
Current Project Goal: Integrate high fidelity models of powertrain and vehicle dynamics in a co-simulation environment to understand the influence of chassis dynamics on fuel efficiency and energy losses. Background: To date, powertrain and vehicle dynamics models make simplified assumptions about their respective interaction. While this is reasonable under steady state conditions, the transient effects are unknown. Applications: Soft soil mobility, obstacle crossing such as step climb, steering loading under a non-straight maneuver such as on a duty cycle course, and fuel economy computation Potential Benefits: Understanding of interaction between powertrain and chassis Enables chassis-powertrain system design optimization Framework for chassis-powertrain system optimal control design Delivers an integrated chassis-powertrain system toolset for modeling & simulation 2
Vehicle Dynamic Simulation Environment In vehicle dynamics simulations, vehicle models with detailed subsystems such as engine/powertrain along with detailed chassis are rarely developed to study the integrated behavior of the combined full vehicle systems. MSC.Adams is a widely used Multi Body Dynamics Software currently used at TARDEC to model military vehicles and to perform vehicle dynamic simulations. The transmission model currently used in these vehicle models are simplified and lacks details in system dynamic behavior. Typical use of look up tables for torque-speed map Lacks automatic transmission (version 2012) No representation of turbo behavior Compromises the accuracy of transient performance of engine and transmission 4
Chassis Vehicle Dynamics Model High Mobility Multi-Purpose Wheeled Vehicle (HMMWV) used by US Army Fully nonlinear model with rigid bodies and lumped masses Parts are connected through idealized joints and/or force elements Linear springs and nonlinear dampers Pacejka 2002 tire model Adams HMMWV Model Manual transmission 5
Powertrain Simulation Environment GT-SUITE is a multi physics platform currently used to model and study engine/transmissions/vehicle behavior at TARDEC 1-D simulations Has the ability to model transmission with much more detail than what is available in MSC.Adams The full vehicle model available in GT-SUITE is a simplified reduced order model Absence of lateral dynamics Absence of detailed tire models Absence of detailed roads and terrains, which are important for military vehicle development GT Simulation Environment Example 6
Powertrain Dynamics Model Transient map based system Engine characterized by torque output map and fuel map Additional dynamics for turbocharger lag 4 speed automatic transmission with lock-up clutch Gear ratio, mechanical efficiency and friction loss included GT Drive HMMWV Model 7
Co-Simulation Framework Improved hardware and computing power have made this framework a viable solution Ability to integrate high fidelity subsystems with detailed full vehicle models Common methodology in integrated simulations Benefit from the individual strengths of each simulation tool Avoid development of duplicate subsystems and components GT-SUITE Integrated Model 8
Co-simulation Full vehicle chassis dynamic model developed in MSC.Adams/Car Powertrain dynamic subsystem model developed in GT-SUITE Use of Simulink as the coupling environment Both Adams/Car and GT-SUITE are coupled to Simulink through S- function blocks Simulink behaves as the Master of both GT-SUITE and Adams/Car Communication interval = 1.0 ms Subject the integrated vehicle model through various handling maneuvers and terrains of interest 9
Integration Validation: Acceleration Event Perform full load acceleration event to validate the model integration Standalone GT-SUITE Standalone Adams Integrated Model Use GT-SUITE full load acceleration results as the baseline. GT- SUITE is currently used as the simulation tool for automotive performance evaluations Update the following parameters in standalone Adams model to match GT-SUITE point mass model Aggregate mass Unloaded tire radius Tire rolling resistance Aerodynamic drag force Gear ratio and shift RPM 10
Integration Validation: Acceleration Event 11
Integration Validation: Acceleration Event Shift RPM Comparison: Model Comparison RPM limits for the integrated model are same as GT-SUITE standalone Adams/Car standalone model uses single shift RPM for all gears 12
Integration Validation: Conclusions Integrated model speed profile from the co-simulation correlates reasonably well with standalone GT-SUITE model speed profile Top speed difference < 1.0mph Differences between the standalone GT-SUITE simulation and integrated simulation results could be attributed to Tire model differences Aero dynamic model difference More details in the integrated vehicle model compared to standalone GT-SUITE point mass vehicle model Standalone Adams simulation speed saturates early due to engine revolution limit in the powertrain subsystem Integrated model is well suited to perform additional correlation studies 13
Additional Simulations To demonstrate the advantages of the integrated cosimulation environment over the standalone GT-SUITE and Adams dynamic models Events selected Typical military vehicle requirements 18 inch step climb 60% graded road 14
18 inch Step Climb Determines the required torque to climb a step of specified height Performed at WOT Starts from standstill position Not supported in standalone powertrain dynamic model Transfer case at low position for increased torque 15
18 inch Step Climb: Vehicle Speed and Torque Simulation Peak Torque (Normalized) Adams Standalone WOT 1.0 Integrated WOT 0.45 16
18 inch Step Climb: Conclusions Initial speed drop in the standalone Adams model is due to vehicle bouncing off the step before climbing The high torques in standalone Adams model results are due to clutch slippage at low engine RPM Integrated model speed controller takes longer to settle down to target speed. This may indicate a need to tune the controller to better follow the target speed at low speeds The ability to evaluate a step climb transiently in a simulation environment has now been realized with the integrated model The integrated model is more suited to evaluate torque requirements compared to the standalone Adams model for step climb simulations 17
60% Graded Road Determines the ability of the vehicle to climb specified inclination at a constant speed Performed at low speed Starts from a flat road Transfer case at low position for increased torque 18
60% Graded Road: Vehicle Speed 19
60% Graded Road: Left Front Halfshaft Torque 20
60% Graded Road: Conclusions The 60% grade maneuver with vehicle dynamics fully integrated has been shown, however steady state speed control at low speed was elusive and further investigation is required Standalone Adams model shows a speed drop when the vehicle was coming off the graded road. This in turn resulted in clutch slippage as seen in the torque results 21
Fuel Economy and Energy Loss Current fuel economy studies are performed in standalone powertrain environment with the reduced DOF vehicle model Studies are constrained to straight line simulations Appropriate for courses with minimal turns and not much influence from lateral dynamics Cross country and secondary road have very steep elevation changes and sharp turns Need to understand the influence of lateral dynamics on energy loss related to these courses 22
Influence of Lateral Dynamics on Energy Loss Perform a straight line simulation for the length of Churchville profile on a flat road Repeat the simulation with Churchville profile on a flat road. Churchville road is considered a cross country terrain 23
Influence of Lateral Dynamics on Energy Loss Road Profile Fuel Economy (normalized) Straight Line 1.00 Churchville 0.70 Lateral dynamics does have an impact on the fuel economy mainly due to tire/road interaction. Fuel economy for Churchville profile is 30% less than straight line. Vehicle speed has an influence on the fuel economy. Higher speeds resulted in larger difference in fuel economy. 24
Influence of Lateral Dynamics on Energy Loss Noticeable speed drop during turns Increased power requirement to maintain required speed 25
Influence of Lateral Dynamics on Energy Loss Increased longitudinal tire forces resulting from increased lateral tire forces 26
Influence of Lateral dynamics on Energy Loss Tires are subjected to simultaneous lateral and longitudinal slip conditions in a turn Application of lateral slip at a given slip ratio tend to reduce the generated longitudinal forces resulting in reduced speed More power is required bring the vehicle back to target speed Reference : Thomas D. Gillespie Fundamentals of vehicle dynamics, 1992 27
Analysis of Energy Losses Focus energy loss analysis on following areas Engine and Accessories Transmission Driveline Engine and Accessories losses Accessories Alternator and Fan Exhaust Indicates the fuel burned 28
Analysis of Energy Losses Transmission losses: Larger losses in the transmission and torque converter for the Churchville course. Torque converter losses are especially apparent due to the longer time in the inefficient unlocked position. Driveline losses: Brakes are not applied during the event Larger losses are shown in the driveline components for the Churchville course. 29
Road Test Comparison on Churchville-B Simulate the integrated model on actual Churchville-B profile Churchville-B profile contains steep grades Road coordinates were measured by profilometer in order to quantify the road roughness Create MSC.Adams road profile from measured data Model Updates Aerodynamic drag coefficient GVW Unloaded tire radius Tire rolling resistance Power loss Event performed at a constant speed 30
Road Test Comparison on Churchville-B Model Configuration Fuel Economy(mpg) - normalized Road Test 1.00 Simulation 0.99 Fuel economy value compared very well with the road test results Integrated model captured all of the energy losses 31
Summary and Conclusions A transient map based powertrain dynamic model built in GT-SUITE was successfully coupled with a detailed chassis dynamic model in MSC.Adams/Car with MATLAB/Simulink as an intermediate coupler Specific simulations pertaining to military vehicles were performed to confirm that the integrated model will be successful in these simulations A detailed study was performed to understand the influence of lateral dynamics on fuel economy and energy loss A study comparing the fuel economy in integrated vehicle model to road test on Churchville terrain resulted in good correlation providing high confidence in the integrated vehicle model and co-simulation frame work. Simulations such as step climb and soft soil (not presented here) provides an early understanding of power and mobility requirements that was not possible in the past 32
Future Work Use FMI framework or direct GT/Adams co-simulation and eliminate the intermediate Simulink layer Replace the constant speed with limit handling which mimics the real world driving scenario 33
Disclaimer Reference herein to any specific commercial company, product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the Department of the Army (DoA). The opinions of the authors expressed herein do not necessarily state or reflect those of the United States Government or the DoA, and shall not be used for advertising or product endorsement purposes. 34
Churchville-B Animation 35