Cooling System Architecture Design for FCS Hybrid Electric Vehicle Sungjin Park, Dohoy Jung, Zoran Filipi, and Dennis Assanis Thrust Area 4 University of Michigan The University of Michigan

Outline Motivation and Challenges Objectives Cooling System Architecture Design Cooling System Component Sizing Results and Discussion Summary and Future Plan

Motivation and Challenges Sprocket Motors Generator Power Bus/ Controller Engine Battery + - Cooling system is critical issue for combat vehicle’s survivability Series Hybrid Electric Vehicle for FCS. Additional powertrain components for SHEV Additional heat sources need additional cooling circuit, pump, fan , sensors, and controllers Complicated cooling system architecture in SHEV due to the additional heat sources with various requirements and various vehicle driving modes Component Heat generation (kW)* Control Target T (oC) Operation Group Engine 187 120 A Motor 27 95 B Generator 62 Charge air cooler 8 - Oil cooler 130 Power bus 70 C Battery 12 45 D

Objectives Develop a guideline/methodology for an efficient cooling system architecture selection for FCS SHEV using modeling and simulation capability Criteria for cooling system architecture design selection: Cooling requirements Parasitic power consumption Thermal shock (temperature fluctuation) Packaging

Cooling System Architecture Development Architecture A - Separate cooling circuit is added for electric components.

Cooling System Architecture Development Architecture A Architecture B Control Target Temp. of Heat Sources Component Control target temp. (oC) Engine 120 Oil cooler 130 Charge air cooler - Motor 95 Generator Power bus 70 Battery 45 - Cooling circuit for electric components is further divided into two circuits based on control target temperatures.

Cooling System Architecture Development Architecture C Operation Group of Heat Sources Component Operation group Engine A Generator Charge air cooler Oil cooler Motor B Power bus C Battery D Cooling Module 1 Cooling Module 2 - The heat source components are allocated into two cooling modules based on the operating groups to minimize redundant operation of the cooling fan.

Vehicle Cooling System Simulation (VECSS) Component Models Radiator1 Coolant pump Engine Thermostat Radiator2 Fan & cooling air Charge Air Cooler A/C Condenser Oil Cooler Power Bus Motor Generator Component Approach Heat Exchanger Thermal resistance concept 2-D FDM Pump Performance data-based model Cooling fan Thermostat Modeled by three-way valve Engine Map-based performance model Engine block Lumped thermal mass model Generator Power bus Motor Oil cooler Heat exchanger model (NTU method) Turbocharger Condenser Heat addition model Charge air cooler

SHEV Configuration (VESIM) Vehicle Specification I C M Sprocket Motors Generator Power Bus/ Controller Engine Battery + - Engine 400 HP (298 kW) Motor 2 x 200 HP (149 kW) Generator Battery (lead-acid) 18Ah / 120 modules Vehicle 20,000 kg (44,090 lbs) Maximum speed 55 mph (90 kmph) Engine Generator Vehicle Motor Battery Controller Power Bus Framework from the ARC Case Study: Integrated hybrid vehicle simulation (SAE 2001-01-2793)

Sequential SHEV-Cooling System Simulation Operation history of each HEV component from VESIM is fed into Cooling system Model as input. Better computational efficiency compared to co-simulation Driving schedule Hybrid Vehicle Model Cooling System Model

Component Sizing Step 1 : Initial Scaling Radiator and pump are the main component that determines cooling capacity Initially, the sizes of radiator and pump are estimated by scaling from well established cooling system Component Heat generation (kW)* Temp. difference (T-Tamb) Engine 187 71.2 Motor 27 46.2 Generator 62 Charge air cooler 8 41.2 Oil cooler 81.2 Power bus 21.2 * Grade load condition at 48.8C ambient temperature Heat rejection at radiator: Therefore, Scaling Factor (a) Hybrid vehicle cooling system criteria for initial scaling 11

Component Sizing Step 2 : Radiator Packaging Radiator occupies largest area The radiator size is limited by the physical dimensions of the vehicle( 20ton 0ff-road tracked vehicle ~ light tank) Packaging constraint is determined by considering vehicle size and radiator size of compatible vehicle (radiators are confined in 1.2x0.75 rectangle) The heights of all radiators are fixed at 0.75m for the convenience of radiator assembly

Component Sizing Step 2 : Radiator Thickness Radiator thickness is another design factor Optimal radiator thickness found by cooling power vs heat transfer test Radiator thickness is designed not to exceed 100mm Radiator Test Device Radiator

Component Sizing Step 3 : Pump Scaling If radiator size is changed by the packaging constraint, cooling pump size should be rescaled First estimation don’t guarantee the cooling performance for vehicle cooling requirement Component Heat generation (kW)* Temp. difference (T-Tamb) q / DT Engine 187 71.2 2.62 Motor 27 46.2 0.58 Generator 62 1.34 Charge air cooler 8 41.2 0.19 Oil cooler 81.2 0.33 Power bus 21.2 1.27 * Grade load condition at 48.8C ambient temperature Heat rejection at radiator: Therefore, or Pump scaling: Hybrid vehicle cooling system criteria for pump scaling

Component Sizing Step 4 : Severe Condition Simulation Three driving conditions were simulated to size the components of cooling system and to evaluate cooling system design performance Ambient Temperature : 48.8 oC (120F) Grade Load (30mi/h, 7%) Maximum Speed (Governed) Grade Load (20mi/h, 12%)

Component Sizing Step 4 : Severe Condition Simulation Detailed design is conducted by trial and error test under severe condition (20mph, 12% grade) Higher coolant temperature close to control target temperature of component is recommended to reduce the radiator size Temperature distribution in components / Coolant temperature change in cooling circuit 1 2 1 2

Driving Schedule for the Evaluation of Cooling System Cooling system architectures are evaluated for representative mission. Heavy duty urban cycle + Cross country driving schedule

Cooling Performance during Driving Schedule Generator Motor Power Bus . Electric Component Temperature

Cooling System Power Consumptions A B C 58% 66% 70% 42% 33% 30% Improvement of Power Consumption by Cooling System Redesign

Summary SHEV model was configured with the previously developed VESIM and cooling system model for the SHEV was developed. The results show that the cooling system architecture of the SHEV should be developed considering various cooling requirements of powertrain components, power management strategy, performance, and parasitic power consumption. It is also demonstrated that a numerical model of the SHEV cooling system is an efficient tool to assess design concepts and architectures of the system during the early stage of system development

Future Plan Co-simulation to study the effect of cooling system on the fuel economy of SHEVs and the interaction between the vehicle and cooling system.

Automotive Research Center (ARC) General Dynamics, Land Systems (GDLS) Acknowledgement Automotive Research Center (ARC) General Dynamics, Land Systems (GDLS) I’d like to thanks to automotive research center and general dynamics land system for their support for this study.

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