Hybrid Technology

Optimization of Hybrid Concepts through Simulation

FEV's simulation models of various hybrid powertrain configurations provide a detailed analysis of the interaction between powertrain components and improve the understanding of engine and component characteristics.

Simulation Work

• All relevant software codes available (Matlab-Simulink, GT-Drive)
• Models available for
  • Parallel, series, and power-split
  • Hybrid-relevant components
  • Hybrid operation strategies
• Flexible boundary conditions (e.g. vehicle class, market segment, ICE type, hybrid concept and driving profile)
• Correlation with vehicle measurements
• Correlation with benchmark data (FEV database)

Combustion Engines in Hybrid Drivetrains

The various hybrid powertrain structures use different strategies to optimize powertrain behavior. Therefore, the demands placed on the internal combustion engine differ, depending on the type of hybrid system that is selected. For example, in vehicles that use a parallel hybrid layout, the engine should be optimized for a large part of its operating area to exploit the full potential of the hybrid technology. Vehicles that utilize power-split hybrid designs should have the engine optimized for a specific operating curve.

Diesel Hybrid

• Diesel hybrid engines usually operate within map areas with low BSFC and low exhaust emissions.
• The overall optimization of diesel hybrid powertrains is strongly dependent on the exhaust gas aftertreatment concept that is selected.
• A well-tuned compromise between fuel consumption and NOx emissions must be found.

Gasoline Hybrid

• Simplification of the combustion engine (e.g. Miller/Atkinson cycle)
• Hybrids offer opportunity for downsizing without the drawbacks of insufficient low-end torque because electric machines are capable of providing high peak torque at low speeds.
• Combining hybrid with lean-burn combustion technology can also be advantageous.

FEV's experience enables the following hybrid concept development:

• Evaluation of IC engine configurations such as naturally aspirated turbocharged and spark ignition diesel versus hybrid powertrain concepts such as parallel, series and power-split
• Monodirectional optimization for fuel economy or multidimensional optimization for areas such as FE, emissions and NVH
• Realization of prototype and production powertrains

Hybrid Transmission Concepts

 Optimum hybrid transmission concepts can be determined during the concept phase, with state-of-the-art CAE technologies. Optimum total system layout can also be achieved applying these technologies.

Development of the concept, building of prototypes and production development continues up to Start Of Production (SOP).

3 Examples of Transmission Concepts can be described as follows:

Hybrid AT Concept (SUV)

• Carry over 6-speed auto. transmission
• Replace conventional converter by electric converters
•  Full hybrid functionality:
  • Performance improved by 30%
  • Fuel economy improved by 20%
  • Premium NVH
  • Same package as base transmission
  • Modular low cost system

Hybrid Belt-CVT/DCT

• Carry over base transmission
• Additional gearset, E-Motor and clutches
• Simplify base transmissions, such as the DNR set
• Full hybrid functionality:
  • Excellent performance
  • Excellent shift quality
  • Increased packaging
  • Modular low cost system

Multi-Shaft E-CVT Transmissions
(Midsize Vehicle)

• Reducing transmission complexity at the cost of required electric motor power
• System strongly dependent on vehicle type
• Full hybrid functionality:
  • Performance improved up to 25%
  • Fuel economy improved up to 25%
  • Premium NVH
  • Tiptronic functionality possible
  • High-volume applications

Transmission Support

• Layout of transmission ratios
• NVH refinement of internal and external excitations as well as structural dynamics
• Hydraulic system layout of components such as clutches and the electric oil pump
• Mode changes and clutch shifts in combination with electric motors
• Software development for shift sequencing
• Parameter excitation of gears (whining)

Hybrid Powertrain Mechanics

FEV offers a development solution which stretches from the design concept phase to SOP. During all development stages, FEV utilizes state-of-the-art CAE tools to calculate and optimize the durability and NVH of hybrid powertrain components. FEV, in partial cooperation with its partners, provides extensive testing of prototype powertrains for function, durability, NVH and benchmarking.

Mechanical Testing

• Temperatures (thermocouples, infra-red)
• Deformation and transmitted forces / torques (strain gauges and telemetry)
• Movement and gear wobbling (Eddy-current)
• Rotation, rotation speed and rotational irregularities
• E-motor/-generator measurements (torque, efficiency and power consumption)

CAE Support

• Planetary gear layout (profile and micro geometry)
• In-depth tolerance analysis
• Durability calculation of gears (planetary gear set)
• NVH calculation and optimization
• Durability calculation for shafts, housing and bearings
• Optimization loops, such as topology opt.
• Model validation using test results
• Parameter excitation of gears (whining)

Benchmarking

• Benchmarking of hybrid powertrain systems including comparisons to conventional powertrains, if requested
• Reporting using FEV's well-known scatter bands

High-Voltage Systems, Wiring Harness and Safety

Increasing electrical power in vehicles introduced powerful high-voltage systems consisting of high-voltage components, related wiring harnesses and dedicated safety concepts.

FEV turns your plans of successfully integrating high-voltage systems into reality.

Engineering Services

• Design of high-voltage power supply systems
• Simulation of energy distribution in the vehicle
• Interfacing with inverter units
• Interfacing with battery management units
• Interfacing with DC/DC converters
• Layout of wiring harnesses
• Integration of relays and fuses
• Layout of safety system measures such as:
  • Pole switches
  • Mechanical master switch
  • Contacted connectors
  • Component housing contacts
  • Shielded/high-voltage cables
  • Grounding concept
  • Insulation specifications

The introduction of high voltage systems must take into account:

• Legislative requirements with respect to EMC/EMI and safety such as EN 61508
• Specifications (ISO, DIN, SAE and GB)
• Special technical problems like "arcing"

Hybrid Control Unit and HiL Testing

Control of components must be optimized to achieve the full benefits of hybridization. The control structure is dependent on the existing topology. The Hybrid Control Unit (HCU) can be separate or can be integrated into existing control units like the Transmission Control Unit (TCU) or the Engine Control Unit (ECU).

Engineering Services

• Controller topology specification (master/slave)
• Hybrid control unit hardware specification
• Hybrid control unit I/O
• Interface protocols
• System diagnosis
• Fail-safe concept
• EOL testing

Hardware in the Loop (HiL) Testing

• Controller topology specification (master/slave)
• Hybrid control unit hardware test
• Hybrid control unit interactions
• Hybrid function frame verification
• Automated testing for 24/7 operation

HCU Software Development

• Rapid prototyping
• Auto-code generation
• Torque arbitration
• Hybrid specific (start/stop, boost, brake energy recovery, SOC management and power split operating modes)
• Transmission functions development driving strategy and gear selection)
• Safety functions

Batteries
One of the key components of the electric hybrid system is the battery. Besides the mature lead acid technology for low power applications, the de facto standard for passenger cars in today's production applications is the NiMH technology. Since the lifetime of these batteries is closely related to the State of Charge (SOC) strategy, overall optimization is mandatory.

New emerging technologies, like Li-Ion, are expected to improve system capabilities within the next few years.

Electrochemical Impedance Spectroscopy (EIS)

• Measurement of the complex impedance
• Galvanostatic measurement
• Frequency range: 10 kHz - 1µHz
• High precision, even for the lowest frequencies and long time stability

Cooling System Layout

FEV has developed a 1D calculation approach to determine a favorable layout of the cooling system and to define system component requirements. This tool allows vehicle simulation in any driving cycle. The tool also allows the calculation of coolant temperatures and flow rates within the cooling systems of the electronics and in the engine, which is dependent on the actual operating status of the vehicle.

Engineering Services

• Pre-design: Definition of the system topography
• Detailing: Definition of required component characteristics
• Basic system calculation and assessment
• System control strategy optimization
• Optimized system:
  • Lowest electrical power demand
• Future development:
  • Fuel consumption reduction and vehicle climate testing

The model includes:

• Combustion engine cooling system
• Engine internal friction losses
• Combustion engine thermal behavior
• Transmission ratio and efficiencies
• Engine independant heater applications including power demand
• Parasitic losses (such as fan and generator)
• Electric drive system including battery SOC
• Heat rejection from the electronic components
• Vehicle driving cycle
• Ambient conditions
• Vehicle interior heating performance

Hybrid Powertrain Design and Integration

FEV offers full design support in hybrid powertrain development from concept to start- of-production. A common design process has been established. The process is characterized by a clear structure that is derived from the well-known Design for Six Sigma methodology.

The motivated design team is highly experienced and fully integrated into the overall development process.

The primary design tasks for developing a hybrid powertrain are the packaging of the various subsystems and the layout and detail design of the hybrid transmission, which is the heart of hybrid powertrain system. FEV also provides the complete production design documentation and engineering support to the component and system suppliers.

Design Services

• Design of power train components
  • Concept development and layout
  • Base engine and accessory adaptation
  • Transmission
  • Transfer case
  • Driveshaft
• Vehicle integration
  • Packaging of powertrain components
  • Packaging of electrical components
  • Packaging of control system
  • High-voltage cable routing
  • Body modification for prototypes
  • Prototype procurement and build
  • Production design documentation

Hybrid Powertrain Calibration

Control unit architecture and functions of a hybrid electric vehicle are highly complex and thus a challenge for calibration. Advanced tools and strategies are required for system optimization:

Engineering Services

• Rapid prototyping, HiL and SiL for function development of hybrid controller
• Offline and online tools for automatic calibration vehicle functions
• Hybrid measurement techniques, including electric machine power, out-of-phase currents and transmission shaft torque with infrared telemetry systems

Calibration focuses on electric boost and generation with an optimum state-of-charge, start/stop and gear selection.

Objective determination of shift and overall transmission quality using tools such as:

• FEVos processing vehicle compartment acceleration sensor data
• FEV Shift Analyser

Hybrid Vehicle NVH, Balancing of HEV Operational Modes

In general, hybrid vehicles can possess a favorable NVH behavior, especially during start and low speed cruising. Nevertheless, detailed NVH refinement of HEV specific electric components, powertrain mounting system and driveline are required to achieve excellent NVH behavior.

The main NVH challenge consists in adjusting the NVH response to the driving condition and the driver's expectation. Consequently, the NVH development focuses on the balancing of HEV operational modes.

By using FEV-Hybrid-VINS software, vehicle operational modes can be balanced with regard to vehicle interior noise based on HEV operational mode strategy, e.g. the relation of vehicle velocity, ICE speed and speed gradient as well as load condition.

Hybrid Vehicle Specific NVH
Development Tasks:

• Smooth internal combustion engine launch at start and during drive-away A
• Moderate ICE start/stop feedback at vehicle stop B
• Unobtrusive ICE deactivation/activation during cruising/acceleration C
• Powerful, i.e. acoustically supported, dynamic acceleration feedback D
• Unobtrusive NVH behaviour of electrical components, e.g. magnetic noise during recuperation at low vehicle speedsE

Hybrid Vehicle Benchmarking

Detailed benchmarking analysis of competitor and prototype systems becomes increasingly crucial as new technologies contribute to greater powertrain complexity. The analysis promotes the development of best-in-class products through a systematic assessment and characterization of competitive products. It also significantly reduces the product development time.

Benchmark Activities
FEV's established vehicle and powertrain benchmarking program was applied for the specific demands of hybrid vehicles:

• On-road vehicle tests
• Roller dynamometer tests
• Powertrain measurements
• Test bench investigations
  • Motor/generator
  • IC engine
• Acoustic assessment
• Friction analysis
• Design evaluation
• Battery testing
• Supportive simulation

The analysis and evaluation process of our customers can be supported, based on scatter band analysis with various levels of detail.

FEV offers tailored benchmarking projects for all classes of hybrid vehicles including Start/Stop systems (14V), Micro (42V) and Mild Hybrid approaches (144V) as well as Full Hybrid Vehicles (>200V).
Market trends are then analyzed based on this data.

Cost/Benefit Considerations of Hybrid Systems

The chart compares different hybrid systems. In general, start/stop functions can be provided with today's vehicle net voltage level, significant electric power assist, however, will require future systems with 42 or even higher voltage levels. While lead / acid based batteries might still be used for 14 V ISG functions, Nickel/Metal-Hydrid (NiMH) batteries will be necessary in ISG's with power assist functions, due to their much higher cycle life expectations.

In general, the introduction of hybrid systems will depend on the one side to a large extend on the progress in the development of new batteries which can tolerate frequent and fast load changes. New electrolytic double layer capacitors or supercapacitors promise to deliver an extremely high power density with almost unlimited cycle life. A major drawback is their poor energy density when compared to electrochemical batteries. For this reason, supercapacitors are expected to become key elements first of all for power assist concepts, where short term support is delivered by the electrical assist avoiding the burden of heavy batteries.

On the other side, the additional production costs of the electrical components will strongly dictate the market introduction time schedule of hybrids together with the availability of 42 V net technology in cars.

 

FEV Electric Hybrid Vehicles

Mature simulation methods and virtual system synthesis allow for the optimization of designs that are close to final production. Verification of project targets require a demonstration vehicle to provide a final proof of the results.

FEV has built several demonstration vehicles, such as a conversion of a base vehicle to a hybrid demonstrator vehicle. The logistics and organization of prototype / pre-pilot production vehicles is also a part of FEV's portfolio.

Engineering Services Offered for Hybrid Vehicles:

• Hybrid system integration of all hybrid concepts, such as parallel, input and compound split
• Hybrid vehicle equipment adaptation for A/C, electrical steering and brake systems
• Safety concept implementation
• Start / Stop operation
• Drivetrain calibration for driveability, fuel economy, emissions
• NVH Optimization

FEV Hydraulic Hybrid Vehicles

FEV possesses a broad range of experience in the design and development of hydraulic hybrid powertrains and vehicle integration. This experience includes clean sheet design and fabrication of hydraulic systems, pumps, motors, and integrated drive units for complete turnkey vehicles, utilizing either parallel or series technology.

Among the advantages of hydraulic hybrids, compared to other technologies, is the very high kinetic energy obtained from braking recovery. The high regenerative efficiency, more than doubles that of other hybrid technologies, translates into significant fuel economy improvements.

• Advantages
  • High power density- improved acceleration
  • High kinetic energy braking recovery (regeneration)
  • Known technologies
  • Significant fuel economy improvement
• Challenges
  • Weight
  • Cost
  • Packaging/NVH of passenger vehicle applications

Industrialization of HEV production development projects
Project Management
In addition to a high level of technical skills, significant management skills are required to make the development of a production hybrid vehicle program a success. FEV has a broad range of experience in managing complex projects from concept phase up to the start of production and beyond. This includes the key area of managing the "Launch-Phase", which includes pilot, pre-production, SOP and ramp-up.

Key FEV Competences

• Overall project management
• Detailed vehicle, subsystem and component technical specifications
• Support of supplier selection
  
• Handling and management of suppliers and engineering partners
• Prototype, tooling and production release of all components
• Launch management including handling of PPAP, quality assurance, logistics and manufacturing engineering
• Support after SOP
• Change management in production and model year programs

Interdisciplinary Skills
The development of a hybrid vehicle encompasses almost all systems and subsystems of the vehicle. In addition to the vehicle's powertrain, areas such as crash testing, Body-in-White, exterior and interior are affected. In order to provide our customers with a turnkey project service, FEV has built up a network of experienced engineering partners and suppliers, which enable us to cover all development aspects on a hybrid vehicle.

Certification and Aftermarket Documentation

Certification
Prior to use on public roads, a vehicle has to undergo the certification process for the respective market. This is especially important for HEVs, because of their additional weight and the potential usage of a high voltage electrical system. Special care must be taken, concerning their certification. Emission and fuel consumption legislation specific to hybrid vehicle applications is extremely important. In addition, changes to the vehicle such as additional battery weight or interior changes due to battery package might deteriorate certification-relevant criteria like the crash test performance and occupant safety. FEV offers certification support to the OEM that includes up to a full responsibility for vehicle certification, including coordination with government authorities for the relevant market requirements. Non-powertrain related subjects can be handled with the assistance of established engineering partners.

Aftermarket Documentation
Hybrid vehicles require detailed documentation for the aftermarket. Documentation is required for the additional safety specifications, training and service information for repair facilities.
The following areas can be part of FEV's scope of work:

• Emergency response guide
• Workshop manuals including diagnostic diagrams
• Support of tester software development for the aftermarket
• Development of training classes for plant and workshop personnel