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FEV's newest member of the PREX transmission family

Full hybrid planetary transmission with on-demand actuation

27. November 2017 | Engineering Service, Featured Article

Full hybrid planetary transmission with on-demand actuation

Today’s state-of-the-art, automated gear set synthesis for planetary structures showed solutions with which big leaps forward in terms of effort vs. degree of functionality in gear set utilization are achieved. Future dedicated hybrid powertrains (DHT) require all hybrid functionalities within a compact gearbox structure. FEV has extended its planetary gear set synthesis by considering two inputs on one planetary gear set, while considering other constraints, such as protection for on-demand, actuation-friendly structures. This design philosophy was further elaborated by FEV´s well-known ePGS structure for efficient launch with a single E-Motor.


By considering total system requirements in the very first phase of gear set synthesis, new planetary structures can be found which can significantly reduce all main energy losses in a modern automatic transmission (clutch losses, actuation losses, creep and launch).
PREX3 is an example of one such solution, setting new benchmarks in terms of both energy consumption and gear set utilization and truly integrating the powertrain electrification with a 48V hybrid or, optionally, an HV hybrid solution in the same transmission.

FEV’s Impressive Track Record

In 2003, FEV presented the world´s first diesel hybrid vehicle. This vehicle already had a highly integrated, oil-cooled E-Machine in the transmission and used ePGS as a launch device. In the next few years, many hybrid programs based on the ePGS-principle followed, and in 2010, FEV presented a seven-speed, planetary hybrid transmission with electromechanical, on-demand actuation. In 2016, the first mass production application using ePGS was launched in the Chery Arrizo7e PHEV vehicle.

Gear Set Synthesis

Analyses of current, state-of-the-art transmissions show that, for over 80%, today’s losses in automatic transmissions come from three sources: hydraulic oil supply, drag torque and energy loss during creeping. For the development of the PREX3 FEV engineers successfully addressed all three items.
Development of the conventional planetary gear set structure was conducted by abstracting the PGS to a lever diagram and combining these levers. This is a largely graphical method, which requires high levels of expertise and abstraction. Good solutions must then be detailed using stick diagrams to show realization friendliness in hardware. Newer methods use CAE programs, which basically scan through the entire theoretical/mathematical solution room, thus analyzing billions of solutions. This requires smart methods of accepting or rejecting solutions, which include the risk that the optimal solution was found mathematically but rejected by the automated analysis. These programs are typically designed for one input and one output.

FEV combined these methods using a graphical screening to narrow down the solution matrix, which was then followed by automated calculation. With the graphical part, further constraints, such as considering two inputs or rejecting structures which are not realization friendly, were also implemented. FEV developed constraints to ensure that the gear set found could be actuated on demand – for example, allowing only one clutch to be nested in-between the planetary gears. This is visible on the stick diagram level, and was converted from the lever diagram level. A first result of this synthesis is FEV PREX 3, which is described in more detail in the following pages.

The PREX3 Gear Set

The latest member in FEV’s hybrid transmission family is the PREX3, the structure of which was specifically optimized for mild hybrid solutions. By using three planetary gears and six shift elements – in total, six forward gears for the combustion engine and three forward/reverse gears for the E-Motor – a mechanical reverse gear and ePGS vehicle launch were realized. By the gear set constraints this system could be further optimized.

Possible Stick diagram PREX 3 base structure

Optimized stick diagram with four friction clutches

In the gear set synthesis phase, constraints were introduced to ensure that only one clutch is located between the planetary gear sets (CL3). This clutch can be actuated through the center of the gear set by a pull actuator. Furthermore, two shift elements are never used at the same time AND have a gear in between them in which they are free (B1 and B2). This allows a reduction in friction elements by replacing the two brakes with one brake, combined with a dual-dog clutch. Furthermore, the shift element B3 is only used in the 1 and R gears. In these gears, only limited coasting capability is required, since a torque converter transmission also never locks up in R and 1st gear coast. Hence, this active element can be replaced with a passive, one-way clutch. In the rare event where coast is required in first or reverse gear it can still be realized using the E-Motor. With an optimized clutch arrangement, the number of friction elements can be further reduced to only four elements , thus setting a new benchmark in planetary gear set structured transmissions. Coast functionality is now limited to E-motor torque, which is more than enough in these low gears.

Sequential and multiple shift possibilities with PREX3 Gear set

Clutch Losses in the PREX3

As indicated earlier, one of the three main energy losses in an automatic transmission are drag losses caused by open shift elements. Here, the non-optimized PREX3 is on par with “normal” planetary structures, which do not allow two power sources. Hybridizing those systems means adding at least one more shift element. With the optimized clutch arrangement as described above, the number of open friction elements is drastically reduced to half, compared to today´s state of the art.

On-Demand Actuation

The second main source of energy losses is hydraulic oil supply for clutch actuation. PREX only has five connections that need to be controlled. Two of those are realized as brakes at the end of the gear set, and can thus be actuated with existing electrohydraulic or electromechanical systems. Two further elements are clutches connecting the input. Here, existing actuation technology can also be used. The only remaining clutch in the gear set is actuated by a pull lever through the center shaft and an actuation piston in the back of the transmission housing. With this architecture, all shift elements can be actuated by a leakage-free, on-demand system. For lube and EM cooling, a small centrifugal pump is used which is driven by a BLDC motor and can also be controlled on demand.

Relative delta speed of open friction per revolution input

ePGS as a Launch Device

The last big energy loss in an automatic transmission is the launch device. In the launch device, energy is dissipated into heat by the clutch or torque converter during creep and launch of the vehicle. Here, PREX3 uses the well-known “FEV ePGS” principle, thus eliminating the energy losses in torque converter or launch clutch. During the first phase of launch, the E-motor is in generator mode, producing electricity instead of dissipating the clutch slip into heat. In the second phase of launch, the generated energy is sent back into the system as a boost, thus maintaining a virtual “torque converter amplification” all the way up to the synchro point, at which the system transitions to conventional parallel mode. With the chosen lever ratio, the energy generated in the first phase of launch is slightly higher than the energy needed to boost in the second phase of launch, thus resulting in a positive charge balance after launching the vehicle.


FEV smart vehicle fleet heading toward SAE level 5 automated driving

Automated driving: FEV brings technology platform on the road

20. October 2017 | Engineering Service

Automated driving: FEV brings technology platform on the road

For OEM, suppliers and developers, automation of vehicles brings with it a wealth of new tasks. At the same time, the classic functions and purchasing criteria fall ever further into the background. As a service provider, FEV supports its clients from the initial concept to start of production in its decision processes associated with these new subjects.
Since 2016, FEV has been bundling all of the steps associated with advanced, fully connected, automated vehicles in its “Smart Vehicle” Center of Excellence. Smart Vehicle includes all sorts of development fields in a rapidly-changing, highly complex environment – from sensor technologies to software algorithms all the way to electrical/electronic architectures and connectivity.
For example, FEV is developing innovative solutions in forward-looking operating strategies, connectivity and cybersecurity in addition to infotainment and driver-vehicle interaction.
The experts have now taken an important demonstration and development vehicle onto the road. Sébastien Christiaens, department manager at FEV, has been keeping track of this project from the Aachen location and he discussed the background with SPECTRUM.

>> Our goal was to develop standardized interfaces and use them to obtain a modular, state-of-the-art development platform

Mr. Christiaens, for a few weeks an automated demonstrator vehicle from FEV has been driving on the roads or on stretches of road for which authorization has been given. What is the background of this demonstration vehicle?

To be accurate, there are three such vehicles driving in the world. The automated smart vehicles are part of an FEV project that we are conducting with our colleagues in the US, Poland, Turkey and our company headquarters in Aachen. Our goal in doing so is to bundle our global expertise and allow others to experience it in a fully automatic development vehicle as a basis for further development, but also for benchmarking. The vehicles show the current status quo that we worked out in recent years in various projects and are now putting together in one vehicle. The smart vehicles thus form the first automatic FEV fleet that we created without any customer orders.

It was possible to take a look at the vehicle driving at this year’s Aachen Colloquium Automobile and Engine Technology. What was to see there?

Right now, the vehicle can safely travel without a driver on a given stretch and the vehicle can suitably react to any events. Thanks to the object recognition implemented, traffic signs are recognized, as are things and people, and appropriate driving maneuvers are started.
At the Aachen Colloquium, we streamed the trip to our exhibition booth. The streaming was done strictly through the vehicle’s network connection. In the process, the vehicle sends data to the cloud. The Aldenhoven Testing Center, where the demonstrator is headed, offers ideal conditions for doing that. At present, an urban testing area is being set up for mobility research. Thanks to the Vodafone-5G Mobility Lab that is also included, this area also has a high-performance network. That is needed to process the large amounts of data.

For example, which sensors are integrated in the vehicle?

We have integrated extensive sensors, including radar, GPS, different types of cameras as well as differential GPS and LIDAR and a vehicle-2-network connection. Thanks to these sensors and interfaces, we are able to perceive the immediate environment of the vehicle as well as to anticipate the oncoming road and traffic conditions on a longer range. Using intentional redundancies in varying technologies, we can thus eliminate the shortcomings of one type of sensor by enriching and comparing the results using those from other systems. This intelligent combination of the different sensor information, referred to as sensor fusion, is a key element in the vehicle environment detection and localization process. Another of our goals was to develop standardized interfaces and use them to obtain a modular, state-of-the-art development platform. Thus, individual sensors can be swapped out with as little effort as possible in later benchmarking activities.


What is the basis for issuing driving commands?

The driving commands themselves are managed using a “decision making algorithm” we developed ourselves. This algorithm has three main parts: perception, planning and decision/action.
This algorithm ensures that the vehicle moves safely. In doing so, we draw amongst other on the expertise of our American colleagues, who already successfully completed automation projects in the past. As a modular development platform, the vehicle is actually equipped with two types of powerful embedded controller hardware. This allows us to test and compare different types of control algorithms, for example a rule based approach and a machine learning/artificial intelligence approach.

If sensors collect environmental data, communication between the vehicle and this environment is surely just an additional logistics step. To what extent have you already planned this aspect?

Communication between the vehicle and its environment is mandatory for automated vehicles. Even today, the vehicles already have a Vehicle-to-Everything („V2X“) connection. The intelligent connection unit – abbreviated as iCU – is based on microservice architecture and processes data and information from all sorts of control units and sensors. The FEV iCU is in a position to process data from vehicle-to-vehicle („V2V“) communication via DSRC. Thanks to the microservice architecture, integration of corresponding 5G standards („C-V2X“) will be possible directly, as soon as they are available. Intermediate data aggregation and data conversion services harmonize the data sets and formats, which often differ a lot from each other.

>> With our Cyber Security Gateway, we offer an important tool to prevent cyber attacks

How are you handling cyber- security when you do this?

Cybersecurity in vehicles is actually one of the greatest challenges. As long as the vehicle lacks a vehicle-2-X connection, the number of ports for attack is still relatively easy to look at. The biggest danger comes from the OBD interface but also from the infotainment system. As soon as the vehicle starts working within a network, the sources of danger grow exponentially. With our Cyber Security Gateway, we offer an important tool to prevent cyberattacks. The cybersecurity gateway is linked with the vehicle’s communications bus in order to detect and prevent malicious attacks. It can also be used as a firewall between external interfaces and the vehicle bus. In addition, FEV works with leading world manufacturers to implement so called Hardware Security Module –HSM- and TPM technologies, known as Trusted Platform Modules, for the automotive industry for secure booting and secure over the air (OTA) software updates to name a few applications.

The cybersecurity gateway is linked with the vehicle’s communications bus in order to detect and prevent malicious attacks. It can also be used as a firewall between external interfaces and the vehicle bus.

What steps are now coming up with the smart vehicle fleet?

As a powerful tool to address important challenges such as integration of new functions, interfaces, and components, these vehicles offer a broad range of possibilities for FEV as well as for our partners and customers.
At first, they have an important role in the development and improvement of our control algorithm as they offer a flexible platform for our engineers to make their innovations in ADAS and automated driving features more tangible. This flexible platform can obviously also be offered to our partners and customers as basis for commonly developed “Proof of Concepts” to demonstrate new technologies or features for example.
As already mentioned above, our automated vehicle fleet is heavily involved in our benchmarking activities. Both for sensor benchmarking as well as for system and overall vehicle benchmarking.
For benchmarking, the most important part is reproducibility of results and test runs, and automation is very important for that. In this case, our smart vehicle is not the technology platform for the test vehicle but is acting as the testing tool. Driving maneuvers of the target vehicle can be automated and done reproducibly and it can be verified that the test object operates reliably.
Finally yet importantly, the vehicles are also supporting the overall calibration, testing and validation activities we offer for ADAS and AD development. For example, we are working on integrating these vehicles into our virtual testing tool chain and environment, among other things as vehicle in the loop platform. FEV also uses these vehicles as a means to develop its Big Data tools and services through extensive data collection and analysis
In general, our vehicle fleet will constantly evolve, helping us to accelerate the delivery of innovative solutions for our customers. The fact that we are developing these vehicles worldwide definitely helps to provide a global answer to questions related to largescale deployment of this technology.

Mr. Christiaens, thank you for the interview!

>> In perspective, we will use the smart vehicle fleet not just to do further development of the individual systems, but also as an important testing tool for level 4 and level 5 functions



Ready for future mobility

FEV´s e-motor test beds

9. September 2017 | Engineering Service

FEV´s e-motor test beds

Electromobility is constantly increasing in importance, and is currently a significant part of daily challenges. Hybrid and electric vehicles continue to represent a minority, but the number of research projects is increasing rapidly. FEV guides its customers on the path to electric mobility and offers solutions for multifaceted and complex challenges.

New Drives, New Challenges

In addition to various hybrid concepts, the focus is on fully electric drives. As a development service provider, FEV manufactures and distributes test bed components and complete test beds with which drive components can be tested.

Components such as high capacity energy storage devices (traction batteries), inverters and electric motors are relatively new and have no application in conventional drive concepts. In addition to the quality of individual components, their combined application in vehicles must also be ensured. Manufacturers and suppliers face a wide range of requirements. For example, both hybrid solutions and purely electric drives require the most modern, high-capacity energy storage devices. The currents and voltages employed in these reach up to 1,500 amperes or 1,000 volts, respectively. Consequently, test beds must be oriented according to the corresponding safety conditions, and employees must be trained.

Component Tests

The testing of an electric motor for mobile application in a vehicle should absolutely be compared to that for a combustion engine. However, the individual components such as inverters and batteries are also tested separately. Special battery test rigs enable tests of battery cells, battery packs, and complete traction batteries. In order to test the lifespan of the batteries, for example, these are subjected to different charging and discharging cycles in climatic chambers.
Decisive differences from combustion engines can be found in the use of current as the drive power and in the far higher rotational speeds of electric motors. Two years ago, the maximum rotational speed was limited to about 15,000 rpm. FEV is currently delivering E-Motor test rigs with 20,000 rpm speed capability. Future test beds will be capable of up to 30,000 rpm.


System Tests

The components are also tested together, and as closely to reality as possible, in the context of a system test. In this context, it is necessary to consider both hybrid drives, meaning the integration of electrical components into the powertrain, and purely electric drive concepts. In addition to traditional drive concepts, there is now a so-called “E-axis” coming into play. This involves a highly integrated electric drive unit, arising from the combination of an electric motor, transmission, inverter and control unit.

The inspection of the E-axis is carried out by connecting right and left dynamometers in order to emulate road stress.

Additional challenges arise from the testing requirements, the design, and the electrical system components. In addition to the familiar driver-vehicle simulation, a simulation of climatic conditions is also carried out. This involves trials in temperatures ranging from -40°C to 120°C. Comprehensive conditioning systems for the test subject’s cooling media, high-precision measurements of rotational speed, torque, voltage and current are only a few of the new challenges FEV meets in this area in order to be able to offer expert solutions.

The Service Range of FEV

FEV operates, plans and implements electromobility test beds for internal and external customers. This involves the use of FEV dynamometers and conditioning systems as well as tailor-made solutions for customer-specific requirements. The MORPHEE automation system offers a high degree of flexibility and simple configuration for various test bench types. In addition, FEV not only supplies the interfaces necessary for the integration of power analyzers (measurement of voltage and currents of up to 1,500 A and 1,000 V), but also provides its customers with advice on the configuration of test rigs with regard to safety and machinery directives for the achievement of CE conformity.

Battery - E-Motor test beds

FEV operates, plans and implements electromobility test beds for internal and external customers.