CTI SYMPOSIUM 2018

A novel inverter and a corresponding high-powered electric machine (“motor”) were developed for a hybrid vehicle. The inverter is a compact oil cooled silicon MOSFET design rated at 25 kW that drives a frameless 6-phase 8 pole, interior permanent magnet (IPM) motor with oil (Automatic Transmission Fluid, ATF) cooling and novel windings. Both Oil- and water-cooled inverter variants were explored. Both the inverter and the motor were designed, built and tested to A-sample level. A major aim of the design was to make it possible to cool the motor, inverter and gearbox from the same oil supply. The focus of the work presented in this paper is reducing the thermal resistance of the inverter through the use of impingement jet cooling. Cooling of the electrically live tab of MOSFETs is well known to reduce thermal impedance, hence improving performance; this was achieved in the oil-cooled design by exploiting the oil’s electrical insulating property.

Vehicle electrification is challenging conventional propulsion system design like never before, especially in transmission development. Of the numerous competing challenges, electrified propulsion systems need to be energy efficient, compact, and flexible, all while meeting vehicle performance criteria.

The transmission application process is more than ever characterized by a shorter and shorter development time and an increasing number of vehicle variants with different engines/weight.

These vehicles are often developed targeting several markets with different requirements in terms of final in vehicle validation (required by a specific brand) or a different final customer mission profile due to driving style and/or road condition.

Furthermore, in recent years, one of the major challenges has been the advent of hybrid and electric powertrains. The new load cases, typical of these new architectures (e.g. regenerative braking), have introduced new critical issues and drastically modified the hardware validation procedures.

The purpose of this methodology (Transmission Durability Objective Assessment) is to establish, with reference to a defined failure modes, an objective criteria to “measure” the level of damage generated on the transmission components by different vehicle/engine variants, vehicle test validation procedure or final customer mission profile.

The procedure consists in two phases: a sample data collection on a vehicle equipped with an instrumented transmission, and the data post processing with the in house developed Software TDOA to obtain an estimate of the damage that the transmission would suffer if it was subjected to the entire test.

This estimate of the damage makes it possible, beside the vehicle test comparison, to set up a representative bench procedure, tuned on the customer’s operation, or to set (with an already established test procedure) a target according to the vehicle requirements for each failure mode considered (wear, power, fatigue).

The legislation limits for pollutants emissions are strongly pushing OEMs to electrification of their vehicle fleet. Even high performance car manufacturers are taking on the challenge of using electrification - a trend also observed for premium and exotic vehicles. This electrification job is seen from some manufacturers as an opportunity to increase the vehicle performances while moving to more “green” powertrains. It means that the installation of electric power on the vehicle should certainly not affect the performances of the vehicle models with only an internal combustion engine, but increase the performances while cutting the pollutants emissions during driving. As such it is no easy task, since the hybrid system (battery, inverter, and electric motor) affects strongly the overall vehicle weight and thus its driving dynamics as well as system cost. On top of this most manufacturers look for synergies between hybrid and standard versions in order to minimize cost and investments of the overall vehicle platform. All the arguments above weigh even stronger focussing on high performance cars due to the challenges posed by low to medium production volumes. Because of this, modularity of the specific subsystems plays a key role during the concept selection.

It remains an open question how the future develops with respect to speed and consequence in the way of electrifying powertrains. Besides the strong influences of local legislation and public credits, the advancement towards competitive key components for electrified vehicles will strongly affect market penetration.

In 2018, Mercedes-Benz launched with the new A-class the first model of a new generation of compact cars. Mercedes-Benz announced already the first three vehicles with the A class, the A class sedan and the B-class. A complete new modular set of drivetrain is available for the 4th generation of compact cars. This drivetrain modular set consists of a new 6-speed manual transmission, three new optimized 7-speed automatic transmission and a completely new 8-speed automatic transmission with many technical features. For all wheel-drive availability, an optimized power take off unit and a new rear torque-on-demand axle is available. Furthermore, the complete drivetrain modular set is not yet complete.

Nowadays, due to the increasing development of automation in automotive vehicles, the demand of Human Factors & Ergonomics (HFE) application has become mandatory for human behavior understanding. In terms of quality perception, manual gearshift activity in passenger vehicles one of the main items perceived by the driver. However, few researches in the available literature support applied methodologies to predict driver shift quality subjective rating, instead of the commonly used objective variables faced by the driver to remove the human portion. This research analyzes the influence of anthropometric variances of several human bony segments on in-vehicle human subjective rating through linear regression analysis applying enhanced statistical methods.

These days, 48-volt P0 and P1 hybrids have established themselves on the market between micro hybrids and full hybrids. P0 and P1 drives based on a 48-volt system allow a significant amount of braking energy to be recuperated when compared to 12-volt systems as well as a dynamic and comfortable start of the internal combustion engine.

Established technologies and high investments are the key factors that determine the long life of automotive manual transmissions. With this assumption continuous improvement is the most effective approach to preserve the acceptance of the product by the market.

Along the years FCA’s low torque manual transmission (C514 MT), mainly used for A/B segment vehicles, was submitted to several changes aimed to improve its performances and these refinements made it well accepted by the customer; nevertheless feedback from the field highlighted that unsynchronized reverse gear engagement, although quite common in this product range, was still perceived as an issue and it was therefore decided to develop a solution.

Having in mind that the transmission is manufactured in high volumes and on a highly automatized plant, the basic requirements of the solution were identified in terms of allowed cost and components affected by the design change.

After a short introduction the paper will describe the patented concept chosen to satisfy these requirements, the main problems detected during its development, the experimental techniques used to investigate these issues and to validate the solution and how the new contents affected the production lines.

Finally an overview of the results that have been obtained and of the customer feedback will be presented.

In 2008, Höganäs together with KBE+ redesigned the transmission for the smart fortwo car. The ambition was to create a PM friendly, reduced weight transmission that could be built into the original transmission housing whilst maintaining reliability. The reverse engineering analysis showed that this could be done without sacrificing service life, and with an accumulated weight reduction on the gears of 1 kg. In 2010, this transmission was built into a smart fortwo, driven to the PM World Congress in Florence and exhibited there. Since the congress, the smart car has been used as an everyday driver for eight years and accumulated 200 000 km.

In this paper, an evaluation of the PM gears will be presented. The gears are visually inspected after 200 000 km of real driving. The wear, as well as any other damage to gears and synchronizers will be investigated and discussed. Topography measurements before and after 200 000 km will be shown for quantification of wear, and pictures of the gear flanks will be shown to establish the general condition of the gears. From the design work the stress conditions are known, and from the logging system in the car, information on cycles and load can be estimated to further understand the load history of the gears.

Discussions in electromobility often focus on product technologies, infrastructure systems and energy management. This unfortunately leads to the neglect of the business aspects concerning electric vehicles (EVs), which often remain a secondary issue. The development and realization of EVs requires new business models and this presupposes the implementation of new value creation networks, new production and sales systems as well as an extensive analysis of the business aspects of EVs.

It is anticipated that many future hybrid electric vehicle (HEV) transmissions will incorporate the e-motor within the transmission housing while being constrained to ever smaller packaging dimensions. The heat from the e-motor confined to the smaller designs will inevitably lead to higher transmission operating temperatures, necessitating the use of higher temperature resistant plastics and requiring the efficient removal of excess heat.

This will pose new challenges to lubricants. In addition to ensuring the lubricant will be durable in the harsher thermal environment, it must also be compatible with these new plastics and able to protect them from thermal degradation products. The ability to transfer heat will become a critical factor in automatic transmission fluid design, especially for e-transmission devices, when such transmissions are hotter. In this paper the heat transfer characteristics of lubricants are reviewed as well as the fundamental factors that impact them and how the drive for greater heat transfer will drive the lubricants to have lower viscosities. This will have a secondary impact on other fluid attributes, such as hardware protection and electrical properties, and the strategies to deal with these are outlined. The lubricant must be compatible with various plastics and this is described also by way of tensile strength testing.

A new dual clutch transmission has been developed to bring the powertrain of the newly introduced generation of Mercedes-Benz compact car family (MFA2) to a new level. The introduction of the 8G-DCT takes place with the newly developed OM654 diesel four-cylinder engine.

The transmission has a classic and compact 3-shaft layout with 8 forward gears and one reverse gear. A gear ratio spread of 8.81 ensures optimum gear steps with outstanding driving performance, while at the same time reducing fuel consumption and emission of pollutants.

The main focus during the development of this transmission was on the reduction of fuel consumption, increase in torque capacity and the reduction of the weight while maintaining the same installation space when compared to the existing 7G – Dual Clutch Transmission.

Special attention was paid to the reduction of mechanical and electrical losses, which could be achieved by implementing a fixed-floating bearing concept, dry sump lubrication, directly actuated electro-hydraulic control system and the use of an on-demand pump concept.

The weight targets have been achieved through lightweight/lean design approach especially for the housings. The use of high-performance plastics in the internal gearshift system and the oil pan was also a major contributor.

Another new feature is the modular design of the actuation system. The internal gearshift system, the parking lock actuator and the electrohydraulic control system can be tested independently. The transmission oil pan is designed as a highly integrated component. Hence the primary and secondary filters, additional pressurized oil filter and the transmission oil cooler are integrated into the oil pan.

The modular design of the transmission allows for variations in final drive ratio, all-wheel drive variants and also electrification.

Double clutch transmissions hold a significant share in worldwide passenger cars, thanks to its combination of dynamic, efficiency and comfort. Current systems with dry as well as wet clutches show good compatibility for electrification through the integration of P2 hybrid modules. However, this requires a disconnect clutch C0 in addition to the existing double clutch. New highly integrated clutch systems are required to minimize the axial installation space, with strong focus on overall efficiency. Electric vehicle launches with P2 hybrid systems lead to a significant reduction in clutch energy allowing innovative designs of compact triple clutch systems. Schaeffler has developed production solutions for wet and dry triple clutch systems and is currently industrializing those for different drivetrains. This article shows how the clutch loads change as a result of the P2 hybridization, resulting in compact triple clutches integrated into the rotor of the electric motor. Furthermore, the overall thermal balance is analyzed and related differences in efficiencies between dry and wet triple clutch solutions are presented. The clutch systems are enhanced through further development of the tribological system as well as a smart and modular actuation.

AVL introduced a fully integrated electric axle for urban delivery trucks, which helps to keep the overall installation volume and the total weight of the e-drive low and to reach good efficiency and power density. Nevertheless, the e-axle changes weight distribution and the unsprung masses, and influences therefore the drivability of the vehicle. Thus, one aspect of the paper is to investigate via simulation if there are significant changes on drivability and if these changes can be handled by adapting the suspension system accordingly.

But, not for all truck and bus applications integrated axles are optimal. The pros and cons of different e-drive solutions, e.g. integrated e-axle, center drive or wheel selective drives will be discussed. Additionally, the possibilities of defining suitable drivetrain families with the target to reach modular and scalable drivetrain architectures for an entire vehicle family are investigated.

As Nils Bohr famously stated, “predictions are difficult, especially about the future”. This is particularly true when the predictions concern the future development of a market as volatile and uncertain as that for electrified vehicles (xEVs). To complicate matters even further, we aimed to not only focus on the market for vehicles themselves but also try to derive forecasts about future sales of the main powertrain components, such as internal combustion engine (ICE), electric motor and the respective associated gearboxes.

This paper presents latest developments and applications of a new electrical motor design which delivers highest power and torque density, while keeping weight and cost at a minimum. This allows for direct drive applications like wheel-hub motors or other mobile drives, where very low weight is mandatory. The motor’s air-gap-winding design reduces the amount of iron and copper and consequently it’s weight and cost significantly. Slotless design completely avoids cogging torque and shows a very smooth operation. The simple geometric design based on two thin-walled hollow cylinders, supports an automated production, which also contributes to very low cost. A flat slotless stator design stands for a homogenous temperature distribution and very efficient cooling, which allows high shortterm overload. In a first application a 40-kW wheel-hub-motor for a 15-inch rim was developed, built and tested. It delivers nominal torque of 300 Nm over the complete range of speed up to 1350 rpm. Total weight of this prototype is only 20 kg. Further applications for an E-Scooter, a Wheel-Hub Generator, an E-Flyboat and an E-Motorbike will be presented. Combining air-gap winding with an additional slot winding boosts torque and power of the motor substantially, without any relevant increase of weight and cost. Both windings share the already existent permanent magnetic field and cooling system, and both contribute to the torque. Converting an existing wheel-hub motor of generation 1 showed a proof of concept by delivering a nominal torque of 450 Nm and nominal power of 60 kW keeping the same size and nearly the same weight. First generation 2 prototypes providing a nominal torque of 600 Nm in a 16-inch wheel rim and a power of 70 kW is designed, built and validated on test stand.

Mercedes-Benz established the premium SUV segment with the launch of the M-Class in 1997. Since 2015, the model family has been called GLE to underline its position as the luxury SUV of the model family belonging to the E-Class.

For the first time, vehicles with four- and six-cylinder engines are available with fully variable all-wheel drive (Torque-on-Demand) that regulates the torque distribution between the front and rear axles according to the selected drive program.

The optional Off-Road package offers the world’s first fully variable all-wheel drive with high and low range modes, turning the GLE into an all-terrain vehicle as never before.

Transmissions are tested and evaluated under an increasing number of criteria owing to diversification of usage environments accompanying the expansion of the global vehicle market and the growing complexity of transmission control systems. Since vehicles are used in evaluating and validating transmission performance of drivability, the number of man-hours required for testing has increased enormously. In order to shorten development lead time and cope with the increasing number of transmission models to be evaluated, it is absolutely necessary to improve testing efficiency. To resolve these issues, we have developed a virtual real simulator test bench that makes it possible to evaluate and validate transmission performance of drivability in a wide range of usage environments. All elements of the test bench are virtual except the transmission. Efficiency has also been improved by automatic operation and automatic evaluation into the test bench. This paper describes the configuration and functions of the test bench and explains their value in the development process.

Reshaping city traffic will require a new mix of transportation. This will range from individual to public, with different technologies filling the gaps of rail, bus, and tram. Amongst others, electrified bicycles will find their spot, e.g. for the first or last mile transportation. Adapting proven and mature automotive technology paves the way for this transition.

Electrical motors is nowadays recognizable in the automotive industry. The global aim is to increase as much as possible the power density and in parallel save costs and increase the system’s efficiency [Sed17].

Within the joint project “Speed2E”, a drivetrain prototype capable of input speeds of up to 30,000 rpm was developed and successfully tested. In particular, the powertrain behavior in terms of efficiency and NVH was investigated, in order to prove the advantages of high-speed concepts [Gwi16b, Gwi17]. In the follow-on joint project “Speed4E”, the idea of increasing the power density through high motor speed is pursued even further. Especially the impact on dynamics, efficiency and costs when increasing speed up to 50,000 rpm will be investigated. Moreover, a highly-integrated drivetrain along with efficiency optimization will be strived in parallel. Aim of this paper is to present the ideated concept and to give an insight on the designed hyper-high-speed gearbox.

The project Speed4E is funded by the German ministry for Economic Affairs (BMWi) under the supervision of the German Aerospace Centre (DLR).

A new hybrid transaxle for 2.0L class vehicle (P711) was developed based on the Toyota New Global Architecture (TNGA) design philosophy. High performances and development efficiency were both realized by using main parts of P710, the larger sister model of P711 for 2.5L class vehicle, commonly and optimizing. A differential case friction part with a drive shaft inboard joint was one of the parts that required optimal design according to vehicle specification. For more efficient development, good design condition to ensure reliability was needed to be clarified quantitatively in this part. It was clarified by experimental analysis that moment force and clearance were sensitive design factors to temperature increase at a differential case friction part. The good design condition was clarified by the test to grasp the limit of reliability. Based on the good design condition, design of a differential case was streamlined, and it was possible to contribute to more efficient development.

Automotive transmissions have evolved over the years from parallel-shaft manual transmissions to automatic transmissions built with planetary gearsets and further to continuously variable transmissions (CVTs) and dual clutch transmissions (DCTs), among other types.

When one thinks of forging, “lightweight” is not a word that immediately springs to mind. However, when speaking of “lightweight forging”, what initially appears to be unrelated is in fact, on closer inspection, a cost-efficient approach for achieving considerable lightweighting advances in automotive applications that is suited to large-series production. By exploiting the potential offered by forging technology, it is possible to reduce the mass of a medium-sized vehicle by 42 kg and that of a light commercial vehicle by 99 kg.

The use of connectivity and automation in mobility applications is rapidly increasing and being introduced into propulsion system controls to reduce energy consumption. With support from the US Department of Energy’s, ARPA-E agency and in partnership with General Motors, the Chevrolet Volt, generation II, is studied and tested for the benefits of Connected and Automated Vehicle (CAV) control applied to Vehicle Dynamics and Powertrain (VD&PT) to reduce energy consumption by 20% in real world driving scenarios. This investigation looks at application of model predictive control, energy utilization forecasting and external data regarding traffic and infrastructure to develop a mission profile for propulsion system and vehicle dynamics. Both a long and short prediction time horizon are created for propulsion system operation, determining blending of charge depleting and charge sustaining, with the objective of reducing the total energy utilized for the trip by upwards of 20%. The presentation/paper will present the VD&PT model predictive control methodology being developed as a supervisory controller and/or driver assistant. Measured data from a test fleet of generation 2 Chevrolet Volts will also be presented illustrating the benefits of CAV on a single vehicle on real world driving cycle. The experimental results cover a range of driving conditions, from rural to heavy urban; representing the potential reduction in energy consumption CAV control can provide a plugin hybrid electric propulsion system architecture.

All-wheel drive (AWD) vehicles are enjoying increasing popularity. The reason for the rising number of sales is, amongst other things, the variety of benefits which AWD vehicles offer relative to comparable front and rear-wheel drive vehicles. In addition to safety aspects, a higher degree of mobility and driving dynamics are particularly significant.

The power train electrification has been remarkably evolving and HEVs or EVs are increasing in world-wide markets. Especially recently, pure electric driving system such as EVs or FCVs without any ICEs are highly desired as better solutions for environmental protection.

Today, discussions about EVs or FCVs are excessively biased and focused on electrical performance issues. Performance of batteries, available EV driving distance, required battery charging time, performance of fuel cells, etc. These issues are certainly important issues for EVs or FCVs development. However, there remains still other critical issues for EVs or FCVs to assure safety of vehicle driving. Discussions about safety are insufficient. Especially in mechanical field. In the long history of ICE based vehicle usage, automotive engineers have found a lot of situations and conditions for which vehicle reliability or safety should be tested and evaluated. Critical issues often come from “very rare case in market usage”, however, for such “rare case”, various kind of preparations to keep reliability and safety has adopted for vehicle reliability and safety. ICE based vehicles has long enough history to adopt various countermeasure for those “very rare case incidents”.

The author has recently found several critical issues for EVs or FCVs. In this paper, such newly found critical issues particularly for EVs or FCVs are introduced, and good way and good testing machines to develop countermeasures to solve those issues are also described. There are two important critical safety issues. One is fade risk of friction brake when EV or FCV is started from high altitude place with full SOC (State of Charge) and then driven on steep, long downhill road. To keep safety downhill driving, newly proposed Down Hill Brake (Hereafter DHB) is also introduced. Another issue is vehicle fire risk by electric devices breakage during frequent rough road or uneven road driving.

These two issues are not so critical for conventional ICE based vehicle. We should solve such particularly dedicated critical issues for EVs or FCVs earlier, because, to establish good solution for such EVs or FCVs dedicated critical safety issues earlier is inevitable hurdle to overcome for EVs or FCVs popularization.

A wide range of different hybrid architectures is available; some of them are based on existing transmissions, others on completely dedicated new transmissions. Existing transmissions allow various configurations from micro/mild hybrid P0/P1 to mild/full P2 P3 and P4 architectures [1]. Future challenges on emission will require more hybridization content and P0/P1 will not enable enough savings. Market requires architectures that give sufficient CO₂ savings and on the other hand that could be use with different powertrains (ICE and transmissions) without impacting too much the vehicle layout and with an acceptable cost for the end user. That is why the mass market will be driven mainly by 48 V architectures in the next decade. This paper will show why the VALEO hybrid P2 off-line module is a solution that address all the constrains of this new market (Fig. 1).

Forced by political regulations, the reduction of the vehicle’s energy consumption is one of the main objectives in today’s vehicle development. In order to meet regulations, various levels of electrification of conventional vehicles can be applied. The range starts at low level electrification – e.g. micro hybrids – and ends at highly electrified plug-in hybrids.