RAPA brings innovations to life
Development cooperation between RAPA and Daimler
Motor-pump unit
for the E-Active Body Control suspension
The new component developed by Daimler AG is being used for the first time in the new Mercedes-Benz GLE. RAPA developed a unique motor-pump-unit for this active chassis.
The driving comfort achieved, the additional features such as the free driving mode or the Curve function – in the overall constellation, a tangible advance for the end customer with high utility value. For RAPA, the successful development of the motor-pump-unit is nothing less than the greatest challenge in terms of system complexity in the company’s own almost one hundred-year history.
Daimler honors RAPA with the Special Award Innovation.
As the overall system is impressive, RAPA received the Special Award from Daimler in February 2019 as the most innovative supplier of 2018.
E-ACTIVE-BODY-CONTROL
Mercedes-Benz SUV GLE
“In the new Mercedes-Benz GLE, Daimler is introducing E-ACTIVE BODY CONTROL, a chassis system developed from scratch. It offers a high level of ride comfort, driving dynamics and off-road characteristics.”
© Daimler AG
“The greatest pride of our developers is the motor-pump-unit integrated into the E-ACTIVE BODY CONTROL chassis. A masterpiece of German engineering that confirms us as a premium product supplier to the automotive industry.
Oliver Henkelmann-Mattheus, Vice President Sales RAPA Automotive
The development project
Since the company was founded almost 100 years ago, RAPA has been known for continuous development and innovative product solutions. Its strategic vision in high-tech niche areas and its reputation as a flexible and innovative development service provider make the family-owned company from Upper Franconia a recognized technology partner and hidden champion in the automotive, medical and industrial sectors.
RAPA has been part of the automotive supplier world since the 1980s – and has been closely associated with Daimler AG ever since. This important partnership for RAPA has also been established for over 20 years in the field of active chassis control systems; since 2005, the so-called ABC© (Active Body Control) has been the non-plus-ultra in the Group’s luxury class vehicles. This is based on a highly complex hydraulic system that can only be used to a limited extent for future innovations, not least because of its dependence on the combustion engine. A completely new solution was needed that would meet the main requirements, such as a pressure-tight, compact four-quadrant unit, high overall efficiency, dynamic volume flow control, 48 V operating voltage, integrated electronics and optimum NVH behavior.
After six years of development, the motor-pump unit (MPE) with integrated control electronics for the E-ACTIVE-BODY-CONTROL of the new Mercedes-Benz GLE SUV has now been created – an important milestone in RAPA’s company history.
E-ACTIVE BODY CONTROL – The world’s most intelligent chassis
E-ACTIVE-BODY-CONTROL is a further development of the established ABC system. The road surface is recorded with the aid of a stereo camera and a corresponding control algorithm is created, which allows the passenger compartment to be calmed and leveled in any driving situation. Four corner models now act as actuators, consisting of an MPU and an active suspension strut in which the shock absorber is used as an actuator. Rolling and pitching moments are compensated. In addition, the driving level can be changed, for example lowered when driving on the highway or raised when driving off-road.
The motor-pump-unit
of the E-ACTIVE BODY CONTROL system is the product of the company RAPA, consisting of three main components: an internal gear hydraulic pump, a permanently excited synchronous machine as an electric motor and the 48 V control unit including software from the company Silver Atena.
An internal gear machine was favored as the displacement principle.
In particular, a four-quadrant version with leakage compensation is used. Leakage compensation is implemented radially via pressure-activated and self-sealed split fillers and axially via pressure plates, which are also sealed on the rear and slide on the gear set. This design enables very high volumetric efficiencies to be achieved. This produces a very good response, particularly in alternating operation around the origin of the machine’s characteristic map. The volumetric efficiency of the machine is almost 100% in this range. The high efficiency is necessary because active cooling should be avoided at all costs.
In addition to the four-quadrant capability and the very high volumetric efficiency, the selected displacement principle also offers a very compact design and very good possibilities for a high level of design integration between the displacer and the electric motor.
Following intensive concept studies, a permanent-magnet synchronous machine was used for the electric motor.
The machine is designed as a wet runner with a slit tube. This posed a particular challenge in the development of the electrical machine, as it was necessary to achieve high efficiency on the one hand and pressure resistance under all operating conditions up to at least 150 bar on the other. An eddy current-free can is a prerequisite for the most efficient operation of the machine, and RAPA has developed a thin-walled plastic part for this purpose. The wall thickness of the tube can be reduced to a few tenths of a millimeter in the magnetically relevant area of the machine. Contrary to this, the containment shell must be designed to be pressure-resistant despite the thin wall thickness, which is necessary for magnetic reasons. After numerous structural-mechanical simulations, RAPA has developed a now patented geometry which is supported by the stator teeth under pressure and automatically stiffens.
The rotor has a classic spoke design. The permanent magnets integrated in the rotor laminated core are fixed in place by a plastic overmold directly integrated into the assembly flow. The overmolding is also used for balancing the rotor, which is also located directly in the assembly line, via openings on the front. The stator consists of a stator star with the individual tooth coils mounted on it and electrically connected, and a return ring radially surrounding the star. After mounting the stator in the housing, the assembly is cast with a 2-component casting compound under vacuum.
The electronic unit integrated in the MPU was developed together with our partner Silver Atena.
The assembled, pre-assembled and pre-tested ECU is mechanically attached to the motor housing and electrically contacted in the assembly line at RAPA. The unit consists of a power board and a signal board. Both boards are designed in the form of a stack with an assembly between the two boards to accommodate the DC link capacitors, the input choke and other components.
A rotor position sensor is used to detect the actual position of the rotor. Thanks to the design of the MPU, the rotor position sensor is positioned directly at the front in the base of the motor housing and is therefore located directly under the ECU with the shortest possible path. A Hall sensor is used as the sensor principle. The magnetic field required for the sensor, depending on the position of the rotor, is provided by a permanent magnet arranged at the electronics end of the shaft. The electrical interfaces to the vehicle consist of a 48V connection for the power supply and the CAN connection for communication. The electronics make numerous status variables of the MPU available on the CAN connection. In addition to the typical variables such as speed, temperature, input voltage and current consumption, two pressure sensors integrated in the hydraulic machine also provide the actual sensed pressure at the two hydraulic connections of the MPU on the CAN bus. The power electronics are of great importance with regard to the overall performance of E-ACTIVE BODY CONTROL, especially due to the high system-side safety requirements (ASIL level C).
The installation space requirements necessitate a highly integrated design of the motor-pump-unit.
For this purpose, the hydraulic displacement machine and the electric machine are integrated into one another and connected via a common shaft. The continuous shaft concept enables a design with only three bearing positions, with the middle bearing being shared by both the internal gear machine and the electric machine. A further advantage of the selected design with wet-running rotor and high integration between hydraulic and electric machine is that only static seals are required for the atmosphere. This ensures robust sealing of the system over its service life and also completely prevents friction caused by the seal, and therefore losses, on the shaft. Depending on the installation space requirements in the vehicle, the MPU can be mounted very easily as a single MPU or as a complete MPU axle set using various brackets.
Testing the MPU posed completely new challenges for RAPA validation.
A complex functional test bench for the new product was designed, built and put into operation at an early stage. In addition, a wide variety of test benches had to be planned and set up for the complex test sequences, which took a total of eight months per test loop. As the device was also to be used in electric driving mode, the noise development of the MPU posed an extreme challenge for the suitability of the new product for series production. After intensive optimization loops consisting of simulative and experimental work in the RAPA noise measurement chamber and accompanying evaluations in the customer’s vehicle, the necessary improvements were achieved. Numerous noise-relevant details in the hydraulic machine were optimized within the optimization loops. Minimizing pressure pulsation played an important role in this.
DAIMLER SPECIAL AWARD INNOVATION
RAPA is named most innovative supplier of the year 2018
At the 11th Daimler AG awards ceremony on February 20, 2019, RAPA received the Daimler Supplier Award Innovation for the development of the motor-pump-unit, whose sophisticated and intelligent control generates pressures individually in each shock absorber. To be experienced in the new Mercedes-Benz GLE as E-ACTIVE BODY CONTROL suspension. The aluminum trophy, weighing almost two kilos, was presented to Dr. Roman Pausch by Ola Källenius, Member of the Board of Management of Daimler AG for Group Research and Mercedes-Benz.
Dr. Roman Pausch, CEO of the RAPA Group, summarizes: “A success that makes us proud and spurs us on to pursue further customer-specific innovations with the same commitment. But without the open and cooperative partnership with our colleagues at Daimler, the development of this world first would not have been possible.”
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“For RAPA, the strong partnership with Daimler over several years is an important building block with which we underline our expertise as a partner to the automotive industry.”
“The automotive industry and its suppliers are important customer groups for RAPA. In addition to close business relationships, RAPA also has numerous research and development projects with these companies.”
“The central task is to maintain the high quality standards demanded by our customers and to adapt to new market requirements.”
The development team
The project team of the innovation project, headed by Jörg Bauer, is made up of the core team of 25 employees and small, efficient, interdisciplinary working groups with 57 employees.
Get to know our experts personally:
Jörg Bauer
Technical project manager
"The RAPA motor-pump unit is a globally unique new development, the result of 6 years of great teamwork."
Falk Lehniger
Test engineer
"Whether as an engine or a generator, it can deliver both enormous power and breathtaking dynamics. A unit like this is madness."
Michael Wolfrum
Project purchasing
"It was only thanks to the team, the individual people behind it and their cooperation that every challenge could be mastered and the original vision successfully turned into reality."
Katrin Ebersbach
Order center & PPS
"The interaction of over 100 purchasing parts is a major challenge. Customer satisfaction is our top priority."
Sandy Geyer
Industrial Engineer
"Only by integrating new processes and continuously analyzing and developing the systems are we able to produce this innovation with process reliability."
In action
With the E-ACTIVE BODY CONTROL suspension, the Mercedes-Benz GLE offers a new vehicle with unique off-road characteristics for the first time. All four wheels can be controlled individually.
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