Motor-Pump Unit

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 cell to be stabilized and leveled in any driving situation. Four corner models now act as actuators, consisting of an MPE and an active suspension strut in which the shock absorber is used as an actuator. Roll and pitching moments are compensated. In addition, the ride height can be changed, for example lowered when driving on the highway or raised off-road.

The MPE of the E-ACTIVE-BODY-CONTROL system is the product of RAPA Automotive, 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 Silver Atena.

An internal gear machine was favored as the displacement principle.

In particular, a four-quadrant design 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 back and slide on the gear set. This design enables the machine to achieve very high volumetric efficiencies. Particularly in alternating operation around the point of origin of the machine's characteristic map, this produces very good response behavior. 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 electric motor.

Following intensive concept studies, a permanent-magnet synchronous machine was used for the electric machine.

The machine is designed as a wet rotor with a can. This posed a particular challenge in the development of the electric 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 Automotive 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 gap tube must be designed to be pressure-resistant despite the thin wall thickness, which is necessary for magnetic reasons. After numerous structural-mechanical simulations, RAPA Automotive has developed a geometry that is now patented, 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 overmoulding directly integrated in the assembly flow. The overmoulding is also used for balancing the rotor, which is also arranged directly in the assembly line, via openings on the front. The stator consists of a stator star with the electrically connected individual tooth coils mounted on it and a back ring radially surrounding the star. Once the stator has been mounted in the housing, the assembly is encapsulated with a 2-component casting compound under vacuum.

The electronic unit integrated in the MPE was developed together with our partner Silver Atena.

The assembled, pre-assembled and pre-tested ECU is mechanically attached to the engine housing and electrically contacted in the assembly line at RAPA Automotive. The unit consists of a power board and a signal board. Both boards are constructed 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 MPE, the rotor position sensor is positioned directly at the front in the base of the motor housing and is therefore located directly underneath the ECU. 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 located at the electronics end of the shaft. The electrical interfaces to the vehicle consist of a 48 V connection for the power supply and the CAN connection for communication. The electronics provide numerous status variables of the MPE 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 MPE on the CAN bus. The power electronics are of great importance with regard to the overall performance of the E-ACTIVE-BODY-CONTROL, especially due to the high system safety requirements (ASIL level C).

The installation space requirements necessitate a highly integrated design of the motor-pump unit.

To this end, the hydraulic displacement machine and the electric machine are integrated into one another and connected via a common shaft. The concept of the continuous shaft enables a design with only three bearing positions, whereby the middle bearing is shared by both the internal gear machine and the electric machine. Another advantage of the chosen design with a wet-running rotor and a high level of integration between the 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 MPE can be mounted very easily as a single MPE or as a complete MPE axle set using various brackets.

Testing the MPE presented RAPA Automotive's validation team with completely new challenges.

A complex functional test bench for the new product was designed, built and commissioned 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 MPE 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 RAPA Automotive's 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 the pressure pulsation played an important role in this.