Solving the powertrain mount dilemma

This year’s VDI Innovation of the Year Award has been won by a technology that breaks new ground to address a problem that so far has found no other solution. Supplied by BWI Group (previously Delphi Chassis Systems), the Magneto Rheological Powertrain Mount substantially reduces the compromise traditionally required between refinement and dynamics. The first application, developed in cooperation with the sports car manufacturer Porsche, is for the recently introduced (2010MY) 911 GT3 and 911 Turbo.

When a company has a reputation for superbly engineered high-performance vehicles, each technological leap has to be carefully considered. Risks have to be controlled, yet a high level of innovation is required to achieve objectives that include a comfortable ride for everyday road use combined with on-track dynamics that, for the 911 GT3, is equivalent to highly focused semi race cars.
“We set ourselves challenging targets for the new 911 GT3 (Mk II),” explains Karsten Schebsdat, who is responsible for the performance of Porsche’s GT-Derivatives, referring to the latest, 3.8-liter incarnation of Porsche’s high-performance 911 derivative. “Our goal was to provide best in class vehicle dynamics on the racetrack in combination with pleasing ride comfort on public roads for everyday use.”

Calibrations that improve handling and responsiveness do, however, usually result in reductions in refinement and that has until now been the case with management of the powertrain mass. Although Porsche has been using highly optimized hydraulic mounts to reduce this compromise, for the most demanding GT3 customers, the sports car manufacturer wanted to offer something even more remarkable. The Porsche team therefore decided to introduce an innovative new type of mount that would help to solve this challenge.

“Based on Delphi’s magneto rheological (MR) dynamic control technology, the MR Powertrain Mount (in Porsche’s terms: dynamic engine mount system) is the first production system that allows precise management of relevant frequencies created by the moving mass of an automotive powertrain, including the challenging low frequencies and higher amplitudes caused by transient torque events,” explains Timothy Schlangen, MR Powertrain Mounts manager with BWI Group, the independent company that acquired Delphi Chassis Systems on November 1, 2009.

Above:

1 Rubber molded assembly with inner insert and interface to engine carrier
2 Inner chamber filled with MR fluid
3 Soft magnetic orifice assembly with coil (4) and valve gap (5)
6 Diaphragm
7 Base plate
8 Electrical connector
9 Pressure sensor
10 Interlock with interface to body

As well as suspending the mass of the engine and transmission, powertrain mounts provide a reaction point and isolate the body of the vehicle from powertrain noise and vibration. In broad terms, excellent dynamics and ride comfort require mounts providing high levels of stiffness and damping, while good isolation of powertrain noise and vibration requires soft mounts.
“With conventional technology it is not possible to optimize the behavior of the mounts for each function and each dynamic state. There is always a need for compromises in order to obtain a good performance across all relevant driving situations,” says Dr Bernhard Pfäfflin, head of Porsche’s NVH (Noise Vibration and Harshness) department. BWI’s Schlangen adds that, “With magnetorheological technology, the mount can be tuned to control or isolate at appropriate frequencies in real time, allowing us to significantly reduce these compromises.”

There were four areas of focus for the Porsche team:

• Improved driving dynamics by increasing the coupling of the engine to the body when required, in real time;
• Improved traction through closer control of vertical powertrain movements;
• Enhanced ride comfort by managing low-frequency powertrain motions excited by the road surface;
• To achieve the dynamic improvements with no reduction in the isolation of powertrain noise and vibration.

In a concept investigation, the Porsche advanced chassis engineering team with its head, Martin Winkler, had analyzed a number of approaches and identified the MR technology as being best aligned to their requirements. “In a common advanced development project with Delphi Chassis (now BWI Group) we confirmed the feasibility for the application of this innovative technology and defined the engineering goals for the realization in the 911 GT3 and Turbo program,” adds Winkler.

Above: The new Porsche 911 GT3 showing the location of the two MR Powertrain mounts and the electronic controller

The development teams of BWI Group and Porsche – including their vehicle dynamics, NVH, and electrical engineers – worked closely together to deliver the application. “BWI provided the physical aspects of the mount and the software block for current control, while Porsche’s activities focused on the software for the overall control including detection and clustering of driving conditions, the safety strategy, vehicle integration, tuning, and testing on the vehicle,” explains Dr Jürgen Wimmer, Porsche’s head of suspension systems development. “This split of responsibilities worked well as our skills are complementary, allowing the team to meet our engineering goals within an ambitious timing schedule.”

Proven MR technology

The new powertrain mount uses magnetically soft (easily, but temporarily magnetised) iron particles suspended in a synthetic base fluid, held within a cavity in the rubber body of the mount. When a magnetic field is applied by a coil, the particles become aligned, increasing the sheer stress and therefore the resistance to flow. The stronger the magnetic field, the higher the dynamic rate (effectively the stiffness) of the system.

The current is controlled by a processor that receives data already available on the vehicle databus. This can include throttle position, road speed, engine speed, temperature, and any other information required to deliver the level of control specified by the vehicle manufacturer. Closed loop feedback is provided by direct measurement of the fluid pressure in the system, ensuring real-time compensation for changing conditions and aging of the system components.

When there are no transient dynamic loads on the powertrain, the MR Mount allows the connection with the vehicle body to be relatively compliant to deliver optimized NVH characteristics. When dynamic loads are applied (lateral, vertical, or in the driving direction), the stiffness can be immediately increased to provide the required level of mass control.

The MR Mount system may also provide a solution to the refinement and comfort issues associated with torque transients created by events such as engine start, sudden wide open throttle, braking, and gear changes, including moving an automatic transmission into drive. It can also improve traction and occupant comfort on rough roads by managing the low frequencies created by the vertical movement of the powertrain mass.

Porsche applications

The Porsche dynamic engine mount system was introduced as an option on the exceptional 3.8-liter GT3, first shown at the 2009 Geneva show. For the 2010 model year, it will also be an option on the revised 911 Turbo and Turbo Cabriolet, and standard on the ultimate high-performance 911, the GT3 RS.
On all of these models, Porsche’s dynamics experts realized further improvement of the already excellent cornering performance and traction, especially during alternating bends and on rough roads. The NVH engineers were also able to enhance ride comfort and solidity (less body shake) without degradation of the well-balanced NVH behavior.

BWI’s Douglass Carson, director of suspension engineering, is understandably delighted. “Porsche ran a very efficient development program and extracted more benefits than even we had expected,” he concludes. “Working with their engineers has been a tremendous experience and the reviews of the final product more than vindicate their confidence in this innovation.”

View video

Click here and then click on ‘Broadband’ to view a video of Walter Röhrl driving the new 911 GT3 and commenting on the Porsche Dynamic Engine Mount System