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P014_NELE_APR27.qxp:Layout 1 22/4/10 08:15 Page 14 On the level How electronics technology is contributing to much improved handling in a range of top end cars. By Graham Pitcher. he automotive industry is the centre of much attention at the moment. A who are contemplating paying a lot of money for a sports type model lot of this attention is focused around emissions, with legislation placing don’t want to have their car handling like a boat. Tincreasingly stringent requirements on manufacturers to reduce the But it’s not just on road performance that is focusing the levels of CO2 produced by their engines. attention of car designers; some models – such as the Range But the recent scrappage scheme has seen the industry get something of Rover – are intended for off road use. Technology is being a new lease of life as owners of older vehicles have taken the opportunity to brought to bear in these models to make the car a lot replace their cars with something more efficient and certainly with more more stable when being driven across the equivalent of a features. ploughed field. The particular problem here is known as Features have always been an important part of the car selection process. Once, this could have been as simple as whether the car was supplied with electric windows or not. Today, potential buyers are faced with a range of options that can, depending upon how much cash you have, boggle the mind. However, one thing remains a constant through all levels of the cars on offer – comfort. With the exception of those seeking a racing experience on the road, ride comfort is an increasing important aspect of automotive design. But providing a comfortable ride – particularly in higher end sport oriented models – can often be at the expense of handling performance. And those European production vehicles featuring second generation MagneRide systems include the Audi R8, right, the Ferrari California and the Ferrari 458, above. 14 27 April 2010 www.newelectronics.co.uk P014_NELE_APR27.qxp:Layout 1 22/4/10 08:15 Page 15 Automotive Electronics Cover Story reliability problems – but also add weight, something manufacturers are keen to avoid. BWI Group, formed by the acquisition of automotive technology specialist Delphi’s chassis systems business, recently introduced the third generation of its MagneRide suspension control system. MagneRide – introduced in the US in 2002 and in Europe in 2006 – is now specified on vehicles from around the world. One of the major claims made by BWI for MagneRide is its relative Generation 2 simplicity: the system features no moving parts, except for the suspension MagneRide coils itself. Instead, it uses dampers whose response can be changed dynamically. (above left) are fitted Sensors feed information on body and wheel motion back to a control unit, to struts used in the which analyses the data and issues control signals to the car’s dampers. Each Audi R8. The Generation 3 coil is shown below. damper has an electromagnetic control system that can vary the properties of the damper fluid in response to those commands. The result is a continuously variable damping system which is simple, cost effective and reliable. Mike Zimmerman, manager of controlled suspension systems development for BWI, explained: “The system is based on a magneto rheological fluid in which iron particles are suspended. When a magnetic field is applied, the fluid reacts and the particles line up to resist flow through a small gap in the actuator. Fine control can be applied because the level of resistance varies with the flux applied.” ‘head toss’, where different undulations on The fluid retains the same viscosity, no matter whether the either side of the car cause occupants’ heads to electromagnetic force is applied or not. When the force is applied and the be thrown about. The problem can be exacerbated by a particles line up, the shear force of the fluid changes dramatically and the combination of stiff stabiliser bars and soft springs. alignment needs to be sheared if the fluid is to move. Ride comfort isn’t, of course, a new problem and Zimmerman says MagneRide offers designers the ability to vary the designers have come up with a range of solutions. Some semi suspension settings infinitely. active control systems have used complex electromechanical Surprisingly, MagneRide is a relatively small control system. It features valves to adjust suspension performance while the vehicle is in two sizes of damper; with 36mm and 46mm diameter pistons, as well as motion. But these not only feature moving parts – and therefore introduce multiple rod diameters. The MagneRide damper is the only semi active suspension system to have no additional moving parts. The system is fitted to the Audi R8. www.newelectronics.co.uk 27 April 2010 15 P014_NELE_APR27.qxp:Layout 1 22/4/10 08:15 Page 16 Automotive Electronics Cover Story Active stabilisation provides better control, cuts weight BWI’s active stabiliser bar system not only provides better control of over and understeer, but also reduces system weight by about 30%. According to the company, the new system offers significant improvements and can deal with all vehicle roll angle and roll velocity inputs, leaving springs and dampers to deal with vertical inputs. This is said to eliminate a major compromise in the balance between ride and handling. Olivier Raynauld said: “The vehicle can be agile in the city at low speed, stable on the highway at high speed and the system can provide improved stability during lane changes, helping to initiate the turn and then resisting overshoot.” The first cars featuring the system will appear in 2012. “The pistons are just 30mm in length,” Zimmerman continued, “and the hard’. It also improves system response at low body velocities, where it has gaps through which the fluid flows vary from 0.5mm to 1.2mm, depending been harder to control movement using conventional suspension techniques. upon the piston size.” Raynauld added: “By developing the new coil technology in generation With generation three of the MagneRide system, BWI has introduced a three of MagneRide, we have moved from single to dual coils. This allows the tapered piston, which Zimmerman said has a larger gap on the rebound side. system’s range to be widened and provides additional speed of control. What “The compression to rebound ratio for most car dampers will offer the same it means is the system can become more or less flexible more quickly.” ratio of force control to compression. It’s essentially a mechanical system, but Where vehicles are equipped with the MagneRide system, they are it needs to be controlled.” completely reliant upon the ecu for suspension. So how does the system ‘fail Zimmerman noted that valve based systems need to include collars to safe’? open and close the valves. “With MagneRide, we can do the whole thing in a Zimmerman explained: “The ecu has a watchdog circuit and a back up device 30mm long, which helps designers to reach suspension travel goals.” current source. If everything fails, the ecu can output a constant current and Control is a relatively simple affair. “There are four position sensors,” this can be set according to the manufacturer’s requirements.” Zimmerman explained, “and an electronic control unit (ecu). The four But the magneto rheological approach isn’t limited to suspension position sensors determine wheel position and allow the relative velocities of systems, BWI has developed a system that can be applied to engine mounts. the wheels to be calculated. Their inputs also allow the ecu to work out The system is being used in some Porsche models. whether the body is heaving – moving upwards or downwards – rolling or The engine mounts used in previous Porsches have been hydraulic in pitching. Based on that, the ecu will send instructions to the dampers on nature. The problem with this approach is that peak damping is only provided each wheel at a rate of 1kHz.” at one frequency and amplitude. Raynauld explained: “It is possible to get According to Zimmerman, development of the third generation ecu has what’s known as ‘power hop’ at the rear wheels and passive engine mounts concentrated on two areas: control frequency; and the drive circuitry. can be too stiff to deal with this. With the magneto rheological system, we can “The ecu has a pwm control frequency of 30kHz. We’ve chosen this take care of the compromises effectively.” frequency in order to take the pwm out of the audible noise range. Meanwhile, The reason for this is that there are some instances where designers developments to the drive circuitry have allowed us to get commands to the would want the engine to move and other instances where engine movement dampers more quickly. In previous systems, we could get current to the is not wanted. The system allows compression to be stiffened if necessary dampers quickly, but there was a natural delay between when the current and rebound managed in order to improve the car’s stability. turned off and when the magnetic field dissipated. Now, we can provide The work on developing MagneRide is part of a broader investigation into quicker current off performance.” how vehicle dynamics can be improved by sharing data with other onboard Providing this higher level of capability has required a change of systems. A global chassis control system would see a supervisory computer microcontroller in the ecu. Olivier Raynauld, manager of forward engineering managing an array of subsystem controllers. Potential candidates for this controlled suspensions at BWI, said: “Previous generations of the ecu were system would include antilock braking, electronic stability control, engine designed around the 16bit ST10; now, the ecu takes advantage of the power of torque, roll control, dampers and electronic steering.

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