BMW's Z22 technology test bed is about as long as a 3-Series, has a wheelbase similar to the 7-Series, the interior space of a 528i Touring, and agility comparable to a Z3 two-seater.
Some of the 70 innovations of the Z22.
The Z22 interior features a rear-view mirror monitor, center monitor, multifunction steering wheel, and central control unit.
The Z22 body structure comprises about 20 components, including this carbon-glass-resin side frame.
A magnesium crankcase (right) like that of the Z22 is up to 25% lighter than a similar aluminum component (left), according to BMW.
The Z18 off-road roadster, which has an X5 drivetrain with 4.4-L V8 engine and four-wheel drive, was created in 1995, but remained a secret project until now.
The Z18's interior presaged that of the new production Z8.
BMW's Landshut facility includes a LITZ light alloy casting machine with a 4400 t (4900 t) clamp force and casting pressure of up to 100 MPa (14.5 ksi).
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A sharp dichotomy is apparent in BMW's research and development philosophy. Its production models generally tend to be evolutionary in their maturation from generation to generation but behind that seemingly cautious and conservative approach is a sharp focus on advancing technology. In the mid-1980s, the company founded BMW Technik GmbH, a "think tank" intellectually separate from the mainstream development groups within BMW, though physically only about five minutes by car from its R&D center. It has wide design and engineering freedom to conceive and pursue far-ranging technologies and vehicle shapes. BMW Technik is also known as ZT: Z for zukunft (future) and T for technology. About 100 specialists work for the innovative ZT, which has a direct line to the top management of BMW's Group Development Division but operates essentially as an independent business.
Much of ZT's work is, by necessity, bound by tight security; but to mark the 15th anniversary of its founding, it lifted the veil on some of its secret projects - past and present - to a small group of specialist publications, including AEI. Most significant among those projects is the Z22, an all-embracing technology demonstrator, while the most surprising is the Z18, a two-seat off-road roadster designed five years ago and based on the X5 platform and drivetrain.
The Z22 is a concept, the styling of which gives no particular signal to any future production car, which is just as well as it is far from handsome. But what is wrapped in this package, and the materials used for the wrapping, are really important. It centers on mechatronics (mechanical systems with electronic control), lightweight construction, and ease of driving. It incorporates 70 innovations and 61 patent applications. Although it was projected to be just a feasibility study, this flagship of technology is a "full-blooded and ready-to-drive car," according to BMW ZT.
Two of the most important elements of the Z22 are its use of drive-by-wire steering and braking. Initially, for both technical and legislative reasons, BMW is aiming to incorporate the world's first mechatronic steering in a production vehicle, combining active hydraulic power steering with steer-by-wire. At present, it is legally necessary to have a physical link between the steering wheel and front wheels, but a full steer-by-wire system is ZT's next target.
Lightweight construction is also a major BMW program with the aim of using carbon-fiber-reinforced plastic (CFRP) for the entire passenger cell of a series production model. Aluminum and magnesium in combination also offer major weight savings: about 7.5 kg (16.5 lb) when used for the door of a coupe. The car's straight six-cylinder engine uses a magnesium block and aluminum cylinder for 10 kg (22 lb) lighter weight than an all-aluminum unit. To help achieve these materials science aims, BMW has opened an Innovation and Technology Center at its Landshut plant (LITZ), which comprises Light Alloy and Plastics and Synthetics divisions. The LITZ develops and tests processes for the production of weight-optimized automotive components.
BMW is now building an experimental vehicle that will be 30% lighter than an equivalent production model and will use fewer components. New technologies for manufacturing plastic surfaces in cockpits and for door coverings are being developed with no loss in quality but with weight savings of up to 35%. Thermoplastics and "duroplastics" figure in BMW's work, with particular attention paid to fiber-reinforced (with glass, carbon, and aramid) materials. The resin transfer molding (RTM) process is playing a major part in work at Landshut. It can give a 50% weight saving against steel for components such as a front fender and also provides added styling opportunities. BMW has an extensively automated RTM plant for CFRP composites that can handle components up to 3.5 m (11.5 ft) in length and could be used for series production. Reducing the mass of car seating is also a target; a rear seat cushion sees a 1.2 kg (2.65 lb) reduction with neutral cost penalty and consistent high quality.
Ideas that have crystallized at ZT and reached production range from the Z1 sports car of the mid-1980s to the C1 two-wheeler just on the market. The Z18 off-road roadster was created in 1995, but has remained a secret project until now. The Enduro on/off-road motorcycle of the 1980s inspired its design.
Z18 is a variable concept that can be used as a two-seater, 2+2, or pickup. Its interior presaged that of the new production Z8. It has an X5 drivetrain with 4.4-L V8 engine and four-wheel drive. Curb mass is 1560 kg (3440 lb) and length 4.25 m (13.9 ft). It is quick and has a thunderous exhaust note.
But it is the Z22 that brings the serious message from ZT. It is a "technology carrier" as ZT's Managing Director, Ulrich Mellinghoff, put it. That technology is for possible production applications after 2005. The criteria used to create the Z22 were many and varied. Mellinghoff stressed that it was not designed as a successor to any current production BMW. Driving performance, comfort, and safety were to compare with a 528i Touring, with 33% less weight and 45% lower fuel consumption. The fuel consumption target was 6.0 litres/100 km (39 mpg). Says Mellinghoff: "In this fully functional prototype, Ôsystems of the future' were to be realized and Ôexperienced' now as a basis for the rigorous further development of concepts and technologies."
The Z22 is about as long as a 3-Series, but has the interior space of a 528i Touring. Wheelbase is similar to that of a 7-Series, but agility is described as being comparable to a Z3 two-seater. The latest safety standards are achieved with a mass of about 1100 kg (2420 lb). Its four-cylinder 2.0-L engine produces 100 kW (134 hp) and is mounted transversely ahead of the rear axle.
Mellinghoff explained ZT's weight-saving technology: "In the case of the body, the rigidity/light-construction conflict of aims is solved by an appropriate horizontal separation in an aluminum functional frame and a CFRP passenger cell including the entire side frame. The functional frame carries all aggregates (suspension, etc.) and meets necessary crash requirements, whereas the passenger cell lies outside the flow of forces. By placing the passenger cell into the vibration node of the functional carrier, good vibration and structure-borne noise insulation is ensured."
The Z22's body structure comprises about 20 components against a norm of 80. It is not a ladder-type frame construction, he said, but it does allow high dynamic rigidity at low weight. The suspension includes titanium springs and magnesium wheel carriers. The weight saving target was 50% against the current 5-Series suspension. Carbon discs are used for the brakes for a 65% savings. "The design of the lighter CFRP cell compared to steel and an aluminum frame facilitates the use of large components," said Mellinghoff. "Six different production processes were applied to those components to reveal the strengths and weaknesses of the processes." This was particularly focused on the possibility of achieving limited (100 units a day) series production. A second Z22 was built to confirm crashworthiness to meet EURO NCAP impact criteria at 64 km/h (40 mph) with a 40% offset/deformable barrier.
The other key technology areas on the Z22 involve drive-by-wire systems. Because legislation does not permit cars without a mechanical link between steering wheel and front wheels to be approved for sale, BMW is working on a compromise system called Active Front Steering (AFS), which combines elements of a regular hydraulic system and a by-wire system. This step toward full by-wire steering has a planetary gear integrated in the steering column. The gear system includes an electric motor, which has a self-inhibiting spiral drive and is able to create additional or reduced steering angle. A regulator controls steering-wheel torque.
Tested by this AEI editor on a production BMW sedan over a very-low-friction surface, it demonstrated added braking stability and yaw control. AFS, which has more direct steering at low speed and less direct at high, copes well in avoiding obstacles, with reduced steering movement required than with a conventional system. This limited steering wheel movement is a central element of the success of the system.
However, it is total by-wire steering for which BMW is aiming, and it is such a system that is fitted to the Z22. The car has a rectangular multi-function steering wheel, regarded as practical because steering wheel angle need only reach ±160 degrees from lock to lock for a turning circle of 11 m (36 ft). Like AFS, at higher speed the steering ratio becomes less direct and at low speed more direct. Sampled on a production BMW sedan, the system was very direct indeed at low speed, with a tendency to make a driver input too much steering movement, but after a few minutes this became less of a problem and on rapid lane change and slalom test courses the system reacted satisfyingly quickly, with little steering-wheel movement. A back-up redundant system is fitted. "Traditional" BMW steering feel can be dialed in.
The by-wire system, which uses much of the AFS principle, comprises a steering-wheel module, steering-rack module, electronic control unit (ECU), and battery module. The steering wheel is connected to a brushless dc motor with integrated power electronics to create steering feel. Two dc motors drive the pinion of the steering rack via a gearbox. The ECU uses the angle data from the steering wheel and steering rack to determine the controlling signals of the actuator's drive. The ECU monitors all system components and alerts the driver to any fault. The battery module provides a connection to the Z22's onboard power network, and via a buffer battery, emergency backup.
Brake-by-wire provides a brake feel similar to that of a regular system and in some instances superior, such as from an ABS stop, an ECU calculating optimal brake force. Instead of conventional brake calipers, the BMW system uses electromechanical actuators to operate the pads. "The actuators consist of permanent-magnet motors which are connected to a gear drive for converting torque and rpm. A spindle creates the translational motion. The application pressure that occurs can reach many tonnes, according to ZT. A fault-tolerant system structure shuts off individual defense actuators, but the system still provides safe emergency braking.
Other elements of technology on the Z22 include the use of fingerprint identification instead of a key for vehicle access and starting, intelligent light technology adapting to specific needs such as narrow radius curves or intersections, cameras using image processing for a panoramic rear view, and head-up display. Energy supply for the Z22 comes from a crankshaft starter/generator with 5-kW output, complemented by buffer batteries. A hybrid energy network provides voltage levels of 14, 42, and 200 V.
Stuart Birch
AEI October 2000
