The all-new 2001 Ford Escape, a smaller sport utility vehicle (SUV) than the Explorer, combines car-like front-wheel drive (FWD), with the added safety and security of a 4×4 for more adverse driving conditions. "Operators in this segment aren't looking for a 'rock-hopper' to climb the Yukon Trail," explains Don Ufford, vehicle engineering manager. "They go off road occasionally on camping or fishing trips, and want extra traction during inclement weather. However, they prefer a system that doesn't require too much thought and changes from full-time all-wheel drive (AWD) to four-wheel drive on-the-fly with the turn of a switch."
To meet the need for such a driver-friendly 4×4 system, Ford Motor Co. developed its first mass-produced FWD/AWD/4×4 system called Control Trac II™. The system consists of a power take-off unit (PTO) that uses a series of gears to turn power 90 degrees from the side of the transmission toward the rear. Between the two-piece drive shaft and the rear axle differential, a rotary blade coupling (RBC) both provides the 4×4 locking feature, and detects differences in front and rear wheel speed to automatically proportion torque to the rear wheels through the differential and rear axles.
Ford worked with Dana Corp. Engineering Centers in Toledo, OH and Fort Wayne, IN to develop the RBC. As the brains of the Control Trac II system, the RBC combines a clutch pack, hydraulic pump, and a solenoid actuator. Set in the "4×4 Auto" position, the system operates in FWD until the wheels slip, at which point the speed difference between front and rear wheels causes relative motion between the rotary blade fan and the RBC housing. Fan motion pressurizes silicone fluid against the thin aluminum piston. The piston pushes on the multi-disk wet clutch to automatically proportion torque to the rear wheels.
Rather than using silicon fluid to transfer torque as in a viscous coupling, the RBC uses the fluid to engage the multi-disk wet clutch.
For more demanding off-road driving, the lockup feature smoothly engages with the turn of a rotary switch on the instrument panel to the "4×4 On" position. In this mode, current through the RBC's electrical connector energizes the electromagnetic clutch windings, forcing the electromagnetic clutch piston to engage a roller-ramp locking mechanism in the pilot clutch. The rolling elements force the pilot clutch against the drive clutch piston, locking it together with the multi-disk wet clutch to distribute torque equally between the front and rear wheels.
—John Lewis, Northeastern Technical Editor
At the heart of the all-new Chrysler Sebring Convertible is a 2.7-l DOHC 24-valve SMPI V6 engine that delivers 32% more horsepower and 23 more lb-ft of torque than the engine it replaces. This engine is 8-10% more fuel-efficient than the 2.5-l V-6 engine and is rated at 200 hp at 5,900 rpm and 193 lb-ft of torque at 4,300 rpm.
Among the design changes: a 26% increase in crankshaft stiffness due to changes in geometry, namely by optimizing: the distance between the main bearings and rod bearings; the size of the main bearings and rod bearings; and the diameter of the cylinder bores. By incorporating a structural, die-cast oil pan, increasing the number of fasteners (from two to six) holding the main bearing caps in place, and adding a structural beam that ties all the main bearing caps together, engineers also achieved a 28% increase in engine block stiffness. Premium seals and gaskets prevent fluid leakage, while cast-iron lined cylinders improve durability. And the block features oil drain passages cast right into the block that speed oil return, even under high-speed conditions.
Heat-treating of the aluminum block makes it stronger than conventional gray iron. Forged steel, instead of nodular iron, increases crankshaft strength.
The 2.7-(liter) engine has an intake-manifold design that improves fuel economy, and reduces emissions and noise. The design incorporates equal length airflow paths from the throttle body to each of the cylinders. For low-induction restriction, a larger throttle body, larger intake valves, and a large throat area sustain the high flow intake port and chamber. To further improve performance, Chrysler engineers reduced piston mass by as much as 15% and reduced tolerances of the rotating components.
—John Lewis, Northeastern Technical Editor
Steering and suspension
Now you don't need a Corvette to make flat turns. In several 2001 S- and CL-Class cars, Mercedes is adding active body control (ABC), which it introduced earlier this year on the flagship CL-500. The system governs both spring force and shock absorber rates by controlling four, fast-acting hydraulic servos, one between the body and each coil suspension spring, combined with electronically regulating shock-valve orifices, which changes damping. The system mitigates 0 to 5 hertz, driver-induced body movements and low-to-moderate amplitude bumps. In its normal mode, Mercedes says a 68% reduction of roll and squat motion is realized. If the driver selects the sport mode, the reduction jumps to 95%.
Thirteen ABC sensors measure body motion and vehicle level, and feed data every 10 msec to the two microprocessors that control the actuators. A high-pressure (2,840 psi) hydraulic system supplies servo muscle and allows rapid response. Twin hydraulic accumulators, one fore and one aft, aid in maintaining pressure to the actuators, and an oil cooler helps manage hydraulic fluid temperature.
An additional benefit of ABC is that the car does not require any stabilizer or anti-roll bars in its suspension. The system even has the capability, if the designers desire, to lean into a turn, much like a motorcycle.
—Rick DeMeis, Senior Editor
Toyota will release the first mass-produced gasoline/ electric hybrid vehicle in the U.S. next year. Configured in parallel, the engine and electric motor are connected to the drive train. This design allows the vehicle to be directly powered by the engine for on-highway use, and assisted by the electric motor for acceleration. In the city, it relies on the electric motor for stop and go and low-speed driving environments.
The company claims that the ratio of power provided by each system is constantly controlled to keep the vehicle in its most efficient mode to deliver a city/highway fuel economy rating of 52/45 miles per gallon. The primary power is provided by a 1.5-l gasoline engine with a peak power of 70 hp at 4,500 rpm. The engine is equipped for variable valve timing, maximizing efficiency across the full speed range. The electric motor is a permanent magnet design that produces 33 kW (44 hp) from 1,040 to 5,600 rpm.
Over 35,000 vehicles have been sold in Japan since 1997. However, the design for the American market is different. In Japan, drivers experience stop and go more frequently in a country in which gasoline is much more expensive than in the U.S. As a result, they typically care more about fuel economy than engine power. "When I test drove the 1998 Prius in Japan it was way too underpowered," claims a Ford engineer. "Low power may be acceptable in Japan because the driving conditions are different, but not in the U.S."
The engines are the same, but for the American market Toyota engineers have increased the engine speed to 4,500 rpm, delivering higher engine horsepower. A redesigned battery pack with a higher energy density also contributes to better handling. In the American Prius, thirty-eight nickel-metal-hydride batteries sealed in a carbon composite case provide a peak power of 25 kW (34 hp).
To further boost system performance, the Prius is fitted with regenerative braking. When the vehicle brakes are applied, the motor is turned into a generator, braking the vehicle while capturing kinetic energy and converting it into electricity to recharge the batteries. What seems like a simple solution to improve fuel economy, regenerative breaking requires sophisticated engineering to work properly.
—Darius Mehri, Technical Editor
Nissan will introduce a navigation system in several of its 2001 models that it says will be easier for drivers to use than alternative technology. Traditional navigation systems direct the driver through planar maps, which requires switching from wide, zoom-out views to detailed versions of the mapping area, potentially distracting the driver's view of the road. "Our research at the Nissan Research Labs in Japan showed that drivers are distracted by this constant zooming in and out," says Hiroshi Tsuda, director of intelligent transportation systems at Nissan. "Our research showed that to be safe, a navigation system has to do both of these functions simultaneously, so we came up with the BirdView idea."
The BirdView™places the driver's viewpoint at an altitude of 350 m and 1 km behind the vehicle. The resulting image is trapezoidal in shape, measuring 500 m at the bottom of the screen, 7 km at the top of the screen, and a spanning view of 7 km. The driver can thus simultaneously see a detailed view of the intersection at the lower part of the screen for guidance on what turn to make, while the upper portion of the screen displays a zoomed-out view so the driver can anticipate the distance of the next intersection.
Unlike conventional navigation systems', Nissan's new Birdview navigation system offers drivers both a detailed, close-in view and a zoom-out view (above) at the same time.
The team experimented with alternative solutions such as a heads-up display locating the mapping area at 2 to 3 meters in front of the car, or a split map showing a detailed map on the left portion of the screen and a zoomed-out area of the map on the right screen. "We found the BirdView system to be the most effective alternative because the driver is not distracted while on the road," says Tsuda.
Gathering mapping information for the navigation system is no trivial task. Satellite, GPS data, and conventional maps must all be collected, digitized, and put onto a CD-ROM. "To gather provide accurate information we also had to physically measure certain distances between key locations," recalls Tsuda.
An enhanced version of the system—currently offered on the Infiniti—is already available in Japan. It automatically downloads real-time traffic information that informs the driver of the most convenient route to take in case of inconveniences such as traffic jams. The system even warns drivers of harmful natural occurrences such as earthquakes or typhoons.
But as the saying goes, you can sometimes have too much of a good thing. "I was driving in Tokyo recently when the navigation system flashed an earthquake warning," recalls Fred Standish, manager of corporate communications, Nissan North America. "I was immediately afraid one of the city buildings would fall on top of my car, but then I realized the location of the earthquake was several hundred miles North in Hokkaido."
—Darius Mehri, Technical Editor
Teaming up with the Austrian driveline supplier Steyr-Daimler-Puch Fahrzeugtechnik (SFT), a team of GM engineers developed the VERSATRAK®all-wheel drive system, which uses front-wheel drive for ordinary road circumstances and automatically adds rear-wheel drive as necessary during travel over slippery road surfaces. "Its design is so light and compact that it fits under a flat rear load floor without any sacrifice to cargo space," says Mark Reuss, vehicle line executive for GM's crossover vehicles.
The mechanical system transfers as much as 44% of the engine's power to each rear wheel either individually or simultaneously as needed.
The VERSATRAK system incorporates a power take-off unit (PTU) mated to the vehicle's front-mounted transaxle. An aluminum driveshaft links the PTU with a rear drive module. Inside the rear module, twin Geromatic units react to any difference in the rotational speed of the front and rear wheels. As long as no speed difference exists, all power is directed to the front wheels. If one of the front wheels begins to slip, rear-mounted pumps pressurize fluid to engage clutches that redirect torque to one or both rear wheels. This helps the rear wheels to take up the slack, allowing the vehicle to keep moving forward despite muddy, snowy, or slippery road surfaces.
Built-in safeguards help prevent damage to the system from overload abuse. When using a compact spare wheel, the ABS wheel-speed sensors detect the spare wheel and tire and automatically prevent system engagement.
—Kevin Russelburg, Midwest Technical Editor
Backup obstacle-warning systems using ultrasonic transducers have been available for some time. Now Jaguar has taken the technology and applied it within the vehicle as part of its Adaptive Restraint Technology System (ARTS) to control passenger airbag deployment. The system is standard in the automaker's 2001 XK Series sports cars.
Four ultrasound sensors are located in the car's A and B pillars, and in a new roof console. These sensors determine the position of the passenger's head and torso relative to the air bag deployment door. If the passenger is too close to the dash, the air bag is deactivated and a warning light comes on to indicate inactive status. Once the passenger is sufficiently clear, the bag is active and the light goes out.
Jaguar says the ultrasound sensors mainly locate the head and torso, which are the two critical areas governing bag deployment. These detectors work in conjunction with a weight sensor in the passenger seat that determines the presence and weight of an occupant. These inputs allow the appropriate bag staging to be used, protecting smaller passengers, or preclude deploying the air bag if unsafe or there is no passenger—saving repair cost.
For the driver, a position sensor determines seat location relative to the steering wheel. On both driver and passenger seat belts, other sensors indicate to the system whether or not the seat belt is fastened. Within the vehicle structure, impact sensors on the front cross-member panel and on the sides of the car determine impact severity.
A central processor monitors all sensor data and will activate the seatbelt pretensioners and stage the air bags for full or partial inflation. While not revealing system suppliers and control details at press time, Jaguar does say that artificial neural network programming architecture was extensively used in developing the ARTS logic.
ARTS also includes new head-and-thorax side-impact airbags stored in the front seat backrests to protect the head and ribs. And the driver's air bag has a "star fold" pattern, which deploys the bag radially to cut the risk of injury for drivers who sit close to the wheel.
For the smallest among us, Volvo is introducing a rear-facing car seat that mounts to the worldwide-standard ISOFIX fittings in its cars. These fittings allow for a simple, correct seat installation process. Volvo selected the rear-facing seat based on company research showing that it maximizes spine, neck, and head support. Statistics support that research: in some 450 accidents involving rear-facing seats, not one child was killed or sustained life-threatening injuries.
Rick DeMeis, Senior Editor