4WS/AWS Vehicles 1987
4WS/AWS - Honda 4WS Prelude
4WS/AWS Vehicles
- Honda 4WS Prelude
1987 Honda Prelude with 4WS aka AWS
Can We Utilize the Rear Wheels of FF [Front-Wheel Drive] Cars?
The 1960s were a decade of dramatic progress in science and engineering. In space, NASA's Apollo missions fostered boundless dreams and aspirations, as man took his first glorious steps upon the surface of the moon. And on earth, people were beginning to see visions of an ever-advancing automotive technology. It all meant the promise of a bright future.
The rapid popularization of automobiles in the 1960s backlashed in the 1970s, however. Various problems began to emerge, from environmental pollution and traffic congestion to growing numbers of traffic accidents and recalls of defective vehicles. In response to public concerns, significant efforts were made to address these problems. The ESV (Experimental Safety Vehicle) program, led by NHTSA (National Highway Traffic Safety Administration, a U.S. agency), was one such effort.
The ESV's objective was to conduct a fundamental review of automobile safety, with the intention of lowering the rising tide of traffic accidents. It was a matter of global consensus, with automobile manufacturers around the world joining the program. With its automobile operations finally getting on track, Honda decided to participate in the program as well, though on a semi-official level. As a result, research was begun on an experimental safety vehicle.
Automotive safety generally falls into two categories: "collision avoidance" and "active safety." Honda's themes of research were explored from the perspective of enhanced active safety in the areas of maneuverability, stability and dynamic performance. In other words, the research aimed at developing responsive vehicles that could more easily avoid obstacles and, when necessary, come to a quick, complete stop. It was this research effort that ultimately laid the foundation for subsequent evolutionary developments in power steering. Another of the possibilities examined through Honda's research was a hydraulic suspension system designed to prevent centrifugal force from affecting the driver.
The assurance of active safety, which was the main target of the research, meant that Honda would have to identify fundamentally effective mechanisms in order to achieve better dynamic performance. At the end of 1977, Honda held a brainstorming session in the hope of returning to the basics through a review of fundamental vehicle structures. This brainstorming session gave birth to the concept of a 4-wheel steering (4WS) system.
Honda vehicles were at the time essentially front-engine, front-wheel-drive (FF) models. In an FF vehicle the rear wheels play a relatively minor role, since the front wheels perform around 80 percent of the steering, driving and braking. Compared to the front wheels, the rear wheels are merely in place as a means of support, ensuring that the car moves ahead in a straight and predictable fashion.
The brainstorming session produced certain discussions that led to an interesting fact: although there were cars with four-wheel brake systems and four-wheel drive, steering control was universally given to the front wheels. Naturally, they wondered if they could utilize the idle rear wheels to provide some steering function. With that, an initial concept was defined. The fact that only Honda had vehicles of FF specification made the idea all the more intriguing. If the rear wheels could be employed in a way that provided some steering control, dynamic performance would improve significantly. The research engineers began to ponder that question, and as they did their desire for a new challenge was awakened.
Ideas Become a Theoretical Model
Test equipment in Oguchi's laboratory at Shibaura Institute of Technology.
The development team's research made real progress, thanks to the drum-type bench tester.
At the Sixth Research Block of the Wako R&D Center, Shoichi Sano and Osamu Furukawa were deep in discussion as to how they should approach the concept identified in the brainstorming session.
The idea, after all, had not yet been approved as an official project theme, so the financial and human resources available to them were quite limited. Moreover, several projects were running concurrently at the time, making a proper development team even harder to come by. Data, too, was hardly sufficient, given the uniqueness of such a concept. For example, although they wanted to modify existing models in order to construct test cars, they didn't even know whether the front and rear wheels should turn in the same direction or in opposite directions. There were so many questions, due to the fact that a steering system based on four wheels would allow considerable flexibility in control. The key question was where to start.
Sano and Furukawa decided to build a theoretical model for the four-wheel steering system, believing it would help define the fundamental concept before the actual research started.
"It was interesting just mulling over ideas in my head, simply because it was such a new system," Furukawa recalled. "Nobody had ever driven a car with such a system before. I had fun just imagining myself driving it. I have to admit, it was something of an obsession. I was always thinking about the 4WS system, even when I wasn't working."
The theoretical model created at this stage eventually led the pair to the basic mechanisms, providing a dramatic motivation in the development of the 4WS system.
Four-wheel steering, however, wasn't an unknown concept.
Daimler-Benz had already developed four-wheel drive, four-wheel steering vehicles for the Forest Service. Their rear wheels were designed to turn in the opposite direction to the front wheels so that the vehicle could make sharp turns along narrow mountain roads. However, the specification had yet to be adapted for use in mass-production units. Even though it was effective in mountain driving, maneuverability was less than perfect elsewhere. Consequently, these cars occasionally had stability problems while being driven on Germany's famed Autobahn.
A special committee under Japan's Ministry of Transport once examined the merits of a vehicle whose rear wheels could turn in the direction opposite that of the front wheels, as part of discussions regarding the safety of large trucks. There was mounting public concern at the time regarding the danger of transport vehicles, particularly in instances where wide left turns were called for. The committee, too, concluded that a vehicle with four-wheel steering would be less stable at high speeds.
Furukawa's theoretical model substantiated these concerns, concurrently defining a direction as to how Honda should proceed. The fundamental principle identified by his model was that the front and rear wheels should turn in the same direction at high speeds and opposite directions at low speeds.
"We used figures to express an ideal car," Furukawa said. "It was one that could make quick, sharp turns, for which we made the proper calculations. And this was the answer we came up with."
The ideal control method for the four wheels was examined from a broader perspective, and those findings were then reflected in a concrete, theoretical model. This approach successfully outlined a 4WS system that was unlike anything before it. The principle mechanism won a basic patent in 1978, which further propelled Honda's development of the 4WS system.
The Test Car: From Theory to Reality
The 4WS test car created by fusing the front sections of two Accords.
Putting together two front sections, instead of modifying one complete vehicle to four-wheel steering specifications,
greatly enhanced the progress of development.
Another group outside Honda was studying a similar system at the time Honda had begun its research into 4WS. Oguchi's laboratory at Shibaura Institute of Technology, led by then assistant professor Oguchi was examining a steering-control system that would allow the front and rear wheels to move independently, thus moderating the negative effects of understeer and oversteer. Honda knew about Oguchi's research group, since the company had earlier commissioned studies on maneuverability and stability in mini cars. When Sano and Furukawa learned that the group was conducting research under a similar theme, they proposed that the two join forces. With that, the two-man development team gained a significant measure of support.
A key benefit of the joint research was the drum-type bench tester installed in Oguchi's laboratory. It was a device made of two drums placed in parallel at the front and back. A test car made of pipe frames was placed on top of the tester. The tester could evaluate maneuverability and stability under various conditions by changing the gearbox setting in order to obtain the desired steering ratios for the front and rear wheels. With this device Sano and Furukawa could substantiate their theory through the collection of quantifiable data. They also acquired other data, including an optimal steering ratio for the rear wheels. This proved very useful when filing the patent application for their aforementioned technology.
The two partners made rapid progress, and soon they were ready to test an actual vehicle. In April 1981, the first drive test was carried out on the west course at Suzuka Circuit. The test car was built from two Accords whose front sections were cut off and welded together to make one vehicle. The link mechanism that interconnected the front and rear steering mechanisms came courtesy of Oguchi and his students, who had fashioned it by hand.
"We had a good feeling about the outcome," Furukawa said. "Still, it was our first attempt, so we were very anxious to see what would happen."
Happily, the test results obliterated any concerns they might have had. The test car demonstrated a level of dynamic performance that far exceeded their expectations, in the process transforming a mere theory into reality. And given such a positive outcome, it was now possible for a formal 4WS development project to get under way.
The Shift from Speed to Steering Angle
The operating mechanism of the rear steering gearbox, which connects two crank mechanisms at different phases using a planetary gear
The control mechanism created through the joint effort, which turned the front and rear wheels in the same direction at high speeds but in opposing directions at low speeds, was initially conceived as a "speed-linked 4WS system"-a control mechanism directly dependent on the speed of the vehicle. However, it required a gear-ratio control in order to successively link the wheel-turning actions in two different directions. Accordingly, a new mechanism had to be developed by combining an electronic control device and variable gear-ratio mechanism.
The layout of such a system would prove to be a difficult, but not impossible challenge. However, excessive complexity could result in problems during production, that would be reflected in the market. Therefore, further discussions were held in order to simplify the system. Eventually, the review process led to a theoretical shift in linking the control function to the angle of steering rather than the vehicle's speed. This became the starting point for a "steering-angle sensing 4WS," which would control the rear wheels in accordance with how much the steering wheel was turned.
This is easier to understand by imagining what one does when driving a car. When changing lanes on a highway, the steering wheel is turned only slightly. However, there are situations in which the steering wheel must be turned considerably more, such as when parking the vehicle in a garage. In view of enhanced dynamic performance, the front and rear wheels should turn in the same direction at high speeds and in opposite directions at low speeds. But when steering angles are applied to this principle, the front and rear wheels should turn in the same direction at smaller angles but opposite directions when greater angles are applied.
Honda had, in fact, already included this concept in a patent the company obtained in 1978. However, it all became a reality with the development of a new crank mechanism, which was designed to turn the wheels in the same direction initially but in opposite directions after a certain point. For example, when the steering wheel was turned to a large angle, the wheels would turn in the same direction for a brief moment after the steering wheel starts to rotate. Then, as the angle of steering increased, the rear wheels would turn toward the opposite direction. One problem had to be resolved, though, in order that the mechanism could be utilized. With a single crank mechanism, the wheels could only be turned at certain instances, regardless of whether the front and/or rear wheels were turning in the same or opposite directions. With the car traveling at high speed, the desired control could be achieved with the rear wheels turned just one or two degrees at most in crank angle. On the other hand, an offset of approximately five degrees would provide more effective control during low-speed maneuvers. In that regard it would not make sense to use only one crank. Therefore, it was decided that the combination of two cranks would overcome the drawback. This led to the development of a simple mechanical system that would not rely on an electronic control device or other such complexities.
High scores were given to the complete 4WS system at its initial evaluation. Even Tadashi Kume, then the president of Honda R&D, was impressed by its simplicity and effectiveness. The achievement was the fruit of hard work by the development staff, who at each occurrence of difficulties used a calm, analytical approach in order that the project could move forward. Simplicity was their byword, and in all respects the 4WS system satisfied that.
The New Concept: A Hard Thing to Promote
The rear steering gearbox used in the 1988 Prelude
It is only human nature that people are suspicious and skeptical of things they do not fully understand. This was certainly true of Honda's 4WS system, which would be a challenge to sell in the marketplace. Compounding the problem was that four-wheel steering control is very complex, making the benefits difficult to understand simply by describing the specifications. It would be hard for anyone to understand just how much the maneuverability and stability have improved without actually driving the car and experiencing its effect. When basic research began, there were as many doubters in the company as there were believers. Some expressed their doubts in an outright fashion, saying that the rear wheels should not turn and that using them for steering control could never work. But as the 4WS development project progressed, moving toward the D-development stage, Furukawa, the newly appointed LPL, had to think of ways to promote confidence in the new system.
Problems were nevertheless manifested in the D-development stage that the team hadn't even imagined during the R-development phase.
For instance, the 4WS system would need long link shafts, but those wouldn't fit on the production line because all extraneous space along the line had been eliminated for maximum efficiency. Suspension alignment, too, became an area of concern. With a conventional vehicle, the alignment process simply requires that the front wheels be adjusted against a fixed reference point,-the rear wheels. But in a car equipped with a four-wheel steering system the body would have to serve as the reference, necessitating changes in the equipment and process used.
Regardless of any possible benefits it might offer, a technology can not be applied to products if it requires an excessive investment, since that will only force the cost of those products higher. To solve the problem, the factory had to work hard to find ways of controlling costs.
Furukawa knew he had to do something to alleviate the sense of doubt that was becoming prevalent among the factory personnel and other staff. So, while working to solve the problems at hand, he decided to give his colleag-ues an opportunity to drive the car themselves. After all, it was the only way for them to experience the sensation of a 4WS system, and the only way to understand its potential impact.
Furukawa formed a 4WS promotional committee so that test drives could be arranged for factory and service personnel. It was through such tests that the people who would actually produce the final product came to perceive it as an entirely new level of dynamic performance. In fact, the test drives not only facilitated communication among all involved, they also sparked enthusiasm about Honda's exciting new technology.
Eventually, the associated staff people at Honda's overseas offices, along with journalists and officials from certifying agencies, were invited to try the system, thus nurturing an accurate understanding of 4WS.
Malicious Tests and Local Adaptability Tests
Exhaustive studies were carried out to identify and eliminate the problems that might occur in the marketplace. Even though the cars were to be driven by different users in different ways, it would be impossible to predict every condition the vehicle would encounter. In other words, it was possible that problems could occur outside the context of what the design engineers had anticipated. To minimize that possibility, trial tests were conducted in various practical settings.
A series of "malicious tests" was devised, so named because the test conditions were set to simulate overly adverse situations that were unlikely to occur during normal use. For example, one test examined whether the steering function would work when the driver started the engine and turned the steering wheel without knowing that one of the rear wheels was caught in a ditch only as wide as the wheel's rim. Another test would determine whether the system would break down during operation if the car was used in a cold climate such as Hokkaido's with the rear wheels frozen under a mantle of snow. Numerous other scenarios were considered, during which all system functions were verified in detail.
The development team even held a number of local-adaptability tests in Europe, along with test drives for personnel at Honda's overseas offices. These helped identify problems during actual driving, as well as driver responses to them. This had all been designed to incorporate user feedback into solutions that would further enhance the system's performance. Of course, there were a few mishaps. During one test drive, a driver who was overly confident in the system approached a corner at excessively high speed and smashed right through the guardrail. Nevertheless, marks for the system were very high and every office in Europe gave it a "thumbs-up." The results couldn't have been more satisfying.
The world was now ready for another first. In April 1987, Honda's unique steering angle sensing 4WS debuted in the form of a stunning new, high-performance Prelude. The system had indeed opened doors to an entirely new perception of automotive possibility.
The Importance of a Challenge
Over a ten year period, Honda's new 4WS system had evolved from the basis of a casual comment-a simple idea-to the production of a car that would set a new standard in handling and dynamic performance. Yet, the reason for Honda's technical leadership was equally simple: use a theoretical model to identify the fundamental principle of operation. Once that was achieved, the other aspects of development would follow suit. And in that regard the final outcome was truly an extension of the original idea.
"We were able to define what we could achieve by turning the rear wheels," Furukawa said, "and that understanding proved to be a real boost. Once we had the concept, we only needed to embody it by experimenting with ideas and solving problems."
The theoretical model's significance is reflected in the fact that it is now a popular method among researchers. Simple in form yet applicable to the most advanced theory of control, the model has been used in various studies, including those leading to today's suspension-control technologies and active, left/right braking systems. In that regard, Honda's development of 4WS became the foundation for many subsequent theories of automotive control.
"It was the desire to bring what we believed to the world, and to see it accepted by users," Furukawa explained. "That's the thing that made our R&D process work."
The act of innovating, then, stemmed from the search for ideas the development team could use to realize a goal. Each time they encountered a problem, they had to stop and find a solution. They knew that failures would occur despite their efficiency in seeking the target-that was simply the price of success. Ultimately the technology they had so diligently endeavored to achieve became a product, and it was well received in the market. It was a real benefit to their confidence as engineers.
"When the 4WS system was in development," Furukawa said, "I truly believed that I was creating a technology. But when I look back at it now, perhaps it was the 4WS technology that was nurturing me."
Honda's 4WS system undeniably established a new standard in driving performance, but without a doubt it did something more. It brought creative minds together in a solution that would one day benefit the automotive world.
Copyright, 2008 Honda Motor Co., Ltd. and its subsidiaries and affiliates. All Rights Reserved.
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4WS/AWS Part 4 - GMC introduces "Quadrasteer" on Sierra Denali
4WS/AWS Vehicles
- GMC introduces "Quadrasteer" on Sierra
The Sierra Denali sports new roof mounted marker lights and flared rear shoulders. Note the angled rear wheel in this shot.
GMC Unveils Three Technologies That Will Change Your Pickup Truck Forever
By: Michael Levine and John Gillies
08 July 2001
PickupTruck.com
Who says you can't drive concept vehicles? Well, you still might not find GMC's Terradyne parked in your driveway anytime soon but in the near future three cutting-edge, concept-worthy technologies will change the way you drive and use your pickup.
We spent two days with GMC in La Jolla, California getting familiar with four-wheel steering and two new powertrains featuring automatic cylinder shutoff and hybrid gasoline-electric propulsion.
Quadrasteer
Back in 1988 Honda became the first auto maker to introduce four-wheel steering, in its compact Prelude sedan. About the same time GM was showcasing a much more advanced version of four wheel steering in its Blazer XT-1 concept vehicle. For whatever reason the feature never took off, probably because the Prelude's purely mechanical setup didn't provide much benefit in the already nimble car and the XT-1's system was as complex and expensive as a NASA X-plane.
Enter the 2002 GMC Sierra Denali, the successor to the 2001 Sierra C3. The Sierra Denali makes an already outstanding truck even better with the addition of Quadrasteer four-wheel steering, aka QS4.
Quadrasteer electronically controls the rear wheels at different speeds and under various load bearing conditions to create an amazing amount of agility and maneuverability - especially when towing or parking. The rear wheels turn in proportion to the front up to a maximum 12-degree angle depending on vehicle speed and driving mode. 12-degrees may not seem like a lot but consider the following: at 37.4 feet the Sierra Denali's turning radius in four-wheel steer mode is only three inches greater than that of a three door Saturn coupe! That's almost 10 feet smaller than the 2001 Sierra C3 was capable of performing! Quadrasteer on the 2002 Sierra Denali is a game-changer.
The 2002 Sierra Denali's turning radius is almost 10 feet smaller than the 2001 Sierra C3.
Quadrasteer steer-by-wire rear axle is controlled by two sophisticated microprocessors. At low speeds the rear wheels turn in the opposite, or negative, direction of the front wheels up to a transition zone of around 40 to 45 mph where the rear wheels track neutrally. At speeds over 45 mph the rear wheels turn in concert, or positively, with the front. If at any time the two microprocessors 'disagree' over the steering information they have received QS4 automatically shuts down and reverts back to traditional two-wheel steering.
Located on the dash of the Sierra Denali is a push button Quadrasteer control panel similar to the four-wheel drive control panel found in many trucks today. The driver pushes the button to change steering modes from two-wheel steer (2WS) to four-wheel steer (4WS) to four-wheel steer tow (4WS TOW). In 4WS mode the rear wheels turn up to the maximum allowable amount below 40-45 mph. The wheels transition and turn in the same direction as the front above this speed. When towing, Denali drivers can select 4WS TOW. 4WS TOW reduces the amount of rear wheel steer at slower speeds, when the wheels are turning in opposite directions, but increases it at higher speeds when the wheels turn in the same direction.
With Quadrasteer, drivers can select 2 Wheel Steer, 4 Wheel Steer or 4 Wheel Steer Tow Modes using a push button control panel on the dashboard.
Created in an exclusive partnership with Tier 1 supplier Delphi automotive, GMC won't comment on how long this arrangement will last. Dana Corporation provides the Sierra Denali's axle and Delphi completes the final assembly, adding the electronics and delivering the final unit to GM's Oshwa, Ontario plant where the Denali is produced.
The Quadrasteer system adds a weight penalty of about 285 pounds to the truck but gives back this amount and more in additional towing and hauling capabilities over the C3. The rear axle's weight rating increases by 250 pounds to 4000 pounds and maximum GCWR (gross combined weight rating) climbs from 14000 to 16000 pounds. Trailering capacity has increased from 8700 pounds to 10000 pounds. The wider rear axle also provides more stability when towing.
Sam Mancuso, the Sierra Brand Manager, proudly proclaims, "The Sierra Denali is the most capable _-ton pickup truck available in its class. There is nothing else like it from Ford, Dodge or Toyota."
The addition of Quadrasteer has required some exterior changes to the Denali further setting it apart from the C3 and adding more testosterone to the truck. The first things you notice are the muscular, composite shoulders added over the rear wheels to accommodate the wider rear axle and turning requirements. Overall body width has grown from 78.5-inches to 83.5-inches. Government regulations stipulate the trucks over 80-inches in width also include roof mounted marker lamps and fender mounted clearance lights so the Denali looks almost like an athletic dually at first glance.
Trailer towing becomes much easier with Quadrasteer engaged. The Sierra Denali's pivot point shifts from the front to the rear wheels providing more maneuverability
We took the Sierra Denali out first-hand to test drive the Quadrasteer's towing and trailer-free capabilities.
The first Sierra Denali we drove came with a 30-foot, 7500 pound trailer attached for a GCWR of 14500 pounds.
GMC engineer Gene Rodden took us out to a closed course, marked with cones, to test out Quadrasteer's maneuverability. Attempting to tow in 2WS mode quickly demonstrated how challenging towing can be and the large amount of attentiveness required by the driver to clearances, the length of both vehicles and placement of the trailer axle. Needless to say the course was not optimized for 2WS trailer towing resulting in the senseless mutilation of multiple orange traffic cones.
Switching to 4WS TOW mode to run the same course again, Quadrasteer provided a clear improvement in maneuverability, measurably improving the driver's level of confidence and margin of error in moving the trailer around and meeting clearances in corners. The cones were also a lot happier.
An interesting demonstration of rear wheel movement was shown in response to increased throttle while holding the brake on. Quadrasteer is also sensitive to throttle response not steering alone. 4WS TOW angles ranged from 7 degrees, increasing to 12 with full lock for low speed maneuvers. Reversing the truck lowered the tolerances and reduced the steering angles available for maneuvering the truck. Not that it was a rally course, but rounding the cones at a decent clip seemed to make trailering easier than maneuvering at very low speeds.
We left the trailer course to make our way to Highway 52 outside San Diego.
Navigating surface streets with the trailer and heavy morning commuter traffic proved to be quite easy with Quadrasteer. When making right turns you could actually keep the Denali in the right lane of the street you had just turned onto. No more wide turns into the middle or left lanes. And when making U-turns the only word that came to mind is amazing. We made a U-turn onto a three lane road and were easily able to make the middle lane towing the 30-foot trailer!
On the freeway Quadrasteer shined again. Lane changes at 60 mph were seamless. The synchronized movement of the front and rear wheels at these speeds reduced the articulation angle between the Sierra and trailer. Reduced side forces acting on the trailer made the entire platform more stable.
If you didn't know you were towing a trailer and looked in the rearview mirror, you would think someone was tailgating.
Rodden remarked that during separate road testing on highways in high wind conditions in 4WS TOW mode the truck / trailer combo was also much more stable than in standard 2WS mode.
The Sierra Denali sports new roof mounted marker lights and flared rear shoulders. Note the angled rear wheel in this shot.
The second Sierra Denali we drove was unloaded. Like last year's 2001 Sierra C3 we drove the Denali displayed the same great on-road driving characteristics.
As the only currently produced all-wheel drive pickup, Quadrasteer enhances the driving experience so you feel like you are driving a luxury sport sedan, albeit a very tall one. On twisty mountain roads the truck was outstanding.
There was no mention of pricing for the 2002 Sierra Denali, but we expect the truck to come in somewhere just north of $40,000. That's a hefty price tag for an extended cab truck. Clearly this is a truck for early adopters but we do expect Quadrasteer to quickly appear on other, less expensive, GM trucks.
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09-03-2011, 04:41 PM
رد: 4WS/AWS Vehicles 1987
