Engineering News 7542

DN Staff

February 6, 1995

20 Min Read
Engineering News

Small engines face big changes

Engine makers look for new ways to meet emission regulations

Chicago--Ready or not, the $79 discount-store lawnmower is in for some changes. New emission regulations are forcing engine manufacturers to crank out a new breed of cleaner engines for lawnmowers, snowblowers, chain saws, and other outdoor equipment.

Though the proposed Environmental Protection Agency (EPA) regulations aren't scheduled to take effect until August of 1996, engine manufacturers already are scrambling to meet them. The toughest task, they say, will be to clean up the commodity engines used on mowers costing $100 and less. "There isn't much room for extravagant changes on a $100 walk-behind mower," notes George Gatecliff, chief research engineer for Tecumseh Research Laboratory in Ann Arbor, MI.

Still, the EPA and the California Air Resources Board (CARB) are set to make small-engine manufacturers comply with the 1990 Clean Air Act. At the federal level, the EPA has proposed emission regulations for engines used on automobiles, boats, and outdoor power equipment, among other items.

In outdoor power equipment, they call for reductions in nitrous oxides (NO), hydrocarbons (HC), and carbon monoxide (CO). The proposed regulations are particularly stringent for small engines. Non-handheld engines under 225 cc, for example, require HC and NO to measure 12 g/BHP-hour. In 1990, such engines averaged 37.7 g/BHP-hour, say engine manufacturers. That's a reduction of approximately 70%.

The regulations directly affect such companies as Tecumseh, Briggs & Stratton, Kohler, and other small engine manufacturers. But they also profoundly affect many original equipment manufacturers, such as Toro, which produce engines for their own equipment.

To meet the regulations, engineers are implementing a raft of design changes, including improvements in cooling, carburetion, ignition systems, oil consumption, engine timing, and air-flow control.

Key among those changes is improved carburetion. In the past, most small engines ran a comparatively rich fuel mixture as a way of ensuring good performance across a wide operating range. Richer mixtures, however, raise undesirable emissions. As a result, engineers must now find a way to make carburetors more precise. Key improvements involve finding more precise ways to drill, ream, and polish metering holes to remove burrs and imperfections.

Engineers also are abandoning "bump-compression relief" to help owners start their outdoor power equipment. In bump-compression relief, manufacturers form a tiny metal bump on the exhaust cam. The bump opens the exhaust valve when the user yanks on the starter cord, thus easing the pull-start process. After the engine starts, however, the bump keeps bumping and more hydrocarbons escape outside the exhaust port.

Now, bump-compression relief devices are giving way to mechanical-compression relief devices. Most use a protruding pin that retracts after the engine picks up speed. "Using mechanical-compression relief, the exhaust valve isn't open at an inappropriate time," Gatecliff says. The upside is fewer emmissions. The downside: higher costs.

Design improvements involve a heavy dose of finite element analysis and computational fluid dynamics. Using those computer tools, engineers analyze air-flow control and structural deformations related to engine sealing.

In some cases, manufacturers have decided that re-design is not cost effective. Kohler, for example, will continue to sell a line of side-valve engines to the construction industry, where the same regulations do not apply, rather than modify it for continued use in outdoor lawn equipment. For that market, Kohler will instead market the Command line, a series of overhead valve engines specifically designed with CARB regulations in mind.

Not every side valve engine, however, can be refocused toward another market. As a result, some may simply be discontinued. "In the worst case, a manufacturer may assess his side valve design and figure that he's so far off the mark that he does not know an economical way to get there except through a clean sheet of paper," says Glenn Keller, executive director of the Engine Manufacturers Association in Chicago.

Two-stroke engines, particularly those used in lawnmowers, face even more difficulties. Because two-stroke emissions are worse than four-stroke, experts fear that they won't meet new regulations for non-handheld equipment."They've put together a standard that two-strokes may not be able to approach," Keller says. "They're in serious jeopardy." Approximately 500,000 of the six million walk behind mowers sold each year use two-stroke engines.

The same regulations, however, won't apply to two-strokes used in handheld power equipment such as chain saws and line trimmers. Those devices must use two-strokes because of their lighter weight and ability to operate in any orientation. As a result, regulations covering handheld power equipment engines are less stringent.

Manufacturers also expect to make the handheld regulations apply to snowblowers. "In the winter time, snowthrowers are not a significant factor in CO emissions," notes Don St. Dennis, a spokesman for Toro. Roughly half of today's snowthrowers use two-stroke engines.

Equipment makers, too, face a new set of concerns. OEMs must now ensure that all new engines are properly certified. They can expect engine costs to rise. And they can no longer make changes to certified engines. "In the past, some customers put their own mufflers on the engines," explains Cam Litt, product manager for twin cylinder engines at the Engine Division of Kohler Co. "Now we won't certify them until we learn more details about their muffler."

Certification will be performed on a small percentage of products, but could cost between $500-$1,000 per engine.

"It's difficult to do and there's a premium price to pay," Gatecliff concludes. "But you get a better engine. And if customers use less fuel, they may get some money back."

Master Series 2.0 takes a bow

Milford, OH--Structural Dynamics Research Corp. has unveiled the second major version of its I-DEAS Master Series(TM) software. Available to engineers now, the new version includes 15 new software modules and hundreds of enhancements to the first Master Series product, which debuted in March 1993.

That first version, the result of six-and-a-half years of development, was a complete re-architecture of the company's software technology. But, there were some technical problems that sprang up after release, and SDRC expended considerable effort to correct them in maintenance releases.

Among the major new features and enhancements in Master Series 2.0:

Up to three times greater performance than previous Master Series versions in model display and response.

  • Improved capabilities for importing and using data from non-SDRC applications.

  • An improved shell operator allowing engineers to create thin-walled parts with a single command.

  • New analysis functions, such as the ability to apply a finite element mesh across disjointed surfaces, automatically calculate meshes based upon mid-surface geometry, and combined h-p adaptive model solution.

  • A Team Conference module that lets multiple users at different locations simultaneously view a model and interact.

Throughout development of the product, SDRC worked with customers to shape the features, functions, and performance of the software. Engineers from Asea Brown Boveri, Abbott Laboratories, AT&T, Fiat Research, Lockheed, Martin Marietta, Motorola, Siemens, Sony, Symbol Technologies, and the Williams Grand Prix Formula One racing team were part of the review team.

Laminate tackles transit vandals

Pittsfield, MA--Commuters who ride buses, trains, and subways will appreciate a new glazing material from GE Plastics. Cost-conscious transit operators will like it even more.

Called Lexan Nu-View, the new laminate will help keep windows of mass transportation vehicles scratch- and graffiti-free. Mass-transit companies should benefit as the new material is expected to double the life of standard polycarbonate windows.

The glazing consists of a Lexan MR5 polycarbonate sheet that features a proprietary abrasion-resistant Margard(R) surface treatment. The MR5 sheet is laminated with clear Lexan HPH abrasion-resistant film (0.10-inch thick) on one or both sides to protect the surface of the MR5 sheet from damage.

What makes the new material unusual, however, is that when the film becomes damaged from abuse it can be easily removed and discarded. As a result, the base MR5 material can remain exposed, effectively doubling the window's life.

"The Chicago Transit Authority (CTA) installed Nu-View laminate in several buses, and has been evaluating the product for over a year," says John Kramer, architectural industry manager for GE Plastics. "Not only have they enthusiastically endorsed it, but they have ordered more than 300 new buses with the laminate specified as original equipment. They also plan to retrofit their fleet of 2,000 buses with the laminate."

Cost-comparison studies conducted for the CTA demonstrated material cost savings of as much as 37% over the authority's current window-replacement program. Kramer adds that transit operators can implement a program with local laminators to take back Nu-View sheets and have the damaged HPH film removed and new film applied.

Lockheed applies co-curing to fighter-plane wing

Fort Worth, TX--As the Japan Defense Agency prepares its initial prototype of the FS-X fighter jet for a summer launch, at least one U.S. company will be on the first flight. Fort Worth-based Lockheed, in conjunction with Mitsubishi Heavy Industries, has designed the plane's carbon composite wing-box assembly using the innovative co-curing method.

Co-curing technology, which was recently transferred successfully from Japan to the U.S., allows composite parts to be cured simultaneously. This results in a single composite structure. The biggest benefit: A vast reduction in the use of conventional metal fasteners.

"For jets like the U.S.'s F-16, fastener placement is very dense on a component like the wing," states Joe Stout of Lockheed. "For the FS-X, we found that reducing that amount of metal through co-curing promoted significant weight savings."

Although the process of co-curing is not new for the aircraft industry, total wing co-curing is unequaled in its complexity, says Stout.

"This is particularly true when you look at the manufacturing and assembly complexity in a wing this size," he states. "Wingspan on the FS-X is about 11m, compared to 9m on the F-16."

Lockheed has no present plans to apply the co-curing capability to other projects, but Stout says the technology transfer has been an enormous asset "especially in the amount of time that would have been spent on research and development."

The FS-X, based largely on the U.S.'s F-16 jet air-craft, is designed to meet the Japan Air Self-Defense Force's support-fighter re-quirements, and is being produced exclusively for the Japan Defense Agency.

Redesigned Carrera still a Supercar

Seal Beach, CA--With the possible exception of Dick Clark, nothing looks-or acts-less its age than the 911 Carrera. For 30 years, Porsche engineers have massaged the original design, and the 1995 model is the most extensively revised ever.

Power comes from the 3.6-liter, air-cooled, flat six-cylinder engine. It produces 270 hp at 6,100 rpm and 243 ft-lb of torque at 5,000 rpm-up from 247 hp and 228 lb-ft in 1994. Credit the increase to the addition of hydraulic valve lifters; a dual-exhaust system; and a reduction in valve-train, piston, and connecting-rod mass. Engineers also cut weight by forming the valve covers, timing-chain covers, and intake manifold from composites.

The engine drives through a 6-speed manual or a new 4-speed Tiptronic S transmission. The Tiptronic S functions as a conventional automatic, or it can be shifted manually via steering-wheel mounted rocker switches. Electronic logic prohibits shifts that would overrev or lug the engine. In 2nd, 3rd, and 4th gears, early torque converter lockup further mimics a manual transmission.

In fully-automatic mode, five distinct program maps adapt to a driver's style by measuring speed, throttle input, and lateral acceleration. For spirited driving, the transmission downshifts during hard braking and suppresses upshifts while coasting.

Zero-to-60 mph arrives in 6.4 sec for the Tiptronic and 5.4 sec with the 6-speed. Both will hit almost 170 mph. In real-world driving, not drag races, the Tiptronic is a joy. With 5 gears it would probably outperform the 6-speed.

To tame the 911's notorious oversteer, engineers designed a new multi-link Lightweight-Stable-Agile (LSA) rear suspension that automatically toes-in during hard cornering. Price of entry for the Tiptronic S Cabriolet: $71,350.

Flexible sensors boost automotive quality

Flint, MI--Wind noise, water leaks, and squeaks topped the list of consumer complaints in a recent automotive survey by J.D. Powers. But a new thin flexible force-sensing system is helping engineers at the Cadillac Luxury Car Division (CLCD) of General Motors eliminate such problems.

The UniForce paper-thin sensor from Force Imaging Technologies, Chicago, gives engineers a new diagnostic tool in the quest for silent, leak-free window seals.

The 0.003-inch thick, flexible sensor appealed to GM engineers for window-seal analysis. "We started using the sensor very early in the development phase of the Riviera and Aurora," explains Sandra LaJoy, project engineer at CLCD. "Since the system is portable, you can use it pretty much anywhere."

GM engineers used the device to test Aurora and Riviera movable window seals. To accommodate the cars' clean design lines, the windows don't use a typical header section around the glass. Instead, the sealing system is incorporated in the interface where the glass meets the header, explains LaJoy. "We used the sensors at critical points to determine if pressure was creating a problem. If we found a problem, the sensor helped us to determine what type of change to make."

The single-point sensor allowed GM engineers to target specific areas. They then used data gathered by the system to better understand the manufacturing process and to make decisions about sealing design improvements. Says LaJoy: "The sensor reads to individual psi. Without it, we weren't able to determine a pressure value for these applications."

In the future, the sensor may find use for indicating pressure in applications where components must be tightened for correct sealing pressures between metal components-such as seals around headlights and decklids. UniForce systems can also be configured to monitor mechanical systems or provide feedback for controlling systems, say Force Imaging engineers. An Experimenter's Kit, including sensors, connector cable, a choice of three PC card interfaces, and software, costs $550 to $750.

Chip helps bring TV-video data to the PC screen

Armonk, NY--IBM Microelectronics has developed a chip for use on computer graphics cards that cuts the need for expensive video memory up to 50 percent.

Key to the new device: in-hardware conversion from TV-type video format, known as YUV, to the RGB format used by computers to display graphics. "It's a fantastic example of backing away from a problem and solving it," says Bert McComas, vice president of technology at In-Stat, a semiconductor market-research firm.

System designers have always faced a compatability problem when trying to display real-time video on a computer. Computers use the 24-bit RGB standard to display color graphics: 8 bits each to define quantities of Red, Green, and Blue. Color television, however, chose a format needing less information-only 16 bits, using half that to define luminescense (intensity) and the other half for color information. Thus, graphics cards which display video on PCs must find some way to convert the 16-bit YUV data for 24-bit RGB displays. This often slows the system by doing calculations in software, and takes up unneeded memory and bandwidth by expanding from 16 to 24 bits.

The IBM RGB624 High-Performance Palette DAC (digital-analog converters) includes fully programmable YUV-to-RGB conversion, allowing YUV data to be stored in the frame buffer and converted in real time as it is displayed. This eliminates the need for some video RAM. IBM officials say the device also permits simultaneous multiple pixel formats, to take advantage of a new Microsoft Windows programming standard allowing YUV and RGB data to appear on screen at the same time.

To display high-quality RGB video at 1024 x 768 resolution, a conventional graphics card needs just over 2 Mbytes of VRAM-requiring card manufacturers to incorporate 4 Mbytes of VRAM. However, with the new IBM chip, card makers need only 2 Mbytes of VRAM-a savings of roughly $80 for the manufacturer.

"For the cost of a mid-range graphics card, you get high-end performance," McComas says. Meanwhile, the new IBM DAC will cost only about $5 more than the older RGB524 it replaces. The new model is pin and register compatible with the earlier version.

Why not simply move over to YUV format for all computer displays, eliminating the need for conversion? Industry experts say that while superior for video, YUV does a poor job displaying digital text and graphics.

Electromagnetic welds provide speedy bonds

San Diego, CA--Engineers at the Consumer Products division of Rain Bird, Inc. are using an electromagnetic welding process to bond PVC valves and save time.

Rain Bird's molded anti-siphon valves work in agricultural irrigation systems to prevent contaminants from entering the fresh water supply. The valves require a pressure-tight, leak-proof seal in order to meet international plumbing regulations and the standards of the American Society of Sanitary Engineers.

"We used to solvent-bond the valve bodies," says Richard Garza, senior project engineer for Rain Bird. "That required additional equipment and floor space for staging, and emissions from the bonding agent caused problems." More importantly, the process required a 72-hour cure before the bonded assembly could be moved to the next operation.

Using an electromagnetic welding process from the Specialty Polymer & Adhesives division of Ashland Chemical Inc., Norwood, NJ, improves quality and saves time and money, says Garza. "Now we have about a 20-second cycle, and the part is ready for packaging," he adds. "It enhanced the overall manufacturing process."

The EMAWELD process uses the basic principles of induction heating by developing fusion temperature at the abutting surfaces of the two valve parts. A layer of electromagnetic thermoplastic provides good joint strength and low reject rates, say Ashland engineers. The process also finds use for hermetic and structural welds in medical, automotive, filter, and consumer applications.

Software tools that work together aid ATM design

Germantown, MD--Integrating their computer tools is helping Hughes engineers more easily design integrated products.

A Hughes Network Systems design team faces several challenges in developing an ATM switch for wide-area networks. ATM-Asynchronous Transfer Mode-is a fast, cell-switched technology that combines advantages of circuit and packet switching.

"At 155 megabits per port, ATM requires you to develop custom hardware to keep up with that data-transfer rate," says Michael Gilbert, a senior member of the technical staff working on hardware/software integration.

In addition, he says that incorporating Intel's i960 32-bit chip calls for more powerful debugging tools to deal with 32-bit address spaces and fast clock rates. He also needs sophisticated logic-analysis systems which can work with other software tools.

The Hughes team turned to Enterprise Instrumentation from Tektronix, which allows engineers to work with more than one tool at a time, as well as cutting and pasting from one tool to another.

"I use a ROM-based 960 debugger to examine memory and single-step through code," Gilbert explains. "I can download software to RAM and execute it using the networked Enterprise DAS to monitor software execution." This shows him what is going on at different levels, and makes it easier to track down bugs.

For example, he uses the Enterprise DAS's library of triggers to choose where to start a trace. He then gathers the trace on the DAS, uploads the trace to his workstation to print out a hard copy, and uses the editor to do complex searches on text or perform other code inspections.

Says Gilbert: "The combination of the visibility and control offered by the Enterprise DAS and my other debugging tools helps me figure out what's going on in my code and how to make the software coexist with the hardware aspect of the ATM system."

Spring secures surgical tool

Valencia, CA--When engineers at Micro Air Surgical designed a bone drill for orthopedic surgeons, they wanted a tool that would help correct hand and foot problems-not cause them.

The design called for the chuck to slide over the drill's nosepiece, "but the chuck was always falling off and hitting the surgeon's foot," says Micro Air Quality Assurance Engineer Linda Panster.

A substantial redesign to correct the problem would have been costly and time-consuming, and engineers were concerned about the loss of customers a production delay might cause. Instead, they worked with engineers from Bal Seal Engineering Co., Inc., Santa Ana, CA, to modify the design to include a coiled wire spring as a latching mechanism for the chuck.

Bal Seal's canted-coil spring uses inclining coils that deflect independently when compressed. The ends of the spring are welded together to form a complete ring, and the springs can be mounted in grooves on inner rods or inside the housing bore of a component. "It was a great fix," says Panster. "The spring saved us time and money, and it didn't change the cosmetic appearance of the hand piece."

Because of the relatively constant force and high deflection of the angled-coil design, the springs adjust to dimensional variations in mating parts. They also re- sist compression-set and fatigue when used within performance parameters, say Bal Seal engineers.

Today, Micro Air's power bone drill is widely used by orthopedic surgeons in Europe and the U.S., says Panster. The springs also are used in pipette tips, hip joints, and pacemakers.

Fasteners enhance connector design

Santa Ana, CA--Engineers at ITT Cannon wanted a simple, efficient way to join the shell and bracket of their electronic connectors.

Earlier connector designs used custom front shells with specially sized holes, which increased cost. The extra step of flaring the fastening hardware during installation added further time and ex-pense to the process, say Cannon engineers. So when they created the new Combo-D Sub connectors, they used standoffs from Penn Engineering & Manufacturing Corp., Danboro, PA, to streamline assembly.

"Our primary objective was to eliminate the need for a custom front shell," says Dave Palmer, product manager at ITT Cannon. The company replaced the fasteners with two Penn products: CONNECT'R WARE self-expanded thru-threaded standoffs for use with a screw, and SNAP-TOP standoffs for snap connection onto boards.

"We install these fasteners simply by pressing them into the shell assembly, and they expand into the front hole," explains Palmer. Now, the connectors use less-costly standard front shells, and the fasteners provide a cleaner surface appearance, say Cannon engineers. In addition, the steel standoffs provide the correct holding power without cracking the connectors' 0.030-0.040-inch-thick metal shell, adds Palmer.

The Combo-D series connectors are available in 19 contact arrangements. They combine signal with power and coax contacts for telecommunications and video applications.

Sign up for the Design News Daily newsletter.

You May Also Like