ausco (3) dm 8/12/04 11:23 AM Page 1 POWERTRAIN
BRIAN P. DENNIS BRAKING A COMEBACK
The off-highway sector is praising a redesigned mechanical brake that fits into tight packages, has low input efforts and eliminates any instability problems B
24 all-ramp technology has advanced greatly in the past decade. As the original inventor of the ball-ramp brake, Ausco Products, Michigan, has set out to change the fundamental design to meet the challenges of 21st century mechanical braking. Today's ball-ramp brake provides more braking in less space with less effort than any other mechanical brake design. These products are more stable, efficient, versatile, and problem-free than any of their predecessors. Their excellent service record, cost effectiveness and flexibility in application make them the brake of choice for mechanical braking in the off-highway industry. User benefits
Ausco's advancements of the ball-ramp brake have major advantages to the end
iVT INTERNATIONAL 2004 user and the OEM alike. These advantages include: · Low cost (compared to other wet, multi-disc mechanical brake designs); · Low-user input effort; · Equal braking in both forward and reverse; · Compact size and low weight; · Able to be actuated mechanically or hydraulically; · Excellent reliability and customer satisfaction; · Constant braking effort throughout the brake's life; · Long service life with minimal maintenance; · Low sensitivity to variations in friction resulting in consistent braking in all conditions ­ no `morning sickness'; · No lock-up potential; · Specifically designed for wet-brake systems, so no corrosion or rust potential. History of ball-ramp brakes:
The ball-ramp brake was invented and patented by Ausco in 1946. At the time, many vehicles were having trouble with pedal effort and fade on the old mechanical drum and band brakes. As vehicles grew heavier, the amount of force that an operator had to exert to achieve adequate braking was also growing. As the drum brakes got hot, they expanded, creating excess brake fade. This created a need for better braking systems. Ausco designed the ball-ramp brake to meet this need. The original design was called an energizing ball-ramp brake, which was a dry, double-acting servo brake that fed back friction from the brake into the actuating mechanism. This provided a `free' 30-40% boost in braking torque. The ball-ramp brake was originally intended for use in automotive ausco (3) dm 8/12/04 11:26 AM Page 2 POWERTRAIN applications, a market that was, at the time, in dire need of better braking. However, it was never successful in that market. While the automotive industry steered clear of the new fangled device, the off-highway sector did not. The agricultural and construction markets were quick to see its advantages ­ and they quickly became a standard product on many tractor lines during the the 1950s and 1960s. The design also found some success in military aircraft, not least of which was the carrier version of the US Navy's F4 Phantom. However, while the energizing brake was an improvement over existing designs in its day, it was not without its drawbacks, and was more susceptible to morning sickness, a dry-brake phenomenon that occurs when a brake lining absorbs moisture. The moisture causes an increase in friction and sometimes noise. It is called morning sickness because it is not uncommon to have aggressive and noisy braking first thing in the morning when the brakes have absorbed dew and moisture overnight. In an energizing ball-ramp brake, this phenomenon is a doubly worse problem, because the servo device feeds friction back into the actuator. As the friction becomes excessive, braking can become overly aggressive. Another disadvantage was the actuation linkage. The design was actuated by a scissors mechanism that had nonconstant mechanical advantage. As the brake wore, torque was decreased. The pull-rod force that actuated the brake was reacted by two cast lugs (or pins) which dragged against the actuator plates. This all resulted in a device that was approximately only 30% mechanically efficient. Changes in the market
Despite some of its shortcomings, the brake remained popular for off-highway use well into the 1970s. However, changes in technology and in the market created new needs for off-highway braking. The popularity of pure mechanical braking on larger machines waned as power-assist braking became more popular, while the popularity of dry brakes gave way to wet-brake technology. Unfortunately, the ball-brake's design was cumbersome to use in wetbrake systems. Customers were also demanding more braking force with less user effort, and the energizing ball-ramp brake was too inefficient to meet that need. Finally, the need to replace asbestos linings resulted in newer organic linings that were much more sensitive to moisture and resulted in more complaints of morning sickness.
iVT INTERNATIONAL 2004 25 ausco (3) dm 8/12/04 11:29 AM Page 3 POWERTRAIN Scissors mechanism mechanical advantage is reduced with wear Reaction pins: high drag forces impede actuator motion, resulting in low mechanical efficiency Lining acts directly on actuator plates ­ friction is fed back into the actuator creating potential instability ABOVE: Views of the traditional ball-ramp brake Fixed actuator allows the balls to provide bearing support ­ eliminates reaction pins and drag losses Pull forces are direct to the actuator ­ no reduction in mechanical advantage with wear Rotating actuator Needle bearing provides low drag, and eliminates friction feedback and directional sensitivity ABOVE: Ausco's new non-energizing ballramp brake proven to be a rock-solid performer that is free of service problems, as some of these application examples include: Wet multi-disc mechanical service/park brake for commercial mowers: The brake is an integrated package that mounts directly to an SAE B-mount hydraulic motor. This application has been in production for more than 10 years with excellent customer satisfaction. Cam-actuated wet, multi-disc ball-ramp transmission parking and service brake for a 25hp utility tractor: The brake has been in service for seven years with more than 125,000 units shipped. The service record on this product has been exceptional: to date, only 80 brake lining kits have been sold. Large, wet multi-disc mechanical parking with hydraulic service brake for an agricultural sprayer: The design is integral to the chain drive and contains the live axle shaft and bearings for wheel mounting. In-axle wet, multi-disc parking and service brake for European dumper vehicle: The OEM wanted to use pure mechanical braking with ultra-low pull-rod forces. Further, the duty cycle of the machine was very high, requiring up to three full-load braking events per minute. It was clear that the industry needed a mechanical brake which would fit into tighter packages, be easy to seal in wet environments, have lower input efforts, and eliminate any instability problems. Redesigning the ball-ramp brake
In the early 1990s, Ausco Products began making major improvements to the ballramp brake. The first application was a parking/secondary transmission brake for an agricultural tractor application. The tractor had been using a band brake which was incapable of holding the tractor on the required grade. The OEM wanted to remove a 23mm-thick gear from the transmission and put a brake into the space. This meant that a wet
TABLE 1: Features and benefits comparison chart brake with more than 9,000in lb of torque that would stop a 12,000 lb tractor from 30km/h was required, and the customer wanted to fit the brake onto a shaft space less than an inch wide. The resulting design (see above) is loaded with customer benefits ­ more braking force, improved stability, decreased user effort ­ all in a much smaller and less expensive package. Future advancements
Currently, Ausco is studying new materials and treatments to new and unique applications. These refinements promise to further improve the technology of the ball-ramp brakes and provide more braking effectiveness at a lower cost to the customer. The technology continues to move ahead, and undoubtedly, the performance and cost gaps between ballramp brakes and other mechanical designs will widen in the coming years. The advances that Ausco has made in ball-ramp braking technology have breathed new life into an old product with an entirely new range of product capabilities. The modern ball-ramp brake is more stable, more efficient, and more versatile than any other mechanical brake. They provide more braking in less space with less effort than any other mechanical brake design. While the concept of the ball ramp brake is very old, these improvements will ensure that the ball ramp brake will continue as a viable and preferred product for many years to come. The Ausco ballramp brake will be the mechanical brake of choice in the 21st century. iVT
Brian P. Dennis, PE, is product engineering manager at Ausco Products, Inc Building on success ­ easy applicability
Following a successful introduction of the brake into the off-highway market, Ausco began investigating new applications. The new technology was easy to apply to a variety of applications with multiple functionality. It has since
Modern, non-energizing brake Lower ­ fewer parts Excellent ­ no friction feedback, no lock-up potential Lower ­ up to 95% mechanical efficiency Designed specifically for these systems Very low ­ wet capable and constant torque with wear Excellent ­ virtually no field service issues Cost Control User input effort Wet brake capability Maintenance Customer satisfaction 26 Traditional energizing ball-ramp brake Higher Problematic, lock-up potential, sensitive to friction changes Higher ­ 30% mechanical efficiency Cumbersome to seal Higher ­ torque reduction with wear Complaints of morning sickness and corrosion iVT INTERNATIONAL 2004