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FOCUS ON: BUS SUSPENSIONS


TABLE OF CONTENTS The Hendrickson Story 3 Data dictates comfort 4 By Gerry Remus

Understanding vehicle stability and handling 5 By Gerry Remus

Transit’s weight loss problem 6 By Gerry Remus

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T H E

S T O R Y

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he Hendrickson story began in 1913 with the founding of The Hendrickson Motor Truck Company by inventor and businessman Magnus Hendrickson. This small Chicago-based manufacturing company built trucks often equipped with cranes, which were used to haul stone and other building materials. In 1978, The Boler Company, whose holdings included manufacturers of leaf springs and metal bumpers, purchased Hendrickson. In the years that followed, Hendrickson would expand into or acquire additional businesses in related areas—trailer suspension systems, auxiliary axle systems, springs, metal bumpers, and other heavy-duty components. Eventually Hendrickson sold the truck manufacturing operation to focus solely on suspension systems and related components. Today, Hendrickson is comprised of state-of-the-art facilities, technical centers and manufacturing centers, in the United States, Canada, Mexico, the United Kingdom, France, Austria, Romania, Turkey, India, China and Australia. Hendrickson is a leading manufacturer and supplier of premium bus chassis components to global bus markets. Utilizing world class design, testing and validation capabilities, Hendrickson provides robust solutions that feature the ride quality, vehicle handling and stability required for bus applications around the world. Hendrickson’s goal is to be positioned as an extension of our customers engineering and product development team, leveraging our technical expertise to execute vehicle integration projects and to bring customized solutions for specific applications. Product lines include: • Air Suspensions • Steer Axles • Steel Leaf Springs • Bumpers • Brakes & Wheel-Ends

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Data dictates

COMFORT By Gerry Remus

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s urban population trends continue to rise, so has the need for an infrastructure to handle these increasing demands. A tremendous opportunity exists for buses to satisfy the need to transport the growing population in a safe, reliable and comfortable manner. Bus manufacturers are challenged with providing solutions that can maximize the number of passengers, maintain the highest level of durability and to ensure passenger safety and comfort. The suspension system and axles are at the root of the bus experience and influence the vehicle in three primary ways: safe handling for the driver, ride comfort for the passengers and reduced vibration that saves wear and tear on the bus body and other components. Bus operators tend to think of ride comfort first when they make the move to an air suspension system. However, suspensions protect more than just the passenger; contributing to safe handling as well as ensuring long life for the vehicle, a substantial investment. While buses around the world may have a similar look and feel, the passenger and equipment loads, environmental factors, road conditions and braking cycles can vary greatly between countries, states and even cities. For example, the potential to overload a transit bus operating in the U.S. is unlikely. However, in more populated countries, such as India and China, overloading can account for up to 40 percent of the rated capacity of the suspension. For these reasons, one suspension will not fit for all markets and consideration must be given to these regional differences to ensure optimal performance.

Understanding ride comfort A principle function of the suspension system is to absorb as much of the vibration and harshness as possible. Ride quality hinges on the degree of isolation the suspension provides the vehicle from vibration and road inputs. It is a measure of how road shock affects the vehicle, driver and passenger as the vehicle encounters bumps, potholes or other road irregularities. Air bags and shock absorbers work together to offer a smooth ride with one passenger on board or with 50. The challenge is to build in ride comfort while maintaining roll stability and vehicle handling. Not all suspensions are created equal, so choosing the right suspension to meet the needs for a given application is critical. Hendrickson, for example, places high value on relationships with bus manufacturers to understand their expectations, needs and wants. The bus OEM typically defines the desired ride quality for their product. In some instances, vehicle handling may be more critical than ride comfort or roll stability may be the priority for the OEM. Once the goals for ride quality are set, building in ride comfort begins by collecting data that defines the application. Hendrickson takes a total vehicle approach, understanding how products are influenced by other chassis components and what factors can change performance. Before design work begins, it is essential to understand everything possible about the environment that the bus will be operating in. Hendrickson goes to great lengths to collect real-world data to 4

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A virtual bus performs a lane-change maneuver using Hendrickson’s advanced simulation software. Before building physical parts, this unique software allows the company to understand how a vehicle will behave in key performance areas like ride quality, roll stability and vehicle handling.

determine the specifications necessary to maximize performance and durability. Extensive data collection from the field along with customer interviews and site visits enable Hendrickson to get a true understanding of what a product must endure while in operation. Ensuring durability and performance Understanding real-world scenarios is essential, but this alone is not enough to bring a solution to the market. Hendrickson invests in the most advanced engineering software to model specific components, identify stress points and simulate suspension performance in different application environments and load conditions. As the design matures, sophisticated in-house research and development facilities are utilized, featuring numerous test rigs designed to simulate realworld scenarios, to ensure that reliability, performance and quality objectives are met before finalizing the design. Once a suitable design has been created, track testing commences and final design refinement occurs as the product endures tests that emulate real-world conditions and are correlated to industry or OEM test tracks. In proving-ground testing, Hendrickson utilizes test tracks that replicate the actual Altoona test track so that a firm understanding of durability and performance are well known. Hendrickson has a rich history of providing the right product for the right application, which requires a series of critical steps to ensure many years of successful operation in the field. As the bus market needs continue to evolve, Hendrickson stands ready to support our customers, developing solutions that exceed expectations for performance and durability. Gerry Remus serves as business unit director – Global Bus for Hendrickson Commercial Vehicle Systems, Woodridge, IL. Visit Hendrickson online at www.hendrickson-bus.com

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Understanding vehicle stability and handling By Gerry Remus

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he primary role of a suspension system on a bus is to offer a level of protection to the vehicle itself, the passengers and for the driver. While the ride quality of a bus garners the most attention, the stability and handling of a vehicle play a key role in how the bus performs on the road. Ensuring that the bus operates in a safe and predictable manner requires the appropriate roll stability and handling performance from the suspension system.

Roll stability is a measure of how well the suspension and chassis resist swaying or any lateral motion. A vehicles’ roll stability is most apparent when in a turn or on a highway off-ramp, where the passengers feel their body leaning or shifting; this movement is defined by a term called “head toss.” The suspensions stiffness is a primary contributor to the vehicles roll stability and defining what is appropriate for a bus lies in how the passenger responds to road events. As an example, while driving through curves or on stretches of road with potholes, a suspension with high roll stability can cause the passengers’ heads to toss side to side in a jerking motion. While this may be okay when driving in a dump truck, this is not the feeling a passenger wants on a motorcoach or transit bus; the preference would be to have a smooth, controlled swaying motion as the vehicle maneuvers. This is where suspension design becomes critical, developing a balance between the appropriate stiffness to safely carry the bus body and chassis while meeting the passengers’ expectations of comfort. Handling is a measure of how well the suspension and chassis optimize the cornering performance of the vehicle in reaction to inputs by the driver at the steering wheel. Handling determines how fast you can drive and what kind of turns you can make while maintaining control of the vehicle. A suspension with good handling characteristics can give the driver greater control and road feel during tight road maneuvers or lane changes. As a passenger, you want a vehicle that has predictable handling to ensure a safe, comfortable ride. The key performance metric for vehicle handling when it comes to a suspension is called roll steer; a vehicle can be characterized as having oversteer, understeer or neutral steer. In an oversteer condition, the vehicle will feel like it is pushing or plowing through a turn. This is viewed as safer and more stable for the driver. With understeer, the vehicle will feel loose or that the tail of the vehicle is coming around into a corner. For the driver, this is directionally unstable or loose. The neutral steer condition is preferred for the bus application, where the vehicle responds exactly as expected when the driver applies steering inputs. Suspension geometry has a direct influence on vehicle handling, specifying the right product with the right characteristics provides drivers the confidence and predictability required for controlling a vehicle filled with precious cargo.

Looking ahead to the next generation of buses, there is growing demand for alternative fuels which changes the complexion of the bus. This will have a definite impact on the areas of stability and handling as the center of gravity changes and additional tanks are mounted on the roof or along the chassis frame. As the center of gravity shifts, frame & body structures are reinforced for more rigidity, causing changes to how the vehicle behaves. This drives the need to evaluate changes to the suspensions kinematics, or functional design, to ensure buses continue to operate in a safe and comfortable manner moving forward. As a suspension system provider, Hendrickson goes to great lengths to understand vehicle performance needs now and into the future. Partnering with OEM’s and integrating into chassis and body designs is essential to achieve these objectives. Gerry Remus serves as business unit director – Global Bus for Hendrickson Commercial Vehicle Systems, Woodridge, IL. Visit Hendrickson online at www.hendrickson-bus.com

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Hendrickson Suspension: Transit’s weight loss challenge By Gerry Of the many obstacles bus operators face today, maintaining or lowering the bus curb weight while complying with regulatory mandates, emission standards and evolving passenger needs is a key challenge facing our market today. The modern transit bus has come a long way over the years with many positive changes to passenger comfort and accessibility, alternative fuel usage, and adoption of technology that improves bus safety and security. While these changes are positive overall, they often times mean incremental weight to the bus. One example relates to alternative fuels, which can add up to over 2,000 pounds of weight to a typical transit bus. The mission to counter these additions and lower overall vehicle weight is of paramount importance. The industry has a few options to address the problem. • Change the rules to allow buses to run heavier and accept the consequences that this will ultimately impact the infrastructure. • Encourage OEMs to add additional axles to spread out the heavier loads, at additional cost and manufacturing complexity. • Engage in “lightweighting.” The most sure-fire way to cut out the weight is through improved specifications, seeking out lighter weight materials or developing efficient designs in a process known as lightweighting. As new materials and manufacturing methods progress, it’s becoming easier and more cost effective for manufacturers to achieve a lighter weight chassis and body components. Buses are getting heavier and, as a key industry supplier partner for the bus market, Hendrickson places heavy emphasis on lowering gross vehicle weights while optimizing for performance and long life. For transit buses, this aids in offsetting the mounting increase in weight of additional systems and componentry. Hendrickson’s approach to lightweighting is three-fold. The first approach is design efficiency. Hendrickson starts with a true understanding of the application and what the suspension or axle must withstand to meet the customers performance & durability requirements when in real world operation. With this knowledge, non-essential weight can be eliminated and the components can be designed to meet the application needs. Hendrickson utilizes advanced methods of design, analysis and testing to drive out weight while delivering best-in-class reliability and achieving the benchmark for performance. Second, integration of components to create systems is used to reduce weight as well as cost; essentially combining two or more components into one to arrive at efficiencies. One example of how Hendrickson is approaching component integration for buses involves the next generation of steer axle and braking systems. Air-disc brakes have become very common in many bus applications. The axle installation of an air-disc brake requires a torque plate to attach the brake to the axle; this is a wasteful component that adds cost and complexity to the system. Hendrickson has pioneered a way to integrate the torque plate into the axle structure, reducing weight and simplifying assembly by 6

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An example of a transit bus suspension component under analysis. Hendrickson utilizes advanced software & proprietary analysis techniques to design lightweight part while ensuring maximum reliability and performance.

reducing the part count. Having one supplier deliver a system also benefits the OEM and end user in the area of parts and service support; one point of contact for a particular system. Third, Hendrickson has broad expertise in the use of lightweight materials. Hendrickson has a number of options to balance cost and weight through the use of different materials for each product need. Robotically welded, steel fabrications are a core competency at Hendrickson that result in a very positive cost to weight ratio. In addition, aluminum castings are a great option for applications where weight is paramount. Composite materials have emerged over the past several years for the heavy duty segment and the future looks promising as this lightweight technology is proven on the road. Having the ability to draw from a multitude of material options allows Hendrickson to meet customer objectives. Looking ahead, the pressure to add weight to transit buses will not subside and changes will be made that affect the future transit bus. While a number of strategies need to be employed to tackle this issue, Hendrickson stands ready to deliver lightweight, reliable suspension & axle solutions that improve driver handling, passenger comfort and overall equipment protection. Gerry Remus serves as business unit director – Global Bus for Hendrickson Commercial Vehicle Systems, Woodridge, IL. Visit Hendrickson online at www.hendrickson-bus.com.

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