Kneeling systems have become widespread on custom wheelchair-accessible vehicles from BraunAbility and other accessible-vehicle converters. Here linear actuators lower vehicles’ rear suspension to reduce the incline angle of wheelchair ramps for easier access. Because the actuators typically mount under the vehicle chassis, they must be rugged.

“Our vehicles typically kneel 2.5 to 3 in. We add a mount near the shock absorber or lower outboard A-Arm pivot and attach a chain that typically runs up into the body and attaches to an actuator,” said Mike Laird, BraunAbility Senior Engineer and Commercial SE Vehicle Manager.

One inch of kneel reduces the ramp angle by roughly one degree, so kneeling yields 2.5 to 3° — a seemingly small angle that significantly reduces the effort a wheelchair user needs to exert to get up the ramp — and that’s a critical feature for someone with limited mobility and strength or using a manual wheelchair.

In fact, the Centers for Disease Control and Prevention (CDC) estimate that 20% of U.S. adults have a disability, with the most common being mobility-related. Aging Baby Boomers contribute to this statistic. But many aging adults with mobility-related disabilities aim to keep a high quality of life, and having a wheelchair-accessible vehicle gives them the freedom and ease of use that keeps them independent.

The Americans with Disabilities Act (ADA) enacted in 1990 didn’t impact the market for personal-use vehicles but did make society more accessible for wheelchair users — and made these people more accessible to the rest of society. With improved access came the need for more personal transportation setups, which contributed to the overall growth of the accessible vehicle industry. So BraunAbility and other vehicle converters have expanded their product offerings and continue to add more user-friendly features to their vehicles. In North America, sales of wheelchair-accessible vehicles could reach $1.9 Billion by 2024, with full-size vans and SUVs accounting for 73% of the market.

Birth of an industry — mobility devices and features

As a young boy, Ralph Braun was diagnosed with spinal muscular atrophy and was unable to walk by the age of 15. So he built himself a scooter for mobility. In 1966, he pioneered the accessible vehicle industry when he installed a wheelchair lift on the back of an old postal Jeep so he could drive to and from work every day. Having an accessible vehicle made him blend in with the rest of society and gave him independence and freedom. He realized other people could benefit from that same mobility, and that’s how BraunAbility and the industry were born.

“Aside from founding the category, other BraunAbility innovations include engineering for ease of use — for example, to ensure the vehicle and conversion electronics communicate and work from the same keyfob.” said Megan Wegner of BraunAbility.

BraunAbility also sells an MXV wheelchair accessible SUV built on the Ford Explorer platform for those who prefer SUVs over minivans.

Converting a standard factory model van or SUV into a fully functional wheelchair accessible vehicle is a challenging endeavor. The process typically includes re-engineering the factory vehicle by lowering the floor, moving fluid lines, installing new seats, and integrating retractable ramps with their electric or hydraulic systems.

“One significant trend is mobility manufacturers continue to engineer for space”, said Wegner. “Wheelchairs are getting larger and more complicated, and every inch of space on the ramps and inside the vehicle makes a big difference for customers. At BraunAbility the focus is on creating space in the vehicle without compromising the ride and handling.”

Integrated limit switches save assembly and installation time

As BraunAbility began incorporating the kneeling feature on their vehicles, they tried some hydraulic units, but there were not many compact actuators available when some of its vehicle model lines began production.

Based on previous successful collaborations, BraunAbility worked closely with Warner Linear to provide an electric actuator setup for the kneeling function. According to Laird, “During development of a new vehicle platform, there’s very little space to mount an actuator inside the cabin. Thus, needing us to position the actuator under the chassis, below the third row of seats or on the top of the vehicle’s rear suspension subframe. These tight envelope spaces minimize space for limit switch mounting brackets. In most cases, limited available space led to external switches being added directly to the actuator.”

To meet the challenging space requirements, Warner Linear engineers developed a modified B-Track K2x model actuator that incorporated adjustable limit switches mounted in a low-profile channel on the cover tube. Adjustable channel caps allow the flexibility of setting the stroke length at any position within the actuator’s full stroke range. “Having the limit switches integrated into the actuator meant we didn’t have to assemble, mount, and service a switch bracket tucked away in a small cavity under the vehicle.” said Laird.

K2x electric actuators have a rated load capacity to 2,800 lb (12,455 N) and travel speeds up to 2.1 in. (53.35 mm) per sec. Units are available with stroke lengths 2 to 24 in. (50 to 600 mm). All models incorporate a patented in-line load transfer design which provides high load capability for rugged-duty use, an integral holding brake, and a ball detent overload clutch.

Models feature a compact package size and an efficient ball nut screw system yielding high-impact capability and long screw life. Double ball-bearing motors with thermal overload, heat-treated gears, heavy wall construction, O-ring seals, and rugged extension rod bearing support provide best-in-class capabilities.

Emphasis on quiet linear-actuator operation and long life

Actuator sound during kneeling was also a concern. Silent operation is ideal, but realistically a modest amount of linear-motor sound is acceptable. As load increases, so does the sound pressure level with no strong peaks. But free impact sounds from engaging and disengaging transmission components can cause user anxiety because it sounds as though malfunction may be eminent. Warner Linear K2x models operate smoothly, but during development on one van model, the actuator seemed to shudder on extension.

“After a vehicle arrived at the lab, we determined that its natural rebound rate and actuator’s extend rate matched closely for some spring and shock packages,” said Jared Zammuto, new product development team manager of engineering at Warner Linear.

“This caused the actuator’s controlling brake to intermittently engage and release — the source of normal sound that was nevertheless a concern for customers. So we made a simple no-cost modification to the load control brake that eliminated the issue,” said Zammuto.

The actuators usually install in a steel housing under the chassis to get some protection from the elements. But on some vehicles, the actuator is fully exposed to water, snow, salt, and debris. Here, the corrosion resistance of Warner Linear K2x models is key to withstanding harsh under-chassis environments.

BraunAbility is satisfied with the Warner K2x actuators’ field performance and uses the actuators for kneeling options on its side-entry Toyota Sienna, Chrysler Town and Country, Dodge Caravan, and Honda Odyssey conversion vans.

For more information on the application and actuator, visit warnerlinear.com.