Are You Still Mowing?

 

Extreme fluctuations in temperature

“The demands on seals of this kind are much greater than one would think,” said Dr. Stefan Geiss, Technical Director, Oil Seals Industry Division, Freudenberg Sealing Technologies. “Mowing robots are exposed to extreme fluctuations in temperature.” Beneath the housing, temperatures during the summer can reach levels similar to those in a parked car on a sunny day. Yet in the spring and fall, the robot has to withstand frost at night. The temperature fluctuations lead to different degrees of stretching in the plastic and metal components, which in turn can cause cracks in the mower’s plastic wheels. “For such cases, we have developed a modular plastic seal,” Geiss said. In this design, the seal is braced between two plastic carriers. They in turn are connected with the housing or the plastic wheel. “With the same material pairing, this kind of seal carrier stretches to a similar degree with the environment. It thus seals effectively even with substantial temperature fluctuations,” he said. When the seal was designed, engineers made sure that there was no dead space where dirt could penetrate. That helped to keep starting torque low while protecting the seal from wear.

Counting Square Meters per Battery Charge

Impermeability alone is not enough. Mowing robots draw their energy from lithium ion batteries that are supposed to power them across an area as large as possible. For example, premium devices are designed to cover up to 5,000 square meters (about 5,470 square yards) of lawn. “That is why each component of the powertrain has to create as little friction as possible – including our seals,” said Dr. Daniel Frölich, Development Manager at Freudenberg Sealing Technologies. Working with the innovation’s first customer, a German manufacturer of mowing robots and many other motorized and garden devices, he developed an especially low-friction version of a modular plastic seal. The Freudenberg solution has been in use since early 2020, and it has performed impressively. “We are unaware of any breakdowns in the field,” said Frölich. That’s no surprise since it underwent thorough tests before series production began, including test-stand trials with so-called “standard dirt.” The approval came after the customer’s endurance tests of the complete mowing robot in various climate zones.

Other manufacturers of mowing robots are now showing an interest in the modular plastic seal. It is giving Freudenberg an opening into the fast-growing market for service robots used at home. The International Federation of Robotics calculates that global sales of automated home aids is expected to more than double from 27 million to 55 million between 2020 and 2023. Mowing robots account for a significant share of the business; the market research firm Technavio puts its annual growth rate at 19 percent. One happy result of the trend: Most subdivisions ought to be less noisy on Saturdays soon.