“Tank OBD,” an onboard diagnostics system that identifies and indicates leaks in a fuel system, has been a requirement in North America and China for some time now and will also be required in South America from 2025. This is an entirely logical move, as tank leakage diagnostics help to spot fuel evaporation early.

Companies looking for a suitable solution are increasingly considering active systems, because the passive systems that have been widespread up until now are struggling to keep pace with increasingly stringent reliability requirements. Among other things, hybrid vehicles require active systems since a passive tank monitoring module will always risk allowing a little gas to escape from the tank. This must be prevented at all costs.

TLM from Thomas: more powerful and robust

“Our tank leakage module integrates an air pump and valve in a single unit,” explains Edwin Kreuzberg, Product Manager at Thomas. “It can generate both positive and negative pressure, so that the change in pressure inside the tank can be determined using a sensor.”

A system like this has obvious benefits: For example, you can pre-set your target pressure precisely and measure it more accurately – and do so regardless of any external factors and whenever you like. This is not the case with passive systems, which rely on changes in the ambient temperature in order to generate a usable pressure differential.

However, the Thomas TLM does not just leave its competitor passive systems in its wake: It also offers advantages compared to the other active systems currently available on the market. Edwin Kreuzberg adds: “The pumping power of our TLM is roughly ten times higher than that of conventional active systems with a rotary-vane pump. Even if there’s a sizable leak, it can still generate the necessary positive or negative pressure.”

And there are two more benefits besides: First, systems fitted with rotary-vane pumps are vulnerable to extreme temperatures and humidity. By contrast, Thomas’s TLM is designed to be virtually immune to these kinds of environmental influence, despite being more or less the same size. It works just as reliably at -15°C (+5°F) as it does at +80°C (+176°F) and at the bottom of a valley just as reliably as it does at 2,500 meters (8,202 feet) above sea level. Second, the Thomas module does not need the opening that other systems use. “Openings like this tend to get blocked, which means extra work and costs because they need an extra filter module to protect them against dirt,” Kreuzberg says. “Our system is much more tolerant of soiling.”

OEM sensor delivers the necessary data

The European carmaker that has opted for the Thomas system was also won over by another of its characteristics: the Thomas TLM simply makes use of the sensor that is already there in the tank. This obviates the need for an additional transducer, keeping the overall complexity and thus the vulnerability of the system low.