This is the man who gave Volvo a green image

“It was a moment I will never forget!” As Stephen Wallman thinks back to the moment of happiness from the past, a big smile appears on his face. For months they had been researching ways to make exhaust gases cleaner, which was necessary to meet future emission regulations. Then the breakthrough finally happened. “We looked at the results of the measurements and at one point all three harmful substances were gone at the same time,” he says. Exhaust gases without carbon monoxide, hydrocarbons and nitrogen oxides: Wallman’s team had invented Lambda 1. At the relevant point, the catalytic converter works optimally, thanks to the lambda probe. The small component that can be found in every petrol and diesel engine today made its debut in the United States in 1976: in a Volvo 244, in Wallman’s baby.

The Lambda sensor debuted on the Volvo 244, in the US.

The early 1970s was a hectic time. The car manufacturers have not yet thought about protecting the environment. California’s Environmental Protection Agency (EPA) had set limits for harmful substances in car emissions for the first time. Automakers who wanted to remain active in the important US market therefore had to deal with the toxic trio of carbon monoxide, hydrocarbons and nitrogen oxides. At Volvo, development began in 1971. Young engineer Stephen Wallman led the project team involved in emissions treatment. “We worked there with about sixty people, a ridiculously low number by today’s standards.”

Lambda sensor was key to success

What his team needed was already available as hardware: catalytic converters operated irregularly in the stationary range and many export Volvos were fitted with petrol injection. The required lambda probe was supplied by Bosch. The German supplier had gained experience with ceramics in the manufacture of spark plugs, but also in the oxygen measurement of batteries. “We had to put everything together so that it worked in a car,” says Wallman. The key to success was the lambda sensor. This sensor was the size of a spark plug and monitored the hot exhaust gas flow. In it, the lambda probe mapped the oxygen content: was the combustion too rich (with too high a fuel percentage) or too lean (with too much oxygen)? “We worked with different teams, including at Engelhard in New Jersey and at Bosch, to which we also made cars available.”

The required lambda probe was supplied by Bosch.

It was very unusual at the time to do that and to conduct research together. Volvo took this step because the brand was faced with a dilemma. The management of the Swedish brand had set the goal of protecting the environment, but there was a long way to go to achieve that. Volvo was particularly experienced in reliability and occupant protection and had a good reputation in these areas. However, that reputation was jeopardized by problems with the new 244. When sales of the model range started, the finish was poor, eroding the long-standing image of the robust Swede. Sales stagnated and alarm bells sounded in Gothenburg. At Volvo they were eager for positive news.

Lambda sensor passed ratio of air per kilo of fuel to engine management

In 1975, the Wallman team took care of this, which had created the control loop together with Bosch. The lambda probe informed the engine management system whether the ratio of the mixture was optimal for a clean combustion: there had to be 14.7 kilos of air per kilo of fuel. If such a mixture was sent to the combustion chambers, the catalyst behind it could convert the emissions for more than 90 percent, while about 50 percent was common with an unregulated catalytic converter. The technicians talked about the lambda range in this regard. After this technique was invented in the laboratory, series production started. The regulated catalytic converter had to operate in extremely low temperatures and at high altitudes while also dealing with poor quality fuel and fluctuations in production. To keep the combustion in the lambda range, the injection of the fuel mixture had to be controlled precisely to the millisecond, depending on the measured lambda value. If not, the catalytic converter behind it would either be too cold to operate ineffectively or too hot, with the risk of overheating.

“In May 1976, we presented our car to the Environmental Protection Agency in the US,” says Wallman. The car ended up on the dynamometer there, where the Americans experienced the same eureka moment as Wallman’s team before. “When the authorities first measured the emissions at our system, they first thought that their device was no longer working properly,” says the engineer.

The first Volvos to receive a lambda sensor from the factory came on the market in the autumn of 1976 and were fitted with a logo in the grille with the Greek letter lambda. A 244 equipped with the new emissions technology drove across the US, ending up at the Capitol in Washington. The Swedes are still proud of that. The tour became a true triumph and caused quite a bit of unrest among the American car manufacturers. Why did the small manufacturer Volvo achieve what they failed to do as major American brands?

After Volvo, Saab and Porsche came up with it

Bosch today also reluctantly admits that they underestimated the potential of the lambda sensor. After Volvo’s example, Saab and Porsche launched the first production models with a lambda sensor six months later. This was followed by Mercedes-Benz and the American manufacturers, so that the lambda sensor was used in huge numbers. This enabled the suppliers to do good business, all the more so because the first lambda sensors did not last as long as they do now. “We gave a 30,000-mile warranty on the probe, then they had to be replaced,” says Wallmann.

In Europe only in the 1980s

The technology only came onto the market in Europe later, because there was only a national coverage of filling stations where you could fill up with unleaded petrol in the mid-1980s. The first Volvo to bear the lambda logo in Sweden was the 760, more than a decade after the debut of the new technology.

In Europe, the technology debuted much later, on the Volvo 760.

His technique has had its day

Stephen Wallman made his career at Volvo and was most recently vice president responsible for engine development until Ford took over the brand in 1999 and Wallman left in 2003. The lambda pioneer remained connected to the manufacturer as an advisor for several years. Today, Wallman spends much of his retired life in the South of France. The probe is as much a part of the internal combustion engine as pistons, but Stephen Wallman is nevertheless convinced that the technology has had its day “Electric motors don’t need a catalytic converter.”

This is how the lambda probe became a billion-dollar success

Exhaust gases can reach temperatures of up to 1,000 degrees Celsius, which is a difficult job for the sensor that must measure the oxygen content in the manifold. In 1970, Bosch had already gained experience with lambda sensors (used in lead smelting) and with heat-resistant ceramics on spark plugs. Despite this, the first lambda sensors in the engines lasted less than an hour. Progress was made through the collaboration with Volvo and catalyst manufacturer Engelhard, but in 1975, despite the best efforts of developers, the sensitive electrodes still failed after about 250 hours. That is equivalent to 20,000 kilometers, not a good argument for introducing the technology. Volvo already gave a warranty of 30,000 miles when the 244 debuted with this technology in 1976, initially with a lot of doubt, says developer Stephen Wallman. A year later, Bosch concluded a supply contract with Ford for three million lambda sensors, after which the German supplier launched an improved variant in 1982.

When the ignition key is turned, the sensor heats up to 400 degrees and becomes less sensitive to exhaust gases suddenly becoming hot. The lifespan is now about 160,000 kilometers. In 1986 Bosch had earned back its investment after producing ten million sensors and in 2016 the manufacturer built the billionth sensor.

This story was previously published in AutoWeek Classics 12 2020.