I’ve been frequently asked : what is lambda sonda, what is it used for, what is the principle of its functioning, if it brokes down – can I continue driving? On this and other questions, I will try to give the answers to all faithful visitors of Automania.
All modern petrol engines, with all available management electronics, wouldn’t work properly if it wasn’t for this small electro-mechanic element placed in the exhaust pipe. The task of lambda sonda is to send certain voltage signal to the electronic control unit (ECU), which with its help recognise the momentary contents of the mixture of air and fuel. The contents of the mixture is very important because it allows the appropriate functioning of the engine and catalyst.
For the regular work, lamdba sonda should be on the specific working temperature. In the majority of cases it is previously warmed up by the current of hot exhaust gases, untill it reaches the needed temperature. Because of that it is usually placed on the exhaust pipe of the engine, or immediatelly in front of the catalyc converter, that is the first in line on the exhaust pipe and the current of hot, exhaust gases go through it. Sonda is formed so that the outer electrode is exposed to the current of exhaust gases, and the interior is exposed to the clean air from the engine space. Basically sonda consists of the special ceramic porter, which surface is covered with porous platinum electrode. The work of sonda is based on the fact that the ceramic material is porous and allows the difusion (penetration) of the oxygen in the air. On higher working temperatures, oxygen turns to transmittor and if the concentration of the oxygen on one side different from the one on the other side of sonda, the tension between electodes in sonda is created. This tension represents the measurement signal which comes to central computer (ECU). In this part you can find the answer to the next question: what happens if instead of petrol you use ordinary super gas. It causes the distraction of the charactristics ceramic and platinum part of sonda because of physical- chemical influence of gages from ordinary gas and lambda sonda permanently looses its characteristics and it need to be replaced.
Exit tension of the giver, as well as resistance, depend on the temperature of sonda. The reliable functioning of sonda is possible on the temperature of ehxaust gases above 3500/C in unheated version of sonda and above 200 0/ C in the heated version of sonda. The big part od design of heated sonda is identical design of an unheated sonda. The difference in an active ceramic of sonda which is heated inside with special heating element, which enables that temperature always stays above the functional limit of 2500/C and with the special pipe sonda is protected from cooling, when the exhaust gases are smaller than temperature than needed (for example, when engine idling), which enables undisturbed work. The advantages of heated lambda sonda are: reliable and efficient control on low temperature od exhaust gases, minimal influence of changes in temperature of exhaust gases, fast achievement of lambda control effect after the engine starting, fast reaction of the giver which prevents big inequality from the ideal contents from exhaust gases as well as the independent position of the installation of sonda on exhaust pipe, because it is independant from the heating of the surroundings.
Ofcourse, if it looses its functionality you can continue driving, but untill first service check, because your engine will be malfunctioned even when it is warmed.
I hope I managed in this short text to enrich the fund of your Auto-moto knowledge...Anyway, that is why we are here....