Bosch LSU 4.9 vs LSU 4.2
Bosch LSU 4.9 Wide Band O2 Sensor Comparison to the legacy LSU 4.2
A very convincing example of comparison comes right out of the Original Bosch Sensor Data-Sheets.
It is the amount of available Lambda calibration reference points for each sensor.
Bosch LSU 4.9 : a total of 25 data points
0.650, 0.700, 0.750, 0.800, 0.822, 0.850, 0.900, 0.950, 0.970, 0.990, 1.003, 1.010, 1.050, 1.100, 1.132, 1.179, 1.429, 1.701, 1.990, 2.434, 3.413, 5.391, 7.506, 10.119, 30.000
Bosch LSU 4.2 : a total of 10 data points
0.700, 0.800, 0.850, 0.900, 1.009, 1.180, 1.430, 1.700, 2.420, 30.000
Accuracy and Response-Time :
The core of a modern AFR controller is a Bosch Cj125 Sensor Data Pre-Processor and a High Performance Embedded CPU.
Let's address the 2nd item 1st. It's not necessary to have a floating point arithmetic quad core CPU spinning in the GHz range. Floating point would be nice, but it would be shooting down pigeons with canons. For sure, if you got them and it's very very easy, but not necessary.
What's available nowadays as a good cost / performance option are 32-bit RISC Type CPUs at around or below 100 MHz ... i.e. Arm Cortex-3 based from various Chip-Houses. Anything below 32-bit is beyond legacy ... sorry about that :)
Now to the Sensor Control for the LSU 4.x Sensors. The overall control effort is quite complex and the only real solution to it, besides a custom ASIC (Innovate), is the Bosch CJ125 (or CJ135 at 70 % higher cost).
It provides the Ion-Pump Current Processing and outputs a Proportional Analog Voltage of it.
This internal Cj125 Signal Process includes a Fast Analog Closed Loop Control for the Nernst Voltage Measurement to Ion Pump Current Feedback Output and Measurement.
The Sensor Temperature is measured via it's inner resistance Ri and the CJ1x5 Chips provide all controls for it.
An Ri proportional analog voltage is output as a comparison measurement value from an external 300 Ohm (LSU 4.9) or 82.5 Ohm (Lsu 4.2) to the measured Sensor Ri.
Now all the CPU has to do, is to PID control the Heater PWM at a rate of around 100 - 200 Hz ... Faster wouldn't bring much because of the sensors thermal inertia. It's still quite a task in integer arithmetic, but we have 32-bits available for it.
Yes ... and the at least 10-bit Analog to Digital Conversion for all Measured Analog Values, sampled at 600 Hz or more with some Digital Filtering ... what do we have a 72 MHz Arm Cortex CPU for ... it should be busy at no extra cost :)
We are lucky and have all ADC and PWM at a 12-bit luxury resolution ... anything above it will be drowned in noise anyway unless you make a very elaborate and expensive effort in an automotive environment.
The other task is to translate the Ion Pump Current into Lambda or AFR units ... Table Look-Up with linear Interpolation ... a bit more 32 bit integer arithmetic. Here is where the Sensor Calibration Points will reflect Accuracy.
There are now still a few more, the system and sensor diagnostic task, the communications processing, ... and more.
As can be seen, the Heart of the System is the Bosch CJ125 being complemented by balanced 32-bit CPU Performance ... End of Successful Control Strategy :)
We have also found a very nice Comparison of the Bosch LSU 4.9 vs LSU 4.2 Wide Band O2 Sensor at http://www.hevosvoima.com/foorumi/viewtopic.php?f=33&p=3968
and took the liberty and copied the content, rather then providing only this link, to keep this info available in case the link ever fades away :)
And of course a nice "Thank You" to whoever originally wrote this very informative comparison.
So here the story goes :
LSU 4.9 is superior to LSU 4.2.
The major difference between LSU 4.9 and 4.2 is LSU 4.9 uses the reference pumping-current, while LSU 4.2 uses the reference air. What does this mean? Let's read this true story from the auto industries: when Bosch first designed a wideband oxygen sensor, a reference air cell was used to provide a reference of stoic AFR. The technology was to keep the pumping cell balanced with the reference air cell, by pumping the oxygen out of the pumping cell. The pumping current was the indication of the actual AFR in the exhaust gas. The bigger the pumping current, the more the oxygen in the exhaust, and vice versa. Therefore the reference air was vital to the accuracy of the sensor, because it was THE reference. It worked well in the lab, but not so good in the real life. Because the enviroment around the sensor on a car was much worse. The reference air cell was susceptible to be contaminated by the exhaust gas, and / or other surrounding pollutions. Once the reference air was contaminated, the whole characteristics of the sensor were shifted to the low side. It was called "Characteristic Shifted Down", or CSD, in the industries. This was the biggest problem of LSU 4.2 that was used by some early OEM applications. And it caused the big warranty issue to Bosch. To fix this problem, Bosch redesigned the LSU sensor, and came up with LSU 4.9 version. LSU 4.9 sensor completely got rid of the reference air. Instead, it used a reference pumping current which was equivalent to the stoic reference air, but without having any physical air in the cell. So the technology became: the actual pumping current was compared to the reference pumping current to maintain the balance. The actual pumping current was still the indication of the actual AFR, but the reference was a calibrated electrical signal, and stayed same all the time, all the situations.
This is the fundamental difference between the LSU 4.2 and LSU 4.9.
LSU 4.9 gets rid of the reference air, and therefore gets rid of the biggest failure mode. As a result, LSU 4.9 has a long life and can maintain the accuracy throughout the life. Only since then, Bosch LSU sensors have been used widely in the auto industires.
Nowadays, all OEMs who use Bosch O2 sensors are using LSU 4.9. GM, Ford, and Chrysler all use LSU 4.9 now. If you check out the O2 sensors on your recently bought vehicles, cars/SUVs/Pickups, (since 2007 or later), on the exhaust manifolds, and you will find that they are all exclusively LSU 4.9. No more 4.2 sensors can you find on OEM cars.
Most aftermarket wideband controllers are still using LSU 4.2, mainly for low cost reasons. Bosch sells the LSU 4.2 to the aftermarket at a much lower price than LSU 4.9. Plus, many of those companies do not want to or are not able to adapt the new LSU 4.9 sensors. There is a big mis-understanding that LSU 4.9 is only for diesel engines, because it can measure very lean AFRs. That's not true. There is a diesel version of LSU 4.9, called LSU4.9D, mainly because of fuel and temperature difference. But LSU 4.9 has been widely used with the gasonline engines. It is actually the most popular gasoline engine O2 sensor now, not only because it measures wide range of AFR, but also because it has the very good reliability, and high accuracy.
There are a few wideband controller companies in the aftermarket using LSU 4.9 already. But that does not mean all controllers with LSU 4.9 are equal. Even with the same LSU 4.9 sensor, the controller can make a big difference. Some wideband controlers are designed for AFR display only. You can imagine that they may not have good accuracy and fast response rate because they are not designed for those purposes. Those gauges are more for good looking than for engine tuning purposes. For engine controls, the accuracy and reponse rate are the most critical characteristics of a wideband controller. In fact, one way to tell whether a wideband controller is good or not, is to see whether it can be used as a feedback device for the ECU. A feedback device must provide a real-time signal in the fast rate and high accuracy, even under dynamic situations. The requirements for a feedback device are much much more than those for a gauge.
Even with a LSU 4.2, the controller makes a big difference. Bosch sensors are not easy to fail even with a LSU 4.2, if controlled appropriately. Especially, LSU 4.9 is designed for more than 10 year life because it has to, for the vehicle life. It should not fail in short time, like a year. Many OEM cars have been running with LSU 4.9 for years. Why so many aftermarket wideband systems have failed LSU sensors? Because many of them don't have a good heating control strategy. The number 1 failure mode of a LSU sensor is being heated up too fast or too earlier. O2 sensors are made of ceramic materials, which can be damaged by severe thermal shocks, like condensations, liquid residuals, or just high heating power when it's still cold. A very careful heating strategy to detect the dew point and a close-loop sensor temperature control are vital for the life of the sensors. That's why the LSU sensor must be controlled in the context of engine controls. You may say, only those know engine controls can design a good wideband controller.
Furthermore, the accuracy of LSU sensors is highly dependent on the operating temperature of the sensing element. The sensor reading can be very different if the temperature of the sensing element is different. LSU sensors must work at the vicinity of certain temperuatures for the good accuracy.
Bosch CJ125 chip is designed for this task. The heating strategy is a close loop control based on the measured sensor temperature. LSU 4.9 has a much higher sensor temperature resolution because of the resistance characteristics, so the heater controls are much better than LSU 4.2. Therefore, 4.9 has a longer life and better accuracy.
In short, not only the sensor LSU 4.9 is superior to 4.2; but also the controller with a Bosch CJ125 chip makes an OE equivalent system.
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