Friday, June 23, 2023 · 0 min read
Tractor Tire Testing for Performance, Efficiency, Safety, and Driving Comfort
The development of tires for agriculture machines is a complex challenge. The product must cover several operational conditions, delivering a range of performances such as effectiveness, fuel efficiency, safety, and comfort, on the road and in the field. The Provana Group needed to measure the tire rolling circumference and the relative slip ratio of the front axle vs. the rear axle. LEANE provided the solution based on Dewesoft data acquisition.
Provana Group is a primary Italian dealer of tires for agriculture machines. The company has long-time experience, direct user feedback, and a well-established relationship with the major OEMs. In recent years, moving a step forward on the quality path, Provana has invested in tire testing to provide better service to their customers and OEM partners.
The customer issue
The market’s need to test agricultural tires has increased over the past few years. In this field, however, getting good objective test results is even more difficult than in the case of, e.g., passenger car tires. Only a few experts, mainly from the OEMs tire industry, have the expertise to manage a test plan and define objective test procedures to characterize the tire behaviour properly.
This case started a few years ago when we helped the guys of the Provana Group Innovation test center to measure the tire rolling circumference and the relative slip ratio of the front axle vs. rear axle. These data are crucial when choosing the correct tire fitment for a tractor.
It is not evident to everyone that in forward operation on the field, the front tires need a specific grade of slip compared to the rear tires to achieve optimal performance. It is more evident that the tire slip depends on the tire circumferences for a given tractor having a given ratio of front-rear mechanical transmission. Hence the need to precisely measure in reel condition, i.e., with the tires fitted to the tractor.
The measurement system
Our starting point was a system for the measurement of the rolling circumference and the front-rear transmission ratio:
One SUCHY XPro Nano 25 GPS sensor/receiver for velocity and distance measurement
A couple of PEISELER wheel encoders for the measurement of the wheels speed
One DEWESOFT DEWE43A - a versatile hand-size 8-channel USB data acquisition system with a good value/price ratio for this kind of application.
Adding some expertise side and preparing a Dewesoft setup with some automation, we provided our friends in Provana with a simple yet very efficient tool to speed up their daily job.
Among the typical missions of large tractors, there are
Jobs on the field, which generally involve towing an implement
Road transports, towing large and heavy trailers at speeds above 50 km/h, with the overall mass of the convoy exceeding 40 tons
In such scenarios, fuel efficiency and road safety are essential requirements for every customer. In 2022, Leane supported Provana on the field, performing testing activity jointly or on behalf of some leading tire OEMs. They did a few test sessions to compare:
Different sets of trailer tires - concerning road transport efficiency, safety, and driving comfort.
Different sets of tractor tires - concerning performance and efficiency in the field.
To capture an overall picture of traction performance, fuel consumption, and vehicle dynamics behaviour, the expanded measurement system used included:
An AIC flow meter for fuel consumption
A load cell for measuring the towing force
A pair of PEISELER encoders for measuring the wheels speed
A thermocouple (via DSI-TH adapter) for monitoring the gearbox oil temperature
A Suchy Data System GPS+IMU (via CAN) for measuring the tractor speed and motion variables
Plus, for the objective analysis of the trailer vehicle dynamics:
Accelerometers (z-axis) on the trailer axle
A Genesys GNSS IMU sensor, ADMA Speed (via Ethernet) for measuring the trailer motion variables and side slip angle
The DEWE-43 was confirmed to be a good choice. It fits easily in the tractor cabin and its fair range of analog and counter channels plus a pair of CAN ports is just perfect for this application.
The measurements
On this kind of big machinery, the installation of the sensors, the DAQ system, and the preparation of the measurement setup is somehow a challenge in itself:
Sensor installation is often tricky on all vehicle types, but dealing with the size and mass of tractors and their implements adds further problems.
Safe routing of (long) cables from the sensors on the trailer and implementation to the DAQ system.
Small space for measurement equipment in the tractor’s cabin.
Harsh environment that equipment needs to work in.
To prevent side forces from affecting the traction load cell, we used a special-designed cradle to house the load cell and the towing pin. This piece of equipment alone weighs some tens of kilograms and must be handled with care by two persons during the installation.
Furthermore, changing the trailer or tractor tires is not a matter of just a few minutes. And also the settling and fine-adjusting of the inflation pressure are not as fast and easy as on passenger cars.
We selected a small airfield as the facility for testing the vehicle dynamics, comfort, and fuel consumption of the tractor & trailer convoy. Using the Dewesoft virtual Polygon plugin, we defined some reference points. These create virtual start/stop barriers delimiting the measurement areas fitted for coast-down, consumption, comfort, and handling tests.
These barriers ensured performing the same test on the same part of the track - better reproducibility, which is essential to investigate minor differences between different tires or vehicle configurations. The overall fuel consumption is affected by many external factors that make the objective evaluation of the tire effect extremely difficult. We developed our test protocol to address these factors, paying attention to
Vehicle warm-up: engine & transmission, tires
Tires temperature check and fine adjustment of the inflation pressure
Environment conditions monitoring (air temperature, road temperature, etc.)
Test repetition at different environment conditions
The following anonymized sample results show an apparent effect of the tire set on the values of the traction force, For instance, the overall drag force of the trailer was measured at different speeds with a limited effect of the speed variation.
Looking at the overall fuel consumption of the whole convoy, we saw that the effect of the tire (rolling resistance) is relatively small compared to that of the speed variation. However, a difference of even a few percent in fuel consumption may be relevant to the cost of machinery operation.
On the side of vehicle dynamics, we could run both subjective and objective tests on the 30 meters wide straight. This gave us consistency in the assessment of different tire specifications in ordinary and high dynamics/emergency driving conditions.
Our testing and evaluation process was only at the initial step. However, we found some correlations between our subjective evaluation and some relevant objective metrics related to the sideslip angle. These allowed us to obtain a meaningful ranking of the tested tire specs, even from a driving dynamics perspective.
When moving our testing from the road to the field, the focus is absolutely on the tractor’s tire. The sensor setup doesn’t change that much compared to the previous application, except that we don’t have channels from the trailer sensors - the accelerometers and the ADMA. We used a different load cell to measure the traction force installed on a purpose-built towing bar. In this case, the fixture is also specifically designed to apply a pure axial force to the load cell.
The tractor fitted with the tires under test pulls another tractor that operates as a resistant load. The velocity of both tractors is regulated to gradually increase the braking effect of the towed tractor, resulting in an increase in the slip ratio of the tires under test. The final result is a typical curve that describes the traction force as a function of the tire slip.
Easy to say, in principle, but not so easy to achieve in practice. As always, the devil is in details - you need to pay attention to quite a few things to get good results.
To precisely calculate the slip ratio requires a preliminary calibration of the wheel speed with no traction load before testing each tire set. This calibration is easy to make with the Dewesoft software using math channels and basic statistics to average the data from the wheel encoders and GPS over a predefined distance.
The calibration factor is calculated online at the end of the averaging window, and then its value is set into a user input channel. The procedure provides a simple way to adjust the wheel speed from encoders without leaving the measure mode - no need to switch from measure to setup and vice-versa.
After the calibration, the tractor moves to the field prepared in advance. Using a tool moving a few centimetres of the upper terrain layer obtained a somewhat soft testing surface, as uniform as possible. Also, some characteristic parameters of the terrain need to be measured: besides the soil composition and structure, a crucial parameter to get comparable results is the moisture level.
During the test, we measure and average the velocities, force, slip ratio, and fuel consumption on a predefined distance to “filter” fluctuations typical of the field operation. After each interval, we increase the traction force by slowing down the towed tractor more and more.
This driving spans the desired range of traction force and slip ratio, which obviously depends on the load of the tractor and the soil characteristics. Not everything is possible. The experience of an OEM test expert proved essential in finding the convoy parameters suited to catch the relevant operation conditions: weight balance, work speed, transmission ratio, etc.
Last but not least, the field is not infinite: We had to reverse and still always drive on “clean” soil, avoiding putting the tires twice in the same path.
Our test procedure was easily set up in the Dewesoft software, using math channels and basic statistics triggered on local coordinates or by manual switch and travelled distance. A sliding bar shows the location compared to the target averaging the distance. An X-Y plot allows live visual checks and monitoring of the ongoing test’s traction characteristic curve.
We complemented Dewesoft measurement and analysis features by developing dedicated Python scripts in our Garage Lab environment to manage data analysis, playing with fitting polynomials, calculating objective metrics, and preparing data for aggregate analysis.
The Garage Lab environment can be launched manually or from the Dewesoft Sequencer to automate the data analysis task, e.g., processing the last test file or a batch of test files. This provides a simple test automation and analysis solution.
Conclusion
By the end of the day, the Provana team was quite pleased with their results and a bit proud of the job done. And we in Leane were happy too - proud to contribute to their success.
As always, there was a lot to learn by doing things:
figuring out how to manage the logistics,
how to perform the tests,
what sensor setup was suitable,
how to install the sensors,
how to manage the data acquisition in the easiest way possible for the operator on the tractor,
how to process the test data, etc.
Having overcome those challenges, we know where we can further improve. Much is still there to learn, but we know we have a solid basis for coming test campaigns and have gained more confidence in our equipment and methods.