JBM (Journal Bearing Machine)

Journal Bearing Machine

Overview

The JBM is a computer controlled journal bearing test machine for the measurement of bearing friction over a wide range of operating conditions. The machine has been designed to accommodate real journal bearings and to accurately simulate the operating conditions experienced by those bearings in commercial gasoline and diesel engines.

Crankshaft main and big end bearings operate over a wide temperature range from ambient up to approximately 150°C and under extreme cyclical loads. Average individual loads are normally of the order 1 - 10 KN, but these loads may rise transiently to 40 KN over the first few degrees of the power stroke. The peak pressures experienced by the bearings under these loads cause significant pressure viscosity enhancement of the lubricant and so influence the operating lubrication regime.

The transient nature of this loading cycle is critical in simulating the operation of journal bearings. Existing test machines apply steady loads which leads to unrealistic thermal behaviour in the journal and a thermal limitation on the maximum load attainable.

JBM Closup

System Components

Bench-top mechanical test unit
Electronics unit which controls the pre-defined bearing speed, load, cam speed and temperatures
Desktop PC that records and processes the data from the electronics unit. Can review and modify test profiles. Results stored in a data file which can be easily read into a spreadsheet package.
Film thickness measurement ability.
User manual, Tool set

Operating Principles

The JBM is designed to overcome these shortcomings by applying transient load cycles by means of a profiled cam operating through a high mechanical advantage, extremely stiff loading system. The load cam, which runs independently from the bearing shaft, is profiled to simulate four stroke loading cycles from a gasoline or diesel engine as appropriate.

Software Screenshot

The journal bearing is end mounted on a relatively large drive shaft located by preloaded taper roller bearings. The main shaft and load cam are driven by a DC servo motor. The load arm to journal bearing interface is designed such that negligible moment is applied to the journal through application of the load. Two high sensitivity force transducers measure the applied load and the torque reaction of the journal. The test oil is circulated through the bearing by an oil pump which is electrically heated and can be rapidly cooled by an optional external refrigerated oil cooler. Platinum RTD type temperature probes measure the reservoir and lubricant temperatures.

Data Logging

The system is controlled by an integrated microcontroller. A separate PC running a custom Windows application allows test definition and communicates with the microcontroller for data logging. Test profiles are stored a simple text files which can be edited and saved using any text editor.

Journal Bearing Machine Results

Friction force at journal diameter vs load and speed

Transient load vs speed

Friction coefficient measurements can be made using the selected load profile over a wide range of speeds and temperatures. Collected data is displayed in graph format as the test proceeds. The data is saved in a spreadsheet compatible format for later analysis.

Safety

The software monitors the temperature and if it exceeds a user-set limit the system will shut down. There is a safety switch on the chamber door which will shut down the motors immediately if tripped. Furthermore, a hardware watchdog circuit continuously checks the operation of the microcontroller, if the controller should fail for any reason, the system will again shut down automatically.

JBM System...

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