For many years the SAE No. 2 friction machine has been used to measure the coefficient of friction obtained through the interaction of fluid, steel and clutch material. In addition, by forcing energy through the wetted clutch-steel interface and measuring the decay of the coefficient of friction over time, the durability of the materials and fluids can be determined. This paper discusses the use of a numerical computer model to duplicate SAE No. 2 data. The inputs for this model include test stand geometry and physical properties as well as output from a low velocity friction apparatus (LVFA). The LVFA uses a small disc of friction material, a small disc of steel material, and a small sample of fluid to generate a coefficient versus speed curve (m vs v). It was found that torque traces and speed traces generated by this model correlate well with actual SAE No. 2 data.
THERE ARE SEVERAL REASONS for creating this model. The model will better define the relationships between test stand geometry, inertias, springs and damping mechanisms, and data measurements. Additionally, the possibility of a smaller, faster and more economical way of generating data is created without an SAE No. 2 friction machine. It is also possible to use the computer model as a screening test for future technologies.
An SAE No. 2 machine is composed of an electric motor, flywheel, head assembly, and data acquisition and control system. The electric motor has shafts at both the front and rear. A flywheel is attached to the rear shaft and the friction head assembly is attached by a bearing to the front shaft. Inside the friction head assembly is a system of reaction steel plates and clutches and a specified amount of fluid. The clutches are attached to the motor and flywheel by an adapting hub and consequently turn at motor speed. The reaction steel plates are splined to the friction head assembly.
A single engagement of an SAE No. 2 machine occurs when the motor, flywheel, and clutches are accelerated to a target speed. The motor is then turned off and air pressure is applied to a piston within the head forcing the clutches and reaction plates together. Friction between the wetted clutches and the reaction plates acts to stop the rotating mass. The friction head assembly is prevented from rotating by being rigidly attached to the test stand. The attachment is composed of a torque arm that connects the friction head to a strain gaged load cell. The load cell is attached to the test stand. By measuring the deformation of the load cell (strain), the torque transmitted through the clutches can be measured. Also measured and controlled in this test are the motor speed, piston apply pressure, and fluid temperature.
The model was constructed using kinematic and dynamic equations, differential equations, and numerical modeling. LVFA data and SAE No.2 data using SD 1777 friction material, fluid A and SAE 1035 steel were used to tune the model.
After tuning the model with fluid A data, fluid B data is entered into the model. Output from the model is then compared to data from an SAE No. 2 plate test, using fluid B.