An Electric Master Cylinder

The Kinitics Piston Pump (KPP) is a shape memory alloy-based positive displacement pump that uses proprietary Bundled Wire technology to deliver a precision stroke in a compact package. Electrically powered, the KPP can be used to precisely control hydraulic devices. This application page introduces fundamental concepts for applying a KPP to hydraulic clutch and brake control systems. The concepts presented here can also be applied to other master – slave circuits, such as those used in hydraulic clamping and gripping applications.

The Connected Device
In order to control a clutch or brake system the designer needs to understand the pressures and displacements involved. Common to many hydraulic clutch and brake systems are slave cylinders that operate one or more clutch or brake devices. In either case it is important to know the operating travel and forces of the slave cylinder’s piston as it is applicable to sizing the piston pump.

The designer can proceed with selecting a suitable piston pump, once the volumetric displacement and operating pressure have been determined

Size the Piston Pump
Once the volumetric displacement and operating pressure have been determined the designer can proceed with selecting a suitable piston pump. A product selection chart for the KPP05 is presented at right.

To use the chart, first find the intersection point of pressure and volumetric displacement values.

Drawing a line horizontally to the right will identify the piston bore and travel modifier. The shaded box that the point lands in, identified in the legend, is used to determine the nominal stroke of the KPP05. For example, if you require a precision pump with 2.5 cc displacement and 5 bar pressure, you would use the above chart to select an actuator with a 25 mm piston bore, a 4 mm nominal stroke and the over-travel modifier.

Fluid Reservoir

Most clutch and brake systems can benefit from the inclusion of a fluid reservoir. These devices can be used to accommodate thermal expansion and friction material wear between operating cycles that can cause residual pressure, or vacuum, to develop inside the system.

Control Model
To develop a robust brake or clutch control system, the control system designer is encouraged to produce a transfer function that relates system inputs, such as hydraulic pressure, to outputs such as transmitted torque. In braking applications the pressure is typically proportional to braking torque while pressure is typically inversely proportional to torque transfer in normally closed (i.e. locked) clutch applications. In either case the KPP is readily adaptable to working inside of a pressure or displacement control loop. By relating pressure and/or displacement to the desired output it is possible to develop an effective closed-loop control strategy.

Full details and specifications for the Kinitics Automation KPP05 Piston Pump.

For more information on using the KPP Piston Pump for clutch and brake applications, or help with your specific application, please contact us.