Research Papers

Modeling the Magnetic Performance of a Fast Pneumatic Brake Actuator

[+] Author and Article Information
Jonathan I. Miller, Tim J. Flack

Engineering Department,
Cambridge University,
Trumpington Street,
Cambridge CB2 1PZ, UK

David Cebon

Engineering Department,
Cambridge University,
Trumpington Street,
Cambridge CB2 1PZ, UK
e-mail: dc@eng.cam.ac.uk

1Corresponding author.

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT, AND CONTROL. Manuscript received December 19, 2011; final manuscript received February 24, 2013; published online January 15, 2014. Assoc. Editor: Nariman Sepehri.

J. Dyn. Sys., Meas., Control 136(2), 021022 (Jan 15, 2014) (12 pages) Paper No: DS-11-1396; doi: 10.1115/1.4025813 History: Received December 19, 2011; Revised February 24, 2013

A novel pneumatic valve was constructed to improve the response of air-actuated brakes for heavy vehicles to demand pressures generated during electronically controlled braking by an order of magnitude. Investigations were made into the interactions between the magnetic, mechanical, and electrical subsystems of the valve with a view toward informing design optimization. The valve was modeled using a magnetic circuit approach. The quasi-static model included the influences of the permanent magnet, field-line fringing, saturation, and the coil. Mechanical forces outputted by the model matched physical measurements with an error smaller than 10%, and magnetic fluxes throughout the circuit were generally within 20% of those found from experiments based on Faraday's law of induction, Gaussmeter measurements, and FEA simulations. A magneto-mechanical simulation of the valve switching states was created using mechanical and electrical equations, and curve-fits to the outputs of the magnetic circuit model. The simulation produced time histories of the valve's armature position that matched experimental measurements and adequately predicted working pressures. The final model required an approximation to the influence of the coil based on experimental results. Consequently, further research is recommended into the influence of solenoid coils on fringing in magnetic circuits.

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Fig. 1

Braking system schematics. (a) Tractor braking circuit, ABS ECU not shown (used with permission of Saskatchewan Government Insurance [6]) and (b) Disk brake [7].

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Fig. 2

Binary-actuated Vibrator valve from Camcon [27]

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Fig. 3

Four stages of Vibrator valve switching. (a) Pulling the flexure to its seat, (b) Sealing, (c) Releasing the flexure from its seat, and (d) Flexure switching.

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Fig. 4

Prototype binary-actuated valve. (a) Cross section of the valve and (b) Photograph of the prototype

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Fig. 5

Binary-actuated valve magnetic circuit

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Fig. 6

Material model used in the simulations of the flexure. (a) B-H curve and (b) Derivative of the B-H curve

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Fig. 7

Flux fringing through an airgap

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Fig. 8

Results of the quasi-static magnetic circuit model for different flexure displacements from one pole-piece to the other. (a) Energy stored in the circuit and (b) Magnetic force on the flexure

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Fig. 9

Flux densities through the binary-actuated valve according to the magnetic circuit. (a) The flexure, φ3/Aflexure, (b) A pole-piece, φ1/Apole-piece, and (c) Back of the yoke, φ1/Aback-yoke

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Fig. 10

Experimental flux linkage measurement results for a 200 turn search coil around the flexure. (a) Test results and (b) Change in flux linkage

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Fig. 11

Flux density through the binary-actuated valve according to FEA simulations, performed by Wladyslaw Wygnanski of Camcon

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Fig. 12

Comparison to Gaussmeter measurements. (a) Flux measurements, (b) Splitting reluctances, and (c) Circuit results

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Fig. 13

Simulated and experimental hold force results with the flexure touching a pole-piece for different coil currents and a 200 turn coil. (a) Two methods of evaluation and (b) Curve fit for dynamic simulations

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Fig. 14

Free body diagram for the magneto-mechanical simulation

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Fig. 15

Sample results from the magneto-mechanical simulation. (a) Sample simulation results and (b) Flexure motion for increasing pressures

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Fig. 16

Experimental flexure position, current, and voltage time histories for a binary-actuated valve

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Fig. 17

Maximum switching pressure for different coil configurations during static tests




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