|Politecnico di Torino|
|Academic Year 2016/17|
Fluid power I
Master of science-level of the Bologna process in Mechanical Engineering - Torino
The module presents and examines fluid power components and basic systems in terms of their layout, specific features, construction and operation. Non-ideal components and their characteristics and performance are introduced. Volumetric units, in diversified architectures, are examined in terms of efficiencies, instantaneous flow rate and torque along with timing solutions. The unit then concentrates on linear and rotating actuators, supply systems, accumulators and valves including several design examples. Students learn how to identify and interpret fluid power circuits, comprehend and explain their purpose in relation with their constitutive components. Theoretical considerations are strengthened by applications grounded on a simulation approach. Aim of the course is to acquaint students with methods for the analysis and critical evaluation of fluid power components and systems.
Expected learning outcomes
Foreword: aim of a fluid power system is to transfer power through a working fluid, typically oil. Fields of applications are off road vehicles (excavators, fork lifts, cranes, agricultural machines), industrial machines (machine tools, hydraulic presses), aeronautics (primary flight controls, landing gear, rudder), automotive systems (steering units, active suspensions, automatic gear shift, variable valve actuation), naval systems (variable pitch propellers, winches) and much more. The design, development, testing and production of fluid power components or systems require very specific competencies, but the prerequisite is a strong and solid knowledge of the basic principles governing the generation and the control of the hydraulic power and the mutual interaction among the components.
In this context, the knowledge acquired by the students upon completion of this course involves:
• to interpret a fluid power scheme according to the ISO standard 1219,
• to identify the main fluid power components, their specific function and operation,
• to understand correctly the purpose of a component within a fluid power system and to determine and contrast from a technical point of view the use of a component or of a whole system in relation to its end use,
• to know the fundamental equations for the evaluation of the flow rate, pressure, speed, torque and power,
• to identify and quantify the sources of power dissipation in a fluid power system and evaluate the efficiency
With the skills acquired during the course, students should be able to:
• design a simple layout of a fluid power system,
• select and size the correct component (pump, actuator, valve) to achieve a specified function,
• analyse qualitatively and quantitatively the different working modes of a fluid power circuit,
• understand the working principle of a fluid power valve starting from its drawing,
• propose different solutions for controlling linear and rotary actuators,
• propose solutions for reducing the power consumption.
Prerequisites / Assumed knowledge
Awareness of concepts covered in Physics, Fluid Mechanics 3D Modelling
• Fundamentals of Fluid Power (7 hours).
• Positive displacement pumps (10 hours): different designs, real steady-state characteristics flow-pressure and flow-speed, instantaneous flow rate and torque, volumetric and mechanical-hydraulic efficiencies, flow and torque losses models, evaluation of the displacement. Controls for displacement variation.
• Fluid Power valves (10 hours): on-off directional control valves; flow and pressure control valves (pressure relief, pressure reducing, sequence, two-port and three-port flow control), single and double stage; ideal and real performance characteristics; analysis of real components.
• Accumulators (2 hours): types, dimensioning criteria and examples of applications.
• Flow generating units (8 hours): constant and variable flow rate (discrete and continuous), for open and closed circuits; constant pressure with absolute pressure limiters and with unloading valves; ideal and real flow-pressure characteristics.
• Users groups (14 hours): mechanical characteristic of linear and rotary actuators. Control of overrunning loads by means of counterbalance and overcentre valves. Flow regeneration in differential actuators. Synchronous movement of two linear actuators by means of a flow divider/combiner. Orbit motors. Speed control of hydraulic motors with flow control valves (meter-in, meter-out, by-pass). Variable displacement motors. Hydraulic transformers. Analysis of real hydraulic motors.
• Basics of Load Sensing systems (3 hours): working principles with fixed and variable flow generating units, local compensators.
During the semester, five numerical exercises will be progressively proposed on the Didactic Web Portal of the Politecnico. This homework must be downloaded and solved individually, according to explicit rules, by all students. The purpose of the homework is twofold: a self-assessment of acquired knowledge and competence; a training route toward the final written test. When successfully registering the exam, students must hand in the complete set of their own homework.
Four sessions of laboratory work (mandatory) are carried out in groups:
• Pumps, motors and linear actuators: various positive displacement pumps and motors (external and internal gear, axial and radial piston and vane machines) of different manufacturers are disassembled, analysed and contrasted to understand and appraise their peculiarities and mode of operation.
• Fluid Power valves: students can analyse different types of valves a such as pressure relief, pressure reducing, sequence, two and three ports flow control, piloted non-return.
• Didactic test rig: students can analyse different circuits and components. Interactions and characteristics of valves and actuators are appraised: the practical settings of relief, reducing and sequence valves, implications in series and parallel operation of linear actuators, velocity control of rotary motor with constant and variable loads via variable restrictors and flow control valves.
• Load test rig: the test rig reproduces the circuit of a hydraulic winch. It includes an orbital motor integrating a holding brake and an overcentre valve. The steady-state characteristic of the winch with resistant and overrunning load is measured during the lab experience. The main components are also dismantled and analysed.
A written report about one of the laboratory topics must be prepared and presented at the examination.
Texts, readings, handouts and other learning resources
In order to avoid students to print on their own the didactic material, the entire set of slides used in lectures in high quality B/W printed form will be available at the beginning of the didactic term:
• Nervegna, N., Rundo, M.: Fluid Power I, Politeko, Torino
Moreover, the slides (with possible minor updates) will be progressively made available only to enrolled students on the Didactic Web Portal in the colour version.
The detailed description of the test rigs used in the laboratory experiences and the eDrawings of some valves will be uploaded on the Web Portal.
For additional insight into specific topics, reference is made to the following material (in Italian):
• Nervegna, N.: Oleodinamica e pneumatica: Sistemi. Vol. 1, Politeko, Torino
• Nervegna, N.: Oleodinamica e pneumatica: Componenti. Vol. 2, Politeko, Torino
• Nervegna, N.: Oleodinamica e pneumatica: Esercitazioni. Vol. 3, Politeko, Torino
• Gilardino, L.: Esercizi di Oleodinamica, Clut, Torino
Some additional information (bibliography, links, animations, test rigs for lab sessions) can be found on the official web site of the Fluid Power Laboratory (http://www.fprl.polito.it).
Assessment and grading criteria
The final exam is grounded on a two-hour written test involving numerical evaluations on a proposed problem as well as theoretical questions on concepts and principles exposed during the lectures and laboratory sessions. The test is a "NO BOOK EXAM": the use of personal notes, books and manuals in any form (hard copies and electronic versions) is strictly forbidden. The use of an English dictionary is allowed.
Some examples of written tests will be available on the Didactic Web Portal before the end of the course.
For those who reach in the written test a mark in the range:
• above 20/30 the oral examination is optional,
• from 15/30 to 20/30 an additional oral examination is required to pass the exam,
• below 15/30 the exam is failed.
In case of oral exam, the final mark will be the average between oral and written exams. If the combined mark is < 18/30 the exam is failed and it will be necessary to retake the written test, otherwise the exam is passed.
The oral exam will focus on lectures, laboratory topics and homework.
The oral exam can be required, regardless of the mark of the written test, in case of:
• unjustified absences in the mandatory laboratory experiences,
• suspicion of student misconduct during the written test.
Programma definitivo per l'A.A.2016/17