|Politecnico di Torino|
|Academic Year 2017/18|
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 (8 hours). ISO standard 1219, fluid properties, functional blocks.
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 (12 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; cartridge valves; analysis of real components.
Accumulators (2 hours): types, dimensioning criteria and examples of applications.
Flow generating units (10 hours): constant and variable flow rate (discrete and continuous), for open and closed circuits; constant pressure with absolute pressure limiters (direct acting and piloted) and with unloading valves; ideal and real flow-pressure characteristics; examples of real circuits.
Users groups (15 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.
The subject is made up of theoretical lectures (the attendance is highly recommended), applied lectures and laboratory sessions.
In the applied lectures, some numerical exercises are solved with the assistance of the teacher and the components/circuits used in the laboratory experiences are explained.
During the semester, five additional 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 have to hand in the complete set of their own homework.
Four mandatory sessions of laboratory work (1.5 hours each) are carried out:
Pumps and motors: 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 dismantle and analyse different types of valves such as pressure relief, pressure reducing, sequence, 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 setting of relief, reducing and sequence valves, implications in series and parallel operation of linear actuators, velocity control of rotary motor with constant and variable load through variable restrictors and flow control valves.
Load test rig: the test rig reproduces the circuit of a hydraulic winch. It includes an orbit motor with holding brake and an overcentre valve. The steady-state characteristics of the winch with resistant and overrunning load are measured during the lab experience and must be presented at the examination. The main components are also dismantled and analysed.
Finally, students are invited (optional activity) to reproduce on their own some simple hydraulic circuits using the free Student Edition of LMS Amesim; some examples of simulation are shown during the lectures.
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 during the semester in high quality B/W printed form will be available at the beginning of the didactic term:
Nervegna, Rundo: Fluid Power I, Epics Edizioni, Collana Politeko, Torino. ISBN 978-88-94802-08-5.
New improved and corrected reprints are available yearly at the end of February.
Moreover, blocks of slides (with possible minor updates) will be progressively made available only to enrolled students on the Didactic Web Portal in electronic and colour version at the end of the lectures. However, students are strongly invited to integrate the material with their own notes.
A glossary with the main Fluid Power terms, the detailed description of the test rigs used in the laboratory experiences and the eDrawings of some components will be also uploaded on the Web Portal.
For additional insight into specific topics, reference is made to the following material (in Italian):
Nervegna: Oleodinamica e pneumatica: Sistemi. Vol. 1, Politeko, Torino
Nervegna: Oleodinamica e pneumatica: Componenti. Vol. 2, Politeko, Torino
Nervegna: Oleodinamica e pneumatica: Esercitazioni. Vol. 3, Politeko, Torino
Gilardino: Esercizi di Oleodinamica, Clut, Torino
Some additional information (bibliography, links, animations) can be found on the official web site of the Fluid Power Laboratory (http://www.fprl.polito.it).
Assessment and grading criteria
It is mandatory to book the exam on the didactic Web Portal; the booking must be cancelled if, for any reason, the student cannot (or no longer wish to) attend the exam. The final exam is made up of a written test and an oral test (optional or mandatory).
The written exam (2 hours) involves numerical evaluations on a proposed problem (max 15 points) as well as theoretical open-ended questions on all concepts and principles exposed during the lectures and laboratory sessions (max 15 points).
In the numerical exercise, the progressive stages of all calculations must be shown: any formula used, how the numbers are substituted into the formula and the final result in the requested unit. The answer is considered fully correct only if the formula used and the final result are both correct.
In theoretical questions, candidates must be able to explain the working principle of a component or of a system, to discuss about advantages and drawbacks of different solutions, to derive analytic governing equations, to obtain the theoretical and real steady-state characteristics and to draw the basic hydraulic circuits using the correct standard symbols.
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. Candidates can have on the desk only blank sheets, writing instruments, a scientific calculator and optionally an English dictionary. Mobile phones and other electronic devices must remain switched off throughout the test.
Some examples of written tests with solutions will be available on the Didactic Web Portal before the end of the semester.
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 withdrawal from the written test (it is possible at any time), the exam paper has to be returned and the exam will be recorded as failed.
Students who have potentially passed the exam (mark in the written test > 20/30) can retake the exam if not satisfied with the mark (the exam will be recorded as failed).
Appropriate actions will be taken against students who use any unauthorised source of information, communicate or share written material with other candidates, attempt to read other candidates work.
In case of misconduct, at discretion of the Exam Board:
the answer to some questions can be nullified (0 points will be assigned)
the student could be expelled from the exam room (the exam will be recorded as failed).
In case of oral exam, the final mark will be the average between oral (max 30 points) and written (max 30 points) part. 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 (typically 2 or 3 questions) will focus on lectures and laboratory topics in a similar manner as the theoretical questions in the written test. The duration of the oral exam is strictly related to the preparation of the student. The mark will take into account the completeness/correctness of the answers, as well as the ability of discussing critically the topics.
The students must also hand in the homework/report on the day of the oral exams. No additional point will be awarded for the homework. On the contrary, a penalty up to 2 points can be applied on the final mark in case of incomplete homework.
The mark "30 cum laude" can be obtained in case of an outstanding exam (written only or written plus oral) demonstrating a very deep knowledge of the subject.
The oral exam can be required at the discretion the Exam Board, 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.2017/18