Other

Question 1

What is Se,mod and Se?

Answer 1

Se,mod is the endurance strength as measured in an experimental setup.
Se is the actual endurance strength for which the differences between actual and experimental setups are taken into account.

Question 2

For which reason are flat belt pulleys crowned?

Answer 2

To prevent the belt from sliding off the pulley sideways

Question 3

Describe how a function-means-tree can be used in a product development process

Answer 3

A FMT is a decomposition of functions (what must be done) into means (how one might do it). The means can be further decomposed into secondary functions that would result from implementing the means.

Question 4

What is the main reason for roller chains having a limited life?

Answer 4

Chain life is limited by wear between the pins and bushings.

Question 5

What is the purpose of the roller in a roller chain?

Answer 5

The rollers prevent sliding when the chain is entering the sprockets.

Question 6

Compare the shaft diameter calculations of ANSI and von Mises

Answer 6

The ANSI equation is used to design the shaft against fatigue. The input load should be effective mean load.
The von Mises equation is used for designing a dhaft against yield. The input load is then the maximum load.

Question 7

Why should not only one bearing be used and why shouldn’t three or more be used?

Answer 7

• One shouldn’t be used because most bearings cannot hold the torque alone
• Three or more shouldn’t be used because of tolerance errors in e.g. the bearing seats would induce high unexpected loads on the bearings

Question 8

What happens if the load of an induction motor is suddenly disengaged and the motor runs without external load?

Answer 8

The motor accelerates to nominal speed (where Tm=0)

Question 9

Function of keys/keyseats?

Answer 9

Transmit torque between gear and shaft

Question 10

Function of spacer?

Answer 10

Bearing inner rings location (A spacer or standoff is a fixed size component designed to separate two other parts by a known amount.)

Question 11

Function of a shim?

Answer 11

A shim is a component used to fill up an unwanted gap. Shims may be flat or tapered, and are often specified as “select to fit” parts, rather than as a part with a predefined thickness.

Question 12

Function of washer?

Answer 12

A washer is a part used to spread the load between the two components, e.g., between a bolt- or screw-head and whatever the bolt or screw is fixing.

Question 13

Give the main reasons for making a bearing arrangement where one bearing is designed to be axially locating and the other non-locating

Answer 13

If both were locating, thermal expansion and/or tolerances would create axial load

Question 14

What are Wöhler diagrams used to study?

Answer 14

Fatigue properties of a material

Question 15

What properties are Wöhler diagrams showing the relation of?

Answer 15

• Load level

- Number of cycles to failure

Question 16

Explain why the stress concentration factor is only used in the first term of ANSI’s shaft diameter equation

Answer 16

Because stress concentrations are very bad for bending but less harmful for static loads

Question 17

Give two advantages for using splines as a shaft-hub connection

Answer 17

• Can transmit higher torque

- Allows axial movement of the hub or shaft under load

Question 18

The right way of pressing a bearing into a housing’s bearing seat

Answer 18

The press force should never go through the rolling elements since this will cause permanent indents and result in premature failure.

Question 19

Give three examples of how a deep groove ball bearing can be axially locked on a shaft

Answer 19

• Nut
• Retaining ring
• Screw and washer
• Step on the shaft

Question 20

Hub reducers are often used as the last speed reduction step in truck drive lines. What is the main reason for using them?

Answer 20

Reducing torque through the driveline

Question 21

Explain the reason for using the modified endurance strength in the first term and the yield strength in the second term in ANSI’s shaft diameter equation

Answer 21

• The first term is bending which causes a pulsating stress

- The second term is torsion which causes a constant stress

Question 22

What is the main advantage using a spring compared with using a nut for creating the preload?

Answer 22

It is easier to achieve the correct preload when using a spring, since the thread that is used with a nut makes load applied uncertain

Question 23

The figure below shows a typical torque speed curve of an induction motor. Explain what is happening when n/ns > 1

Answer 23

The motor is forced to run faster than the synchronous speed (ns). The torque then becomes negative and the motor generates electric power (generator mode)

Question 24

Define constraints and objectives

Answer 24

Constraints: Essential condition that must be met (e.g. maximum temperature 60 degrees)
Objectives: Quantity for which an extreme value is sought (e.g. minimize cost, minimize weight)

Question 25

There are several matrix based methods for evaluation of alternative design solutions for a given problem. One of these is Pugh’s evaluation method. What are the main
characteristics of this method?

Answer 25

You define different criterias and you compare different concepts to one set concept (which acts like a template/datum). You score the other concepts in relation to your template, with the signs + - =, depending on if they are better, worse or equal to the template.

Question 26

What are the consequences of having a cylinder bearing instead of ball bearing?

Answer 26

Replacing the balls with cylinders greatly increases radial load capacity due to the contact area being much bigger, thus reducing contact stress. Although, cylindrical bearings are worse at accommodating angular misalignment

Question 27

Benefit of having a spherical roller bearing?

Answer 27

Due to their geometry, these bearings are self-aligning, which means they are excellent when it comes to misalignment

Question 28

Benefits of having tapered bearing?

Answer 28

Can handle great thrust and high radial loads

Question 29

What are thrust bearings?

Answer 29

Bearings designed against high axial loads

Question 30

When is an adjusted bearing arrangement usually used?

Answer 30

For short shafts, where thermal expansion has only a little effect. The most suitable bearings are angular contact ball bearings or tapered roller bearings

Question 31

Advantage and drawback of sealing?

Answer 31

Keeps dust out but increases friction

Question 32

What are shear pins commonly used as?

Answer 32

A common case is the shear pins on the shafts of boat motors, that break if the load on the engine grows to big (to protect the more expensive motor from being damaged).

Question 33

How are shrink fits “made”?

Answer 33

With shrink fits, the shaft is cooled (to reduce diameter) while the mating part is heated (to increase bore), and pressed onto each other

Question 34

Explain the polygon effect / chordal action

Answer 34

A chain running on a sprocket is geometrically the same as a string running on a polygon. Since the radius varies the speed will vary

Question 35

Explain context mapping

Answer 35

It is technique for capturing emergent conversation themes in complex problems to show integrated context. It can be used in different ways during the understanding phase of the project, starting from a very general topic to more detailed aspects of this topic

Question 36

Explain progression curves

Answer 36

They are graphical representations that explain the progression of changes in themes of technological, social and related filters. It’s possible to graphically list different steps of a process of diverse events in a specific context and place them on the curves according to time or importance. The more curves created, the more useful the tool is, because it’s possible to cross and overlap the curves obtaining interesting results and insights

Question 37

Explain janus cones

Answer 37

It is a foresight tool for looking backwards and forwards in time to indentify the timing of historical events and how these timings effect potential future events. The cone is double: the left part is referred to the past. The right part is for the future, so either potential future events or certain facts that are likely to happen in the imminent future can be placed inside the cone

Question 38

What is the most specific property of spherical roller bearings?

Answer 38

They can take a certain amount of misalignment

Question 39

Stationary outer ring, rotating inner ring and constant load direction. Sliding between inner ring and shaft or outer ring and housing?

Answer 39

Sliding between outer ring and housing. Inner ring and shaft need to spin together to get positive effects from the bearing. Also, sliding between inner ring and shaft would result in the shaft getting scoring marks

Question 40

When dimensioning a press fit between a shaft and a hub there are two main criteria that must be fulfilled. What are the critera?

Answer 40

• That it’s capable of transferring the required torque

- The stresses due to the press fit don’t exceed the tensile strength

Question 41

Enumerate the parameters having the greatest influence on the transmittable torque in a belt transmission

Answer 41

• Pitch radius
• Belt tension
• Friction
• Shape/design of belt (cogged/multi/standard)
• Wrap angle / arc of contact

Question 42

When are Woodruff keys particularly useful?

Answer 42

In smaller (tunnare) shafts where their deeper penetration helps prevent key rolling (glapp)

Question 43

Compare flat belt drives and v-belt drives

Answer 43

Flat belt drives have higher efficiency, are less noisy and absorbe more torsional vibration from the system than v-belt drives.

Question 44

Basic features of chain drive?

Answer 44

• Constant ratio (since no slippage or creep is involved)
• Long life
• The ability to drive a number of shafts from a single source of power

Question 45

Suggest 4 ways to prevent the nut to loosen in a bolted joint

Answer 45

• Nyloc nut (locknut with a nylon collar insert that resists turning)
• Split pin (the pin goes through the nut and the ends are pulled in different directions to secure fastening)
• (Split) Washer (fjäderbricka, delad bricka som är böjd i en fjäderform, fungerar som en låskraft mellan skruvskallen och materialet skruven fästs i)
• Adhesives (e.g. Loctite glue that you put in the thread where the nut goes on)

Question 46

Explain the product breakdown structure

Answer 46

A product breakdown structure (PBS) is a tool for analysing, documenting and communicating the outcomes of a project, and forms part of the product based planning technique. It is a form of a tree consisting of all products needed for the whole product that you are investigating

Question 47

Explain the matrix-based product representation Design Structure Matrix

Answer 47

It is a simple, compact and visual representation of a system or project in the form of a square matrix. A design structure matrix lists all constituent subsystems/activities and the corresponding information exchange, interactions, and dependency patterns. For example, where the matrix elements represent activities, the matrix details what pieces of information are needed to start a particular activity, and shows where the information generated by that activity leads. In this way, one can quickly recognize which other activities are reliant upon information outputs generated by each activity. (Dependency marks are what you fill out in the squares)

Question 48

Explain the graph-based product representation Function Block Diagram

Answer 48

The Function Block Diagram (FBD) is a graphical language for programmable logic controller design, that can describe the function between input variables and output variables. A function is described as a set of elementary blocks. Input and output variables are connected to blocks by connection lines.