PINARELLO DOGMA K8-S

Transcription

PINARELLO DOGMA K8-S WHITE PAPER 1.0
© Cicli Pinarello Spa - All rights reserved - March 2015
CONTENTS
2
3
1. Introduction
4
a. Collaboration with Team Sky and Jaguar Land Rover
5
b. Purposes and engineering method
7
2. Structural Design
8
a. CSs shape
11
b. SSs shape
12
c. Suspension design
12
d. Rapid Prototyping
15
e. Seatpost design
17
3. Test & final design
18
a. Laboratory test
19
b. Field test
21
c. Final design of frame and suspension
1. INTRODUCTION
Racing bicycles are always designed to be light, stiff and aerodynamic: in one word, to be fast!
To achieve all these purposes, designers often sacrifice the comfort of the rider,
which is more difficult to evaluate.
Everybody knows that the performance of a road bike depends on many factors, such as stiffness, aerodynamics, etc. The stiffer a bike is the less energy is lost in useless deflections of the frame; the lighter it
is, the less energy is needed to climb or accelerate.
Beyond these advantages, a stiff frame transmits most of the vibrations from the ground to the rider,
increasing fatigue and decreasing performances.
A new and useful point of view while developing a bike frame is to consider the comfort
as much as the previous properties: this would reduce, on one side, the fatigue of the rider,
especially on long courses, and, on the other side, the instances of loss of control and resultant crashes.
This is the reason why we developed Dogma K8-S: we have understood that comfort is as important
as the other well-known properties (especially if the road surface is not smooth),
so we decided to offer an innovative frame to our riders,
able to increase comfort significantly and, consequently, performances.
3
Collaboration with Team Sky and Jaguar Land Rover
Pinarello and Team Sky have had an intense and successful partnership all over several years, with many wins
in the most important World Tour races, Olympics and World Championships. Thanks to this partnership, we
share information and knowledge, to improve bikes and performances and push our limits further.
During the development of Dogma F8, we have also begun the collaboration with Jaguar Land Rover (from
now JLR), innovation partner of the Team Sky. On this new project, they have collaborated with us during the
intense test campaign, to record and analyse the results. In particular, they shared their expertise in vibration
and ride tuning, to create a bike that could improve rider isolation from the challenging road surfaces, improving the overall performance.
4
b. Purposes and engineering method
At the beginning of the project, we fixed the targets to reach with this new frame: these helped us to define
the characteristics of the frame and to verify the results.
The aims were:
a. Increase the comfort of the bike without any loss of torsional stiffness, to increase the performances of
the rider. The dedicated design of chainstays (from now CSs) and seatstays (from now SSs), in addition to the
new suspension to absorb and dampenthe vibrations from the ground, increasing the comfort of the rider.
In parallel, the design of the CSs, with a specific cross section, guarantees high values of torsional and lateral
bending stiffness, to avoid useless deflections of the frame and consequent loss of energy. Furthermore, we
want to avoid engaging the suspension when not necessary, for example, when the rider is sprinting: this has
been solve with the preload adjusting system.
b. Increase handling and stability, with a dedicated geometry. Considering that this bike will be used especially on rough terrains, handling is very important to avoid loss of control and crashes and to optimize the performance. Starting from the Dogma F8 geometry, we have decreased the steer angle and increased the rake,
to reach this purpose. Furthermore, we have increased the wheel clearance, to allow the use of bigger tyres.
c. Improve the aerodynamics, which is another important feature on a road bike: this, in effect, will help to
reduce the waste of energy due to the air resistance. To give you an idea, just consider that almost the 80% of
the Paris Roubaix course is on flat smooth roads; a more aerodynamic frame would guarantee more energy
saved for the cobbles sectors. Considering the deep development dedicated, and the great results obtained
on the Dogma F8, we used the same tubing sections for the main triangle and the fork, which are the parts
which most interact with the air flow. At the same time, this allowed us to minimize the overall air drag of the
frame (compared with the Dogma K 2015), while maintaining high torsional stiffness values.
d. Reduce the overall weight, because a lighter frame will allow quicker accelerations and braking, and less
energy required in a hilly route. It is clear that this frame will be heavier than a traditional high-end frame, because of the suspension itself; we looked for minimizing the overall weight of a high comfort bike. To reach this
purpose, we used the new Torayca T1100 for the frame and fork, and, during the development, we designed
the whole suspension to be as light as possible, without compromising safety and performances. This allowed
us to have an overall weight of 990 grams for a raw frame (size 530) with the suspension assembled.
e. Optimize every single frame’s size. Consider, for example, that a big frame, as size 595, needs to be stiffened much more than a small size as size 440, because the rider’s body and weight and the riding style is
very different. As made on the other Pinarello bikes, the Dogma K8-S also adopts the Made4you concept, to
ensure the same feeling to every rider. In particular, we developed 2 different suspensions (different length)
to be used with the different frame sizes. The frame will be available in 11 different sizes, this allows optimal
fit for all riders.
5
Beyond these purposes, the engineering method used was intended to optimize shape and performances of
the frame, plus durability and safety of the suspension.
The first phase was dedicated to the frame, designing and analysing the proper shape (i.e. cross sections) for
CSs and SSs. The whole analysis was validated through the FEA (Finite Element Analysis) and tests on real
prototypes, which confirmed the targets required, in terms of vertical compliance and frame’s strength.
The second phase was relative to the suspension’s preliminary development: we developed different solutions to reach the initial purposes (lightness, travel, safety, etc.). From this phase, we realized the first samples
of the suspension, which have been later evolved through the tests.
The final phase consisted in a large amount of tests, both in laboratory and on the road. The results, in terms
of performances and durability, allowed us to define the optimal configuration for the suspension, finalizing
every single component.
Chainstays
& Seatstays
development
Suspension
development
SAMPLES
LABORATORY TESTS
FIELD TESTS
FINAL DESIGN
& PRODUCTION
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2. STRUCTURAL DESIGN
The initial stages of this project were dedicated to the design of the frame, in particular CSs and SSs, and their
capability to work with the suspension.
a. CSs shape
CSs are an important part for optimal performance of the whole frame. They support the power transfer, and
their lateral and torsional deflections must be minimized to save energy; at the same time, they should have
vertical compliance, to absorb the vibrations of the rear wheel and, in our case, let the suspension work.
In normal frames, SSs link rigidly to the dropouts with the upper part of the seat tube (from now ST): this
consequently limits the vertical deflection of the CSs, even if they are designed to flex. The innovative frame
of Dogma K8-S instead, assembling the suspension in place of the monostay, has no rigid constrain between
SSs and ST, and thus allows greater vertical deflections of the CSs.
The CSs of Dogma K8-S are therefore designed to allow almost 10 mm of vertical deflection, and, at the same
time, to guarantee enough torsional stiffness of the rear triangle.
To reduce the flexural inertia in the vertical direction, we reduced the height of cross sections and, to increase
the lateral stiffness and contain the loss of torsional stiffness due to the reduced height, we increased their
width.
Pictures below compare the CSs of Dogma K8-S (orange) and Dogma F8 (blue); it is clear how these differ
and behave.
DOGMA K8-S
DOGMA F8
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Even if the idea to “squeeze” the cross section is quite intuitive, it is not easy to define the correct dimensions
(height and width) of the cross section to have 10 mm of vertical deflection and enough torsional stiffness and
strength. We used the Dogma F8 as reference point for the comparison.
Through FEA we compared different solutions to find the optimal one. The aim of the study was to investigate the combined effect of more vertically compliant CSs with a large pedalling load. We investigated different
section heights, beyond changing the location of the minimum section (for example in middle of the CSs or
towards/away from the BB); also the width changing was investigated, within maximum limiting parameters
such as chainring, rim spacing, etc. In this way, we were able to define many sections and, from these, the
whole shape of the optimal CSs.
The final result from the FEA, as visible in the images above, is a CS where the thickness continuously tapers
off from the bottom bracket to the rear drop outs.
Below an example of the stresses distribution on the Dogma F8 and Dogma K8-S, when loaded with a high
vertical displacement at the dropout: you can clearly see that, on Dogma K8-S, the stresses are more distributed, and the peak value is lower, due to the shape optimization.
DOGMA F8
DOGMA K8-S
8
Below an example of vertical deflection of the CSs of Dogma K8-S, compared with the undeformed shape.
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PINARELLO DOGMA F8 WHITE PAPER 1.0
b. SS Shape
SSs link the rear dropouts (i.e. the rear wheel) with the ST, transferring great part of the vibrations to the
saddle and the rider. Considering how they are joined to the frame, and how they will work together with the
suspension (consider 10 mm of the suspension travel), they are subjected to high compression stresses. Even
if they could obviously react to shear stresses, they act similarly to link elements, so important characteristics
to investigate are the buckling and the modal analysis.
Using FEA we could deeply investigate the behaviour of the SSs when subjected to compressive stresses,
to guarantee the strength and safety of the frame. Below an example which shows the undeformed SSs of
Dogma F8 (green) and the deformed version, when subjected to compression load.
At the same time, the modal analysis allowed to define the natural frequencies of the SSs, which must be
compared with the frequencies of the vibrations from the ground, to avoid the dangerous resonance of the
system. Images below show the first normal modes of the Dogma F8 SSs.
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Another important role for these SSs is to maintain the proper alignment of the suspension: if misaligned, the
suspension brings about abnormal wear and rough functioning. The suspension indeed is fixed on the frame
with 2 different screws: the upper one, which connects the suspension with the ST bracket, creates a pivot
point which allows a relative rotation between these parts.
The connection between suspension and SSs’ bridge is instead rigid, so none relative rotation is allowed: if
no other pivot point is created, when the CSs deflect vertically, SSs and suspension are subjected to shear
stresses, which reduce the performances of the system. This is the reason why we designed the SSs able to
bend easily near the dropout; in this way, we created a virtual pivot point, which maintains the alignment of
the suspension and increases the performances.
Finally, traditional brakes are usually fixed with one screw on the SSs’ bridge or on the monostay. Since the
Dogma K8-S has the suspension in place of the monostay, we moved for a direct mount brake. This solution
helped us to find enough space for the suspension and, at the same time, guarantees the braking performance.
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c. Suspension Design
In parallel with the frame development, we worked on different solutions of the suspension. Initially, we had
very different solutions, such as using a spring in place of the elastomer, or a cam wheel to adjust the preload,
as shown in the images below.
During this phase, we discussed with the parts’ suppliers, to find the optimal solution for every single piece.
At the end of this phase, we got the preliminary sample of the new suspension. We used this, during the test
campaign, to verify if it reached the initial purposes and to finalize every component, in terms of material’s
combination and dimensions.
As you can see in the pictures below, which show the first samples of the preliminary suspension, we had
already defined the general shape, the preload adjusting system and many other features that have been
later finalized through the tests.
The final design of the suspension allows 9 mm of total travel.
This means stiff enough to not feel it when the rider stands on the pedals but soft enough
to make all the difference in comfort over long distance rides on tarmac roads.
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d. Rapid Prototype
During these phases, we produced some Rapid Prototyping samples of the parts: these were useful to evaluate some important features of the bike, and the assembling of all the components. For example, considering the large width of the CSs, we can assemble a rear wheel on the RP sample, to verify the assembly.
Below some pictures of RP samples of frame and suspension parts.
We also used some RP samples of the suspension, to evaluate the aesthetics of the overall frame (in the
pictures below, the suspension is a painted RP sample).
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e. Seatpost Design
Vibrations from the ground pass through the frame, the saddle and the handlebar to the rider. If the seatpost
(from now SP) dampens part of these, the rider will have a better comfort. For this reason, we designed a
specific SP that increases the vertical compliance of the saddle, absorbing some of the vibrations.
We verified through FEA and laboratory tests the performances of this SP, which has more than 40% greater
vertical compliance than the standard Dogma F8 SP.
To adapt the SP to many different “seatpost heights”, we developed 2 different versions, with longer or
shorter straight section. In addition, the cross section is the same of Dogma F8, so it is interchangeable with
the normal one.
Finally, to avoid slipping of the SP, we increased the SP clamp force making it longer and adding a third screw;
on the smaller sizes, we maintained 2 screws, considering the lower weight of the smaller riders.
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3. Test & Final Design
Dogma K8-S is the first road bike that uses a proper suspension to damp the vibrations; this means that,
before the whole system was finalized, we spent much time and resources to test every single component.
Considering the innovative system, we also designed and realized a specific machine to test the parts in our
laboratory; in parallel, Team Sky riders tested the bikes on the cobbles, to verify the bike on the most critical
situations.
a. Laboratory test
Fatigue test
We always test our frames in laboratory, following the ISO rules, to verify performances and safety. During
the development of this new frame, we realized that common tests could not give us the results we needed,
because they are not intended to validate “suspended road frame”. Considering this, we defined new tests
and realized a specific machine to try the Dogma K8-S.
First of all, we fixed 2 important testing parameters: vibration amplitude and frequency.
Regarding the amplitude, we fixed a value of 6 mm; this is a greater value than common cobbles (consider the
gap between 2 cobbles), so it allowed us to test very critical conditions, like big bumps or holes.
Regarding the frequency, we considered a rider’s speed between 40 and 45 km/h (the average speed of
2014 Paris-Roubaix is 41,5 km/h), and cobbles’ lengths between 15 and 25 cm; from simple calculations, we
derived a frequency between 43 and 83 Hz.
15
Starting from the above considerations, we realized a test machine that can apply 6 mm of vertical travel on
the rear hub at a specific frequency, and, at the same time, can apply weight force on the saddle and pedalling
forces on the pedals. This configuration allowed us to simulate the most critic conditions for the frame.
To apply dynamic loads, we designed 2 different cam wheels, which act on the rear hub; adjusting the rotation
speed, we can modify the frequency.
We realized 2 different cam wheels (with different number of lobes), to vary the stress on the frame.
We performed many tests on this machine, with different purposes.
First of all, we have to determine the durability and safety of every single component. Using the machine we
checked how every component behaves under controlled loads, and how much it wears; this gave us useful
feedback to define the final specifications for the entire system. For example, we chose the final chamber plug
between 7 different configurations, comparing their wear after a test of 80000 pedalling cycles and 680000
bumps on the rear hub.
At the same time, this test was useful to verify the strength of the frame, considering the limits of ISO tests
in this case.
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Shock absorption test
We also used the machine to measure the performances of the suspension, in terms of shock absorption; to
do this, using some accelerometers, we recorded the vibrations and analysed the results. This analysis was
made in collaboration with the JLR’s engineers.
Initially, we should find the proper equipment to record the data. This involved finding suitable surfaces to use
as a representative road inputs for measurement, and also procuring and testing the measurement equipment, appropriate for bicycle measurement. Indeed, JLR’s test kits are designed to be fitted onto passenger
vehicles and they are clearly not suitable for very small and lightweight applications as the bicycles. In addition,
since these accelerometers have been used also on the road tests, we not only have to find appropriate kit,
but also attach it on the bike without interfering with the riders.
Once we found the proper equipment, we applied the accelerometers on specific points of the frame, recording the vibrations under controlled loads; records were later analysed and compared, to determine the
system’s performances (more details in the following paragraphs).
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b. Field Test
In parallel with laboratory tests, we performed a large number of field tests, to validate frame and the suspension parts in real conditions. In particular, we wanted to acquire the performances of the suspension when
subjected to high loads due to very rough terrains, as much as compare different configurations to define the
optimal one.
We tested samples of the new frame and suspension, varying the elastomers and the preload settings,
beyond the tyre pressure; we also tested the Dogma K 2015 and the Dogma F8 to have reference points
during the analysis of the results.
Race course tests
In particular, we performed long run tests on the Paris Roubaix and Tour of Flanders courses: these gave us
the opportunity to test the bikes on the cobbles and rough terrains.
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During these tests, we placed some accelerometers, to acquire the vibrations in different zones of the frame:
- on the front and rear wheel, to acquire the incoming vibrations from the terrain
- on the stem and SP, to acquire the outgoing vibrations to the rider
- on either side of the suspension, to determine its own performance
We analyzed the data acquired through the FFT (Fast Fourier Transform), to identify the peak vibration levels
and the transfer functions, varying the configurations. For example, we plotted the acceleration versus frequency (FFT plot) at the rear wheel (left image) and at the SP (right image), where X is the fore/aft direction, Y
the lateral, Z the vertical and RSS the overall vibration.
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In this particular configuration of the bike, the overall vibration peak is as high at the rear wheel as at the SP
but, at the same time, the peak of the vertical acceleration Z is almost 35% lower on the SP than on the
wheel.
Please consider that, at this first view, these results could seem not to be very advantageous, but they
are influenced by the rider’s speed and the course (type of cobbles, line choosen, etc.), so they need further
analyses. For example, the chart below compares 2 different sectors ridden with the same bike: the number
2 was ridden at about 27 kmh, while the number 4 at about 38 kmh. As intutive, the vibration peak seems to
decrease with a lower speed.
Furthermore, it is not always easy and immediate to understand the behavior from the FFT plots, so we divided the SP vibration by the vibration at the rear wheel to obtain the tranfer function: this shows the vibration
at the SP for a given input at the wheel.
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If this value is lower than 1, it means that the vibration transmitted to the SP (i.e. to the rider) is muﬄed. This
analysis eases the comprehension of the suspension’s performances: using the transfer function, we compared different bikes and different configurations.
The graph above, for examples, highlights that the Dogma K8-S muﬄes the vibrations much more than Dogma K 2015, even with a higher tyre pressure.
Below we have the transfer function across the suspension unit. Please note that this analysis could not be
done on the Dogma K 2015: since it does not have any suspension, the SSs transmit exactly what they feel
(no damping), so theoretical transfer function is 1. It is evident that, in this configuration, the suspension unit
is working, especially at high frequencies.
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Controlled course tests
It is intuitive that the results above discussed are deeply influenced by the rider’s speed and the course (type
of cobbles, line chosen, etc.). To solve this problem and increase the repeatability of the test, which means
results more accurate and true, we performed some similar tests at the MIRA Technology Park, where we
could compare different configurations (elastomer, cups, etc.) on the same controlled conditions.
The bikes tested were also equipped with powermeters, so we could record and compare the speed and
power of the rider. We repeated multiple times the same sector, varying the bike or the general configuration;
some results are shown below.
DOGMA K
OUT
BACK
AVERAGE
speed (mhp)
speed (kph)
Power (W)
22.4
19.0
20.7
35.8
30.4
33.1
307.4
313.0
310.2
DOGMA K8-S
OUT
BACK
AVERAGE
speed (mhp)
speed (kph)
Power (W)
23.8
21.4
22.6
38.0
34.2
36.1
316.0
304.5
310.2
DIFFERENCE
+9% Faster
The previous chart shows an example of these tests and compares the Dogma K 2015 (above) with the Dogma K8-S (below); please note, on the Dogma K8-S the tyre pressure of the rear wheel was higher.
Shortly, to cover the same section, spending the same energy, with the Dogma K8-S the rider was about 9%
faster. As he reported, the suspension, absorbing the shocks, allowed him to ride in a better way, remaining
seated on the saddle and better pushing on the pedals.
In addition, the effect of the suspension, allowed to increase the tyre pressure: this condition is advantageous,
especially considering that reduces the tyres’ friction when riding on smooth surfaces, like the normal roads
(just to have an idea, almost the 80% of the Paris Roubaix course is on flat smooth roads).
Furthermore, with the Dogma K8-S, the rider could maintain the hands on the drops of the handlebar, while
with the traditional bikes (i.e. Dogma K 2015 or Dogma F8), he put his hands on the levers or the top of the
handlebar: this increases the aerodynamics and the handling of the bike.
Finally, when he tested the bike on smooth roads, simulating quick sprints, he did not feel any bobbing (useless
functioning of the suspension due to pedalling forces); the preload system allows the suspension to absorb
only the road’s vibrations (not the vibrations due to the pedalling) and, at the same time, guarantees the stiffness of a proper road bike.
Resuming all the previous results in a single value, the Dogma K8-S has an overall performance 4.6% greater
of the Dogma K 2015, in terms of handling, energy saving and higher comfort.
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c. Final Design
Final design of the frame
Results and feedbacks from the whole test campaign allowed us to define the optimal configuration of the
frame and suspension: every single component has been developed to ensure the highest performance, as
much as safety and durability.
Images below show some 3D renderings of the final design, where the main features (specific CSs and SSs,
suspension, etc.) are clearly visible.
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Final design of the suspension
The exploded view below specifies the main components
and their specific function:
Upper mount: this contains the piston chamber. It is fixed onto the ST
bracket and creates the upper pivot point of the SSs. There is a low
friction bushing that minimizes the friction between piston and chamber,
increasing the performances and the life of the system
Piston: it is thermal treated, to increase its life. It contains a “bump stop”
to avoid dangerous bump of the piston on the chamber.
Chamber plug: it allows assembling and disassembling quickly the whole system, for maintenance; it also uses a low friction bushing to reduce
the friction with the piston.
The preload can be adjusted with a specific bushing, placed on the upper
mount; this is easily reachable with a spanner.
Elastomer: it damps down the vibrations from the wheel; 2 different
material densities allow adapting the suspension to every rider.
Pot: on the one hand, this protects the elastomer from dust and water,
on the other it constricts the elastomer, modifying its behaviour; using
different pots, the rider could modify the suspension reaction. It incorporates a seal to protect the elastomer from water, mud and dust, ensuring the durability of the system.
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Team Sky configuration
Carbon Torayca T1100 1K the Dream Carbon
Frame Size 53 - 990 gr ( with Suspension )
Weight Suspension 95gr
26
consumer configuration
Carbon Torayca T1100 1K the Dream Carbon
Frame Size 53 - 990 gr ( with Suspension )
Weight Suspension 95gr
27
Gallery
28
Gallery
29
Cicli Pinarello SpA
Viale della Repubblica 12
31020 Villorba (TV) Italy
tel. +39 0422 420877 fax +39 0422 421816
[email protected]
www.pinarello.com
30

PINARELLO DOGMA K8-S

Transcription

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