BE1020626A4 - BIKE FRAME STRUCTURE WITH MULTIPLE ELEMENTS FOR IMPROVED STIFFNESS AND IMPROVED AERODYNAMICS BY USING THE VENTURI EFFECT. - Google Patents

Description

TITLE PATENT:

Bicycle frame structure with multiple elements for improved stiffness and improved aerodynamics through the use of the Venturi effect.

DESCRIPTION

1. Achterarond / Uitdaainaen

There are two conflicting principles in the development of bicycle frames:

Bicycle frames need a certain stiffness for efficient power transfer Time trial bikes must have specific aerodynamic performance

After analyzing which location is the most suitable to get the most benefit, it can be decided that the down tube is the most suitable: the down tube must withstand the most torsional load and at the same time it forms the greatest barrier to the wind (Figure 2: Torsion vs. Wind load)

It is very difficult to optimize the performance for both loads:

Optimization for torque (power transmission) is achieved by a wide cross-sectional profile.

Optimizing the wind load (aerodynamics) is achieved by a narrower cross-sectional profile.

This is shown in Figure 3: Round vs. Aero profile.

CHALLENGE: How can a structural element with a wider profile be made that has a good performance in terms of torsional rigidity and that at the same time has comparable aerodynamic performance as an aerodynamic profile? 2. Structural / Aerodvnamic principles a. Structural principles

The lower tube of the bicycle frame undergoes, among other things, a torque (Figure 4: Schematic representation of Torsion load). The basic equation for Torsion Moment that describes the relationship between the moment and the accompanying angular rotation is:

• V

With: MT is the torque Torque G is the sliding modulus J is the polar moment of inertia of the cross-section L is the length of the loaded structure, measured transversely to the cross-section Θ is the angular rotation

The two most important parameters mentioned above are the sliding modulus (G), a material constant, and the polar moment of inertia of the cross-section (J) obtained with the following equation:

Where r is the distance of the mass measured radially with respect to the central axis of the profile.

Optimization for Torsion Stiffness will be achieved by positioning as much structural material (mass) as possible as far as possible from the central axis.

b. Aerodynamic principles: Luch resistance coefficient

Improving the aerodynamic performance of a bicycle frame is achieved by lowering the air resistance. The comparison to determine the air resistance is:

With: D is the Resistance Force

Cd is coefficient of resistance p is density (of air under normal atmospheric conditions: 1.225 kg / m3) V is the air velocity A is the reference area (in most cases the frontally projected area)

The two most important parameters that influence the aerodynamic resistance are: the resistance coefficient and the reference surface. The accompanying figure gives an overview of how the resistance coefficient can be influenced since it can represent the most gain (Figure 5: Examples of Resistance coefficient (Cd)).

It can be deduced from the examples that a thin "streamlined" profile has the lowest resistance coefficient. The reason for this low resistance coefficient has to do with the fact that there is a better laminar flow around the profile. Releasing the flow and creating turbulent air flow is the main reason for air resistance (Figure 6: Laminar vs. Turbulent air flow). The turning point, where the airflow changes from laminar to turbulent, depends on various parameters: air speed, surface quality, profile shape (length, width, curvature, ...).

The curve of the profile in relation to the air speed also plays a major role in the location of the tipping point. (Figure 7: Transition zone around different profiles)

The challenge for profile designers is to determine an optimum shape that reduces the resistance to a minimum at a given speed spectrum without compromising the strength and stiffness of the internal structure.

c. Venturi Effect

A "Venturi" tube is a deliberate narrowing of an air flow to achieve a local reduction in air pressure. The "Venturi" effect is a physical phenomenon that can be used to attract gases through a locally generated low pressure zone.

The corresponding figure (Figure 8: Theoretical representation of the Venturi effect) shows the theoretical representation of the Venturi principle: a reduction in air pressure between point "1" and point "2".

The equation to explain the Venturi principle is the "Bernoulli law" combined with the equation for volumetric flux (Q):

These comparisons show that in all cases there will be a reduction in air pressure at the outflow.

3. Venturi Powerbox principle

By opening the lower tube in the longitudinal direction, a new type of air flow is created. Where the air flow will normally flow around a closed profile, the air flows through the profile at the Eddy Merckx ETT. (Figure 9: Venturi Powerbox)

The opening of the profile is given a specific shape so that the bottom tube of the Eddy Merckx ETT achieves comparable aerodynamic performance with a closed aerodynamic profile of the same width.

A possible cross-section of the profile is given in the attached figure (Figure 10: Venturi cross-section of the Eddy Merckx ΕΤΓ). The table below shows the values for the dimensions that a Venturi profile will satisfy.

By using the principles described in Structural / aerodvnamic principles, a new type of bicycle structure is obtained:

Structurally, the bicycle structure has a wide profile to absorb Torque. Aerodynamically, by using the Venturi principle, there is a possible reduction in air resistance.

Both situations (open and closed profile) are represented in the attached figure (Figure 11: Open and closed profile in an air stream). The aim is to reduce air resistance, related to an aerodynamic profile where it has already been mentioned above that the dimensions and shape of the profile determine the aerodynamic performance.

A cyclist cycles at a constant speed VI. The air pressure at that time, outside the profile, is pl. Under normal circumstances this will be atmospheric pressure.

Situation 1: Open profile with Venturi Effect

The constant air flow will be divided into two air flows: one flow will go around the profile (above and below) and the other air flow will go through the center of the profile.

The air flow that goes around the profile will slow down and a transition will occur from laminar to turbulent air flow. This turbulent air flow is the main reason for air resistance around the profile. As the air slows down, a high pressure area will arise locally.

The airflow that goes through the profile will accelerate due to the narrowing further down in the section: this is the Venturi principle. The accelerated air will cause a local low pressure area just behind the profile (p3 <p2).

The difference in pressure between p2 and p3 will disrupt the continued existence of the turbulent air flow and will create a new transition to a laminar flow. This is simplified: the low pressure area will attract the air from the turbulent flow and make it laminar again. This interaction between air flows will cause a reduction in air resistance.

Situation 2: Closed aero profile with the same width as an open profile

As described above, the air flow around a profile depends on various characteristics: length, width, specific shape of the profile. The resistance coefficient is directly dependent on these parameters.

Somewhere along the profile there will be a turning point / transition zone where the laminar flow turns into a turbulent flow. When this happens the air resistance will increase drastically. The purpose of developing an aerodynamic profile is to optimize it for laminar flow.

FIGURES

Figure 1: Cross section of the Venturi bicycle structure

Figure 2: Torsion vs. Wind load

Figure 3: Round vs. Aero profile

Figure 4: Torsion load diagram

Figure 5: Examples of Resistance Practitioner (Cd)

Figure 6: Laminar vs. Turbulent air flow Figure 7: Transition zone around different profiles Figure 8: Theoretical representation of the Venturi effect Figure 9: Venturi Powerbox

Figure 10: Venturi cross section of the Eddy Merckx ETT Figure 11: Open and closed profile in an air stream

Claims (1)

CONCLUSION The bicycle frame structure with multiple elements and with integrated Venturi effect can drastically improve the overall performance of a bicycle frame; both structural and aerodynamic. The dimensions and general shape of the profile are the most important parameters that contribute to the final performance of the bicycle frame: the general torsional stiffness and obtaining a Venturi effect. The combination of the dimensions and the unique shape of the bicycle structure form the innovation of this invention.