GB2164300A

GB2164300A - Bicycle frame and bicycle

Info

Publication number: GB2164300A
Application number: GB08423272A
Authority: GB
Inventors: Francis George Kirk
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-09-14
Filing date: 1984-09-14
Publication date: 1986-03-19
Also published as: IN164175B; GB8423272D0; GB2164300B

Abstract

A cross bar 1, a lower bar 2, a bridge 31, a saddle stem 3, and rear forks 11 and 12 are cast in one piece from a magnesium-based alloy. An important feature of the frame is the additional stiffening of the frame against torsion by means of the structural bridge 31. The bridge is cast solid with the cross bar 1 and lower bar 2 and acts as a torsion arm so that any twisting of the frame due to deflection of the head 4 out of the plane of the frame is not resisted by the ends of the cross bar 1 and lower bar 2 remote from the saddle stem 3, but at locations considerably nearer the saddle stem 3. A further improvement is achieved by shifting the junction of the bottom bar 2 upwardly from the lower end of the saddle stem 3 as illustrated in Figure 1. By this means, the overall length of the bottom bar is reduced, thereby further reducing the length of the beam it forms, and also saving material and therefore weight. In addition, there is some reinforcement of the saddle stem 3 itself. <IMAGE>

Description

SPECIFICATION Bicycle frame and bicycle This invention relates to bicycle frames.

My co-pending application 8307749, which was unpublished at the date of filing the present application, relates to bicycle frames cast in open section lightweight metal or alloy, such as magnesium or an alloy thereof.

A conventional bicycle frame is basically of steel or alloy tubing and consists of a saddle tube or stem and a head which are joined by a lower bar and an upper bar. The upper bar may be generally horizontal, as in a man's bicycle, in which case it is known as a cross bar, or it may be oblique and generally parallel with the lower bar, as in a lady's bicycle. The head carries a bearing for an assembly of front forks and handlebar, while rear forks are carried by the saddle stem.

In accordance with the invention of the abovementioned co-pending application, the frame has parts cast in open section of a lightweight metal of alloy, and the open section upper and lower bars are joined by a structural bridge linking them at a location between the head and the saddle stem.

The bridge, which may be of I section, has the effect of considerably increasing the torsonial stiffness of the frame, which enables the use of I section bars for the upper and lower bars.

In a conventional bicycle frame, the lower bar is connected between the lower end of the head and lower end of the saddle tube or stem, adjacent the bearing for the crank wheel.

I have discovered that when using an arrangement with open section bars, advantages are obtained by having the lower bar join the saddle tube or stem at an intermediate point. This effectively shortens the length of the beam formed by the lower bar, thereby stiffening it, and also saving some material and therefore some weight.

In accordance with a first aspect of the present invention, there is provided a bicycle frame including a saddle stem and a head interconnected by upper and lower bars cast in open section of a lightweight metal or alloy, in which the lower bar us connected between the lower end of the head and joins the saddle stem at an intermediate point spaced above the lower end thereof.

As in the co-pending application, the upper and lower bars are preferably joined by a structural bridge, which may be of I section, linking them at a location between the head and the saddle stem.

In accordance with a second aspect of the invention, there is provided a bicycle incorporating a bicycle frame in accordance with the invention as set forth above.

The invention will be further described with reference to the accompanying drawings which show a preferred embodiment of the present invention, and in which: Figure 1 is an elevation of a bicycle in accordance with a presently preferred form of the invention; and Figures 2 to 8 are respectively sections taken along the line Il-Il, Ill-Ill, IV-IV, V-V, VI-VI, VII-VII, and VIII-VIII of Figure 1.

The bicycle frame illustrated in Figure 1 has a top or cross bar 1, a lower bar 2, a saddle stem 3, and a head 4. The head 4 carries a bearing for an assembly of a handle bar 5 and a front fork 6, which assembly supports a front wheel 7 in a gen erally conventional manner.

The saddle stem 3 receives a support tube 8 for a saddle 9. In addition, the saddle stem 3 carries a rear fork arrangement, consisting of upper and lower rear forks 11 and 12 respectively, to support a rear wheel 13.

At the lower end of the saddle stem 3 there is located the conventional crank wheel 14, with pedals 14a, only one of which is illustrated.

In the arrangement illustrated, the crossbar 1, the lower bar 2, a bridge 31, the saddle stem 3, and the rear forks 11 and 12 are cast in one piece from a magnesium-based alloy and have the sections as illustrated in Figures 2 to 8.

An important feature of the frame as illustrated is the additional stiffening of the frame against torsion by means of the structural bridge, which is illustrated by the reference numeral 31 in Figure 1 and extends between the cross bar 1 and the lower bar 2. The bridge is cast solid with the cross bar 1 and the lower bar 2 and acts as a torsion arm so that any twisting of the frame due to deflection of the head 4 out of the plane of the frame is not resisted by the ends of the cross bar 1 and lower bar 2 remote from the saddle stem 3, but at locations considerably nearer the saddle stem 3.

The cross bar 1 is of I section as shown in Figure 2, and also has lightening holes 15. The bridge 31 also has lightening holes 31a and is of I section as shown in Figure 3.

Figure 4 shows that the lower bar 2 is also of I section, with one flange wider than the other, and Figure 1 shows lightening holes 2a in this bar as well.

Figures 5 and 6 illustrate the section of the saddle stem 3 as being modified U section, as shown in Figure 6, merging into (or having inset) a tubular portion 16, as shown in Figure 5, to receive the saddle support tube 8, which is clampable as is conventional.

Figures 7 and 8 shows that each of the rear forks 11 and 12 is of C section. As is conventional, the arrangement includes two upper and lower rear forks 12, one on each side of the rear wheel 13.

The C sections are arranged back to back so that the open sections face outwardly.

The head 4 may be an integral casting of tubular form.

The effect of the bridge 31 is to decrease the effective resisting length of the beams formed by the cross bar 1 and bottom bar 2, making both the beams formed by the bars stiffer in bending and torsion. But more significant is that the increased length of torque arm across the stiff bridge creates large bending deflections in both the beams 1 and 2 for unit deflection of the head. This makes the torsional stiffness of the beams 1 and 2 considerably less important and the bending stiffness more important. This effect enables I section beams, which are stiff in bending and weak in torsion, to give a torsionally rigid structure in the frame described. Conventional bicycles use tubes which have high torsional rigidity and relatively low bending strength, creating frame stiffness by the torsional rigidity of the tubes.The described frame uses weak rigidity sections which are forced to deflect in bending, which they can resist, when torsion at the head is applied.

It has been found that a further improvement can be achieved by shifting the junction of the bottom bar 2 upwardly from the lower end of the saddle stem 3, as illustrated in Figure 1. By this means, the overall length of the bottom bar is reduced, therefore further reducing of the length of the beam it forms, and also saving material and therefore weight. In addition, there is some reinforcement of the saddle stem 3 itself.

Various modifications may be made within the scope of the invention.

Claims

1. A bicycle frame including a saddle stem and a head interconnected by upper and lower bars, the frame being cast in a lightweight metal or alloy, in which the lower bar is connected to the lower end of the head and joins the saddle stem at an intermediate point spaced above the lower end thereof.

2. A bicycle frame as claimed in claim 1, in which the upper bar is cast in open section.

3. A bicycle frame as claimed in claim 1 or 2, in which the lower bar is cast in open section.

4. A bicycle frame as claimed in any of the preceding claims, in which the upper and lower bars are joined by a structural bridge linking them at a location between the head and the saddle stem.

5. A bicycle frame as claimed in claim 4, in which the structural bridge is of I section.

6. A bicycle frame substantially as hereinbefore described with reference to the accompanying drawings.

7. A bicycle incorporating a bicycle frame as claimed in any of the preceding claims.