WO1995005966A1

WO1995005966A1 - Bicycle saddle post suspension unit

Info

Publication number: WO1995005966A1
Application number: PCT/GB1994/001834
Authority: WO
Inventors: Bernard Derek Frutin
Original assignee: Rocep-Lusol Holdings Limited
Priority date: 1993-08-23
Filing date: 1994-08-22
Publication date: 1995-03-02
Also published as: GB9317498D0; AU7465094A

Abstract

There is provided a suspension unit for a bicycle saddle post. The unit is in the form of a cylindrical casing (102) which contains a shaft (138), one end of which is adapted to receive a bicycle saddle, the other end of which communicates with a resilient restoring means (114) and a damping unit (130).

Description

Bicycle Saddle Post Suspension Unit

This invention relates to a bicycle saddle post suspension unit.

Saddle posts have traditionally been simple extruded or seamed tubes with a saddle at the top and with the lower simple tube portion dimensioned so as to be able to fit into a receiving tube of the frame a bicycle. The receiving tube normally comprises a bracket which can be tightened to fix the saddle post in place.

The well known advantage of this system rather than fixing the saddle directly onto a suitably configured portion of the frame is that the height of the saddle can be easily adjusted. In addition to this, saddles can be replaced easily, removed for repair etc. Traditionally saddle posts have been substantially rigid as have the frames of bicycles. Cycling over rough or bumpy surfaces has therefore been uncomfortable throughout the history of the bicycle, with jarring caused by irregularities in the surface being cycled over being absorbed partly by pneumatic tyres and partly by springing or other resilience in the saddle but mainly by the rider of the bicycle.

The recent increase in popularity of the mountain bike and other off-road cycling has compounded the problem of jarring being transferred to the cyclist and has also led to the development of shock absorbing suspension for bicycles.

The first commercially successful shock absorbers for bicycles were those incorporated into the front forks, and more recently rear wheel suspension has been developed. Both front and rear wheel suspension can improve comfort and performance over very irregular and, in particular, irregular and steeply descending terrain. However, such frame mounted suspension has the disadvantage of decreasing performance when the cyclist is pedalling hardest. This is because the power is imparted from the cyclist to the bicycle via the pedal on the downward stroke of the pedal, and when there are suspension units between the pedal assembly and the wheels some of the impetus of the cyclist's downstroke is dispersed. This effect is most pronounced when the downstroke is hardest, that is when the cyclist is standing on the pedals rather than being seated upon the saddle.

In the interests of performance therefore, bicycle fork suspension should be kept hard so as to minimise the dispersion of energy on the down stroke. However, such stiff suspension does not give the required increase in comfort over bicycles without suspension. It is therefore desirable to incorporate suspension into bicycles in such a way that the suspension unit increases comfort for the cyclist but does not disperse energy imparted to the pedals by the cyclist. Thus the suspension unit must be incorporated between the saddle and the wheels but not between the pedals and the wheels, and the saddle post seems to be the best position.

There are problems associated with locating a suspension unit in the saddle post, most notably the size constraint and the fact that a wide range of cyclist weights and cycling conditions should be catered for. Weight is also an important factor as the total weight of competition bicycles is best maintained as low as possible. Because of the size and weight constraints the saddle post suspension units that have been available so far have comprised a resilient restoring means which are compressed by the weight of the cyclist and compressed still more and then released by the dynamics of the bicycle moving over an irregular surface while some or all of the cyclist's weight is on the saddle. Typical resilient media used are steel coil springs and elastomer units. In such units a typical stroke length has been only an inch or so and specific adjustmenent has been necessary for use of the units with varying weights of cyclist.

According to the present invention there is provided a bicycle saddle post suspension unit comprising a resilient restoring means and a gas or fluid filled damping unit.

Preferably, the resilient restoring means is a solid object, and may be a spring, an elastomer unit or some other suitable solid.

Preferably, the resilient restoring means is contained inside the damping unit. Preferably, the resilient restoring means and the damping unit are situate inside a cylindrical casing.

Preferably, a shaft attached or supported by the restoring means and or the damper and slidingly engaging the cylindrical casing is attached to a bicycle saddle.

Preferably, the restoring means and damping unit are such as to be suitable for bearing the weight of a person on a bicycle traversing an irregular and/or steeply inclined or declined surface.

Preferably, the damping unit approximately critically damps the restoring means under such conditions.

Preferably, the degree of damping can be controlled by choice of the properties of the oil used in the damping unit.

Embodiments of the present invention will now be described by way of example, with reference to Fig. 1 which shows a cross-sectional view of a bicycle saddle post suspension unit in accordance with the invention.

Referring to Fig. 1 a bicycle saddle post suspension unit comprises a gas damping unit 130, a coil spring 114 and a cylindrical outer casing 102. The gas damping unit 130 is fixed to the casing 102 at its base by a pin 108. The gas damping unit 130 comprises a tubular housing 131 defining a gas-filled cavity 132 in which a metal piston head 133 may slide. The piston head 133 is attached to a metal shaft 138 which passes through a seal 134 into an oil-filled chamber 135. Fixed to the shaft 138 in the oil filled chamber 135 is a bung 136 which fills the width of the cylinder preventing flow of oil from one side of the bung to the other but for a small hole 139 in the bung 136 which allows a restricted amount of oil to flow under pressure.

Passing through the bung 136 the shaft 138 passes out of the oil filled chamber 135, then out of the tubular housing 102 of the damping unit 130 and then, after a length determined by the state of compression of the damping unit, into a loctite assembly 148. The loctite assembly 148 fixes the metal shaft of the damper 138 to a metal post 121 . The metal post 121 extends out of the cylindrical housing 102 up to the saddle mounting.

Close to the loctite assembly 148 there is a slot 141 in the post 121. The slot 141 is lateral to the post and passes through a diameter of the post. Passing through the slot 141 is a pin 140. Said pin also passes through opposing holes in the outer casing 102, said holes being dimensioned to receive and fit closely around the pin 140. The length of the pin 140 is greater than the inner diameter of the cylindrical outer housing 102 but smaller than the outer diameter. The pin 140 is held in place by a circlip 105 which fits around the outer housing 102 in a recess 112.

The slot 148 in the post 121 allows the post to move in the direction of its axis with the limits of the motion being set by the engaging of the pin 140 against the ends of the slot.

The whole device from the first supporting member 108 up to a substantial way up the steel tube 121 is contained by the cylindrical casing 102.

The cylindrical casing 102 has outer diameter of the same dimension as a standard saddle post, enabling it to be fitted into a standard bicycle frame and locked into place by a standard saddle post bracket, though shims may be used to facilitate fitting to differently proportioned brackets and tubes. Such a bracket could hold the casing 102 at any convenient point, depending on the required saddle height.

The post 121 passes out of the cylindrical casing 102 by passing through a seal 103 which prevents the entrance of dirt, debris and other foreign objects to the mechanism of the suspension unit.

In use the changing force on the saddle caused by the weight of the cyclist on the saddle and the bicycle's transit over irregular terrain will be transmitted down the post 121 and down the shaft of the damper 138. This causes the piston head 132 to move in the tubular housing of the damper 130, compressing the gas in the gas filled chamber 132, which acts as an air spring. If the forces are great enough the piston head 133 will engage the spring 114 which will provide an additional restoring force. At the same time the bung 136 will be moving in the oil filled chamber 135, and the viscose oil passing through the small hole 139 will provide a damping effect, changing degrees of compression in the damping unit 130 and in the spring 114.

The changing degrees of compression in the air spring and the coil spring 114 allow the shaft 138 loctite assembly 148 and steel tube 121 and thus the saddle (not shown) to displace vertically with respect to the outer casing of the unit 102 and the rest of the bicycle. The displacement is limited by the action of the pin 140 on the slot 141. The pin 140, being constrained by the outer housing 102 also prevents the post 121 rotating about its axis.

On both compression and extension of the spring the vertical motion of the parts which move relative to the outer casing 102 is damped, the degree of damping being controlled by varying the viscosity of the oil in the damper.

A benefit of having both a spring and a gas damper is that a large amount of vertical displacement of the saddle is made available, giving greater comfort and providing for use of the unit under a wider range of conditions and cyclist's weights than might otherwise be practicable, and yet the displacement remains controlled since it is damped and, 'bounce' from sudden changes in displacement dies away more quickly than it would without the damping unit.

The benefit of having the spring inside the chamber of the gas damper is that the length of the unit and thus the weight of the unit, can be reduced with little or no effect on the desirable characteristics of the unit.

Suspension unit substantially as hereinbefore described could be used in other positions on a bicycle, for example as a suspension unit for the forks.

Modifications and improvements may be incorporated without departing form the scope of the invention.

Claims

1. A bicycle saddle post suspension unit comprising a resilient restoring means and a gas or fluid filled damping unit.

2. A suspension unit as claimed in Claim 1, wherein the resilient restoring means is a spring, an elastomer unit or other resilient solid member.

3. A suspension unit as claimed in either Claim 1 or Claim 2, wherein said resilient restoring means is contained inside the damping unit.

4. A suspension unit as claimed in any preceding claim, wherein the resilient restoring means and the damping unit are located inside a cylindrical casing.

5. A suspension unit as claimed in Claim 4 and including a shaft attached to or supported by the restoring means and/or the damping unit and slidingly engaging the cylindrical casing.