Spring-action seat suspension assembly for a two-wheeler

A springy seat recliner assembly for a bicycle comprises three sections, namely a seat post member (20) to be entered and clamped in a seat tube, further a movable intermediate section (3, 4), and a seat attachment part (2) having attachment details for a conventional saddle. The intermediate section comprises substantially parallel or the seat post member (20) and on the seat attachment part (2), as well as a springing mechanism mounted in between two diagonally placed bearings (23, 28) to push the seat attachment part (2) upwards. When the rear wheel receives a shock, a very good compensating cushioning movement directed obliquely downwards and backwards is obtained.

FIELD OF THE INVENTION 
The present invention relates to a cushioning system in connection with the 
sitting means of a bicycle, and relates more precisely to a springy seat 
retainer assembly intended to be mounted on a standard bicycle in the 
position in the bicycle frame where the conventional seat post is usually 
entered down into the seat tube. Further, it is intended that a standard 
seat shall be mounted on top of the seat retainer assembly in accordance 
with the invention. 
BACKGROUND OF THE INVENTION 
There are several types of previously known cushioning solutions in 
connection with bicycle seats, the most well-known one is the means having 
two helical springs at the rear end of the seat and constituting a part of 
the seat itself. Such helical springs have a very limited travel, at the 
same time as the front edge of the seat remains un-cushioned. This type of 
cushioning will increase comfort somewhat, but is not appropriate to 
accommodate the type of shock which occurs in particular in off-road 
bicycling. 
Among recent types of cushioning for bicycle seats, a solution can be 
mentioned wherein the seat has a spring action in a telescopic assembly 
inside or along the seat tube, which tube in most bicycles is slanted in a 
direction down toward the crank bearing. This type of cushioning has a 
clear limitation in that the travel of the system along the seat tube in 
the spring action, is as much as 45.degree. mis-directed. This also has 
the effect that all attempts to obtain a long travel for such systems have 
not been successful, because the movement component in the wrong direction 
increases with an increase in the travel along the seat tube, and this 
becomes very noticable whenever the bumps are larger than a certain size, 
typically 10-15 mm. 
Another previously known type of cushioning is the one in which a seat is 
springy by being mounted on a long and flexible arm attached to the 
bicycle's top tube adjacent to the handlebar bearing. This system makes it 
impossible to provide any bias, which leads to a tendency to swing up and 
down for the bicyclist during ordinary bicycling. Further, such a system 
has the problem that the seat will bound upwards quite far, when the 
bicyclist slides off the seat while moving his body rearwardly to avoid 
falling forward over the handlebar in a steep downhill ride, and this 
makes it rather difficult to get back onto the seat again afterwards. The 
correct distance to the pedals is achieved while the bicyclist sits on a 
seat which is pushed down, and without a weight on top, the seat will take 
a relatively high position. 
From European patent application with publication number 0418429 there is 
known a springy saddle device for a two-wheeled vehicle, particularly for 
a moped or a motorcycle. An articulated system having parallel swinging 
arms connected to a helical spring down inside a saddle post, is attached 
directly to the frame, and the saddle framework is also attached directly 
to the swinging arms. A substantially downwardly directed movement is 
achieved with this device, however the device cannot be used as an 
optional part inserted between a standard bicycle frame and a standard 
seat. 
A springy device for a bicycle seat is previously known from German 
Offenlegungsschrift number 4224941, which device is based upon a helical 
spring built into a seat post substitute. An adapted cylinder can slide up 
and down in a substantially vertical guide element behind the seat tube, 
and the cylindrical slide member is connected to the helical spring inside 
the seat post via a wire drive passing over one or more guide wheels. The 
seat is mounted on top of the cylindrical slide member, and thus will be 
able to spring substantially vertically up and down. The wire drive 
solution entails obvious weaknesses, and the construction does not seem 
particularly robust in practice. 
In a situation where the bicycle rear wheel hits a bump, the whole frame 
and everything mounted thereto, will start to rotate around the front 
wheel hub of the bicycle. This causes the seat, which is situated much 
higher than the bicycle hubs, to move forward in the speed direction in 
addition to an upward movement. With a built-in option for e.g. telescopic 
springing down along the seat tube, as mentioned above, one further 
forward movement component will arise when this type of springing goes 
into operation, as long as the frame seat tube is slanted as is normally 
the case for pedal bicycles. In practice this means that the seat, in 
addition to travelling up an down, will also travel forward and back 
beneath the cyclist at any bump. If the bump is 40 mm in height, the seat 
will attempt to move approximately 40 mm forward and back beneath the 
buttocks of the cyclist. Thereby the forces involved in these movements 
will try to pull the bicycle in a rearward direction, while the bicyclist 
attempts to push the bicycle in a forward direction by producing a force 
against the pedals and the bicycle drive unit. Thus, the forces will 
appear in opposition to the bicycle propulsion. In addition, also some 
energy will be lost because the transfer of forces will create friction in 
the system due to an unfavourable attack angle. In general the cushioning 
effect will also be reduced. These consequences are due to the horizontal 
movement components which are not compensated for in previously known seat 
post constructions. 
SUMMARY OF THE INVENTION 
Hence, the present invention has been conceived to solve the problem of 
compensating for both vertical and horizontal movement components when the 
rear wheel receives a shock, and to be able to achieve a transfer to the 
springy medium with a very low friction. Further, the invention has been 
provided to produce a sturdy seat retainer assembly where all forces 
involved in the shock absorption are transferred as free of friction as 
possible to the springy medium by compensating for movements and forces 
which would otherwise be applied to the seat and the bicyclist, where the 
cushioning movement has a long travel, and where, as a consequence of the 
construction, it is possible to achieve a good return damping of the 
springing. 
The above goals are attained in accordance with the invention by providing 
a springy seat retainer assembly of the type defined precisely in the 
appended patent claim 1. Further favourable embodiments of the invention 
are stated in the appended dependent claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In general the seat retainer assembly of the invention will comprise three 
main sections, namely at the bottom a seat post member, further a movable 
intermediate section, and on top a saddle attachment part to which a 
standard bicycle seat can be attached. In FIGS. 1, 2 and 3 appears a 
favourable embodiment of the invention, and the seat post member, which is 
adapted to be entered and clamped in a standard seat tube 21 as a 
substitute for a conventional seat post, is provided with reference 
numeral 20. The seat attachment part on top, which is equipped with 
attachment details for a conventional bicycle saddle, is provided with 
reference numeral 2. Between these two sections there is a movable 
intermediate section which in one end thereof is attached to an upper part 
of seat post member 20, in the following referred to as the post head 1, 
and in its other end the movable intermediate section is attached to the 
seat attachment part 2. The intermediate section comprises substantially 
parallel bars 3, 4 each of which being journalled in one end on a bearing 
27, 28 in the post head 1, and in the other end on a bearing 23, 24 in a 
lower portion of the seat attachment part 2. Reference numerals 3 and 4 
may each designate two respective bars, i.e. in total four bars where two 
by two are placed right behind each other in FIGS. 1-3 so that only one 
upper and one lower bar is visible in the drawing. Thereby a necessary 
space is provided for a spring mechanism (see below) between the bars. 
Optionally a two-bar configuration may be used, in which case the 
necessary space between bars 3 and 4 is provided by each respective bar 
having a cross-sectional shape similar to a "box" or a "U". (FIG. 4 shows 
such a design of bars 3 and 4.) An intermediate solution with three bars 
is of course also possible, for example using one upper U cross section 
bar 4 on top and two separate bars 3 therebelow. 
At the outset the bars are equal in length, and hence they are able to 
provide a swinging movement for the seat attachment part 2 about the 
bearings 27, 28 in the post head 1, which swinging movement is such that 
the seat attachment part 2 maintains its orientation in space during the 
movement. This is referred to as a parallellogram motion. However, in 
certain cases it will be desirable to achieve a movement which deviates 
somewhat from a perfect parallellogram motion, and it may then be 
interesting to shorten e.g. the upper one of the bars 4 a little as 
compared to the lower one 3. It may be desirable e.g. to rotate the saddle 
somewhat during a downward directed cushioning movement in order to 
compensate for the rotating movement of the bicycle during the shock from 
below against the rear wheel. Thereby the saddle is maintained parallel 
with the ground during the shock, instead of parallel to an imagined 
horizontal line fixed to the bicycle frame, corresponding to the top tube 
of an "old-fashioned" frame. 
The actual springing is provided by a spring mechanism which is mounted in 
between two diagonally situated ones of the bearings 23, 24, 27, 28 in 
order to provide a force which urges the seat attachment part 2 upward 
(and against a load from above on the saddle or against a blocking stop 
means for upwardly directed movement, see below). Thus, in an unloaded 
condition, a favourable embodiment of the seat retainer assembly of the 
invention may appear as in FIG. 1, where no saddle has been drawn in the 
upper part of the figure. However, FIGS. 2 and 3 show the same embodiment 
of the seat retainer assembly with a saddle mounted, respectively in a 
maximum depressed position and an unloaded upper position of the assembly. 
When looking at FIG. 1, it appears clearly that there are two possibilities 
for placing the spring mechanism between two diagonally situated bearings, 
and the option shown in FIG. 1 is the first preferred embodiment, where 
the spring 6, which in the embodiment shown is a helical spring, provides 
an expansion force out against the lower bearing 28 and the top bearing 23 
(alternatively, such a spring might be mounted between the top bearing 27 
on the post head 1 and the lower bearing 24 on the seat attachment part 2, 
but in that case the spring would have to be of a type providing a 
contraction force between the two bearings in order to push the seat 
attachment part 2 upwards.) 
The helical spring 6 is arranged in the vicinity of elongated opening 22 on 
the outside of a telescopic-action guide having an outer member 13 in the 
bottom, into which an inner member 11 on top is able to slide. The two 
telescopic members 11 and 13 are fixed to bearings 28, 23 in both ends by 
fixing means 7, 19. A slit 5 in the upper member 11 of the telescopic 
guide cooperates in the embodiment shown here, with a stop cotter 12 in 
the lower member 13 of the telescopic guide, and constitutes together with 
a threaded cog rim on top of member 11, a biasing means 10 to define an 
upper position for the saddle or the seat attachment part 2 by the stop 
cotter 12 engaging the lower end of the slit 5. When the seat is pushed 
down in a load situation, the upper telescopic member 11 travels down into 
the lower telescopic member 13, the stop cotter 12 then sliding in the 
slit 5. A smooth and linear movement of spring 6 is ensured by the inner 
telescopic guide 11, 13. 
In order to avoid a hard jolt finally when a full deflection occurs, i.e. 
as far as the assembly is able to spring, stop devices are arranged to 
provide soft limiting of the deflection in both directions. An attachment 
detail 8 on the seat attachment part 2 may e.g. be equipped with a member 
of a resilient material 30 to operate as a soft stopping device in order 
to limit the downward deflection of the assembly, by letting the resilient 
member 30 engage the top surface of the upper bar 4, see the illustration 
in FIG. 2, where member 30 engages the top surface on bar 4. 
Such a soft limitation of the deflection may also be necessary for the 
upward return movement, and in this respect there may be arranged e.g. a 
stop bolt 33 on the seat attachment part 2 in a position between the 
bearings 23 and 24. The stop bolt 33 then has an outer layer 32 of 
resilient material to provide a soft final jolt for the upward movement 
when the stop bolt hits the lower edge of the upper bar 4. 
Other configurations which provide a soft final cushioning are of course 
possible, for example the stop cotter 12 may encounter a resilient 
material at the end of slit 5. Optionally, this whole problem may be 
solved by means of a (not shown) longitudinal sleeve device inside the 
helical spring 6, having a central rod with two shoulders in spaced 
relation, which shoulders, upon movement of the system, encounter cup 
spring disks arranged in two end positions in a surrounding sleeve, which 
sleeve will also provide the option of bias adjustment by providing one 
end of the sleeve with an outer part having threads for screw adjustment. 
To achieve the most favourable cushioning movement the way the seat 
retainer assembly is shown in FIG. 1, with upward/rearward slanting bars 
3, 4, the center 25 of saddle attachment in the seat attachment part 2 
should be placed above and somewhat in front of the rear bearings 23 and 
24, so that a vertical line through the center 25 both in an unloaded 
assembly position and in any other position will be situated between 
bearing pair 27, 28 on the post head 1 and bearing pair 23, 24 on the seat 
attachment part 2. Another important feature to ensure optimum movement 
during spring-action, is that bearing pair 23, 24 on the seat attachment 
part 2 already in an unloaded seat position is situated behind the 
extension of the seat tube axis 26. 
In the embodiment of the seat retainer assembly shown in FIG. 1, the seat 
attachment part 2 is equipped on top with two attachment halves 8 
(previously referred to as "attachment details") for clamping a standard 
saddle in the seat attachment part 2. A screw 16 and a hoop 9 hinged to 
the seat attachment part in a suspension point 14, completes the seat 
attachment part. (For the rest, such attachment details are shown in part 
in FIG. 4.) Reference numeral 15 designates a counterpart to the screw 16, 
in the form of a cylindrical bed nut. As previously mentioned, there may 
be a resilient material 30 as an outer layer surrounding at least the 
lower one of the attachment halves 8, serving as a soft stop. In order to 
retain the resilient material in place, e.g. plastic strips 31 may be used 
around the halves 8. 
The resilient material which in the shown embodiment is used as a spring 
medium in addition to the helical spring 6 in the extreme phases of the 
cushioning sequence to prevent that the metal structures of the 
construction collide when the load is high due to a sharp bump, is 
preferably neoprene or a similar material. The stop bolt 33 may for 
example be a through bolt having threads in both ends, and having a 
neoprene ring 32 and a screw mounted thereto on both sides of the seat 
attachment part 2. 
The location of the center 25 on top of the seat attachment part 2 in 
relation to the axis 26 in the seat tube 21, will be in the same range as 
ordinary for saddle posts without cushioning, by having this center 25 
placed in an advanced position with respect to the rear bearing pins 23, 
24, however preferably not so far as to place the center in front of the 
extension of axis 26. The distance from center 25 to the extension of the 
axis 26 is defined as the seat post "offset", and is typically between 0 
and 25 mm in bicycles without a cushioning seat post. It is therefore 
possible to define the seat post offset by choosing bias. The distance 
should typically be between 0 and 25 mm when the seat retainer assembly is 
part depressed, i.e. when the bicyclist is sitting on the saddle in a 
normal riding position. 
In use the invention will operate as follows: When receiving a pressure 
from below when the bicycle runs over a bump, the post head 1 will move 
obliquely upwards. The parallel bars 3, 4 will rotate opposite to this 
movement, and at the same time the diagonal distance from the lower 
bearing 28 on the post head 1 to the upper bearing 23 on the seat 
attachment part 2 will decrease, whereby the helical spring 6 is 
compressed simultaneously with a compression of the telescopic guide 11, 
13 which provides a linear and stable compression of spring 6, until the 
neoprene material 30 on the attachment detail 8 for the saddle possibly 
engages the top bar 4 so that the neoprene material is compressed in 
addition to the helical spring. If the bars are equally long and parallel, 
the bicycle saddle will remain parallel to itself (and the bicycle frame) 
during this movement. 
Return damping in the cushioning movement is obtained at the outset in the 
following manner: Swinging movements that the helical spring attempts to 
impose on the system, are damped by the attempt to force the bicyclist's 
body forward and back when the saddle changes its average distance to the 
foundation. The forces in the up/down movement which one tries to dampen, 
act against the forces acting forward and back. These forces try to 
nullify each other, and the result is that the system settles down in that 
distance to the foundation which was pre-determined when setting the bias 
and the seat height. Thus, damping is achieved without any special damping 
means, and can be stated to be a "passive" damping effect. 
In the cases where it is nevertheless desirable with additional return 
damping, this can possibly be achieved by mounting an optional equipment 
which is to be discussed in the following text, and which then provides an 
"active" type of return damping. In this connection it is referred to 
FIGS. 5 and 6. 
As appears from FIG. 5, a return damper device which mainly consists of two 
telescopically operating members 18 and 36, wherein member 18 has an 
internal friction/damper medium against movement of member 36, is attached 
to the lower bearing 28 on the post head and the top bearing 23 on the 
seat attachment part. The attachment is made by utilizing the fact that 
the bearings 23, 24, 27, 28 are configured having central through holes 
such as shown in FIG. 4. Extended bolts 17, 41 can be inserted in these 
holes to provide a basis for mounting the damper device. As appears from 
FIG. 5, the upper extended center bolt 41 is equipped with an outer 
resilient sleeve made of e.g. neoprene material. Further it is to be noted 
that to accommodate the upper part of the damper device between a 
conventional saddle bar and the sitting portion of the saddle, compare 
e.g. FIG. 4, there is inserted an additional spacer on the extension bolt 
41 so that the damper device 18, 36 is somewhat tilted outwards in the 
upward direction. For this reason the attachment hole 40 (see FIG. 6) in 
the lower end of member 18 must at the same time be shaped so as to make 
the attachment possible, e.g. by having a curved inside shape. A similar 
tilting option (at bolt 17) for the damper device may also be achieved by 
means of a special (standard) type of bearing for angle deviation 
suspension. 
When the main spring 6 inside the "parallellogram" is compressed, the 
distance between bearings decreases. During such a compression the guide 
bar 36 will be pushed down into the sleeve member 18 by the extension bolt 
41. However, an elongate, longitudinal hole 37 is provided in the upper 
part of the guide bar 36, see FIG. 6. Thus, in a successive upward 
movement of the assembly, the extension bolt 41 will be able to travel 
some distance upwards in the elongate hole 37 without starting any 
friction effect. The length of this free travel can be determined by means 
of a screw in the upper end of the guide bar 36, the screw tip 38 being 
movable downwards to effectively shorten the elongate hole 37 upon 
operating the screw head 39. If active damping is desirable throughout the 
cushioning movement, the screw tip 38 is screwed all the way in to engage 
bolt 41, see FIG. 5. If it is desirable having ranges without active 
friction/damping, which may be favourable e.g. to pass small bumps without 
losing too much energy to the damping system, this is achieved by choosing 
a certain effective length of the elongate hole 37 using the screw head 
39. In this manner it is possible to achieve an optional frictionless 
movement in an "average activity range", i.e. when the bicyclist sits down 
on the saddle, the guide bar 36 is pushed down against friction, and small 
frictionless movements may be made around a mean sitting height, while 
larger deflections will be exposed to active damping. 
In FIG. 6 there is also shown an example of an embodiment of the friction 
device inside sleeve 18. A friction sleeve 34, made of e.g. teflon 
material, directly engages the guide bar 36, and is prone to wear. Right 
outside the friction sleeve 34 there is arranged a surrounding sleeve made 
of a resilient material, for example rubber or neoprene. 
Tightening/adjustment of friction can be made by having the two parts 34 
and 35 with a conical shape, such as shown, and surrounding them by a 
tightening sleeve 29 with threads, which can be screwed so that the 
resilient sleeve 35 is tightened harder and harder against the friction 
sleeve 34. Some automatic readjustment is achieved by the resilient sleeve 
35 itself, so that it is not necessary to readjust the amount of friction 
too often. Of course, alternatively the sleeve member 18 may equally well 
comprise an oil damper of per se known type. 
As an alternative to the screw with a head 38 and tip 39, there may e.g. be 
arranged a threaded outer sleeve on the elongate hole section in the upper 
end of guide bar 36, with the same limiting function as the screw 38, 39. 
A consequence of the function of the seat retainer assembly of the 
invention, is that the bicycle saddle will move further upward and forward 
when a lower weight is applied to the saddle. This means that the sitting 
position will change somewhat during bicycling, the saddle will actually 
be shifted somewhat upward and forward the harder the bicyclist is 
pedalling (and thereby lifts his own body or eases the pressure on the 
saddle). Such an effect arises e.g. in a steep hill, where it is necessary 
to push hard on the pedals. This will actually contribute to provide a 
more correct positioning of the bicyclist's center of gravity, and a more 
correct pedalling ergonomy in such situations. Another situation where the 
same effect is favourable, is at high speeds on flat ground. 
In order to make the seat retainer assembly less heavy, and to enable 
locking of the seat retainer assembly together with the rest of the 
bicycle, a round or elongate hole 22 can advantageously be cut out in the 
post head 1 below the upper bearing 27, such as appears in the embodiment 
shown in FIGS. 1, 2 and 3.