The invention relates to a device in braking systems for motor vehicles.
Particularly, the invention has its main application in connection with braking
systems for commercial vehicles. The invention also relates to a method when mounting
such a braking system on a motor vehicle.
BACKGROUND OF THE INVENTION:
Larger motor vehicles, e.g. commercial vehicles, are today designed
with lower and lower ground clearance. A primary reason for this is the need to
maximize the available cargo space of the vehicle. Since the maximum cargo space
is limited by the maximum height allowed and the height of the vehicle chassis,
there is consequently a desire to reduce the height of the chassis in order to
thereby increase the cargo space. At the same time, maximum ground clearance is
desired in order to avoid damage to the vehicle when driving over rough ground.
The demands of low height of the chassis and large ground clearance in turn set
limitations when designing the braking system of the commercial vehicle. This
is particularly true in the cases where the braking system comprises a compressed-air
driven brake cylinder, which may be mounted standing in a given position in relation
to a wheel shaft, and when the brake cylinder comprises a substantially vertically
projecting push rod. With such a construction, the height of the chassis of the
vehicle is limited by the length of the push rod.
According to the prior art, the end of the push rod, which protrudes
from the brake cylinder, is normally threaded and connected to a brake key via
a special lever member.
When the braking system is activated by the driver of the vehicle,
the push rod is pressed out from the brake cylinder, thereby influencing the brake
key via the lever. The brake key, in its turn, activates the wheel brake.
With reference to Fig. 1, a previously known system of the above
mentioned kind will be described. Fig. 1 shows a brake cylinder 1, intended to
be mounted at a wheel shaft in a commercial vehicle. The brake cylinder 1 comprises
a push rod 2, which is pressed out essentially in a vertical direction (i.e. downwards
in the drawing) when the braking system is activated by the driver of the vehicle.
The movement of the push rod 2 is transferred to a brake key 3 via a braking lever
4. The brake key 3 is arranged substantially parallel to the wheel shaft which
is to be braked.
When mounting this previously known device, i.e. when the braking
lever 4 is to be mounted in order to join the push rod 2 to the brake key 3, the
brake cylinder 1 and the brake key 3 have to be pre-installed, i.e. the are placed
in the vehicle in advance. In this way, the installation of the lever 4 may be
done by mounting one end of it, comprising an aperture 5 with internal splines,
onto outer splines 6 on the brake key 3. The spline separation which is utilised
in this spline coupling will cause the opposite end of the lever 4 to be positioned
adjacent to the push rod 2 in a certain position which may vary within a certain
interval in relation to the end of the push rod 4. The exact position for the
end of the lever 4 is determined by the fixed spline separation and the length
of the lever 4. The splined coupling 5, 6 is thereafter locked by means of a locking
screw 7 with appurtenant nut 8.
The next step in the mounting operation is that a link element, consisting
of two link members 9 and 10, respectively, is brought together on both sides of
the push rod 2 and the end of the lever 4 which now has been placed adjacent to
the push rod 2. The first link member 9 is joined to the second link member 10
by means of two screws 11, 12, which are inserted into corresponding holes 13,
14 in the second link member 10, while a pin 15 in the first link member 9 is
passed through a hole 16 in the lever 4 and into a further hole 17 in the second
link member 10. Thereafter, the link element 9, 10 is screwed on by means of the
screws 11, 12 and nuts 18, 19. The link members 9, 10 further comprise internal
threads 20 (only evident from the link member 10 in Fig. 1) which interact with
threads 21 on the push rod 2. In this way, the push rod 2 may be locked to the
link elements 9, 10 and transfer its movement to the brake key 3 via the lever
As mentioned above, the spline separation of the splined coupling
5, 6 implies that the end portion of the lever 4 facing towards the push rod 2
will be positioned in a certain position which may vary vertically within a certain
interval. This interval is normally of the magnitude of approx. 30 mm. Thus, the
length of the link element 9, 10 cannot be below this interval, since it has to
be utilised for bridging the distance between the push rod 2 and the lever 4.
The fact that the interval must be possible to be accomodated by the link element
9, 10, in its turn, means that this has to project downwards a relatively long
distance below the push rod 2. This constitutes a disadvantage, since it creates
an essential limitation when the ground clearance and the height of the chassis
of the vehicles are concerned.
SUMMARY OF THE INVENTION:
A main object of the present invention is to achieve an improved
device for joining a push rod and a brake key in a braking system, particularly
for commercial vehicles, which braking system utilises a compressed-air driven
brake cylinder with a vertically projecting push rod. In particular, it is an
object of the invention to create conditions for optimizing the relation between
the ground clearance and the height of the chassis of the vehicle.
A further object of the invention is to provide a simplified mounting
of a braking system for a commercial vehicle, having a minimum of components and
working steps in the mounting operation.
The above-mentioned objects are achieved by means of device of the
kind mentioned in the introduction, the characterizing features of which are evident
from the subsequent claim 1. The objects are also achieved by means of a method
of mounting a braking system, the characterizing features of which are evident
from the subsequent claim 9.
The invention is based on the principle that it comprises a special
mounting device which, together with the braking lever, comprises means for coupling
the push rod to the braking lever, via said mounting device, at a point which
is situated within the end of the push rod which projects from the brake cylinder.
In this way, the only limitation for the height of the chassis/ground clearance
is given by the length of the push rod, i.e. the distance between the brake cylinder
and the lever may be made shorter than in previously known devices.
According to a preferred embodiment, the push rod may be coupled
to the lever via said mounting device since the mounting device comprises a modification
of shape, preferably in the form of a pin, which interacts with a corresponding
modification of shape, preferably a hole, which has been worked into the braking
Further advantageous embodiments are described in the subsequent
BRIEF DESCRIPTION OF THE DRAWINGS:
In the following, the invention will be described in greater detail
with reference to the attached drawings, in which
- Fig. 1
- is a perspective view of a previously known device in a braking system,
- Fig. 2
- is a perspective view of a device in a braking system according to the present
- Fig. 3
- is a perspective view of a rear axle in which the invention may be utilised,
- Fig. 4a-4c
- show detailed views of the invention, seen from above, illustrating how the
device according to the invention is mounted.
In Fig. 2, a perspective view of a device in accordance with the
present invention is shown, which according to a preferred embodiment is utilised
in connection with a braking system for a commercial vehicle. The drawing shows
the device in its mounted state. The braking system comprises a compressed-air
driven brake cylinder 22, of a per se previously known type, which may be influenced
by the driver of the vehicle when braking. The brake cylinder 22 comprises a push
rod 23, the lower end of which is provided with external threads 24. According
to the embodiment, the brake cylinder 22 is mounted standing up via an attachment
bracket 25, which is firmly affixed to the vehicle. The brake cylinder 22 may be
mounted with an extension substantially in the vertical direction, or with another
The push rod 23 is in a known way arranged to be pushed out from
the brake cylinder 22 when the braking system is activated. Thereby, the movements
of the push rod 23 are transferred to a brake key 26 via a braking lever 27. The
brake key 26, in its turn, is connected to a (not shown) wheel brake. The brake
key 26 is preferably oriented with an extension which runs along an axis 28 which
is substantially parallel to the wheel shaft of the vehicle which supports the
wheel which is to be braked.
The lever 27 and the brake key 26 may be connected by means of a
splined coupling 29, which is formed by external splines 30 on the brake key 26,
and internal splines 31 arranged in a hole 32 in one end of the lever 27. The hole
32 is slotted, whereby the splined coupling 29 may be clamped by means of a locking
screw 33, interacting with a (not shown) nut on the underside of the right end
portion of the lever 27.
When mounting the device, it is required that the brake cylinder
22 and the appurtenant push rod 23 have been pre-mounted and are in position. Furthermore,
the brake key 26 is pre-mounted. For this reason, the lever 27 must be brought
into position in the direction which is marked with an arrow 34 in Fig. 2, i.e.
in a direction which is mainly parallel to the axis 28. Before the lever 27 is
brought into position, however, in accordance with the invention, a special mounting
device, in the form of a cross 35, is mounted on the push rod 23. According to
what will become evident in detail below, the cross 35 is constituted of a sleeve-shaped
element which is provided with internal threads, interacting with the threads 24
on the push rod 23. Furthermore, the cross 35 comprises an intermediate portion
36, having a square (optionally rectangular) cross-section and which is provided
with two pins, out of which a first pin is intended to project through a hole in
the lever 27 (not evident from Fig. 2), and a second pin 37 is intended to project
through a hole 38 which has been tooled into a separate supporting member 39. This
supporting member 39 may, in turn, be mounted to the lever 27 by tightening two
screws 40 which interact with corresponding holes in the lever 27.
In Fig. 3, a rear axle 41 for a commercial vehicle is shown, for
which the invention has its main application. The location of the brake cylinder
22 on the bracket 25 is evident from the drawing. The brake cylinder 22 is arranged
such that the push rod 23, when activated, can project a certain distance from
the brake cylinder 22. Furthermore, the push rod 23 is connected to the braking
lever 27 via the supporting member 39. The brake key 26 runs inside a brake key
cover 42 comprising an opening which emerges where the braking device of the rear
axle 41 (not shown) is arranged, i.e. in connection to a wheel shaft 43.
In Figs. 4a-4c, the procedure when mounting the device in accordance
with the invention is illustrated. Fig. 4a shows the initial position, whereby
the push rod 23 is shown in cross section, and the brake key 26 is arranged in
a certain predetermined position in relation to the push rod 23. Firstly, the
cross 35 is screwed upwards a certain distance on the push rod 23. Thereby, it
is seen to that the pins 37, 44 on the intermediate section 36 of the cross 35
are directed substantially parallel to the brake key 26.
As is evident from Fig. 4b, the braking lever 27 is thereafter mounted
substantially parallel to the direction in which the brake key 26 has its extension.
The mounting direction is indicated by the arrow 34. When mounting, it is ensured
that the hole 32 in one end of the lever 27 is brought inwards over the brake key
26 so that the external splines 30, which are located on the brake key 26, come
into contact with the internal splines 31 located in the hole 32. Furthermore,
it is ensured that the pin 44 is aligned with the pin hole 45 in the lever 27.
If a fine adjustment of the position of the cross 35 along the push rod 22 is
necessary, this is achieved by screwing the cross 35 a number of turns upwards
The lever 27 is curved in such a way that it comprises an intermediate
portion 46, the extension of which is mainly parallel to the brake key 26. In this
way it is made possible that the location of the pin hole 45 is slightly displaced
in the length direction in relation to the hole 32 in the opposite end of the lever
27. This in turn implies that the lever 27, may be brought a small distance over
the brake key 26, while the cross 35 still may be turned in order to be finely
adjusted. This facilitates the mounting of the lever 27.
The construction of the above-mentioned supporting member 39, comprising
a planar support surface 47 for contacting the intermediate portion 46 of the lever
27, is also evident from Fig. 4b. As mentioned above, the supporting member 39
additionally comprises a pin hole 38 arranged to interact with the pin 37. Furthermore,
the supporting member 39 comprises two holes 48 (of which only one is evident
from Fig. 4B), intended for the through screws 40, which are screwed into the corresponding
holes in the lever 27.
In Fig. 4C, the device is shown in its mounted state, whereby the
cross 35 has been adjusted into the correct position and its pins 37 and 44 have
been fitted into the lever 27 and the supporting member 39, respectively. When
the lever 27 thereafter is pushed completely into position on the brake key 26,
the splined coupling 29 is locked by means of tightening the fastening screw 33.
Finally, the supporting member 39 is locked by means of the screws 40.
By means of the invention, it is ensured that the end portion of
the lever 27, facing the push rod 23, is positioned so that it is connected to
the cross 35 at a point which lies within the end of the push rod 23 which projects
from the brake cylinder. In case the brake cylinder is mounted vertically, this
accordingly implies that said point is situated above the lower end of the push
rod 23 (cf. Fig. 2). This means that no unnecessary extension of the push rod
23 has to be done. Instead, it is the maximum length of the push rod 23 which sets
the limit to the height of the chassis and the ground clearance of the vehicle.
The invention is not limited to the above-mentioned embodiment, but
may be varied within the scope of the subsequent claims. The intermediate portion
46 of the lever 27 may, for instance, be adapted in length according to an existing
mutual distance between the push rod 23 and the brake key 26. Furthermore, the
cross 35 may be provided with small holes which interact with pins in the lever
and the supporting member, instead of the opposite.