Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1066'736
Canadian Patent Application Serial No. 215,134, filed
December 3, 1974, describes an axle pivoting system for terrain
vehicles, e.g. skidders forest tractors and the like, with cen-
trally suspended rigid pivotable axles. The design implies that
the chassis is suspended on each axle at only one point, prefer-
ably in the middle of the axle, and that the suspension point is
hinged so that the axle can pivot in a plane approximately at
right-angles to the longitudinal direction of the chassis. A
single-acting or alternatively a double-acting pressure cylinder
is arranged between the chassis and the rigid oscillating axle
on each side of the suspension point and a pressure fluid can be
trar.sferred via a distribution valve and associated pressure con-
duits between cylinder chambers in a predetermined number of
combinations. A pressure fluid pump is arranged for supplying
pressure fluid to the pressure cylinders individually or in pairs,
the direction of flow of the pressure medium being controlled by ~
a setting valve. The description of this patent application -
assumes that all cylinders have the same diameter and are coupled -
to the axles equidistantly from their pivoting axes. This means -
that the cylinders have the same load capacity for one and the
same fluid pressure and that two c~linders coacting by means of
the fluid pressure have the same piston rod movements, but with
reversed sign, which means that one piston rod moves inward just
as much as the other moves outward to provide equally large turn-
ing angles of the axles with respect to the associated vehicle
chassis portions. ~ -
The axle pivoting system according to the said appli-
cation has now been applied to a prototype working in full scale,
which has been tested in very severe practical trials. All the
provi9ions in the original set of problems have been met with a
wide margin and the structure functions extremely satisfactorily.
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Without uncomfortable effect on the driver and without the risk
of overturning, a vehicle with this axle pivoting system can be
driven in terrain which is regarded as too rugged and difficult
for a normal vehicle, i.e. practically impassable. The primary
reason for this situation is that in relation to the chassis the
axles are centrally suspended and the pressure cylinders contin-
ually adjust the position of the chassis in accordance with the
setting of the distribution valve in relation to the terrain, so
that the inclination of the chassis in relation to the horizon-
tal plane will be the least possible, thereby reducing to a mini-
mum the inclining movements and tipping accelerations for both
chassis and driver.
~he embodiment particularly described in the above-
identified patent application comprises a forest tractor with a
chassis in two parts having intermediate articulation. A first
part is thereby shown designed as a cabin for the driver and a
second part as the prime mover. In the range of products
including forest machines there are however cases where the
driver's cabin is arranged in combination with the prime mover,
and the second part i~ designed as a load carrying means which
can be specially arranged for log hauling, or can be provided
with a lifting crane or a dumper platform body or the like.
In such cases, an axle pivoting system with cylinders of the
same size according to said application can also be successfully
applied.
In practice, however, it has been found that even
greater advantages can be obtained using the present invention,
which has the object of further reducing swaying movements
which cause accelerations and stresses on the driver.
According to the present invention there is provided
a pivoting axle system for a vehicle, comprising a first wheel
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axle centrally suspended from an adapted to support a first
vehicle chassis portion and being pivotable in a plane transverse
to a longitudinal direction of the first vehicle chassis portion,
a bogie arrangement adapted to support a second vehicle chassis
portion and comprising at least one second centrally suspended
axle pivotable in a plane transverse to a longitudinal direction
of the second vehicle chassis portion, means coupling tlle first
and second vehicle chassis portions together in a torsionally
rigid manner, and motion transmitting means to transmit pivotal : ~
movement of the first wheel axle with respect to the first ~ .
vehicle chassis portion to each of the second axles to cause
a smaller and oppositely directed pivotal movement of each second :
axle with respect to the second vehicle chassis portion. :
Said motion transmitting means preferably comprises at -
least one first hydraulic fluid cylinder coupled between the ~.-
first wheel axle and the first vehicle chassis portion, at --
least one second hydraulic fluid cylinder coupled between each
second axle and the second vehicle chassis portion, each second -
hydraulic fluid cylinder having an absolute working area which .
. is greater than that of each first hydraulic fluid cylinder,
and hydraulic fluid pipes for interconnecting the first and ~- -
second hydraulic fluid cylinders to provide said oppositely
directed pivotal movements of the first and second axles.
In a particularly advantageous embodiment of the inven- .
tion each second hydraulic fluic cylinder has an absolute working
area which is substantially double that of each first hydraulic
fluid cylinder. -
In one embodiment of the invention the bogie arrangement
comprises a bogie wheel pair on each side of the second vehicle
chassis portion, each bogie wheel pair being carried by a respec-
tive bogie box carried by a single second axle which is centrally
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suspended from the second vehicle chassis portion. In an
alternative embodiment the bogie arrangement comprises a bogie
box carried by the second vehicle chassis portion and two of
said second axles each centrally suspended from said bogie box,
each of said second axles carrying a wheel on each side of the
second vehicle chassis portion.
Expediently said motion transmitting means further
comprises valve means, to which the hydraulic fluid pipes are
coupled, arranged for blocking or redistributing hydraulic fluid
in the pipes.
The invention also extends to a vehicle comprising a
pivoting axle system as recited above, a driver's cabin and
prime mover part of the vehicle provided on the first vehicle
chassis portion, and a load carrying part of the vehicle pro-
vided on the second vehicle chassis portion, the chassis
portions being articula~ed to each other.
The invention enables the provision of an automatic
redistribution of fluid flow to the different pressure cylinders
in cases where there is a risk of overloading and overturning ;`
the vehicle, for example when it is equipped with a lifting
crane, dumper platform body or the like, in which the resultant
of the common centre of gravity for the raised or supported
mass and the parts of the vehicle can come outside the
stability area of the vehicle.
In an embodiment of the invention the fluid cylinders
for the pivoting shaft carrying the combined prime mover and
driver's cabin, i.e. generally speaking the front part of the
vehicle, are made with a substantially lesser diameter than the
cylinders coacting with the pivoting axle for the load carrying
part. In order to completely eliminate, or as far as pos~ible
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limit, the risks of overloading and overturning when the lifting
crane or dumper body is arranged on the load carrying part, sens-
ing means such as switching valves are suitably arranged in com-
bination with the pressure cylinder or pressure cylinders opera-
ting the lifting crane or the dumper platform body. The switch-
ing valve is actuated at a predetermined maximum load, i.e. the
maximum pressure in the pressure cylinders, in such a way that a
redistribution of the hydraulic fluid to the fluid cylinders of
the pivoting axles takes place in such a direction that the stab-
1~ ility of the vehicle substantially increases.
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The invention will be further understood from the
following description by way of example of embodiments thereof
with reference to the accompanying drawings, in which:-
Figure 1 shows a side view of a terrain vehicle with adriver's cabin/prime mover part and a load carrying part arranged
with bogies, both parts being articulated to each other and the
vehicle being equipped with an axle pivoting system according to
an embodiment of the invention;
Figure 2 shows schematically and in a plan view a chas-
sis of the vehicle according to Figure 1, with wheels, bogies,pivoting axles and a universal joint in conjunction with the
waist articulation, together with associated coupling means;
Figures 3 and 4 are respective schematical vertical
projections taken on the lines III-III and IV-IV of Figure 2;
Figures 5 - 9 are principle diagrams in conjunction
with the calculations set forth in the following description; :-
Figure 10 shows schematically, in perspective, and in
conjunction with the calculations, the angular variations on the
bogies, pivoting axles and chassis arising when a bogie wheel . -
goes over a hump in the ground;
Figure 11 shows schematically and in perspective an
alternative embodiment of the load carrying bogie;
Figures 12 - 14 schematically show the automatically :
operating means for redistribution of a pressure fluid working : :
in an axle pivoting system for elimination or reducing the risk -::
of overturning or tipping in case of overload, when the vehicle : -
is equipped with a lifting crane or a dumper body.
Referring to Figures 1 to 4, a terrain vehicle, gener- -
ally designated by the numeral 1 in Figure 1, is equipped for ..
transporting logs or the like and comprises a driver's cabin/
prime mover part 2 and a load part 3, coupled to each other with
a waist articulation 4. The vehicle 1 has a forward wheel pair
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5 which via a piYoting axle 6, Figure 2, is arranged under the
prime mover part 2, and two pairs of rear wheels 7, ~ connected
to each other in a bogie arrangement with bogie boxes 9, lO in -
coaction with a pivoting axle ll arranged under the load part 3.
All six wheels are driven by an engine (not shown) arranged in
the prime mover part 2, via differentials 12, 13, a universal
joint 14, transmission shafts 15, 16, and transmissions, e.g.
chains (not shown), arranged in the bogie boxes 9, lO. Comple-
tely mutually independently, the bogie boxes 9, lO can oscillate
about the pivoting axle ll, as indicated by the angle ~, Figure
l, about the jou.rnalling centres 17, 18, which are preferably
coaxial with the pivoting axle ll.
The driver's cabin/prime mover part 2 and the load part
3 form together torsionally rigid chassis l9 via the articulation
4. It should be noted that the articulation 4 and the universal
joint 14 lie in substantially the same vertical plane. The cha~sis
l9 is rigidly suspended on the axles 6, ll in mounting means 20,
21, which give the pivoting axles freedom of movement for oscil- :
lating in a plane substantially at right angles to the longitudi-
nal direction of the prime mover part 2 and the load part 3.
Pressure cylinders 22 ~25 are arranged between the chassis l9 and
the pivoting axles 6, 9, each of the pressure cylinders being
connected to the chassis l9 and the pivoting axles 6, 9, respec-
tively, via pivoted connections, preferably so that the pressure -~
cylinders' piston rods are connected to the respective pivoting
axles. The pressure cylinders 22 - 25 are connected via pressure ~
fluid pipes (not shcwn) to each other and to a distribution valve, a resetting : ~ :
valve and a pressure fluid source (not shown). .
The sections according to Figures 3 and 4 further clar- :
ify the pivoting connection between the driver's cabin/prime ;:
mover part 2 and the pivoting axle 6, and between the load part
3 and the pivoti~g axle ll, the angles ~f and ~b denoting the ;
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angular range within which the axles 6, 11 can oscillate in rela-
tion to the chassis 19. AS iS also seen from Figures 1 and 4,
the load part 3 is designed for transporting logs 26 or the like,
in the case illustrated.
In terrain vehicles of this kind it is extremely impor-
tant to arrive at a stability safety which is as high as possible.
The problem is that of providing the axle pivoting system, inclu-
ding the function of the pressure cylinders 22-25, with the most
favourable area possible within which the resultant of the centre
of gravity of the load can come without risking overturning of
the vehicle in any direction. This area, which is denoted
"resultant area" hereinafter, should also have the most suitable
shape in consideration of the use to which the vehicle is to be
put.
It will be appreciated that in load carrying terrain
vehicles of the type shown in Figure 1, the centre of gravity of
the resultant area should be displaced backwardly, i.e. towards
the centre of gravity of the load. To illustrate this relation- - -
ship more closely and to clarify the calculation methods which
can be applied, the following analysis is made while referring
to Figures S - 9.
A chassis for a four-wheeled vehicle is shown schema-
tically in Figures 5 - 7, the vehicle having waist articularion
and an axle pivoting system according to Canadian Patent applica-
tion 215,134. Component~ corresponding to components previously
described with reference to Figures 1 to 4 have been given corre-
sponding reference designations with the addition of apostrophes.
It is pointed out that the number of wheels with which the vehicle is
provided does not affect the theoretical analysis in the present
consideration. For the sake of clarity, the no~mal forward tra-
velling direction of the vehicle is denoted by an arrow Pl.
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For a first case shown in Figure 5, if it is imagined
that the pressure fluid to the rear pressure cylinders 24', 25'
is blocked, their piston movements will also be immobilised. If
the forward pressure cylinders 22', 23' are connected to each
other at the same time, the front axle 6' will be able to pivot
freely as shown in Figure 3. A resultant area Rl in the shape
of an isosceles triangle will obviously be obtained if the vehicle
travels straight forward. Every location for a load centre of
gravity Ll within the resultant area Rl gives full stability
without risk of the vehicle overturning, while on the other hand
a load centre of gravity L2 outside the resultant area Rl creates
a tipping moment.
According to the premises for the axle pivoting system
for normal driving in terrain, the cylinders on the same side of
the longitudinal axis of the vehicle shall cooperate, which means
that the cylinders 22', 24' and 23', 25' respectively, are con-
nected with each other by pressure conduits (not shown). If all ~ -
cylinders are the same size and are positioned equidistantly of
- the central pivoting points of the axles, the result for cylinders
.
? on the same sidè will be that one piston rod moves outwardly just
as much as the other moves inwardly. It is therefore necessary
to examine the stability conditions in these circumstances. ;
In Figure 6, an arbitrarily chosen load centre of
gravity F has the coordinate x in relation to the longitudinal -
axis of the vehicle and the coordinates a and b in respective ~;
relation to the front axle and the rear axle. The distance
between the axles is 1 and the distance between the longitudinal
axis and the pressure cylinders is d, half the track being denoted
by e. In a section, also pertaining to Figure 6, on the line -
X-X in Figure 6, the vehicle chassis 19' is also schematically
denoted for further clarifying the relationship.
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If the opposing force from the pressure cylinders affec-
ted by the load through the centre of gravity F is denoted by R,
the following moment equation is obtained about the longitudinal
axis:
Fx = 2Rd, i.e. R = F2d .
In a similar manner the following moment equation about
the front wheels is obtained, if their own weight is neglected:
Fa = Rl + Fml,
where Fm is the opposing for~e through the pivoting point 21'
(corresponding to the mounting means 21 in Figures 2 and 4) for
the rear axle 11'.
Substituting for R and rearranging gives:
Fm = F(l ~ 2d) '
from which it follows that the opposing force Fm on the longitu- -- :
dinal axle of the vehicle will be less than zero~ in which case :
there is risk of overturning, if x ~ 2da .
It will be found that the resultant area of stability
is represented by a four-cornered figure which in Figure 7 is ~
denoted by R2 and which in conjunction with the calculations ~ -
relates to the supporting points for the pressure cylinders
22'-25'. The actual supporting points for the vehicle lie on the
lines 27, 28 in Figure 7 for the wheels, and the following calcu-
lation for the final stability is therefore made, again referring -
to Figure 6,M denoting the moment about the line 27 for the
left-hand wheels in Figure 7: -
M = R(e-d) + Fme . ~ .
After substitution of R and Fm and rearranging this
gives
M = F(~- _ x2) . ~;~
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Moment M will be less than zero if
x > 2 a i e
i.e. if the centre of gravity F of the load lies outside a resul-
tant area indicated by dashed lines and denoted R3 in Figure 7.
In this case it is found that the resultant area R3 in
Figure 7, i.e. when the area of the front pressure cylinders 22',
23' is equal to the area for the rear pressure cylinders 24', 25',
is represented by a rhombus the centre of gravity of which lies
at the centre of the longitudinal axis of the vehicle, and half-
way between the axles.
It has however been pointed out before that in load -
vehicles of the kind discussed here it is desirable to move the
centre of gravity rearward. This condition is met according to
an embodiment of the invention by having the pressure cylinders
of the rear axle made substantially larger than those of the front -
axle. For example, if the areas of the back axle pressure
cylinders 24", 25" in Figure 8 are made twice as large as the
areas of the front axle pressure cylinders 22', 23', which is -
the case in an especially advantageous solution, calculations -
analogous with the ones carried out above give a kite-shaped
resultant area R4, whose apices at the sides of the vehicle have
a distance from the rear axle of 1/3.
The resultant area centre of gravity has thus been
displaced backward to substantially increase the stability of the
whole vehicle. It will also be appreciated that the greater the
difference in working area between the forward and rear pressure
cylinders, the more the resultant area centre of gravity is
displaced backwardly, and that in the limit, when the rear pres-
sure cylinders are infinitely great in relation to the front ones,
the resultant area passes over into the triangular shape shown
in Figure 5.
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The mathe~atical relationship for non-identical cylin-
der areas still assuming equal distances of the cylinder from the
central longitudinal axis of the vehicle, will be the following:
( Al + rA2)d, i.e. r = Fx .
where r = pressure/unit and Al and A2 = cylinder areas.
The moment equation about a pair of wheels gives:
F-a = rAll + Fmll, ie Fml = ~ rAl
Substituting for r gives:
1 o ml T ~ AI + A2 ~ ~
The stability equation about one wheel gives:
M = (e-d)rAl + eFml,
from which substituting for r and Fml and rearranging gives:
M = F (i ~ ~
The moment M will be less than O for
(Al + A2) ae ,
Al 1 , .
i.e. when x is lying outside the four-cornered figure.
If the weight of the wheel pair is included in the
stability equation there is obtained (where H is the weight of a
pair of wheels):
(1 ~ 2) + He
The moment M will be less than O for
X> ( 1 2) (~ + -~e,
i.e. when x is lying outside the four-cornered figure.
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When taking a curve with the vehicle, Figure 9, the
driver's cabin/prime mover part 2 will be angularly disposed in
relation to the load part 3 while turning about the articulated
joint 4. The kite-shaped resultant area will have its configuration
altered somewhat, i.e. as shown in Figure 9 with dashed lines de-
noted R5. The centre of gravity ~or the resultant area R5 will
thus clearly be displaced in the same direction towards which the
vehicle turns, this also being advantageous for stability. The
corners of the resultant area lying at the sides will retain their
relative positions in relation to the supporting points for the
wheels, as also shown in Figure 9.
In Figures 5 - 7 the vehicle has been shown with four
wheels for the sake of simplicity, whereas in Figures 8 and 9 the -
vehicle has been shown according to the invention with a bogie
arrangement for the rear wheels. It will be appreciated that this
difference does not affect the purely mathematical analysis. On
the other hand, the solution with a bogie arrangement of the rear
wheels has in practice very great importance with relation to
the swaying movements and accelerations in driving over rough
country for the chassis and thereby for the driver and the load.
The conditions here are illustrated by Figure 10, which shows the
terrain vehicle 1 schematically and in perspective, with symbolic
denotations for the incorporated components and with previously
used reference designations provided with apostrophes. Figure 10
thus shows the chassis 19' as a rigid frame, and also shows the
pivoting axles 6', 11'. Bogies 9', 10' are arranged on the latter
for the rear wheels 7', 8' and 7", 8", and pressure cylinders
22', 23' and 24", 25" are arranged in the described manner between
the chassis 19' and the respective pivoting axles 6' and 11'.
The rear pressure cylinders 24", 25" are presupposed,
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according to the discussion hereinbefore, to have double the
working areas of the forward pressure cylinders 22', 23'.
If now a rear wheel, e.g. a bogie wheel 8", passes
over a hump in the ground, e.g. a projecting stone 29, Figure 1,
the bogie box 10' will pivot through the previously mentioned
angle ~ in Figure 1, a forward bogie wheel 7" functioninq as a
pivot in the illustrated case. If it is presupposed for a case
conceivable in practice, that the wheel base Sl for the bogie
wheels 7", 8" is the same as a distance S2 between the connecting
points for the pressure cylinders 24", 25" on the rear axle 11',
the angle ~ causes an inclined attitude with the angle ~ to the
horizontal plane for the rear axle 11', whereby ~ will be equal
to half ~, for easily understood geometrical reasons.
The inclined attitude with the angle ~ for the rear
axle 11' causes in its turn an alteration in attitude for the ~ -
chassis 19' relative to the horizontal plane with an angle y,
the size of which is a function of the area relationship between
the forward pressure cylinders 22, 23 and the rear cylinders
24", 25". If the relationship between the cylinders is 1:2, as ;~
prqviously assumed, and the cylinders are hydraulically directly
communicating with each other, moving the piston rod of the pres-
sure cylinder 25" inwardly a certain distance will cause the
piston rod of the pressure cylinder 23' to move out double this
distance. It will be easily appreciated from a simple analysis
that the angle y will be equal to 2/3 ~, i.e. 1/3 a. As an exam~
ple, if the angle ~ is 15 degrees, the angle ~ will be 7.5 degrees
and the angle y will be 5 degrees. From analytical considerations
it will also be found that if one of the front wheels passes
over a hump, giving rise to an inclined attitude of the front axle
6' of lS for example, then as a result of the function of the -
pressure cylinders and the assumed area relationship, the angle y
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will in that case only be 5.
The axle pivoting system in combination with an advan- -
tageously selected relationship between the cylinder areas, e.g.
1~2, and a bogie arrangement for the rear wheels thus gives con-
siderable improvements relating to higher load stability (the
resultant area centre of gravity is displaced backwards), less
propensity to sway when passing over ground obstacles, and con-
sequential lower acceleration stresses for both the driver and
the load. In other words, the working conditions of the driver
are improved and the loading capacity of the vehicle is increased.
The travelling speed in difficult terrain can also be increased.
In conjunction with practical trials and theoretical calculations,
it can be established that the driving speed for a vehicle with
the apparatus described here can be increased by a factor of 4-5
in relation to a conventional terrain vehicle starting out from
equivalent driver conditions and safety margins against tipping.
In Figure 11 there is shown, schematically and in per-
spective, an alternative embodiment of the bogie arrangement of
the rear wheels in combination with previously described appara-
tus. The two bogie boxes 9, 10 in Figures 2, 4 are replaced in
this embodiment by a central bogie box 62 which is centrally
suspended at pivoting points 63, 64 on a chassis 65 denoted sym-
bolically by dashed lines and having a waist articulation 66.
Centrally suspended axles 67, 68, substantially equidistant from
the pivoting points 63, 64 are arranged in the bogie box 62,
the axles having pressure cylinders 69-72 with upper attachment~
73, 74 to the bogie box 62. A universal joint 75 is arranged on
a transmission shaft 76 in conjunction with the ar~iculation 66,
while unillustrated transmission elements, differentials, etc.
are arranged in the bogie box 62, 80 that this can freely move
about the pivoting points 63, 64 and the axles 67, 68 can carry
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out their pivoting movements. Pressure cylinders 77, 78 are, in
a way shown previously, mounted between the chassis 65 and a
front axle 79, which in Figure 11 is shown to be centrally sus-
pended at the chassis 65. On the respective sides of the vehicle
pressure conduits 80, 81interoonnect the pressure cylinders 69, 71,and
77 and the pressure cylinders 70, 72, and 78, respectively.
With a bogie arrangement as shown in Figure 11 there
are obtained the same advantageous stability conditions as pre-
viously described, while the design is simplified in certain
respects. In this alternative it is also possible to connect the
pressure cylinders 69-72 directly to the chassis 65, in which
case they are suitably mounted substantially vertically, i.e. as
shown for the fror.t pressure cylinders 77, 78 in Figure 11.
For almost completely circumventing the risk in practice
of overturning, preferably there is provided special safety
means coming into operation if the load centre of gravity comes
outside the resultant area; this is specially advantageous when
the terrain vehicle is arranged with a lifting crane, dumper
- body or the like. These safety devices are coupled to the fluid
.;, .
system of the pressure cylinders and are shown schematically in
Figures 12 - 14. In Figure 12 there is shown arranged on the
vehicle 1 a lifting crane 30 with a load 31. The mounting point
32 of the lifting crane to the vehicle is suitably in or adjacent
to the centre of gravity ~or the resultant area. Lowering and
raising the lifting crane 30 is controlled by a pressure cylinder
33 which is operated separately from the driver's cabin and which - -
is arranged with a pilot duct 34 connected to a control cylinder ~ -~
35 on a four-way valve 36. The valve 36 is automatically reset
by means of a compression spring 37, and is coupled into the
pressure circuits 38-41 between the forward pressure cylinders
22', 23' and the rear pressure cylinders Z4", 25". A resetting ~
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1066736
valve 42 is shown in the pressure conduits 38, 39, the conduits
38-41 being connected to each other by this valve in a way which
is shown in Figure 12.
The compression spring 37 is so adjusted that it yields
for a certain predetermined pilot pressure through the conduit
34, the valve 36 thereon being set to the position shown in
Figure 12, i.e. so that the conduits 38-41 are individually
blocked. Fluid communication between the pressure cylinders 22',
23', 24", 25" is then blocked and the cylinder movements immo-
bilised, which in turn means that the vehicle becomes rigid.
The predetermined pilot pressure through the conduit 34 is
adjusted to conform to a maximum working pressure in the pressure
cylinder 33, which occurs when the resulting load centre of
gravity for the crane 30 with the load 31 comes outside the
resultant area.
A centre of gravity location outside the resultant
area R4 is obviously a momentary occurrence which can be quickly
corrected by measures on the part of the driver. Blocking by . -
means of the valve 36 and the increased stability of the vehicle
caùsed thereby is thus to be regarded as a safety measure against ~ ~-
tipping which automatically comes into action and which is simi-
larly directly neutralized by an action of the driver. -~
A similar arrangement is shown schematically in Figure
13 where the vehicle 1 is shown arranged with a dumper body 43, ~ -
indicated by dashed lines, in combination with a pressure cylin-
der 44 and tipping points 45, 46 mounted on the vehicle chassis.
The presQure cylinder 44 is controlled from the driver's cabin,
the cylinder being provided with a pilot oonduit 47 connected to a
control cylinder 48 on a four-way valve 49, corresponding to the
valve 36 in Figure 12 and having pressure conduits 50-53 respec-
tively connected to the front and rear pressure cylinders 22',
23' and 24", 25".
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1066~736
E~ecially when tipping the dumper body 43, it may
occur that the load centre of gravity comes outside the resultant
area, due to uneven load distribution and above all to too great
a load. The pilot pressure in the conduit 47 then exceeds a
predetermined value and sets the valve 49 so that the pressure
conduit~ 50, 51 to the forward pressure cylinders 22', 23' com-
municate with each other while on the other hand the pressure
conduits 52, 53 to the rear pressure cylinders 24", 25" are
blocked. The front axle 6' will then be free while the rear axle
10 11' will be rigid resulting in an increase in the stability of
the load carrying part of the vehicle.
In Figure 14 there is shown as an alternative to the
valve 49 in Figure 13 a braking valve 54 comprising two opposing
non-return valves 55, ~6 coupled in parallel in the conduits 50,
52, and non-return valves 57, 58 coupled in parallel in the con-
duits 51, 53. All non-return valves are equipped with compress-
ion springs 59, 60 in known manner, the compression springs 60 of
the non-return valves 56,58 in the biassing direction being actu-
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ated by two pressure pistons 61. The pressure pistons 61 run in ~ `
20 a pressure cylinder and are exposèd to the pilot pressure throughthe conduit 47.
It may be seen from Figure 14, and the flow directions
shown there for the non-return valves 55-58, that pressure fluid
can flow unhindered according to the double arrows P3, P4 through
the pressure conduits 50-53 on condition that the pilot pressure ~
through the conduit 47 is zero or thereabouts. If the pilot ;
pressure increases, corresponding to increased load on the pres-
sure cylinder 44 in Figure 13j the pressure pistons 61 are pushed
away from each other which means that the flow pressure through
30 the non-return valves 56, 58 increases. At a certain predeter-
mined pilot pressure the flow pressure through the non-return
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~.. ~f. '' "' "
1066736
valves 56, 58 will be so high that fluid flow will be blocked.
In turn, this means that the pressure cylinders 24", 25" will be
blocked, and the rear axle 11' will be rigid in relation to the
chassis. This being so, the increase of stability striven after
for the load carrying part of the vehicle is attained.
It will be understood that the described braking valve
S4 can also be used in conjunction with the lifting crane accor-
ding to Figure 12, and that the above described measures can
similarly be applied to the arrangement illustrated in Figure 11.
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Y
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