VEHICLE ON WHEELS OF THE ARTICULATED PUSHER TYPE

VEHICULE ARTICULE A ROUES MOTRICES ARRIERES

English Abstract

ABSTRACT OF THE DISCLOSURE:
Technical fields: vehicles on wheels of the articulated
type, i.e. vehicles comprising at least two parts which are
articulated to each other in the direction of the length of the
vehicle, and the pusher type, i.e. the type in which it is
mainly the set of wheels of a part located at the rear of the
vehicle which is the driving set. Technical problem: avoid a
"folding-up" of the vehicle in the event of loss of adherence of
the wheels of the front part of the vehicle. Gist of the solu-
tion: in the case where a set of wheels of the front part is a
steering set of wheels, regulating means for the part of the
motor-transmission unit which is connected to the front driving
set of wheels comprises a threshold means for bringing the part
of the motor-transmission unit into action. The threshold means
is moreover connected to means for mesuring a parameter which
at least approximately translates the transverse stability of the
vehicle. Main use of the invention: articulated buses of the
pusher type.

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A vehicle comprising a chassis which has at least a
front part and a rear part and articulation means articulating
the two parts of each other in the direction of the length of
the vehicle, each part being provided with at least one set of
wheels which may be a driving set of wheels, a motor-transmission
unit connected to said two sets of wheels for this purpose the
front part being provided with a steering set of wheels, the
motor-transmission unit having a part connected to the front
driving set of wheels, regulating means for
regulating said part of the motor-transmission unit, said regu-
lating means comprising a threshold means for bringing said
part of the motor-transmission unit into action, and means for
measuring a parameter which at least approximately translates the
transverse stability of the vehicle connected to the threshold
means.
2. A vehicle as claimed in claim 1, wherein the means for
measuring the parameter of stability comprise a detector of a
transverse component of the vehicle driving force which is
transmitted through the articulation means to the front part of
the vehicle and the threshold value of the threshold means is
defined by the relation:
<IMG>
in which represents the sum of the products of the type Pfl.a
taken for each one of the sets of wheels of the front part of
the vehicle, Pfl is the lateral resistance to skidding of the
considered set of wheels, a the distance between the point of
application of this resistance and the centre of gravity of the
- 15 -

front part, and c the distance between said articulation means
and said centre of gravity.
3. A vehicle as claimed in claim 1, wherein the means for
regulating said part of the motor-transmission unit further
comprise means for distributing the vehicle driving force
between the front driving set of wheels and the rear driving set
of wheels, and means for measuring the load on the front driving
set of wheels and means for measuring the load on the rear
driving set of wheels are connected to said regulating means.
4. A vehicle as claimed in claim 2, wherein the means for
regulating said part of the motor-transmission unit further
comprise means for distributing the vehicle driving force
between the front driving set of wheels and the rear driving
set of wheels, and means for measuring the load on the front
driving set of wheels and means for measuring the load on the
rear driving set of wheels are connected to said regulating means.
5. A vehicle as claimed in claim 1, wherein at least one
of two parts of the transmission which are connected respectively
to the front driving set of wheels and to the rear driving set
of wheels is a fluid transmission.
6. A vehicle as claimed in claim 5, wherein the other part
of said two parts of the transmission is a mechanical transmis-
sion which is driven by the motor part of the motor-transmission
unit and is directly connected to one of the two driving sets
of wheels.
7. A vehicle as claimed in claim 6 wherein it is the part
of the transmission which is connected to the front driving set
of wheels which is a fluid transmission.
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8. A vehicle as claimed in claim 5, wherein the part of the
transmission which is connected to the rear driving set of wheels
is also a fluid transmission.
9. A vehicle as claimed in claim 5, wherein each fluid
transmission comprises a pump which is mechanically driven, a
fluid driven motor and a fluid circuit connecting the pump to
the fluid driven motor.
10. A vehicle as claimed in claim 9, comprising between each
pump and each associated fluid driven motor which is a hydraulic
motor, a hydraulic energy accumulator, a hydrostatic loop con-
necting the pump to the hydraulic motor and comprising two
branches, two electric valves respectively inserted in the two
branches of the hydrostatic loop, a hydraulic accumulator
selectively connectible to the two branches through the two
valves, regulating means for selectively controlling the valves
by regulating means for the valves being associated with means
for detecting pressures at various points of said loop for the
purpose of sending the fluid pressure coming from the hydraulic
motor into said accumulator in the course of a braking and/or
deceleration of vehicle and re-injecting the overpressure thus
stored in the accumulator into the circuit of the hydraulic
motor as the vehicle commences to move off again and/or re-
accelerates.
11. A vehicle as claimed in claim 10, wherein said regulating
means for the valves act on the valves in such manner that they
cannot be opened simultaneously and that they remain closed when
the direction of flow of the hydraulic fluid is reversed by a
reverse speed control of the vehicle.
12. A vehicle as claimed in any one of the claims 9 to 11,
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comprising two hydraulic motors drivingly connected to left
wheels and right wheels of the front set of wheels, a first
pump which is connected to supply fluid to two first hydraulic
motors, two second hydraulic motors drivingly connected to left
wheels and right wheels of the rear set of wheels, a second
pump connected to supply fluid to the second hydraulic motor,
and a single motor drivingly connected to the two pumps.
13. A vehicle as claimed in claim 1, wherein the motor-
transmission unit comprises a single motor disposed in the rear
part of the vehicle and the part of the motor-transmission unit
which is connected to the front driving set of wheels is a
mechanical transmission driven by motor part of the unit, and
the means for regulating transmission part of the unit comprise
coupling means inserted in said mechanical transmission and
connected to the threshold means for bringing said regulating
means into action.
14. A vehicle as claimed in claim 13, wherein the part of
the motor-transmission unit which is connected to the rear
driving set of wheels is also a mechanical transmission driven
by the motor part of the unit.
15. A vehicle as claimed in claim 14, wherein the two
parts of the motor-transmission unit which are connected res-
pectively to the driving set of wheels of the rear part and to
the driving set of wheels of the front part, are connected in
series with interposition of said coupling means.
16. A vehicle as claimed in claim 15, wherein a third
differential is inserted in the transmission driving the front
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set of wheels, and the coupling means are interposed between
the differential of the rear set of wheels and said third
differential.
17. A vehicle as claimed in claim 2, wherein the motor-
transmission unit comprises a single motor disposed in the rear
part of the vehicle and the part of the motor-transmission unit
which is connected to the front driving set of wheels is a
mechanical transmission driven by motor part of the unit, and
the means for regulating transmission part of the unit comprise
coupling means inserted in said mechanical transmission and
connected to the threshold means for bringing said regulating
means into action.
18. A vehicle as claimed in claim 17, wherein the part
of the motor-transmission unit which is connected to the rear
driving set of wheels is also a mechanical transmission driven
by the motor part of the unit.
19. A vehicle as claimed in claim 18, wherein the two
parts of the motor-transmission unit which are connected respec-
tively to the driving set of wheels of the rear part and to the
driving set of wheels of the front part, are connected in
series with interposition of said coupling means.
-19-
20. A vehicle as claimed in claim 19, wherein a third
differential is inserted in the transmission driving the front
set of wheels, and the coupling means are interposed between
the differential of the rear set of wheels and said third diffe-
rential.

21. A vehicle as claimed in claim 3, wherein the motor-
transmission unit comprises a single motor disposed in the
rear part of the vehicle and the part of the motor-transmission
unit which is connected to the front driving set of wheels is
a mechanical transmission driven by motor part of the unit, and
the means for regulating transmission part of the unit comprise
coupling means inserted in said mechanical transmission and
connected to the threshold means for bringing said regulating
means into action.
22. A vehicle as claimed in claim 21, wherein the part of
the motor-transmission unit which is connected to the rear
driving set of wheels is also a mechanical transmission driven
by the motor part of the unit.
23. A vehicle as claimed in claim 22, wherein the two parts
of the motor-transmission unit which are connected respectively
to the driving set of wheels of the rear part and to the driving
set of wheels of the front part, are connected in series with
interposition of said coupling means.
24. A vehicle as claimed in claim 23, wherein a third
differential is inserted in the transmission driving, the front
set of wheels, and the coupling means are interposed between
the differential of the rear set of wheels and said third dif-
ferential.
-20-

25. In an articulated vehicle having a forward and
a rear section connected at an articulation connection, a
source of driving power, the rear section having a first set
of wheels driven by the source of driving power, the forward
section having a second set of wheels for steering the
vehicle and a third set of non-steering wheels, the improve-
ment comprising:
means for selectively driving the third set of wheels
with power from said source;
means for monitoring parameters having at least one
output from which a value for a force at the articulation
connection tending to jackknife the vehicle may be derived;
means for calculating a value according to a pre-
determined drive system rule representing the threshold above
which jackknifing may occur;
means for comparing the value for the derived force to
a value calculated to be the threshold above which jack-
knifing may occur;
means for generating a control signal which varies
depending upon the results of the comparison; and
means for controlling the selective driving means for
the third set of wheels to apply a portion of the power from
said source to the third set of wheels when said force
exceeds the threshold according to a predetermined drive
system rule.
26. An articulated vehicle comprising:
a source of driving power;
a rear section having a first set of wheels driven by
the source of driving power;
a forward section connected to the rear section at an
articulation connection, the forward section having a second
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set of wheels for steering the vehicle and a third set of
non-steering wheels;
means for selectively driving the third set of wheels
with power from said source;
means for monitoring parameters having at least one
output from which a value for a force at the articulation
connection transverse to the longitudinal of the forward
section and tending to jackknife the vehicle may be derived;
means for calculating a value according to a pre-
determined drive system rule representing the threshold above
which jackknifing will occur;
means for comparing the value for the derived trans-
verse force to a value calculated to be the threshold above
which jackknifing will occur;
means for generating a control signal which varies
depending upon the results of the comparison; and
means for controlling the selective driving means for
the third set of wheels to apply a portion of the power from
said source to the third set of wheels when said derived
force exceeds the threshold according to a predetermined
drive system rule.
27. An articulated vehicle according to claim 25,
wherein the threshold being a function of the instantaneous
articulation angle and the connection force, the monitoring
means comprising at least two transducer means at the
articulation connection having outputs from which values for
the instantaneous articulation angle and the magnitude of the
connection force may be derived.
28. An articulated vehicle of claim 27, wherein the
means at the articulation connection comprising two force-
-22-

measuring transducers oriented in a predetermined geometric
relationship to one another and detecting components of the
connection force, the monitoring means further comprising
means for deriving the instantaneous articulation angle and
the magnitude of the connection force from the transducer
outputs.
29. A method of driving an articulated vehicle having
a forward and a rear section connected at an articulation
connection and further having means for selectively operating
the vehicle either as a push-type vehicle with rear section
drive only or with both forward and rear section drive, the
method comprising:
monitoring parameters with at least one transducer
having an output from which a value for a force at the
articulation connection tending to jackknife the vehicle may
be derived;
comparing the value for the derived force to a value
calculated according to a predetermined drive system rule
representing the threshold above which jackknifing may occur;
generating a control signal which varies depending
upon the results of the comparison; and
controlling the operating means with said control
signal to selectively operate the vehicle as a push type
vehicle with rear section drive only when said derived value
for the force is less than the threshold and to operate the
vehicle with both forward and rear section drive when said
derived value for the force exceeds the threshold.
30. A method of propelling an articulated vehicle
having a forward and rear section connected at an articula-
tion connection, the vehicle having a source of driving power,
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the rear section having a first set of wheels driven by the
source of driving power, the forward section having a second
set of wheels for steering the vehicle, a third set of wheels
and means for selectively applying driving power to the third
set of wheels, said means being selectively actuated by a
control means, the source of driving power generating a total
propulsion force to be divided among and applied at the road
surface by any driven wheels of the vehicle, the total propul-
sion force being applied to the road surface solely by the
first set of wheels at times when the third set of wheels is
not driven and applied in part by the first set of wheels
and in part by the third set of wheels when both of said sets
are simultaneously driven, the articulation connection trans-
mitting a connection force between the forward and rear
sections, the method comprising:
monitoring parameters with at least one transducer
having an output from which values for the instantaneous
angle of articulation between the sections and the magnitude
of the connection force may be derived;
monitoring further parameters with at least one
additional transducer having an output from which a value
for the instantaneous magnitude of the total propulsion force
generated by the source of driving power may be derived;
determining the actual ratio of the value for the
derived connection force to the value for the derived propul-
sion force;
comparing the actual ratio to a ratio calculated from
a predetermined drive system rule, the ratio calculated
from the rule being a function of the instantaneous articula-
tion angle;
driving only the first set of wheels when the actual
ratio is less than the calculated ratio for the instantaneous
-24-

articulation angle value; and
actuating the means for applying power to the third
set of wheels with the control means when the actual ratio
is greater than the calculated ratio, thereby driving both
the first and third sets of wheels, the proportion of the
propulsive force applied by the third set of wheels being
that sufficient to maintain the actual ratio less than the
calculated ratio.
31. The method of claim 29, the ratio calculated from
the predetermined drive system rule being a function of the
reciprocal of the sine of the articulation angle for at
least the upper range of articulation angles.
32. The method of claim 29, the values for the
instantaneous articulation angle and the magnitude of the
connection force being derived from the outputs of two force-
measuring transducers oriented in a predetermined geometric
relationship to one another and detecting components of the
connection force.
33. The method of claim 32, the components of the
connection force detected by the two force-measuring
transducers being the components directed radially from the
effective point of articulation at 45 degree angles to each
side of the longitudinal axis of the forward section.
-25-

Description

:3L17~Lt7~LO
The present invention relates to a method of
driving an articulated vehicle and to such an articulated
vehicle.
Vehicle on wheels of the articulated pusher type
comprise a chassis having at least two parts which are
articulated to each other in the direction of the length of
the vehicle and are each provided with at least one set of
wheels which may be driving set of wheels, the motor-trans-
mission unit of the vehicle being connected for this purpose
to the two sets of wheels, the part of this motor-transmission
unit which is connected to the front driving set of wheels
being associated with means for regulating said part of the
motor-transmission unit.
It is known that the dynamic performance, i.e. the
performance in the course of displacement, of this type of
vehicle is related more than for any other, to the adherence
of the pneumatic tires on the ground, although in most cases
the value of this adherence is sufficient to enable the
front part to impose its direction on the rear part.
However, when the adherence decreases, owing for
example to the nature, evenness or orientation of the ground,
drawbacks appear when steering in a sharp turn. Indeed, the
part of the driving effort transmitted to the front part of
the vehicle through the articulation is divided, relative to
the axis of this front part, into an axial component which is
the driving component and a transverse component which is not
a driving component. This transverse component produces
around the centre of gravity of the front part a moment of
force which is opposed to and larger than that produced by
the lateral resistance of the front part to skidding so that
the vehicle has a tendency to close or fold up beyond the
angle corresponding to the desired steering angle.

~74'7~0
Vehicles of the considered type are known which
comprise for the purpose of overcoming this undesired folding,
abutment or lock means for the articulation which become
operative beyond a certain steering angle. However, in this
arrangement, the transverse component of the force trans-
mitted is completely lost so that the driving efficiency is
markedly reduced and this constitutes a particularly serious
handicap in a bend.
Consequently, the object of the invention is to
provide a vehicle which has none of the aforementioned draw-
backs, i.e. a vehicle which does not tend to close and in
which there is no reduction in the driving efficiency.
According to the present invention there is provided
a vehicle comprising a chassis which has at least a front
part and a rear part and articulation means articulating the
two parts of each other in the direction of the length of
the vehicle, each part being provided with at least one set
of wheels which may be a driving set of wheels, a motor-
transmission unit connected to said two sets of wheels, for
this purpose the front part being provided with a steering
set of wheels, the motor-transmission unit having a part
connected to the front driving set of wheels, regulating means
for regulating said part of the motor-transmission unit, said
regulating means comprising a threshold means for bringing
said part of the motor-transmission unit into action, and
means for measuring a parameter which at least approximately
translates the transverse stability of the vehicle connected
to the threshold means.
According to the present invention there is also
provided a method of driving an articulated vehicle having a
forward and a rear section connected at an articulation connec-
tion and further having means for selectively operating the
.,,
~ - 2 -

'71(~
vehicle either as a push-type vehicle with rear section
drive only or with both forward and rear section drive, the
method comprising: monitoring parameters with at least one
transducer having an output from which a value for a force at
the articulation connection tending to jackknife the vehicle
may be derived; comparing the value for the derived force to
a value calculated according to a predetermined drive system
rule representing the threshold above which jackknifing may
occur; generating a control signal which varies depending
upon the results of the comparison; and controlling the
operating means with said control signal to selectively
operate the vehicle as a push-type vehicle with rear section
drive only when said derived value for the force is less than
the threshold and to operate the vehicle with both forward
and rear section drive when said derived value for the force
exceeds the threshold.
This arrangement thus permits a part of the vehicle
driving force to be directly applied to the front part of the
vehicle as soon as the fixed stability threshold has been
exceeded, without passing through the articulation, so that
the transverse component of the force transmitted through the
articulation can be maintained constantly within the value
causing a closure of the vehicle and safe operation is
ensured irrespective of the steering angle.
The invention may further presents the following
preferred or advantageous features taken singly or in
combination with each other.
It may be advantageously arranged that the means
for measuring the stability parameter be formed by a detector
of the transverse component F2pR of the vehicle driving force
transmitted through the articulation of the vehicle to the
front part of the latter and that the threshold value of the
threshold ~
2a -

~l~7~7~
means be defined by 'che expression
;~ Pfl.a
-
in which~ represents the sum of the products of the type Pfl.a
taken for each one of the sets of wheels of the front part of
the vehicle, Pfl is the lateral resistance to skidding of the
considered set of wheels, a the distance between the point of
. application of this resistance and the centre of gravi-ty of the
front part, and c the distance between the articulation of the
vehicle.and said centre of gravity. The interest of this is to
make it possible to take into account the resistance of the
front part to forward travel and therefore, to ensure safe opera-
tion.in all the positions of the vehicle, for example in the case
of bends on a slope, the abutment of the front wheels against an
obstacle, etc.
It may also be particularly advantageous arranged that the
means for regulating said part of the motor-transmission unit
.also comprise means for distributing the vehicle driving force
between the front driving set of wheels and the rear driving set
of wheels and connected to means for measuring the load on the
front driving set of wheels and the load on the rear driving set
of wheels. This enables the efficiency of the drive to be main-
tained even in cases where, in known vehicles in which the drive
depends on the load on the driving set of wheels, the drive
would be distinctly diminshed, if not eliminated owing to slip,
namely when the front part of the vehicle is much overloaded at
the expense of the rear part or when the coefficient of adherence
of the rear set of wheels is considerably reduced, for example on
ice.
In some specific embodiments of the invention, it may be
arranged that at least one of the two parts of the transmission
-- 3

~1:3L74'71V
:~`
which are connected respectively to the front driving set of
wheels and to the rear driving set of wheels be a fluid trans-
mission to which fluid transmission the regulating means are
preferably connected, the motor-transmission unit also preferably
comprising a single motor.
In one of these embodiments a single motor, disposed in the
rear par-t, mechanically drives the rear driving set of wheels, a
hydrostatic transmission being interposed between the differen-
tial of the latter set and the differential of the front driving
set of wheels. In another embodiment, a single motor, also
~isposed in the rear part, drives two hydraulic pumps which act
on hydraulic motors of the rear set of driving wheels and front
set of driving wheels of the right and left sides respectively.
It is also possible in accordance with the present invention
to take advantage of the reversibility of such a hydrostatic
transmission by means of a hydraulic pump and motor so as to at
least partially recover, when braking, the kinetic energy stored
by the vehicle and usually dissipated in the form of heat in the
brake devices. This recovery consists advantageously in a
storage of a part of said kinetic energy and then a restoration
of the stored energy when the vehicle starts to move so as so
reduce the work required of the motor.
For this purpose, there may be particularly advantageously
provided, between the pump and the hydraulic motor, a hydraulic
energy accumulator connected to two electric valves each connec-
ted toone of the two branches of the hydrostatic loop connecting
the pump to the motor, the valves being selectively controlled
by regulating means which detect pressures at various points of
said loop so as to send the fluid pressure from the motor to
said accumulator in the course of a braking and/or slowing down
and to re-inject the overpressure thus stored in the accumulator,
-- 4

`~ ~
into the circuit of the hydraulic motor when the vehicle once
again moves off and/or accelerates.
In another specific embodiment o the invention, it may be
arranged that the part of the motor-transmission unit which is
connected to the Eront driving set of wheels be a mechanical
transmission driven by the engine part of the unit and that the
regulating means of this transmission part of the unit comprise
coupling means interposed in this mechanical transmission and
connected to the threshold means for bringing the regulating
means into action.
With this arrangement, when the vehicle travels in a
straight line or in a relatively wide bend, i.e. so long as it
remains within the limits of transverse s-tability, the actuating
threshold means maintain the coupling means in the uncoupled or
"declutched" position so that the vehicle is drivens solely by
its rear set of wheels or axle. On the other hand, if the vehicle
enters a sharp bend in respect of which it becomes necessary to
control the transverse stability, said threshold means causes the
coupling means to change to the coupled or "clu-tched" position
so that a part of the vehicle driving force can be transmitted
to the driving set of wheels of -the front part and a perfect
stability of the whole is ensured.
~ part from this essential advantage concerning stability,
this particular embodiment has the great interest of being
adaptable, with no considerable modification, if only the inter-
position of the coupling rneans, to articulated pusher vehicles
in which a set of wheels of the front part is driven through a
mechanical transmission. Moreover it improves, in vehicles of
this type, the efficiency integrated with respect to time on the
operation considered as a whole since, in the absence of the
arrangement according to the invention, thls efficiency is

~7~
.
permanently reduced owing to the multiplicity of the gears and
other intermediate elements of the transmission. The same is
true as concerns the noise level and the reliability of the
transmission chain also integrated with respect to time.
Preferably, it may also be arrangecl that the part of the
motor~-transmission unit which is connected to the rear driving
set of wheels be also a mechanical transmission driven by the
motor park of the unit, the motor part of the unit being advan-
tageously formed by a single motor, preferably a heat motor,
disposed in the rear part of the vehicle.
In a particularly advantageous manner, the two parts of the
motor-transmission unit, which are respectively connected to the
driving set of wheels of the front part and to the driving set
of wheels of the rear part, may be connected in series with
interposition of said coupling means, this arrangement resulting
n the most simple configuration and maximum efficiency.
Further features and advantages of the invention will be
apparent from the ensuing description which is given merely by
way of example with reference to the accompanying drawings in
which:
- Fig. 1 is a diagrammatic plan view of an articulated
vehicle according to a first embodiment of the invention, shown
in its position on a rectilinear path;
- Fig. 2 is a similar view of a second embocliment according
to the invention;
- Fig. 3 is a diagrammatic elevational view of either of
the vehicles of Figs. 1 and 2 shown in the position in which it
is steered away from a rectilinear path;
- Fig. 4 is a diagrammatic illustration of the energy
recovering circuit according to the invention, and
- Fig. 5 is a diagrammatic plan view of a vehicle in a thircl
-- 6
,. .

ît3LV
specific embodiment according to the invention.
The two vehicles shown in Figs. 1 to 3 are articulated buses
comprising a chassis which has two parts 1 and 2 which are
articulated to each other in the direction of the length of the
vehicle, the ront part 1 be:ing provided with a front steering
set of wheels 3 and a rear supporting set of wheels 4, whereas
the rear part 2 is provided with a single supporting set of
wheels 5. The two parts are articualted to pivot about a vertical
pin 6 which is part of a rotary platform 7 on each side of which
10. are provided connecting "accordeons" or bellows 8.
In the embodiments of Fig. 1 which corresponds to a semi-
hydrostatic arrangement, the motor-transmission unit of this
vehicle comprises, on one hand, a single heat engine 9 disposed
in the back of the part 2 and provided with a gear ~ox 10 and, on
the other hand, ~ transmission unit which comprisesl one one hand,
a mechanical transmi.ssion 11 driving the rear set of wheels 5
through a differelltial 12 and, Oll the other hand, a hydrostatic
- transmission 13 driving the centre set of wheels 4 through a
second differential 14, this transmission 13 comprising a variable
displacement hydraulic pump 15 driven by the differential 12, a
hydraulic motor 16 driving the differential 14, and a hydraulic
circuit 17 connecting the pump 15 -to the motor 16.
This vehicle further comprises a regulating system 18 which
includes an electronic regulating unit 19 having three inputs
connected to three detectors 20, 21 and 22, and an ou-tput con-
nected to the hydrostatic transmission 13 or 13a. The two
detectors 20 and 21 are forrned by load detectors whlch are dis-
posed in the vicinity of respectively the centre set of wheels 4
and the rear set of wheels 5. As concerns the detector 22, it
is formed by a detector of the transverse component of the vehicle
driving force trans]nitted through the arti-culation 6 of the

3~ 7~
vehicle to the front part 1 o the latter, this detector beiny
disposed on the considered articulation 6 and being formed, for
example, by a stress gauge or a ~uartz detector or by a hydraulic
cylinder which delivers a pressure, The regulating unit 19
comprises a threshold means 23 for bringing the hydrostatic
transmission 13 into action and means 24 for distributing the
vehicle driving force between the centre set of wheels 4 and the
rear set of wheels 5.
The embodiment of Fig. 2, which corresponds to an entirely
hydrostatic arrangernent, differs from the embodiment of Fig. 1
only in that the mechanical transmission 11 and the hydrostatic
transmission 13 are replaced by a single h~drostatic transmission
unit 13a. This unit comprises tWQ variable displacement
hydraulic pumps 15a and 15b, both driven by the heat motor 9, and
four hydraulic motors 16a and 16b associated respectively with
the left wheels and right wheels of the centre se-t of wheels 4
and the rear set of wheels 5, the mo-tor 16a of the rear set of
wheels being connected to the pump 15a through a hydraulic circuit
17a and the motor 16b of the centre set of wheels being connected
to the pump 15b through a circuit 17b. The output of the
regulating unit 19 of the unit 13 (not shown) is connected to the
transmission unit 13a.
The vehicles just described operate in the following manner:
If the centre set of wheels 4 of the vehicle received no
direct driving force in a bend, the front part 1 would be sub-
jected, as shown in Fig. 3, on one hand, to the lateral resist-
ances to skidding Pfl and Pf2 f the front set of wheels 3 and
the centre set of wheels 4 which are applied at respective dis-
tances a and b from the centre of gravity G of this front part,
and, on the other hand, to the part FpR of the driving force
furnished by the motor which is transmitted through the articula-

tion 6 to this front part. This driving force FpR is divided,relative to the a~is of the front part, into a driving axial
component FlpR which participates in the displacement of the
front part and a transverse component F2pR which is lost for
the driving force and, moreover,.participates in the tendency of
the front part to skid, and therefore in the "closure" of the
vehicle. As this transverse component is applied at a distance
c from the centre of gravity, in order to avoid a skidding of
the centre set of wheels 4, the following relation must bé
10 . approximately satisfied:
PR ~ Pfl.a ~ Pf2.b
When the vehicle -travels in a rectilinear path, the trans-
verse component F2pR is zero and the above relation is always
.satisfied. The vehicle is wholly drivens by the rear set of
wheels 5 and this results in optimum efficiency in respect of
this drive.
When the vehicle travels in a bend, it behaves in the sa~e
way as in.a rectilinear path as long as the steering angle
2.0 remains less than a certain threshold value which corresponds to
a thr.eshold value o the transverse component F2pR, which is
itself a function of the masses of the two parts of the vehicle.
When the value of F2pR tends to exceed this threshold if the
steering radius decreases, the detector 22 cooperates with the
.threshold means 23 of the regulating unit 19 and the latter
brings into action the hydrostatic transmission 13 so that a
vehicle driving force can be transmitted to -the centre set of
wheels 4.
Owing to the action of the regulating Ullit 19, F2pR never
exceeds the authorized threshold so that there is no risk of the
"closure" of the vehicle, the moment of force due to the adherence
~ ~ _

:~7~0
of the sets oE wheels 3 and exceeding the force F2pR applied to
the articulation 6.
This assumes that the load detectors 20 and 21 were not in
operation. On the other hand, when these detectors cooperate
with the distribution means 24 of the regulating unit 19, the
latter acts on the hydrostatic transmission 13 or 13a so as to
distribute the total vehicle driving force between the two sets
of wheels 4 and 5 as a function of the load on the corresponding
two axles, this distribution being effected as a percentage of
the total value oE the force.
Safety against skidding is achieved in the sarne way as
before, a part of the vehicle driving force being transmitted to
the centre set of wheels 4 as soon as the transverse component
F2pR exceeds the fixed threshold value. With respect to the case
where the detectors 20 and 21 are inoperative, the sole difference
resides in the fact that the two sets of wheels 4 and 5 are
always drlving sets and onl~ the relative values of the driving
forces applied to these two sets varying in such manner as to
maintain the transverse component F2pR within the fixed threshold.
Fig. 4 shows a hydraulic pump 61 which is driven by the
motor (not shown) of the vehicleA The pump 61 is connected to
a hydraulic motor 62 driving the front (or centre) set of wheels
of the vehicle (not shown).
The hydrostatic loop connecting the pump 61 to the motor 62
comprises (for the normal forward travel of the vehicle) a high
pressure (HP) branch HP 63 and a low pressure (LP) return
branch 64. A hydraulic accumulator 65 is connected to two
electric valves 66 and 67, the valve 66 being connected to the
branch 63 and the valve 67 to the branch 64.
The valves 66 and 67 are controllecl by regulating means 6
which detect thc pressure at the various points of the pulnp-
-- 10 --

1~7A~'7~l[)
motor loop.
Fig. 4 also shows a draning and booster circuit for the
pump which comprises in particular a Eilter 69, a tank 70 and
an exchanger 71.
In normal operation, the pump 61 normally delivers fluid to
the circuit at pressure Pl (HP). The motor 62 delivers an output
pressure P2~Pl. rrhe two electric valves 66 and 67 are closed
(by the regulating means) and the accumulator 65 is isolated
from the hydraulic loop 63, 64.
In the course of a braking and/or slo~ing down (provided it
is suffic1ently intense), the motor 62 is driven by the wheel or
wheels and consequently operates as a pump and the pressure P2
becomes higher than the pressure Pl.
If P2 is higher than P3, which is the pressure in the
accumulator 65, the electric valve 67 opens and the pressure in
the accumulator 65 rises. If P2 is lower than or equal to P3,
the electric valve 67 remains closed and nothing happens.
The energy thus s-tored in the accumulator 65 is restored or
returned as the vehicle again starts to move off or reaccelerates.
Indeed, as soon as the operation of the hydrostatic transmission
becomes normal again and Pl again becomes higher than P2, the
electric valve 66 opens, provided that P3 is higher than Pl, and
the accumulator 65 supplies fluid to the HP circuit 63 and
consequently reduces the effort required from the pump 61.
O~ course, the valves 66 and 67 are piloted by the regulating
means 68 in such manner that they cannot be opened at the same
time and thereby produce a short circuit. Further, both of them
remain closed when the direction of flow of the oil in the
hydraulic circuit has been reversed by the action of the reverse
speed control oE the vehicle.
Such a circuit is applicable to both the embodiment of Fig. 1

~L~7~7~L)
and the embodiment of Fig. 2. In Fig.l, only the front set of
wheels is driven hydraulieally by a hydraulie motor supplied
with fluid by a pump which is driven by the differential of the
rear set of wheels aetuated by a single motor. Such a hydro-
static transmission may be provided with the improvement o~ the
present invention.
In Fig. 2, the sing~e motor drives in parallel two h~draulie
pumps, one being for the front wheels and the other for the rear
wheels. Eaeh pump aetuates the hydraulie motors of the rear and
. 10 front (eentre) sets of wheels. In this embodiment, the reeovery
eireuit ma~ be provided by incorporation between each pump and
their assoeiated motors an aecumulator-electric valves unit
aecording to the diagram of Fig. 4.
The vehiele shown in ~`ig. 5 is an articulated bus whieh
eomprises a ehassis having two parts 31 and 32 whieh are articu-
lated to eaeh other in the direction of,the length of the vehiclet
the front part 31 being provided with a steering set of wheels 33
- and a rear supporting set of wheels 34, where as the rear part 32
is provided with a single supporting set of wheels 35. The two
- 20 parts are articulated about a vertieal pin 36 which is part of a
rotary platform 37 on each side of which connecting "accordeons"
or bellows 33 are provided.
The motor-transmission unit of the vehicule comprises, on one
hand a single motor in the form of a heat engine 39 located in
the back of the part 32 and provided with a gear box 40 and, on
the other hand, a transmission unit which eomprises, on one hand,
a first meehanical transmission 41 which drives the rear set of
wheels 35 through a diEEerential 42 oE the rear axle and, on the
other hand, a second meehanical transmiss`ion 43 which drives the
eentre set of wheels 34 through a seeond differential 44 of the
eentre axle. This seeond transmission ~3 comprises a plurality
.
. ,,._,
,

~7~
of elements which are articulated through double universal joints
45, a low frequency beariny 46 being morever provided on the first
of these elements disposed on the axis of the rear part 32, this
element being itself driven by a third differential 47 which is
adapted to absorb differences in the radii curveture of the paths
and consequentl~ in the speeds of the two parts of the vehicle.
This vehicule further comprises a regulation system 48 which
includes an electronic regulating unit 49 consisting of a ~
actuating threshold means. This unit has an input which is con-
nected to a detector 50 disposed on the articulation 36 of thevehicle, this detector being a detector which detects the trans-
verse component o the vehicle driving Eorce transmitted by this
articulation 36 to the front part 1 oE the vehicle, constituted
for example by a stress gauge or a quartz detector or a hydraulie
cylinder whech delivers a pressure. The unit 49 also has an
output which is connected to a coupling means 51 interposed in
the second mechanical transmission 43 between the rear driving
axle differential 42 and the third differentia] 47 This coupling
means may be formed by an electromagnetic coupling, for example
an electromagnetic clutch, a hydrostatic coupling or a hydro-
dynamic coupling.
The vehicle just described operates in the following manner.
When the vehicle travels in a rectilinear path, the trans-
verse component F2pR is zero and the detector 50 does not act on
the threshold means of the unit 49 so that the latter maintains
the coupling means 51 in its uncoupled or "declutched'l position.
The vehicle is thus driven wholly by the rear set of wheels
35 and this ensures optimum efficiency of this drive.
When the vehicle travels round a bend or turn, it behaves in
- the same manner as in a rectilinear path as long as the steering
angle remains less than a certain threshold value which corres-
- 13 -
..

L7~7~C~
ponds to a pre-fixed value of F2pR
When the value of F2pR tenc1s to exceed this threshold value,
i.e. when the raclius of the bend decreases, the detector 50 co-
operates with the threshold means oE the unit 49 so as to bring
the coupling means 51 to the coupled or "clutched" position.
This permits the tranmission of a vehicle driving force to the
centre set oE wheels 34 and thus the distribution of this force
between the two parts of the vehicle.
Thus, irrespective of the con~iguration of the path oE the
vehicle, the components F2pR never exceed the authorized thres-
- hold so that there is no risk of the closure of the vehicle and
perfect transvérse stability of the latter is ensured.