Downloaded from www.Manualslib.com manuals search engine OPERATION No MA. 450-00 : Ch nrnclcrislics ortd sp~~c-i~l (c~c~trlrc>s 01 the hokiug S SI~IN Op. MA. 450.00 5
A brake pressure limiter is fitted to the rear braking system on Estate vehicles.
Its object is to vary the maximum
pressure in the rear braking system as a function of the load imposed on the rear suspension and the pressure in
the front braking system. It is secured horizontally on the front subframe, behind the safety valve.
L 45-6
Rear brakes Air-chamber
A
Front brakes
Rear brakes Air-chamber
A A --
7 Front brakes OPERATION
* I
f Vchtclcs - ‘I/]‘,?(, i
The brake pressure limiter consists mainly of a
slide-valve, the positions of which allow or do not
allow the supply of fluid under pressure from the
brake valve to the rear brakes.
The ends of this slide-valve are submitted to the
action of two forces
- Force F
exerted by the fluid under pressure in
the rear suspension.
= Force R
exerted by spring ( 1 ) and increased by the
value of force Fl
exerted by the front brake fluid
pressure during braking action.
a) \‘~~I~i~-/~~s irt Ilte t( lorl r /tr,.silioti f t/o /trc~.s.surc’ )
Under the only force R,that of the spring. slide-valve
is in the position indicated in figure 1. The fluid
cannot pass from the brake valve to the rear brakes,
( and vice-versa ).
Force
F exerted by the rear suspension pressure
is greater than Force R
exerted by the sprinq.
The slide-valve is in the position indicated by
Figure 2. which allows flow of fluid from brake
valve to rear brakes ( and vice-versa ).
c ) Vvhiclc il2 ntotior/. rr,ith 111~’ broke pednl ncl~~fit~~c/ :
Fluid from the front brakes exerts a Force Fl
which is added to Force R exerted by the spring.
When these two forces are smaller than force F,
slide-valve is in position shown in Figure 2.
The rear brakes are supplied.
When these two forces are greater than Force
F,
slide-valve is in the position shown on Figure 1.
The rear brakes are not supplied.
NOTE Fl
+ R -b F is true, when the pressure
in the front brakes + 28 bars ( 406 psi ) becomes
greater than the’pressure in the rear suspension.
When F
increases, Fl increases. Consequently,
maximum pressure in the rear brakes increases.
In order to avoid a sudden cut-out of the supply
to the rear brakes, a ball-valve slows the flow
of liquid from the front brakes. The action of this
valve is increased by the fact that an air-bubble
trapped in its chamber, secured at the rear of the
front subframe upper.crossmember on the L.H. side,
has to be compressed. Once the slide-valve has
started moving, the supply of fluid is not slowed
down, and it then flows through the by-pass channel.
Downloaded from www.Manualslib.com manuals search engine FIG. 1
Supply to brake valve Rear suspension
i
Filter
\--Iii
I
Rear brak
. .
One-way valve
I units
Rl
Feed to brake valve F Rear suspension /
One-way valve II Rear brake
Rl Fl
units The brake pressure limiter consists mainly of a
slide-valve, the position of which allows or does
not allow supply of fluid under pressure from the
brake valve to the rear brakes.
-
one end of the slide-valve is constantly subjected
to the pressure of the rear suspension fluid ( which
varies according to the load )
- the other end of the slide-valve is subjected to
force Rl,
increased during braking action by force Fl
exerted by the fluid under pressure from the
rear brakes
a)
Vvhirlc, irl the n IOU N positiolt (,,o /)rc,.ssurc, )
.Under the action of force Rl alone, the slide-
valve is in the position shown on Fig. 1.
The fluid cannot flow from the brake valve to
the rear brakes.
On the other hand, the one-way valve allows fluid
to flow from the rear brakes to the brake-valve.
Force F
exerted by the rear suspension fluid under
pressure is qreater than force Rl
produced by the
spring. The slide-valve is in the position shown
on Fig. 2 which allows fluid to flow from the brake
valve to the rear brakes and vice-versa.
Fluid flowing from the rear brakes, exerts a
force Fl
which is added to force Rl produced
by the spring.
H~prc 6
CNt’Out 11
At the start of the brake pedal movement, force Fl
being still very small, we have Fl t Rl < F. The
slide-valve allows liquid to flow to the rear brakes.
Aitcr t( CIIIW~~ H
Force Fl
having increased, and being added to
Force Rl,
we have Fl + Rl> F. The slide-valve
interrupts the flow of fluid to the rear brakes.
The (( easing )) of the braking at the rear is then
allowed to proceed via the one-way valve.
NOTE : Fl
+ Rl> F is true when the rear brake
pressure + 28 bars
( 406 psi ) becomes greater
than the rear suspension pressure. If F
increases, Fl
Increases as well until cut-out occurs.
Consequently, maximum pressure in the rear
brakes increases.
