Hydraulic control means for a sweeping roller held by two cylinders in a sweeping machine

The sweeping roller of a sweeping machine is held on the ground in sweeping operation by two hydraulic cylinders in such a manner that the degree of wear is small. For this purpose in each cylinder a static and different holding pressure must be set. The higher pressure is set at a pressure-limiting valve and the lower pressure at the series circuit parallel thereto of a nozzle with an adjustable throttle.

BACKGROUND OF THE INVENTION 
The invention relates to a hydraulic control means for a sweeping roller 
held by two cylinders in a sweeping machine. 
In sweeping machines the aim is to keep the degree of wear of the sweeping 
rollers as low as possible and consequently excessive pressing of the 
sweeping roller onto the ground is to be avoided. In sweeping operation in 
which the sweeping roller bears on the ground due to the offset holding 
structure of the sweeping roller unequal holding forces arise. If the 
sweeping roller is held by two hydraulic cylinders in sweeping operation 
constant but different pressures must be adjusted in the cylinders in 
order to guide the sweeping roller satisfactorily and to avoid excessive 
or one-sided wear. 
The problem underlying the invention resides in providing a hydraulic 
holding and guide means of a sweeping roller which makes it possible in 
simple manner to maintain different constant pressures in the cylinders 
holding and guiding the sweeping roller. 
SUMMARY OF THE INVENTION 
Said problem is solved according to the invention by the features set forth 
in claim 1. Advantageous further developments will be apparent from the 
subsidiary claims. 
According to the invention it is thus possible in simple manner to set the 
higher pressure at the pressure-limiting valve and the lower pressure at 
the half bridge consisting of the nozzle and throttle by adjusting the 
throttle. The distributing circuit according to the invention generates 
only a static pressure in the holding cylinders of the sweeping roller 
which is not sufficient to raise the sweeping roller. According to the 
invention the application force of the sweeping roller can be adjusted by 
setting the pressures so that the sweeping roller has an optimum degree of 
wear.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A fluid source not shown, for example a gear pump, delivers via the 
connection P fluid into a pressure line 2 which is protected via a 
pressure-limiting valve 3. The pressure line 2 and a line or conduit 4 
leading to a tank T are connected to a directional control valve 5 which 
has a pair of actuating electro magnets S and H. 
For sweeping operation the magnet S of the directional control valve 5 is 
energized so that the pressure line 2 is connected to the line 6 and fluid 
passes via the check valve 7 to the inlet 9 of a distributing circuit. The 
distributing circuit consists of a pressure-limiting valve 12 and a series 
circuit of a nozzle 10 and an adjustable throttle 14. This series circuit 
lies in parallel with the pressure-limiting valve. The outlet 26 of the 
distributing circuit is connected via a conduit 17 in the position 
described of the directional control valve 5 to the conduit 4 leading to 
the tank T. In the connecting line 15 between the throttle 14 and the 
outlet 26 a check valve 16 is disposed. 
In a conduit 19 connected via a nozzle 11 to the inlet 9 the inlet-side 
higher pressure adjustable at the pressure-limiting valve 12 exists. 
Downstream of the nozzle 10 and upstream of the throttle 14 the conduit 13 
is connected in which the lower pressure adjustable by the variable 
throttle 14 exists. 
Via a directional control valve 18 the conduits 19 and 13 are connected to 
the conduits 20 and 21 leading to the singly acting cylinders 22 and 23. 
By switching over the directional control valve 18 the pressures adjusted 
in the cylinders can be reversed. 
The cylinders 22 and 23 each hold the sweeping roller 24 at different 
distances from the ends of the roller 24. The suspension of the sweeping 
roller is not shown in detail because it is not essential to the 
invention. In any case, in normal sweeping operation the holding forces F1 
and F2 applied by the cylinders are different due to the different 
distances the cylinders are spaced from the respective roller ends and in 
the example of embodiment chosen the force F1 is to be greater than the 
force F2. 
The pressure in the conduit 20 for the cylinder 22 which generates the 
force F1 is set at the pressure-limiting valve 12. Since this pressure or 
the force exerted by the cylinder 22 is not sufficient to raise the 
sweeping roller, i.e. only a static pressure is adjusted in the cylinder 
22, no fluid flows through the nozzle 11. 
The amount delivered by the pump is on the contrary conducted via the 
pressure-limiting valve 12 and the half bridge 10, 14 into the conduit 17 
and via the directional control valve 5 back into the tank T. 
The setting of the lower pressure which is adjusted in the cylinder 23 is 
by adjustment of the throttle 14. With the nozzle 10 and the throttle 14 a 
quantity-independent pressure may be generated because the pressure in the 
conduit 13 depends only on the setting of the throttle 14, as can be 
mathematically demonstrated. 
Thus, a static pressure also arises in the cylinder 23 which is smaller 
than the pressure in the cylinder 22. The application force is calculated 
on the weight of the sweeping roller G minus the sum of the holding forces 
F1 and F2. Since the holding forces F1 and F2 can be exactly adapted to 
the weight of the sweeping roller the degree of wear of the sweeping 
roller is optimized. 
In sweeping machines of the type in question here the sweeping roller 24 
can be displaced in the axial direction to enable sweeping to be carried 
out also laterally outside the vehicle. If the sweeping roller 24 is 
displaced for example in the direction x2 the new end position is detected 
by an electrical limit switch 25 via which the directional control valve 
18 is switched so that the pressures set at the pressure-limiting valve 12 
and at the throttle 14 in the cylinders 22 and 23 are reversed due to the 
reversal of the distance between the cylinders 22 and 23 and the 
respective ends of the roller 24. 
Due to the design of the directional control valve 18 a small amount of 
leakage continuously flows from the conduit of higher pressure over into 
the conduit of lower pressure. In the present circuit this cannot lead to 
an undesirable buildup of pressure in the conduit of lower pressure 
because said conduit is connected via the throttle 14 to the tank. 
In normal travelling operation of the sweeping machine the sweeping roller 
is to be raised from the ground. For this purpose the directional control 
valve 5 is switched over by energizing the magnet H so that the fluid 
delivered by the pump is conducted through the conduits 17 to the outlet 
26 of the distributing circuit. The lifting pressure is substantially 
higher than the pressure set at the pressure-limiting valve 12. The fluid 
passes from the conduit 17 only through the check valve incorporated into 
the pressure-limiting valve 12 to the outlet 9, the check valves 7 and 16 
being in a blocking position. 
Thus, the fluid from the inlet 9 can flow only via the nozzles 10 and 11 to 
the conduits 13 and 19 and thus to the cylinders 22 and 23. The nozzles 10 
and 11 have the same cross-section so that the cylinders 22 and 23 are 
supplied with identical amounts and consequently the pistons of the 
cylinders move with the same velocity. Pressure builds up in the cylinders 
until the resultant force F1 plus F2 is greater than the weight G of the 
sweeping roller so that the latter is raised from the ground. Once the end 
position is reached the pressure increases up to the value set at a 
pressure limit switch 8 which then interrupts the power supply to the 
magnet H of the directional control valve 5 so that the spring-centered 
piston of the directional control valve 5 is pushed back into the neutral 
position. As a result, the amount of oil delivered from the fluid source 
is conducted pressureless to the tank and the power loss in travelling 
operation is kept low.