Hydraulic-electric control circuit for earth-moving machine main engine

An earth-moving machine has an automatic device for minimizing the running speed of the main engine when no power is required by the hydraulic actuators. This device establishes a predetermined hydraulic fluid flow-rate in the servocontrol in the non-neutral position of the servocontrol itself. This flow-rate is indicated by an on-off flow-rate sensor inserted in the auxiliary hydraulic control circuit between the pump and the servocontrols, this sensor controlling the variation in the operating condition of the injection pump of the main engine by means of an electromagnet.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an earth-moving machine of the type 
including a plurality of servocontrols operable from a neutral position by 
the operator and connected to respective hydraulic distributors by means 
of an auxiliary hydraulic circuit including a pump driven by the main 
engine of the machine. 
By "main engine" is meant the internal combustion engine which normally 
drives all the hydraulic jacks and hydrostatic motors of the machine 
through a pump unit and associated hydraulic circuitry. 
During operation of an earth-moving machine, for example an excavator, the 
operator fixes the running speed of the main engine at a value close to 
its maximum speed in order to have sufficient power to operate the working 
members under any conditions. In this situation, even when the members are 
temporarily inoperative, the main engine of the machine continues to run 
at high speed with consequent high fuel consumption and wear of the engine 
itself. 
DESCRIPTION OF THE PRIOR ART 
Devices have already been proposed which attempt to reduce the running 
speed of the main engine when no power is required for the working 
members. Such systems include a plurality of sensors for detecting all the 
operating pressures of the working members. This makes the device very 
complicated, given that current earth-moving machines have a large number 
of controls. 
SUMMARY OF THE INVENTION 
The object of the pressent invention is to provide an earth-moving machine 
which solves the problem of the automatic reduction of the running speed 
of the main engine in a simple and cheap manner, but without the 
disadvantages of the prior art solutions. 
This object is achieved by virtue of the fact that, in the non-neutral 
position, the servocontrols allow a predetermined flow of hydraulic fluid 
through the auxiliary circuit, and in that at least one flow-rate sensor 
device is interposed between the pump and the servocontrols and is 
arranged to pilot, through actuator means, the variation in the running 
speed of the main engine between a minimum speed and an operating speed, 
or vice versa, in order to establish or stop the flow. 
By virtue of these characteristics, the operation of any one of the 
numerous servocontrols present in the machine is detected with a single 
flow sensor. Moreover, it is possible to regulate the operating time of 
the device by means of a single sensor. 
Further advantages and characteristics of the machine according to the 
present invention will become apparent from the detailed description which 
follows, purely by way of non-limiting example, with reference to the 
appended drawings, in which:

DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to the drawings, there is generally indicated 10 an 
auxiliary hydraulic circuit for controlling the distributors (not 
illustrated) of the working members of an earth-moving machine through 
manually-operable servocontrols, indicated 12. The hydraulic circuit 10 
includes a hydraulic fluid reservoir S, a pump 14, a safety diverter 16, a 
flow sensor 18, and a manifold 20 for dividing the supply to the 
servocontrols 12. 
The sensor 18 is connected through an electrical circuit, generally 
indicated 22, to an electromagnet 24 with the interposition of a 
manually-operable switch 26 and a power relay 29. The electromagnet 24 
controls the operating condition of an injection pump 28 of the diesel 
engine of the machine (not illustrated) through a linkage 26. 
An independent supply line T is provided between each servocontrol 12 and 
the manifold 20. As will be seen from FIG. 3, the servocontrols 12 are 
essentially of a type known to an expert in the art, whereby they will be 
described briefly to indicate the characteristics which distinguish them 
from the known ones. 
Each servocontrol 12 has a control lever 12a and a support base 12b. In the 
base 12b there are respective connectors 30, 32 and 34 for connection to 
the supply line T of the servocontrol, for connection to a control line D 
of the respective distributor, and for eventual discharge of hydraulic 
fluid. In correspondence with the connector 32, the base 12b has a 
cylindrical seat 36 in which a piston 38 is slidable axially by means of a 
rod 40 operated by the lever 12a. The piston 38 has transverse holes 42 
for putting the connector 30 into communication with the connector 32 in 
the non-neutral or control configuration of the servocontrol 12. In the 
neutral configuration of the servocontrol 12, there is no communication 
between the two connectors, that is, between the lines T and D. 
The difference between the servocontrols 12 of the invention and the 
servocontrols normally used relates to a hole 44 present in the crown of 
the piston 38 which, in the non-neutral configuration of the servocontrol 
12, puts the connector 30 into communication with the discharge connector 
34. In normal servocontrols, the connector 34 is used to discharge only 
the small quantity of hydraulic fluid, of the order to a few cm.sup.3 per 
minute, which leaks between the piston 38 and its seat 36. According to 
the invention, however, in the non-neutral position of the servocontrol 
12, a predetermined flow of hydraulic fluid considerably greater than that 
resulting from the leakage passes through the holes 42 and the hole 44. 
The sensor 18, which is of the electro-hydraulic type, comprises a hollow 
body 46 having respective connectors 48 and 50 for connecting it to the 
pump 14 and the manifold 20. The hollow body 46 has a threaded aperture 
46a into which a stopper element 52 is screwed. The element 52 has a 
closed end portion 52a and a tubular portion 52b with a mouth 52c. The 
tubular portion 52b defines an annular interspace 53 with the body 46 and 
has two series of through-holes 56 and 57 respectively. The cavity formed 
by the body 46 and the element 52 is divided into two chambers, 54 and 58 
respectively, by a piston 60 sealingly slidable within the tubular portion 
52b. The piston 60 has a skirt 60a, a circumferential edge 60b, and a 
crown 60c of conical cusp shape. Between the piston 60 and the portion 52a 
of the element 52 is a helical spring 62 for biasing the piston 60 
resiliently into contact with a proximity switch 64 carried by the body 
46. The internal diameter of the tubular portion 52b of the element 52 is 
less than the internal diameter of the portion 52a so as to define an 
annular shoulder 66 in correspondence with the series of holes 56. 
A duct 68 is also provided between the chamber 58 and the connector 50 and 
has a calibrated orifice 70 whose cross-section can be adjusted by means 
of a conical pin 72 the axial position of which is varied by means of a 
screw 74. 
In order to describe the operation of the device of the invention, it is 
supposed that one starts from the condition in which all the servocontrols 
12 are in their neutral positions and the main engine of the earth-moving 
machine is idling. When the lever 12a of a servocontrol 12 is actuated, 
the piston 38 is thrust downwardly to enable communication between the 
lines T and D through the connector 30, the holes 42 and the connector 32. 
At the same time, a predetermined flow of hydraulic fluid is created 
through the hole 44 in the direction of the discharge connector 34. This 
flow causes a pressure difference between the connectors 48 and 50 in the 
sensor 18, this pressure difference causing the movement of the piston 60 
from a first position, illustrated in FIG. 2, in which the piston prevents 
communication between the chambers 58 and 54, to a second position (not 
illustrated) in which the hydraulic fluid can pass through the holes 57 
and in which communication between the chambers 58 and 54 is allowed by 
the holes 57, the interspace 53 surrounding the portion 52b of the element 
52, the holes 56, and the space between the skirt 60a of the piston 60 and 
the internal diameter of the portion 52a of the element 52. 
The movement of the piston 60 and its crown 60c away from the proximity 
switch 64 activates the power relay 29 through the electrical circuits 22 
and the electromagnet 24 which puts the injection pump 28 of the main 
engine of the machine into operative running conditions, these conditions 
being settable beforehand by the operator. 
When the operator returns the servocontrol 12 to the neutral position, the 
flow through the hole 44 in the piston 38 stops, apart from the usual and 
negligible leakage, whereby the corresponding pressure difference between 
the connectors 58 and 50 of the sensor 18 is lost. The helical spring 62 
then makes the piston 60 slide from its second position to an intermediate 
position in which the skirt 60a covers the holes 57 to prevent direct 
communication between the chamber 58 and the chamber 54 through the holes 
57, the interspace 53 and the holes 56. From this intermediate position to 
the first position, in which the piston 60 is in contact with the switch 
64, communication between the chamber 58 and the chamber 54 is allowed 
only through the calibrated orifice 70, the duct 68, the interspace 53 and 
the holes 56. Thus, by varying the cross-section of the orifice 70, it is 
possible to adjust the period of delay between the positioning of the 
servocontrol 12 in the neutral position and the putting of the main engine 
of the machine into idle. This delay time enables too sensitive an 
operation of the sensor 18 to be avoided, together with too frequent a 
variation in the running speed of the engine. Moreover, the reduced flow 
of hydraulic fluid due to normal leakage from the servocontrols passes 
through the orifice 70 and the duct 68. 
Whenever necessary, the operator can prevent the intervention of the sensor 
18 on the circuit 22 by means of a manual switch 26 illustrated in the 
closed configuration in FIG. 1.