GB2215700A

GB2215700A - Hydraulic circuits

Info

Publication number: GB2215700A
Application number: GB8806249A
Authority: GB
Inventors: Michael Appleyard
Original assignee: AGCO Manufacturing Ltd
Current assignee: AGCO Manufacturing Ltd
Priority date: 1988-03-16
Filing date: 1988-03-16
Publication date: 1989-09-27
Also published as: GB8806249D0

Abstract

A hydraulic consumer (43) is supplied with pressurised hydraulic fluid from a first fixed displacement pump (31) under the control of a first pressure regulator (41) and from a second fixed displacement pump (32) of lower delivery volume rate than the first pump under the control of a second pressure regulator (52) set to give a higher fluid pressure than the first regulator. A selector valve (60) is provided to enable the first pump (31) to be disconnected from the consumer (43) during certain operating modes of the consumer to provide a lower speed higher force operation of the consumer when supplied by the second pump (32) only. The hydraulic circuit is particularly suitable for the control of a boom cylinder (49), a dipper stick cylinder (44), a bucket cylinder (45) and a boom swing cylinder (48) of a backhoe during craning operations. Thus when the selector valve is operated to disconnect the first pump (31) the backhoe will move more slowly (due to the lower pump delivery volume rate) but will be capable of providing a greater lifting force (due to the higher fluid pressure) for craning. <IMAGE>

Description

HYDRAULIC CIRCUITS This invention relates to hydraulic circuits and particularly, though not exclusively, to such circuits used to actuate hydraulic consumers for powering a backhoe boom, dipper stick and swing system.

The use of backhoes for a variety of craning operations, such as laying pipes in a trench previously dug by the backhoe, is becoming increasingly common. This can lead to problems since the hydraulic circuits of backhoes are not conventionally designed with the somewhat different operating requirements of a craning operation in mind.

It is an object of the present invention to provide an hydraulic circuit which is specially designed to enable easy switching for operation in a mode better suited to craning uses.

Thus according to the present invention there is provided an hydraulic circuit comprising an hydraulic consumer supplied with pressurised hydraulic fluid from a first fixed displacement pump means under the control of a first pressure regulating means and from a second fixed displacement pump means of lower delivery volume rate than the first pump means under the control of a second pressure regulating means set to give a higher fluid pressure than the first regulating means, and selector valve means to enable the first pump means to be disconnected from the consumer during certain operating modes of the consumer to provide a lower speed higher force operation of the consumer when supplied by the second pump means only.

If the hydraulic circuit is applied to the control of a backhoe, hydraulic consumers in the form of a boom cylinder, a dipper stick cylinder, a bucket cylinder and a boom swing motor or cylinders may all be supplied by the first and second pump means. Thus operation of the selector valve means will then disconnect the first pump means so that the backhoe is only supplied with fluid by the second pump means. Thus the backhoe will move more slowly (due to the lower pump delivery volume rate) but will be capable of providing a greater lifting force (due to the higher fluid pressure).

Thus as will be appreciated the backhoe is better suited to craning operations when the selector valve is operated to supply the backhoe from the second pump means only.

In a typical example the delivery volumes of the first and second pump means may be 113 and 34 litres/min respectively and the relief pressures of the pump means may be 190 and 240 bar respectively.

Conveniently the first and second pump means may comprise separate pumping elements of a dual element pump.

One embodiment of the present invention as applied to a backhoe will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a backhoe being used in a craning mode, and Figure 2 is a schematic diagram of an hydraulic circuit for the control of the backhoe of Figure 1.

Referring to Figure 1, this shows an industrial tractor 10 provided with a front loader 11 and a rear-mounted backhoe 12. As is conventional, each loader beam 13 is raised and lowered by an associated beam cylinder 14 and loader bucket 15 is pivoted relative to the beams 13 by a bucket cylinder 16 and associated linkage 17.

Similarly, in the conventional manner, the backhoe 12, which is of the side shift type, is provided with a pair of vertically spaced swing cylinders 18a and 18b which may be operated to swing the backhoe to left or right about a vertical swing axis X-X. Vertical pivoting of the beam 19 of the backhoe is controlled by a boom cylinder 20 and pivoting cf the dipper stick 21 of the backhoe relative the boom 19 is controlled by dipper cylinder 22. Pivotir of the bucket 23 relative to the dipper 21 is controlled by a bucket cylinder 24 and associated linkage 25.

In the arrangement of Figure 1 the backhoe is equipped with a craning sling 70 for craning pipes 71 into a tench 72.

The sling may be attached in any convenient manner to tre bucket 23.

Thus far described the industrial tractor and its loader and digger attachments are of a conventional form.

Figure 2 shows in a schematic form an hydraulic circuit accordance with the present invention which sets out to enable the supply circuit for the various actuating cylinders associated with the backhoe to be selectively set in a condition rendering the manner of operation of the backhoe more suited to craning operations.

Thus referring to Figure 2, the engine E of the tractor drives a dual element fixed displacement pump 30 in which a first element 31 has a rated delivery volume of say 113 litres per minute and the second pumping element 32 has a rated delivery volume of say 34 litres per minute. As can be seen from Figure 2 these pumping elements draw hydraulic fluid fror a sump 33 via a strainer 34. Pumping element 31 delivers pressurised fluid to a loader control valve 35 via line 39. Valve 35 is built up from a first spool valve 36 for operation of the bedm cylinders 14 and a second spool valve 37 for operation of the bucket cylinder 16. The valve is of the open centre type with an open centre line 38.

In the conventional manner the spool valves 36 and 37 are controlled from a single loader control lever (not shown) which is pivotable about two perpendicular axes so that pivoting of the lever about one axis operates spool valve 36 and pioting about the other axis operts spocl valve 37. In this manner either end of each of the cylinders 14 and 16 car be either connected with pressurised fluid from line 39 or be connected with a drain line 40 which returns fluid to sump 33 thus extending or contracting the associated cylinders 14 and 16 to raise and lower the loader beams 13 and pivot the bucket 15.

The pressure of fluid in supply line 39 is regulate3 by a first pressure control valve 41 which ensures that the pressure in line 39 does not rise above 190 bar.

The second pumping element 32 is connected via a line 42 with a backhoe control valve 43. This valve, in the conventional manner, is built up from a number of individual spool valves assembled into a single valve block. In the arrangement illustrated the valve block includes dipper spool valve 44 which controls dipper cylinder 22, a bucket spool valve 45 which controls bucket cylinder 24, stabiliser spool valves 46 and 47 which are used for raising and lowering two stabiliser legs associated with the backhoe mounting frame using cylinders 66 and 67, a swing spool valve 48 which controls the swing cylinders 18a and 18b, and a boom spool valve 49 which controls boom cylinder 20.In the conventional manner dipper and bucket vat es 44 and 45 are controlled by a first backhoe control le;- - (not shown) and the swing and boom valves 48 and 49 are controlled by a second backhoe control lever (not shown). Each stabiliser spool valve 46 and 47 has a separate control lever (not shown).

The valve block is of the open centre type with an open centre line 50. Operation of the appropriate spool valve can be arranged to connect either end of each associated hydraulic cylinder with either supply line f or a drain line 51 in the normal manner. Open centre line 50 also returns fluid to sump 33 on exiting the backhoe valve block 43.

The maximum level of pressure in line 42 is ~suited by a second pressure control valve 52 which dumps fluid to the sump 33 at line pressures above 240 bars.

In accordance with the present invention a selector valve 60 is provided which is biased to the condition shown in Figure 2 in which the open centre line 38 of loader valve 35 is connected with line 42 so that fluid passing, unused, through the loader valve 35 can be used to power the backhoe. When operating in this mode, which is the normal digging mode, a total pump flow rate of 147 litres per minute at a maximum pressure of 190 bar under the control of pressure control valve 41 is available to the backhoe.

Selector valve 60 is provided with a solenoid 61, which, when operated, displaces the selector valve to cut off the connection between lines 38 and 42 an. to connect open centre line 38 with the sump 33. When the selector valve is operating in this mode only the output of the second pumping element 32 is available to the backhoe control valve 43 so that the associated backhoe will operate at a lower speed in view of the lower pump displacement, but will be capable of generating higher lifting forces in view of the higher operating pressure which will be maintained under the control of second pressure control valve 52.

Thus when operating in this mode the hhoe is better suited to use in craning operations where a lower speed of operation and higher lifting forces are required.

The use of a dual element pump, in which the loader only receives flow from the larger element, also means that, while the full amount of the engine's power can be used for digging with the machine static, a lower amount of power is consumed by the loader hydraulic syste-. leaving some engine power available to move the machine while loading.

Claims

1. An hydraulic circuit comprising an hydraulic consumer supplied with pressurised hydraulic fluid from a first fixed displacement pump means under the control of a first pressure regulating means and from a second fixed displacement pump means of lower delivery volume rate than the first pump means under the control of a second pressure regulating means set to give a higher fluid pressure than the first regulating means and selector valve means to enable the first pump means to be disconnected from the consumer during certain operating modes of the consumer to pr .-ize a lower speed higher force operation of the conser when supplied by the second pump means only.

2. An hydraulic circuit according to Claim 1 in which the first and second pump means comprise separate pumping elements of a dual clement pump.

3. An hydraulic circuit according to Claim 1 or Claim 2 applied to the control of a backhoe in which an hydraulic consumer in the flow of at least one hydraulic cylinder for the movement of the backhoe is supplied with pressurised fluid by the first and second pump means so that on operation of the selector valve means to disconnet the first pump means the cylinder will move the backhoe more slowly but with greater force.

4. An hydraulic circuit according to Claim 3 in which hydraulic consumers in the form of a backhoe boom cylinder, a dipper stick cylinder, a bucket cylinder and a backhoe boom swing motor are supplied with pressurised fluid by the first and second pump means.

5. A backhoe controlled by an hydraulic circuit according to any one of Claims 1 to 4.

6. An hydraulic circuit constructed and arranged substantially as hereinbefore described with reference to and as shown in the accompanying drawings.