Pumps – Condition responsive control of drive transmission or pump... – Plural pumps with individual or relative control
Patent
1991-12-17
1992-11-24
Smith, Leonard E.
Pumps
Condition responsive control of drive transmission or pump...
Plural pumps with individual or relative control
417287, F04B 4900
Patent
active
051658623
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a loading machine which is equipped with two pumps which function to supply hydraulic oil to at least one hydraulically operated working component, such as a hydraulic piston-cylinder device or a hydraulic motor having variable oil-pressure and oil-flow requirements, wherein the pumps can be connected one with the other for mutual coaction, when necessary.
Some loading machines of this kind are equipped with two fixed displacement pumps instead of one large pump of fixed displacement. Fixed displacement pumps, however, result in relatively large throttle losses and consequently a single variable displacement pump is used in some instances. When a large variable displacement pump is required, however, the cost entailed is considerable and much higher than that entailed by two fixed displacement pumps intended for the same purpose.
In the case of one known machine equipped with two fixed displacement pumps, one of said pumps is able to produce a high hydraulic pressure and a small hydraulic flow, whereas the other pump is able to produce a lower hydraulic pressure and a larger hydraulic flow. The first pump is activated when a high fluid pressure and a relatively small fluid flow is required, and the second pump is isolated from the system, by coupling said pump to the tank. The second pump is also coupled to the system when a smaller hydraulic pressure but greater flow is required. Such requirements occur, for instance, in the case of relatively large loading machines equipped with lifting jibs and a bucket or shovel, e.g. machines intended for loading gravel removed from a gravel pit. When such a machine is driven into the gravel pit with the bucket or shovel in contact with the ground, maximum tractive force is required on the loader wheels in order to drive the shovel into the gravel and, in conjunction therewith, a large hydraulic force is required in the system in order to tilt the shovel upwards while filling the same. The need of a large force is great in this phase of a gravel shifting operation, whereas flow requirements are less pronounced. Subsequent raising of the jib requires less force, whereas the need for fluid flow is great, in order to achieve a relatively high lifting speed.
In known pump units comprising two pumps, the hydraulic system is required to work in a low pressure range and in a high pressure range. When the pressure developed by the first pump approaches the limit value, this is detected by a regulator device, which activates the second pump in response thereto. The drawback with this system, however, is that the large fixed displacement pump with associated throttle losses is brought into operation on those occasions when its larger flow capacity is not required. The known regulator or control device does not take this into account and the object of the invention is therefore to provide a loading machine with a regulator device which will eliminate this drawback, by causing the second and larger pump to be activated solely when there is a need for greater flow and when this need cannot be satisfied by the first pump alone.
This object is achieved with a loading machine constructed in accordance with the invention. The principle difference between the inventive regulator device and the known regulator device is that the inventive device is constructed to sense a region of low flow and a region of high flow, and at the border between these regions to connect-up both pumps in the system when there is a need for greater flow, so that the two pumps together will achieve the desired greater flow of hydraulic medium in the upper flow region.
Although it lies within the scope of the present invention for the first pump to be a fixed displacement pump, the pump is preferably a variable displacement pump provided with a known load-sensing pump regulator. When the first pump is a fixed displacement pump, the pump will be provided with a load-sensing pump regulator equipped with a shunt valve. The losses experienced with a fixed displacement pump are reduc
REFERENCES:
patent: 3526468 (1970-09-01), Moon et al.
patent: 3947194 (1976-03-01), Schlecht
patent: 3985472 (1976-10-01), Virtue et al.
patent: 4382485 (1983-05-01), Kirkham
Smith Leonard E.
VME Industries Sweden AB
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