Power plants – Pressure fluid source and motor – Having apparatus control by timer or delay means
Reexamination Certificate
2000-03-06
2001-11-13
Ryznic, John E. (Department: 3745)
Power plants
Pressure fluid source and motor
Having apparatus control by timer or delay means
C060S421000
Reexamination Certificate
active
06314726
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an apparatus and a method for driving a hydraulic system of a construction machine, in particular a hydraulic excavator.
2. Discussion of the Prior Art
As is generally known, the hydraulic system of a powerful hydraulic excavator has a plurality of control blocks fed via a pump each. Each control block is used to drive a plurality of hydraulic actuators. Thus, for example, a first control block can drive the working equipment as well as the right-hand running gear, a second control block can drive the working equipment as well as the left-hand running gear, a third control block can drive the working equipment as well as the slewing mechanism, and a fourth control block can drive the working equipment as well as, likewise, the slewing mechanism. This division of the pump output between the control blocks ensures the effective supply of the various hydraulic actuators with pressure medium.
Since it is customary for the slewing mechanism to be switched on only for about 25% of a working cycle, here the pump of the slewing mechanism circuit can also be used for the working equipment circuit. When the movement of the slewing mechanism is initiated, however, the quantity delivered by the pump is concentrated onto the slewing mechanism circuit. As a result of this, it is no longer available to the working equipment circuit, in particular the boom cylinder. On the other hand, a major part of the available quantity delivered by the pump is only needed at the end of the acceleration phase of the slewing unit, since at the beginning of the acceleration phase it is a high torque (pump pressure) at a low speed (pump delivery quantity) which is preferentially needed. Only when the angular speed of the slewing mechanism superstructure rises does the requirement on the quantity delivered by the pump rise accordingly, the ultimate consequence of which is that as the angular speed of the superstructure rises, a slowing down of the movement of the working equipment, in particular the boom, occurs.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to reduce the impairment to the performance of a hydraulic system of the type mentioned above.
In a hydraulic system in which at least two control blocks are designed to drive the same actuator, the invention includes the technical teaching of connecting up the delivery capacity of the pump of the second control block to the actuator via a delay element.
It is preferred if this drive is used for the hydraulic slewing mechanism motor as an actuator. By contrast with switching on both pumps simultaneously for the slewing movement of the superstructure, initially only one pump is used in order to accelerate the superstructure out of the rest position. Since the requirement for pressure medium rises with increasing angular speed, the second pump is connected up only when the first pump reaches its delivery limit. Up to this point, the second pump is still completely available to the other actuators which can be driven by the control block assigned to it. Overall, switching on with a delay reduces the impairment to the performance of a hydraulic system of the type specified at the beginning.
Switching on the second pump with a delay can be implemented in accordance with three preferred alternatives. Firstly, the delay element can be constructed in the manner of a time relay which connects up the pump of the second control block after the expiration of a permanently predefinable time period. In this case, the predefinable time period has to be determined and optimized by trials. Secondly, the delay element can contain a sensor element which registers the speed of the actuator and whose output data is processed by an electronic unit which connects up the pump of the second control block when the final speed of the actuator is reached. As the third alternative, it is possible for the delay element to comprise a sensor element which determines the pressure in the hydraulic circuit of the actuator and whose output data is processed by an electronic unit which connects up the pump of the second control block at a pressure drop which occurs after the acceleration phase of the actuator. In the case of the two alternative embodiments mentioned last, the final speed or the pressure drop are those events on the basis of which the demand for additional pump capacity is indicated. As a result of the second pump being connected up, the actuator experiences an additional acceleration thrust which is suitable at the time of the demand, so that the stewing mechanism as a whole can be positioned rapidly and, at the same time, minimum impairment occurs to the supply to other actuators to be driven via the same control block.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.
REFERENCES:
patent: 4369625 (1983-01-01), Izumi et al.
patent: 5029067 (1991-07-01), Nishida et al.
patent: 5365737 (1994-11-01), Moriya et al.
patent: 5950428 (1999-09-01), Nam et al.
Ehrich Gerd
Meyer Joachim
Cohen & Pontani, Lieberman & Pavane
Komatsu Mining Germany GmbH
Ryznic John E.
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