Pumps – Condition responsive control of drive transmission or pump... – Adjustable cam or linkage
Patent
1993-11-15
1995-06-06
Bertsch, Richard A.
Pumps
Condition responsive control of drive transmission or pump...
Adjustable cam or linkage
60450, F04B 4900
Patent
active
054217059
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
A hydraulically driven thick-material delivery pump, e.g., a two-cylinder pump for concrete, includes delivery cylinders are each driven by a hydraulic drive cylinder, that by whose alternating pressurization with the outlet pressure from a hydraulic pressure generator and depressurization of said drive cylinders to the tank of the hydraulic pressure generator a continuous concrete supply is achieved. In the event of a drastic load variation due to malfunctions occurring in the area of the thick-material pump, in order to prevent stalling of, e.g., a load-sensing main pump of the hydraulic pressure generator regulated to a constant flow volume, it is known to detect the rotational speed of the diesel engine electronically and when this speed drops beneath a threshold value considered critical, to control through an electrohydraulic control device, the delivery volume adjusting element of the main pump of the hydraulic pressure generator to reduce the volume flow generated by the main pump. This reduces the pump's torque requirement to the point that it can still be supplied by the drive motor and stalling of the latter can be avoided.
This type of overload protection of the diesel engine and of the hydraulic pressure generator as a whole is, however, overly complex from a technical standpoint and too trouble-prone for the rough operating conditions under which thick-material pumps must often be operated. The goal of the invention therefore is to provide a protective device of the type recited at the outset which, though simple in design, provides reliable overload protection for the hydraulic pressure generator, and in particular prevents its drive motor from stalling.
The overload protection device for the drive motor in accordance with the invention includes an auxiliary pump, flow resistance devices, and a pressure-controlled valve. The drive motor drives the main pump of the pressure generator, whose output flow rate is stabilized by a hydraulic regulating valve, which senses a pressure drop across a choke in the main hydraulic circuit connected to the main pump. The hydraulic regulating valve adjusts the output flow of the main pump such that when the pressure drop across the choke increases, the output flow rate of the main pump is reduced and when the pressure drop across the choke decreases, the output flow rate of the main pump is increased.
The auxiliary pump is also driven by the drive motor and generates an output flow rate proportional to the rotational speed of the drive motor. An auxiliary hydraulic circuit, including the first and second flow resistance devices connected in series, connects the auxiliary pump to the tank of the hydraulic pressure generator. The auxiliary hydraulic circuit includes a tapping point at which flow pressure in the auxiliary hydraulic circuit may be sensed. The pressure-controlled valve includes a control chamber connected with the tapping point of the auxiliary hydraulic circuit. The pressure-controlled valve is connected with the regulating valve of the hydraulic pressure generator and to the main consumer circuit connected to the main pump of the pressure generator. The pressure-controlled valve is biased by a pretensioned valve spring into a basic position that causes the second control chamber of the regulating valve to be relieved of the comparison pressure in the main consumer circuit. By charging the control chamber of the pressure-controlled valve with pressure prevailing at the tapping point of the auxiliary hydraulic circuit, the pressure-controlled valve may be moved into a functional position in which the comparison pressure prevailing in the main consumer circuit may be applied to the second control chamber of the regulating valve. With the overload protection device, if the rotational speed of the drive motor falls below a threshold value, the output flow generated by the auxiliary pump will not hold the pressure-controlled valve in a functional position. The pressure-controlled valve will instead move to its basic posi
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patent: 4478041 (1983-10-01), Pollman
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patent: 5129230 (1992-07-01), Izumi et al.
patent: 5326230 (1994-07-01), Fischer
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"Die hydraulische Grenzlastregelung eines stufenlosen hydrostatischen Getriebes" by H. Hoffman, W. Koenig and D. Zeus; Konstruktion Dec. 1976, pp. 459-464.
Bertsch Richard A.
Korytnyk Peter
Putzmeister-Werk Maschinenfabrik GmbH
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