Pumps – Expansible chamber type – Valved piston
Reexamination Certificate
1999-03-18
2001-03-27
Walberg, Teresa (Department: 3742)
Pumps
Expansible chamber type
Valved piston
C417S545000, C417S262000
Reexamination Certificate
active
06206663
ABSTRACT:
The invention relates to a piston pump for delivering a fluid at low pressure and at a higher pressure, a higher delivery volume being provided in one pumping cycle at low pressure than at a higher pressure, having a low-pressure delivery piston, which is moved inside a pump cylinder and acts upon a pressure chamber under prestress into its delivery end position, a high-pressure delivery piston, and an inlet valve and an outlet valve, a fluid delivery path furthermore being provided between the inlet valve and the outlet valve, and the low-pressure delivery piston being able to be moved back counter to its prestress into a delivery starting position.
Piston pumps of this type are used, for example, in manually operated or motor-driven hand tools. In this context, reference is made to prior art, for example, in accordance with U.S. Pat. Nos. 432,107, 5,195,354 and 2,688,231. This prior art relates to motor-driven hand tools for compressing cable terminals or cable connectors. Furthermore, however, the subject-matter of the invention is also important, for example, with regard to shears, for example cable shears. In this context, reference is made to the German Utility Model 94 16 535 and the German Patent Application 196 49 932 which is not a prior publication. Moreover, pumps of this type are also used in other areas of technology. Reference is made, for example, to U.S. Pat. Nos. 2,845,033 and 674,381.
Pumps which have two pressure stages are frequently used, primarily for the drive of hydraulic tools. Such pumps supply a far greater volume of oil up to a certain limit pressure, which may be 5% of the maximum pressure, than at maximum pressure. The operating speed of hydraulic devices can thus be increased substantially because, in many tools, such as for example compression tools for the compression of cable terminals, a certain idle stroke must first be travelled before the workpiece is contacted and the actual operation takes place with a high power requirement. During the idle stroke, only the force of the piston restoring spring of the hydraulic cylinder of the tool generally has to be bridged. A low oil pressure is sufficient for this purpose.
Many different construction types of two-stage pumps are known. It is possible, for example, to combine two different pump construction types with one another and drive them at the same time, that is to say, for example, a gear pump for the low pressure range and a piston pump for the high pressure range. As soon as the required starting pressure exceeds the operating pressure of the low-pressure pump, its delivery flow is fed back into the tank via a pressure relief valve.
Two-stage piston pumps are particularly common for manually actuated hydraulic tools, where partial piston pumps are used both for the low pressure and for the high pressure. A widespread construction is one in which both pistons are combined in the form of a pump plunger with two different diameters. The hydraulically active surface in the low-pressure part is the annular surface between the two diameters and, in the high-pressure piston, it is the entire cross-sectional area of the small diameter. Both the low-pressure and the high-pressure pump each have an inlet valve connected to the tank and an outlet valve connected to the delivery side. A pressure relief valve is required additionally for the low-pressure stage, by means of which valve the oil flows back into the tank when the pressure of the low-pressure stage has been exceeded.
U.S. Pat. No. 4,492,106 relates to a lever-actuated hand tool in a configuration for the compression of cable terminals. Proposed in this case is a pumping device which has a high-pressure delivery piston and a low-pressure delivery piston. The low-pressure delivery piston comprises a spring-mounted pipe section with a pipe bottom which forms the piston head. The low-pressure delivery piston is displaced counter to the spring force by a continuation of the high-pressure delivery piston, hydraulic liquid being sucked in from a supply container. The projection of the high-pressure delivery piston then moves back and, on account of the spring acting upon it, the low-pressure delivery piston delivers the sucked-in hydraulic liquid into the working space. The delivery stops as soon as the pressure in the delivery chamber can no longer be overcome by the spring force. In the known pump, then only the high-pressure piston continues to operate.
Setting out from the above mentioned prior art, the invention deals with the technical problem of specifying a piston pump for delivering a fluid at low pressure and at a higher pressure, which permits effective delivery with a construction which is as simple as possible.
This technical problem is solved initially and substantially in the subject-matter of Claim 1, the solution being based on the fact that the fluid delivery path passes through the low-pressure delivery piston, that a valve is provided in the low-pressure delivery piston, which valve shuts in the case of movement in the delivery direction, and that the high-pressure delivery piston operates in the pressure chamber of the low-pressure delivery piston. There is only one common pressure chamber for the low-pressure delivery piston and for the high-pressure delivery piston. The low-pressure delivery piston is inevitably pushed back, namely by the high-pressure delivery piston. According to the invention, a simplified design of the piston pump is firstly achieved by the fact that the low-pressure delivery piston and the high-pressure delivery piston operate on the same pressure chamber. There is only one pressure chamber or pump chamber. The losses due to throttling operations are minimized or are no longer present. Furthermore, the fluid delivery path passes through the low-pressure delivery piston with a valve which shuts when the low-pressure delivery piston moves in the delivery direction. This also means that fluid flows into the pressure chamber when the low-pressure delivery piston moves counter to the delivery direction, the pressure in the pressure chamber not being higher than in the inflow direction ahead of the low-pressure delivery piston. On the contrary, the prevailing pressure is generally the same as in the inflow direction ahead of the low-pressure delivery piston, reduced by the force of a spring acting on the low-pressure delivery piston. When the valve in the low-pressure delivery piston is open, the pressure is virtually the same on both sides of the low-pressure delivery piston. The embodiment advantageously has few individual parts. Apart from the inlet valve and the outlet valve, only the valve in the low-pressure delivery piston is still required. Moreover, the constructional shape is simpler. There is only one pressure chamber, both for the low-pressure stage and the high-pressure stage. Furthermore, provision is made for the movement of the low-pressure delivery piston to take place counter to its prestress by the high-pressure delivery piston. The high-pressure delivery piston can act, in particular, directly on the surface of the low-pressure delivery piston. The high-pressure delivery piston preferably has, with regard to the pump, a smaller active cross-sectional area than the low-pressure delivery piston. The ratio may be, for example, 4:1 with regard to the area of the low-pressure delivery piston relative to the area of the high-pressure delivery piston. Good values are also achieved in practice with ratios of 6 to 7:1. In a further preferred embodiment, provision is also made for the high-pressure delivery piston to actuate the valve which is provided in the low-pressure delivery piston and shuts when the low-pressure delivery piston moves in the delivery direction. Owing to the fact that the high-pressure delivery piston does not have to bear against the low-pressure delivery piston when the low-pressure delivery piston moves in the delivery direction, in continuation of this concept, a valve which is very simple in construction, namely a plate valve, may-be provided in the low-pressure delivery
Campbell Thor
Gustav Klauke GmbH
Trexler, Bushnell Giangiorgi, Blackstone & Marr, Ltd.
Walberg Teresa
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