Abstract:
A method and apparatus for supplying liquids by means of a pump combination comprising two single oscillating displacement pumps is provided, wherein a supply pressure of the pump supplying liquid into a user duct is used as a control value of a pressure controller, such that a pressure stroke movement of the other pump which is generating a pre-compression pressure, is discontinued when the pre-compression pressure equals the supply pressure, and the pre-compression pressure is maintained.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method for supplying liquids by means of a pump combination consisting of two single oscillating displacement pumps wherein during the displacement operation of the one pump the other pump is started and pre-compresses the supplied medium with the outlet valve closed, then is stopped while holding the pre-compression final pressure reached, and is continued with its stroke while supplying the supplied medium only when the corresponding other pump ends its supply. Therein the pulsing, when transferring the supply from the one pump to the other, may be kept very small. 
     Such and similar pumps are known from the documents AU 1 450 400, U.S. Pat. No. 5,141,408, U.S. Pat. No. 4,127,360 and U.S. Pat. No. 4,191,309. 
     The known single pump comprises a suction stroke which is faster than the compression stroke, such that with movements offset by 180° of the two pumps, a time reserve is present between the end of the suction stroke of the one pump and the beginning of the subsequent supply stroke of the same pump, with the time reserve bridged by a stop of the displacing member after the pre-compression stroke. During the pre-compression stroke, the displacing member performs its pressure stroke with the outlet valve closed, until a required pressure is reached for the pressure medium enclosed in the supplying cylinder, whereupon the movement of the displacing member is stopped while maintaining this pre-compression final pressure. 
     In the pump described in U.S. Pat. No. 1,450,400, referring to FIGS. 1 and 2, the movement of the displacing members is generated by means of electrical step motors acting upon spindles. During the pre-compression stroke of the one displacing member, the associated step motor is supplied with electrical power which is associated with a slipping torque corresponding with the required final pressure. After having reached the required pressure, the step motor starts to slip while maintaining the pre-compression pressure reached, wherein the displacing member comes to a stand still. When the other single pump supplying to the user reaches the end of its supply stroke, the outlet valve of the single pump standing still and presented with the pre-compression stroke is opened, and simultaneously the electrical power for the step motor is increased, such that this pump continue its pressure stroke while supplying the medium to the user. 
     The drive unit and the control of this pump system is costly and complicated and there is no automatic adaption or modification of the final pressure of the pre-compression when the supply pressure changes. 
     In the pump system described in U.S. Pat. No. 5,141,408 the pre-compression pressure is sensed by a pressure sensor. When a preset pressure is reached, the sensor supplies a signal by means of which the drive unit, in this case a hydraulic drive, is deactivated for the hydraulic cylinder driving the displacing member stops. Also, in this case, the final pressure of the pre-compression has to be adjusted to the required value from the outside, and has to be adapted to the supply pressure acting in the ducts to the user. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a method and a device avoiding the above described disadvantages and adapting the final pressure of the pre-compression automatically to the supply pressure present. 
     According to the invention, the supply pressure of the single pump supplying into the user duct is presented as a control value to that device which discontinues the pressure stroke movement of the other single pump when the pre-compression pressure, defined by the supply pressure, is reached, while maintaining this pressure. 
     Referring to a drawing for a pump system the displacing members of which are driven by hydraulic cylinders the invention is further described. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates the schematic design of the pump combination. 
     FIG. 2 illustrates one of the two pressure controllers for one of the two hydraulic oil flows to the hydraulic cylinders. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, two single pumps 1a, 1b comprise displacing members 2a, 2b which are connected to pistons 3a, 3b of hydraulic cylinders 4a, 4b, such that a movement of the hydraulic pistons 3a, 3b is transferred to the displacing members 2a, 2b. When the pistons 3a, 3b are moved, because oil is supplied to the cylinder chambers 5a, 5b, the supply medium in the pump chambers 6a, 6b is compressed, and after having reached a pressure present in a duct 8 to the user, is pressed into the duct 8 through an outlet valve 7a, 7b. The hydraulic oil is supplied to the cylinder chambers 5a, 5b through ducts 9a, 9b. For accomplishing the suction stroke, the hydraulic oil is supplied to the cylinder chambers 10a, 10b. The control of the oil streams to the cylinder chambers is accomplished by means of valves 11a, 11b. Each of the two displacing member piston combinations 2a, 3a and 2b, 3b oscillate between an upper and a lower dead point. Switches or sensors 18a, 18b and 19a, 19b sense the dead points of the corresponding displacing member piston combination and control the oil streams, such that the stroke is reversed by switching the corresponding hydraulic valves 11a, 11b. The downwards stroke is the pressure or supply stroke, respectively. The upwards stroke is the suction stroke. Closely preceding the switch 19a, 19b, enacting the switch from the supply stroke to the suction stroke, there is a further switch 20a, 20b. It is the object of this switch 20a, 20b, to accomplish a discontinuation of the oil stream through the ducts 12a or 12b, respectively, to the oil reservoir, and that in the correspondingly other pump standing still at the end of the pre-compression stroke. Therefore the switch 20a is dedicated for the discontinuation of the oil stream through the duct 12b, and the switch 20b is dedicated for the discontinuation of the oil stream through the duct 12a. 
     Ducts 12a, 12b are connected to the ducts 9a, 9b. The ducts 12a, 12b lead to the pressure controllers 14a, 14b, and therefrom with a common duct 15 through connecting ducts 15a, 15b back to the hydraulic oil reservoir. The pressure controllers 14a, 14b are designed such that an oil stream is passed only when a certain pressure is reached, which pressure is defined by the pressure in the cylinder chambers 5a or 5b, respectively, of the pump 1a or 1b, respectively, supplying into the duct 8. For this reason, the pressure controllers 14a, 14b are connected to the cylinder chambers 5a, 5b with control pressure ducts 17a, 17b. The pressure controller 14a associated with the single pump 1 a is connected with the cylinder chamber 5b of the single pump 1b through the duct 17a, and the pressure controller 14b of the pump 1b is connected with the cylinder chamber 5a of the single pump 1a through the duct 17b. 
     The pump 1b is illustrated in the supply situation, which means the pump supplies medium through the opened outlet valve 7b into the duct 8 to the user. The pressure pre-sent in the cylinder chamber 5b and in the ducts 9b, 17a, and 17b depends on the pressure of the supply medium in the pump chamber 6b. 
     The pump 1a is illustrated in the stand still position after the pre-compression stroke has ended. The pressure controller 14a is in the opened position, such that the hydraulic oil flowing into the duct 9a is discharged through the duct 12a to the duct 15. Therein the pressure in the duct 9a, and in the cylinder chamber 5a, and in the pump chamber 6a, is maintained at a level by the pressure controller 14a, which is defined by the geometrical conditions in the pressure controller 14a, and the pressure present in the cylinder chamber 5b of the pump 1b acting as a control pressure through the duct 17b onto the pressure controller. 
     When the displacing member 2b performing the supply stroke reaches the switch or sensor 20b, the discontinuation of the oil stream through the duct 12a is performed by the switch or sensor. This may be accomplished in different ways. In the example illustrated, the discontinuation is enacted by supplying an additional force onto the valve slider of the pressure controller 14a, whereupon the pressure controller is closed. Thereupon the displacing member 2a will continue with the pressure stroke, now as a supply stroke, wherein supply medium is pressed through the opening outlet valve 7a into the duct 8 to the user. 
     When the displacing member at the end of its supply stroke reaches the lower dead point, the suction stroke is triggered by the switch 19b, whereupon the outlet valve 7b will close, and the supply medium flows into the chamber 6b through an opening inlet valve 21b. 
     While the displacing member 2a now is in its supply stroke, the displacing member 2b performs the suction stroke because hydraulic oil is supplied into the cylinder chamber I Ob, with the velocity of the suction stroke greater than that of the pressure stroke. The switch or sensor, respectively, 18b enacts the termination of the suction stroke and a transfer to the pressure stroke beginning with the pre-compression of the supply medium. The oil pressure present in the duct 9b to the cylinder chamber 5b also acts upon the pressure controller 14b through the duct 12b. Because of the oil pressure acting as a control pressure on this pressure controller through the duct 17b, with the oil pressure generated in the cylinder chamber 5a of the single pump 1 a performing the supply stroke, the pressure controller remains closed until reaching the opening pressure. As mentioned before, this value is defined by the geometrical conditions in the pressure controller, and of the control pressure. After opening the pressure controller 14b, the hydraulic oil supplied to the duct 9b flows through the duct 15 to the oil reservoir while maintaining the opening pressure. 
     In FIG. 2 one of the two pressure controllers, in this case the pressure controller 14a, is illustrated as an example. Both pressure controllers in function the same. In a housing 25a there is a slider 26a comprising at one end a closing member 27a with a cone-shaped projection. This cone will close an aperture 28a with a cross section A 2  connected with the duct 12a and the hydraulic cylinder chamber 5a. Towards the closing member 27a, the aperture 28a is enlarged to a chamber 29a. The chamber 29a is connected with the duct 15 leading to the hydraulic oil reservoir. The end of the slider 26a facing away from the closing member 27a has an effective area A 1  and, together with the housing 25a, forms a chamber 30a which is connected with the duct 17a and with the hydraulic cylinder chamber 5b of the single pump 1b supplying medium into the duct 8 to the user. 
     Furthermore, the housing 25a comprises a chamber 31a with a piston 32a. This piston is connected with a piston rod 33a which sealingly projects into the chamber 30a, and presses upon the front face of the slider 26a when the chamber 31a is put under pressure. The pressure medium is supplied to the chamber 31a through a duct 34a. 
     Because of the oil pressure in the chamber 30a, the force F 1  equaling A 1  ×P (5b) acts upon the slider 26a, wherein P (5b) is the hydraulic pressure of the cylinder chamber 5b. In the aperture 28a a force F 2  equaling A 2  ×P (5a) and opposite to the force F 1  acts upon the slider, wherein P (5a) is the hydraulic pressure of the cylinder chamber 5a of the pump 1a performing the pre-compression stroke. While the force F 2  increases from zero with growing pre-compression in the pump chamber 6a, and therefore with correspondingly growing hydraulic pressure P (5a), the force F 1  is constant. When the forces F 2  and F 2  are equal, the closing force for the aperture 28 becomes zero and hydraulic oil begins to flow from the aperture 28a through the chamber 29a to the duct 15 while the closing member 27a is lifting. 
     The oil pressure reached corresponds with the final pressure of the pre-compression of the supply medium in the pump chamber 6a. At that point the piston displacing member combination 3a, 2a comes to a stand still. The oil still flowing through the duct 9a will flow through the pressure controller 14a to the duct 15, wherein the oil pressure in the aperture 28a is maintained at a constant value by the force F 1  acting upon the aperture. The ratio of the pre-compression final pressure of pump 1a to the supply pressure of the pump 1b is defined by the area ratio A 1  to A 2  and is independent of the value of the supply pressure. 
     When the oil stream through the aperture 28a is to be stopped, the pressure controller chamber 31a is presented with pressure through the duct 34a upon action of the switch 19b or 20b, respectively, such that the additional force necessary for closing the aperture 28a is generated. The piston-displacing member combination 3a, 2a then performs its pressure stroke from the stand still situation as a supply stroke. By a control not illustrated, the pressure impingement of the pressure controller chamber 31a is maintained at least until the end of the supply stroke. 
     When the outlet valves 7a are designed as automatically opening valves, in the example illustrated as check valves, by means of the area ratio A 1  to A 2  the pre-compression final pressure has to be selected smaller than the supply pressure. In the other case, the valves 7a, 7b would remain open as a result of the pre-compression pressure raising over the supply pressure in the duct 8. This would mean that now both single pumps would supply into the duct 8. When the outlet valves 7a, 7b are designed as valves positively controlled with an auxiliary energy, or with an additional close force generated by an auxiliary energy, than the pre-compression final pressure may be selected equal to or larger then the supply pressure. 
     As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art.