Device for controlling the delivery volume of a positive displacement pump, positive displacement pump and method for controlling the delivery volume of a positive displacement pump

Abstract

A device (7) for regulating the delivery volume of a positive displacement pump (1) comprises a control piston (8) displaceable in a recess (9) and a cam ring (4), via the position of which the delivery volume of the positive displacement pump (1) can be adjusted. A pressure switching valve (12) is arranged in a leakage line (11) connected to the recess (9). This pressure switching valve closes the leakage line (11) when a specific pressure acting on it is exceeded.

Description

[0001] The invention relates to a device for regulating the delivery volume of a positive displacement pump, comprising a control piston movable in a recess and a cam ring, via whose position the delivery volume of the positive displacement pump can be adjusted. Furthermore, the invention relates to a positive displacement pump with a suction port and a pressure port, as well as a method for regulating the delivery volume of a positive displacement pump.

[0002] A generic device and a corresponding positive displacement pump are known from DE 10 2005 050 216 B4.

[0003] DE 10 2005 016 181 A1 describes a further control device for a hydraulic conveying device designed as a vane pump.

[0004] A hydraulic system with a positive displacement pump designed as a vane pump is known, for example, from DE 10 2008 042 728 A1.

[0005] These devices make it possible to automatically adjust the delivery volume of variable displacement pumps. For this purpose, the device comprises a rotatably or slidably mounted cam ring and a control piston, which is shifted in position by a differential pressure in a control pressure chamber and the force of a spring usually located within the control pressure chamber. This allows the required pump stroke to be set and the delivery volume of the displacement pump to be automatically controlled.

[0006] However, with the known devices, the delivery volume of the positive displacement pump can only be limited to a fixed value.

[0007] It is therefore an object of the present invention to provide a device for controlling the delivery volume of a positive displacement pump, a positive displacement pump and a method for controlling the delivery volume of such a positive displacement pump, with which the delivery volume of the positive displacement pump can be easily adapted to the respective operating situation.

[0008] According to the invention, this object is achieved by the features mentioned in claim 1.

[0009] By means of the leakage line according to the invention connected to the recess, the delivery rate or the delivery volume of the positive displacement pump can be reduced, which also reduces the power consumption of the positive displacement pump, so that energy savings can be achieved in this way.

[0010] However, if a specific performance of the positive displacement pump is required and the hydraulic pressure within the system or within the positive displacement pump increases, the pressure switching valve according to the invention, arranged in the leakage line, closes, so that the flow rate of the positive displacement pump is increased compared to the state in which the leakage line is open. By appropriately selecting the pressure switching valve, it releases the leakage line at a specific pressure acting on it or present at the same pressure, without the need for further steps to control and / or regulate the positive displacement pump.

[0011] The device according to the invention thus ensures, on the one hand, the full performance of the positive displacement pump and, on the other hand, enables energy savings when a lower performance is required.

[0012] A particular advantage of the solution according to the invention is that the reduction in the flow rate and the increase thereof when a certain pressure is exceeded, i.e., pressure-dependent control of the positive displacement pump, can be implemented purely mechanically and no control via electronics or the like is required. As a result, the device according to the invention is very low in complexity, since only a leakage line extending from or connected to the recess and a pressure switching valve arranged in the leakage line are required.

[0013] To prevent losses of the hydraulic medium, a very advantageous development of the invention provides for the leakage line to be designed as a return line to a tank. At the same time, this represents a very simple design for the device according to the invention.

[0014] A further advantageous embodiment of the invention can consist in the provision of a closure element in the leakage line. Such a closure element, which can be opened or closed as desired, allows further influence on the delivery volume of the positive displacement pump equipped with the device according to the invention by opening or closing the leakage line.

[0015] A particularly advantageous embodiment in this context can be that the closing element releases the leakage line when a certain speed of the positive displacement pump is exceeded. This allows a reduction in the flow rate as the speed increases and thus, in addition to the pressure-dependent control of the positive displacement pump described above, also a speed-dependent control of the same.

[0016] It is particularly advantageous if the opening state of the closing element can be changed by means of a component of the positive displacement pump that is movable depending on the speed of the positive displacement pump. This allows the closing element to be opened or closed very easily using a component of the positive displacement pump itself, thus reducing or increasing the flow rate.

[0017] A positive displacement pump with a suction connection, a pressure connection and with a device according to the invention is specified in claim 6.

[0018] Such a positive displacement pump can be used, for example, in motor vehicles as a power steering pump using the device according to the invention. The device according to the invention enables energy savings, particularly at high speeds. As described above, it ensures that the full performance of the positive displacement pump can be accessed at all times.

[0019] Especially when used in motor vehicles, it has proven advantageous if the positive displacement pump is designed as a vane pump.

[0020] Furthermore, it can be provided that the opening state of the closure element can be changed by means of the cam ring. This embodiment takes advantage of the fact that the position of the cam ring changes at higher speeds of the positive displacement pump. It is only necessary to arrange the opening of the leakage line so that it is released at a certain deflection of the cam ring.

[0021] Claim 9 results in a method for controlling the delivery volume of a positive displacement pump.

[0022] The displacement volume of the positive displacement pump is adjusted via the position of the cam ring. A pressure control valve located in a leakage line leading from the control piston closes the leakage line when a certain pressure acting on the valve is exceeded.

[0023] The method according to the invention enables the pressure control valve to be closed very simply, thus closing or blocking the leakage line when a certain system pressure is exceeded. This ensures that the positive displacement pump operated with the method according to the invention can deliver the desired power at all times.

[0024] An additional possibility for controlling the displacement pump's delivery volume is provided by releasing the leakage line when a certain speed of the displacement pump is exceeded.

[0025] An embodiment of the invention is shown in principle below with reference to the drawing.

[0026] It shows: Fig. 1 a section through a positive displacement pump according to the invention with a device arranged on the same for regulating the delivery volume of the same; Fig. 2 a characteristic curve of a first embodiment of the positive displacement pump according to the invention; and Fig. 3 a characteristic curve of a second embodiment of the positive displacement pump according to the invention.

[0027] Fig. Figure 1 shows a positive displacement pump 1, known in its basic features from DE 10 2008 042 728 A1, which in this case is designed as a vane pump. Since the basic structure and operation of the positive displacement pump 1 are known, they will not be described in detail here.

[0028] The positive displacement pump 1 has a suction port and a pressure port, which are not designated in this case since their positions are very easy for a person skilled in the art to understand. Furthermore, the positive displacement pump 1 comprises, in a manner known per se, a housing 2, an outer ring 3 arranged in the housing 2, a cam ring 4 arranged within the outer ring 3 and mounted rotatably or displaceably relative to the housing 2, and a rotor 5 mounted on a rotational axis 6 designed as a drive shaft and stationary relative to the housing 2. The rotor 5 comprises, in a manner known per se, a plurality of vanes 5a.

[0029] By displacing the cam ring 4 within the housing 2, the displacement volume delivered by the positive displacement pump 1 is changed in a manner known per se. Since this change in the displacement volume due to the displacement of the cam ring 4 within the housing 2 is also known per se, it will not be discussed in detail here.

[0030] The delivery volume is controlled by a device 7 comprising a control piston 8, which is displaceably mounted within a recess 9 of the housing 2 in a displacement direction designated "x." Furthermore, the device 7 comprises a spring element 10 acting on the control piston 8 in an effective direction "a."

[0031] The position of the control piston 8 within the recess 9 determines, in a manner known per se, the pressure acting on the cam ring 4 and thus adjusts the position of the cam ring 4.

[0032] The control piston 8 is therefore mounted within the recess 9 for displacement in two directions (back and forth) as indicated by the double arrow "x." Although the effective direction "a" of the spring element 10 is parallel to the displacement direction x of the control piston 8, due to the nature of the spring element 10, which can only apply force in one direction, it only runs in one direction.

[0033] The device 7 further comprises a leakage line 11 connected to the recess 9 and a pressure control valve 12 arranged in the leakage line 11. A portion of the hydraulic medium sucked in via the suction port flows out through the leakage line 11, so that a lower delivery volume of the positive displacement pump 1 is achieved due to the leakage line 11. The leakage line 11 is designed as a return line and leads to a tank 13, so that the hydraulic medium flowing out via the leakage line 11 is returned to the circuit.

[0034] However, the pressure switching valve 12 arranged in the leakage line 11 is acted upon by the system pressure of the positive displacement pump 1, and the pressure switching valve 12 is designed such that it closes the leakage line 11 when a certain pressure acting on it is exceeded. As a result, the above-described limitation of the displacement pump's delivery volume is lifted at a higher pressure within the displacement pump 1. This ensures that the desired delivery volume of the displacement pump 1 is achieved when the power requirement for the displacement pump 1 is increased, which is accompanied by a correspondingly higher pressure.

[0035] Furthermore, a closing element 14, designed for example as an orifice, is arranged in the leakage line 11, which in the present case is closed at low speeds of the positive displacement pump 1 and opens the leakage line 11 when a certain speed of the positive displacement pump 1 is exceeded. In the illustrated embodiment, the opening state of the closing element 14 can be changed by means of a movable component of the positive displacement pump 1, in the present case the cam ring 4. Since, as explained above, the cam ring 4 is displaced at a higher speed of the rotor 5 of the positive displacement pump 1, a corresponding arrangement of the leakage line 11 relative to the cam ring 4 can ensure that the closing element 14 is opened at a desired speed, so that in this case the leakage line 11 is opened. The relative arrangement of the cam ring 4 relative to the leakage line 11 is not shown in the present case.

[0036] With the device 7 described above, a method for regulating the delivery volume of the positive displacement pump 1 can be implemented, in which the pressure switching valve 12 arranged in the leakage line 11 closes the leakage line 11 when a certain pressure acting on it is exceeded. This results in pressure-dependent control of the positive displacement pump. If the closing element 14 is present, it can be opened depending on the speed of the positive displacement pump 1, resulting in speed-dependent control of the positive displacement pump.

[0037] In the Fig. 2 and Fig. 3 shows the respective characteristic curves of two different positive displacement pumps 1. Here, Fig. 2 the characteristic curve of a positive displacement pump 1 without the closing element 14 and Fig. 3 shows the characteristic curve of a positive displacement pump 2 with the closing element 14. Both positive displacement pumps 1 have the leakage line 11 and the pressure switching valve 12 arranged therein.

[0038] In the diagram according to Fig. 2, line A shows the delivery rate versus engine speed when no steering assistance is requested and the leakage line 11 is open; this is therefore the minimum delivery rate. In this case, the system pressure is low, for example, below 5 bar. Line B shows the delivery rate of the positive displacement pump 1 versus engine speed when steering assistance is requested, and it can be seen that the delivery rate increases at a certain engine speed. The increase in the delivery rate is caused by the increasing pressure at the pressure switching valve 12, which closes the leakage line 11, as described above. This is the maximum delivery rate at a high system pressure of, for example, > 5 bar.

[0039] In Fig. 3 is analogous to Fig. 2, with line A the delivery rate is shown as a function of speed when no steering assistance is requested and the leakage line 11 is open. Line B, in turn, shows the delivery rate as a function of speed when steering assistance is requested, i.e. when the pressure acting on the pressure switching valve 12 is higher. Furthermore, it can be seen that in the case of line A, i.e. when no steering assistance is requested, the delivery rate is higher in the lower speed range marked with "C" and in the middle speed range marked with "D" than in the higher speed range marked with "E". The reduction in the delivery rate in the lower range of the higher speed range marked with "E" results from the displacement of the cam ring 4, which, as described above, opens the closing element 14 and thus opens the leakage line 11. This is done analogously to Fig.2, only by the increased pressure acting on the pressure switching valve 12, whereby this, as described above, closes the leakage line 11. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2005 050 216 B4

[0002] DE 10 2005 016 181 A1

[0003] DE 10 2008 042 728 A1 [0004, 0027]

Claims

[1] Device (7) for controlling the delivery volume of a positive displacement pump (1), with a control piston (8) displaceable in a recess (9) and with a cam ring (4), via the position of which the delivery volume of the positive displacement pump (1) can be adjusted, characterized by that a pressure switching valve (12) is arranged in a leakage line (11) connected to the recess (9), which closes the leakage line (11) when a certain pressure acting on it is exceeded. [2] Device (7) according to claim 1, characterized by that the leakage line (11) is designed as a return line to a tank (13). [3] Device (7) according to claim 1 or 2, characterized by that a closing element (14) is arranged in the leakage line (11). [4] Device (7) according to claim 3, characterized by that the closing element (14) releases the leakage line (11) when a certain speed of the displacement pump (1) is exceeded. [5] Device (7) according to claim 4, characterized by that the opening state of the closing element (14) can be changed by means of a movable component of the positive displacement pump (1). [6] Positive displacement pump (1) with a suction connection, a pressure connection and with a device (7) for regulating the delivery volume of the positive displacement pump (1) according to one of claims 1 to 5. [7] Positive displacement pump (1) according to claim 6, characterized by that the positive displacement pump (1) is designed as a vane pump. [8] Positive displacement pump (1) according to claim 7 with a device (7) according to claim 5, characterized by that the opening state of the closing element (14) can be changed by means of the cam ring (4). [9] Method for controlling the delivery volume of a positive displacement pump (1), in which the delivery volume of the positive displacement pump (1) is adjusted via the position of a cam ring (4), wherein a control piston (8) is displaceably arranged in a recess (9), characterized by that a pressure switching valve (12) arranged in a leakage line (11) connected to the recess (9) closes the leakage line (11) when a certain pressure acting on it is exceeded. [10] Method according to claim 9, characterized by that when a certain speed of the displacement pump (1) is exceeded, the leakage line (11) is released.

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