Abstract:
A pump includes an outflow channel configured for discharging fluid out of the pump. The outlet area thereof is formed by a throttle. The throttle includes a spring element configured to change the size of the outlet area of the outflow channel.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2011/068566, filed on Oct. 24, 2011, which claims the benefit of priority to Serial No. DE 10 2010 064 114.6, filed on Dec. 23, 2010 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The disclosure relates to a pump having an outflow channel for discharging fluid out of the pump, the passage area thereof being determined by a throttle. 
     In the case of pumps, in particular piston pumps with pulsating hydraulic pressure generation, and especially in the case of pumps for use in motor vehicle brake systems, a throttle is often arranged in the outflow channel or discharge channel thereof. The throttle is intended to reduce the effect of pressure pulsations arising in the pump on the downstream hydraulic system and, in particular, to reduce the noise made by the pump. Throttles of this kind with a fixed passage area are known as a low-cost means of noise reduction. 
     Typical pumps for motor vehicle brake systems comprise a cylinder, in which a piston is movably mounted. As it moves, the piston pumps a fluid in the form of brake fluid into the outflow channel of the pump. 
     SUMMARY 
     According to the disclosure, a pump having an outflow channel for discharging fluid out of the pump is provided, the passage area thereof being determined by a throttle. The throttle is designed with a spring element which changes the size of the passage area of the outflow channel. 
     According to the disclosure, the passage area of the throttle in an outflow channel of a pump is of variable design. By varying or changing the size of the passage area, the throttling effect can be adapted to the operating situation of the pump. The variation in the size of the passage area is provided in a particularly simple way that can be produced at low cost by means of a deflectable spring element. The spring element is subjected to the hydraulic pressure produced by the pump and is pushed back accordingly. As it is pushed back, the spring element simultaneously increases the passage area, reducing the throttling effect. As a result, the throttling effect is reduced at a high delivery rate of the pump, whereas the throttling effect is greater at a low delivery rate. 
     In the case of known fixed throttle cross sections, in contrast, throttling is excessive at a high delivery rate of the pump and too little at a low delivery rate. 
     The passage area of the pump is preferably designed with a bypass area that cannot be closed by the spring element. The bypass area forms a passage area or cross-sectional area in the outflow channel, through which flow is always possible. It thereby ensures a minimum outflow from the pump. 
     The bypass area is preferably formed next to the spring element, along the direction of movement thereof. In this case, the bypass area is preferably designed as a gap, a slit or the like next to the spring element. This gap is not closed and therefore always allows free flow. Moreover, the gap serves to compensate for tolerances in the dimensions of the width of the spring element and the width of the outflow channel. As a result, the mounting of the spring element in the outflow channel is also simpler. 
     In the pump, the spring element is preferably formed by a leaf spring. The spring element designed in this way is particularly simple to arrange and fixed in position in the outflow channel. Moreover, the leaf spring has only a small installation space requirement. 
     As an alternative, a diaphragm spring can be chosen as a spring element. A diaphragm spring allows a greater range of variation as regards the size of the passage area when the passage is largely closed and when it is largely open. 
     The leaf spring is preferably designed and arranged in such a way that it projects in an arc shape into the outflow channel. The fluid flowing through the outflow channel can then flow against the arc shape of the leaf spring in a specifically intended manner, thereby making it possible to keep turbulence formation low. A leaf spring subjected to an incident flow in this way is thus pushed back in a defined manner by the pressure force of the incident flow. In this way, the size of the passage area and hence the throttling effect are varied in a precise manner. It is thus possible to produce a defined flow situation at the spring element, leading to a correspondingly defined throttling behavior of the throttle, which is variable according to the disclosure. 
     The leaf spring furthermore preferably rests by means of at least one section on a wall of the outflow channel and is of rounded design in this section. The leaf spring designed in this way can be positioned simply by being inserted or placed within the outflow channel. The at least one rounded section reduces the friction of a leaf spring placed against the wall of the outflow channel in this way. Consequently, the bending behavior of the leaf spring is improved when it is forced back and, in the process, deformed by the pressure force of the approaching hydraulic fluid. 
     At least one offset, by means of which the spring element is positioned in the longitudinal direction of the outflow channel, is preferably formed in the outflow channel. The offset prevents the spring element from shifting along the outflow channel. When designed in this way, the spring element can be positioned in a simple and, at the same time, precise way in the outflow channel. 
     A pump cap is preferably provided on the pump, acting as a cap element, in particular a disk-shaped cap element, for the cylinder of the pump and having an end face that faces the cylinder. The outflow channel with the spring element arranged therein is formed in the end of the pump cap. An outflow channel formed in this way in the end of a cap element and, in particular, also an offset, formed at the same time in the outflow channel, for the positioning of the spring element can be produced in a particularly simple and low-cost manner. The spring element can simply be inserted or fitted from the side in the outflow channel in the end face. In interaction with another component of the pump, in particular the cylinder, the flow channel formed in this way in the end face can be made to form a closed channel shape or tubular shape. 
     It is advantageous if the pump is formed along a cylinder axis, and the outflow channel with the spring element arranged therein is oriented radially with respect to the cylinder axis. With the radial flow path of this kind out of the center of the pump toward the outside thereof, a solution which is very space-saving overall and hence optimized in terms of installation space is formed. 
     The pump described is preferably used in a motor vehicle brake system. The variable throttling effect achieved according to the disclosure is particularly advantageous especially for use in the case of motor vehicle brake systems and the noise reduction that is aimed at there. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An illustrative embodiment of the solution according to the disclosure is explained in greater detail below with reference to the attached schematic drawings, in which: 
       FIG. 1  shows a longitudinal section through a pump according to the disclosure, and 
       FIG. 2  shows the section II-II according to  FIG. 1  on an enlarged scale. 
    
    
     DETAILED DESCRIPTION 
     The figures illustrate a pump  10 , in which a first piston element  12  and a second piston element  13  are mounted in such a way as to be movable in a substantially block-shaped housing  11 . The piston elements  12  and  13  are coupled to one another for the transmission of force, in particular being connected at the ends, and are driven by means of a drive  14  in the form of an eccentric. In this case, the piston element  13  is preloaded toward the drive  14  by a spring  16  in the form of a helical spring. The spring  16  is arranged in a pumping chamber  18 , which is surrounded by a cylinder  19 . Piston element  13  slides in a fluidtight manner in the cylinder  19 . 
     An inlet  20  is connected fluidically to an inlet opening  28 , which is formed centrally in the piston element  13  in relation to the longitudinal axis of the arrangement. This inlet opening  28  is part of an inlet valve  22  and, as such, interacts with a closure element  24  in order selectively to allow brake fluid to flow into the pumping chamber  18 . The inlet valve  22  is designed as a nonreturn valve, with the closure element being in the form of a ball which is preloaded toward the inlet opening  28  by means of a spring  26 . 
     There is furthermore a central outlet opening  36  at an end of the cylinder  19  remote from the inlet opening  28 . This outlet opening  36  is part of an outlet valve  30  and interacts with a ball-shaped closure element  32 . The closure element  32  is preloaded toward the outlet opening  36  by means of a spring  34 . The outlet valve  30  is thus likewise designed as a nonreturn valve. 
     A pump cap  37  is arranged on the end of the cylinder  19 , after the outlet opening  28  in the direction of flow of the outflowing brake fluid (and hence outside the pumping chamber  18 ). The pump cap  37  is mounted on the end of the cylinder  19  and supports the spring  34 . The pump cap  37  furthermore makes available sufficient installation space for an accumulator or damper (not shown), if appropriate. 
     An outflow channel  38  is formed, in particular milled, radially from the pump cap  37 , at the end facing the cylinder  19 , said outflow channel leading to an outlet  40  in the housing  11 . A spring element  42  in the form of a leaf spring acting as a throttle is arranged in the outflow channel  38 . The leaf spring is shaped in such a way that, in the rest position thereof, it substantially closes the outflow channel  38  and can be deformed by an incident flow of outflowing brake fluid so as then to provide an enlarged passage area in the outflow channel  38  in comparison with the rest position. 
     Overall, the leaf spring has an arc-shaped cross section (see  FIG. 1 ) and is provided in the end regions thereof with respective oppositely bent or rounded sections  46 . In this arrangement, the sections  46  rest against one of the walls of the outflow channel  38  which are formed by the pump cap  37 . The leaf spring is thus bent in a manner similar to a Greek omega (Ω). The bent sections  46  reduce the friction of the leaf spring on the supporting or contact surfaces in the outflow channel  38 . 
     The width (measured in the circumferential direction of the pump cap  37 ) of the leaf spring is matched to the width of the outflow channel  38  in such a way that a gap  54  remains on both sides of the leaf spring. The gaps  54  thus extend along the direction of movement of the spring element  42  and form a bypass line or a minimum passage area for the outflow channel  38 , ensuring a resistance-free minimum outflow from the pump  10 . The gaps  54  also serve as a means of compensating for tolerances in respect of the width dimensions mentioned. 
     An offset  44  is furthermore formed as a kind of step in the outflow channel. A section  46  of the spring element  42  rests against this offset  44 , thereby preventing the spring element  42  from being able to shift or slip radially. In particular, this prevents the spring element  42  from being able to shift in the direction of the outlet valve  30  (owing to pressure pulsations in the outflow channel  44 ). Here, the outflow channel  38  is divided from the inside outward into a first radial subsection  48 , a second radial subsection  50  and a third, axial subsection  52 . The offset  44  is formed in subsection  48 , and the spring element  42  is formed in subsection  50 . The transition from subsection  50  to subsection  52  is of L-shaped configuration, thereby ensuring that the spring element  42  is restrained in the direction toward the outlet  40 . Subsection  48  is of slightly longer configuration than the leaf spring, thus allowing the latter sufficient space for the bending movement thereof. 
     The operation of the variable throttle provided by the spring element  42  is explained below: when there is a pumping operation triggered by the drive  14 , which pushes the coupled piston elements  12  and  13  into the pumping chamber  18 , fluid is forced under pressure into the outflow channel  38  through the outlet valve  30 . 
     As far as possible, the fluid can flow through the outflow channel  38  through the gaps  54 . Moreover, a backpressure builds up ahead of the spring element  42 , leading to the spring element  42  being moved out of the rest position thereof into a deformed position. In this deformed position, the shape of the spring element  42  is less arched, i.e. it is bent back. It then no longer blocks the outflow channel  38  to a substantial degree but exposes an enlarged passage area in said channel, through which fluid can pass to the outlet  40 . 
     The spring element  42  is thus deformed as long as a relatively large quantity of fluid is supplied from subsection  48  of the outflow channel  38 . The deformation begins only above a certain pressure value or above a certain force exerted by the fluid on the spring element  42 . The flow cross section through the outflow channel  38 , which was previously largely closed, is increased. The throttle thus regulates the flow of fluid through the outflow channel  38  in accordance with the delivery rate of the pump  10 . 
     The advantageous aspect of this embodiment is that the spring element  42  can be produced at low cost as a simple bent sheet-metal part by means of stamping. Moreover, only a small amount of space is required for the spring element  42 . In principle, just one outflow channel  38  with an associated variable throttle is necessary. However, it is also possible for a plurality of such outflow channels to be provided, in particular a plurality of outflow channels distributed around the circumference of the pump cap  37 .