DE102021128311A1 - Piston pump for a hydraulic vehicle braking system in a brake-by-wire application - Google Patents

Abstract

A piston pump (1) for a hydraulic vehicle brake system (100) in a brake-by-wire application is proposed. The piston pump (1) comprises a piston (2) with a front (2.1) and a rear (2.2) which are arranged transversely to a piston axis (A). The piston pump (1) also includes a piston rod (3), which is connected to the piston (2) in a non-displaceable manner and extends with its longitudinal extension away from the rear side (2.2) of the piston (2) and is set up to be driven by a drive device (50 ) to be driven to actuate the piston (2). Furthermore, the piston pump (1) comprises a base body (4) with a piston chamber (5) in which the piston (2) is accommodated so that it can move back and forth in the axial direction with respect to the piston axis (A), the piston (2) with its The front side (2.1) delimits a front chamber (5.1) of the piston space (5) and its rear side (2.2) delimits a rear side chamber (5.2) of the piston space (5). In addition, the piston pump (1) comprises at least two fluid connections (6, 7), one of which is assigned to the front chamber (5.1) and at least one other to the rear chamber (5.2). A piston opening (2.3) is provided on the front side (2.1) of the piston (2). A surface-reducing element (9) is also provided, which is arranged fixed to the housing with respect to the base body (4) and engages in the piston opening (2.3) in an axially displaceable manner. Furthermore, a hydraulic vehicle brake system (100) in a brake-by-wire application and a method for setting a maximum pumping force of a piston pump (1) in the forward stroke are proposed.

Description

The present disclosure includes a piston pump for a hydraulic vehicle braking system in a brake-by-wire application, such a vehicle braking system and a method for adjusting the maximum pumping force thereof.

Piston pumps are used, for example, in hydraulic brake-by-wire braking systems in vehicles. Brake-by-wire usually refers to brake systems in which the actuating device, such as the brake pedal, and the actuating device, such as the hydraulic brake, are mechanically decoupled from one another and instead a coupling is realized by electrical signal transmission. For this purpose, the brake-by-wire braking systems usually have a piston pump driven by an electric motor, which generates the hydraulic braking pressure required for braking. When the driver actuates the brake pedal, the electric motor is actuated by an electric control unit in order to generate a corresponding hydraulic brake pressure generated by the piston pump for the braking request exerted by the driver via the brake pedal. The publications disclose further details in this regard WO 2016/049653 A1 and WO 2014/145454 A1 , to which reference is made here for the purpose of supplementing the disclosure with the note that identical terms in the cited documents may have a meaning that differs from the present disclosure.

The piston pumps used in brake-by-wire braking systems have, for example, a piston that acts on both sides. In other words, these piston pumps are set up so that the piston can carry out a forward stroke and a backward stroke, and a pump pressure is built up by the respectively acting piston surface. Due to the design, however, the effective piston area is larger in the forward stroke than in the reverse stroke, since the back of the piston acts in the reverse stroke, on which a piston rod that is drive-connected to the electric motor acts. As a result, the pump pressure generated by the piston is always smaller in the forward stroke than in the reverse stroke for the same driving force applied by the electric motor.

Due to the design, the fluid volume that can be pumped per stroke is greater in the forward stroke than in the reverse stroke. The piston pump is therefore usually connected hydraulically in the brake system in such a way that, to carry out basic braking, the piston pump starts with a forward stroke in order to first use the larger fluid volume that can be pumped to build up the hydraulic brake pressure. In braking situations in which the hydraulic brake pressure built up in the forward stroke is not sufficient for braking, the electric motor is switched over after the forward stroke and the piston pump begins a reverse stroke in order to cause a further increase in the hydraulic brake pressure. Further details in this regard are also disclosed in the documents already mentioned above WO 2016/049653 A1 and WO 2014/145454 A1 .

The pump pressure that can be achieved by the piston pump in the forward stroke and in the reverse stroke is limited by the designed load capacity of the electric motor and the other components of the drive unit for the piston pump. Customer requests, which are based on such a hydraulic brake pressure that is only reached by the piston pump in the reverse stroke, and at the same time a fluid volume to be delivered that is covered by the piston pump only in the forward stroke, can only be realized so far at best by the drive unit is operated in overload and the drive unit is overloaded to such an extent that the required hydraulic braking pressure is already reached in the forward stroke of the piston pump.

A customer request of this kind relates, for example, to ABS braking with a blocking pressure to be provided in the range of the maximum hydraulic braking pressure of the piston pump in the reverse stroke. With such braking, sufficient fluid volume should still be able to be conveyed when the maximum hydraulic braking pressure is reached in order to avoid a possible reduction in the braking effect due to heating of the brake (fading). However, this is no longer possible in the reverse stroke of the piston pump when the maximum hydraulic braking pressure is reached.

Against the background of the situations described above, one task can also be seen as counteracting any overload conditions or largely or completely avoiding overload conditions from the outset. This is based on the expectation of being able to meet a customer request of the above type without or largely without limiting the service life of the brake.

The object is achieved with a piston pump which has the features of claim 1. Furthermore, a hydraulic vehicle brake system with the features of claim 10 is proposed to solve the problem. In addition, a method for setting a maximum hydraulic pumping force with the features of claim 11 is provided to solve the problem hit. Advantageous embodiments and/or refinements and/or aspects result from the dependent claims, the following description and the figures.

According to one aspect, a piston pump for a hydraulic vehicle braking system, for example in a brake-by-wire application, is proposed. The piston pump includes a piston having a front and a back. In particular, the front side is arranged transversely, for example orthogonally, to a piston axis. In particular, the rear side is arranged transversely, for example orthogonally, to the piston axis.

In particular, the proposed piston pump includes a piston rod. In particular, the piston rod is non-displaceably connected to the piston. In particular, the length of the piston rod extends away from the rear of the piston. In particular, the piston rod is set up to be driven by a drive device in order to actuate the piston.

In particular, the proposed piston pump comprises a base body with a piston chamber in which the piston is accommodated so that it can move back and forth in the axial direction with respect to the piston axis and/or in the direction or along the piston axis. In particular, the front side of the piston delimits a front-side chamber of the piston space. In particular, the rear of the piston delimits a rear chamber of the piston chamber.

In particular, the proposed piston pump comprises at least two fluid connections, for example in order to hydraulically connect the piston pump to the vehicle brake system. For example, one of the fluid connections is assigned to the front chamber, in particular arranged on the base body. For example, at least one other of the fluid connections is assigned to the rear chamber, in particular arranged on the base body.

In the proposed piston pump, in particular, a piston opening is provided on the front side of the piston. In particular, a surface-reducing element is also provided, which is fixed to the housing with respect to the base body and engages in the piston opening in an axially displaceable manner, for example to allow the piston to move back and forth relative to the surface-reducing element in the axial direction with respect to the piston axis. In the present description, the term “area-reducing element” is to be understood in particular as meaning that the element reduces the area of the front side of the piston or reduces the area with respect to the effective piston area on the front side of the piston.

The proposed piston pump improves the situations described above compared to the piston pump of the same design that has been used up to now, in that the piston surface available for generating the pump pressure in the forward stroke of the piston is reduced due to the front piston opening and the surface-reducing element engaging therein. As a result, the maximum pump pressure to be reached in the forward stroke of the piston, ie the pump pressure at nominal load of the drive device, is greater in the proposed piston pump than in the piston pump of the same design that has been customary up to now. Consequently, the maximum hydraulic brake pressure to be achieved in the forward stroke is also greater in the proposed piston pump than in the piston pump of the same design that has been customary up to now.

The proposed piston pump allows customer requests, such as those described above, to be implemented in such a way that the required blocking pressure tends to be reached as early as the forward stroke of the piston until the rated load of the drive device is reached. In the event of brake fading occurring, a remaining forward stroke of the piston can still be carried out until the nominal load of the drive device is reached, and a fluid volume from this residual forward stroke is then also available to brake to a standstill without a drop in deceleration. The fluid volume from the backward stroke of the piston also forms a reserve. By switching the drive device to the backward stroke of the piston, the standstill state could also still be reached during braking. Any overload conditions of the drive device are avoided or at least reduced in this way.

In particular, in the proposed piston pump, the fluid volume that can be pumped in the forward stroke of the piston is reduced compared to the piston pump of the same design that has been customary up to now, due to the area-reducing element. This is accepted in view of the advantages described above. In principle, it can also be provided that in the proposed piston pump, the front-side chamber accommodating the pumpable fluid volume is correspondingly enlarged by the volume occupied by the surface-reducing element.

The proposed piston pump can have the same size and the same dimensions as the design that has been used up to now Piston pump are performed, the proposed piston pump compared to the previously used piston pump has the advantages described above. In this respect, the proposed piston pump makes it easy to replace the previously used piston pump in a vehicle brake system, with any structural modifications to the vehicle brake system not being necessary.

The proposed piston pump can be designed in such a way that the area-reducing element is fastened on the one hand to a wall delimiting the front-side chamber, in particular the wall of the base body, and on the other hand engages in the piston opening in an axially displaceable manner. As a result, the surface-reducing element can also serve as a guide for the piston during its stroke movement in the forward stroke or reverse stroke, in addition to its surface-reducing function with respect to the piston surface. Any forces acting on the area-reducing element can be absorbed by the wall.

The proposed piston pump can also be designed in such a way that the surface-reducing element has a peripheral contour that corresponds or essentially corresponds to the peripheral contour of the piston opening. In particular, the peripheral contour of the area-reducing element and the peripheral contour of the piston opening correspond or essentially correspond to one another. This promotes a stroke movement of the piston without being disturbed by the surface-reducing element engaging in the piston opening. The peripheral contour of the piston opening and the corresponding peripheral contour of the surface-reducing element can be round, for example circular or oval, or non-round, in particular angular or polygonal, such as square or hexagonal.

It is advisable for the at least one surface-reducing element to be of cylindrical design and to have a cylinder axis which runs in the direction of the piston axis. This promotes a stroke movement of the piston without being disturbed by the surface-reducing element engaging in the piston opening. The end faces of the cylindrical element can be round, for example circular or oval. The end faces can also be non-round, in particular angular, for example polygonal.

For example, the area-reducing element is designed as a pin element whose longitudinal axis forms the cylinder axis.

The proposed piston pump can also be designed in such a way that the surface-reducing element, in particular the longitudinal axis and/or the cylinder axis of the surface-reducing element, is coaxial with respect to the piston axis and, in particular, the surface-reducing element engages in the piston opening so that it can be displaced along the piston axis. This promotes a rotationally symmetrical design of the piston with respect to the piston axis. Alternatively, the area-reducing element can also be offset from the axis of the piston. In principle, a coaxial or off-axis arrangement of the surface-reducing element can be selected accordingly depending on the existing piston geometry and/or existing piston-piston rod arrangement.

The proposed piston pump can also be designed in such a way that the piston opening has a predetermined opening area and in particular the outer circumference of the surface-reducing element corresponds to the outer circumference of the predetermined opening area of the piston opening. As a result, the effective piston area of the piston can be set within certain limits by specifically realizing a specific opening area of the piston opening as required. Accordingly, the pump pressure that can be built up by the piston stroke at nominal load of the drive device can be adjusted within certain limits in this way.

The proposed piston pump can also be designed in such a way that the piston has a through hole running in the direction of the piston axis, into which the surface-reducing element is introduced in an axially displaceable manner via the piston opening. This avoids or at least largely avoids a counterforce being able to build up during a stroke movement of the piston, for example due to the formation of a fluid cushion at the engaging end of the area-reducing element. This also facilitates simple production of the piston opening, since only the passage has to be made in the piston for this purpose. The measure that, according to one embodiment, the through-hole is designed as a bore also aims in this direction. The through hole can extend over the piston and, if necessary, into the piston rod or over the piston rod.

The proposed piston pump can also be designed in such a way that the surface-reducing element engages in the piston opening in a fluid-tight manner. This counteracts a possible fluid leakage of the fluid volume contained in the piston chamber, in particular the front chamber. The fluid-tight engagement of the surface-reducing element in the piston opening is appropriate if the piston opening is a through-opening is formed and / or the above-described through hole is present, for example, to avoid or largely avoid a leakage of fluid.

A possible embodiment can consist in a sealing element being provided which, for example, seals the area-reducing element in relation to the piston or the edge of the opening. The sealing element can be arranged in the through opening or the through hole. For this purpose, a peripheral depression can be provided on the circumference of the through-opening or the through-hole, in which the sealing element is accommodated. In particular, the sealing element encompasses the area-reducing element and in particular the sealing element seals against the outer circumference of the area-reducing element.

The proposed piston pump can also be designed in such a way that the piston rod has a hollow body for accommodating a threaded spindle, at least over a length section. For example, the hollow body forms a counter-element for the threaded spindle in order, for example, to form a spindle drive together with the threaded spindle, which is, for example, a component of the drive device. For this purpose, a thread corresponding to the threaded spindle can be provided on the inner circumference of the hollow body.

If the piston opening is designed as a through-opening or the through-hole described above is provided, it is possible for the through-opening or the through-hole to extend into the hollow body. As a result, the through hole or the through opening ends in the hollow body, so that there is a passage from the front side of the piston to the end of the piston rod.

According to a further aspect, a hydraulic vehicle brake system is proposed which includes the piston pump proposed above. For example, the vehicle brake system is a brake-by-wire brake system.

According to a further aspect, a method for setting a maximum hydraulic pumping force of a piston pump in the forward stroke is proposed. The piston pump includes a piston having a front and a back. In particular, the front side is arranged transversely, for example orthogonally, to a piston axis. In particular, the rear side is arranged transversely, for example orthogonally, to the piston axis.

In particular, the piston pump includes a piston rod. In particular, the piston rod is non-displaceably connected to the piston. In particular, the length of the piston rod extends away from the rear of the piston. In particular, the piston rod is set up to be driven by a drive device in order to actuate the piston.

In particular, the piston pump comprises a base body with a piston chamber in which the piston is accommodated so that it can move back and forth in the axial direction with respect to the piston axis and/or in the direction of or along the piston axis. In particular, the front side of the piston delimits a front-side chamber of the piston space. In particular, the rear of the piston delimits a rear chamber of the piston chamber.

In particular, the piston pump comprises at least two fluid connections, for example in order to hydraulically connect the piston pump to the vehicle brake system. For example, one of the fluid connections is assigned to the front chamber, in particular arranged on the base body. For example, at least one other of the fluid connections is assigned to the rear chamber, in particular arranged on the base body.

1. i) Einbringen einer Kolbenöffnung mit einer vorbestimmten Öffnungsfläche an der Vorderseite des Kolbens;
2. ii) Bereitstellen eines flächenreduzierenden Elementes mit einer Umfangskontur, welche mit einer Umfangskontur der Kolbenöffnung korrespondiert;
3. iii) Anordnen des flächenreduzierenden Elementes derart, dass es einerseits an einer die vorderseitige Kammer begrenzenden Wandung befestigt ist und andererseits in die Kolbenöffnung axial verschiebbar eingreift.

The proposed procedure includes the steps or consists of the steps:

1. i) providing a piston port having a predetermined opening area at the front of the piston;
2. ii) providing an area-reducing element having a peripheral contour which corresponds to a peripheral contour of the piston opening;
3. iii) arranging the surface-reducing element in such a way that it is fastened on the one hand to a wall delimiting the front-side chamber and on the other hand engages in the piston opening in an axially displaceable manner.

With the proposed method, the maximum pumping force of the piston pump in the forward stroke, that is to say the maximum pumping force at the rated load of the drive device, can be set in a simple manner depending on the customer's requirements. This is done using the piston opening and the area-reducing element, through which the effective piston area of the piston and thus the maximum pumping force can be influenced. In this regard, reference is made to the above statements on the proposed piston pump, which are used in the same way with regard to the piston pump on which the proposed method is based can. The piston pump of the proposed method can be the piston pump proposed above.

In order to set the maximum pumping force, the proposed method is based on the piston opening having a predetermined opening area and the peripheral contour of the area-reducing element corresponding to the peripheral contour of the piston opening. The maximum pumping force of the piston pump can be set in such a way that the opening area of the piston opening is correspondingly predetermined depending on the desired maximum pumping force. This makes it possible to specifically avoid any overload conditions of the brake or to counteract them, depending on the customer's individual requirements.

• 1 ein mögliches Ausführungsbeispiel einer Kolbenpumpe für ein hydraulisches Fahrzeugbremssystem in einer schematischen Darstellung,
• 2A die wirksame Kolbenfläche eines Kolbens der Kolbenpumpe gemäß der 1 bei einem Druckaufbau im Rückwärtshub des Kolbens,
• 2B die wirksame Kolbenfläche des Kolbens der Kolbenpumpe gemäß der 1 bei einem Druckaufbau im Vorwärtshub des Kolbens,
• 2C die wirksame Kolbenfläche des Kolbens der Kolbenpumpe gemäß der 1 bei einem Ansaugen von Fluidvolumen in eine vorderseitige Kammer im Rückwärtshub des Kolbens und
• 3 ein mögliches Ausführungsbeispiel eines hydraulischen Fahrzeugbremssystems in einer Brake-by-Wire-Anwendung mit der Kolbenpumpe gemäß der 1 in einer schematischen Darstellung.

Further details and features emerge from the following description of two exemplary embodiments with reference to the drawings. Show it:

• 1 a possible embodiment of a piston pump for a hydraulic vehicle brake system in a schematic representation,
• 2A the effective piston area of a piston of the piston pump according to 1 with a pressure build-up in the backward stroke of the piston,
• 2 B the effective piston area of the piston of the piston pump according to 1 with a pressure build-up in the forward stroke of the piston,
• 2C the effective piston area of the piston of the piston pump according to 1 upon suction of fluid volume into a front chamber in the return stroke of the piston and
• 3 a possible embodiment of a hydraulic vehicle braking system in a brake-by-wire application with the piston pump according to 1 in a schematic representation.

1 shows an exemplary embodiment of a piston pump 1, which is suitable, for example, in a (in the 1 not shown) hydraulic vehicle brake system to be used. Such a piston pump 1 is also referred to in technical circles as a reciprocating piston pump or displacement pump. The hydraulic vehicle brake system can be a brake-by-wire brake system.

The exemplary piston pump 1 preferably comprises one or at least one piston 2 with a front side 2.1 and a rear side 2.2. The front side 2.1 is preferably arranged transversely, for example orthogonally, to a piston axis A of the piston 2. The rear side 2.2 is preferably arranged transversely, for example orthogonally, to the piston axis A.

The exemplary piston pump 1 preferably comprises a piston rod 3 which is connected to the piston 2 in a non-displaceable manner. The length of the piston rod 3 preferably extends away from the rear side 2.2 of the piston 2. The piston rod 3 is preferably set up to be driven by a drive device 50 in order to actuate the piston 2 .

The exemplary piston pump 1 preferably comprises a base body 4 with a piston chamber 5 in which the piston 2 is accommodated so that it can move back and forth in the axial direction with respect to the piston axis A. The piston 2 preferably delimits a front chamber 5.1 of the piston chamber 5 with its front side 2.1. The piston 2 preferably delimits a rear chamber 5.2 of the piston chamber 5 with its rear side 2.2 build up a pumping pressure in a forward stroke and also via the rear 2.2 in a reverse stroke. Due to the design, for example, the volume of the front chamber 5.1 is greater than the volume of the rear chamber 5.2.

The exemplary piston pump 1 preferably comprises at least two fluid connections 6, 7, for example in order to be hydraulically connected to the vehicle brake system. The fluid connections 6 , 7 are preferably arranged on the base body 4 . One of the fluid connections 6, 7, in particular the fluid connection 6, is preferably assigned to the front chamber 5.1, in particular hydraulically connected to the front chamber 5.1, in particular permanently hydraulically connected. At least one other of the fluid connections 6, 7, in particular the fluid connection 7, is preferably assigned to the rear chamber 5.2, in particular hydraulically connected to the rear chamber 5.2, in particular permanently hydraulically connected.

A first sealing element 10 can be provided for hydraulically sealing the piston 2 with respect to the base body 4 . For example, the first sealing element 10 is arranged in a circumferential groove of the piston 2 . For example, the first sealing element 10 seals against a peripheral wall section 4.1 of the base body 4, which delimits the piston chamber 5 on the peripheral side. The first sealing element 10 preferably separates the front chamber 5.1 from the rear chamber 5.2 in a sealing manner. For example, the first sealing element 10 is an O-ring.

A second sealing element 11 is preferably provided, which is arranged between the piston rod 3 and the base body 4 in order to achieve hydraulic sealing of the rear chamber 5.2. For example, the second sealing element 11 is arranged in a circumferential groove on a circumferential wall section 4.2 of the base body 4, which surrounds the piston rod 3. For example, the second sealing element 11 seals against the outer circumference of the piston rod 3. For example, the second sealing element 11 is an O-ring.

The exemplary piston pump 1 preferably has a further fluid connection 8 . For example, the further fluid connection 8 can be hydraulically connected to the rear chamber 5.2 via a bypass 13 arranged in the area of the piston rod 3, depending on the stroke position in which the piston 2 is located. For example, the bypass 13 is formed by a groove that extends longitudinally in the axial direction with respect to the piston axis A, or the bypass 13 has such a groove.

The further fluid connection 8 is preferably arranged between the first sealing element 10 and the second sealing element 11 in the axial direction with respect to the piston axis A. In order to avoid a hydraulic short circuit between the rear chamber 5.2 and the further fluid connection 8, a third sealing element 12 is preferably provided. For example, the third sealing element 12 is arranged between the rear chamber 5.2 and the further fluid connection 8 for this purpose. The third sealing element 12 is preferably arranged in a circumferential groove, in particular a further groove, on the wall section 4.2 of the base body 4 and seals, for example, against the outer circumference of the piston rod 3. For example, the third sealing element 12 is designed as a sealing lip or has a sealing lip.

In the exemplary piston pump 1, the drive device 50 comprises, for example, a spindle drive 51 and an electric motor drive 52, which has a driving effect on the spindle drive 51. The spindle drive 51 is used, for example, to convert a rotary drive movement into a translational output movement. For example, the spindle drive 51 includes a threaded spindle 53 which, for example, interacts with a counter-element 54, such as a spindle nut. The threaded spindle 53 can be accommodated or protrude into a receptacle which is part of a hollow body 3.1 of the piston rod 3. The counter-element 54 of the spindle drive 51 is formed, for example, in or on the receptacle.

The drive device 50 for driving the piston 2 is preferably set up in such a way that the piston 2 can be brought into both a forward movement and a backward movement in the axial direction with respect to the piston axis A. The drive device 50 thus enables both a forward stroke and a backward stroke of the piston 2 . In the forward stroke, the piston 2 builds up pumping pressure on its front side 2.1. In the reverse stroke, the piston 2 builds up a pumping pressure on its rear side 2.2. The maximum value of the pump pressure in the forward stroke as well as in the reverse stroke is limited by the design of the drive device 50.

In order to increase the maximum pump pressure of the example piston pump 1 that can be reached at the nominal load of the drive device 50 in the forward stroke, the piston 2 can have a piston opening 2.3 on its front side 2.1, into which an area-reducing element 9 engages in an axially displaceable manner, which is arranged fixed to the housing with respect to the base body 4 is. As a result, the effective piston area for building up the pump pressure is reduced on the front side 2.1 of the piston 2, in particular reduced by the opening area of the piston opening 2.3. As a result, at nominal load of the drive device 50, a higher pump pressure results in the forward stroke of the piston 2 compared to the state in which the piston opening 2.3 and the area-reducing element 9 are not provided.

The area-reducing element 9 is fastened, for example, to a wall 4.3 delimiting the front-side chamber 5.1. The wall 4.3 is, for example, a front wall of the base body 4 and/or a cover or piston cover, which is arranged on the front side of the piston 2 on the base body 4. The area-reducing element 9 preferably has a peripheral contour which corresponds to the peripheral contour of the piston opening 2.3. For example, the surface-reducing element 9 is designed as a cylinder 9.1 or in the shape of a cylinder and has a cylinder axis 9.2, which runs in the direction of the piston axis A.

The area-reducing element 9 preferably has a cross section which is round, for example circular. The area-reducing element 9 preferably lies with its central axis or cylinder axis 9.2 on the piston axis A. The piston opening 2.3 preferably has a central axis which also lies on the piston axis A, ie is arranged in the center of the piston 2.

In the exemplary piston pump 1, the piston 2 has, for example, a through-hole 2.4 running in the direction of the piston axis A, into which the area-reducing element 9 passes the piston opening 2.3 is introduced in an axially displaceable manner. The through hole 2.4 preferably extends into the hollow body 3.1 of the piston rod 3. As a result, the through hole 2.4 does not have any area-reducing effect on the effective piston area on the rear side 2.2 of the piston 2, since the effective piston area there extends around the cross-sectional area spanned by the outer circumference of the piston rod 3 is reduced anyway ( 2A) .

The surface-reducing element 9 preferably engages in the piston opening 2.3 in a fluid-tight manner. For this purpose, a sealing element 9.3 can be provided, which is used to seal the surface-reducing element 9 from the piston 2. For example, the sealing element 9.3 is accommodated in a circumferential groove on the circumference of the through hole 2.4 and provides a fluid-tight seal with respect to the outer circumference of the surface-reducing element 9 .

2A and 2 B illustrate by way of example the effective piston area in the forward stroke and in the reverse stroke of the piston 2 using a view of the rear side 2.2 of the piston 2 ( 2A) and a view of the front 2.1 of the piston 2 ( 2 B) .

The effective in the reverse stroke of the piston 2 piston area is in the 2A shown hatched and provided with the reference number 20 . The effective piston surface 20 is the peripheral surface that is radially outside of the outer circumference formed by the piston rod 3 . The effective piston surface 20 is, for example, an annular surface that runs around the outer circumference of the piston rod 3 . The through hole 2.4 extending into the hollow body 3.1 of the piston rod 3 with the surface-reducing element 9 accommodated therein therefore does not have a surface-reducing effect on the effective piston surface 20 on the rear side 2.2 of the piston 2.

The effective in the forward stroke of the piston 2 piston area is in the 2 B shown hatched and provided with the reference number 30 . As illustrated there, the opening surface formed by the piston opening 2.3 on the front side 2.1 of the piston 2 with the surface-reducing element 9 engaging therein is not part of the effective piston surface 30. The piston opening 2.3 and the surface-reducing element 9 accommodated therein is therefore the effective piston surface 30 reduced accordingly. The front surface, which corresponds to the effective piston surface 20 on the rear 2.2 of the piston 2, is also not part of the effective piston surface 30 on the front 2.1 of the piston 2.

2C shows an example of the effective piston area in the backward stroke of the piston 2, through which a suction of fluid volume into the front-side chamber 5.1 is effected. The effective piston area is hatched there and provided with the reference number 30'. As can be seen from this, the opening area generated by the piston opening 2.3 is not part of the effective piston area 30'. The effective piston area 30' is thus reduced by the opening area of the piston opening 2.3. For example, the effective piston area 30' when filling the front chamber 5.1 in the backward stroke of the piston 2 is identical or largely identical to the effective piston area 30 during the forward stroke of the piston 2.

3 12 shows an exemplary vehicle braking system 100 in a brake-by-wire application. The vehicle brake system 100 acts on all four wheels of a vehicle and in this respect has a wheel brake 150 for each vehicle wheel. The vehicle braking system 100 further includes a piston pump having the features of the exemplary piston pump 1 above. Otherwise, the vehicle brake system 100 is essentially identical in construction and/or functionally identical to that in FIG DE 10 2021 112 434 Vehicle braking system described on May 12, 2021; in this respect, on the DE 10 2021 112 434 referenced, the disclosure of which is hereby incorporated into the present disclosure.

The vehicle braking system 100 further includes a brake cylinder module 110 having a brake pedal 120. The brake cylinder module 110 is hydraulically connected to a fluid reservoir 130. The fluid reservoir 130 is in turn hydraulically connected to the piston pump 1 via the fluid connection 8 . The fluid connections 6, 7 of the piston pump 1 are in turn hydraulically connected to different control valves of the vehicle brake system 100. With regard to these control valves, their mode of operation and interconnection in vehicle brake system 100 will not be discussed in detail; this is on the corresponding disclosure in the DE 10 2021 112 434 is referenced.

In the present specification, reference to a particular aspect, embodiment or configuration means that a particular feature or characteristic described in connection with that aspect, embodiment or configuration is at least included therein is, but need not necessarily be included in all aspects or embodiments or configurations.

The use in the text of any or all examples or exemplary language is intended only for illumination of the disclosure and should not be construed as a limitation on the scope of the disclosure unless otherwise indicated. Nor should any language or wording of the specification be construed as implying an unclaimed but essential element of practice.

Reference List

1

piston pump

2

Pistons

2.1

front

2.2

back

2.3

butt opening

2.4

through hole

3

piston rod

3.1

hollow body

4

body

4.1

wall section

4.2

wall section

4.3

wall

5

piston space

5.1

front chamber

5.2

back chamber

6

fluid connection

7

fluid connection

8th

fluid connection

9

area-reducing element

9.1

cylinder

9.2

cylinder axis

9.3

sealing element

10

first sealing element

11

second sealing element

12

third sealing element

13

bypass

20

effective piston area (reverse stroke)

30

effective piston area (forward stroke)

30'

effective piston area

50

drive device

51

spindle drive

52

electric drive

53

lead screw

54

counter element

100

vehicle braking system

110

brake cylinder unit

120

brake pedal

130

fluid reservoir

150

wheel brake

A

piston axis

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• WO 2016/049653 A1 [0002, 0004]
• WO 2014/145454 A1 [0002, 0004]
• DE 102021112434 [0058, 0059]

Claims (11)

Piston pump (1) for a hydraulic vehicle braking system (100) in a brake-by-wire application comprising a piston (2) with a front (2.1) and a rear (2.2) which are arranged transversely to a piston axis (A), a piston rod (3) which is non-displaceably connected to the piston (2) and extends with its longitudinal extension away from the rear side (2.2) of the piston (2) and is set up to be driven by a drive device (50) in order to to actuate piston (2), a base body (4) with a piston chamber (5) in which the piston (2) is accommodated so that it can move back and forth in the axial direction with respect to the piston axis (A), the piston (2) having a front side chamber (2.1). (5.1) of the piston chamber (5) and with its rear side (2.2) delimiting a rear chamber (5.2) of the piston chamber (5), at least two fluid connections (6, 7), of which one of the front chamber (5.1) and at least one other are assigned to the rear chamber (5.2), a piston opening (2.3) at the front (2.1) of the piston (2) and a area-reducing element (9), which is arranged fixed to the housing with respect to the base body (4) and engages in the piston opening (2.3) in an axially displaceable manner. piston pump after claim 1 , wherein the area-reducing element (9) is fastened on the one hand to a wall (4.3) delimiting the front-side chamber (5.1) and on the other hand engages in the piston opening (2.3) in an axially displaceable manner. piston pump after claim 1 or 2 , wherein the area-reducing element (9) has a peripheral contour which corresponds to the peripheral contour of the piston opening (2.3). Piston pump according to one of the preceding claims, wherein the surface-reducing element (9) is cylindrical and has a cylinder axis (9.2) which runs in the direction of the piston axis (A). Piston pump according to one of the preceding claims, wherein the area-reducing element (9) is coaxial with respect to the piston axis (A) and displaceably engages in the piston opening (2.3) along the piston axis (A). Piston pump according to one of the preceding claims, wherein the piston opening (2.3) has a predetermined opening area. Piston pump according to one of the preceding claims, wherein the piston (2) has a through hole (2.4) running in the direction of the piston axis (A) and into which the surface-reducing element (9) is introduced in an axially displaceable manner via the piston opening (2.3). Piston pump according to one of the preceding claims, wherein the surface-reducing element (9) engages in the piston opening (2.3) in a fluid-tight manner, in particular a sealing element (9.3) is provided for sealing the surface-reducing element (9) relative to the piston (2). Piston pump according to one of the preceding claims, wherein the piston rod (3) comprises a hollow body (3.1) over at least one length section for receiving a threaded spindle (51) and wherein the piston opening (2.3) is designed as a through-opening which extends into the hollow body (3.1 ) extends. Hydraulic vehicle braking system (100) in a brake-by-wire application, comprising a piston pump (1) according to any one of Claims 1 until 9 . Method for setting a maximum hydraulic pumping force of a piston pump (1) in the forward stroke, the piston pump (1) comprising a piston (2) with a front (2.1) and a rear (2.2) which are arranged transversely to a piston axis (A), a piston rod (3) which is non-displaceably connected to the piston (2) and extends with its longitudinal extension away from the rear side (2.2) of the piston (2) and is set up to be driven by a drive device (50) in order to To actuate the piston (2), a base body (4) with a piston chamber (5) in which the piston (2) is accommodated so that it can move back and forth in the axial direction with respect to the piston axis (A), the piston (2) with its Front side (2.1) delimits a front chamber (5.1) of the piston space (5) and with its rear side (2.2) a rear side chamber (5.2) of the piston space (5), at least two fluid connections (6, 7), one of which is the front side chamber (5.1) and at least one other of the rear chamber (5.2), the method comprising the steps or consisting of the steps: i) making a piston opening (2.3) with a predetermined opening area on the front side (2.1) of the piston (2) ; ii) providing an area-reducing element (9) with a peripheral contour which corresponds to the peripheral contour of the piston opening (2.3); iii) arranging the area-reducing element (9) in such a way that it is fastened on the one hand to a wall (4.3) delimiting the front chamber (5.1) and on the other hand engages in the piston opening (2.3) in an axially displaceable manner.

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