U.S. patent application number 14/438186 was filed with the patent office on 2015-10-15 for pump element for a hydraulic unit having a pump piston.
The applicant listed for this patent is ROBERT BOSCH GMBH. Invention is credited to Bernd Haeusser.
Application Number | 20150292491 14/438186 |
Document ID | / |
Family ID | 49382419 |
Filed Date | 2015-10-15 |
United States Patent
Application |
20150292491 |
Kind Code |
A1 |
Haeusser; Bernd |
October 15, 2015 |
Pump Element for a Hydraulic Unit having a Pump Piston
Abstract
A pump element for a hydraulic unit of a vehicle braking system
includes a pump piston that has two piston parts. A first piston
part of the two piston parts is produced from a sintering
material.
Inventors: |
Haeusser; Bernd;
(Neckarwestheim, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ROBERT BOSCH GMBH |
Stuttgart |
|
DE |
|
|
Family ID: |
49382419 |
Appl. No.: |
14/438186 |
Filed: |
October 16, 2013 |
PCT Filed: |
October 16, 2013 |
PCT NO: |
PCT/EP2013/071610 |
371 Date: |
April 23, 2015 |
Current U.S.
Class: |
92/172 ;
419/26 |
Current CPC
Class: |
F04B 1/0408 20130101;
F04B 53/16 20130101; B22F 5/008 20130101; F04B 53/14 20130101 |
International
Class: |
F04B 1/04 20060101
F04B001/04; F04B 53/16 20060101 F04B053/16; B22F 5/00 20060101
B22F005/00; F04B 53/14 20060101 F04B053/14 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 23, 2012 |
DE |
10 2012 219 348.0 |
Claims
1. A pump element for a hydraulic unit of a vehicle brake system,
comprising: a pump piston having two piston parts, wherein a first
piston part of the two piston parts includes a sintered
material.
2. The pump element as claimed in claim 1, wherein the first piston
part is configured with a ring shape and includes at least one duct
passing radially through the ring shape and having an axially open
configuration.
3. The pump element as claimed in claim 2, wherein the at least one
duct has duct walls axially oriented obliquely.
4. The pump element as claimed in claim 1, wherein the first piston
part defines a valve orifice with a valve seat, the valve seat
having a surface that is impregnated.
5. The pump element as claimed in claim 1, wherein the first piston
part is configured to partially surround the second piston
part.
6. The pump element as claimed in claim 1, wherein the second
piston part is of circular-cylindrical configuration.
7. The pump element as claimed in claim 1, wherein the second
piston part includes ceramic.
8. The pump element as claimed in claim 1, further comprising a
valve cage arranged on the first piston part, the valve cage being
configured in one piece with a sealing ring.
9. A method for producing a pump piston of a pump element of a
hydraulic unit of a vehicle brake system, comprising: forming a
first piston part by a sintering method; and pressing the first
piston part onto a second piston part.
10. A hydraulic unit of a vehicle brake system, comprising: a pump
element for the hydraulic unit, the pump element including a pump
piston having two piston parts, wherein a first piston part of the
two piston parts includes a sintered material.
Description
PRIOR ART
[0001] The invention relates to a pump element for a hydraulic unit
of a vehicle brake system, having a pump piston which has two
piston parts. The invention relates, furthermore, to a method for
producing such a pump piston and to the use of a pump element of
this type.
[0002] Generic pump elements are used in hydraulic units of vehicle
brake systems, in order, particularly during the regulation of
brake pressure, to generate brake pressure actively or reduce brake
pressure actively on associated vehicle brakes. For this purpose,
as a rule, the pump elements have at least two pump piston sides
which, in the configuration of an axial piston pump, are driven by
an eccentric. The eccentric engages on one end face of the
respective pump piston, in order to move it axially back and forth
for a pumping movement. This end face of the pump piston is
consequently exposed to particular mechanical load. The opposite
end face of the pump piston serves for sealing off a pump space or
pressure space of an associated pump cylinder. For this purpose,
this end face of the pump piston is sealed off with respect to the
pump cylinder by means of a sealing element arranged on the pump
piston.
DISCLOSURE OF THE INVENTION
[0003] According to the invention, a pump element for a hydraulic
unit of a vehicle brake system, having a pump piston which has two
piston parts, is provided. Of the two piston parts, a first piston
part is produced by means of a sintered material or sintered stock.
For the piston part according to the invention, the sintered
material used is especially preferably Al.sub.2O.sub.3.
[0004] Sintered material is produced in that one or more
fine-grained or pulverulent, in particular metallic substances are
heated, mostly under increased pressure, to temperatures below
their melting temperature. In contrast to a pure melt, however, in
this case none or at least not all of the starting materials are
melted down. Hence, formulated in colloquial language, the starting
materials are "caked together". Sintering is therefore a primary
forming method.
[0005] During sintering, the starting materials are brought, if
appropriate by means of a binder, into the form of a desired
workpiece. This takes place, as a rule, by pressing. This green
compact, as it is known, is subsequently compressed and cured by
heat treatment below the melting temperature. In sintering, casting
is also employed as shaping method in addition to pressing.
[0006] In general, sintered parts have a comparatively porous
configuration in terms of their material structure and therefore,
in view of requirements, such as seal tightness and compressive
strength, are not advantageous for use as pump pistons. According
to the invention, however, such a sintered part is provided in
combination with a further piston part. As a result, each of the
two piston parts can be assigned specific different
functionalities. In this case, the sintered part according to the
invention can be given the functions advantageous for it, and
therefore the other advantages of such sintered parts can be
utilized at the same time. Thus, for example in comparison with
milled parts, sintered parts have considerably lower manufacturing
costs. In light of their tensile strength which is in this case
achieved, they are far better than equally costly components made
from other materials.
[0007] Particularly advantageous in this regard is the use of
sintered steel for the piston part according to the invention, and
therefore this can also be designated as a steel sintered part. A
component of this type, while having identical or lower costs,
tolerates higher load, and therefore, in particular, it becomes
possible to operate the associated pump piston at higher
pressures.
[0008] These advantages according to the invention are especially
beneficial in that the sintered part according to the invention is
assigned the function of a valve seal, a valve seat being formed
around a valve orifice on the sintered part. The sintered material
selected according to the invention results at the valve seat in an
advantageous optimum of low production costs and low wear. The
valve seat of this type made from sintered material has a long
service life, while at the same time being produced
cost-effectively.
[0009] In an advantageous development of the pump element according
to the invention, the first piston part is configured with a ring
shape, in which at least one duct passing radially through the ring
shape and having an axially open configuration is provided. The
duct of this type serves particularly as an inflow line for brake
fluid radially from the outside radially inward into the interior
of the pump piston according to the invention. The duct is
advantageously formed between the two piston parts according to the
invention in such a way that it can be formed without extra outlay
at the same time the sintered part is being produced. Separate
machining with through bores, as is the case at the present time
with regard to milled or drilled piston parts, is therefore
dispensed with.
[0010] In this case, especially preferably, the at least one duct
is configured with duct walls obliquely oriented axially. The
geometry of the duct and, in particular, the entire sintered part
according to the invention is then configured in such a way that
this sintered part can be formed by means of two die halves of a
sintering mold, and in this case the two die halves merely need to
be moved in the axial direction. The axially oblique duct walls
form mold removal slopes, by means of which the sintered part can
be removed from the sintering mold after production. In particular,
the sintered part according to the invention preferably has no
undercuts, such as are to be regularly found in known valve seat
components of pump pistons of a hydraulic unit of a vehicle brake
system.
[0011] On the first piston part, especially preferably, the valve
orifice is designed with a valve seat, the surface of which is
impregnated. By means of impregnation, both the sealing-off and the
wear situation on the valve seat can be improved.
[0012] Preferably, for this purpose, the entire sintered part is
impregnated. Alternatively, hardening or stamping of the valve
seat, heated for this purpose to annealing temperature, is
expedient. For annealing, the valve seat sintered part according to
the invention is preferably heated by means of an induction current
device or a laser device. Furthermore, by means of steam treatment,
the pores of the sintered material can be closed and the wear
resistance of the valve seat can be increased.
[0013] Advantageously, furthermore, the first piston part partially
surrounds the second piston part. By means of such a configuration,
it is possible to have an especially large inlet cross-sectional
area for the at least one said duct for the inlet of brake fluid
into the interior of the pump piston. The configuration,
surrounding the second piston part, of the first piston part then
makes it possible for the first piston part to be joined, in
particular pressed, onto the outside diameter of the second piston
part. Consequently, the entire outer circumference of the first
piston part, which in this case is even larger than the outer
circumference of the second piston part, is available for the inlet
cross-sectional area.
[0014] In order to obtain a pump element which overall can be
produced very cost-effectively, all the essential delivery and
sealing-off functions can be integrated in the first piston part
which according to the invention is configured as a sintered part.
In particular, the second piston part may have a
circular-cylindrical configuration. By means of this
circular-cylindrical shape, this second piston part can be produced
very cost-effectively, so that even a comparatively costly material
can be selected for this.
[0015] Thus, in the pump element according to the invention, the
second piston part is advantageously to be produced from ceramic. A
piston part produced in this way from ceramic has high wear
resistance. At the same time, it is comparatively lightweight and
therefore also has especially low mass inertia. As a cost-effective
alternative, the second piston part according to the invention may
be formed by plastic or by steel.
[0016] For the pump element according to the invention to have a
design which overall is simple to assemble, it is advantageous to
arrange on the first piston part a valve cage which, in particular,
is formed in one piece with a sealing ring. The sealing ring may in
this case be configured as a high-pressure sealing ring and be
pressed onto the first piston part. Both the valve cage and the
sealing ring can be produced cost-effectively in one operation by
injection molding with a correspondingly suitable plastic. For
simple assembly, preferably when the valve cage, together with the
sealing ring, is being mounted, an associated valve spring and a
valve closing body are inserted at the same time.
[0017] The invention is also directed, correspondingly to the above
explanation, to a method for producing a pump piston of a pump
element of a hydraulic unit of a vehicle brake system, in which a
first piston part is produced by a sintering method and is pressed
onto a second piston part.
[0018] Such a pump element according to the invention is preferably
used on a hydraulic unit of a vehicle brake system. By means of the
solution according to the invention, the requirements with regard
to reliable pressure sealing can be fulfilled especially well there
throughout the entire service life, and at the same time along with
especially low production and assembly costs.
[0019] An exemplary embodiment of the solution according to the
invention is explained in more detail below by means of the
accompanying diagrammatic drawings in which:
[0020] FIG. 1 shows a side view of an exemplary embodiment of a
pump piston according to the invention with a first and a second
piston part,
[0021] FIG. 2 shows a longitudinal section of the pump piston
according to FIG. 1,
[0022] FIG. 3 shows a perspective view of the first piston part of
the pump piston according to FIGS. 1, and
[0023] FIG. 4 shows a longitudinal section of the first piston part
according to FIG. 3.
[0024] FIG. 1 illustrates a pump piston 10 of a pump element, not
illustrated any further, of a hydraulic unit of a vehicle brake
system. The pump piston 10 is configured in two parts and has a
first annulus-shaped piston part 12 and a second
circular-cylinder-shaped or circular-cylindrical piston part 14.
Furthermore, a sealing ring 16 and a valve cage 18 are located on
the pump piston 10.
[0025] The sealing ring 16 serves for sealing off the pump piston
10 on the inside at a pump cylinder, not illustrated. The pump
piston 10 is mounted displaceably in this pump cylinder by means of
the sealing ring 16, in order in an associated pump space or
pressure space to exert high pressure upon a brake fluid located
there. The brake fluid passes into this pump space through an inlet
valve, of which the valve cage 18 forms an integral part. The inlet
valve includes, furthermore, a valve orifice 20 which is formed
centrally in the first piston part 12. A valve seat 22 is formed
around the valve orifice 20 on the end face of the first piston
part 12 and likewise belongs to the inlet valve. A valve closing
body is urged by means of a valve spring (neither is illustrated)
against the valve seat 22, by means of which valve closing body the
valve orifice 20 can then be selectively closed or opened.
[0026] Located on the outer portion of the associated end face of
the first piston part 12 is a shoulder 24, against which the
sealing ring 16 is pressed, the sealing seat 16 being produced in
one piece with the valve cage 18 from plastic by means of injection
molding. The valve cage 18 is thereby also held, fixed in place, on
the first piston part 12.
[0027] Shaped out on the first piston part 12, on the opposite end
face of the latter are three end-face ducts 26 passing radially
through the annular shape of the first piston part 12. The ducts 26
serve for feeding brake fluid radially from the outside radially
inward to said inlet valve and then further on into the associated
pressure space.
[0028] The ducts 26 are also configured as being open in the axial
direction, and they are equipped with axially slightly oblique duct
walls 28. Overall, therefore, a crown shape is obtained on this end
face of the first piston part 12. The duct walls 28 oblique in this
way serve as mold removal slopes which, inter alia, make it
possible that the first piston part 12 can be formed from a
sintered material, in particular as a steel sintered component.
[0029] To produce appropriate surface quality, particularly at the
valve seat 22, this steel sintered component has been impregnated
overall after its production as a sintered part.
[0030] In the region of the crown shape of the first piston part
12, an essentially right-angled step 30 is formed radially on the
inside on those portions of the piston part 12 which are located
between the ducts 26. By means of this step 30, the adjacent second
piston part 14 is surrounded on its end face 32 there, over its
entire outer circumference 34, by the first piston part 12. The
surround is in this case configured both positively and
nonpositively, in that the first piston part 12 has been pressed
axially onto the second piston part 14.
[0031] As already mentioned above, the second piston part 14 has
itself a circular-cylindrical configuration and in this case is
produced from a high-strength and at the same time very lightweight
ceramic material. In this case, when the associated pump element is
in operation, the end face 36, lying opposite the end face 32, of
the second piston part 14 serves for pushing the pump piston 10 by
means of an eccentric, not illustrated, which rotates there.
* * * * *