Piston for a piston pump with a two part inlet valve body

The invention relates to a piston, through which a fluid can flow, for a piston pump, which piston has a longitudinal bore into which a spring-loaded inlet valve body is inserted. In order to be able to bring a helical compression spring, which loads the inlet valve body, to bear against an annular shoulder in the longitudinal bore and to be able to check and if necessary improve its seating after installation, the invention proposes to produce the inlet valve body in two parts comprising the inlet valve disk and the inlet valve stem and to join these two parts to one another after the helical compression spring has been correctly inserted into the piston. The inlet valve disk can for example be joined to the inlet valve stem by ultrasonic welding, thermoplastic riveting or screwing.

PRIOR ART 
The invention relates to a piston, through which a fluid can flow, for a 
piston pump which has an inlet valve arranged in the piston, as set forth 
hereinafter. 
In German Patent Application P 43 20 902.5 a piston pump is described which 
has a piston of this type having a longitudinal bore through which a fluid 
can flow and into which an inlet valve body is inserted. An inlet valve 
disk is pressed sealingly by an inlet valve spring, which acts on an inlet 
valve stem integral with the inlet valve disk and is supported against an 
annular shoulder in the longitudinal bore of the piston, against an inlet 
valve seat which is situated on a front end face of the piston and leads 
into the longitudinal bore of the piston. The inlet valve spring is a 
conically coiled helical compression spring and is joined to the inlet 
valve stem for rotation therewith. The annular shoulder on which the inlet 
valve spring is supported has projections projecting radially inwards or 
an opening in the form of a helical flute to mount the inlet valve spring: 
the inlet valve body consisting of the inlet valve stem integral with the 
inlet valve disk is introduced, with the inlet valve stem foremost, into 
the longitudinal bore of the piston, while being turned at the same time. 
In this movement the inlet valve spring engages on the projections or in 
the helical flute-shaped opening of the annular shoulder and is "screwed 
in" by the turning movement until it lies with its widened end against a 
side of the annular shoulder facing away from the inlet valve seat. 
This design and this mounting of the inlet valve has the disadvantage that 
during installation the inlet valve spring is masked by the inlet valve 
disk and therefore cannot be seen. Its seating on the annular shoulder 
cannot be checked after the inlet valve has been installed in the piston. 
This is so-called blind installation. This kind of installation results in 
a relatively high fault and failure rate. 
ADVANTAGES OF THE INVENTION 
In comparison therewith the piston according to the invention, which has a 
two-part inlet valve body consisting of the inlet valve stem and the inlet 
valve disk, has the advantage that the inlet valve stem together with the 
inlet valve spring can first be inserted into the longitudinal bore of the 
piston before the inlet valve disk is joined to the inlet valve stem. 
During insertion into the piston the inlet valve spring is not masked by 
the inlet valve disk, but can be seen and its seating on the annular 
shoulder in the longitudinal bore of the piston can be checked after 
installation. The inlet valve spring is also accessible from the front end 
face of the piston as long as the inlet valve disk has not yet been fitted 
onto the inlet valve stem. Correct seating of the inlet valve spring can 
be achieved before the inlet valve disk is fitted onto the inlet valve 
stem. Poor seating of the inlet valve spring resulting from incorrect 
installation can be very largely eliminated, so that failures of the 
piston according to the invention are avoided. 
Through the welding or riveting of the inlet valve disk to the inlet valve 
stem a nondetachable connection is obtained, which even in continuous 
operation will not be detached by vibrational and shock loads. 
Thermoplastic riveting or ultrasonic welding of the inlet valve disk to the 
inlet valve body enables a durable connection of this kind to be made in a 
simple manner and inexpensively. The inlet valve stem and/or the inlet 
valve disk consist in this case of a thermoplastic material. A light inlet 
valve body is obtained.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
The piston pump 10 shown in FIG. 1 is intended for a slip-controlled brake 
system (ABS) for motor vehicles. It has a piston 12 guided longitudinally 
in a cylinder 14. For the purpose of driving the piston 12 a rotationally 
drivable eccentric (not shown) is provided, a peripheral surface of which 
presses against an outer or rear end face 16 of the piston 12 and pushes 
the latter into the cylinder 14 for a working stroke. A circumferential 
groove 18 on a rear end, projecting out of the cylinder 14, of the piston 
12 is provided for the engagement of a spring element, which is likewise 
not shown and which pulls the piston 12 out of the cylinder 14 for an 
induction stroke and holds the piston 12 bearing against the eccentric. 
The cylinder 14 is inserted into a casing 20 of a hydraulic unit of a 
slip-control installation. At its front end remote from the piston drive 
it is closed by a closure cap 22. The cylinder 14 is held in the casing 20 
by means of a screw-in stopper 24. 
In a pump outlet 25 is arranged a nonreturn valve 26 provided with a valve 
ball 28 pressed sealingly, by a helical spring 30 supported against the 
closure cap 22, against a valve seat 32 facing away from a pump chamber 
34. 
The piston 12 has an inlet valve 36, which is likewise in the form of a 
nonreturn valve. For this purpose said piston is provided with a stepped 
longitudinal bore 38 starting from its front end face situated in the 
cylinder 14 and ending approximately in the middle of the piston. The 
longitudinal bore 38 is in communication with a pump inlet 42 via a 
transverse bore 40 at the end of the longitudinal bore 38 in the interior 
of the piston. At the front end face of the piston 14 the longitudinal 
bore 38 leads out via a conical valve seat 44 into the pump chamber 34. 
An inlet valve body 50 consisting of an inlet valve disk 46 and an inlet 
valve stem 48 is received in the longitudinal bore 38 of the piston 12. 
The inlet valve disk 46 has a sealing surface 52 having the shape of a 
spherical segment and also four guide projections 54 which are arranged 
radially and are situated in front of the front end face of the piston 12 
and by means of which the inlet valve body 50 is guided and centered in 
the cylinder 14. 
The inlet valve stem 48 projects into the longitudinal bore 38 of the 
piston 12 without touching the piston 12. The valve stem has a 
constriction 56 with which an approximately conically coiled helical 
compression spring 58 engages by its end of smaller diameter. By its end 
of larger diameter the helical compression spring 58 is supported against 
an annular shoulder 59, which is formed by a side, facing away from the 
valve seat 44, of an inwardly projecting flange 60 in the longitudinal 
bore 38 of the piston 12. The flange 60 is situated closer to the front 
end of the piston 12 than the constriction 56, so that the sealing surface 
52 of the inlet valve disk 46 is held in sealing contact with the valve 
seat 44 of the piston 12 by means of the helical compression spring 58. 
The annular shoulder 59 may also be formed in a different way, for example 
by means of a circlip which is inserted into a groove cut in the 
longitudinal bore 38 (not illustrated). 
An end portion 62 bent over in the longitudinal direction at the end of 
smaller diameter of the helical compression spring 58 engages in a 
longitudinal groove 64 in the inlet valve stem 48 and the end of smaller 
diameter of the helical compression spring 58 is thereby held fast on the 
inlet valve stem 48 for rotation therewith. 
At its end situated in the interior of the piston the inlet valve stem 48 
is extended by a pin 66 as far as the transverse bore 40 of the piston 12. 
For installation purposes the inlet valve body 50 is composed of two parts, 
comprising the inlet valve stem 48 and the inlet valve disk 46. Various 
possible connections joining the inlet valve disk 46 to the inlet valve 
stem 48 are illustrated as examples in FIGS. 2a, 2b, 3 and 4 and are 
explained below. For identical parts use is made of reference numerals 
corresponding to FIG. 1. 
FIGS. 2a and 2b show an ultrasonic welding connection before welding (FIG. 
2a) and during welding (FIG. 2b). Both the inlet valve disk 46 and the 
inlet valve stem 48 are made of a thermoplastic material in this 
embodiment of the invention. The inlet valve disk 46 has an axial bore 68, 
which is cylindrical over a short length and thereupon widens conically in 
the direction of a side facing away from the piston 12. The inlet valve 
disk 46 is pushed onto the inlet valve stem 48. The inlet valve stem 48 is 
substantially cylindrical in shape in the region onto which the inlet 
valve disk 46 is pushed on. In the insertion region it has circumferential 
beads 70 as welding projections. 
From its end carrying the valve disk the inlet valve stem 48 is provided 
with an axial blind hole 72, the bottom of which is rounded. 
The ultrasonic welding of the inlet valve disk 46 to the inlet valve stem 
48 is illustrated in FIG. 2b: the conical tip 74 of a so-called sonotrode, 
that is to say a tool for ultrasonic welding, is introduced into the the 
blind hole 72 of the inlet valve stem 48 and excited to vibrate in the 
ultrasonic frequency range. The vibration may be torsional vibration. That 
end of the inlet valve stem 48 which is inserted into the inlet valve disk 
46 is thereby conically expanded and comes to bear against the conically 
expanding part of the bore 68 in the inlet valve disk 46. Excitation to 
vibration using ultrasonic frequency leads to a relative movement between 
the inlet valve stem 48 and the inlet valve disk 46, and this movement 
brings about the welding of the two parts 46, 48 to one another. During 
the welding the inlet valve stem 48 is supported by means of its pin 66 
against an arbor (not shown), which for this purpose is inserted into the 
transverse bore 40 of the piston 12 (FIG. 1, the piston is situated 
outside the cylinder 14 during welding). 
In the embodiment illustrated in FIG. 3 the inlet valve disk 46 is 
thermoplastically riveted to the inlet valve stem 48. The inlet valve stem 
48 is once again composed of a thermoplastic material, and the inlet valve 
disk 46 may likewise consist of a thermoplastic material; in the example 
described it is made of metal (steel). An axial bore in the inlet valve 
disk 46 narrows from the stem side in stepped form and thus forms an 
annular locating surface 76 for the inlet valve stem 48. From that point 
the bore 74 widens conically to receive a rivet head. 
The inlet valve stem 48 merges integrally at its end on the valve disk side 
into a pin 78 which, when the inlet valve disk 46 has been fitted onto the 
inlet valve stem 48, projects out of said disk on the side facing away 
from the stem (dashed lines in FIG. 3). With the aid of a heated 
head-forming dolly (not shown) this pin is converted into a rivet head, 
whereby the inlet valve disk 46 and the inlet valve stem 48 are joined to 
form the inlet valve body 50. In the case of thermoplastic riveting the 
inlet valve stem 48 is also supported by means of its pin 66 against the 
arbor (not shown), which is inserted into the transverse bore 40 of the 
piston 12. 
In the exemplary embodiment of the invention illustrated in FIG. 4 the 
inlet valve disk 46 is screwed to the inlet valve stem 48: the inlet valve 
stem 48 has in its end face a threaded blind bore 80, into which a 
countersunk screw 82 holding the valve disk 46 is screwed. As in the 
exemplary embodiment illustrated in FIG. 3, the inlet valve disk 46 is 
provided with a stepped axial bore 84, which has an annular locating 
surface 86 for the inlet valve stem 48 and a conical countersink 88, on 
the side facing away from the valve stem, to receive a screw head 90. The 
pairing of materials for the inlet valve disk 46 and the inlet valve stem 
48 can be selected from a multiplicity of materials in the case of the 
screwed embodiment. 
The one-piece design of the piston 12 makes it necessary to introduce the 
inlet valve body 50 together with the helical compression spring 58 into 
the longitudinal bore 38 of the piston 12 from the front end face. This is 
done in the following manner. 
The helical compression spring 58 is first mounted on the inlet valve stem 
48, which has not yet been joined to the inlet Valve disk 46, by inserting 
its end of smaller diameter into the constriction 56 of the inlet valve 
stem 48. No means preventing rotation between the inlet valve stem 48 and 
the helical compression spring 58 is required, because the helical 
compression spring is accessible from the front end face of the piston 
during installation in the piston 12 and therefore can be brought to bear 
against the annular shoulder 59 of the piston 12. In the examples 
described, security against rotation is nevertheless achieved in that the 
end part 62 at the end of smaller diameter of the helical compression 
spring 58 is bent over parallel to the axis and inserted into the 
longitudinal groove 64 of the inlet valve stem 48. 
For the installation of the inlet valve a mandrel (not shown) is inserted 
through the transverse bore 40 of the piston 12, which has not yet been 
introduced into the cylinder 14, and thereupon the inlet valve stem 48 
together with the helical compression spring 58 is introduced into the 
longitudinal bore 38 of the piston 12 from the front end face of the 
piston. Since the inlet valve disk 46 is not yet mounted on the inlet 
valve stem 48, the helical compression spring 58 is freely accessible from 
the front end face of the piston and can be brought to bear against the 
annular shoulder 59, against which it is supported. The helical 
compression spring 58 presses the inlet valve stem 48 into the interior of 
the piston and, by means of its pin 66, against the arbor (not shown), 
which has been inserted into the transverse bore 40 of the piston 12. 
To make installation easier, the inwardly projecting flange 60 is provided 
in the exemplary embodiments with a snug 92 (FIGS. 2 and 3) projecting 
radially inwards or with an opening 94 in the form of a helical flute 
(FIG. 4). Turning the inlet valve stem 48 during its introduction into the 
longitudinal bore 38, with the helical compression spring 58 joined to and 
rotating with it, has the effect of bringing the helical compression 
spring 58 to bear against the projection 92 or into the opening 94, so 
that it is "screwed" into the longitudinal bore 38 until it has completely 
passed the flange 60 and bears against the annular shoulder 59 of the 
latter. The seating of the helical compression spring 58 against the 
flange 60 can be checked, and if necessary improved, as long as the inlet 
valve disk 46 has not yet been fitted. 
As soon as the helical compression spring 58 has been inserted in the 
prescribed manner into the longitudinal bore 38, the inlet valve disk 46 
can be joined to the inlet valve stem 48 as described in connection with 
FIGS. 2 to 4. By means of its pin 66 the inlet valve stem 48 is supported 
for that purpose against the arbor (not shown) inserted into the 
transverse bore 40 of the piston 12. 
After the inlet valve disk 46 has been joined to the inlet valve stem 48, 
mandrel (not shown) is withdrawn from the transverse bore 40 of the piston 
12, and the piston 12 can then be inserted into the cylinder 14. 
The foregoing relates to preferred exemplary embodiments of the invention, 
it being understood that other variants and embodiments thereof are 
possible within the spirit and scope of the invention, the latter being 
defined by the appended claims.