Method for producing pressure plates used in hydraulic pumps

Method for producing a pressure plate used in a hydraulic pump by connecting first and second plate sections together include the steps of pressing metal powders to individually form the first and second plate sections and a ring member into predetermined configurations, placing the first plate section properly on the second plate section while the ring member is inserted in a bore formed in the first plate section, placing brazing metal along the upper side diameter of the bore, and heating the first and second plate sections and the ring member so as to connect the first and second plate sections and the ring member together by the brazing metal and simultaneously sintering the same.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method for producing a pressure plate 
used in a hydraulic pump, and more particularly to a method for producing 
a pressure plate used in a hydraulic pump by connecting two plate sections 
together. 
2. Description of the Prior Art 
In a conventional hydraulic pump having a pressure plate which includes two 
plate sections connected together, the pressure plate is provided with a 
plurality of ports through some of which fluid is sucked into expanding 
chambers of the hydraulic pump and through the rest of which fluid is 
discharged from chambers which are being compressed. Such a pressure plate 
is shown in FIGS. 1 and 2. A conventional method for producing the 
pressure plate employs the following steps. At first, a plate section 1A 
is formed with a pair of outlet ports 2 around which annular grooves 4 are 
formed on a side surface 3 of the plate section 1A and another plate 
section 1B is formed with a pair of ports 5. Next, the another plate 
section 1B is properly placed on the plate section 1A, while brazing metal 
6 is put in the annular grooves 4 and, then, the assembled pressure plate 
including the plate sections 1A and 1B is heated in a heating furnace (not 
shown) under pressure, so that the brazing metal 6 is melted and is forced 
to spread on the side surface 3 to thereby connect the plate sections 1A 
and 1B together. However, in the pressure plate produced in the 
conventional method, leakage between the plate sections 1A and 1B may be 
caused, since the amount of the brazing metal 6 is limited due to the 
small area where the groove 4 is formed and cannot be supplied on the 
surface 3 so much as to prevent leakage. Furthermore, the plate sections 
1A and 1B may suffer from distortion due to the pressure during the 
heating operation. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a new and 
improved method for producing a pressure plate used in a hydraulic pump by 
fluid-tightly connecting two plate sections together so as to prevent 
fluid leakage. 
Another object of the present invention is to provide a new and improved 
method for producing a pressure plate used in a hydraulic pump, which 
pressure plate includes two plate sections and is formed by brazing and 
sintering in a single heating operation. 
Briefly, according to the present invention, a method is provided for 
producing a pressure plate used in a hydraulic pump by fluid-tightly 
connecting first and second plate sections together, as mentioned below. 
Metal powders are first pressed so as to form the first and second plate 
sections and a ring member into predetermined configurations. The first 
and second plate sections are set in place, while the ring member is 
inserted in a bore formed in the first plate section so as to provide a 
fluid port in cooperation with a port formed in the second plate section. 
Brazing metal is placed along the upper side diameter of the bore. 
Finally, a heating operation is performed for fluid-tightly connecting the 
first and second plate sections and the ring member together by the 
brazing metal and for simultaneously sintering the same.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings and particularly to FIG. 3, reference numeral 
10 denotes a pump body which is formed with a chamber 11. A support member 
12 is secured to the open end of the pump body 10 and a rotor drive shaft 
13 driven by an automotive engine (not shown) is rotatably carried by the 
support member 12. In the chamber 11, a cam ring 14 and a pressure plate 
15 are slidably inserted and urged towards the support member 12 by a coil 
spring 16 inserted in the chamber 11. The cam ring 14 is formed with an 
internal cam surface 17 in which a pump rotor 19 is carried by the shaft 
13 through a spline connection therewith. The pump rotor 19 carries a 
plurality of vanes 18 which are free to move radially in following the 
internal cam surface 17 so as to constitute a plurality of pump chambers 
20 therebetween which are partitioned by the vanes 18. The pressure plate 
15 is formed by connecting two plate sections 15A and 15B together in 
accordance with the method of the present invention. The plate section 15A 
which contacts the side of the cam ring 14 is formed with a pair of 
admission ports 21 and a pair of discharge ports 22. The plate section 15B 
is formed with a channel 23 and a pair of bores 26 in each of which a ring 
member 25 having a hole 24 is inserted. A pressure chamber 30 is defined 
as a portion of the chamber 11. The pump body 10 is provided with a bypass 
port 34 and a supply port 35 for supplying fluid from a reservoir 36 
mounted on the hydraulic pump to the pump chambers 20 through the supply 
port 35, the bypass port 34, the channels 23 and the admission ports 21, 
and further with a port 32 and an orifice 31 for discharging pressurized 
fluid from the pump chambers 20 to the port 32 through the discharge ports 
22, the hole 24, the pressure chamber 30 and the orifice 31. A spool valve 
33 is provided in the pump body 10 for bypassing excessive flow from the 
pressure chamber 30 to the bypass port 34 in response to the pressure 
differential across the orifice 31 in a well known manner. 
The method according to the present invention for producing the pressure 
plate 15 is now described with reference to FIGS. 4 and 5. At first, each 
of the plate sections 15A and 15B and the ring member 25 is formed by 
pressing metal powders into its predetermined shape. The metal powders for 
producing the plate sections 15A and 15B and the ring member 25 consist of 
96.5% of iron, 2.0% of copper, 0.5% of carbon and 1% of other materials. 
The metal powders are pressed until the density thereof becomes 6.4 to 6.8 
g/cm.sup.3 for press-forming each of the plate sections 15A and 15B and 
the ring member 25. 
In the next step, the plate section 15B is properly set on the plate 
section 15A which is set horizontally and, then, the ring member 25 is 
inserted in the bore 26, wherein the diametetral clearance between the 
bore 26 and the ring member 25 is set from 0.05 to 0.1 mm so as to enable 
the melted brazing metal 28 to flow downwardly through the clearance 
during the subsequent heating operation. The diametral clearance is not 
limited to that range, but may vary depending upon various condition, such 
as, composition of the powdered metal or the brazing metal 26. 
Subsequently, powdered brazing metal 28 is placed along the upper side 
diameter of the bore 26 as shown in FIG. 4, and then, the assembled 
pressure plate 15 including the plate sections 15A and 15B and the ring 
member 25 is heated in a heating furnace for fluid-tightly connecting them 
together by the brazing metal 28 and for simultaneously sintering them. 
The powdered brazing metal is a nickel-base alloy including other 
materials, such as, manganese and copper. As the assembled pressure plate 
15 is heated and the brazing metal 28 is melted, the liquid metal 28 flows 
downwardly into the diametral clearance between the bore 26 and the ring 
member 25 and further into a connecting area 27 between the plate sections 
15A and 15B so as to fluid-tightly connect the plate sections 15A and 15B 
and the ring member 25 together and simultaneously sinter the same. The 
heating operation occurs at about 1,130.degree. C. for about 20 minutes, 
but it may vary depending on the size and the composite materials of the 
plate sections 15A and 15B and the ring member 25. Accordingly, the 
assembled pressure plate 15 is fixedly and fluid-tightly connected 
together so as to prevent fluid leakage between the channel 23 and the 
discharge ports 22. 
In the method of the present invention, it should be noted that the plate 
section 15A is connected to the plate section 15B by using the ring member 
25. Accordingly, amount of the brazing metal 28 is not limited but can be 
freely controlled, so that the plate sections 15A and 15B at the 
connecting area 27 can be reliably connected with a sufficient amount of 
the brazing metal 28 to thereby prevent fluid leakage. Furthermore, since 
no pressure is applied to the plate sections 15A 15B during the heating 
operation, such are free from distortion. 
Further, it should be noted that the brazing operation and the sintering 
operation are carried out in a single heating operation. Accordingly, 
production time can be reduced to that efficiency in production can be 
achieved. 
In this embodiment, powdered brazing metal 28 is used, however, it should 
not be limited to powder since a ring-shaped brazing metal of, for 
example, 2 to 3 mm in thickness can also be used. Further, the brazing 
process is not limited to furnace brazing but other processes, such as, 
induction brazing can be used in the method of the present invention. 
Obviously, many modifications and variations of the present invention are 
possible in the light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described.