Reservoir with integrally formed window and method of making same

A master cylinder reservoir molded of glass fiber filled nylon. An integrally molded window in a side wall is thinner than the reservoir walls and has a lower concentration of fibers so that it is sufficiently translucent to permit visual determination of the level of hydraulic brake fluid in the reservoir by observation through the window. The method of making the reservoir by molding, in which the flow of fibers into the window section is restricted to reduce the fiber concentration in the window and make it more translucent, is also disclosed.

The invention relates to a liquid reservoir with a window integrally formed 
in a side wall so that the level of liquid in the reservoir can be 
visually determined by observing the liquid level through the window. The 
invention also relates to the method of making the reservoir with the 
integrally formed window. 
It has been considered desirable for some years to provide some means of 
indicating the level of fluid in reservoirs, and particularly in brake 
master cylinders for automotive vehicles. Numerous types of indicators 
have been proposed and utilized. Some indicators utilized a magnetically 
operated switch which is closed when the fluid level reaches a low limit 
requiring warning to the vehicle operator. Thermistor probes have also 
been utilized in a similar manner. Glass sight gages have been installed 
in a side wall of the master cylinder so that the liquid level may be 
visually determined through the sight gage. Typically such sight gages are 
threaded into an opening formed in the cylinder wall and sealed against 
leakage. Plastic reservoirs made of polypropylene or polyethylene have 
been utilized primarily on automotive vehicles made for the European 
market. Such reservoirs are transparent or translucent throughout the 
reservoir body and the level of liquid therein can be observed. Reservoirs 
have also been provided with sight gages extending from the main reservoir 
housing and connected so that the fluid level in the reservoir is also 
found in the sight gage. Such sight gages are typically glass or plastic 
tubing connected by a short length of piping or tubing to the reservoir. 
It is well known to mount glass or other transparent material in the side 
wall of a reservoir, often providing graduation markings on the glass to 
indicate the liquid level. 
It has been found that polypropylene and polyethylene reservoirs are usable 
in vehicles where the engine compartment temperatures remain sufficiently 
low so as not to cause adverse effects on the plastic. However, engine 
compartment temperatures on some automobiles, and particularly on those 
with larger engines and several engine driven accessories, tend to exceed 
the limit for use of such materials in the engine compartment. It has 
therefore been found to be desirable, when using a plastic type reservoir, 
to utilize a plastic such as nylon which has a much higher usable range of 
temperature. It has also been found to be advisable to utilize a 
reinforcing or strengthening agent in the nylon. Such an agent may be a 
fiber filling. Glass fibers have been found to be very acceptable for this 
purpose. The problem with regard to fluid liquid indication in the use of 
such materials is that the reservoir no longer is sufficiently translucent 
to be able to observe the level of the fluid in the reservoir through any 
portion of the reservoir side wall. This then requires a fluid level 
indicator to be provided which operates satisfactorily even though the 
reservoir housing is not translucent. Several of the types of indicators 
noted above can still be used, but have been found to be more expensive 
and also less reliable than a visual indication through the reservoir side 
wall. The use of sight gages or window inserts create the potential for 
leakage and damage which is not found if the reservoir is provided with an 
integral translucent area. 
It is therefore an object of this invention to provide a one-piece 
reservoir housing having an integrally formed window in a housing side 
wall which is sufficiently translucent, even though the major portion of 
the reservoir housing is not sufficiently translucent, to visually 
determine the level of liquid in the reservoir by observation of the 
liquid level through the window. The invention also involves the method of 
making such a reservoir.

The master cylinder assembly 10 includes a cylinder housing 12 and a brake 
fluid reservoir 14. The cylinder housing has bosses 16 and 18 formed 
thereon which provide for the mounting of the reservoir on the cylinder 
housing and also provide for transmission of brake fluid between the 
reservoir and the master cylinder housing. The reservoir housing 20 has a 
bottom wall 22 from which integrally molded spigots 24 and 26 extend 
downwardly. These spigots are received through grommets 28 and 30 and snap 
into place in the upper ends of the passages formed through bosses 16 and 
18. The reservoir housing 20 also has side walls. The forward side wall 
32, the rear side wall 34, and one of the lateral side walls 36 are shown 
in FIG. 1. A cover 38 is suitably secured to the reservoir housing 20. 
The housing side wall 36 has a window 40 integrally formed therein and 
extending vertically a sufficient distance to cover the usual range of the 
level of the hydraulic fluid contained within the reservoir. The window 40 
is an integrally formed part of the housing 20 and is made during the 
molding process at the same time as the remainder of the housing. 
A reinforcement member or bead 42 extends laterally outward from the outer 
surface 44 of the side wall 36 and surrounds the window 40. A gage mark 
46, illustrated as being formed as a part of the reinforcement member 42 
and extending to either side thereof at about the middle portion of window 
40, is also provided on the outer surface 44 of the housing side wall 36. 
A suitable legend may be provided to indicate the meaning of the gage mark 
46. In the illustration in the drawing, the gage mark 46 indicates the 
minimum fluid level desired within the reservoir 14. 
The outer surface 48 of the window 40 is recessed within the reinforcement 
member 42 so that the reinforcement member will also function to protect 
the window from exterior contact by tools or debris, for example. The 
window inner surface 50 is continuous with the inner surface 52 of the 
side wall 36. As seen in FIGS. 2 and 3, the fluid level 54, indicated by 
the free surface of the hydraulic fluid in the reservoir, may be located 
so that it is along a portion of the window inner surface 50. Since the 
master cylinder assembly 10 is of the dual master cylinder type, the 
reservoir 14 is illustrated as also having a divider 56 separating the 
reservoir into front and rear chamber sections. The divider 56 is seen in 
FIG. 3. 
The reservoir 14 is made of a plastic with discrete particle filling. The 
plastic is preferably nylon and the discrete particles providing the 
filling are fibers which are preferably glass fibers. The fibers act as a 
strengthening or reinforcing agent. One of the problems in establishing a 
direct observation fluid level indicating device of this type occurs when 
some plastics are utilized which are not as translucent as might be 
desired. The use of the discrete particles also add to the problem by 
decreasing translucence. This is true of glass fiber as used in a mixture 
with nylon to form the reservoir housing 20. It is therefore desirable to 
provide a lower concentration of fibers in the material forming the window 
40 as compared to the concentration found in the mixture introduced into 
the mold as the housing is made. The concentration of fiber in the housing 
side and bottom walls is preferably substantially the same as the 
concentration found in the mixture introduced into the mold for making 
this housing. Translucence of the window 40 is also obtained by making the 
window of a much thinner section as compared to the thickness of the 
housing walls. This is clearly illustrated in FIG. 3. When the mold for 
making the housing is provided, one of the mold elements forming and 
defining the outer surface 44 of side wall 36 as well as the outer surface 
48 of the window 40 is positioned relative to the mold element defining 
the window inner surface 50 and the side wall inner surface 52 to provide 
a cavity area for molding a thin window cross section, and cavity areas 
for molding thick wall cross sections. The mixture of nylon and fiber 
filling introduced into the mold is such that the fiber filling will flow 
with the nylon into the wider cavity areas without any substantial 
restrictions so as to define the various walls as well as the spigots 24 
and 26. However, the restriction between the mold sections in the area of 
window 40 is such that the fibers do not flow as readily into the cavity 
area which defines the window 40. Therefore the concentration of fibers in 
the material forming the window 40 during the molding process is 
substantially less than the concentration of fibers found in other parts 
of the housing, and the window is predominantly nylon. Relatively thin 
window sections and the absence of much of the fiber filling in the window 
section contribute to the light transmittal capability of the window and 
renders it sufficiently translucent to permit the level of liquid 
contained within the reservoir housing to be visually determined by 
observation through the window. Thus the window 40 is molded concurrently 
as the reservoir housing is molded, is made of the same material, and has 
desirable light transmittal characteristics which are not found in the 
thicker housing walls, and particularly in the walls because of the 
concentration of fiber filling therein.