FORM 2
THE PATENTS ACT 1970
[39 OF 1970]
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[see section 10 and rule 13]
"A COMBINATION OF ZINC TRIVALENT COATED STEEL EN1 MATERIAL PISTON WITH ALUMINIUM WHEEL CYLINDER"
Name and address of Applicant:
TATA MOTORS LIMITED, Bombay House, 24 Homi Mody Street, Hutatma Chowk, Mumbai - 400 001, Maharashtra, India.
Nationality: INDIAN
The following specification particularly describes the invention and the manner in which it is to be performed.

TECHNICAL FIELD
Present disclosure relates to Combination of Zn trivalent coated steel EN1 material piston with aluminum wheel cylinder. The present disclosure relates more particularly towards corrosion resistance by plating of steel piston with Zn trivalent and usage of the Zn plated piston in combination with aluminum wheel cylinder.
BACKGROUND OF THE DISCLOSURE
Brake system uses drum brake generally in rear wheels of the vehicle. This brake assembly has wheel cylinder as major part which actuates the brake shoes against the rotating brake drum to generate deceleration. This invention is evolved from the study and work done on designs having blackodizing on steel piston, being used in aluminum wheel cylinder. Though blackodizing is used as surface protection but it has been experienced that, whenever there is moisture like situation and vehicles are stored for long period the steel piston absorbs the moisture and therefore the steel piston gets corroded generating the red rust. This red rust is trapped between wheel cylinder and piston which causes friction initially and then further deteriorates the piston surface in working condition. The deteriorated surface again accelerates the corrosion and eventually blocks the piston movement in the aluminum cylinder.
The corrosion is a chronic issue in hydraulic cylinders used in the brake system of vehicles which impede the performance partially to nearly 100%. The corrosion takes place on the piston outer surface which is exposed to the environment. The moisture in the environment reacts with piston made of steel and rust is generated. This rust gets accumulated in the system in due course of time and as a result it does not allow the piston to move in the cylinder freely during brake application and release. In situation of the restricted movement of piston on application and release of brake causes reduction in performance of the complete brake system, and this problem also at times causes brake jamming. The effect of corrosion is detrimental to the performance and safety of the vehicle. To meet the low cost requirement chemical blackening on steel piston is being normally chosen for low cost production vehicle, these blackodized pistons deteriorates very fast in high humid condition specifically in coastal area. The level of deterioration is in such magnitude that it stops the function and stuck in wheel cylinder, caused drop in overall brake performance of the vehicle.

Though, the use of high cost nickel plating is very good in corrosion resistance however is not suitable for low cost high volume production due to high cost. There are various combination of the materials used in wheel cylinders and pistons available with corrosion preventive coating which are costly and not feasible as cost effective solution.
Therefore, there exists a need in the art, to provide a cost effective corrosion preventive coating solution.
OBJECTS OF THE DISCLOSURE
One object of instant disclosure is to address corrosion problem by using a combination of Zn trivalent plated EN1 steel piston with aluminum wheel cylinder.
One object of the present disclosure is a wheel cylinder assembly for drum brake comprising an aluminium body provided with a bore, a fluid conduit provided on circumference of the aluminium body to pass brake fluid to the bore, atleast one Zinc chromate coated steel pistons disposed inside bore of the aluminium body, wherein said pistons are configured to slide outwardly in opposite directions when brake is applied; and a preloaded spring connected to opposite ends of the steel pistons for retracting said pistons when brake is released.
One object of the present disclosure is a drum brake system comprising a wheel cylinder assembly as described above.
SUMMARY OF THE DISCLOSURE
The shortcomings of the prior art are overcome and additional advantages are provided through the provision as claimed in the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.
In an embodiment of the present disclosure, a wheel cylinder assembly for drum brake comprising an aluminium body provided with a bore, a fluid conduit provided on circumference of the aluminium body to pass brake fluid to the bore, atleast one Zinc chromate coated steel pistons disposed inside bore of the aluminium body, wherein said pistons are configured to slide outwardly in opposite directions when brake is applied and a

preloaded spring connected to opposite ends of the steel pistons for retracting said pistons when brake is released.
In another embodiment of the present disclosure wherein, adeast one bleed screw is provided in the wheel cylinder assembly for removing trapped air.
In another embodiment of the present disclosure wherein, plurality of rubber seals are provided on circumference of the pistons.
In another embodiment of the present disclosure wherein, the bore is a longitudinal bore.
In another embodiment of the present disclosure wherein, plurality of rubber boots are provided at either ends of wheel cylinder to prevent entry of foreign particles into the cylinder.
In another embodiment of the present disclosure wherein, the zinc chromate is Zinc trivalent chromate or Zinc hexavalent chromate.
In another embodiment of the present disclosure wherein, a drum brake system comprising a wheel cylinder assembly as claimed in claim 1.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
The features of the present disclosure will become more fully apparent from the following description taken in conjunction with the accompanying drawings. Understanding that the drawings depict only several embodiments in accordance with the disclosure and are therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings:
Figure 1 shows reference photographs of corroded pistons having chemical blackening surface treatment.
Figure 2 illustrates the brake drum assembly.
Figure 3 illustrates the wheel cylinder assembly.
Figure 4 illustrates the comparison of salt spray test results for various zinc coatings.
Figure 5 illustrates Salt spray test as per DIN 50 021 SS.

The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DETAILED DESCRIPTION OF DISCLOSURE
The instant proposed solution addresses the corrosion issue of steel piston in combination with aluminum wheel cylinder body. The present disclosure describes about plating of steel piston with Zn trivalent and using it in combination with aluminum wheel cylinder to address the corrosion issue.
This innovation describes the combination of steel EN1 piston material with Zn trivalent plating in aluminum wheel cylinder used in brake system. The present innovative combination prevents the corrosion in severe environmental conditions. The use of Zn trivalent plated steel piston in aluminum cylinder is unique combination used in the proposed solution which acts as a resistance to corrosion which tends to happen in condition of high humidity atmosphere.
In another embodiment of the present disclosure, the process of plating Zn trivalent on Steel piston involves the following steps:
i) The surface of the wheel cylinder piston is cleaned in alkaline detergent type
solutions, and it is followed by treatment with acid, in order to remove any rust or
surface scales; ii) Zinc is the connected as an anode, and the wheel cylinder piston is connected as a
cathode; iii) Zinc is then deposited on the wheel cylinder piston surface by immersing it in an
Alkaline-Zinc bath containing dissolved zinc; iv) a DC electric current is applied, which results in zinc being deposited on the
cathode; v) the zinc coated piston is then immersed in a solution of 182 g/l sodium dichromate
crystals (Na2Cr2O7.2H2O) and 6 ml/1 concentrated sulfuric acid at room
temperature for a time period ranging from about 5 seconds to about 10 seconds; vi) an oxidation-reduction reaction occurs on the metal surface with the formation of
substrate metal ions and trivalent chromium ions.

vii)an accompanying increase in the pH of the solution immediately adjacent to the metal surface results in the precipitation of a gelatinous film, comprised largely of chromic hydroxide, and in which soluble chromares are incorporated; and
viii) the piston is then rinsed and dried by heating up to about 70 °C.
The chromates can be either clear blue, bright yellow, opaque, black and organic. The present disclosure has made use of yellow chromate for the wheel cylinder piston.
In another embodiment of the present disclosure, in addition to Zinc trivalent chromate (ZnCr3) even Zinc hexavalent chromate (ZnCr6) can also be used.
in another embodiment of the present disclosure, the figures are depicted herein only for illustrative purposes and are not to be considered to be limiting the scope of the instant disclosure.
In an another embodiment of the present disclosure, referring to the figure 2, the drum brake assembly comprises; brake drum which rotates with the wheel two brake shoes (1) which are mounted on a stationary brake plate. The brake shoes are pivoted on one end (3) and connected to the wheel cylinder (5) at the other end. When the brakes are applied, the pressurized brake fluid acts on the pistons in the wheel cylinder to push the brake shoes (1) outward against the drum. The friction linings are bonded on the brake shoe. The friction between the friction material on brake shoes and the brake drum creates a braking torque which slows down the vehicle. The return spring (4) pulls back the brake shoes away from the surface of the brake drum when the brakes are released.
In another embodiment of the present disclosure, referring to the figure 3, the wheel cylinder assembly has seven major parts. When brake is actuated due to pressure build, wheel cylinder piston (2) move inside the wheel cylinder (1) and expands the brake shoes connected against the brake drum to apply the brake. Rubber boot (5) prevents dust entry into piston (2) glide path on wheel cylinder (1). Bleed screw (7) helps to remove air trapped inside the wheel cylinder (1). Number of pistons does not impose any restriction on the invention. One design the brake assembly with one or more pistons.

The reference numerals of the components of figure 3 are as follows:

Referral Numerals Description
1 Aluminium wheel cylinder body
2 ZnCr3 coated steel piston - 2Nos.
3 Rubber piston pressure seal - 2 Nos.
4 Steel insert - 2 Nos.
5 Rubber Boot - 2 Nos.
6 Springs - 1 No.
7 Bleed Screw-2 Nos.
The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.
The primary focus of the present disclosure is the ZnCr3 coating on steel piston (EN1) working in combination with aluminum cylinder under brake fluid.
When two different materials are operating together, especially a cylinder and piston arrangement, corrosion of either piston or cylinder or both is more contributed by Galvanic effect between the materials of piston, cylinder and working medium.
In another embodiment of the present disclosure, it is established that, the ZnCr3 coating can be used for rust prevention on steel piston (EN1) in combination with aluminum wheel cylinder working continuously under brake fluid.
Example 1:
In another embodiment of the present disclosure, apart from the above combinations, Tin-Zinc, Zinc-Nickel, and Zinc-Iron alloys are also being used for corrosion resistance.

Salt spray test was conducted on blackodised piston and ZnCr3 coated piston. Red rust is observed on blackodised piston after 1 hour, whereas in ZnCr3, red rust observed after 230 hrs.
Apart from Zinc, other metal coating such as Chrome, Nickel and processes such Sintered Nitro carburizing is used on steel surface to provide corrosion resistance. The graph as illustrated under Figure number 5 shows the comparison of salt spray test results for various such coatings and processes.
EQUIVALENTS
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.
It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should typically be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention

analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, eithei of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."
In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.
While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

We Claim:
1. A wheel cylinder assembly for drum brake comprising:
an aluminium body provided with a bore:
a fluid conduit provided on circumference of the aluminium body to pass brake fluid
to the bore;
atleast one Zinc chromate coated steel pistons disposed inside bore of the aluminium
body, wherein said pistons are configured to slide outwardly in opposite directions
when brake is applied; and
a preloaded spring connected to opposite ends of the steel pistons for retracting said
pistons when brake is released.
2. The wheel cylinder assembly as claimed in claim \, wherein atleast one bleed screw is
provided in the wheel cylinder assembly for removing trapped air.
3. The wheel cylinder assembly in claim 1, wherein plurality of rubber seals are provided on circumference of the pistons.
4. The wheel cylinder assembly as claimed in claim 1, therein the bore is a longitudinal bore.
5. The wheel cylinder assembly as claimed in claim 1, wherein plurality of rubber boots are provided at either ends of wheel cylinder to prevent entry of foreign particles into the cylinder.
6. The wheel cylinder assembly as claimed in claim 1, wherein the zinc chromate coated steel pistons is Zinc trivalent chromate or Zinc hexavalent chromate.
7. A drum brake system comprising a wheel cylinder assembly/as claimed in claim 1.