Description:FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
&
THE PATENTS RULES, 1003
COMPLETE SPECIFICATION
[See section 10, Rule 13]

TITLE OF INVENTION
A HYDRAULIC SLAVE CYLINDER FOR ACTUATING A CLUTCH OF A VEHICLE

APPLICANT
Mahindra & Mahindra Limited, an Indian company, having its address at Mahindra Research Valley, Mahindra World City, Plot No:41/1, Anjur P.O., Chengalpattu, Kancheepuram District, Tamil Nadu – 603004, India

PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed.
FIELD OF THE INVENTION
[001] The present invention relates to a field of a transmission system of a vehicle. More particularly, the invention relates to a hydraulic clutch system of a vehicle.

BACKGROUND OF THE INVENTION
[002] A clutch is a transmission device that engages and disengages the transmission from the engine. The evolution from a cable-operated clutch system to a hydraulic clutch system marked a significant advancement in automotive technology, enhancing both performance as well as the user experience. The transition brought about improvements in terms of efficiency, reliability, and ease of operation.
[003] In the cable-operated clutch system, a mechanical cable connects a clutch pedal to a release fork, transmitting the force exerted by a driver's foot to disengage the clutch. While this system is functional, it has certain drawbacks. Over time, cables could stretch or fray, leading to a decrease in performance and potentially resulting in clutch engagement issues.
[004] The hydraulic clutch system, on the other hand, introduced a more sophisticated improved mechanism. Typically, the hydraulic clutch system includes a master cylinder, a slave cylinder, and a hydraulic line connecting both. The master cylinder, typically located near the clutch pedal, contains a hydraulic fluid. When the driver depresses the clutch pedal, it actuates the master cylinder to pressurize the hydraulic fluid. This pressurized fluid is then transmitted through the hydraulic lines to the slave cylinder, located near the clutch release mechanism. The slave cylinder used this hydraulic pressure to engage/disengage the clutch, providing a smoother and more responsive operation as compared to the cable system. This hydraulic mechanism offered several advantages. Firstly, it eliminated the issues associated with cable wear and stretching. Secondly, the hydraulic system reduced the pedal effort required to operate the clutch and also allowed for more precise control over the clutch engagement, enhancing the overall driving experience. Additionally, the hydraulic clutch system required less maintenance and offered increased durability compared to its cable-operated counterpart.
[005] A further development in hydraulic clutch systems was made which led to the introduction of the concentric slave hydraulic cylinders. In this design, the slave cylinder is integrated concentrically with the release bearing, creating a more compact and space-efficient arrangement. This design minimizes the moving parts and simplifies the installation process. The concentric slave hydraulic cylinder enhances clutch control and response even further, providing a seamless and efficient power transmission between the engine and the transmission.
[006] Typical concentric slave cylinder utilizes a single hydraulic chamber and piston arrangement to operate the clutch. It has been observed that as the clutch undergoes wear and tear over time, there is a consequential rise in the force needed on the pedal to disengage the clutch which is undesirable. This leads to a diminished level of comfort and efficiency during driving and further causes fatigue and inconvenience to a driver and thus renders the driving experience unpleasant. Further, due to worn-out clutch, an additional force is required to move the piston with increased pedal effort and due to which the components of the piston like seal, seal ring etc. exert an additional fluid force which poses the risks of fluid leakage and shortens the life span of the seal ring and the seal.
[007] Attempts to solve this problem have been made which included or suggested the implementation of self-adjusting clutches. However, these solutions failed to effectively mitigate the problems and adversely resulted into increased costs.
[008] Thus, there is a need for a slave hydraulic cylinder for actuating the clutch which may solve one or more aforesaid problems.

SUMMARY OF THE INVENTION
[009] In one aspect, a hydraulic slave cylinder for actuating a clutch of a vehicle is disclosed. The hydraulic slave cylinder comprises a housing. The housing having an outer hydraulic chamber and an inner hydraulic chamber. The inner hydraulic chamber being concentrically placed inside the outer hydraulic chamber. The outer hydraulic chamber and the inner hydraulic chamber being in fluid communication with each other. The hydraulic slave cylinder includes a primary piston. The primary piston is reciprocatably disposed inside the inner hydraulic chamber. The primary piston is configured to actuate the clutch. The hydraulic slave cylinder includes a secondary piston. The secondary piston being reciprocatably disposed inside the outer hydraulic chamber. The secondary piston operably engaged with the primary piston and configured to actuate the primary piston.
[010] In an embodiment, the primary piston includes a first end and a second end. The second end extends away from the first end. The first end being configured to be sealably and slidably disposed between cylindrical walls of the inner hydraulic chamber. The second end is configured to receive a clutch release bearing.
[011] In an embodiment, the primary piston includes an engagement member formed on a portion being adjacent to the second end. The engagement member is configured to extend outwardly from an outer surface of the primary piston.
[012] In an embodiment, the secondary piston includes a first end and a second end. The second end extends away from the first end. The first end is configured to be sealably and slidably disposed between cylindrical walls of the outer hydraulic chamber.
[013] In an embodiment, the second end of the secondary piston being configured to engage with one of the cylindrical walls of the inner hydraulic chamber in a fully retracted position of the secondary piston. The second end of the secondary piston being configured to engage with the engagement member of the primary piston in an actuating state of the secondary piston.
[014] In an embodiment, the secondary piston includes a detent formed on an outer surface of the secondary piston between the first end and the second end. The detent is configured to engage with an end of the cylindrical wall of the outer hydraulic chamber. The end is configured to restrain the secondary piston in a fully extended position of the secondary piston.
[015] In an embodiment, the primary piston has a larger reciprocating length than the secondary piston.
[016] In an embodiment, a portion of an outer surface of the housing being configured to receive a spring. The spring is adapted to be engaged with the clutch release bearing.

BRIEF DESCRIPTION OF THE DRAWINGS
[017] Reference will be made to embodiments of the invention, examples of which may be illustrated in accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Figure 1a illustrates a cross-sectional view of a hydraulic slave cylinder in a disengaged condition of a clutch being in a new condition, in accordance with an embodiment of the invention.
Figure 1b is a partial cross-sectional view of the hydraulic slave cylinder illustrating the flow fluid communication between the outer hydraulic chamber and the inner hydraulic chamber, in accordance with an embodiment of the invention.
Figure 2 illustrates an exploded view of cross-sectional view of the hydraulic slave cylinder shown in Figure 1a, in accordance with an embodiment of the invention.
Figure 3a illustrates a cross-sectional view of the hydraulic slave cylinder in an engaged condition of the clutch being in a worn-out condition, in accordance with an embodiment of the invention.
Figure 3b illustrates a cross-sectional view of the hydraulic slave cylinder in a partially disengaged condition of the clutch being in a worn-out condition, in accordance with an embodiment of the invention.
Figure 3c illustrates a cross-sectional view of the hydraulic slave cylinder in a disengaged condition of the clutch being in a worn-out condition, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION
[018] The present invention is directed towards a hydraulic clutch system and provides a concentric slave cylinder connected to a master cylinder of the hydraulic clutch system. The hydraulic cylinder incorporates dual hydraulic chamber(s) and dual piston(s) configuration to enhance responsiveness, control, and efficiency during clutch actuation in order to provide consistent pedal effort for operating the clutch even when the clutch is worn-out.
[019] Figure 1a illustrates a cross-sectional view of a hydraulic slave cylinder 100 in an engaged condition of a clutch (not shown), in accordance with an embodiment of the invention. The hydraulic slave cylinder 100 includes a housing 102. The housing 102 is constructed from durable and corrosion-resistant material. The housing 102 includes an outer hydraulic chamber 110 and an inner hydraulic chamber 130. The inner hydraulic chamber 130 being concentrically placed inside the outer hydraulic chamber 110. The outer hydraulic chamber 110 and the inner hydraulic chamber 130 being in fluid communication with each other. The fluid communication between the outer hydraulic chamber 110 and the inner hydraulic chamber 130 ensures that hydraulic fluid flows between these chambers 110, 130 to actuate the clutch.
[020] Figure 1b is a partial cross-sectional view of the hydraulic slave cylinder 100 illustrating the fluid communication formed between the outer hydraulic chamber 110 and the inner hydraulic chamber 130, in accordance with an embodiment of the invention. As shown, the housing 102 of the hydraulic slave cylinder 100 includes a main hydraulic passage (P) connected to a master cylinder (not shown) of the hydraulic clutch system. The main hydraulic passage (P) splits into a first hydraulic passage (Pa) and a second hydraulic passage (Pb). The first hydraulic passage (Pa) connects the outer hydraulic chamber 110 with the main hydraulic passage (P). Similarly, the second hydraulic passage (Pb) is configured to interconnect the inner hydraulic chamber 130 with the main hydraulic passage (P) and first hydraulic passage (Pa). Due to such configuration, the flow of the hydraulic fluid from the main passage (P) is directed towards the second hydraulic passage (Pb) when the clutch is in the new condition. The flow of the hydraulic passage from the second hydraulic passage (Pb) is directed towards the outer hydraulic chamber (110) if a primary piston 140 is displaced by a diaphragm spring of the clutch when the clutch is in worn out condition.
[021] Referring now to Figure 2, the housing 102 includes an outer hydraulic chamber 110 and an inner hydraulic chamber 130. The outer hydraulic chamber 110 is configured to receive a sealing member (S1), a sealing ring (R1) and a secondary piston 120. The inner hydraulic chamber 130 is configured to receive a sealing member (S2), a sealing ring (R2), and the primary piston 140. The primary piston 140 being configured to receive a clutch release bearing 150. A multicoil spring 160 is to be adapted on an engagement portion formed on an outer surface 103 of the housing 102. A spring ring 165 is adapted to be attached to a peripheral portion of a clutch release bearing 150 to engage with the engagement portion of the housing 102 for providing a spring action to the clutch release bearing 150 with respect to the hydraulic slave cylinder 100. The clutch release bearing 150 is configured to receive a stop ring 155.
[022] Referring back to Figure 1a, the housing 102 includes passages P, Pa, Pb (shown in Figure 1b) formed to operably connect the outer hydraulic chamber 110, the inner hydraulic chamber 130 and the master cylinder. The hydraulic slave cylinder 100 is configured to receive hydraulic lines/pipes extending from the master cylinder (not shown) of the hydraulic clutch system. The master cylinder is actuated by a clutch pedal disposed inside a vehicle cabin by a foot of a driver. The master cylinder is configured to multiply the pedal effort and supply a pressurised hydraulic fluid to the hydraulic slave cylinder 100 through the passages (P, Pa, Pb) for operating the clutch of the vehicle through the primary piston 140 and the secondary piston 120.
[023] The outer hydraulic chamber 110 being formed by spaced apart cylindrical walls 112, 116. The space between these cylindrical walls 112, 116 is configured to receive the hydraulic fluid and accommodate the components viz. the secondary piston 120, the sealing member (S1), the sealing ring (S2) etc. Similarly, the inner hydraulic chamber 130 being formed by spaced apart cylindrical walls 132, 136. The space between these cylindrical walls 132, 136 is configured to receive the hydraulic fluid and accommodate the components viz. the primary piston 140, the sealing member (S2), the sealing ring (R2) etc
[024] The primary piston 140 is reciprocatably disposed inside the inner hydraulic chamber 130. The primary piston 140 is configured to actuate the clutch. The primary piston 140 includes a first end 140a and a second end 140b. The second end 140b extends away from the first end 140a. The first end 140a being configured to be sealably and slidably disposed between the cylindrical walls 132, 136 of the inner hydraulic chamber 130. The second end 140b being configured to receive a clutch release bearing 150. The primary piston 140 includes an engagement member 142 formed on a portion being adjacent to the second end 140b. The engagement member 142 being configured to extend outwardly from an outer surface 141 of the primary piston 150. The primary piston 140 is connected to the clutch mechanism through the clutch release spring 150, and its movement influences the engagement of the clutch, allowing power transmission between the engine and the transmission system.
[025] The secondary piston 120 is reciprocatably disposed inside the outer hydraulic chamber 110. The secondary piston 120 includes a first end 120a and a second end 120b. The second end 120b extends away from the first end 120a. The first end 120a being configured to be sealably and slidably disposed between the cylindrical walls 112, 116 of the outer hydraulic chamber 110. The second end 120b of the secondary piston 120 being configured to operably engage with the engagement member 142 to actuate the primary piston 140. The secondary piston 120 assists the first piston 140 to actuate the clutch. Fluid communication between the inner hydraulic chamber 130 and the outer hydraulic chamber 110 is established through the first hydraulic passage (Pa) and the secondary hydraulic passage (Pb) formed in the housing 102 of the hydraulic slave cylinder 100. This configuration allows hydraulic fluid to flow between the chambers 110, 130 enabling coordinated movement of the primary and secondary pistons 140, 120 for clutch actuation.
[026] In an embodiment, once the clutch is worn out, a diaphragm spring of the clutch moves the clutch release bearing 150 axially and in a direction towards the primary piston 140. When the clutch release bearing 150 moves beyond a position, the engagement member 142 of the primary piston 140 contacts the second end 120b of the secondary piston 120.
[027] Due to such displacement of the primary piston 140 inside the inner hydraulic chamber 130, the hydraulic fluid flows from the inner hydraulic chamber 130 towards the outer hydraulic chamber 110 as both are connected via the second hydraulic passage (Pb). Due to such displacement of the hydraulic fluid and under the action of the pressurized fluid from the master cylinder, the hydraulic pressure increases inside the outer hydraulic chamber 110. When the clutch lever is pressed, the pressurised fluid flows more inside the outer hydraulic chamber 110 in comparison to the inner hydraulic chamber 130 which in turn moves the secondary piston 120 in a direction towards the clutch. In this condition, the secondary piston 120 while moving contacts the primary piston 140 and actuates the primary piston 140 to actuate the clutch. When the secondary piston 120 achieves its fully extended position, the movement of the secondary piston 120 is restrained by a detent 122 and thus cannot move further and the pressurised hydraulic flow coming from the master cylinder acts on the primary piston 140 as the clutch lever is still being pressed. From this position, the primary piston 140 extends to actuate the clutch.
[028] In an embodiment, due to presence of the outer hydraulic chamber, an additional hydraulic area increases inside the housing 102 of the hydraulic slave cylinder 100. The hydraulic ratio is calculated as follows:

Hydraulic Ratio = [(Hydraulic Area of the outer hydraulic chamber) + (Hydraulic Area of the Inner hydraulic chamber)] / Hydraulic Area of Master cylinder

[029] Due to such additional hydraulic area, a hydraulic ratio inside the hydraulic slave cylinder also increases which substantially maintains a constant pedal effort of the clutch as the hydraulic fluid displaced by the movement of the diaphragm spring of the clutch is used to compensate the additional pedal effort needed to operate the worn-out clutch.
[030] In the worn out condition, when the primary piston moves back and engages with the secondary piston, it displaces fluid in the secondary chamber, resulting in added pressure determined by the hydraulic area of the secondary chamber. This enhances the hydraulic ratio, ensuring consistent pedal effort over time.
[031] Referring back to Figure 1a, as shown Figure 1a illustrates respective positions of the secondary piston 120 and the primary piston 140 when the clutch is in a new condition or originally installed state. In this condition, the secondary piston 120 has no role or interference in actuating the clutch as the detent 122 of the secondary piston 120 restrains the movement of the secondary piston 120 or the secondary piston 120 is already in the fully extended position as shown in the Figure 1a. The pressurised hydraulic fluid coming from the master cylinder flows towards the inner hydraulic chamber 130 and acts to move the primary piston 140 to actuate the clutch.
[032] In an embodiment, the primary piston 140 has a larger reciprocating length than the secondary piston 120. The length of the primary piston 140 is greater than the length of the secondary piston 120. The outer hydraulic chamber 110 and the inner hydraulic chamber 130 are formed such that the secondary piston 120 is positioned to assist the primary piston 140 whenever the secondary piston 120 moves forward (i.e., towards clutch side).
[033] In an embodiment, the second end 120b of the secondary piston 120 engages with the cylindrical walls 132 of the inner hydraulic chamber 130 in a fully retracted position of the secondary piston 120.
[034] Figure 3a illustrates a cross-sectional view of the hydraulic slave cylinder 100 in an engaged condition of the worn out clutch, in accordance with an embodiment of the invention. Due to the worn out condition of the clutch, the primary piston 140 exerts an increased force by the pressure plate of the clutch. The clutch release bearing 150 makes the primary piston 140 to travel backward i.e. in a worn travel (WT) direction. Due to such worn travel, the engagement member 142 of the primary piston 140 contacts the second end 120b of the secondary piston 120 to move the secondary piston 120 to go backward from the position shown in Figure 1a and engage with the cylindrical wall 132 of the inner hydraulic chamber 130. Due to such movement, there is a shift in hydraulic fluid from the inner hydraulic chamber 140 to the outer hydraulic chamber 110.
[035] Figure 3b illustrates a cross-sectional view of the hydraulic slave cylinder in a partially disengaged condition of the worn out clutch, in accordance with an embodiment of the invention. When the clutch pedal is depressed, the hydraulic pressure inside the outer hydraulic chamber 110 is increased and the outer hydraulic chamber 100 is provided with an increased hydraulic force acting on the secondary piston 120 to move the secondary piston 120 forward. In such condition, the second end 120b of the secondary piston 120 engages with the engagement member 142 of the primary piston 140. Due to such engagement, the secondary piston 120 enables the primary piston 140 to actuate the clutch of the vehicle.
[036] Figure 3c illustrates a cross-sectional view of the hydraulic slave cylinder in a disengaged condition of the worn out clutch, in accordance with an embodiment of the invention. As mentioned hereinabove, in the partial disengaged state, the secondary piston 120 moves the primary piston 140. When the clutch pedal is fully depressed to disengage the clutch completely, the detent 122 formed on an outer surface 121 of the secondary piston 120 engages with an end 112a of the cylindrical wall 112 of the outer hydraulic chamber 110. The end 112a is of curved structure and is configured to restrain the secondary piston 120 being in a fully extended position of the secondary piston 120.
[037] In an embodiment, when the clutch is worn out, an additional pedal force required to actuate/operate the clutch and move the primary piston 140 is compensated by providing an additional assistance from the secondary piston 120 by increasing the hydraulic fluid pressure inside the outer hydraulic chamber 110.
[038] In an embodiment, a uniform hydraulic pressure is maintained inside the hydraulic slave cylinder 100 by transferring the increased hydraulic pressure from the inner hydraulic chamber 130 to the outer hydraulic chamber 140.
[039] The second end 120b of the secondary piston 110 being configured to engage with the cylindrical walls 132 of the inner hydraulic chamber 130 in a non-actuating state of the secondary piston 120.
[040] Advantageously, the present invention provides a hydraulic slave cylinder for actuating a clutch of a vehicle. The present invention ensures a consistent pedal effort required to operate the clutch with the gradually increasing wear and tear of the clutch. The present invention mitigates the discomfort associated with increased effort as the clutch wears. Additionally, the invention improves seal life by sustaining a uniform pressure inside the inner hydraulic chamber and the outer hydraulic chamber, thereby enhancing the longevity and reliability of the clutch system. Moreover, the configuration of incorporating dual hydraulic chambers required to effectively operate the clutch, reduces the overall complexity of the clutch systems by incorporating fewer components, promoting efficiency and ease of maintenance. The present invention provides a simpler construction/configuration of the hydraulic slave cylinder and can easily be manufactured, installed, serviced, or repaired and thus offering a more economical solution without compromising performance. The present invention increases the capability of the clutch system to easily adjust the fluid pressure in the worn condition of the clutch.
[041] While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.
, Claims:We Claim:

1. A hydraulic slave cylinder (100) for actuating a clutch of a vehicle, the hydraulic slave cylinder (100) comprising:
a housing (102) having an outer hydraulic chamber (110) and an inner hydraulic chamber (130), the inner hydraulic chamber (130) being concentrically placed inside the outer hydraulic chamber (110), the outer hydraulic chamber (110) and the inner hydraulic chamber (130) being in fluid communication with each other;
a primary piston (140) reciprocatably disposed inside the inner hydraulic chamber (130), the primary piston (140) being configured to actuate the clutch; and
a secondary piston (120) reciprocatably disposed inside the outer hydraulic chamber (110), the secondary piston (120) being operably engaged with the primary piston (140) and configured to actuate the primary piston (140).

2. The hydraulic slave cylinder (100) as claimed in claim 1, wherein the primary piston (140) comprises a first end (140a) and a second end (140b) extending away from the first end (140a), the first end (140a) being configured to be sealably and slidably disposed between cylindrical walls (132, 136) of the inner hydraulic chamber (130) and the second end (140b) being configured to receive a clutch release bearing (150).
3. The hydraulic slave cylinder (100) as claimed in claim 1, wherein the primary piston (140) comprises an engagement member (142) formed on a portion being adjacent to the second end (140b), the engagement member (142) being configured to extend outwardly from an outer surface (141) of the primary piston (140).

4. The hydraulic slave cylinder (100) as claimed in claim 1, wherein the secondary piston (120) comprises a first end (120a) and a second end (120b) extending away from the first end (120a), the first end (120a) being configured to be sealably and slidably disposed between cylindrical walls (112, 116) of the outer hydraulic chamber (110).

5. The hydraulic slave cylinder (100) as claimed in claim 4, wherein the second end (120) of the secondary piston (110) being configured to engage with one of the cylindrical walls (132, 136) of the inner hydraulic chamber (130) in a fully retracted position of the secondary piston (110).

6. The hydraulic slave cylinder (100) as claimed in claim 4, wherein the second end (120b) of the secondary piston (120) being configured to operably engage with the engagement member (142) of the primary piston (140) in an actuating state of the secondary piston (120).

7. The hydraulic slave cylinder (100) as claimed in claim 4, wherein the secondary piston (120) comprises a detent (122) formed on an outer surface (121) of the secondary piston (120) between the first end (120a) and the second end (120b).

8. The hydraulic slave cylinder (100) as claimed in claim 7, the detent (122) being configured to engage with an end (112a) of the cylindrical wall (112) of the outer hydraulic chamber (110), the end (112a) being configured to restrain the secondary piston (120) in a fully extended position of the secondary piston (120).

9. The hydraulic slave cylinder (100) as claimed in claim 1, wherein the primary piston (140) has a larger reciprocating length than the secondary piston (120).

10. The hydraulic slave cylinder (100) as claimed in claim 1, wherein a portion of an outer surface (103) of the housing (102) being configured to receive a spring (160) adapted to be engaged with the clutch release bearing (150).
Dated this 5th day of March 2024
MAHINDRA & MAHINDRA LIMITED
By their Agent & Attorney

(Janaksinh Jhala)
of Khaitan & Co
Reg No IN/PA-2193