The present invention relates to hydraulic lash adjusting systems of valve trains.
DEFINITION
Positive lash: Positive lash is the phenomenon which occurs when a gap is created between the valve train components, due to which the effective length of the valve train shortens. Positive lash creates unwanted noise and vibrations while the engine is in operation.
Negative lash: Negative lash is the phenomenon which occurs when the effective length of the valve train lengthens. Negative lash causes asynchronous opening of the intake and exhaust valves, which ultimately results in considerably higher power loss of the engine.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
In an internal combustion engine, the camshaft is configured to transfer energy to the valve train with the help of cam lift. However, the length of the different components of the valve train often varies because of change in temperature and wears of the components, and therefore creates a gap between the components. More specifically, when the effective length of the valve train shortens, a gap known as a positive lash is generated between the components. On the other hand, when the effective length of the valve train extends, a gap known as a negative lash, is generated between the components of the valve train. Both positive lash and negative lash impact the valve train adversely. The positive lash results in generation of unwanted noise while the operation is in operation, and the negative lash causes asynchronous opening of the intake and exhaust valves, thereby resulting in considerably higher power loss.

A generally practiced method for overcoming the valve lashes is regularly adjusting mechanical tappet screw mounted on the rocker arm of the valve train. However, it is quite difficult to adjust the tappet screws while the engine is running. Therefore, a hydraulic lash adjuster (HLA) system has been devised for many years to auto-adjust the tappet clearance while the engine is running. The conventional HLA system consists of plunger disposed in a preferably open high pressure chamber filled with a high pressure hydraulic fluid. The plunger is configured to expand during the positive lash by allowing hydraulic fluid to accommodate the space in the plunger.
During positive lash, the hydraulic fluid is trapped in the chamber by a check valve. Due to incompressibility, the fluid acts as a rigid element in the valve train and pushes the HLA up. Conversely, the HLA shortens by compressing the plunger, during negative lash, by allowing constant leakage of a controlled amount of oil through the gap between the outer periphery of the plunger and the inner wall of the chamber.
These types of HLA necessitate the need for close clearance tolerances created between the plunger and the chamber and thus, requires selective fitment while assembling the HLA. Further, leak down rate of these HLAs depends on the magnitude of the above-mentioned gap to at least a third power, which means, infinitesimal change in gap related dimensions affects the leak down rate. Therefore, the surfaces associated with gap are generally lapped or polish finished for accurate control in leak down rate. Thus, the conventional HLA have relatively increased manufacturing cost. In addition to this, the leak down rate also depends on viscosity, and hence temperature, of the trapped hydraulic fluid. As a result, more than often the conventional HLAs are significantly sensitive during expansion but take more time to shrink during compression. For instance, at cold start of the vehicle, the high viscosity of the hydraulic fluid reduces the leak-off rate. It must be noted that the negative lash is the highest at cold start but due to the sensitivity of the conventional HLA, minimum leakage rate is caused. As a result, the negative lash is not effectively curbed and the engine loses power,

while at the same time oil deposits are built on the valve stems. On the other hand, the positive lash occurs at hot running conditions of the engine but because of less viscosity of the oil, the leak down rate is high. Since the conventional HLA is an open system, some amount of the fluid is lost every time the plunger is displaced, thus contributing to need for replacing the fluid after a predetermined number of runs.
For certain conventional HLAs designed for medium and heavy-duty diesel engines, the vehicle includes auxiliary vehicle brakes in the form of exhaust engine brakes. These brakes are provided with additional valves in the engine exhaust manifold. During braking, this additional valve provided in the exhaust manifold closes and consecutively, the fuel supply is cut-off. As a result, the high back pressure produced by the exhaust manifold generates negative torque which slows down the vehicle. Further, this high back pressure causes engine exhaust valve to remain open even without any actuation from the camshaft. Consequently, the HLA expands due to positive lash, which forces the exhaust valve to remain open even after deactivation of the exhaust manifold braking valve, which subsequently leads to power loss.
There is therefore felt a need for a system that alleviates the aforementioned drawbacks.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
An object of the present disclosure is to provide a hydraulic lash adjusting system for a vehicle.
Another object of the present disclosure is to provide a hydraulic lash adjusting system for a vehicle, which effectively neutralizes positive lash and negative lash.

Yet another object of the present disclosure is to provide a hydraulic lash adjusting system for a vehicle, which is relatively less sensitive while in operation.
Still another object of the present disclosure is to provide a hydraulic lash adjusting system for a vehicle, which does not affect other components of the valve train.
One object of the present disclosure is to provide a hydraulic lash adjusting system for a vehicle, which does not require frequent replenishment of hydraulic fluid therein.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure envisages a hydraulic lash adjusting system for a valve train. The system comprises a chamber partially filled with hydraulic fluid, a biased plunger displaceably provided in the chamber and a control valve. The plunger has an expandable bag fluidly communicating with the chamber. The control valve is configured to be opened during positive lash to allow fluid flow from the bag into the chamber to displace the plunger to a first position, and during negative lash to allow fluid flow from the chamber into the bag to displace the plunger to a second position.
In an embodiment, displacement of the plunger to a first position facilitates neutralization of positive lash.
In another embodiment, the first position is a position of the plunger when in positive lash, relatively higher than the position of the plunger when in neutral lash.
In an embodiment, displacement of the plunger to a second position facilitates neutralization of negative lash.

In another embodiment, the second position is a position of the plunger when in negative lash, relatively lower than the position of the plunger when in neutral lash.
In an embodiment, the chamber is a closed pressurized chamber.
In one embodiment, the plunger is biased with the help of a spring.
In another embodiment, the spring is configured to be supported between an operative external surface of the base of the plunger and an operative inner surface of the base of the chamber.
In an embodiment, the control valve is configured to be opened in response to the position of cam lobes of the valve train.
In one embodiment, the system includes a sensor configured to sense the position of a cam lobe. The sensor is configured to generate a sensed signal when the cam lobe is in its base circle position.
In another embodiment, the system includes a control unit communicating with the sensor and with the control valve. The control unit is configured to receive the sensed signal. The control unit is further configured to generate an actuating signal, based on the sensed signal, for opening the control valve.
In another embodiment, the control valve is an electrically actuated control valve.
In yet another embodiment, the control valve is a solenoid valve.
In an embodiment, the gap between the peripheries of the plunger and the chamber is sealed using an O-ring.
In another embodiment, hydraulic fluid is a deaerated hydraulic fluid.
The present disclosure further envisages an engine having a hydraulic lash adjusting system.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

A hydraulic lash adjusting system, of the present disclosure, for a vehicle will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates a schematic view of a conventional hydraulic lash adjusting system;
Figure 2 illustrates a first schematic view of the system of the present disclosure; and
Figure 3 illustrates a second schematic view of the system of Figure 1.
LIST OF REFERENCE NUMERALS

10 conventional hydraulic lash adjusting system
12 chamber
14 plunger
15 opening
16 ball valve
17 spring
100 hydraulic lash adjusting system of the present disclosure
101 camshaft

102 closed pressurized chamber
103 hydraulic fluid
104 spring-loaded plunger
105 extension
106 expandable bag
108 control valve
110 camshaft phase sensor
112 control unit
113 electric connection
114 O-ring
115 spring
DETAILED DESCRIPTION
Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth,

relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a," "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," "including," and "having," are open ended transitional phrases and therefore specify the presence of stated features, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, elements, components, and/or groups thereof.
When an element is referred to as being "mounted on," "engaged to," "connected to," or "coupled to" another element, it may be directly on, engaged, connected or coupled to the other element. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
Terms such as "inner," "outer," "beneath," "below," "lower," "above," "upper," and the like, may be used in the present disclosure to describe relationships between different elements as depicted from the figures.

Positive lash is the phenomenon which occurs when a gap is created between the valve train components, due to which the effective length of the valve train shortens. On the other hand, negative lash is the phenomenon which occurs when the effective length of the valve train lengthens. It is necessary to neutralize both the positive lash and the negative lash to curb production of unnecessary noise and asynchronous opening of the intake and exhaust valves that take place due to positive lash and negative lash, respectively.
Figure 1 shows a schematic view of a conventional hydraulic lash adjusting system (10). A plunger (14) is fitted in an open chamber (12). The plunger (14) has a pair of openings (15), each configured on the top and bottom walls of the plunger (14). A ball valve supported by a plurality of helical springs is fitted between the plunger (14) and the chamber (12). Pressurized oil is allowed to flow through the openings in the plunger (14) into the chamber (12). The ball valve displaces the plunger (14) to enable the oil to act as a rigid member to neutralize positive lash, whereas the oil is purposely leaked from the gap between the plunger (14) and the chamber (12) to neutralize negative lash. However, due to the open condition of the chamber (12), the viscosity of the oil changes due to temperature changes, thereby affecting the working of the system (10). Further, there is a continuous need for continuously replenishing the oil supply.
There is therefore required a system that alleviates the aforementioned drawbacks.
A hydraulic lash adjusting system (100), of the present disclosure, for a vehicle will now be described in detail with respect to Figure 2 and Figure 3. The vehicle has a camshaft (101) and a valve train which help in the running of the engine. The camshaft (101) is configured to transfer energy to the valve train.
The hydraulic lash adjusting system (100) (hereinafter referred to as 'the system (100)') is provided in the valve train, and is configured to neutralize positive lash and the negative lash generated by the valve train due to shift in the camshaft (101) position, for ensuring the smooth functioning of the valve train.

The system (100) comprises a chamber (102) partially filled with hydraulic fluid
(103) and a biased plunger (104) displaceably provided in the chamber (102). The
plunger (104) has an expandable bag (106) attached thereto. The bag (106) is
configured to be in fluid communication with the chamber (102). In an
embodiment, the chamber (102) is a closed pressurized chamber. In a preferred
embodiment, the plunger (104) is defined by a hollow body having a hollow,
preferably cylindrical extension (105) extending operatively inwards.
A control valve (108) is connected to the plunger (104). The control valve (108) is configured to be opened during positive lash and negative lash. During the positive lash, the control valve (108) is opened to allow fluid flow from the bag (106) into the chamber (102) to displace the plunger (104) to a first position. During the negative lash, the control valve (108) is opened to allow fluid flow from the chamber (102) into the bag (106) to displace the plunger to a second position.
In an embodiment, the plunger (104) is biased with the help of a spring (115). In an embodiment, the spring (115) is configured to be supported between an operative external surface of the base of the plunger (104) and an operative inner surface of the base of the chamber (102).
In an embodiment, displacement of the plunger (104) to a first position facilitates neutralization of positive lash. Typically, the first position is a position of the plunger (104) when in positive lash, relatively higher than the position of the plunger (104) when in neutral lash. More specifically, when the fluid flow is enabled into the chamber (102), the force exerted by the fluid pushes the plunger
(104) against the spring (115). The force exerted causes the plunger (104) to be
displaced away from the base of the chamber (102). As a result, the effective
length of the system (100) increases to neutralize the positive lash.
In another embodiment, displacement of the plunger (104) to a second position facilitates neutralization of negative lash. Typically, the second position is a position of the plunger (104) when in negative lash, relatively lower than the

position of the plunger (104) when in neutral lash. More specifically, when the fluid flow is enabled into the bag (102), the bag (102) acts as a reservoir to store the fluid therein. As a result, the spring (115) is compressed, thereby causing the plunger (104) to be displaced towards from the base of the chamber (102). As a result, the effective length of the system (100) decreases to neutralize the negative lash.
In one embodiment, the control valve (108) is configured to be opened in response to the position of cam lobes of the valve train.
In an embodiment, the system (100) includes a sensor (110). The sensor (110) is configured to sense the position of a cam lobe to which the system (100) is attached. The sensor (110) is configured to generate a signal when the camshaft (101) is in its base circle position.
In another embodiment, the system (100) includes a control unit (112) communicating with the sensor (110) and with the control valve (108). The control unit (112) is configured to receive the sensed signal. The control unit (112) is further configured to generate an actuating signal based on the sensed signal to open the control valve (108).
In an embodiment, the control unit (112) is the ECU of the vehicle.
In a preferred embodiment, the control valve (108) is an electrically actuated control valve (108). In another embodiment, the control valve (108) is a Normally Close valve. In yet another embodiment, the control valve (108) is a solenoid valve.
In an embodiment, the gap between the peripheries of the plunger (104) and the chamber (102) is sealed using an O-ring (114) to avoid any leakage of the fluid out of the system.
In one embodiment, the hydraulic fluid (103) is a deaerated hydraulic fluid (103). In a preferred embodiment, the hydraulic fluid (103) is an engine lubricating oil.

When compared to the system (100) of the present disclosure, the conventional system requires a continuous supply of high pressure fluid for its operation. However, as the system (100) of the present disclosure is a closed system, it does not need any additional fluid supply. Further, as there is no loss of the fluid, the cost of replenishing the fluid is saved. Moreover, there is no requirement for a particular type of finishing to be done on the walls of the plunger (104) for ease in movement thereof.
Additionally, since the system (100), of the present disclosure, makes use of the expandable bag (106) to act as the rigid member and not the fluid (103) itself, the system (100) is highly accurate in control as compared to the conventional systems, and handles negative lash perfectly as the system (100) is relatively less sensitive.
The present disclosure also envisages an engine having the hydraulic lash adjusting system (100) of the present disclosure.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
TECHNICAL ADVANCEMENTS
The present disclosure described hereinabove has several technical advantages including, but not limited to, the realization of a hydraulic lash adjusting system for a vehicle, which:
• effectively neutralizes positive lash and negative lash;
• is relatively less sensitive while in operation;
• does not affect other components of the valve train; and

• does not require frequent replenishment of hydraulic fluid therein.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
he use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

CLAIM:

1. A hydraulic lash adjusting system (100) for a valve train, said system
(100) comprising:
• a chamber (102) partially filled with hydraulic fluid (103);
• a biased plunger (104) displaceably provided in said chamber (102), and having an expandable bag (106) fluidly communicating with said chamber (102); and
• a control valve (108) configured to be opened during positive lash to allow fluid flow from said bag (106) into said chamber (102) to displace said plunger (104) to a first position, and during negative lash to allow fluid flow from said chamber (102) into said bag (106) to displace said plunger to a second position.

2. The system (100) as claimed in claim 1, wherein displacement of said plunger (104) to a first position facilitates neutralization of positive lash.
3. The system (100) as claimed in claim 2, wherein said first position is a position of said plunger (104) when in positive lash, relatively higher than the position of said plunger (104) when in neutral lash.
4. The system (100) as claimed in claim 1, wherein displacement of said plunger (104) to a second position facilitates neutralization of negative lash.
5. The system (100) as claimed in claim 4, wherein said second position is a position of said plunger (104) when in negative lash, relatively lower than the position of said plunger (104) when in neutral lash.
6. The system (100) as claimed in claim 1, wherein said chamber (102) is a closed pressurized chamber.

7. The system (100) as claimed in claim 1, wherein said plunger (104) is biased with the help of a spring (115).
8. The system (100) as claimed in claim 7, wherein said spring (115) is configured to be supported between an operative external surface of the base of said plunger (104) and an operative inner surface of the base of said chamber (102).
9. The system (100) as claimed in claim 1, wherein said control valve (108) is configured to be opened in response to the position of cam lobes of the valve train.
10. The system (100) as claimed in claim 1, which includes a sensor (110) configured to sense the position of a cam lobe, said sensor (110) configured to generate a sensed signal when said cam lobe is in its base circle position.
11. The system (100) as claimed in claim 10, which includes a control unit (112) communicating with said sensor (110) and with said control valve (108), said control unit (112) configured to receive said sensed signal, said control unit (112) further configured to generate an actuating signal, based on said sensed signal, for opening said control valve (108).
12. The system (100) as claimed in claim 9, wherein said control valve (108) is an electrically actuated control valve (108).
13. The system (100) as claimed in claim 9, wherein said control valve (108) is a solenoid valve.
14. The system (100) as claimed in claim 1, wherein the gap between the peripheries of said plunger (104) and said chamber (102) is sealed using an 0-ring(114).

15. The system (100) as claimed in claim 1, wherein hydraulic fluid (103) is a deaerated hydraulic fluid (103).
16. An engine having a hydraulic lash adjusting system (100), as claimed in any one of the preceding claims 1 to 15.