Claims:WE CLAIM:
1. A control system (100) for automatic engagement of front wheels during braking in four wheel drive (4WD), comprising:
one or more toggle pins (15) configured to lock in slots;
brake pedals (RH 50, LH 51); ECU (53) with logic, hydraulic circuit;
one or more toggle pins (15); drive shaft (11), coupler (17); face dog teeth (18),
spline connection (22), radial oil chamber (25); annular chamber (23) and tank
line (24), pressure line (27); one or more springs comprising inner push rod
spring (21), outer push rod spring or spring-output gear (16), spool or push rod (20); actuating switch;
one or more solenoids (53) , one or more valves; and
characterized in that the toggle pin (15) has circular or rounded ends, the coupler chamfer (17) angle is 25-35 degrees, the spring stiffness of the outer spring is in synchronization with the spring stiffness of the inner spring, and wherein the system has a ECU optimum response time i.e. reaction time between Pedal switch actuation and energerising solenoid is 0.05 to 0.8 milli sec for smooth engagement and disengagement of four wheel drive.

2. The control system (100) for automatic engagement of front wheels during braking in four wheel drive (4WD) as claimed in claim 1, wherein the spring stiffness of the outer spring (16) is synchronized with the spring stiffness of inner spring (21) in the range of 5-15 N/mm.

3. The control system (10) for automatic engagement of front wheels during braking in four wheel drive (4WD) as claimed in claim 1, wherein the coupler chamfer angle is 30 degrees.
4. A method for automatic engagement of front wheels during braking in a four wheel drive (4WD), comprising steps:
actuation of system by operator using a switch (50, 51);
transmission of input signal to one or more solenoid valves (53) after optimization of electrical delay in an ECU module (52);
energizing of solenoid after a ECU delay of 0.05-0.8 msecs;
diversion of high pressure from annular chamber to tank,
drop in the pressure, retraction of spring-output (16) gear pushing the coupler (17) against the drive gear (19), transmission of drive from drive gear (19) to the Coupler (17) through the Face dog teeth (18) in both Coupler (17) and drive gear (19), transmission by the coupler (17) the drive from drive gear (19) to the drive shaft (11) through spline connection (22), wherein steps comprise:
placement of push rod (20) with spring (21) in position keeping the oil gallery (25) open to tank line (24), and wherein on actuation the coupler (17) moves first & travels towards right by 4-6 mm during which inner spool (20) is stationary (203a, 203b), at 7-8 mm travel, the coupler (17) movement frees the toggle pin (15) , raises & makes inner spool (20) to move freely (203c),
movement of inner spool, crossing of ramp by the pin (203d), resulting in sequential movement with time lag and smooth engagement of the four wheel drive (4WD).

5. A method for automatic dis-engagement of front wheels during braking in a four wheel drive (4WD), comprising steps:
actuation of system by operator using a pedal switch;
transmission of input signal to one or more solenoid valves, energizing of solenoid in 0.05-0.8msecs, optimized by electrical delay in a ECU module (52), causing diversion of high pressure from annular chamber to tank, with drop in pressure, spring output gear retracts making the coupler move from left to right during release of brake pedal, rising of brake speed vs linear displacement plot (201),
a delay followed by rise in pressure vs time (203),
rise in inner spring linear displacement vs time (204) ;
rising in the outer spring linear displacement vs time (202), wherein as the pedal is released, pedal switch sends signal to solenoid;
energizing of solenoid causes the direction valve to divert the High pressure from annular chamber (23), causing increase in pressure (203), sequence of steps comprising:
movement of push rod or spool (20) from right to left against the Spring push rod (21);
coupler remains stationary (203e),
traveling of push rod (203f) At 6-10 mm travel (right to left), dropping of toggle pin (15) and free movement of the coupler (203g) (from right to left) by the influence of High pressure oil against the spring-output gear and crossing of the ramp by the toggle pin,
lowering in position of Toggle pin (203h), spool remaining stationary;
traveling by spool a distance of 15-16mm (At 203i), and
crossing of ramp by pin crossed the ramp and movement by coupler (17), wherein the sequential movement with time lag is smooth disengagement of four wheel drive (4WD).

Dated this 31st day of December 2021

, Description:FRONT WHEEL ENGAGEMENT CONTROL SYSTEM FOR FOUR WHEEL DRIVE IN AGRICULTURAL VEHICLE AND METHOD THEREOF

FIELD OF INVENTION
The present invention relates to the field of Agricultural vehicles. Particularly the invention relates to four wheel drive agricultural vehicles, and transmission. The invention specifically relates to control system for automatic and smooth engagement and disengagement of front wheel drive in 4WD based agricultural vehicles. It also relates to method of engagement of Front wheel drive engagement control system.

BACKGROUND OF INVENTION
Farm tractors typically operate in a two wheel or a four wheel mode of operation. When pulling heavy agricultural equipment through a field, it is often beneficial to utilize a four wheel mode of operation. In other circumstances, such as travel over highways and the like, it is beneficial to condition the tractor in a two wheel mode of operation. Agricultural tractors which automatically disengage the four wheel drive when the tractor ground speed exceeds nine miles per hour are known in the art.

Thus, there is a need and a desire for a drive system which improves braking performance of the tractor especially in cases where the tractor is operated in a two wheel mode.
US5802489A discloses control system for engaging, disengaging and re-engaging a front wheel drive in an agricultural vehicle includes a control circuit configured to receive signals representative of vehicle operating parameters and to generate control signals corresponding to the desired state (i.e. engaged or disengaged) of a front wheel drive engagement circuit. Sensors are associated with the rear wheels to provide parameter Control logic executed by the control circuit in a continuously cycled routine determines the desired state of the engagement circuit based upon all operating parameters. The control circuit applies an appropriate control signal to the engagement circuit causing engagement or disengagement in accordance with the desired state.

US5248020A a drive system for a tractor which is operable in either a two wheel or a four wheel mode of operation. The drive system includes a control apparatus which automatically establishes a drive connection between a power source on the tractor and a front pair of tractor wheels through regulated operation of a normally engaged clutch assembly in response to application of service brakes on the tractor. Thus, the decreasing inertia of the power source, inherent with deceleration due to braking, is utilized to substantially equalize wheel slippage between front and rear pairs of wheels thereby advantageously improving braking performance especially as the tractor operates at relatively high speeds.

Accordingly there is a requirement to provide an improved front axle engagement system with optimized controlled response time, and improved design of coupler and toggle pin to provide smooth engagement of the 4WD. The invention accordingly provides smooth transitions between engagement and disengagement of 4WD by improving the signal response time at optimal cost and positive engagement causing higher reliability

OBJECTIVES OF THE INVENTION
The main objective of the present invention is to provide a braking system for an agricultural vehicle, wherein the automatic engagement of front wheels is smooth.

It is another object of the present invention is to provide a braking system for an agricultural vehicle which has both two wheel drive (2WD) and four wheel drive (4WD).

It is another object of the present invention to provide a braking system comprises control system for an agricultural vehicle which has both two wheel drive and four wheel drive.

It is another object of the present invention to provide control system for automatic engagement of front wheels during braking in 4WD of an agricultural vehicle.

It is another object of the present invention to provide a control system for automatic engagement of front wheels during braking in 4WD, wherein the agricultural vehicle is a tractor and the like.

It is yet another objective of the present invention is to provide a control system for automatic engagement of front wheels during braking in 4WD, wherein the system comprises optimized response time in electrical, hydraulic and mechanical components to make the engagement with dog teeth smooth.

It is another object of the present invention to provide a system with ECU reaction time in milli seconds, provides smooth ramp by toggle pin due to toggle pin end rounds.

It is yet another object of the present invention wherein coupler chamfer has an improved chamfer angel and optimized relative Spring stiffness between Spool and coupler return springs.

SUMMARY OF THE INVENTION
It is a primary aspect of the present invention to provide a control system (100) for automatic engagement of front wheels during braking in four wheel drive (4WD), comprising:
one or more toggle pins (15) configured to lock in slots;
brake pedals (RH 50, LH 51); ECU (53) with logic, hydraulic circuit;
one or more toggle pins (15); drive shaft (11), coupler (17); face dog teeth (18),
spline connection (22), radial oil chamber (25); annular chamber (23) and tank
line (24), pressure line (27); one or more springs comprising inner push rod
spring (21), outer push rod spring or spring-output gear (16), spool or push rod (20); actuating switch;
one or more solenoids (53) , one or more valves; and
characterized in that the toggle pin (15) has circular or rounded ends, the coupler chamfer (17) angle is 25-35 degrees, the spring stiffness of the outer spring is in synchronization with the spring stiffness of the inner spring, and wherein the system has a ECU optimum response time i.e. reaction time between Pedal switch actuation and energerising solenoid is 0.05 to 0.8 milli sec for smooth engagement and disengagement of four wheel drive.

It is another aspect of the present invention to provide a system, wherein the spring stiffness of the outer spring (16) is synchronized with the spring stiffness of inner spring (21) in the range of 5-15 N/mm.

It is another aspect of the present invention to provide a system, wherein the coupler chamfer angle is 30 degrees.
It is another aspect of the present invention to provide a method for automatic engagement of front wheels during braking in a four wheel drive (4WD), comprising steps:
actuation of system by operator using a switch (50, 51);
transmission of input signal to one or more solenoid valves (53) after optimization of electrical delay in an ECU module (52);
energizing of solenoid after a ECU delay of 0.05-0.8 msecs;
diversion of high pressure from annular chamber to tank,
drop in the pressure, retraction of spring-output (16) gear pushing the coupler (17) against the drive gear (19), transmission of drive from drive gear (19) to the Coupler (17) through the Face dog teeth (18) in both Coupler (17) and drive gear (19), transmission by the coupler (17) the drive from drive gear (19) to the drive shaft (11) through spline connection (22), wherein steps comprise:
placement of push rod (20) with spring (21) in position keeping the oil gallery (25) open to tank line (24), and wherein on actuation the coupler (17) moves first & travels towards right by 4-6 mm during which inner spool (20) is stationary (203a, 203b), at 7-8 mm travel, the coupler (17) movement frees the toggle pin (15) , raises & makes inner spool (20) to move freely (203c),
movement of inner spool, crossing of ramp by the pin (203d), resulting in sequential movement with time lag and smooth engagement of the four wheel drive (4WD).

It is yet another aspect of the present invention to provide a method for automatic dis-engagement of front wheels during braking in a four wheel drive (4WD), comprising steps:
actuation of system by operator using a pedal switch;
transmission of input signal to one or more solenoid valves, energizing of solenoid in 0.05-0.8msecs, optimized by electrical delay in a ECU module (52), causing diversion of high pressure from annular chamber to tank, with drop in pressure, spring output gear retracts making the coupler move from left to right during release of brake pedal, rising of brake speed vs linear displacement plot (201),
a delay followed by rise in pressure vs time (203),
rise in inner spring linear displacement vs time (204) ;
rising in the outer spring linear displacement vs time (202), wherein as the pedal is released, pedal switch sends signal to solenoid;
energizing of solenoid causes the direction valve to divert the High pressure from annular chamber (23), causing increase in pressure (203), sequence of steps comprising:
movement of push rod or spool (20) from right to left against the Spring push rod (21);
coupler remains stationary (203e),
traveling of push rod (203f) At 6-10 mm travel (right to left), dropping of toggle pin (15) and free movement of the coupler (203g) (from right to left) by the influence of High pressure oil against the spring-output gear and crossing of the ramp by the toggle pin,
lowering in position of Toggle pin (203h), spool remaining stationary;
traveling by spool a distance of 15-16mm (At 203i), and
crossing of ramp by pin crossed the ramp and movement by coupler (17), wherein the sequential movement with time lag is smooth disengagement of four wheel drive (4WD).

BRIEF DESCRIPTION OF DRAWINGS
Figure 1 illustrates the control system according to embodiments of the present invention.

Figure 2. Illustrates a cross sectional view of the drive system in a 4WD agricultural vehicle in 4WD engaged condition (prior art/ conventional design).

Figure 3. Illustrates a cross sectional view of the drive system in a 4WD agricultural vehicle in 4WD disengaged condition (prior art/ conventional design).

Figure 4. depicts optimized system response in 4WD engaged condition in accordance with embodiments of the present invention.

Figure 5. depicts optimized system response in 4WD disengaged condition in accordance with embodiments of the present invention.

Figure 6a. depicts conventional toggle pin design.

Figure 6b depicts toggle pin design according to embodiments of the present invention.

Figure 7a depicts conventional coupler with 60 degree ramp design.

Figure 7b depicts coupler with 60 degree ramp design according to embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION
The present invention discloses a “front wheel drive engagement control system for agricultural vehicles and method thereof” that succinctly fulfills the above-mentioned need[s] in the art. The present invention has objective[s] arising as a result of the above-mentioned need[s], said objective[s] having been enumerated hereinabove.

In as much as the objective(s) of the present invention are enumerated, it will be obvious to a person skilled in the art that, the enumerated objective(s) are not exhaustive of the present invention in its entirety, and are enclosed solely for the purpose of illustration. Further, the present invention encloses within its scope and purview, any structural alternative(s) and/or any functional equivalent(s) even though, such structural alternative(s) and/or any functional equivalent(s) are not mentioned explicitly herein or elsewhere, in the present disclosure. The present invention therefore encompasses also, any improvisation[s]/modification[s] applied to the structural alternative[s]/functional alternative[s] within its scope and purview. The present invention may be embodied in other specific form[s] without departing from the essential attributes thereof.

Furthermore, the terms and phrases used herein are not intended to be limiting, but rather are to provide an understandable description. Throughout this specification, the use of the word "comprise" and variations such as "comprises" and "comprising" may imply the inclusion of an element or elements not specifically recited.

Embodiments of the present invention provides an improved drive system for an agricultural vehicle with improved engagement and disengagement of 4WD. The invention provides a method for smooth transition from 2WD to 4WD in an agricultural vehicle. For exemplary purpose only, the embodiments discuss a tractor system. It should not be construed that the system and method are merely applicable to Tractor, but find application to any vehicle which has 2WD to 4WD transition.

The invention particularly discloses a drive system with control unit for automatic and smooth engagement and disengagement of front wheel drive in 4WD based agricultural vehicles.

In view of the above, and in accordance with the present invention, there is provided a drive system (100) comprising a front wheel engagement system which allows the tractor to be conditioned for a two wheel mode (2WD) of operation and which automatically shifts the tractor into a four wheel drive mode (4WD) of operation in response to application of service brakes on the tractor. The braking involves engagement of face dog teeth (18), which if not in synchrony leads to noise. The drive system of the present invention includes a Coupler (17) with Face dogteeth (18) disposed to couple a front pair of wheels at front axle (55) to a power source on the tractor. The drive system (100) of the present invention includes a control apparatus which regulates operation of the Coupler (17) with Face dogteeth (18). Upon application of the service brakes (50, 51), the coupler with face dog teeth (18) is engaged in a controlled manner such that decreasing inertia of the tractor power source, inherent with deceleration of the tractor, is utilized to substantially equalize the wheel slippage between front and rear pairs of wheels on the tractor thereby advantageously improving braking performance of the tractor especially at high speeds.

In the preferred form of the invention, the control apparatus includes electro/hydraulic circuitry for controlling operation of the actuator assembly comprising of spool or push rod (20) and coupler (17) which is responsive to hydraulic pressure provided thereto. The dog teeth (18) in coupler remain engaged in 2WD mode and disengaged in 4WD mode in a particular embodiment of the present invention.

A brake switch assembly, preferably including one or more brake switches (58) operatively coupled to the service brakes (50, 51) on the tractor, is interfaced with the control apparatus or the (Electronic control unit or ECU (52). Moreover, an operator settable mode switch assembly conditions the tractor for a two wheel or four wheel mode 4WD of operation as a function of the position of an actuator (54).

In reference to Figure 1, is disclosed a transmission system (100) of an agricultural vehicle, particularly a tractor. The present invention in figure 1, discloses a tractor transmission system comprising of 2 foot operated brake pedals for the Right hand side (50) and Left hand side (51), (RH, LH). Pedal switches (58) located at pedals Tractor has 2 Foot operated Brake pedals, LH pedal for Braking LH wheel & RH pedal for Braking RH wheel. Pedal switches (58) located at pedals get trigger when pedals (50, 51) are pressed and released. Pedal switches (58) send signal to ECU modules (52) located beneath the Instrument cluster. This ECU (52) interprets all input signal & using inbuilt logic sends signals to solenoids (53) placed at Hydraulic pack. This Hydraulic pack system directs the High Pressure / Low pressure hydraulic oil to the Actuators comprising the coupler (17) and spool (20) which are placed in 4WD actuating.

The control apparatus of the present invention is configured to automatically return the tractor to a two wheel mode of operation after the service brake is released. The release of the service brake and the return of 4WD to 2WD is depicted in figures 3 and figure 5. Moreover, the control apparatus includes logic circuitry which automatically shifts the tractor into a four wheel mode of operation in response to electrical/hydraulic failure. The drive system of the present invention is responsive to an ON/OFF switch which controls overall operation of the tractor. Moreover, the drive system further includes means for providing an indication to the operator whether the tractor is conditioned for a two wheel or a four wheel mode of operation.

In reference to Figure 2 is provided a 4WD engagement mode in the agricultural vehicle of the present invention. Particularly exemplified herein by a Tractor. In the default condition when assembled in Tractor & when tractor is in OFF (No Pressure in system). Spring-Output gear (16) keeps the Coupler (17) engaged with Drive gear (19) through face dog teeth (18). The coupler transmit the drive to the Drive shaft (11) through spline connection (22). This shaft (11) is connected to Front axle & 4WD is engaged and live. The Push rod with spring is in position keeps the oil gallery open to tank line (24). In figure 2, represents 4WD engagement mode wherein in the default condition when assembled in Tractor & when tractor is in OFF. No Pressure in system-the space filled by low pressure oil connected to tank line (24) are shown as shaded region. Spring-output (16) at its installed position forces the coupler (17) against the drive gear (19). drive is transmitted from drive gear (19) to the coupler (17) through the face dog teeth (18) available in both coupler (17) and drive gear (19). The coupler (17) in turn transmits the drive from drive gear (19) to the drive shaft (11) through spline connection (22). This shaft (11) is connected to front axle (55) & 4WD is engaged and live. The push rod with spring (21) is in position keeps the oil gallery (25) open to tank line (24).

Figure 3 represents 2WD condition (4WD disengaged condition), wherein when oil pressurised is directed to Chamber 1 or annular chamber (23). The push rod or spool (20) is pushed against the spring-push rod or inner spring (21). This movement opens the oil gallery (25) to outer chamber. The pressurised oil in this annular area (23) forces the coupler (17) away from the Drive gear (19) against the spring-output gear (16), thereby disconnecting drive from drive gear (19) to drive shaft (11), changing the mode to 2WD. In 2WD condition (4WD disengaged condition) as depicted in Figure 3, High pressurised system-space filled by high pressure oil connected to pressure line is shown shaded. High pressure oil pushes the push rod or spool (20) against the spring-push rod or inner spring (21) (push rod is moved from right to left) in annular chamber (23). This movement of the push rod directs the high pressure oil towards coupler (17) through radial oil gallery (25) Now pressurised oil forces the coupler (17) away from the Drive gear against the spring-output gear, thereby disconnecting drive from drive gear (19) to Drive shaft (11). Now Drive shaft (11) and the drive gear (19) are disconnected & the mode is 2WD.

A preferred embodiment of the present invention relates to an agricultural vehicle, comprising: an engine; front and rear wheels driven by the engine, operably interconnected by a selectable four-wheel drive including a coupling for selectively applying torque to the front wheels of the vehicle to switch between a two-wheel drive mode of operation and a four-wheel drive mode of operation, said coupling including a drive member rotatable with the rear wheels and a driven member rotatable with the front wheels, the drive and driven members being movable axially relative to one another; wherein a control system or control unit is operated for automatic engagement of front wheels during braking in 4WD.
Particular embodiment of the present invention devised an improved control system (100) for automatic engagement of front wheels during braking in 4WD, comprising 4WD actuation system including one or more toggle pins (15) configured to lock in slots; brake pedals (50, 51); ECU (52) with logic, hydraulic circuit; electrical components comprising pedal switch, sensors, module or ECU (52); one or more springs comprising inner push rod spring (21), outer push rod spring (22) and spring-output gear (10); actuating switch (58); a module (52); one or more solenoids (53) , one or more valves; and a spool (20). This improvisation also includes rounded ends in the toggle pin design (figure 6b) as compared to conventional design (6a). Pedal switch (58), one or more sensors (not shown in the drawings) and ECU (52) are the electric components. Response time between switch actuation and Solenoid energization is preset in ECU is in milli seconds. This time is optimized by the embodiments of the present invention to 0.05-0.8msecs. The present invention in preferred embodiments has provided system and method for smooth engagement of the 4WD to 2WD and 2WD to 4WD in an agricultural vehicle. This is achieved by optimization of: response time in Electrical, Hydraulic and Mechanical makes this toggle pin to slide smoothly and help the synchronization between mating dog teeth’s there by making engagement and disengagement smooth.

The followings outcomes are provided by the present invention:
Electrical: response time between switch actuation to Solenoid energizing in milli seconds.
Hydraulic : shorter pipeline and less number for bends
Mechanical: Smooth ramp by toggle pin due to toggle pin end rounds as shown in figure 6b, Coupler chamfer (Figure 7b) and optimized relative Spring stiffness between Spool and coupler return springs.
Coupler chamfer angle is 30 degrees and the spring stiffness of the outer spring (16) is synchronized with the inner spring (21). All these factors cause the smooth engagement and disengagement of the 4WD.

In reference to Figure 2 discloses the 4WD engagement and figure 4 the graphical representation of, 4WD engagement according to embodiment of the present invention, which includes on actuation of the switch (23) by the operator of the vehicle, the input signal is transmitted to module in the control unit (52), or ECU (52), followed by transmission of the signal to the solenoid valves (53) which direct the high pressure oil from 4WD actuators (54) (pilot and main), relieving of toggle pin (15) resulting in rebounding of outer spring or outer push rod spring (16), drop in pressure to result in rebounding of inner spool spring or inner push rod spring (21) for smooth engagement.

Reference is drawn to Figure 4, depicting smooth ramp down line during which 2WD changes to 4WD mode is important to avoid crash noise & mechanical failures. The Modulation is done by means of spring stiffness & detent raise/ fall relative to spool movement.

Reference is drawn to Figure 5, wherein the system pressure is measured with respect to time when 4WD is engaged. A hump shown in Graph has Ramp up line due to increase in Pressure (causing 4WD to 2WD).

Graph in figure 4 & 5 explains the pressure modulation in system. 3 time response graphs is shown, (201) line is pedal travel movement, pressure vs time graph plot is the Pressure in Tank/ Pressure line (203), (204) is Spring push rod (Inner spring, 21) linear displacement, (202) is Spring –output gear linear movement (Outer spring, 16). Rise in line is Pedal (50, 51) release travel, Pressure rise, Spring push rod travel from right to left in Fig 4, Spring output gear travel from right to left in Fig4. Drop in line is vice-versa i.e., Spring output gear moves left to right, Spring-push rod moves from left to right, Pressure drops.

Actuating system internals are shown & explained during Ramp down line due to decrease in Pressure (causing 2WD to 4WD).

A start of ramp down, pressure just starts to drop, the coupler (17) moves first & travels towards right by 4-6 mm during which inner spool (20) is stationary. At 7mm travel, this coupler (17) movement will free the toggle pin (15) which raises & makes inner spool (20) to move freely, now the inner spool starts moving. This sequential movement wit time lag will make smooth engagement.
In Fig 4, Ramp down phenomena where mode changes from 2WD to 4WD is explained by showing the position of push rod (20) and coupler (17). As the Brake pedal (50, 51) is applied, (201) starts dropping and after an intentional delay the pressure (203) drops, then with a delay outer spring displacement (202) drops and finally the inner spring displacement drops (204). This sequential movement with delay makes the 4WD engagement smooth. As the pedal (50, 51) is pressed, pedal switch (58) sends signal to Solenoid (53). As the solenoid is energized, the direction valve diverts the High pressure from annular chamber (23) to tank. As the pressure drops (shown in ramp down (203)), Spring output gear (16) retracts making the coupler (17) move from left to right during which push rod (20) is stationary (203a). At about 4-7 mm travel (left to right) of coupler (17), coupler relieves the toggle pin (15), the pin raises ramp (203c) & makes spring push rod (21) to retract & make the push rod (20) to move freely (203b). Toggle pin crosses the ramp (203d). This sequential movement wit time lag will make smooth engagement.

The response time is optimized based on the 2WD and 4WD lag times as represented by 203a, 203b, 203c and 203d. In both the 4WD engaged and disengaged condition, the aspects pressure rise and ramp down phenomenon, wherein pedal when pressed the pressure drops, spring output gear retracts, makes the coupler to move from left to right. After movement of 4-7mm of coupler, toggle pin raises and makes spring push rod retract and makes push rod (20) move smoothly. There is a lag in time derived from inner spring displacement (204), Outer spring linear displacement (202), brake speed vs time (201) and pressure vs time (203). The plot of linear displacements vs time graphs as depicted in Figures 4 and figure 5 represent the displacement vs time and to be able to decipher the lag between, drop in brake speed, drop in pressure, delay outer spring and delay in inner spring. The ECU response time and the spring stiffness are determined based on these values.

DISENGAGEMENT OF 4WD
In reference to Figure 5, wherein for 4WD disengagement on actuation of the switch (58) the ECU module (52) manipulates the signal within an optimized signal transmission time, moving the solenoid valves to direct high pressure oil to 4WD actuators (54), increase in pressure causes the Spring-push rod or inner spring (21) to compress relieving the toggle pin to drop on ramp, compression of outer coupler spring (16) and gliding of the coupler (17) over toggle pin (15) resulting in 4WD disengagement.

In reference to Figure 3, 2WD condition (4WD disengaged condition), High pressurised system-space filled by high pressure oil connected to pressure line is shown in shaded. High pressure oil pushes the push rod (20) against the Spring-push rod (push rod or inner spring (21) is moved from right to left) in annular chamber (23). This movement of the Push rod directs the high pressure oil towards coupler (17) through radial oil gallery (25). Now pressurised oil forces the coupler away from the drive gear against the spring-output gear (16), thereby disconnecting drive from drive gear to drive shaft (11). Now drive shaft (11) and the drive gear (19) are disconnected & the mode is 2WD.

In reference to Figure 5, for disengagement of 4WD and engagement of 2WD, system pressure is measured with respect to time (203) when 4WD is disengaged & engaged. A hump shown in Graph has Ramp up line due to increase in Pressure (causing 4WD to 2WD).

Smooth Ramp up line during which 4WD changes to 2WD mode is important to avoid crash noise & mechanical failures. The Modulation is done by means of spring stiffness & Detent raise/ fall relative to Spool movement.

Actuating system internals are shown & explained during Ramp up line due to increase in Pressure (causing 4WD to 2WD).

A start of ramp rise, pressure just starts to rise, the spool (20) moves first & travels towards left. First enables the toggle pin (15) to drop & relieves the coupler (17). Once pin crossed ramp, Coupler starts to move. Now coupler can freely move towards left making smooth disengagement.

Fig 5, Ramp up phenomena where mode changes from 4WD to 2WD is explained by showing the position of push rod (20) and coupler (17). As the brake pedal (50, 51) is released, brake speed vs linear displacement plot (201) starts rising and after an intentional delay the pressure vs time (203) (pressure) rises, then with a delay inner spring linear displacement vs time (204) rise and finally the outer spring linear displacement vs time (202) rises. This sequential movement with delay makes the 4WD disengagement smooth. As the pedal is release, pedal switch sends signal to solenoid. As the solenoid is energized, the direction valve diverts the High pressure from annular chamber (23). As the pressure rises (shown as 203), push rod or spool (20) is forced to move (from right to left) against the spring push rod (21), and the Coupler remains stationary (203e). At 203f, At 6-10 mm travel (right to left) of push rod (20), the toggle pin (15) drops & enables to Coupler to move freely (from right to left) by the influence of High pressure oil against the Spring-Output gear and toggle pin crosses the ramp (203g). Next is 203h, wherein the toggle pin is in low position and spool stops. At 203i, intermediate spike spool has travelled about 15.7mm, pressure is 14.4bar, pin crossed the ramp and coupler (17) starts moving. This sequential movement with time lag will make smooth disengagement.

In preferred embodiment of the present invention is provided an improvised positive lock & safety system (Toggle pins riding over ramp & locking in slots) fitted in actuators which prevent unintentional engagement and disengagement. This toggle pin arrangement and its actuation is critical to make the connections smooth. Further, in an embodiment of the present invention and in reference to figure 6a, figure 6b the toggle pins edges are rounded and the ramp angle is 30 degrees for coupler (7b) in comparison to conventional coupler (of ramp fig 7a) angle 60 degrees. The lesser ramp angle makes the toggle pin rise & lower at slower rate than higher ramp angle due to the friction factors. This slower rate is helping smoother pin movement and jerk.

Another embodiment of the present invention provides a method for automatic engagement of front wheels during braking in a 4WD, comprising steps:
4WD engagement and 4WD disengagement;
4WD engagement comprises steps as illustrated in Figure 4: Ramp down phenomena where mode changes from 2WD to 4WD is explained by showing the position of push rod and coupler.

As the Brake pedal is applied, brake speed linear displacement (203a) starts dropping and after an intentional delay the pressure vs time (203c) (pressure) drops, then with a delay outer spring linear displacement (203b) drops and finally the inner spring linear displacement drops (203d). This sequential movement with delay makes the 4WD disengagement smooth. As the pedal is pressed, pedal switch sends signal to Solenoid. As the solenoid is energized, the direction valve diverts the High pressure from annular chamber (23) to tank. As the pressure drops (shown in ramp down 203) spring output gear (16) retracts making the coupler (17) move from left to right during which push rod (20) is stationary. At 6-10 mm travel (left to right) of coupler (17), the toggle pin (15) raises & makes spring push rod (21) to retract & make the push rod (20) to move freely. This sequential movement wit time lag will make smooth engagement.

Actuation of system by operator using a switch and actuation or application of brake pedal pedal switch 58 sends signal to solenoid, which is transmitted as input signal to one or more solenoid valves after optimization of electrical delay in a module;

steps comprises), drop in pressure causing 203a, retraction of spring output gear, movement of coupler (203a), and spool is idle, spool starts to move (203b), movement of coupler by 6-10 mm to relieve toggle pin (15) which raises to ramp (203c), causing spring push rod (21) to retract and push rod (20) to move freely, toggle pin crosses the ramp (203d), sudden pressure drop causes outer spring (16) to rebound, relieving of the toggle pin, rebounding of inner spool spring (21) and resulting in 4WD engagement.

Another embodiment of the present invention in reference to figure 5, discloses the method of 4WD disengagement comprising steps:
actuation of system by operator using a switch;
transmission of input signal to one or more solenoid valves after optimization of electrical delay in a module;

Fig 5, Ramp up phenomena where mode changes from 4WD to 2WD is explained by showing the position of push rod and coupler. As the Brake pedal is released, brake speed displacement graph or line (203a) starts rising and after an intentional delay the (203) pressure vs time graph rises, then with a delay (204) and finally the outer spring (202) rises . This sequential movement with delay makes the 4WD disengagement smooth. As the pedal is release, pedal switch sends signal to Solenoid. As the solenoid is energized, the direction valve diverts the High pressure from annular chamber (23). As the pressure rises (203),
203e, spool or push rod (20) is forced to move (from right to left) against the spring push rod (21). The coupler (17) remains stationary.
203f, 203g, At 6-10 mm travel (right to left) of push rod, the toggle pin drops & enables to coupler to move freely (from right to left) by the influence of High pressure oil against the Spring-Output gear (16),
203g, pin crossed ramp, 203h pin lowers in position and spool stops, 203i, at about a pressure of 14.4bar, intermediate spike spool travelled 15.7mm, pin crossed the ramp and coupler starts moving. This sequential movement with time lag will make smooth disengagement, and
movement of the valves and directing of high pressure oil from actuators, increase in pressure causing movement of spools (20) when coupler is idle, lowering of toggle pin in the idle coupler state, crossing of ramp by toggle pin, and initiation of coupler movement, stopping of spool with outer spring to rebound and relieve the toggle pin and rebounding of inner spool spring resulting in disengagement.

REFERENCE NUMERALS
(10)-Control system
(11)-Drive shaft
(15)-Toggle pin
(16)-Spring output gear or outer spring
(17)-coupler
(18)-Face dog teeth
(19)- Drive gear
(20)-Spool or Push rod
(21)-Spring push rod or inner spring
(22)-Spline connection
(23)-Annular chamber
(24)-Tank line (24)
(25)-Radial oil gallery
(27)-Pressure line
(50)-Brake pedal right
(51)-Brake pedal Left
(52)-ECU
(53)-Solenoid
(54) Actuator
(55) Front Axle
(56) Rear Axle