DESC:FORM 2

THE PATENTS ACT, 1970
[39 of 1970]

&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION

(Section 10; Rule 13)

MANUAL TRANSMISSION SYSTEM FOR LIGHT COMMERCIAL VEHICLES

AVTEC LTD.
Pithampur Industrial Area, Sector III, Pithampur, Sagore 454774,
Dist Dhar (M.P.), India

INDIAN ENTITY

The following Specification particularly describes the invention and the manner in which it is to be performed

RELATED APPLICATION
The present invention claims benefit of the Indian Provisional Application No. 201621004681 titled "Manual Transmission System for Light Commercial Vehicles” by AVTEC Ltd., filed on 10th February 2016, which is herein incorporated in its entirety by reference for all purposes.

FIELD OF THE INVENTION
The invention relates to the field of automobile engineering, more particularly relates to a manual transmission system with optimized gear shift performance for light commercial and passenger vehicles.
BACKGROUND
Transmission system in an automobile is a speed reducing mechanism, equipped with several parts like gears and shafts. It may be called a sequence of gears and shafts, through which the engine power is transmitted to the vehicle’s wheels. The complete path of power from the engine to the wheels is called power train.

Figure 1 illustrates a schematic representation of a transmission system for commercial vehicles according to prior art. The conventional transmission system includes a single cone synchronizer for controlling axial motion of the sleeve for any of the gears 1 to 5.

The transmission system has four main functions: “Moving-off from rest”, “Changing ratio/rotational speed”, “Shifting/establishing power flow” and “Operating/controlling the gearbox”.

The “Moving-off from rest” function can be carried out mechanically, electromechanically or hydraulically. The “Changing ratio/rotational speed” function can be carried out using spur and helical gears, planetary gears, hydrodynamic or hydrostatic transmissions or mechanical continuously variable transmissions. The “Shifting/ establishing power flow” function can be divided into the two functional principles positive engagement or frictional engagement. The “Operating/controlling” function can be carried out by manual shifting, automation or an automatic system with associated control unit.
The transmission system is one of the main parts that determines the behavior, power and fuel economy of a vehicle. Transmission performance is usually related to gear efficiency, gear noise and gear shift comfort during gear change.
Now a days the drivers of commercial vehicles and passenger vehicles, being exposed to driving more cars, are comparing the shift-ability of their commercial vehicles with these cars. Normally, on a light commercial vehicle’s shift knob (1), the shift efforts, which are required, are in the range of 4-5 kg force (50N).
In the existing arts, the solution provided is either by increasing in the length of gear shift lever (1), which will have adverse impact on the driver ergonomic condition during drivability, alternately the shifting efforts can be increased for gear engagement manually which is going to affect human comfort ability and drivability will be difficult in conditions where frequent change of gears are required, or by redesign of new transmission from, leads to increase in the size of transmission and cost impact will be very high , which may also impact on the adaptability with vehicle tunnel, as per growing automobile technology the compact design of transmission (250-400 mm) is generally preferred.
The constraints in modifying the design is the identifying the limiting condition of design parameters which are affecting the performance. Second is the cost; third is interchangeability in service of existing transmissions and finally validation of change designs.
So there is a need for an improved transmission system for commercial and passenger vehicle(s), which not only provides a relatively fatigue free driving experience to the drivers but also will not only be cost effective but also easy in production, is the strong requirement of market.
SUMMARY OF INVENTION
An embodiment of the present invention discloses a vehicle transmission system. The vehicle transmission system comprises one or more gears, one or more sleeves operatively connected to the gears, one or more clutch hubs connected to the sleeves, and one or more synchronizer rings. Each of the synchronizer ring is operatively connected to the sleeve and the gear for controlling axial motion of the sleeve. The synchronizer rings comprise a multi-cone synchronizer ring for a lower gear and a single-cone synchronizer ring for a higher gear. The lower gear includes gear 1 and 2, and the higher gear includes gear 3, 4, and 5.

In one embodiment, the multi-cone synchronizer ring is having a predetermined surface area for providing a predetermined torque.

In another embodiment, the multi-cone synchronizer is provided with a threading on its inner surface at a predetermined angle to optimize coefficient of friction. The predetermined angle is between 6 degree to 8 degree.

In another embodiment, the system comprises one or more synchro cone. Each of the synchro cone is configured with a plurality of holes for enabling engagement & lubricant flow within the synchronizer ring.

In yet another embodiment, the multi-cone synchronizer ring is provided with a predetermined space between threading to enable lubricant flow with in the synchronizer ring.

In yet another embodiment, the single cone synchronizer ring comprises a friction coated synchronizing ring. The friction coated synchronizer ring is coated with a predefined material of a predetermined friction coefficient on its inner surface. The predefined material coated on the inner surface of said ring comprises a carbon material.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

The invention can be better understood with reference to the following figures. The components within the figures are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. It will also be understood that certain components and details may not appear in the figures to assist in more clearly describing the invention.

Figure 1 illustrates a schematic representation of a transmission system for commercial vehicles according to prior art.

Figure 2 illustrates a schematic representation of a transmission system according to an embodiment of the present invention.

Figure 3 illustrates an exploded view of child parts for 1st and 2nd gear Synchropack according to an embodiment of the present invention.

Figure 4 illustrates an exploded view of child parts for 3rd and 4th gear Synchropack according to an embodiment of the present invention.

Figure 5a illustrates a schematic representation of a synchronizer ring for 1st and 2nd Gear according to prior art.

Figure 5b illustrates a schematic representation of synchronizer rings for 1st and 2nd Gear according to an embodiment of the present invention.

Figure 6a illustrates an exploded view of a system for 3rd, 4th, and 5th gears according to prior art.
Figure 6b illustrates an exploded view of a system for 3rd, 4th, and 5th gears according to an embodiment of the present invention.

Figure 7a shows a conventional Synchro cone and figure 7b shows the modified Synchro cone and the design change in Sleeve according to the present invention.

Figure 8 shows the various stages of synchronization in the synchronizer according to an embodiment of the present invention.

Figure 9 shows the schematic representation of the Synchronizer layout according to an embodiment of the present invention.

Figure 10 shows the gear shifting layout according to an embodiment of the present invention.

Figure 11 shows a variation of Cone angle with respect to (w.r.t.) Torque.

Figure 12 shows impact of coefficient of friction (COF) on shift force with respect to (w.r.t.) Torque.

Figure 13 shows shift time variation with friction coated.

DETAILED DESCRIPTION OF THE INVENTION
The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the present embodiments. The size, shape, position, number and the composition of various elements of the device of the invention is exemplary only and various modifications are possible to a person skilled in the art without departing from the scope of the invention. Thus, the embodiments of the present invention are only provided to explain more clearly the present invention to the ordinarily skilled in the art of the present invention. In the accompanying drawings, like reference numerals are used to indicate like components.
The specification may refer to “an”, “one” or “some” embodiment(s) in several locations. This does not necessarily imply that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments.
As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms “includes”, “comprises”, “including” and/or “comprising” when used in this specification, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. Furthermore, “connected” or “coupled” as used herein may include operatively connected or coupled. As used herein, the term “and/or” includes any and all combinations and arrangements of one or more of the associated listed items.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
The present invention discloses a manual transmission system with improved gear shift performance for light commercial and passenger vehicles. In an embodiment of the present invention, the present invention discloses the transmission system having multi-cone synchronizer and synchronizer with a friction material. An embodiment of the present invention is adapted to provide a compact design of synchro-pack keeping shifting parts envelope same with improved shift performance.
Figure 2 illustrates a schematic representation of a transmission system according to an embodiment of the present invention. The transmission system comprises a multi-cone synchronizer ring for a lower gear such as 1st gear (201) and 2nd gear (202) and a single-cone synchronizer ring for a higher gear such as 3rd gear (203), 4th gear (204) and 5th gear. Additionally, bearings (205, 206) mounted at the two end of the transmission system.
The synchronizer of the transmission system allow gear changing in a smooth, noiseless and without vibrations manner, both for the durability of the transmission system and the comfort for the users.
The function of synchronizer is to provide exact friction load for reducing the relative motion /velocity/RPM of clutch gear and output shaft in stipulated time without the feel of delay or jerking while changing from Gear-1 to Gear-2 during driving or coasting condition of vehicle.

There are the following types of synchronizer:
1. Cone Synchronizer (Multi-layer and plate synchronizer): During a gear shift, the force is acting by vehicle driver constantly through gear shift mechanism (either cable of floor) to spring loaded insert clutching arrangement for the engagement of blocker ring with Synchro cones (the only condition to be adhere is the cone torque should be higher than index torque) .
a. Brass synchronizer (Axial and radial Synchronizer)
b. Friction material coated synchronizer

The multi cone surface provide more interfaces, which leads the reduction of shift efforts at ball knob with higher cone torque by optimum cone angle , considering improvement in axial wear parameters amount.

2. Servo Synchronizer: This type of synchronizer is commonly used in porsche designs. The idea behind the synchronization is same as internal expanding drum brakes. The movement of selector sleeve towards a gear leads to contact made with split ring, which is connected with gear directly, creating friction between sleeve and the split ring causing synchronization process and when the relative rpm tends to zero, leads to the complete engagement of gear.

3. Pin synchronizer: The pin loading synchronizer is basically blocking synchronizer which plays the synchronization process through the tapper portion of the pin.

There are basically the following main parameters on which synchronization depends, these are:
- Coefficient of friction: the coefficient of friction on cone-shaped surfaces varies with the thickness of lubricant between the clutch gear/cone (if multiple cone type) and the ring. The coefficient of friction on the cone surfaces increases suddenly, while the sleeve forces the outer ring to move forward the clutch gear/cone for draining lubricant out. It decreases after finishing synchronization, fact that leads the outer ring to slide away from the cone. The synchronization torque is expressed as a function of the coefficient of friction, see it is preferable to select a material with a high value, such as carbon fiber, molybdenum or brass, in order to increase the synchronizer capacity and, thus reduce the changing time.

- Cone angle: Higher cone torque is exerted with a smaller cone angle. However, in order to avoid self-locking between synchronizer ring and cone and let the cone leave from contacting the ring after synchronization.

- Mean cone radius: A higher torque will be achieved with a higher radius. However, this also increases the size and weight of the synchronizer. In addition, it has to be taken into account that the available space in the transmission is limited.

- Ratio step: is the distance between each one of the gear ratios in a gearbox. A high step will result in a high relative rotating speed between the input and the output shafts. Therefore, the synchronizer will need more mechanical energy to perform its role.

- Roof angle of the sliding sleeve and synchro ring teeth / Pointing angle / Chamfer angle: Determines the way the sleeve and synchro ring are in contact and affect the components of the applied forces. With a lower angle the braking capacity increases since the circumferential force increases. On the contrary, the axial component decreases and could lead to a gear clash due to an inefficient braking.

- Drag torque: are the power losses due to the clutch drag, transmission oil churning and friction of rotating components. Always acts to slow down the speed of rotating components.

In the present invention, the novelty and inventive step lies in the transmission system, due to which gear shift is smoother and comfortable for driver than conventional gear shift. In an embodiment of the present invention, the transmission system comprises a multi-cone synchronizer and synchronizer with a friction material which are novel and inventive over the conventional transmission system.

Following are the constraints observed in modifying the existing knowledge:
- the identifying the limiting condition of design parameters which are affecting the performance;
- the cost: it has to be cost effective;
- third is interchangeability in service of existing transmissions and
- finally, validation of change designs.

Experimental results & computer-aided engineering results in the synchronizer action at different level of friction coefficient and frictional cone area of mating surfaces for better shift feel, shift force and overcoming bumpy observations during shifting are provided for sample case in Figure 11, Figure 12 and Figure 13, respectively.
Cone Torque: Generally known as synchronization torque, is the result of the friction force between the conical surfaces in the synchronizer.
Index Torque: Arises from the shift sleeves chamfered teeth applying an axial force on Synchro cone chamfered teeth. Index torque always opposes the cone torque.

An ideal synchronizer should have cone torque higher than the index torque at all times during the synchronization to ensure blocking of axial shift sleeve motion. The cone torque should always be higher than index torque for proper synchronization without clash or seize of block rings. Generally, the cone angle used in the know art is in the range of 6 to 8.5 degree. But the cone angle less than or equivalent to 6 have the tendency to seize or stick, even the cone angle higher than 8 has limitations for selection of cone torque and index torque.
The percentage increase of cone torque and index torque is stabilized by CAE estimation and validation on Test-rig and vehicle testing to have the best shift feel for customers.
Arriving to the relation of cone torque and index torque is by the experience of designer on drawings platform well as vehicle running conditions to get the maximum desire satisfaction to the end user with respect to the shift feel rating of best in class.

Keeping in view of the above referred challenges, the present invention has been designed with clarity on input conditions and possible options to fulfil the same. With various input condition with theoretical estimates and the design validation through CAE is done and fine-tuned with respect to other factors in transmission shift performance.
The objective of the synchronization is to reduce to zero the angular speed difference between the rotating shaft and the gear wheel. The principle used is generating a friction torque with a friction contact between conical surfaces before the gear is engaged through a positive locking for torque transmission. As a consequence, it is aimed of the present invention to provide for improvement of the dynamic shift quality, by reducing shifting time and effort, especially.
In an embodiment, the present invention comprises of the redesign of Gear system, Synchro Pack system, shifting system for achieving particular level of shift quality for customer satisfaction by optimizing the parameters like Cone torque, Synchronization Time, Axial Wear etc.
In the present invention, synchronization processes are used in order to get a smooth gear shift and a good shift feel, by reducing the time of synchronization inside the gearbox and the load required at the driver's hand. This prevents transmission from double bump, double clutching, synchronizer wear etc.
The synchronizer rings, of the present invention, are so designed that it give comfort feel to the driver during driving because driver have to exert maximum 1.8-3 kgf force to shift the gear position. The losses during gear shift, lubricant, bush, bearing, frictional movement between parts, reflected inertia are calculated and minimized by the present invention.
In yet another embodiment, the present invention provides for the compact design of synchro-pack keeping shifting parts envelope same with improved shift performance which was earlier negative observation i.e. perception by Customer on gear shift quality on vehicle.
Multi-speed transmissions, of the present invention, are designed in such a way so that the running gears of the individual speeds, even if they are not involved in the power transmission, are constantly engaged. While a gear is fixedly connected to the countershaft, the associated idler wheel can rotate freely on the main shaft. When a specific speed is needed, the free wheel has to be fixed to the shaft. At this moment is when the synchronization processes and synchronizers act. They are positioned between two different speeds hence the synchronizer system is double: apart from the idler position they can choose between two gears.
According to an embodiment of the present invention, two type of synchronizer ring is designed for various applications:
1) Dual cone synchronizer ring or multi cone synchronizer ring explained in Figure 3 and 5; and
2) Friction coated (Carbon Lining) Synchronizer ring explained in Figure 6.

Figure 3 illustrates an exploded view of child parts for 1st and 2nd gear Synchropack according to an embodiment of the present invention. In this embodiment, the exploded view indicates 1st Gear (201) and 2nd Gear (202) at the opposite ends. Since the Synchropack is for the lower gears such as 1st and 2nd gear, the synchropack comprises multi-cone synchronizer. The synchropack for 1st and 2nd gears comprises a sleeve (302), a hub (303), a synchro cone (301A) for 1st Gear, a synchro cone (301B) for 2nd Gear, a first set of rings, such as an inner ring (304A), a mid-ring (305A), and an outer ring (306A), between the sleeve (302) and the synchro Cone (301A) for 1st Gear, and a second set of rings, such as an inner ring (304A), a mid-ring (305B), and an outer ring (306B), between the hub (303) and the synchro Cone (301B) for 2nd Gear.

Figure 4 illustrates an exploded view of child parts for 3rd and 4th gear Synchropack according to an embodiment of the present invention.
In this embodiment, the exploded view indicates 3rd Gear (203) and 4th Gear (204) at the opposite ends. The 4th Gear (204) is mounted on the shaft. Since the Synchropack is for the higher gears such as 3rd, 4th and 5th gears, the synchropack comprises a single-cone synchronizer. The synchropack for 3rd and 4th gears comprises a sleeve (302), a hub (303), a Synchro cone (301C) for 3rd gear, a Synchro cone (301D) for 4th gear, a Synchro Ring (401A) placed between the sleeve (302) and the Synchro cone (301C) for 3rd gear, and another Synchro Ring (401B) placed between the hub (303) and the Synchro cone (301D) for 4th gear.

Figure 5a illustrates a schematic representation of a synchronizer ring for 1st and 2nd Gear according to prior art. In the prior art, a single cone synchronizer ring is used for 1st and 2nd gears. The single cone synchronizer ring is placed between the sleeve mounted on hub and a synchro cone in the transmission system.

Figure 5b illustrates a schematic representation of synchronizer rings for 1st and 2nd Gear according to an embodiment of the present invention. In an embodiment of the present invention, a multi-cone synchronizer ring is used for 1st and 2nd gears. The multi-cone synchronizer ring is placed between the sleeve mounted on hub and a synchro cone. The multi-cone synchronizer ring comprises an inner ring (304), a mid-ring (305) and an outer ring (306).
In the present invention, cone torque is increased by increasing the surface area of multi cone synchronizer ring and modification in cone tooth design, also the coefficient of friction is adjusted by doing threading/groove on the inner surface of synchronizer ring at a particular angle (preferably between 6 degree to 8 degree) and some space is left (12b) (Figure 7b) between the threading set due to which lubricant can be easily flow within the dual cone synchronizer ring. In one embodiment of the present invention, the surface area of multi cone synchronizer ring is designed for 135 square cm to increase the cone torque whereas surface area of the conventional synchronizer ring was 66 square cm.

Figure 6a illustrates an exploded view of a system for 3rd, 4th, and 5th gears according to prior art. The system comprises a single cone synchronizer ring which is placed between the sleeve mounted on hub and the synchro cone. The gear could be 3rd, 4th, and 5th gears.

Figure 6b illustrates an exploded view of a system for 3rd, 4th, and 5th gears according to an embodiment of the present invention. The system comprises a single cone synchronizer ring which is placed between the sleeve mounted on hub and the synchro cone. In this embodiment of the present invention, a friction material is coated on the inner surface of the single cone synchronizer ring. The Friction coated (such as Carbon Lining) Synchronizer ring of the present invention comes with unique design and by adjusting coefficient of friction, smooth gear shift is achieved.

The function of synchronizer is to synchronize the rpm difference between shifting gears (say 1st to 2nd or 3rd to 4th and vice versa) in stipulated time (0.12 sec to 0.30 seconds) with acceptable shift force (25 N to 50 N). Hence role of synchronizer is to gradually increase or decrease the rpm (Sleeve, Hub and Main shaft) with friction force & heat dissipation between Synchronizer and Cone.
Figure 7a shows a conventional Synchro cone whereas figure 7b shows the modified Synchro cone and the design change in Sleeve, according to the present invention. According to an embodiment of the present invention, some space is created (12b) between the threading set due to which lubricant can be easily flow within the dual cone synchronizer ring. Additionally, the Synchro cone is provided with a plurality of holes (12a) for enabling engagement & lubricant flow within the synchronizer ring. In one embodiment, the design of sleeve modified (19a) to optimize the performance of the transmission system.
Figure 8 shows the various stages of synchronization in the synchronizer according to an embodiment of the present invention. Step 1 shows neutral gear condition. Step 2 shows neutral detent. Step 3 shows pre-synchronization. Step 4 shows the synchronizing stage. Step 5 shows the synchronization. Step 6 shows block ring release. Step 7 shows engagement of tooth contact. Step 8 shows the full engagement.
In an embodiment of the present invention, the system uses the friction material coated (like Carbon) synchronizers in 3rd gear and 4th gear; while the dual/multi-cone Synchronizer is used in 1st gear and 2nd gears.
This results in a clear and smooth gear shift feeling in the range of about 1.8kgf to maximum about 3kgf with lesser synchronization time in the range of about 0.15 - 0.3 seconds only (refer Table 3 below), in Gear shift performance to have ergonomics inside vehicle shift knob position and also have a desired level of performance for product life. Also Synchronizer life can be matched with warranty expectations of vehicle which increasing from about 25000 km to about 200,000 km and the Synchronization time has also come down almost average about 30% less comparing with traditional transmission synchronization timing.

Table 1

Table 2

Table 3
This will help to achieve the shift performance (frugal engineering) at optimum cost and also the durability and Gear shift performance of transmission will significantly increase with quick response time for change without losing inter-changeability of synchro-pack on transmission.
The synchronizer rings of the present invention are so designed that it give comfort feel to the driver during driving because driver have to exert of about 1.8kgf to maximum about 3kg force to shift the gear position - with lesser synchronization time in the range of about 0.15 - 0.3 seconds only and the multi-speed transmissions are designed in such a way so that the running gears of the individual speeds, even if they are not involved in the power transmission, are constantly engaged.
Figure 9 shows the schematic representation of the Synchronizer layout according to an embodiment of the present invention.
Figure 10 shows the gear shifting layout according to an embodiment of the present invention.
Figure 11 shows a variation of Cone angle with respect to (w.r.t.) Torque.
Figure 12 shows impact of coefficient of friction (COF) on shift force with respect to (w.r.t.) Torque.
Figure 13 shows shift time variation with friction coated.
Beside the above, the invention is designed to optimize for ease of production at relatively a low cost. Addition to this it will significantly improve drivability and safety where frequent change of Gears is required.
Although the invention of the system and method has been described in connection with the embodiments of the present invention illustrated in the accompanying drawings, it is not limited thereto. It will be apparent to those skilled in the art that various substitutions, modifications and changes may be made in blob identification, blob classification, pairing logic and pair validation and verification without departing from the scope and spirit of the invention.
,CLAIMS:We claim:
1. A vehicle transmission system, comprising
one or more gears;
one or more sleeves operatively connected to the gears;
one or more clutch hubs connected to the sleeves; and
one or more synchronizer rings, each of the synchronizer ring being operatively connected to the sleeve and the gear for controlling axial motion of the sleeve,
wherein the synchronizer rings comprise a multi-cone synchronizer ring for a lower gear and a single-cone synchronizer ring for a higher gear.

2. The system as claimed in claim 1, wherein the multi-cone synchronizer ring having a predetermined surface area for providing a predetermined torque.

3. The system as claimed in claim 1, wherein the multi-cone synchronizer is provided with a threading on its inner surface at a predetermined angle to optimize coefficient of friction.

4. The system as claimed in claim 3, wherein the predetermined angle is between 6 degree to 8 degree.

5. The system as claimed in claim 1 further comprising one or more synchro cone,
each of the synchro cone is configured with a plurality of holes for enabling engagement & lubricant flow within the synchronizer ring.

6. The system as claimed in claim 1, wherein the multi-cone synchronizer ring is provided with a predetermined space between threading to enable lubricant flow with in the synchronizer ring.

7. The system as claimed in claim 1, wherein the single cone synchronizer ring comprises a friction coated synchronizing ring,
the friction coated synchronizer ring is coated with a predefined material of a predetermined friction coefficient on its inner surface.

8. The system as claimed in claim 7, wherein the predefined material coated on the inner surface of said ring comprises a carbon material.

9. The system as claimed in claim 1, wherein the lower gear includes gear 1 and 2, and the higher gear includes gear 3, 4, and 5.

Dated this the 9th day of February 2017

Signature

SANTOSH VIKRAM SINGH
Patent agent
Agent for the applicant