FIELD OF THE INVENTION

[001] The invention relates to an Automated Manual Transmission System and more particularly, it relates to a gear shifting mechanism for Automated Manual Transmission System.

CROSS-REFERENCE TO RELATED APPLICATION

[002] This invention takes priority from provisional application No. 202221030206 filed on May 26,2022; the entirety of which is incorporated herein as reference.

BACKGROUND OF THE INVENTION

[003] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[004] Conventional manual transmission system comprises a gear lever and a clutch pedal, which is manually operated by the driver. This type of system is cumbersome for the driver specifically disabled people and during city driving. Therefore, there is an increasing trend towards making gear shifting operation automatic. Various types of automated transmission systems have evolved over recent years including Automated Manual Transmission system which has become, one of the major types of automated transmission system. It comprises an actuator system, configured to operate clutch and gear shifting based on certain predefined conditions, thereby eliminating need to manual operations. Another type of transmission is Complete Automatic Transmission, which is employed in modern vehicles, but it is expensive and more fuel hungry than the Automated Manual Transmission systems. The Automated Manual Transmission has various advantages, for example: it gives great driving pleasure, reduces effort of the driver, enhanced fuel efficiency, quick acceleration at less cost.

[005] However, the challenges in implementing the same in any vehicle include expensive gearbox, high-cost of maintenance due to requirement of frequent servicing, repair being cumbersome for vehicle owners. More importantly, for electric vehicles that operate on rechargeable lithium-ion batteries, has limited power retention capacity, and is provided for operating motor for vehicle locomotion. As automated manual transmission generally employs electrical motor as actuator to change or shift gears, thus much power is drained behind transmission, hence frequent charging for electric vehicles adds to the miseries of the vehicle user. Hence, there is a need to design an AMT system, which consumes less power and has high efficiency.

[006] Traditionally two types of gear shifting arrangements are widely used in the transmission system i.e. clash mesh arrangement and a synchromesh-type transmission. The clash mesh arrangement has an advantage of providing a simple and low-cost solution, but it suffers from drawback of gear clashing as well as high driveline backlash resulting in higher noise and vibrations, more wear and tear of the gear which leads to increased serviceability.

[007] The synchromesh-type transmission mechanism has a synchronizer comprising a synchronous ring along with a sleeve configured to engage the targeted gears. The synchronous ring is responsible for synchronizing the speeds of rotating gear with sleeve to achieve precise and smooth engagement of gears. As synchronous ring is of considerable weight, it results in increased gearbox weight. The synchronous ring in high intensity working state like commercial vehicles will subject to wear and tear, thus reducing the service life of the synchronous ring. Also, synchronous ring is made of expensive metal with precise design that increases cost of the transmission system. A synchro type of arrangement is highly complex but having an advantage of exceptionally low driveline backlash. Hence, the need is felt to optimally design a transmission system which is low in cost, less complex and have effortless precise engagement of the gears with sleeve. Also, a need is felt to avoid use of synchronous ring.

[008] In conventional AMT systems, a drum is used to actuate the synchronizer to engage the gears. This high-cost structure is bulky and occupies significant space. To obviate the said pitfalls, in some systems, a gear shifter motor with a lead screw along with a fork is used. The fork is coupled with the synchronizer to engage/ disengage the gears. Retaining and holding the gears in engaged position is an important requirement in AMT systems for which variety of retaining means are used such as pins or back taper on engaging teeth. However, this is difficult to manufacture, increases cost and space. The currently available system has infirmities of inaccurate, harsh movement of the fork along the screw, inability to hold the gears in engaged position, undue vibration and noise leading to shorter lifespan of the components and increased maintenance. [009] Another drawback of existing system is the gear shifter motor, which consumes substantial power to linearly move the synchronizer that is heavy in weight due to the synchronizer ring. This, results in increased power consumption and cost for AMT systems as high rating motor is employed, which is concerning specifically in case of electric vehicles.

[0010] To overcome all the disadvantages and shortcomings in above-described Automated Manual Transmission System applications like large space requirement, noise and vibration during operation, manufacturing complexities and cost escalation an effective, and improved Automated Manual Transmission System in vehicle is necessitated.

[0011] The details described as the background art are intended merely for the purpose of promoting an understanding of the background of the present disclosure and should not be construed as an acknowledgment of the prior art that is previously known to those of ordinary skill in the art.

OBJECTIVE OF THE INVENTION: -

[0012] An objective of the invention is to provide an improved Automated Manual Transmission System, which improves fuel efficiency and electric efficiency of a vehicle.

[0013] Another objective of the invention is to provide an Automated Manual Transmission System, which has improved manufacturability.

[0014] Yet, another objective of the invention is to optimally design a transmission system, which is of low cost and is less complex. SUMMARY OF THE INVENTION

[0015] With these objectives in view, the present invention provides an automated manual transmission (AMT) system for a vehicle comprising; a drive source for driving the vehicle; a transmission system comprising an output shaft selectively engaged with the drive source through at least a gear pair comprising at least an output gear coupled with at least an input gear to transfer power/ torque; wherein the output gear engaged or disengaged with the output shaft using at least one sleeve connected to the output shaft; and the sleeve actuated using a fork wherein the fork mounted on a lead screw; wherein the lead screw rotated using an actuator to linearly move the fork.

[0016] According to one of the embodiments, an automated manual transmission system comprising of a gear shift controller configured to synchronize rotational speed of the output gear with the sleeve by controlling the power delivered by the drive source.

[0017] The rotational speed of the output gears and the output shaft is sensed by detecting at least the speed of a drive shaft or speed of a vehicle or speed of a wheel. [0018] The detected rotational speeds of the drive shaft and the rotational speed of the output shaft are provided as input to a gear shift controller.

[0019] The input gear mounted on an input shaft linked with the drive shaft wherein; the drive shaft is an output shaft of the drive source.

[0020] The lead screw is having a lead angle between six to twelve degrees.

[0021] The lead screw is connected to a guide shaft mounted parallel to the output shaft. [0022] The lead screw connected to the actuator through a gear assembly comprising a gear pair wherein; the actuator is a gear shifter motor.

[0023] The gear A of the gear assembly is fixed on the lead screw by a nut and bearing assembly.

[0024] The fork has a position sensor, to detect the position of the fork.

[0025] The sleeve and the output gears comprise of dog teeth, having a straight profile with a backlash of one degree between them in an engaged position.

[0026] The output gear engaged or disengaged with output shaft using at least one sleeve with shift time below 100 milli-seconds.

[0027] According to an embodiment of the invention, intermediate shafts with intermediate gears may be linked to both the input and the output shafts.

[0028] The output shaft is coupled by a gear set with a differential gear and the differential gear is further connected to at least one wheel via a wheel shaft.

[0029] A method of operation of an automated manual transmission system for a vehicle comprising: driving the vehicle by a drive source; engaging selectively an output shaft with the drive source through at least a gear pair comprising at least an output gear coupled with at least an input gear for transferring power/ torque; detecting the speed of the output shaft using a sensor and detecting the speed of the drive shaft of the drive source; controlling the power/ torque produced by the drive source for matching rotational speed of the output gear, with a sleeve connected to the output shaft; actuating an actuator for engaging the sleeve with the output gear for transmitting power delivered by the drive source to the output shaft. [0030] An automated manual transmission system applicable for two or three or four wheeled vehicles; wherein the drive source is a motor, or an engine or both.

BRIEF DESCRIPTION OF DRAWINGS

[0031] The above and other objects, features, and advantages of the present disclosure will be more apparent from the detailed description taken in conjunction with the accompanying drawings. One or more embodiments of the present invention are now described, by way of example only with reference to the accompanied drawings wherein like reference numerals represent like elements:

[0032] Fig.l illustrates an isometric view of an Automated Manual Transmission System assembly employed in a vehicle, according to an embodiment of the present disclosure;

[0033] Fig. 2 depicts a cross sectional view of an Automated Manual Transmission System according to an embodiment of the present disclosure;

[0034] Fig.3A illustrates a top view of a lead screw with guide shaft arrangement, according to an embodiment of the present disclosure;

[0035] Fig.3B illustrates an isometric view of an actuator assembly comprising a fork, a lead screw and a guide shaft according to an embodiment of the present disclosure;

[0036] Fig. 3C depicts a fork, according to an embodiment of the present disclosure;

[0037] Fig.4 illustrates a cross sectional view of the assembly of a gear shifter motor with a lead screw and a guide shaft according to an embodiment of the present disclosure; [0038] Fig.5 depicts a lead screw with thread profile according to an embodiment of the present disclosure;

[0039] Fig.6 illustrates a graph of lead screw thread efficiency curve, according to an embodiment of the present disclosure;

[0040] Fig.7 illustrates an exploded view of the electro synchro actuator, sleeve(s) with two speed gears, according to an embodiment of the present disclosure;

[0041] Fig.8 depicts an isometric view of one of the gear(s), according to an embodiment of the present disclosure;

[0042] Fig.9 depicts an isometric view of sleeve, according to an embodiment of the present disclosure;

[0043] Fig.10 illustrates a front view position when the sleeve(s) is engaged with the gear(s), according to an embodiment of the present disclosure;

[0044] Fig. 11 A depicts a magnified front view of a gear dog teeth and a sleeve dog teeth when engaged with each other, according to an embodiment of the present disclosure;

[0045] Fig. 11B depicts a magnified top view of the gear dog teeth and the sleeve dog teeth when engaged with each other, according to an embodiment of the present disclosure;

[0046] Fig. 11C depicts a top view pictorial representation of the gear dog teeth and a sleeve dog teeth angular width, according to an embodiment of the present disclosure; and

[0047] Fig. 12 represents an isometric view of an Automated Manual Transmission assembly, according to an embodiment of the present disclosure. DETAILED DESCRIPTION:

[0048] A preferred embodiment will now be described in detail with reference to the accompanying drawings. The preferred embodiment does not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.

[0049] It will be readily understood that components of present invention as generally described and illustrated in figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the invention as represented in the figures is not intended to limit the scope of the invention but is merely representative of certain examples of presently contemplated embodiments in accordance with the invention. The presently described embodiments will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout.

[0050] The present invention provides an Automated Manual Transmission system (125) that includes a drive source (10) for driving the vehicle transmission system. The technology described here caters to precise and smooth engagement and disengagement of gear pair(s) in transmission system.

[0051] Fig. 1 and Fig. 2 illustrate an Automated Manual Transmission System (125) employed in a vehicle, according to an embodiment of the invention. The Automated Manual Transmission System, herein also referred as AMT. The transmission system according to one of the embodiments is engaged to a drive source (10) and comprises of an input shaft (20) and an output shaft (30) connected through set of gear pairs. The input shaft (20) has a plurality of input gears (40) mounted on it and the output shaft (30) supports a plurality of output gears (50). The output shaft (30) is coupled by a gear set with a differential gear (60). The differential gear (60) is further connected to wheels via a wheel shaft (15). The input shaft (20) is driven by a drive shaft (70) of a drive source (10) through a drive gear pair (80). The input gears (40) are in constant mesh with the output gears (50) to transmit power/ torque received from the drive source (10). The drive source (10) may be an internal combustion engine, an electric motor, or a hybrid system. The output gears (50) are suitably engaged with the output shaft (30) to transmit power/ torque to the wheel/s of the vehicles suitably.

[0052] Further, according to the present invention, an electro synchro actuator assembly (90) is provided to suitably couple the output gears (50) with the output shaft (30) based on predefined operating conditions. The electro synchro actuator assembly comprises of an actuator (130) for actuating a lead screw (100), a fork (110) mounted on the lead screw (100), which is further connected with at least a sleeve (120) mounted on the output shaft (30) to linearly move the sleeve (120) for engaging or disengaging the output shaft (30) with the output gears (50). The actuator is configured to provide necessary drive for the fork (110) through the lead screw (100) to actuate the sleeve (120). The lead screw (100) converts the rotatory motion provided by the actuator (130) into translatory motion to actuate the fork (110), which in turn engages or disengages the sleeve (120) with the output gears (50).

[0053] According to the present invention, an actuator is a gear shifter motor (130), though other type of actuators may also be employed including hydraulic or pneumatic actuator. The gear shifter motor (130) is directly coupled with the lead screw (100) preferably through a gear assembly (140). The gear assembly (140) preferably comprising a gear pair (140A,140B) is configured to regulate power delivered by the gear shifter motor (130) suitably to the lead screw (100) and the fork (110) according to the requirement, this helps to deliver optimum power to the lead screw (100) and reduces the power requirement of the gear shifter motor (130) thereby saving considerable power being essential in case of the electric vehicle. Preferably, a low rated power output motor may be employed with the help of gear assembly (140).

[0054] Fig. 3A, 3B illustrates a lead screw (100) with a guide shaft (150). The fork (110) position needs to be retained to hold the sleeve (120) in an engaged position to prevent undesirable disengagement of gears, noise, undue vibrations. The sleeve (120) engaged to the gear(s) is subjected to excessive vibrations and external forces, which pushes the sleeve (120) out, thereby forces disengagement. According to the present invention, the guide shaft (150) helps in retaining the position of fork (110), thereby accurately holding the sleeve (120) in the necessary position. Hence, the guide shaft (150) provides a support for the fork (110) arrangement and provides an opposite force to restrain the sleeve (120) with the gear(s). The fork (110) mounted on the guide shaft (150) is actuated by the lead screw (100) to linearly move the fork (110) and the sleeve (120). The lead screw (100) and the guide shaft (150) may be positioned through the holes carved on the fork (110) head. The guide shaft (150) maintains an axis parallel to the output shaft (30), which further aids in providing stability to the fork (110). [0055] The fork (110) as illustrated in Fig. 3C may be a prong like structure having two arms connected to the sleeve (120) for better support and stability of the sleeve (120) on the output shaft (30).

[0056] Fig.4 illustrates a cross sectional view of the assembly of gear shifter motor (130) with the lead screw (100) and the guide shaft (150) according to another embodiment of the present disclosure. The nut and bearing assembly (160) are essential to hold the gear (140A) of the gear assembly (140) at a fixed position and prevents any vibration and play of the gear (140A). The nut is attached to one end preferably at the gear shifter motor (130) side and bearing placed at the opposite end of the gear (140A). The induction of nut and bearing enhances the efficiency of gear assembly (140) almost to -100%.

[0057] In AMT applications, use of back taper on teeth of sleeve (120) and engaging gears is prevalent to hold and retain the sleeve (120) with the rotating gear at engagement position. Providing a back taper increases complexity in teeth design of gears and adds to the machining cost. Hence, to reduce manufacturing cost and for simplicity, as illustrated in Fig. 5, according to the present invention, the lead screw (100) is having a unique thread arrangement precluding a back taper arrangement. The lead screw (100) is designed in such a way that it provides an optimization for lead angle of the thread. The lead angle may have range from six degree to twelve degrees for optimum efficiency. When a lead angle is less than six degrees, more torque is required from the gear shifter motor (130) to actuate the lead screw (100) in the desired position. Further, when a lead angle is more than twelve degrees, the lead screw (100) cannot effectively retain the fork (110) and the sleeve (120) with the rotating gear, thus possibility of undesirable disengagement arises, thus, optimization is required. The lead screw (100) thread design having lead angle between six degrees to twelve degrees is required to provide a tradeoff between the torque provided by the gear shifter motor (130) to move the fork (110) across the lead screw (100) and the restraining limit to hold the sleeve (120) by the fork (110), when it is engaged to the rotating gear, without any other provision for holding the sleeve (120) in engaged condition. Fig. 6 depicts a graphical representation of lead screw (100) efficiency (%) vs lead angle.

[0058] According to the present invention, the sleeve (120) position may be detected by a detector/ sensor (170) to accurately determine the position of the fork (110) and the sleeve (120) with respect to the engaging gear(s). The detector/ sensor (170) is preferably mounted on the fork (110). The fork (110) is designed in such a way to accommodate the sensor (170), which is mounted on the fork assembly to correctly determine the position.

[0059] Fig.7 illustrates an exploded view of the electro synchro actuator assembly (90) with two speed gears, according to the present disclosure. The fork position sensor (170), which is mounted on the fork (110), can be used as a position sensor (170) and a magnet (180) of the sensor (170) is attached to the fork (110) designed to detect the position of a fork (110) that moves with the sleeve (120). The fork position sensor (170) judges the accurate transmission shift position of the fork (110) and the sleeve (120) with respect to the gear(s) and sends signal to the gear shifter motor (130) that makes exact gear shifting action for engagement of the sleeve (120) with the gear. Thus, when the heads of the dog teeth (190, 191) of the sleeve (120) and gear(s) having a straight profile (190A, 191A) connect with one another, the gear shifter motor (130) on receiving signal input from the sensor (170) slows the sleeve moving speed. Further, once engagement is complete the fork position sensor (170) sends signal to the gear shifter motor (130) for operation to stop.

[0060] Further, according to the present invention, the fork position sensor (170) is provided to identify the accurate position of the fork (110).

[0061] In AMT systems, backlash is a common occurrence. This problem frequently impacts gear systems, and it is a disadvantage when constant angular velocity is required. When the driving gear reverses direction or the traction torque changes from positive to negative in a transmission system with backlash, it results in unwanted noise and vibrations, which also reduces efficiency. Meanwhile, backlash causes the relationship between the output shaft (30) and the input shaft (20) in the transmission system to become nonlinear, complicating the control work. All the circumstances will have a detrimental effect on the transmission system's control precision.

[0062] According to the present invention, Fig. 8 depicts a gear, which has entry chamfers etched out in respective dog teeth (191) along its internal periphery to match with the dog teeth (190) of the sleeve (120) depicted in Fig. 9.

[0063] According to the present invention, Fig. 10 depicts both the sleeve (120) and the gear in engaged position.

[0064] According to Figs. 11 A, 11B and 11C to mitigate the above-mentioned problem related to backlash in teeth of the gear(s) and sleeve (120), the teeth are so designed that they have only one degree of backlash between them at engaged position. Use of the dog teeth (190, 191) having a straight profile in both sleeve (120) and gear(s) having only 1 degree of backlash between them, avoids extensive backlash during synchronous motion of the sleeve (120) and gear(s) in the engaged position. This helps in reducing noise and vibrations and also precludes the use of back taper resulting in cost reduction and enhanced efficiency in the AMT system. [0065] Further, in the present invention, the synchronizer ring is eliminated with the help of a control strategy, which helps in accurately engaging and disengaging sleeve (120) mounted on the output shaft (30) with the output gear(s) (50), thereby minimizing gear clash problem, which helps in precise and smooth engagement of a sleeve (120) with rotating gears at reduced cost and weight. The AMT system is designed with shift time below 100 milli-seconds to achieve smooth gear shift.

[0066] The dog teeth (190, 191) of the sleeve (120) and the gear (s) can be engaged with each other without a synchro ring interposed in between them by complementing the rotations of the sleeve (120) and the gear. Further, due to implementation of the control strategy to engage the gear(s) and the sleeve (120), time required for gear engagement can be diminished.

[0067] According to the present invention, the vehicle may possess an Engine Control Unit (ECU) or a Motor Control Unit (MCU) or a gear shift controller, to sense the speed of the drive shaft (70) as the input gears (40) are in constant mesh with the drive source (10) and the output gears (50) are engaged to the input gear (40), the speed of the drive shaft (70) is equivalent to the speed of the output gears (50). A vehicle speed sensor (not shown) detects the speed of the output shaft (30) and the sleeve (120) mounted on the output shaft (30), which ultimately is the speed of the wheels. The sensed speed is provided as input to the Motor Control Unit. The Motor Control Unit controls the torque produced by the drive source (10) to match rotational speed of the output gear with the sleeve (120) connected to the output shaft (30) and only then synchronization happens between the output gear(s) (50) and the sleeve (120) resulting in an uniform rotational speed of both the output gears (50) and the sleeve (120). Further a gear shift controller may also be present to control the power delivered by the drive source (10) & matches the rotatory motion of the output gears (50) with the sleeve (120) that is rotating with the vehicular speed in order to have smooth engagement of the sleeve (120) and the respective output gears (50). After the matching of speed of the output gear (50) with the rotational speed of the sleeve (120) (vis a vis the output shaft (30)), and according to first or second gear requirement, the gear shifter motor (130) controls the electro synchro actuator assembly (90) comprising the lead screw (100) and the fork (110) arrangement to move the sleeve (120) from neutral position to first speed in-gear position or second speed in-gear position accordingly thereby achieving smooth engagement.

[0068] Fig. 12 depicts isometric view of an Automated Manual Transmission system (125). The system (125) comprises a wheel shaft (15) protruding from one end of the AMT system (125). A gear shifter motor (130) is mounted on a transmission casing (1250). Further, an electric motor as a drive source (10) is also mounted on the transmission casing (1250). The transmission system including differential, gears and input/ output shafts is covered using a transmission casing (1250), which may be a single integrated casing or may be provided as an assembly of separate covers. The depicted arrangement is a compact arrangement suitable for mounting in any type of vehicle.

[0069] Consequently, because the shifting manipulation is conducted with fewer components, a more compact transmission system may be built which helps in employment of the AMT in two, three and four wheeled vehicles. As can be seen from the above description, the present disclosure allows for the construction of a transmission with a more basic and compact structure, hence it is feasible to increase a vehicle's electric efficiency as well as its durability by lowering its cost. In another embodiment, the transmission system may comprise more than two output gears. Also, in another embodiment two or more sleeve(s) may be employed to engage with the output gears, actuated using multiple electro-synchro actuator assemblies. Further, in another embodiment plurality of intermediate shafts with intermediate gears may be preferred linked to both the input and the output shaft. Preferably, helical gears are used to have smooth gear engagement, although other type of gears may also be employed such as spur gears.

[0070] The invention has the following beneficial consequences: The gearbox does not need a synchronous ring of large synchronous capacity to realize the electric gear shifting process because the control unit actively adjusts the rotating speed of the output gear(s) with sleeve (vis a vis the output shaft) synchronous speed, reducing transmission weight, cost and improving service life of the shifting sleeve, as well as reducing gear-shift energy loss and improving the transmission efficiency of the gear box. [0071] The present invention may be implemented in variety of applications and preferably to any types of vehicles, (such as an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), a fuel cell vehicle, and the like). Also, a two, three or four wheeled vehicles can employ an AMT system described in this invention. The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics or essential characteristics. The described embodiments are to be considered in respects as illustrative and not restrictive.

[0072] Although the exemplary forms of the present disclosure have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the present disclosure.

Reference Numerals: -

Drive Source (10)

Wheel Shaft (15)

Input Shaft (20)

Output Shaft (30)

Input Gears (40)

Output Gears (50)

Differential Gear (60)

Drive Shaft (70)

Drive Gear Pair (80) Electro Synchro Actuator Assembly (90)

Lead Screw (100)

Fork (110)

Sleeve (120)

Gear Shifter Motor (130)

Gear Assembly (140)

Gear Pair of the gear assembly (140A, MOB)

Guide Shaft (150)

Nut and Bearing Assembly (160)

Position Sensor (170)

Magnet (180)

Dog Teeth (190, 1 1)

Straight Profile (190A, 191A)

Automated Manual Transmission System (125)

Transmission casing (1250)