Dual Clutch Transmission System

Abstract— Efficiency and comfort are the major aspects of automobile industries. Manual Transmission provides power and automotive transmission provides comfort and Dual Clutch Transmission was the centre path or the mixture of these two transmissions and resolution to the problem. After the invention of Dual Clutch Transmission (DCTs) first time in 1980s the two major aspects of comfort and power were in one engine or transmission. Our paper is mainly focus on the explanation about the power train, from its evolution to future aspects. There are many types power transmission available now-a-days which are manual transmission, automatic transmission, dual clutch transmission & continuous variable transmission. In this paper we mainly focus on the DCT & their aspects. DCTs technology has gained a substantial market share in the recent times (up from 3.4% to 8.5% market share in the last 5 years). We also use a prototype examination of the DCT so we can study its pro & cons.

Keywords— Dual clutch transmission; automobile; gear shift; clutch;

I.	Introduction 

Traditionally vehicle transmission systems have incorporated either a single clutch or a torque converter between the engine and the drivetrain. These allow the engine to run while the vehicle is at rest without the engine stalling. To date the majority of consumer vehicles have featured either a manual transmission or an epicyclic automatic transmission, while a small number of vehicles have incorporated continuously variable transmission (CVT) systems. In recent years, however, a growing number of manufacturers have been developing and manufacturing dual clutch transmissions (DCT) for use on consumer vehicles. This type of transmission offers benefits over both traditional manual transmissions and epicyclic automatic transmissions. This report investigates the technology employed in DCT systems and the benefits which such systems provide.

Recently, dual-clutch transmissions (DCTs) have garnered substantial attention in the global automotive industry because they have demonstrated significant improvements regarding both efficiency and ride quality of vehicles

The Dual Clutch Transmission (DCTs) was firstly introduced in 1980s when some big automobile companies were introduced to racing and start working on racing cars. The DCTs was the mixture of two transmission engines one was manual transmission and the other was automatic transmission. As the companies were in the market of racing and commercial vehicles so they needed power and as well as they needed efficiency. The manual transmission engine gives power while the automatic transmission engine gives comfort. The DCTs came up with a new concept of high quality gear shifting with a pre-selection procedure of gear. This was the indistinct control theory from the other transmission engines.

The Dual Clutch Transmission has dynamic shifting of gears with the help of two different shafts which are connected to two different clutches. The outer clutch is bigger in size and is for the odd gears and the smaller clutch is for the even gears. The DCTs have a fast clutch to clutch shifting and this is a robust structure and a fine and accurately designed engine transmission. The clutch actuator time constant (the time needed to shift the gear) is reduced and some people had problems with the three pedal vehicles as they found it very difficult to control. The DCT is the combination of two manual transmissions one for odd gears and other for the even gears with their two different clutches and thus the name was given as the Dual Clutch Transmission. The basic need of today is efficiency and with this bend towards fuel we needed an engine with a greater efficiency and with the ease to drive for everyone and with the removal of clutch pedal this was achieved. There are two types of DCTs one which is for super cars and other for the economical vehicles. The wet clutch which is dipped in the oil well gives high power torque and used in super cars but is less economical while on the other hand the dry clutch give us low power torque used in economical or commercial cars but is highly economical.

The components of the dual clutch transmission are: - Clutch- The clutch is device which is use to transmit the motion b\w to co axial shaft.

Gear- These are use to transmit the motion b\w two parallel shaft & perpendicular shaft.

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Shaft- This a solid rod on which the transmission does occur. Synchronizer- These are devices used to lock the gear through shaft for being transmission

ECU- This is used in DCT to calculate that which gear is to be shifted that may be up or down.

Figure 1: Dual Clutch Transmission System

The DCT are those power train in which the constant power transmission & regular torque is applied (also when shifting of the gears occurs). According to the characteristics of DCT synchronizer which can be pre-engaged in the shift, under the premise of ensuring the accurate realization of the synchronizer’s function, which would help us in getting the constant power & torque.

This paper conducts dynamics analysis of the DCT shifting process and makes model and analysis of key parts; on this basis, it develops a shift schedule based on driver intention, and makes detailed analysis for gear shifting process to develop a shift control strategy; finally, based on the MATLAB/SIMULINK simulation platform, it builds DCT shift model and conducts simulation test to verify the validity of the shift control strategies.
II.	LITERATURE REVIEW

The bulk of the modeling work done on DCTs is very similar. The power train is treated as a multi-degree of freedom dynamic system with a series of inertial and compliant elements. Internal components of the transmission are often treated as rigid bodies. Torque relationships are developed at various points within the system, including engine, road load, and clutch friction torque, and then shift and clutch controllers are developed [3]. Once the model is completed numerical examples of control of shift change is presented and “successful” results are discussed. Commonly, the engine makes up one pair of elements and the driveshaft, wheels, differential, etc are grouped and reduced into one or more inertia-compliant sets. The transmission itself is considered as two separate clutches, each with a gear pair, attached to the output shaft. With synchronizers considered as a second clutch setup by Goetz [3] or as a switch Zhang, et al,

[8] or not at all Lei, et al, [9]. These components make up the remainder of the dynamic system as individual elements of either rigid Lei [9] or flexible type Goetz [3]. This develops a model that hybridizes rigid body and flexible body motion, which is useful in generating and simulating control over the DCT. In general these modeling methods are relatively simple, where more extensive models could be used in conjunction with model reduction techniques to improve the accuracy of results. Control of DCTs has been attempted using fuzzy [10], closed [3], and open methods [11] with closed loop being the best. Goetz [3] uses engine control, output torque, and clutch slip control to achieve the best results. Other methods include opening the clutch when negative torque is generated [9] and clutch slip in conjunction with engine speed [7] are also used for closed loop control. Overall a highly integrated transmission and engine controller is required to achieve the best results. Fuzzy logic and open loop methods that have been presented are questionable in application primarily as the transmission and powertrain are both well established torsional systems that have a long history of successful modeling and simulation. Ergo the use of fuzzy logic is questionable, and the need for closed loop control is almost critical to achieving the levels of precision required. When used in simulation the results vary depending on the comprehensiveness of both model and control method adopted. Goetz [4] shows that the best quality shift is achieved using integrated controller discussed above. Kulkarni and Zhang [7,8] generate relatively high tensional results for launches and shifts with a less developed system. While [9] results show abrupt torque changes associated with transient generation, but poorer modeling has limited the result accuracy. The primary issue is then how does one assess the accuracy of the results if a limited model is presented. Are the results representatives of the physical responses of the transmission. Typically, this type of question would be resolved through either powertrain or in-car testing. This is where the main issue lies; there is very little published work on the validation of DCT powertrain control methodologies. However, the simulations can be assessed based on the presented model. For example, Kirshstein [6] and Goetz [3] both present comprehensive model development within the published work, with this established it is then possible to review results critically and understand how results were achieved.

III.	WORKING OF DCT

This is two independent manual transmission controlled by a computer. If we press the outer clutch plate then the power is transmitted to the blue set or the odd gear set and if we press the inner clutch set then the power is transmitted to the grey set or the even gear set. The blue set is connected to the odd gear set and the grey is connected to the even gear set. Now suppose the vehicle is moving in 3rd gear and we want to shift to the

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4th gear the 4th gear sleeve is connect in advanced even when the 3rd gear sleeve is already connected thus all we have to do is just release the blue clutch set and engage the grey gear set this pre-selection gives us better comfort just like automatic transmission and power just like manual transmission. This gives us constant power with break in power and torque which we suffer in manual transmission.

A.  Structure & principle of DCT

The name given to the power train by the two clutches does may have single or multiple disk, wet or dry type, mainly depend upon the amount of load (heavy or low) transfer requirement. In this train we have used 5 forward gears & 1 reverse gear. The systematic arrangement of the gears is shown below:

When the engine starts the power to the transmission system is preceded. Firstly, both the clutches are open & torque transmitted to the wheels is zero. When driver shifts the gear to 1st the clutch cl2 will close & torque transmitted to the wheels, until the driver shift (or think of shifting the gear) to 2nd gear the ECU command to the synchronizer syn2 engage with the respective gear 2nd. Similarly, the cycle goes on until the 5th gear will engage to the shaft. For the down shifting of the gears the ECU computes the speed & analyze it so that when we downshift the gear (consider 2nd gear to 1st gear) the synchronizer syn1 will come into the action.

the same time: the ECU must avoid the concurrent lock of the two clutches in order to prevent damages to the gearbox.

B.  Transmission system model

This transmission system model is taken from the MATLAB\SMULINK r2016b. This model consists of vehicle, output, engine, DCT, transmission controller electronic transmission unit the transmission controller converts the pedal deflection into a demanded torque. This demanded torque is then passed to the engine management.

The pedal deflection and the vehicle speed are also used by the transmission controller to determine when the gear shifts should occur. Gear shifts are implemented via the two clutches, one clutch pressure being ramped up as the other clutch pressure is ramped down. Gear pre-selection via dog clutches ensures that the correct gear is fully selected before the on-going clutch is enabled.

Figure 3: Transmission system model of DCT

C.  Gears subsystem

Five dog clutch components from simscape driveline are connected between the follower shaft of each gear to the transmission output shaft. The controller preselects the next gear to which the transmission will shift by engaging the dog clutches. At any point, two of the dog clutches will be engaged, that for the current gear and that for the next gear to which the transmission will shift.

Figure 2: Structure & principle of DCT

In contrast to these evident advantages, DCT systems are more complex, both in their mechanical architecture and in the automatic handling of the gear change task. Furthermore, the presence of two clutches and of a greater number of bearings determines a reduced efficiency with respect to traditional manual or automated manual gearboxes; however, their efficiency is still greater than that of automatic transmissions with torque converters and continuously variable transmissions. A distinctive characteristic of the DCT is represented by the fact that during normal operating conditions the dual clutch gearbox has two different gear ratios engaged at

Figure 4: Gear Subsystem of DCT

D. Vehicle subsystem

Tire models from simscape driveline that are characterized by the magic formula are connected to a longitudinal model of the vehicle dynamics. The driveshaft is connected to the rear wheels. The normal force for each axle is used in the slip calculation for each wheel.

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Figure 5: Vehicle Subsystem of DCT

IV.	Pros and Cons of DCTs

These are semi-automatic or automated manual automatic transmission. Due to the dual clutch the clutch slippage is controlled and the shifting is smoothly done. Due to connection of the sleeve and gear in advance reduces the discontinuity in speed controlling and the discontinuity in the torque due to the gear shifting. The up shift takes place in 8 milliseconds to 30 milliseconds which is less than half a second due to the perfect gear shifting operation the fuel consumption is reduced and the efficiency of the engine is increased. The speed of the DCTs are very high which gives a better dynamic drive and a perfect controlling of the vehicle and due to the dual clutch system the jerks are reduced and the comfort of the vehicle is highly increased. The absence of clutch pedal makes a simpler experience for the driver as some of the driver have problem with the three pedal systems. As this transmission system is so advanced it has certain drawbacks as if the applying time of the clutch is not perfect then there is an undesired disturbance in the torque and due to this the fuel economy of the vehicle also gets affected. This transmission system is simpler, smoother, and quicker. When the vehicle with dual clutch transmission is moved from a stopped position, it can be felt that the vehicle hesitates a moment before actually engaging gears. There is jerkiness in low gear while the vehicle is moving slowly this creates a problem where there is a compact space in the parking where the vehicle is to be parked. The engine with this transmission is very heavy and the size is also very large as compared to other transmission engines and that’s the reason

DCTs become expensive and less economical but this was also overcome by dry DCT which has low torque power but highly economical.

V. Simulation results from simscape logging

The plots below show the engine and vehicle speed as it accelerates through the first three gears in the dual-clutch transmission. The half-gear states indicate gear shifts are taking place by engaging and disengaging the dual clutches.

Figure 6: Simulation results

VI.	Conclusion

When normal clutch or the manual were used then there was a breakage in the torque, when the gear was changed but because of the dual clutch transmission this failure was resolved as before even changing the gear, the next gear came in contact with the driving shaft and that’s why without losing speed or torque the gear was changed. Due to this technology the entire racing industries were changed as the cars with this technology were having good efficiency and a minimal loss of torque and maximum amount of power was transmitted.

References

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