Design and Optimal control of Automated Manual transmission.pdf

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ME-50400-27819 SAMPAD KUMAR PANDA

DESIGN AND OPTIMAL CONTROL OF AUTOMATED MANUAL TRANSMISSION Date:05-01-2016

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Abstract: The concerned topic deals with the design of basic modelling and control system for an automated manual transmission. The project also emphasizes on optimal control techniques to get the maximum output. The main purpose of the paper relates to improving the drivability and optimum fuel utilization by using the techniques and controlling the unnecessary fluctuations. The transmission system is based on the dyno test obtained from an engine to get the optimal input maps. The clutch phases are adjusted in such a way that the loss in torque shifting is minimum. The gearbox transmission is optimally controlled to get maximum efficiency. In order to control, we use different techniques for control and observation. The results obtained are compared to generic results without use of controllers. With the help of controllers, the stability of the system increases mostly in the area of vibration and torque fluctuations during upshifting from neutral and vice versa. The paper presents a systematic approach to control the clutch movement automatically and subsequently an actuation free from the influence of the driver. The driveline speed and transmission cogging torque is controlled to give a desired output. The results indicate a controlled speed and torque output with minimal losses and disturbances. For better accuracy, we use updated controller techniques which are newly updated so as to get more predictive results.

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Contents Page: 1. What is an AMT?

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2. Objective

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3. Modelling the system

8-20

4. Clutch and driveline controller design

21-49

5. Conclusion

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6. Bibliography

51

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What is an AMT? An automated manual transmission (AMT) doesn't have a clutch pedal; there's only an accelerator and a brake pedal, just like a regular automatic transmission. And if you leave an AMT in D mode, it basically performs like an automatic transmission -- all you have to do is worry about when to start and when to stop. [1] The main difference between a conventional automatic and these newer automated manuals/DSG is the way the power is transmitted from the engine to the transmission/gearbox. In a conventional automatic, there is a torque converter that transfers power from engine to gearbox. Additionally, they have a planetary gear-set which is different from a conventional manual gearbox .The low and higher gears in these are usually controlled with hydraulics where as in an AMT you use electronics to control the hydraulic valves. Advantages over automatic transmission

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1. AMTs also tend to yield better fuel economy and acceleration than regular automatics. The reason is that AMTs are more efficient; that is, they allow more of the engine's energy to flow directly to the wheels. For the same reason, stick-shifts have historically edged automatics in both categories. The magic of the AMT lies in its ability to combine the fuel economy and performance of a true manual with the everyday convenience of an automatic. 2. Dual-clutch AMTs, on the other hand, are designed to eliminate lurching, and the best units provide incredibly quick yet perfectly smooth shifts. Most AMT-equipped cars use dual-clutch technology. 3. The gearbox used in case of AMT is still the manual transmission gear system in which the shifting is controlled by the controllers in the AMT control module where as in automatic transmission the gearbox is controlled by solenoids actuated by transmission fluid flow. The manual gearbox is more robust and high lurch resistant as compared to automatic transmission gearboxes. Diagrammatic representation of AMT [2]

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Manual gearbox (5 speed) but the actuation of the shifter is

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done by hydraulic valves. [3]

The control system design objective/Driving strategy for controlling

Look up table for optimal torque and velocity map

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Driver knob controller/dSpace microcontroller which detects change

Engine management system

AMT CONTROLLER

Clutch controller

Electronic gear control unit/dSpace for gear shifting 1. Drive speed control

Clutch actuator by electrohydraulic mechanism

Feedback to AMT controller loop close

2. Transmissi on torque control 6-speed gear shifting

Feedback to AMT controller loop close

Objective: Our main objective in this report will be to design a controller (AMT) which will process to take inputs from other controllers and driver inputs to synthesize a signal for actuating clutch and gearbox. The system is designed to improve drivability in terms of compensating drive speed control and drive transmission cogging torque losses .We will use different controller techniques to control the actuators and finally minimize the cost function parameters to get better efficiency.

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Modelling the system: As described in the model, the AMT system has a unique power transmission where the engine power is transmitted directly to the wheels with minimal losses. In order to get the final output, we need to model the system as per following requirements:

  

Engine map calculation to make the look up table for input parameters(ECM) Clutch design technique for smoother engagement and less lurch. Gearbox hydraulic actuation for gear shift

1. Modelling engine system: [4] The engine gives us the parameters for calculating the conditions of clutch engagement, gear shifting positions and time delays. -The parameters in the report are obtained from a 697 engine (6 cylinders, 97 mm bore diameter) which has following specifications as rated: - Engine maximum torque-430NM - Rear Axle ratio-5.85 - Mass of the vehicle-11000Kg(unloaded) - Loaded tire radius-20.69cm - Gear ratios are-

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1st Gear

6.568

2nd Gear

3.567

3rd Gear

2.124

4th Gear

1.383

5th Gear

1

Overdrive Revr Gear RAR

0.777 5.726 5.86

radius

0.5

unload

11000

load

16200

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-Calculation of indicated braking torque was done by using a dynamometer. This is the dyno test of the vehicle required to get the dynamic engine data. - The engine friction torque was calculated as a function of temperature. By an experimental thumb rule, its value is generally taken as 20% of the indicated braking torque. -Net braking torque=indicated braking torque-fiction braking torque -gear ratio for 6 speed manual gearbox is calculated from design of gears; - We calculate the velocity in individual gears by using the formulaev= (2*pi*RPM*radius)/gear ratio 1. The data for velocity is calculated and the specific fuel consumption is also deduced from the flowmeter experiments in the vehicle: d1.xlsx d2.xlsx 2. The acceleration and the thrust force on the vehicle was given by the equations of motion: d3.xlsx 3. The BSFC is calculated with variation in the engine RPM and the data is used in the logger. d4.xlsx

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Now using the above data, we have to calculate the maximum velocity by imposing the resistances on the vehicle. The tractive forces was calculated from the formula(F_tr=T_w/r_w); T_w= wheel torque, r_w=effective radius of wheel Air resistance= rho*0.5* A*C*V*V; rho C(drag coeff) A mass g

1.17 0.9 7.45 16000 9.81

kg/m^3 m^2 kg m/s^2

The rolling friction is calculated from the regression analysis as enclosed in the file. This is done by a coast down test on the engine. After obtaining coefficient of rolling, we get rolling resistance = F*W Ac project data\Report LM1211025 Coast-Down TATA Hybrid Bus pdf-1.pdf The maximum velocity is obtained as F_tr= R_air + Rerolling; Tractive force and maximum velocity for gears.xlsx The torque difference is calculated after the shift from each gear to the other neglecting few losses during transmission: Torque at transmission = gear ratio* (torque at engine-Torque at clutch) The data is enclosed in the excel sheet below: Torque in output shafts of different gears during N shift.xlsx

Summing all the data we will now deduce the conditions of velocity and torque which will act as reference pulse for the clutch controller and then the gear shift speed and transmission so that the engagement is smooth according to the look up produced in the excel file produced. 1. The file gives the condition for higher shifting or upshift and this will be used in the data logger for the input to clutch controller to synchronize and shift in transmission. Project final file\upshift condition and range.xlsx (A) 2. Similarly for lowering of gears, downshift data is used. The acceleration flag is on only when the pedal is 100% and the KK switch cuts of the pedal to take the control and reduce the controller gains to slow or stabilize the speeds.

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Project final file\downshift condition.xlsx (A)

Thus, after we get he values from engine through ECM, we use the ECM output signals as reference for clutch to nesh with the speed and torque of the engine. ** The vehicle speed signal gives the data by acquisition to the ECM so that with the torque maps, the upshift and downshift in the form of torque pulses/voltage which moves the piston and

2. Clutch modelling [5] 1. The clutch packs are connected to the engine and the main shaft respectively (the clutch disc is connected to the main shaft, and the flywheel disc is connected to the engine). The surfaces of the clutch packs are covered with friction material. 2. During the slipping-closing phase, the clutch disc on the main shaft is moved towards the flywheel disc until the friction between the two discs is high enough to transmit engine Torque to the driveline. 3. The clutch displacement position determines the direct normal force F_N between the flywheel disc and the clutch disc, and therefore the torque transmission capacity of the Simulation of an automated manual transmission clutches. Tc=n*FN*mu*R N= number of clutch packs F_N=normal force Mu=coefficient of slip/friction which gives the difference in the Te and Tc R= radius of the clutch Tc= torque at clutch

Phases of torque modulation The torque output of the engine is a function of the throttle and engine speed .The controlled engine torque in the simulation is determined by a pre-calibrated engine map, which is a look-up table with the throttle and the engine speed as inputs and the engine torque as output. 1. Slipping phase (when the velocity of drive shaft slowly tends to velocity of crankshaft) 2. Engaged phase (We=WC) 3. Synchronizing phase (friction acts between clutch and flywheel Clutch driveline modelling 1. When the clutch packs are in slipping phase, the transmitted clutch torque capacity is also the transmitted torque Tc, which is determined via a non-linear relationship.

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Je*Wedot=Te-Tc (xp) ----1 [Jc+Jeq (ig, id)]*Wcdot=Tc (xp)-1/ig/id*[ktw*Del (thetacw) +Btw*(Wc/ig/id-Ww)] -2 Jw*Wwdot=ktw*Del (thetacw) +Btw (Wc/ig/id=Ww)-Tl (Ww)-3 Del (thetacwdot) =Wc/ig/id-Ww—4 The Torque at clutch is tuned so that the output is used to actuate the clutch actuator. Nomenclature: Je is the engine inertia, Jc is the clutch inertia, Jw is the wheel inertia, Te is the engine torque, Tc is the clutch torque, Ve is the engine rotational speed, Vc is the clutch speed, Vw is the wheel speed, and Xc is the throw-out bearing position. Furthermore, ig is gear ratio; id is differential ratio

, Js1 and Js2 are the inertias

of the two discs connected to the synchronizer, Jm is the main shaft inertia, Jt is the transmission gear box inertia, TL is the load torque, thetacw is the driveshaft torsional angle, ktw is the elastic stiffness coefficient, and Btw is the friction coefficient. Jeq (ig, id) = (Jm+1/ig*2(Js1+Js2+Jt/id*id) 2. During engagement phase, we take the condition as We=Wc and the modelling equations remain the same. 3. Synchronization phase: When the clutch disc is fully disengaged from the engine flywheel, the gears are shifted, which results in the rotational speed difference between the transmission gear shaft and the driveline shaft. The speed difference introduces friction between the collar gear and the synchronizer, which generates the synchronization torque Ts due to friction. By controlling the synchronization torque, the transmission shaft and gear shaft could be synchronized smoothly. During this synchronization process, there is no torque transmitted from the engine to the powertrain driveline. Thus the driveline dynamics during this process can be modelled as

[Jc+Jeq (ig, id)]*Wcdot=-Ts/ig--1 Jw*Wwdot=Ts*id-Tl (Ww) ----2

Note: In the controlling section we basically control the slipping torque out by using all the three phases to get the accuracy and reducing slip time.

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We will use a PID control by Ziegler Nichols method for tuning.(as damping frequency and damping ratio is unknown for the project). Clutch actuator design:

In the AMT system, the electrohydraulic actuator is mainly composed of a hydraulic piston, a housing, and return springs. The piston is controlled by the oil flow which determines the force on the actuator. In this section, a dynamic model for the hydraulic clutch actuator that is currently used in the actual transmissions is developed

A simplified schematic diagram of the electrohydraulic clutch actuation system is shown in Figure, where Ps is the supply pressure command and also the control input to the system, Pp is the pressure inside the clutch chamber, and Xp is the piston actuation. The clutch chamber and pushes the clutch piston to the right; finally it contacts and engages with the clutch pack. This process is called clutch fill and engagement. The dynamics associated with clutch engagement can be modelled : Hydraulic clutch actuator model

Modelling equations for piston actuation with torque input from controller

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X1dot=x2 X2dot=1/Mp*[Ap*(x3+Ps-Patm)-Dp*x2]-Fdrag(x3+Pc)*tanh(x2/alpha)-Kp*(x1+x0)-Fn

X3dot=B/V0+Ap*x1[sgn (u-x3)*Cd*Aorifice*(2|u-x3|/p-Ap*x2]

U=Ps (T) X3=Pp X1=Xp X2=Xpdot The PID control is designed by finding the gain values in the coming section to modulate the actuation of the clutch.

The parameters are as follows by experimental analysis:

Mp

0.4 (kg)

T

0.3 (s)

X0

1.5928 (mm)

∆t

0.000375 (s)

kP

242640 (N/m)

Aorifice

2.0442e-5 (m2)

135.4 (N/m/s)

ρ

880 (kg/ m3)

0.00628 (m2)

Cd

0.7

4.1054e-6(m/s)

Patm

1 (bar)

7.8e-5 (m3)

β

1625 (bar)

0.001517 (m2)

ks cs

0.00153(m2)

Dp Ap α V0 km cm

Fdrag

5.22 (N)

5.26(N)

In subsequent section, we device the controller for clutch phases torque modulation and clutch actuation. Further, the optimal clutch law is defined to get minimal loss.

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Gear shifting modelling strategy and gear shift logic: -After the clutch torque modulation has been done, the closed feedback goes to the AMT controller which then with the help of look up table(engine maps defined earlier) and gear shift (upshift ,downshift)logic changes the gear in the manual system. The gear shifting actuation is controlled by a microprocessor dSpace controller. (Out of project course) -In this project we are restricted to find the modulated drive speed and Transmission torque correction and then optimizing control law for minimal loss. We decide the logic control for shifting of gear by the help of crisp logic. The 2 main parameters to be controlled are velocity and torque. For this, we need to find a coupled system of clutch and drive shaft so that the flexibility and non-linear nature of clutch is assumed. Flexible system with non-linearity modelling 1. The non-linear clutch modelling is done by use of several springs with some being large and some small. This balances the non-linearity which is the higher the stiffness, the smaller is the spring and the smaller is the twist. 2. This prevents vibrations and acts as an insulation.

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[6]

Kc(x) = Kc1 if |x|