1 BRIEF ON TRANSMISSION:

The transmission is an intermdiate powerline component intended to receive the power developed by prime mover power and the same is altered in terms torque and speed in finite steps, to suit the load and speed demand requirements of vehicle.
During vehicle in motion, jerk is felt by the operator / passengers whenever gear shift is being done. This is due to sudden change in vehicle speed caused by the (a) difference in gear ratio and (b) a momentary deceleration caused by discordance of the driving torque of the engine and the load torque coming from the wheels. The operator continues to experience Innumerable jerks with innumerable gear shifts during travel. This will not only results in operator fatigue but affects the component life. Further due to operator fatigue, operator cannot work for longer time and hence affects productivity. Therefore, it is required to eliminate the jerk using shift smoothness to have comfortable driving and to improve the power train life. To obtain the shift smoothness, the absorbed torque rise In the clutch pack during engagement shall be gradual. The minimum slip time is between 0.6 to 1.0 sec. Slip time affects the total energy input to the clutch. Hence sufficient quantity of pressure plates has to be provided to have a balance between adequate heat carrying capacity and adequate slip time to reduce the wear rate.

1.1 GEAR SHIFTS THROUGH SHIFT CONTROL

The major focus on today OFF HIGHWAY dump truck transmission market is shift quality. Today's transmission with automatic gear shift with variable clutch modulation (pressure ramp) represents significant Increase in the state of the art technology provides improved safety, durability of power train components, reduced operator fatigue. Modulated shift points offer better fuel economy and improved safety, particularly in braking modes. The proper control system also permits cost advantages in many areas of the vehicle besides improving the life of drive train by minimizing the shift shock in both automatic and manual powershift transmissions through clutch modulation.

1.1.1 MANUAL POWER SHIFT TRANSMISSION

In conventional transmissions, jerk due to gear shift is optimized by carrying out following steps:
• Reducing the engine speed
• Disconnect the engine power from the transmission using main clutch
• Up shift / down shift to the next gear

• Release the clutch slowly to connect the engine output to Transmission input
During the process, the prime mover power is interrupted and hence there is power loss due to frequent rise and lowering of engine power. This results in loss of vehicle acceleration and higher fuel consumption. The amount of jerk optimization depends on skill of the driver.

1.1.2 PLANETARY POWERSHIFT TRANSMISSION:
Torque converters being used to ensure uninterrupted power flow from Engine to Transmission during gear shifting. The Torque converter consists of 4 major components viz., pump, turbine, stator and oil. The pump Is coupled to engine output, rotates with the speed of engine. The turbine Is coupled to Input of Transmission. The stator is coupled to stationary member. When engine rotates, the pump coupled to It rotates making oil inside the torus of pump to gain kinetic energy and throws the oil on to the turilne, thereby making the turbine to rotate and hence power is transmitted through the fluid media. The stator diverts the oil coming out of the turiDlne back to pump. The oil media not only transmits the power, but also absorbs the shock resulted during gear shift process to some extent.
The planetary transmissions uses manual hydraulic and electro hydraulic valves to arrest the 3" member viz.. Sun / Canier / Ring by use of multi disc hydraulic clutch system.

1.1.3 AUTOMATIC GEAR SHIFT TRANSMISSIONS:
In automatic Transmissions, a pre programmed microprocessor is being used called as controller to decide the gear up-shift and down-shift points, change over from converter phase to lockup phase, safety interiocks, user friendly diagnostic en-or codes and vehicle health monitoring systems. These are the state of the art of current generation Transmissions, well accepted by the customer.
2 TRANSMISSION CONTROL SYSTEM:
Transmission control system consists of Transmission control valve and its electronic controller and its in-built logics to continuously monitor vehicle operating conditions and to provide command / feed back for gear shifts, controlled clutch pressure rise for smooth gear engagements to eliminate the shift shocks. Apart from the above, the transmission controller is embedded with inbuilt logics to ensure vehicle safety, by monitoring sub systems such as speed sensors, pressure transducers, terhperature sensors and its wire harness. Further the Transmission controller is provided with in buiit logics to indicate the enx)r code for easy maintenance to rectify / repiace the sub system for speedy rectification. In short the development of transmission control logics has been achieved to:
a) Optimize shift smoothness to reduce the operator fatigue.
b) Ensure vehicle safety interlocks when vehicle In motion.
c) Ensure vehicle manual ovenide operation in case of vehicle electrical system failure / mechanical failure to bring the vehicle to workshop.
d) Optimize the wear rate of clutches to Improve the clutch useful life.
e) Transmission health monitoring feed back systems
f) Transmission diagnostic en-or codes for easy vehicle maintenance

2.1 TECHNOLOGY RAMP-UP ON TRANSMISSION CONTROL SYSTEM:
Dump tnjcks used for construction and mining industry are operated under load & no-load conditions combined with speed operations to improve the productivity. Hence clutch pressure modulation developed with fixed modulation using valves operated by spring; provide jerk free gear shift will suit to one particular speed and load condition only. The same valve doest provide similar riding comfort under different load and speed conditions viz.
1 a) Full throttle up-shift
b) Full throttle down-shift
c) Closed throttle down-shift
2 a) Load condition
b) No-load condition
A trimmed pressure rise provides a hard shift, results In high degree of jerk. An extended pressure rise results in longer clutch slippage time. This will results in faster wear of clutches as well as temperature rise and hence bigger cooler Is required. This has necessitated the optimizations of clutch slip time to have a balance between 'jeri<' and clutch wear under various operating conditions to have comfortable vehicle ride by operator as well as to improve the power train life.
Until 1990's open loop system was adopted for clutch modulation to provide fixed modulation using microprocessors with ON / OFF electrical solenoids. The shift quality achieved was excellent for one vehicle condition, Is not adequate for other vehicle conditions due to developing of one modulation, in-espective of vehicle load, speed and throttle position.
In the past 2 decades, remaricabie technology developments has seen in gear shifting to have more synchronous speeds which will benefit the life of clutches and drastically Improved the shift perfomnance using closed loop feedback system by use of microprocessors, which precisely controls the clutch pressure in accordance with
vehicle operating conditions. Existing proven concepts developed by other OE Transmission manufacturers are as below:

ALLISON CONCEPT 1 (US origin):

2.1.1 TRANSMISSION CONTROL SYSTEM USING TRIMMER VALVES
Allison has developed trimmer valves, to provide the controlled pressure modulation (fixed) in its Transmission control valves used on its 5000 and 6000 series Transmissions to improve the shift quality. (Refer SAE transaction 730839 published by m/s Detroit Diesel Allison, USA)
Here the jeri(s / shift shocks resulted during gear shifts are controlled using individual trimmers for each clutch and overiap controls for Its new line of Automatic Transmissions.
Individual trimmers for each clutch are used In the transmission. Trim valves are pressure sensitive and the system uses a trim valve and trim plug. When shift is signaled main pressure flows to the piston cavity stroking the piston in to initial engagement of the clutch plates. After quick initial fill time, pressure rises rapidly to the preset value of the trimmer spring. The differential area of the trim valve provides the necessary force to stabilize the trim valve. The basic system and typical torque pressure curves obtained are as indicated in FIG-1.
The trim rate of pressure rise Is achieved by varying the orifice In the system. If a reduction in clutch absoried is desired at the expense of an increase in shift shock, which can be accomplished by increasing the orifice size. This allows a faster feed to the trim plug and hence higher trim rate of pressure rise. The only problem with this basic system is that the pressure required engaging the clutch varies with engine throttle setting. If the shift engagement time is set for throttle shift, then the close throttle shift occur eariler and produces undesirable shift shock.

ALLISON CONCEPT 2 (US Origin):

2.1.2.1 TRANSMISSION CONTROL SYSTEM USING DIFFERENTIAL PRESSURE TRIMMER VALVES (FIG-2) (Refer SAE transaction 932418 published by m/s Detroit Diesel Allison, USA)
A differential trimmer valve is placed in the clutch pressure circuit to allow the clutch pressure to increase at a controllable rate once the signal is given for shift. FIG-3

shows a typical trimmed clutch pressure curve using two or three springs to establish the slope of the pressure rise and use a spring to provide a force to close the valve.
The differential area trimmers are used to obtain pressure rise in multi step modulation. Here the consistency of the pressure rise for the clutch is improved due to use of mechanical spring. The differential area trimmer increases the slip time. Hence change of rate of torque Is decreased, thereby reducing the torque spike and improving the quality of shift. This reduces stress on Internal components with initial less unit loading on clutch plate material. Since electrical valves are not involved provides more consistency.

Advantages:

The differential pressure trim valves allows for better clutch fill with low Initial trim spring loads and hence Improves shift quality.

Limitations:

Trimming of clutches generally increases the slip time. This rationale works well in the closed throttle area where there is very little power. Due to longer slip time affects clutch life. During full throttle shifts, longer slip time is detrimental to clutch life and results in more loss of power which will adversely affect power loss.

2.1.2.2 TRANSMISSION CONTROL SYSTEM USING PROGRAMMABLE
PRESSURE TRIMS BOOST:

There is need to have one type of pressure valve for closed throttle condition and another type for full throttle conditions. Trim boost is the future used in conjunction with electronic controls. Trim boost pressure provides a hydraulic force against the trimmer valve that worths in conjunction with spring to build up pressure for clutch. The trim boost level can be varied by changing the springs. The trim boost speed is controlled by a solenoid which In turn is controlled by electronic controls. The effect of pressure is shown in fig below. By using this feature the trimmer valve can be designed to develop a very shallow build up of pressure, with trim boost being the vehicle with which to vary the slip times for the different throttle conditions. The longer the slip time needed for the closed throttle shifts can be obtained by trimming off the trim boost pressure and using the trim valve alone. By tuming the trim boost pressure 'ON' at full throttle, the pressure for the clutch Is bumped up and the clutch is mal
Advantages:
• The programmable trim booster can be optimized, for use with variety of shift calibrations.
• oth modulated and fixed shift point calibrations can be accommodated.

• Differential area trimmers with programmable trim boost control; substantial
percentage of reduction in torque is achieved.
Limitations:
Precise control of pressure rise can not be acliieved to extent of variable current proportional valve.

KOIWIATSU CONCEPT 1(JAPAN origin):
2.2.1 TRANSIVIISSiON CONTROL VALVE WITH FIXED MODULATION USING ELECTRO HYDRAULIC CONTROL CONTROLS (FIG-5):

During gear sliift, when oil is directed to the clutch by use of ON / OFF solenoid through modulation valve, to have defined ramped pressure rise to optimise the jerk. The ramped pressure rise is achieved through the combination of mechanical spring and puppet valve by seating In the spool. The achieved pressure rise can provide best results for one particular vehicle speed & load. Hence complete elimination of Jerk could not be obtained for all vehicle conditions.
The control valve contains a set of modulation valves, which caters oil to range spools and speed spools. For every speed a combination of two clutches, one each from range clutch and speed clutch requires to be engaged. The modulation valve is connected in series one each to range valves and speed valves. During gear shift, the controller sends signal to the solenoid valve of the outgoing clutch oil is drained to the sump to bring down the clutch pressure to zero before initiating command to fill the 'incoming clutch'. The incoming clutch during engagement rises slowly depending on spring stiffness. This will result in momentary torque off period during gear shift which results in drop in vehicle acceleration and also sudden loading and unloading of engine.
Advantages:
• Simple design,
• Gear up-shift and down shift points are programmable and microprocessor controlled
• Less operator effort due to electro hydraulic assisted valves minimizes linkages.
• Up-shift and down shift points for each gear based on transmission inter gear ratio is possible to program.
Limitations:
• Between gear shifts, there exists momentary torque off period' due to the
'incoming clutch' gets oil only after 'outgoing clutch' is disconnected. During the
process there exists drop in vehicle acceleration and hence sudden load and

unloading of engine. The valves are cwnnected In series rather than parallel. This affects vehicle fuel economy.
• The achieved pressure ramp (modulation) is obtained by mechanical means, provides best results for one particular vehicle speed & load. Hence complete elimination of jerk could not be eliminated for all vehicle conditions.
• Overlapping of 'incoming' and 'outgoing' clutches Is not possible due to the valves are connected in series. This results in increased clutch slip time. Hence faster wear of clutches, increased heat rejection due to increased clutch slippage.
To overcome the drawbacks present in fixed modulation valve, a new transmission control system having independent electro hydraulic valves, which are individually equipped to each clutch. During gear shift clutch controlled pressure
KOMATSU CONCEPT 2 (JAPAN origin):

2.2.2 TFtANSIMiSSiON CONTROL VALVE WiTH VARiABLE iVIODULATION USiNG CLUTCH CONTROL VALVE (FiG-7):
To improve the driving perfomiance, gear shifting through variable pressure modulation is used to precise control of transmisston clutches. This has been achieved by providing electronically controlled modulation valves (ECMV) for individual clutches. The hydraulic schematic of the ECMV is shown at FIG-8.
The ECMV is an actuator system installed on individual clutches to precisely control the clutch pressure. In a clutch system a larger oil flow operates the circuit more quickly, since with the larger oil flow fill time gets reduced. To control the jerk upon engagement of clutches, precise oil control is required.
This is achieved using ECMV, a compact actuator which quickly regains the necessary pressure for the clutch operation and provides a precise control of the clutch even at low pressure. The ECMV valve is made up combination of 2 types of valves, (a) Flow sensor valve which is activated upon filling, and (b) pressure control valve to precisely control the pressure.
Pressure controi valve:
The pressure control valve adjusts the clutch oil pressure to make It balance with the propelling force coming from the proportional solenoid. The solenoid transduces the electric current from the controller in to force. The pressure control valve also generates the trigger of oil pressure which actuates flow sensing valve.
Flow sensing vaive:
The control pressure developed by the pressure control valve is transmitted to the clutch port through the orifice of the spool In the flow sensor valve. Hence upon filling; there generates a pressure gap between both sides of the orifice. The

pressure gap activates the flow sensing valve and large oil flow is pumped in to the clutch, thus reducing the filling time.
When filling is completed, the oil flow stops and therefore the oil pressure at both sides of the orifice become equal to each other. The flow sensing valve then retums to the original position, thus enabling closing of the valve without a command from the controller.
A filling sensor, which detects the position of the flow sensing valve, is installed in the system, to report the completion of filling and the clutch oil pressure to the controller.
Advantages:
By adding sensors to the conventional transmission control system, the system provides self diagnosis on oil pressure, mechanical malfunction as well as electrical abnomnaiity. The system successfully controls the clutch oil pressure under following shifting conditions.
1. Up-shifting during acceleration
2. Downshifting during acceleration
3. Downshifting with throttle off period
Limitations:
The system does not provide the following:
a) Forward / Reverse safety
Since a parallel circuit Is used for both fon/ard and reverse speeds, due to electrical malfunction, controller malfunction, ECMV valve malfunction, possibility exists for simultaneous clutch engagement of both Forward and Reverse clutches. This may lead to sudden power train damage and affects the life of operator & co-passenger.
b) iManuai override safety
During mechanical failure of any clutch or electrical failure due to controller, it is required to move the vehicle to workshop for rectification. For Highway vehicles, and lighter vehicles, it Is possible to toe the vehicle to workshop. In case of OFF High way vehicle, it is preferable to provide manual ovenlde. so as to drive the vehicle by self propellent to the nearest work shop. This feature is not available in Transmission control system. 2.3 POWERSHIFT TRANSiMiSSiON CONTROL SYSTEiM (FIG-9)
To address the vehicle critical safety features not focussed by others, the new power shift transmission control system has been developed for 'OFF HIGHWAY' dump truck application. The concept used is different from others.
The new power shift transmission control system is provided with independently operated pressure control valve to control the clutches Individually with precise

control of pressure. The precise control of pressure rise is achieved using Pressure Controlled Modulation Valve (PCMV) combined with Fill valve connected in parallel circuit known as PCMV assembly schematically as shown at FIG-10.
The new system developed predominantly improves the 'jerk' generally known as 'shift shock'. Shift shocks are developed when vehicle In motion undergoes gear change, which results in sudden change of momentum caused by sudden difference in speed due to change in gear ratio. The jerk is avoided by smooth engage of clutch achieved through modulation of clutch pressure. The electronic controller continuously monitors transmission input and output speeds, throttle position and vehicle load. The new Transmission control system is operated by its pre programmed electronic controller is operated by its exclusively developed algorithm, which optimizes shift smoothness to reduce the operator fatigue.
The precise control of pressure rise in clutch is made possible by use of variable pressure modulation. With the Introduction of new transmission control system, following drawbacks unattended in previous versions released by others have been addressed. The control logics are extensively tested and proved the concept under various operating conditions. 2.3. Optimization of shift smoothness to reduce the operator fatigue
Shift smoothness Is important in automatic gear shift transmissions compared to manual power shift transmissions, since in manual power shift transmissions the vehicle driver anticipates the jeri< and its associated "feel". With the automatic transmission, shifts are not necessarily anticipated and when a jerk occurs it must be precised smooth to the satisfaction of driver / passengers. Jeri< means a sudden variation in torque encountered by the drive train during gear shift forni one range to another. The difference between a smooth shift and hard shift will have neariy the same amount of peak torque; however the hard shift has a very high rate of torque change at the engaging clutch with respect to time. This results in rapid cliange of acceleration and lience lilgher magnitude of 'Jerk'. Delay in clutch engagement means, allowing the clutch to slip. Longer the slip time, means faster wear of clutch disc and temperature rise. Hence a balance is required to be stuck between faster engagement and slower engagement of clutch. In automatic transmission, this has been achieved by clutch overiapping concept by allowing the Immediate fall of releasing clutch pressure to a lower level, which Is just enough to transmit the torque. Further the incoming clutch is filled just enough to close the stroke, using fill valve. Based on the pressure transducer feed back of the incoming clutch, controller closes the oil supply to fill valve and controlled pressure rise command is given to the proportional valve. The controller triggers the command for simultaneous release of clutch pressure, and raising the pressure of incoming clutch, which is just enough to transmit the torque. Hence there is no torque off" period. Once the incoming
clutch pressure reaches optimum pressure level to transmit the power, the controller sends the command to PCMV to open the valve fully to raise the desired pressure. This has resulted in no break in driving torque during gear shifting. Hence called as 'torque continuous shifting'

2.4 BEML TRANSMISSION CONTROL SYSTEM ADDITIONAL FEATURES:
The BEML Transmission control system is developed with new concepts, which are not present on any of the proven OEM Transmission control systems. Following are the additional features:
a) Forward / Reverse safety
b) Manual over ride safety
c) Fill valve as drain valve
d) Control system concept for clutch modulation for variable pressure modulation.
2.4. a) Forward / Reverse safety
To select a gear speed, transmission power train uses, one clutch each from group 'A' known as range clutch and group 'B', known as speed clutch. Group 'A' consists of clutch (H, L) and group 'B' consists of clutch (1, 2, 3, 4 & R). In group 'B' except clutch R, the rest is fonAard clutches.
In variable modulation, to achieve the overlapping of clutches, individual clutch valves were connected in parallel circuit for oil flow as shown in FIG-11. When vehicle is moving in top gear, In case of electronic system malfunction / controller malfunction / PCMV malfunction, possibility exists for simultaneous clutch engagement of both fon/vard and reverse clutches. When vehicle is moving in fOHA/ard direction and sudden engagement of reverse clutch, may result in catastrophic failure of power train system and will lead to accidents which may endanger the operator life. An additional valve known F & R is connected as shown in FIG-11 as a safety feature to prevent such unwanted Fonward / Reverse clutch engagement due to electronic system malfunction / controller malfunction / PCMV malfunction. F & R valve is 2 way, 4 port valve is schematically as shown below:
The oil entering to group B clutches. Initially enters F & R valve. When F&R solenoid is not operated, oil flows to 'F' valve and 'R' valve Is connected to sump. To engage 'R' clutch, it is required to energize F&R solenoid, to divert the oil from 'F' port to 'R' port. Hence simultaneous engagement of fon/vard & reverse clutches is prevented.

2.4. b) Manual override safety
During mechanical faiiure of any clutch or electrical failure due to controller, manual over ride safety option has been provided in Transmission control system. The hydraulic schematic of manual oven-ide is as shown in FIG-12.
To operate the manual ovenlde safety, the electrical wire hamess to Transmission control system is disconnected after identifying the particular clutch failure. One number each of manual ovenide valve from group 'A' and group 'B', which are being identified as defect free clutches will be considered to engage the clutch by operating manual over ride safety. When manual ovemde valve is pulled out, it prevents the oil drain to sump from valve port. Before equipment is started, mode selection lever is pulled from auto mode to manual mode and allowed vehicle to start. Transmission oil gets pumped and is filled up to port position '1' of all fonnard clutches.
• When clutch not engaged, the leakage oil between valve body and spool gets drained to sump through port position '4'.
• For clutch being operated by manual over ride, the sump port passage gets closed resulting in oil blocl
This feature ensures moving the equipment to work shop without the toeing
assistance of equipment. This feature is not available In Transmission control
system.
2.4. c) Use of fill valve for quick oil drain from releasing clutch
One of the major advantages of clutch overlapping is to optimize the clutch slippage time, so as to reduce the torque off period. Fill valves are generally used to ensure faster filling of engaging clutch and keep ready to take over the clutch. This is achieved by increasing the pressure a little above the atmospheric pressure using fill switch feedback to controller. The controller then raises the clutch pressure at the free defined rate using PCMV valve. This concept is used available in few models. However no one has used fill valve for faster drain of oil from disengaging clutch.
During gearshift, electronic controller sends the signal for the engaging clutch to ensure faster filling of clutch and simultaneously to bring down the pressure of disengaging clutch to optimum level, which is just enough to keep transmitting torque. When the engaging clutch attained the minimum pressure, which is just safe enough to transmit the torque. The clutch pressure of engaging clutch is further raised at a faster rate to the required level. At the same time, oil in releasing clutch is drained from both PCMV valve and fill valve to ensure faster oil drain from releasing

clutch. This feature reduces the clutch slip time and hence clutch disc wear. The schematic representation of both engaging and disengaging clutches are as shown schematically below along with the pressure graph.
The use of fill valve as quick drain valve, during disengaging cycle of clutch Is unique
innovation.
2.4. d) Control system concept for clutch modulation for variable pressure modulation
The logics used for variable clutch modulation for the BEML Transmission control system through new concept Is enclosed as shown in FIG-13:

We claim,

1. Forward / Reverse safety

2. Manual override safety

3. Use of fill valve for quick oil drain from releasing clutch

4. Control system concept for clutch modulation for variable pressure modulation