SAE TECHNICAL
`PAPER SERIES
`
`950896
`
`
`
`Developments in Automated
`Clutch Management Systems
`
`Knut Nordgard
`Kongsberg Automotive Technology
`
`Hans Hoonhorst
`Siemens Automotive SA
`
`Reprinted from: New Developments in Transmission and Driveline Design
`(SP-1087)
`
`The Engineering Socie
`
`GaArEForAdsaneingMobility,
`LandSea Air and Space,
`INTERNATIONAL
`
`international Congress and Exposition
`Detroit, Michigan
`February 27 - March 2, 1995
`
`a 4
`
`00 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A. Tel: (412)776-4841 Fax:(412)776-5760
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`Copyright 1995 Society of Automotive Engineers,inc.
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`950896
`
`Developments in Automated
`Clutch Management Systems
`Knut Nordgard
`Kongsberg Automotive Technology
`
`Hans Hoonhorst
`Siemens Automotive SA
`
`ABSTRACT
`
`Since the very beginning of the automotive era the
`industry has tried to automate control of the clutch.
`Until very recently such control was impossible. In-
`tensive use of new system simulation tools com-
`bined with the latest developments in electronics
`now allow the realisation of comfortable and reli-
`able automated clutch systems at an affordable
`price. This paper describes clutch system require-
`ments, their realisation through a close co-operation
`between system, hardware and software engineer-
`ing, as well as field test results.
`
`1, INTRODUCTION
`
`The vast majority of European cars are equipped
`with manually operated gearboxes. When asked,
`customers indicate they prefer manual shifting to
`automatic gearbox control because of
`the lower
`cost of manuals and also because of the feeling of
`having complete control of the car in the dense and
`nervous European traffic. On the other hand most
`people also admit that in traffic jams operating the
`clutch requires an important effort and may divert
`their attention from the traffic.
`
`From the opinions above and from the car industry's
`tendency to continuously enhance the driver's
`comfort, we can conclude that automatic Clutch
`Management Systems (CMS)will have a bright fu-
`ture provided such systems combinereliability and
`low cost with control strategies that
`insure very
`comfortable and safe shifting. Since the invention of
`gearboxes various systems have been invented and
`even been produced, yet the existing technology did
`not
`allow to satisfy the above conditions
`for
`success.
`
`It
`
`is quite strange to observe that clutches arestill
`
`operated directly by the driver wherein the last ten
`years most other car functions have seen the intro-
`duction of electronic conirol in replacement of either
`driver operation or mechanical control. Electronic
`control
`in general enhances comfort (e.g. remote
`access control), safety (e.g. ABS) or
`increases
`performance(e.g. electronic engine managementor
`automatic gearbox control) and should therefore
`naturally be applied to the cumbersome clutches.
`Absence of electronic control until now is mainly
`dueto the fact that, although the replacementof the
`driver's left foot seems fairly straightforward, auto-
`matic clutch control requires rather sophisticated
`control strategies and therefore high end elec-
`tronics. Only recently has the evolution of
`tech-
`nology allowed an automatic clutch control
`to be
`offered at a reasonable cost. This paper describes
`an automatic clutch management system (CMS)
`which is the result of the combination of more than
`ten years of control strategy development and up to
`date electronic technology.
`
`2. ADVANTAGES OF CMS
`
`CMSoffers advantagesto both the driver as well as
`to the car manufacturer.
`
`From the driver's point of view the first and most
`obvious advantage is the increase of comfort due to
`2 pedal operation. CMS takes away the stress of
`continuous clutch operation (clutches require forces
`up to 250 N)in city start-stop traffic; it facilitates hill
`starts as well as parking in tight spaces and it
`im-
`proves handling of the car at low speeds. In addition
`high end CMS offer the possibility of
`limited yet
`tightly controiled slip to reduce low speed driveline
`noise and vibration. Both easier operation as well as
`a quieter environmentfavorably impact safety.
`
`137
`
`Obviously Automatic Gearboxes offer these same
`advantages; CMS howeveroutperforms Automatics
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`in many fields such as price, fuel economy, quick
`response and engine braking. CMSalso offers the
`absence of creeping and the satisfaction of
`the
`driver to be in control by determining himself his
`gear switch points.
`
`To the car manufacturer CMS offers first of all a
`competitive advantage due to customer satisfaction.
`In addition CMS eliminates drive train stress due to
`rather frequent mishandling of
`the clutch by the
`average
`driver. Reduced
`drive
`train
`stress
`translates into both a potential down sizing of the
`gearbox and drive train as well as a reduction in
`warranty costs.
`In normal driving conditions the
`precision and the speed of electronic control leads
`to lower clutch wear than with the average human
`driver. For this reason CMS can usecontrolled slip
`to reduce noise and still comply with clutch wear
`standards. This has been proven by tests on cars
`as well as on durability benches.
`
`3. PREVENTION OF NOISE AND VIBRATION
`
`As already indicated, in addition to its main function,
`CMS can be used to improve noise and vibration
`levels. Various types of noise can be distinguished:
`
`jerk:
`1.
`when driving in 1st or 2nd gear at very low speed at
`very low throttle and an engine operating close to
`idle,
`the car may jerk ahead onlight tip-ins and
`eventually oscillate close to 1 Hz.
`The introduction of limited controlled slip prevents
`this very uncomfortable situation.
`
`2. shunt(tip in -tip out clunk):
`Due to backlash in the driveline, a sharp bang or
`clunk is heard and felt when the driver lifts his foot
`off the gas pedal and then presses it down again
`while the clutch is fully engaged thus causing drive
`line torque to change directions.
`A responsive Clutch Management System can
`eliminate shunt through quick disengagementof the
`clutch at the momentthe torque direction inverts.
`
`3. booming :
`When driving at high power in a high gear at low
`engine RPM, torque spikes from the engine gener-
`ate audible resonances in the passenger compart-
`ment.
`A precise Clutch Management System can prevent
`booming by precisely controlling a relative slip be-
`tween 50 and 100 RPM.
`
`idle rattle :
`4.
`When the clutch is engagedin idle with the gearbox
`in neutral,
`torque spikes from the engine may
`generate resonance frequencies in the gearbox.
`CMSeasily prevents this by opening the clutch.
`
`5. gearboxrattle :
`At high loads at 1200-2500 RPMin 2nd or 3rd gear,
`the gearbox may generate a rattling noise when the
`oil is hot.
`Gearbox rattle can be eliminated by a relative slip
`between 50 and 100 RPM provided the Clutch
`Management System is precise enough to control
`this slip accurately.
`
`Responsiveness and precision are key to noise
`prevention; these parameters require high process-
`ing power, and therefore directly determine the sys-
`tem architecture of a high end Clutch Management
`System.
`
`
`Hydraulic
`
`Power Unit
`+
`
`—
`
`Electronic
`Control Unit
`
`
`Clutch actuator
`
`0) with position
`sensor
` Brakelight
`
`Proportional
`
`
` switch Gear position
`
`
` -} Inputshaft
`Engine
`
`speed sensor
`
`
`speed
`
`sensor
`
`
`
`
`figure 1: CMS SYNOPTIC DIAGRAM
`138
`
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`4. CLUTCH MANAGEMENT SYSTEM SET-UP
`
`All CMS systems basically consist of (see synoptic
`diagram in figure 1) :
`
`» sensors reading both driver intention and the
`current status of clutch and gearbox
`eo aclutch actuator
`o an electronic control unit (ECU)
`
`One of the main difficulties of CMS is that the sys-
`tem cannot anticipate driver intention; it only detects
`the driver wants to shift gears, when he starts
`operating the shift lever or releasing the gas pedal.
`The detection strategies must
`therefore be very
`fast, yet they must also avoid unintentional opening
`of the clutch for instance whenthe driver plays with
`the lever while driving normally. As soon as the in-
`tention to shift gears has been recognised the sys-
`tem must open the ciutch as fast as possible to
`avoid the driver feeling resistance when he starts
`moving the lever. On the other hand,
`it must not
`open so fast that the sudden release of tension in
`the drive line will cause a shock. Once the gearshift
`has taken place, CMS must close the clutch again
`in a controlled manner. Especially at low speeds
`operating comfort
`is dramatically enhanced when
`the Clutch Management System is set-up to offer
`
`the possibility of precisely controlled slip in this
`phaseof operation.
`
`Speed and precision are thus the key parameters
`for the clutch actuator. Hydraulic systems outper-
`form electric actuators because they allow slow
`building of pressure in an accumulator that will
`in-
`stantly deliver the power required for fast shifting.
`Opposite to electric actuators, hydraulic systems
`also offer an inherent safety feature since the ac-
`cumulator load can deliver the energy for several
`clutch activations independentof the power source.
`To be noted that the hydraulic power source can
`eventually be shared with ABS or power steering
`reducing the CMS system cost.
`
`The objective of our development being a clutch
`management system with a high performance / cost
`ratio, a hydraulic actuator was an obvious choice.
`This
`choice
`implied
`also the need for
`high
`performance wide
`bandwidth
`electronics
`and
`therefore an in depth analysis and simulation of the
`system to insure optimum performance and stabil-
`ity. More details on all these items will be presented
`in the next sections.
`
`
`rt=EE
`
`@‘ea
`
`©
`
`@
`
`
`
`
`
`
`
`ce2 [Slave position
`
`sensor
`|3] OT tank
`Electronic
`Control Unit
`pet
`Electric motor
`rassur
`Persson
`Proportional
`valve
`a Piston pump
`Fie
`2
`ump motor
`rele
`t
`3} Stoet
`lock
`re
`le
`pe[Beer
`Warning light
`
`
`
`
`
`
`
`
`
`
`8|Ignition key
`
`S
`7} Broke light
`sv
`itch
`al]
`
`"8 Throttle sensor
`or
`Geer
`lav
`
`q
`
`8|position sensor
`Ny
`
`GO{ Crutch speed
`on
`sensor
` i
`
`
`
` Ni 1} Engine speed
`sensor
` SET ri
`
`
`
`i
`[=
`E>,SOP
`a
`
`0
`
`figure 2: CMS SYSTEM LAYOUT
`
`139
`
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`5. DETAILED CMS DESCRIPTION
`
`the clutch required to insure the
`
`engagement of
`driver's comfort.
`
`
`5.aHYDRAULICARCHITECTURE
`
`
`
`1.5
`1
`0.5
`:
`.
`Required slave cylinder movement
`
`2
`
`2.5
`
`(seconds)
`
` °
`
`The system layout of figure 2 shows the hydraulic
`system consists of 2 main items:
`
`o a Slave cylinder with an integrated contactless
`position sensor. This cylinder moves the clutch
`arm and signals it's position back to the ECU.
`External or concentric slave cylinders can be
`used. The slave cylinder's diameter and stroke
`are the only hardware items that have to be
`adapted to a particular car.
`
`o
`
`the hydraulic power module (HPU) integrating a
`DC motor driven pump, an accumulator, a pres-
`sure switch and a proportional volume control
`valve delivering the appropriate oil flow to the
`slave cylinder. Separation of HPU and slave
`cylinder facilitates installation in the car's engine
`compartment.
`
`The proportional valve is a key componentfor sys-
`tem performance. A substantial developmenteffort
`has been invested in it's design. The basis for this
`work has been intensive computer simulations to
`optimize the valve not as a stand alone component
`but as a part of the complete CMS. Optimization of
`valve overlap in it's center position is a good ex-
`ample of
`such system design trade-offs. System
`control theory requires the overlap of shuttle open-
`ing and the input and output ports to be as small as
`possible, however small or negative overlap induces
`leakage
`and
`therefore
`increases
`the
`power
`consumption. Small overlap also requires tight tol-
`erances and clearances between the spool! and the
`casing which increasescost.
`
`The right compromise between these incompatible
`considerations strongly depends on the specifica-
`tions the system must meet, and hence the evalu-
`ation has to take into account howthe different sys-
`tem components interact. Carrying out this investi-
`gation by physical testing in the laboratory is very
`time consuming and practically, comprehensive
`results can only be obtained by means of computer
`simulations. Some early simulation results are
`shownin the figures 3 and 4.
`
`Figure 3 shows a complete clutch activation se-
`quence. So as to disengage the clutch the
`slave
`cylinder position is required to move about 15 mm.
`As soon as gearshifting has taken place the clutch
`is progressively engaged again. Picture 3 of
`figure
`3 shows how the system pressure must evolve to
`obtain the above movement whereas picture 4 of
`the same figure gives a recording of the current in
`the proportional valve: after a 2 Amp spike to sud-
`denly increase pressure, the current is continuously
`monitored and modulated to control
`the smooth
`
`0.5
`1
`1.5
`
`Real slave cylinder movement
`
`2
`
`2.5
`
`(seconds)
`
`
`
`
`
`
`
` 1 1.50.5 2.5
`.
`ids
`Working pressure at 70 bar system pressure
`(seconds)
`
`
`
` 0.5 1
`
`
`
` (seconds)
`Solenoid current
`
`2.5
`
`
`
`figure 3: slave cylinder movement
`
`Figure 4 showsthe typical small signal system re-
`sponse during a controlled slip operation and the
`way in which the real slave cylinder movementfol-
`lows the calculated reference with a small lag.
`
`reference
`
`(seconds)
`
`
`0,25
`0.3
`
`140
`
`figure 4: small signal response
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`
`
` ==
`
`ren |
`
`ih
`
`
`
`-
`
`$
`
`_—
`
`oe)
`
`Typical operation parameters of ine complete hy-
`draulic CMS design are:
`
`Sysiem pressure :°
`Working
`Pressure :
`Temperature range :
`Disengagement 100%stroke
`Disengagement 70%stroke :
`Relative slip control
`
`p & f
`
`igure 5: proportional valve outline
`
`At the compietion of the simulation several proto-
`types were manufactured and tested confirming de-
`sign criteria such as:
`
`valve port shape which is critical both for the
`system's closed loop stability as well as for mini-
`mising system response time. Best performance
`is obtained by iailor mace ports.
`
`
`
`is excessive and hence customising
`valves
`allows an optimisation of responsetime.
`;
`eas
`;
`;
`to avoid
`careful solenoid design is essential
`unintended added viscosity dependent damping
`:
`-
`ai low temperatures.
`
`;
`;
`Figure S shows the outer dimensions of the CMS
`proportional valve in it's final revision.
`
`some hydraulic damping in the vaive is needed
`to avoid closed icop instability. However the
`normal damping of conventional proportional
`
`The resulting typical disengagement anc conirailed
`slip curves are shownin figures 6 and7.
`
`
`
`}Clutch
`arm
`move-
`iment
`
`1 100%
`Reference
`signal
`
`Processing time
`
`Response time,
`proportional valve
`
`7,4
`
`7,45
`7,5
`7,55 |
`(seconds)
`
`figure 7 ; controlled relative slip
`
`figure 6: disengagement sequence
`
`:
`
`“Clutch disk speed
`
`
`a MAL UAT. tee leet ee eee.
`
`sod
`
`A
`
` wood YAee,
`
` 1650.
`z
`z.
`3
`ca
`5.
`10,
`g
`a
`7.
`6.
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`
`
`In addition processing requirements are prone to
`increase in the next years due to the sophistication
`of on board diagnostics and the exchange with
`other systems through the vehicle's communication
`bus.
`
`So as to guarantee adequate power, the CMS con-
`trol unit has been designed around a brand new
`member of the very fast SAB 80C167 family of
`16 bit microprocessors. Provided fast memory is
`used more than 5 MIPS are available; total proc-
`essing poweris further enhanced by a wide range
`of fast peripheral functions that reduce the CPU
`overhead for input/output functions (see functional
`description in figure 8). This power is more than
`adequate for current requirements as well as future
`enhancements including the use of fuzzy logic con-
`trol where we havebuilt up extensive know-how.
`
`5.b ELECTRONIC CONTROL
`HARDWARE AND SOFTWARE
`
`The complete dynamic computer model of the sys-
`tem has been the basis for the development and
`optimisation of the control strategies. This simula-
`tion has shown that accurate and responsive CMS
`control requires the availability of quite impressive
`processing power.
`
`Less power would mean slower calculations and
`therefore less sophistication and precision in the
`control strategies. Such a system wouldstill allow a
`minimum level of clutch automation, that is simple
`"replacementof the left foot". However it would not
`achieve the comfort levels required by modern cus-
`tomers. These expected levels of comfort will also
`increase rapidly with the foreseen fast development
`of the clutch control market and therefore low end
`CMSsystem can not expect to have a long market
`life time.
`
`EOS
`
`“ADD-ON FEATURES.
`
`CORE
`
`2K XRAM on Xbus
`
`PERIPHERALS
`
`PLL clock generator
`
`“ADD-ONFEATURES.
`
`CORE
`
`Xbus feature
`
`1K dual port RAM
`5 Chip Select
`16M Bytes addr space
`24 interrupt sources
`
`PERIPHERALS
`
`MISCELLANEOUS
`
`16 channel CAPCOM2
`
`Programmableinput...
`..thresholds TTLYCMOS
`
`Temp. -40 to + 125C
`
`OPTIONS
`
`VAN
`
`4 channel PWM unit
`
`3 I/O ports (up to 35 I/O)
`6 channel 10-bit ADC
`
`MISCELLANEOUS
`
`144-pin MQFP
`
`OPTIONS
`
`CAN
`
`Temp. -40 to +110 C
`
`uP 2000
`
`oS
`
`SAB 80C166
`
`CPU 16-bits CORE
`
`PERIPHERALS
`
`Risc-like core
`
`16 channel CAPCOM1
`
`4 pipe-line levels
`Fastinterrupt response
`1 machinecycle instructions
`PEC function
`
`GPT1, 2 (5 16-bit timers)
`10 channel 10-bit ADC
`2 USART
`
`5 I/0 ports (up to 76 I/O)
`
`1K dual port RAM
`32 interrupt sources
`32 vectors / 16 levels
`
`256K Bytes address space
`Dynamic bus configuration
`DMAfeature
`
`Watchdogtimer
`
`MISCELLANEOUS
`
`100-pin BQFP / MRFP
`
`figure 8 : microprocessorfunctional description
`
`Early in the design the safety aspects of clutch
`operation were analyzed and a strategy was
`designed that allows safe limp home even when
`one of
`the primary sensors fails.
`In addition a
`second low cost microprocessor was designed into
`
`the system to monitor it's operation and act as an
`intelligent watchdog similar to the one used in ABS
`systems. The general layout of the ECU is shownin
`figure 9.
`
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`IGN
`
`Speeds
`
`Analog
`
`Binary
`
`
` Proportional
`
`valve
`
`
`
`
`Power Supply
`
`Main
`
`auxilliary uP
`
`Auxilliary
`outputs
`
`figure 9 : ECU general layout
`
`CONTROLSOFTWARE
`
`speed is
`reached. As speed decreases,
`the
`
`clutch is graduaily engaged more until vehicle
`speed corresponds to maximum engine speedin
`the
`selected
`gear. This
`function
`permits
`maximum engine braking without damage to the
`engine.
`
`The main task of CMS software is to control the
`movementof the clutch arm, which requires various
`calculations and algorithms to be performed:
`
`»
`
`software filtering and processing of
`reading,
`sensor signals as well as monitoring of sensor
`plausibility
`
`o clutch slip control to reduce noise and enhance
`comfort as explained above
`
`e control and monitoring of the clutch proportional
`valve
`
`o adaptive routines to automatically adapt the sys-
`tem to sensordrift, component wear and even-
`tual offset due to servicing.
`The system also adaptsitself to individual driver
`style. While driving carefully the system gives a
`soft clutch engagement. When driving in a sporty
`way with fast gear changes and a lot of power,
`ihe system tightens
`itself up resulting in a
`tougher engagement.
`
`o diagnostic, limp home and watchdog functions
`
`o @ngine overrun protection to avoid engine over-
`speed or dangerous engine braking if the driver
`shifts down to too low a gear. When this situ-
`ation occurs, the systems starts to engage the
`clutch until
`the maximum allowable engine
`
`2 clutch overload caiculations where the clutch
`temperature is estimated based on the rate at
`which heat energy is generated in the clutch and
`the various heat capacity and transfer coeffi-
`cients.
`Dependent on the calculation results and the
`driving situation, the driver will be warned and
`eventually protective action will be engaged
`without overriding the driver.
`The overall system philosophyis in fact that the
`system should never override the driver. This
`means that nothing unexpected or surprising to
`the driver is allowed to happen.
`If
`the driver
`chooses to burn the clutch by holding the car on
`a slope he will be allowed to do so because he
`may be in a dangeroussituation (e.g. brake fail-
`ure). Visible and audible warnings will alert the
`driver, but the clutch will stay engaged if the
`driver chooses to disregard the warnings.
`
`Size and interaction between the various functions
`make software quite complex and high ievel
`lan-
`guage programming mandatory. The SAB80C167
`microprocessors architecture facilitates compiler
`efficiency and thus the exhaustive use of high level
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`time
`real
`languages programming even for fast
`functions. The use of structured analysis and design
`further enhance software quality. The software is
`made up out of
`small
`independent
`functional
`modules designed around a real time kernel so as
`to ease the understanding of the interaction of the
`various functions and hencefacilitate maintenance
`and future evolution.
`
`6. TEST STATUS
`
`This new CMS system is currently installed on cars
`of more than 7 car manufactures and has been
`successfully tested in various conditions including
`winter tests in northern Sweden and summer tests
`in Death Valley. Durability has been tested in Swit-
`zerland, where cars towing heavily loaded caravans
`have been operated in long term evaluations in
`mountainous areas. Driveability has been the object
`of several very successful
`tests,
`including com-
`parative ones, which were directly run by several
`car manufacturers.
`Currently final industrialisation is ongoing as Job1 of
`several applications is approaching.
`
`the first applications,
`During the development of
`several tools have been developed to facilitate the
`application, the tuning and the testing of CMS on
`new carlines. These tools include items like flight
`recorders to record the behaviour of the car on the
`road as well as development cards with numerous
`
`spare inputs, outputs and functions that facilitate the
`integration of CMS in a new environment. The
`development cards offer for instance interfaces to
`various communication buses as well the possibility
`to control semi shift gearboxes, which probably are
`the step beyond automatic Clutch Management
`Systems.
`
`7, CONCLUSION
`
`After a very long development process, the combi-
`nation of modern control
`theory and the latest
`technology in electronics now finally allow automno-
`tive clutches to become automated. We have tried
`to present an overview of the features of a modern
`CMS system and of the means it takes to develop a
`system that satisfies present and future comfort,
`driveability and safety standards. Automated Clutch
`Management Systems now have reached the ma-
`turity level where one can imagine phasing out of
`the traditional foot operated clutches. Together with
`electronic actuation of a Manual Gearbox, CMS
`may also prove to be an interesting alternative to
`Automatic Gearboxes.
`However, changing something as traditional as a
`clutch also requires subjective acceptance of the
`new system. In this field a paper presentation alone
`cannot be convincing. The best way to fee! what
`automated Clutch Management Systems
`really
`means to a driver is to test a car equipped with
`CMS.
`
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