Improving Automatic Transmission Shift Quality by Feedback Control with a Turbine Speed Sensor

<div class="htmlview paragraph">A customer's perception of vehicle quality very closely parallels the noise vibration and harshness (NVH) characteristics of the vehicle. Consequently, automotive manufacturers are investing significant resources into optimizing the NVH performance of their vehicles. Automatic transmission shift quality is one of a number of attributes where NVH optimization is critical towards providing customers with a pleasant driving experience. This paper addresses various aspects of understanding, quantifying and optimizing a vehicle's shift quality characteristics.</div> <div class="htmlview paragraph">Following an introductory treatment of automatic transmission planetary gear systems, the interaction between the engine/transmission system during shifts is summarized. Various shift quality metrics used to quantify a vehicle's response and its sensitivity to transient inputs are provided. Approaches to manage the engine torque output during the shifts are discussed. Examples from various case studies are used to show the influence of the interaction between engine/transmission as well as the vehicle's sensitivity on the overall perceived shift quality behavior of the vehicle. The examples considered show how refined powertrain controls and upfront vehicle sensitivity considerations can be used to achieve superior shift quality.</div>

<div class="htmlview paragraph">Conventional automatic transmissions (AT) use wet friction components, such as plate clutches and band brakes to engage gears or change speed ratios during vehicle operation. The quality of engagements and ratio changes depends greatly on the frictional characteristics of the friction components, which are typically evaluated with industry standard SAE #2 test machines. These inertia absorption-type dynamometer test stands energize a friction component with prescribed level of apply force and load of inertia flywheels rotating at a specified speed until the friction elements are brought to a stop. During the slip, apply force, engagement torque, and rotating speed are digitally recorded for visual evaluation of dynamic engagement behavior. The shape of the dynamic torque curve during the engagement is known to affect AT shift quality. When many curves are generated, it becomes intractable to quantify torque curve shape differences. A new digital rating method is developed that allows these torque curves to be efficiently compared and differences effectively quantified. Single number ratings can be generated representing deviation of the individual curve from a pre-determined ideal shape.</div>

<div class="section abstract"><div class="htmlview paragraph">Automatic transmission (AT) is a complex hydroelectromechanical system, since it consists of hydraulic, electrical and mechanical parts.</div><div class="htmlview paragraph">On cars produced by “UzAuto Motors” mainly AT of the 6T family, 6-speed AT family GM: 6T30, 6T40, 6T45, 6T50 “Hydra-Matic” are used.</div><div class="htmlview paragraph">Production of parts of these transmissions is carried out both at American GM plants and at GM plants in China and Korea.</div><div class="htmlview paragraph">The differences between AT 6T30/6T40/6T45/6T50 are in the thickness of the output chain and in the planetary gear, in the sizes of some other units and the housing itself. But the differences are much more influenced by the settings of the transmission unit, which select operating modes with different engines so as not to overload the thinnest places of the automatic transmission.</div><div class="htmlview paragraph">Automatic transmissions 6T30, 6T40, 6T45, 6T50 have the ability to manually shift gears and activate the “kickdown” mode (for quick acceleration of the car, when you sharply press the gas “all the way” it makes the automatic transmission downshift, and sometimes by two steps).</div><div class="htmlview paragraph">The operation of the transmission is controlled by various electronic systems that are responsible for the operability and structural integrity of the gearbox.</div><div class="htmlview paragraph">Failure of the automatic transmission can occur as a result of one or a combination of malfunctions of the following parts: in the torque converter; in the mechanical part of the gearbox; in the hydraulic part of the control system; one or more clutches of the gearbox; in the electrical part of the control system; in the electronic control unit.</div><div class="htmlview paragraph">The authors of the work investigated and determined the occurrence of malfunctions and failures depending on the temperature of the working fluid of the automatic transmission of a passenger car.</div><div class="htmlview paragraph">Also, the dependence of the resource of the automatic transmission on the temperature of the hydraulic fluid was obtained. High-quality diagnostics of the automatic transmission and its control system can in many cases save the car owner from expensive repairs: <ul class="list disc"><li class="list-item"><div class="htmlview paragraph">without thorough diagnostics, the automatic transmission cannot be subjected to routine or major repairs. Only on the basis of diagnostic information can a conclusion be made about the technical maintenance or repair of the automatic transmission;</div></li><li class="list-item"><div class="htmlview paragraph">based on real experience of operating passenger cars equipped with automatic transmission, we recommend changing the oil every 35000 miles under operating conditions in Tashkent. We also recommend conducting diagnostics of the automatic transmission every 12500 miles of the car's mileage.</div></li></ul></div></div>

<div class="section abstract"><div class="htmlview paragraph">This paper presents a methodology to represent automatic transmission clutch-to-clutch shift dynamics with a two degree of freedom, lumped inertia model. The method of reducing the automatic transmission to a lumped, two inertia model as a function of shift and input shaft acceleration is detailed using a full kinematic representation of the automatic transmission. For a given clutch-to-clutch shift maneuver there are two dependent equations that utilize the two lumped inertias and represent the response of the transmission system from input to output shaft. Applicability of the method is shown for planetary automatic and layshaft dual clutch transmissions. Typical clutch-to-clutch shift maneuvers are illustrated with the two inertia model for power on upshifts and downshifts. The simplification of automatic transmission shift dynamics using this method enables rapid synthesis of a given transmission powerflow for estimation of shift quality potential, required clutching torques, inertia phase engine torque intervention and output torque through all phases of a shift event.</div></div>

<div class="section abstract"><div class="htmlview paragraph">The parameters determining shift quality control in automatic transmissions are determined as part of the calibration of the transmission control. The resulting control system typically has three components: feedforward control, where the control output is determined before a gearshift; feedback control, where the control output is determined during the gearshift based on sensed feedback; and learning control (adaptation), where the feedforward or feedback controller parameters are modified after the current gearshift has ended and before the next similar gearshift begins. Gearshifts involving the same ratio change are referred to here as similar gearshifts, though such gearshifts may involve differences in other variables such as vehicle speed or engine torque. In most automatic transmissions, gearshifts are controlled by hydraulic clutches, and operating conditions for these clutches may vary widely, requiring a dedicated transmission controller involving significant calibration effort.</div><div class="htmlview paragraph">In the current work, novel model-based methods are used to accomplish feedforward control of gearshifts, involving offline calibration of fill and torque phase control parameters and learning control of the fill phase. Towards this end, a physics-based model of the oncoming clutch involved in an upshift of a production automatic transmission was developed and experimentally validated against test bench experiments for a wide variety of inputs and operating conditions. The resulting model is used to generate a feedforward controller, offline model-based calibration algorithm, and a learning controller that corrects for clutch under-fill and over-fill. The effectiveness of the resulting controller is validated by simulation studies using the experimentally validated transmission hydraulic system model, in conjunction with a powertrain model. In particular, it is demonstrated that the learning controller corrects for initial under- or over-fill error in two to three gearshifts. Convergence and robustness properties, and transient performance of the learning controller are also discussed.</div></div>

Robust Nonlinear Control of Inertia Phase in Clutch-to-Clutch Shifts

<div class="htmlview paragraph">Improved performance creates a need for a limited slip differential for widespread application. Existing types suffer from the disadvantage of high cost and they are generally not well suited to front wheel drive applications.</div> <div class="htmlview paragraph">The ‘Suretrac’ differential meets this enhanced requirement. In this new design torque is transmitted through the unit using a cam and follower principle. Any relative rotation of the cams on the output shafts is opposed by friction forces which generate a torque ratio between the output shafts. The design is novel in using helical faces to give large contact areas and avoid high Hertzian stresses.</div> <div class="htmlview paragraph">The performance of this type of differential differs from viscous types or traction control because the torque difference is established before any relative motion takes place. The tyre dynamics dictate the torques generated so that the differential always provides the optimum torque balance. This maintains tyre adhesion and enhances directional stability and safety.</div> <div class="htmlview paragraph">The complexity of the shapes involved precludes machining as an economic production process, so nett shape forming methods are used. This also has to apply to the prototype phase, and so simultaneous engineering has been implemented throughout the product development.</div> <div class="htmlview paragraph">The operation of the differential should normally not impinge on the driver's consciousness, so the performance can only be established by special tests carried out with full instrumentation. These tests include acceleration with the wheels on different surfaces, “split mu”, and acceleration on a curve to give unequal wheel loading. Test results are presented. Durability tests have also been completed.</div> <div class="htmlview paragraph">The differential is shown to give substantial advantages in operation, is capable of being installed in the same space as a conventional differential and has a minimum additional cost and so should gain widespread acceptance in all types of vehicle.</div>

<div class="section abstract"><div class="htmlview paragraph">The brass synchronizers are not resistant to abusive conditions of gearbox operations, but they are very durable and cheap when used on their favorable material property working limit. The main failure which can occur in the gearbox due to the synchronizer is crash noise. During gear shifting the gear crash will create high discomfort for the driver and must apply high force to change the gears. The main factors which contribute to the crash phenomenon are the insufficient coefficient of friction, high drag in the system, and high wear rate of the synchronizer rings before the intended design life of the synchronizer.</div><div class="htmlview paragraph">The brass synchronizers were tested on the SSP-180, ZF synchronizer test rig to know the effect of the synchronizer performance parameters like the coefficient of friction, sleeve force, slipping time as well as durability parameters like wear rate when the operating temperature of the oil is changed. This study will help to predict the impulse behavior, surface pressure, and power of the brass material and oil for enhancing the endurance life of the synchronizer.</div><div class="htmlview paragraph">The effect of gearbox oil drag induced on the synchronizer system in different temperature conditions is also studied in this research work. This helps to reduce the contribution of the drivetrain losses of the gearbox, and it will also give the better shift quality. The wear rate analysis makes it possible to predict the warranty life of the gearbox in the design phase itself. In the case of shift quality, it was identified that the presence of the drag is creating the speed difference between the gear and synchronizer hub. This is creating a gear clash noise when shifted at a slow speed. The data was captured at low temperatures and high temperatures. It was found that the increase in the temperature helps in reducing the drag locally which allows smoother gear shift without speed difference.</div></div>

<div class="htmlview paragraph">Automatic transmissions require that the transition or shift quality between the various gears be smooth and uniform. Driveability is improved by optimizing the shift time of certain gear changes. An added benefit of improved shift quality is reduced clutch wear.</div> <div class="htmlview paragraph">During the investigation of an electronic transmission control system for agricultural, off highway and, heavy duty on highway vehicles, it became apparent that a key element in the hydraulic system was the need to accurately regulate oil pressure to the various clutches in the gear train.</div> <div class="htmlview paragraph">The valve described herein accurately regulates oil pressure at low levels and progressively increases pressure, with respect to time, by means of an electronically programmable pressure vs time control to any level up to supply pressure.</div>

<div class="section abstract"><div class="htmlview paragraph">The worldwide increasing acceptance and success of modern automatic transmissions in passenger cars is based on innovative technology, driving comfort, shifting dynamic and - most important - fuel consumption reduction.</div><div class="htmlview paragraph">New concepts are facing the challenge of further improvements in internal efficiency and very tough future goals on CO2 emissions in connection with more sophisticated gasoline and diesel engine technologies. Based on the competition and current diversity in automatic transmission concepts, high investments in production facilities must be taken also well into account when thinking about follow-up technologies of installed 8-speed and 9-speed technologies. This must also be considered for the different demands in regions and markets.</div><div class="htmlview paragraph">So, how may a successful automatic transmission system look like in 2020 and beyond? Do we have even more gears than the current 8-speed and 9-speed? Does it make sense to increase the total gear ratio any further? Are there measures to improve the overall mechanical efficiency by several percent? What is the prevailing transmission system: torque converter planetary, dual-clutch countershaft or belt-type stepless transmission? How does the electrification and hybridization of the powertrain in the next years effect the system?</div><div class="htmlview paragraph">This article will give some brief answers on how ZF is planning the future of automatic transmissions and how successful systems should look like.</div></div>

<div class="htmlview paragraph">This paper introduces mathematical equations for power loss calculations of major automatic transmission components.</div> <div class="htmlview paragraph">It also presents a theoretical investigation on contributions of each component's power loss to transmission total power losses.</div> <div class="htmlview paragraph">A computer program for automatic transmission efficiency calculation has been developed based on mathematical equations.</div> <div class="htmlview paragraph">Efficiency calculations for the Hyundai A4BF1 electronic 4 speed automatic transmission has been executed in order to validate the program.</div> <div class="htmlview paragraph">The calculated efficiency under various input and operating conditions - such as different input torque & RPM, transmission gear state, ATF temperature, torque converter clutch on/off - showed quite good agreement with the test results.</div>

<div class="htmlview paragraph">An automatic transmission for heavy duty trucks and buses has been developed. Automatically controlled dry clutch and synchromeshed gear transmission make driving easier, while maintaining good fuel efficiency of a mechanical transmission.</div> <div class="htmlview paragraph">The system consideration and design philosophies of the electronic controller are described here, as well as the mechanical hardware for conversion of a manual transmission into a fully automatic transmission.</div> <div class="htmlview paragraph">This transmission control system has not only the functions of an automatic transmission but also driveability and efficiency same as that of a skilled driver by incorporating various kinds of control logics.</div> <div class="htmlview paragraph">It is our fair judgement that this transmission can well meet market requirements in new age.</div>

<div class="section abstract"> <div class="htmlview paragraph">This SAE Recommended Practice is intended as the definition of a standard test, which may be subject to frequent change to keep pace with experience and technical advances. This should be kept in mind when considering its use.</div> <div class="htmlview paragraph">The SAE No. 2 Friction Test Machine is used to evaluate the friction characteristics of automatic transmission plate clutches with automotive transmission fluids. It can also be used to conduct durability tests on wet friction systems.</div> <div class="htmlview paragraph">The specific purpose of this document is to define a µPVT Test for the evaluation of the variation of wet friction system performance as a function of speed, temperature, and pressure. This procedure is intended as a standard for both suppliers and end users.</div> <div class="htmlview paragraph">The only variables selected by the supplier or user of the friction system are:</div> <ol class="list nostyle"> <li class="list-item"> <span class="li-label">a</span> <div class="htmlview paragraph">Friction material</div></li> <li class="list-item"> <span class="li-label">b</span> <div class="htmlview paragraph">Fluid</div></li> <li class="list-item"> <span class="li-label">c</span> <div class="htmlview paragraph">Reaction plates</div></li></ol> <div class="htmlview paragraph">These three variables must be clearly identified when reporting the results of this test. If any of the test parameters or system hardware as described in this document are changed, other than the friction material, test fluid, or reaction plates, the data may not be reported as having been obtained using this document.</div> <div class="htmlview paragraph">This procedure is intended to evaluate the midpoint, endpoint, and breakaway coefficients and endpoint/midpoint ratios. The procedure can be used to demonstrate changes that occur between the different levels of engagement speed, sump temperature, and apply pressure. Refer to SAE J2487, SAE J2488, or SAE J2489 for coefficient variations due to changes in power level.</div> <div class="htmlview paragraph">The procedure, as described in detail in <span class="xref">Table 1</span>, consists of four 50 cycle break-in levels at 3500 rpm with increasing steps of apply pressure, followed by 16 levels consisting of 25 dynamic engagements, and one breakaway following completion of the 25th dynamic cycle. The 16 levels are achieved by varying initial engagement speed, apply pressure, and oil sump temperature while the inertia is kept constant at 0.701 kg/m<sup>2</sup>.</div></div>

<div class="htmlview paragraph">A silencer to attenuate engine exhaust noise using active control methods has been developed. The device consists of an electrically driven valve, combined with a buffer volume, which is connected to the exhaust outlet. Using the mean flow through the valve and the pressure fluctuations in the volume, the valve regulates the flow in such a way that only the mean flow passes through the exhaust outlet. The fluctuations of the flow are temporally buffered in the volume.</div> <div class="htmlview paragraph">To carry out optimization and validation experiments, a cold engine simulator has been developed. This device generates realistic exhaust noise as well as the matching gas flow using compressed air. The simulator allows quick and reliable acoustic and fluid dynamic experiments on exhaust prototypes.</div> <div class="htmlview paragraph">The silencer is developed using electrical equivalent circuits, wherein at first instance a feedforward control is applied. The silencer has been built and the transfer function between electrical motor current of the valve and resulting acoustic pressure is measured. Based on these measurements, the feedback controller is developed and tested.</div> <div class="htmlview paragraph">The active silencer is capable to reduce the exhaust noise with 13 dBA using feedforward and 16 dBA using feedback control, with a back pressure of 10 kPa to the engine.</div>

<div class="section abstract"> <div class="htmlview paragraph">This SAE Recommended Practice is intended as the definition of a standard test, but may be subject to frequent change to keep pace with experience and technical advances. This should be kept in mind when considering its use.</div> <div class="htmlview paragraph">The SAE No. 2 Friction Test Machine is used to evaluate the friction characteristics of automatic transmission plate clutches with automotive transmission fluids. It can also be used to conduct durability tests on wet friction systems.</div> <div class="htmlview paragraph">The specific purpose of this document is to define a 3600 r/min Stepped Power Test for the evaluation of wet friction system performance variation as a function of power level. This procedure uses an initial engagement speed of 3600 r/min and is intended as a standard procedure for common use by both suppliers and end users.</div> <div class="htmlview paragraph">The only variables selected by the supplier or user of the friction system are:</div> <ol class="list nostyle"> <li class="list-item"> <span class="li-label">a</span> <div class="htmlview paragraph">Friction Material</div></li> <li class="list-item"> <span class="li-label">b</span> <div class="htmlview paragraph">Fluid</div></li> <li class="list-item"> <span class="li-label">c</span> <div class="htmlview paragraph">Reaction Plates</div></li></ol> <div class="htmlview paragraph">These three variables must be clearly identified when reporting the results of using this test. If any of the test parameters or system hardware as described in this document are changed, other than the friction material, test fluid, or reaction plates, the data may not be reported as having been obtained using this document.</div> <div class="htmlview paragraph">This procedure is not intended to evaluate the initial coefficient or break-in characteristics. For this information, refer to SAE J2490 SAE No. 2 Friction Test Machine μPVT Test.</div></div>