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Technical Paper

Piecewise 1st Order Hydraulic Actuator Model for Transient Transmission Simulations

2017-03-28
2017-01-1140
A transmission system model is developed at various complexities in order to capture the transient behaviors in drivability and fuel economy simulations. A large number of model parameters bring more degree of freedom to correlate with vehicular test data. However, in practice, it requires extensive time and effort to tune the parameters to satisfy the model performance requirements. Among the transmission model, a hydraulic clutch actuator plays a critical role in transient shift simulations. It is particularly difficult to tune the actuator model when it is over-parameterized. Therefore, it is of great importance to develop a hydraulic actuator model that is easy to adjust while retaining sufficient complexity for replicating realistic transient behaviors. This paper describes a systematic approach for reducing the hydraulic actuator model into a piecewise 1st order representation based on piston movement.
Technical Paper

Implementation of Torque Hole Filling for Transmission Shift Control

2018-04-03
2018-01-1169
Torque Hole Filling (THF) is a model based approach for controlling the automatic transmission clutches and input torque during a part-pedal upshift or zero-pedal downshift. A desired transmission output torque is first calculated and then the clutches and input torque are controlled to achieve that output torque. This is a system design approach with drivability as one of the direct design objectives. This paper presents the control design and implementation of Torque Hole Filling. First, the paper introduces the topic, defines the terms, and explains the basic operation and intended result. Next, it describes how it works with one instance of implementation and its corresponding dynamics equations, for both torque transfer and ratio change phases. Lastly but most importantly, it covers the various robustness considerations for real-world applications.
Technical Paper

Effect of Road Excitations on Driveline Output Torque Measurements

2011-05-17
2011-01-1538
This paper presents the characterization of the random noise in driveline output shaft torque measurements that is commonly induced by road disturbances. To investigate the interaction between the shaft torque and road side excitation, torque signals are measured using a magnetoelastic torque sensor, as well as a conventional strain gauge sensor, under various types of road surfaces and conditions such as unevenness. A generalized de-trending method for producing a stationary random signal is first conducted. Statistical methods, in particular the probability density function and transform technique, are utilized to provide an evident signature for identifying the road excitation effect on the vehicle output shaft torque. Analysis results show how the road surface can act as a disturbance input to the vehicle shaft torque.
Technical Paper

CFD Modeling of Squeeze Film Flow in Wet Clutch

2011-04-12
2011-01-1236
An oil-lubricated wet clutch has a direct impact on the drivability and fuel economy of a vehicle equipped with an automatic transmission system. However, a reliable analysis of clutch behavior still remains a challenge. The purpose of this study is to advance the state-of the-art in CFD methodology for modeling transient clutch behavior. First, a new iterative scheme is developed, in combination with commercial CFD software, which is capable of simulating the squeeze film process in a wet clutch. The numerical results are then validated using analytical solutions of the Reynolds equation for simplified clutch geometry and various boundary conditions. It is found that the choice of boundary conditions has a strong influence on squeeze film simulation. The iterative scheme is further validated by comparison to clutch engagement experiments.
Technical Paper

Dynamic Characterization of Wet Friction Component under Realistic Transmission Shift Conditions

2006-04-03
2006-01-0151
A wet friction component continues to play a critical role in a step-ratio automatic transmission (AT) system. It is hydraulically actuated to alter planetary gear configurations for automatic shifting. During a shift event, its engagement torque is transmitted to AT output shaft, directly affecting vehicle shift quality. The friction component behaviors vary widely under different conditions. In a vehicle development process, unanticipated behaviors often lead to an inefficient trial-and-error approach for adjusting shift feel. Thus, a shift improvement process can benefit from upfront characterization of friction component behaviors. The so-called SAE#2 test system has served as the industry-standard since 1960's for evaluating friction components. It provides a useful means for evaluating friction component design variables. However, its standardized test conditions do not adequately capture dynamic effects of AT shift control variables.
Technical Paper

Review of Wet Friction Component Models for Automatic Transmission Shift Analysis

2003-05-05
2003-01-1665
In a step-ratio automatic transmission system, wet friction components are widely utilized to alter planetary gear configurations for automatic shifting. Thus, their engagement characteristics have a direct impact on shift quality or drivetrain NVH. A vehicle design process can benefit from predictive friction component models that allow analytical shift quality evaluation, leading to reduced development time. However, their practical application to shift analysis is seldom discussed in the literature although there are many references available for friction component modeling itself. A successful shift analysis requires a balance of model complexity, predictability and computational efficiency for a given objective. This paper reviews three types of friction component models found in today's open literature, namely, first principle based, algebraic, and empirical models. Model structure, assumptions, computational efficiency, and utilities are discussed.
Technical Paper

Automatic Transmission Shift Control for Canceling Inertia Torque

2018-04-03
2018-01-1167
A step-ratio automatic transmission is a system of planetary gear sets, wet clutches, hydraulic control system and torque converter to provide the flexibility in gear ratio selection. Gearshifting is realized by the engagement and disengagement of clutches which are commanded by control strategy through the hydraulic actuators. A complex interaction between components results in transient drive shaft torque, affecting shift quality. In particular, it is difficult to achieve fast upshift without inducing a large inertia torque spike due to changing speed ratios. A deep understanding of the system kinematics and dynamics becomes critical to control clutches for fast and smooth gearshifting. This article performs detailed analytical study to explain the upshift behaviors of a 10-speed automatic transmission by deriving the system’s governing equations. These equations show insights of working principles of the transmission and provide a new method to improve shift quality.
Journal Article

Development of Magneto-Elastic Torque Sensor for Automatic Transmission Applications

2013-04-08
2013-01-0301
Progress in the design and application of the magneto-elastic torque sensor to automotive drivetrain systems has taken the technology from the concept level to the point where it is considered production feasible. The latest generation of the sensors shows promising results regarding both the capabilities and applications to powertrain controls. Sensor designs, electronics and packaging layout are maturing. Well-defined component specifications and requirements are becoming available. The sensor utilities for real-time shift analysis and friction element control are established through vehicle-level investigation to demonstrate the production feasibility of the technology for transmission torque sensing.
Journal Article

Two-Phase MRF Model for Wet Clutch Drag Simulation

2017-03-28
2017-01-1127
Wet clutch packs are widely used in today’s automatic transmission systems for gear-ratio shifting. The frictional interfaces between the clutch plates are continuously lubricated with transmission fluid for both thermal and friction management. The open clutch packs shear transmission fluid across the rotating plates, contributing to measurable energy losses. A typical multi-speed transmission includes as many as 5 clutch packs. Of those, two to three clutches are open at any time during a typical drive cycle, presenting an opportunity for fuel economy gain. However, reducing open clutch drag is very challenging, while meeting cooling requirements and shift quality targets. In practice, clutch design adjustment is performed through trial-and-error evaluation of hardware on a test bench. The use of analytical methodologies is limited for optimizing clutch design features due to the complexity of fluid-structure interactions under rotating conditions.
Journal Article

Accuracy and Robustness of Parallel Vehicle Mass and Road Grade Estimation

2017-03-28
2017-01-1586
A variety of vehicle controls, from active safety systems to power management algorithms, can greatly benefit from accurate, reliable, and robust real-time estimates of vehicle mass and road grade. This paper develops a parallel mass and grade (PMG) estimation scheme and presents the results of a study investigating its accuracy and robustness in the presence of various noise factors. An estimate of road grade is calculated by comparing the acceleration as measured by an on-board longitudinal accelerometer with that obtained by differentiation of the undriven wheel speeds. Mass is independently estimated by means of a longitudinal dynamics model and a recursive least squares (RLS) algorithm using the longitudinal accelerometer to isolate grade effects. To account for the influences of acceleration-induced vehicle pitching on PMG estimation accuracy, a correction factor is developed from controlled tests under a wide range of throttle levels.
Journal Article

In-Vehicle Characterization of Wet Clutch Engagement Behaviors in Automatic Transmission Systems

2018-04-03
2018-01-0395
A new generation of a planetary-gear-based automatic transmission system is designed with an increasing number of ratio steps. It requires synchronous operation of one or more wet clutches, to achieve a complex shift event. A missed synchronization results in drive torque disturbance which may be perceived by vehicle occupants as an undesirable shift shock. Accurate knowledge of clutch behaviors in an actual vehicle environment is indispensable for achieving precise clutch controls and reducing shift calibration effort. Wet clutches are routinely evaluated on an industry-standard SAE#2 tester during the clutch design process. While it is a valuable tool for screening relative frictional behaviors, clutch engagement data from a SAE#2 tester do not correlate well with vehicle shift behaviors due to the limited reproducibility of realistic slip, actuator force profiles, and lubrication conditions.
Technical Paper

Development of Empirical Asperity Contact Model for Wet Friction Material

2019-04-02
2019-01-0346
A wet clutch couples or decouples gear elements to alter torque paths in an automatic transmission system. During the gear shifting event, the clutch torque is directly transmitted to the output shaft. Hence, clutch torque heavily influences the dynamics of the transmission. In order to evaluate the behavior of the transmission early and efficiently, the development process increasingly relies on high-fidelity transmission system simulations with added complexity. However, a wet clutch continues to be modeled using Coulomb’s friction in a typical shift simulation. Its linear framework does not physically represent non-linear hydrodynamic effects due to the presence of oil layer during clutch engagement. To make up the lack of physics, Coulomb’s clutch model often requires extensive tuning to match actual shift behaviors.
Technical Paper

Application of Empirical Asperity Contact Model to High Fidelity Wet Clutch System Simulations

2019-04-02
2019-01-1301
Wet clutches are complex hydrodynamic devices used in both conventional and electrified drivetrain systems. They couple or de-couple powertrain components for applications such as automatic shifting, engine disconnect and torque vectoring. Clutch engagement behaviors vary greatly, depending on design parameters and operating conditions. Because of their direct impact on vehicle drivability and fuel economy, a predictive CAE model is desired for enabling analytical design verification processes. During engagement, a wet clutch transmits torque through viscous shear and asperity contact. A conventional Coulomb’s model, which is routinely utilized in shift simulations, is inadequate to capture non-linear hydrodynamic effects for higher fidelity analysis. Extensive research has been conducted over the years to derive hydrodynamic torque transfer models based on 1D squeeze film or 3D CFD. They are typically coupled with an elastic asperity contact model for mechanical torque transfer.
Technical Paper

Quantifying the Effect of Initialization Errors for Enabling Accurate Online Drivetrain Simulations

2019-04-02
2019-01-0347
Simulations conducted on-board in a vehicle control module can offer valuable information to control strategies. Continued improvements to on-board computing hardware make online simulations of complex dynamic systems such as drivetrains within reach. This capability enables predictions of the system response to various control actions and disturbances. Implementation of online simulations requires model initialization that is consistent with the physical drivetrain state. However, sensor signals and estimated variables are susceptible to errors, compromising the accuracy of the initialization and any future state predictions as the simulation proceeds through the numerical integration process. This paper describes a drivetrain modeling and analysis method that accounts for initialization errors, thereby enabling accurate simulations of system behaviors.
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