Automotive Drivelines Research Articles

Parametric excitation as a cause of clutch judder: theoretical study and experimental validation

Judder is a friction-induced torsional vibration generated during clutch engagement in automotive drivelines. To the best of the authors’ knowledge, three are the causes attributed by the scientific community to the onset of the clutch judder: stick-slip phenomena, negative gradient of the coefficient of friction and geometric disturbances.With the help of a methodological approach that integrates the analysis of a mathematical model with the experimental data obtained on a specially designed test bench, this paper shows that, in some cases, the clutch judder may also be due to the presence of parametric excitation.This new understanding overcomes the limits of the existing explanations because it does not preclude the occurrence of clutch judder at high slip speeds, with positive gradients of the friction coefficient and at excitation frequencies different from the eigenfrequencies of the system.The four degrees of freedom model developed for the study of the transmission provides maps that allow to identify the instability conditions of the system. The analysis described in this paper has been aimed at solving a judder problem in a transmission already in production, but the same approach can be used to avoid the conditions that cause the onset of clutch judder on other transmissions in the design phase.

Optimization of drivability control functions with two-stage rate limiters

Load changes in automotive drivelines may cause uncomfortable vibrations. A suitable motor torque control is able to remedy this problem. Often, a two degrees of freedom structure is used in these drivability control functions. In this structure, the desired motor torque is pre-filtered by a multi-stage rate limiter. However, those functions are still parametrized experimentally by laborious test drives or on the test-bench. This paper addresses the model-based optimal parametrization of these rate limiters in automotive drivability functions. For this, a recently published gear specific model is identified and validated for another gear position. In addition, a linear transfer function of multi-stage rate limiters is approximated by the transient input describing function method. The characteristics of this transfer function are used to reduce the number of design variables for the multi-objective optimization of a two-stage rate limiter for drivability control.

Multi-state control strategy of starting for a wet friction clutch via a fuzzy logic algorithm

Wet multi-plate friction clutches are used in automotive drivelines to transfer torque, change gears, and prevent motion by locking-up components in the transmission. The control strategy of starting is a crucial technology for the application of a wet multi-plate friction clutch in the automotive industry. In this paper, a multi-state fuzzy control strategy for starting is presented and applied to a continuously variably transmission (CVT) powertrain for the validation of this strategy. The operation of the clutch was divided into four states: parking, starting, riding and emergency. The starting state was investigated in detail. A fuzzy algorithm was employed to control the pressure of the hydraulic cylinder acting on the clutch. A distinguishing feature is that the pressure does not increase but decreases to implement smooth starting during the initial period of starting. The rapid-control prototype (RCP) of the wet friction clutch was developed to validate the new control strategy onboard a test vehicle. Based on the experimental results, the multi-state control strategy for a wet friction clutch is a viable candidate for engineering applications.

Torque Transmissibility Assessment for Automotive Dry-Clutch Engagement

Dry clutches are widely used in conventional and innovative automotive drivelines and represent a key element for automated manual transmissions (AMTs). In practical applications, it is fundamental to model the clutch behavior through its torque transmissibility characteristic, i.e., the relationship between the throwout bearing position (or the pressure applied by the clutch actuator) and the torque transmitted through the clutch during the engagement phase. In this paper, a new model for the torque transmissibility of dry clutches is proposed. It is analyzed how the transmissibility characteristic depends on: friction pads geometry, cushion spring compression, cushion spring load, and slip-speed-dependent friction. Corresponding functions are suitably composed determining the torque transmissibility expression. An experimental procedure for tuning the characteristic parameters is presented. The clutch-torque transmissibility model is tested on a detailed cosimulation model with a typical AMT controller.

Virtual product development for an automotive universal joint

Constant velocity universal joints play a very important role in automotive drivelines. The traditional development method, based on a physical prototype and experimenting, is time consuming and costly. This test-based method does not easily identify rational design clues. Therefore, a virtual product development method, which is based on dynamics modeling and simulation, is necessary. Virtual prototyping for a universal joint has been developed using the simulation software package MSC.ADAMS. Dynamics simulation has been performed to predict and evaluate joint behaviors. This virtual product development method has been implemented by the WanXiang Group Co., which is one of the most famous Chinese automotive component manufacturers.

Simulation and experimental validation of the dynamic behavior of an electromechanically actuated multiple‐disk clutch

AbstractAutomated multiple‐disk clutches in automotive drivelines are at present hydraulically or electrohydraulically actuated. The electromechanical clutch actuation represents an alternative. The subject of the investigation is a functional model of an electromechanical clutch actuator which consists of a servo motor, a reduction gear and a mechanism for the realization of the force acting on the disks. For the simulation of the dynamic behavior of the electromechanically actuated multiple‐disk clutch a detailed multibody model is developed which includes models of the electromechanical actuator and the wet multiple‐disk clutch. The multiple‐disk clutch is described by coupled partial models for the rotational and translational dynamics. The coupling parameters are the relative disk distances and the forces between the disks. The results of test bench measurements are compared to simulation results. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Measurement and Control of Slip in a Continuously Variable Transmission

Continuously Variable Transmissions are used to optimize engine efficiency in automotive drivelines. The efficiency profit however, is lost due to inefficiencies in the CVT itself. These losses occur mainly in the (hydraulic) actuation system and in the variator. The losses can be lowered by minimizing the clamping force of the pulleys on the belt. Lowering the clamping force too much also leads to heavy slipping between belt and pulley, causing damage to the system.By controlling the clamping force in such a way that a limited amount of slip is allowed, the clamping force can be minimized without risking damage to the system. A nonlinear control scheme is used to control slip in the variator. Results show that such a control method is feasible and robust to torque peaks.

Drive-by-Wire Control of Automotive Driveline Oscillations by Response Surface Methodology

The first torsional mode (otherwise known as "shuffle" mode) of automotive drivelines is excited by engine torque transients and is typically around 2-5 Hz. The effect is particularly severe during step changes from the throttle pedal ("tip-in" or "tip-out"). Shuffle is manifest as a low-frequency longtitudinal acceleration oscillation which, if of sufficient magnitude, leads to driver discomfort. This brief examines the control of this aspect of "driveability" (the error between expected vehicle response and actual vehicle response to an arbitary control input) using feedforward control. The overriding principle to be obtained in this examination is the assessment of electronic throttle control in the context of rapid prototyping. The response surface methodology is adopted to achieve this goal. The potential of the electronic throttle for launch control is analyzed and investigated experimentally, confirming its effectiveness in controlling the first torsional mode.

Automotive drive by wire controller design by multi-objective techniques

The presence of flexibility in automotive drivelines, coupled with nonlinear elements such as gear lash leads to the presence of an undesirable oscillatory acceleration response to step changes in throttle input. This oscillation is generally low frequency (approximately 2– 5 kHz ) and can be of sufficient amplitude to cause driver discomfort and subjective disappointment with the driveability of the vehicle. A pole placement controller is developed for a “drive-by-wire” (electronically operated throttle) system, with the objective of reducing or eliminating the oscillatory response. The results of an existing factorial study are used to calculate the required number of poles. Due to the inherent nonlinearities present in the system and the various constraints which must be applied to the controller design, the polynomial values for the pole placement controller are selected by the application of multi-objective optimisation. The controller is shown to achieve excellent performance and robustness to parameter variations and operating conditions.

A Bearing Application Using Magnetorheological Fluids

A conventional automotive driveline center bearing (CB) consists of a roller bearing that rests on a U-shaped support, which includes a bladder formed by an elastomer, providing damping for radial vibrations between the roller bearing and the housing. In order to improve the vibration and force handling characteristics for a driveline CB, use of magnetorheological (MR) fluids has been envisioned in place of the traditional elastomer. In this work, expressions for the forces acting on a vehicle center bearing have been derived along with a simulation of the magnetic field in a MR-CB. Experimental studies have been conducted on a MR-CB prototype. It is seen that such a system can be effectively used in vehicle center bearings to improve the vibration and force handling characteristics for the automotive drivelines.

Analysis of driveline loads in an automotive powertrain with multiple Cardan joints

A general equilibrium analysis of automotive drivelines with multiple universal joints and numerous supporting conditions is presented. For the analysis, components of the driveline in terms of their angular rotation, angular velocity and acceleration are defined. Using kinematic conditions and a known torque and speed, the angular speed of the axle output shaft and all intermediate shafts and forces at contact points are computed using software developed to perform the analysis. To perform a time domain analysis, the quasi-static equilibrium conditions are imposed on the system at an instant. The instantaneous behaviour of the system is determined as a function of the transmission output shaft rotation. Finally, a numerical example is provided to illustrate the analysis. The results of the numerical example are plotted with respect to time. The general behaviour of the forces is found to be oscillatory and harmonic in nature.

Driveline Load Analysis with Multiple Cardan Joints.

A general equilibrium analysis of automotive drivelines with multiple universal joints and numerous supporting conditions is presented. For the analysis, components of the driveline in terms of their angular rotation, angular velocity and acceleration are defined. Using kinematic conditions and a known torque and speed, the angular speed of the axle output shaft and all intermediate shafts and forces at contact points is computed using a software developed to perform the analysis. To perform a time domain analysis, the quasi-static equilibrium conditions are imposed on the system at an instant. The instantaneous behavior of the system is determined as a function of the transmission output shaft rotation. Finally numerical example is provided to illustrate the analysis. Results of the numerical example are plotted with respect to time. The general behavior of the forces is found to be oscillatory and harmonic in nature.

Clonk: An onomatopoeic response in torsional impact of automotive drivelines

Vehicular driveline is a lightly damped non-linear dynamic system that is prone to noise and vibration response when subjected to excitation. There are many sources of excitation such as torsional impact caused by the take-up of backlash in the powertrain system. Such sources of excitation exist in transmission backlash, in driveline splines and in pinion-ring gear contact in the differential. Abrupt application or release of the throttle in slow moving traffic or rapid engagement of the clutch can be followed by an onomatopoeic response of the driveshafts, referred to in the industry as clonk. This is a disagreeable, audible and tactile response in some vehicles and can also coincide with every cycle of low-frequency longitudinal vehicle response, commonly referred to as shuffle or shunt. This paper describes the phenomenon of clonk and investigates its occurrence both by an experimental technique and by detailed modal analysis of driveshaft pieces. It is shown that finite element predictions agree well with the experimental findings and that the high-frequency structural modes can lead to discernible radiated noise. The preliminary findings reported here point to a need for a more detailed elasto-acoustic analysis.

5620804 Metal matrix composite bodies containing three-dimensionally interconnected co-matrices

A multiple harmonic method is presented in this paper for obtaining the internal resonant steady state vibration of a Jeffcott rotor with a piecewise-linear non-linearity at the bearing support. The method utilizes thehypertimeconcept, which isolates each frequency component of a response into pseudo-time domains. Explicit Jacobians are derived to obtain stable convergence solutions in the iteration process. The frequency components of the non-linear restoring force part are analytically expressed from those of the displacement part, using the Galerkin technique to guarantee a convergent solution. As the method utilizes general and systematic computational procedures, it can be applied to analyze the multi-tone or combination-tone responses for higher-dimensional non-linear systems such as multi-disk rotors or automotive drivelines with multiple excitational inputs. To demonstrate the accuracy and effectiveness of the proposed method, various simulation results are studied and the results of multiple HBM are compared with those from numerical integration.

A MULTIPLE HARMONIC BALANCE METHOD FOR THE INTERNAL RESONANT VIBRATION OF A NON-LINEAR JEFFCOTT ROTOR

A multiple harmonic method is presented in this paper for obtaining the internal resonant steady state vibration of a Jeffcott rotor with a piecewise-linear non-linearity at the bearing support. The method utilizes the hypertimeconcept, which isolates each frequency component of a response into pseudo-time domains. Explicit Jacobians are derived to obtain stable convergence solutions in the iteration process. The frequency components of the non-linear restoring force part are analytically expressed from those of the displacement part, using the Galerkin technique to guarantee a convergent solution. As the method utilizes general and systematic computational procedures, it can be applied to analyze the multi-tone or combination-tone responses for higher-dimensional non-linear systems such as multi-disk rotors or automotive drivelines with multiple excitational inputs. To demonstrate the accuracy and effectiveness of the proposed method, various simulation results are studied and the results of multiple HBM are compared with those from numerical integration.