Francesco Bucchi

How the Autonomic Nervous System and Driving Style Change With Incremental Stressing Conditions During Simulated Driving

This paper reports on the autonomic nervous system (ANS) changes and driving style modifications as a response to incremental stressing level stimulation during simulated driving. Fifteen subjects performed a driving simulation experiment consisting of three driving sessions. Starting from a first session where participants performed a steady motorway driving, the experimental protocol includes two additional driving sessions with incremental stress load. More specifically, the first stressing load consists of randomly administering mechanical stimuli to the vehicle during a steady motorway driving by means of a series of sudden and unexpected skids, such as those produced by a strong wind gust. These skids were supposed to produce in the driver a given level of stress. In order to assess this mental workload, dedicated psychological tests were performed. The second stressing load implied an incremental psychological load, consisting of a battery of time pressing arithmetical questions, added to the mechanical stimuli. For the whole experimental session, the drivers physiological signals and the vehicles mechanical parameters were recorded and analyzed. In this paper, the ANS changes were investigated in terms of heart rate variability, respiration activity, and electrodermal response along with mechanical information such as that coming from steering wheel angle corrections, velocity changes, and time responses. Results are satisfactory and promising. In particular, significant statistical differences were found among the three driving sessions with an increasing stress level both in ANS responses and mechanical parameter changes. In addition, a good recognition of these sessions was carried out by pattern classification algorithms achieving an accuracy greater than 90%.

A fail-safe magnetorheological clutch excited by permanent magnets for the disengagement of automotive auxiliaries

This work was carried out in the framework of a funded project aimed at evaluating the feasibility of an ad hoc clutch for the disengagement an auxiliary device, i.e. the vacuum pump used with the powerbrake in diesel engine vehicles, when its operation is not required. In this way it is possible to improve the overall vehicle efficiency. Strict design specifications were defined with reference to available room, torque transmission, absence of axial loads and fail-safe operation. A magnetorheological clutch with permanent magnets was conceived to fulfil the technical requirements. Different clutch geometries were compared with particular reference to the fail-safe operation and torque capabilities. After an iterative procedure, in which both mechanical design and magnetic field analyses were considered, the most promising solution was defined and a prototype was built and tested. A four-pole sliding permanent magnet was adopted to generate the magnetic field. The experimental results validated the developed models and demonstrated the feasibility developed models and demonstrate the feasibility of the proposed solution. A principle for the automatic clutch actuation is also presented.

Temperature Effect on the Torque Characteristic of a Magnetorheological Clutch

In this article the torque characteristic of a permanent magnet magnetorheological (MR) clutch is investigated focusing on the influence of temperature. An experimental campaign was carried out on a test bench equipped with a caulk oxen, heating up to 80°C. The torque characteristic was measured monitoring both fluid and clutch case temperature. Torque data were processed and well fitted by a formula where the temperature dependence is expressed by Arrhenius law. In particular, a loss of transmitted torque for increasing temperature was found. An approximate dependence of MR fluid shear stress on temperature, useful for similar devices, was also obtained.

A multi-gap magnetorheological clutch with permanent magnet

This paper describes the design and testing of a novel permanent magnet clutch based on a magnetorheological fluid. It was inspired by a prototype previously developed by the authors and contains a novel gap shape conceived to reduce torque loss in the disengaged operating mode. Several geometries and material arrangements were investigated and the performance in terms of transmissible torque in different operating conditions was assessed using finite element numerical models. The prototype was manufactured and some experimental tests were performed. The new prototype was rated on the basis of performance indices and the design effectiveness was proven by a higher value of efficiency in the disengaged operating mode.

A magnetorheological clutch for efficient automotive auxiliary device actuation

In this paper the results of a project funded by Regione Toscana aimed at reducing the power absorption of auxiliary devices in vehicles are presented. In particular the design, testing and application of a magnetorheological clutch (MR) is proposed, aimed at disengaging the vacuum pump, which draws in air from the power-brake booster chamber, in order to reduce the device power absorption. Several clutch preliminary studies done to choose the clutch geometry and the magnetic field supply are illustrated. The final choice consisted in an MR clutch with permanent magnet, which satisfied size, torque and fail-safe specifications. The clutch characteristics, in terms of torque versus slip, were obtained experimentally for three different clutch prototypes on an ad-hoc developed test bench. As result of a preliminary simulation, a comparison between the power absorption of a current production vacuum pump, an innovative vacuum pump and both vacuum pumps coupled with the MR clutch is presented. The New European Driving Cycle is considered for simulating the vacuum pump operation both in urban and highway driving. Results show that the use of the innovative vacuum pump reduces the device consumption of about 35%, whereas the use of MR clutch coupled with the innovative vacuum pump reduces it up to about 44% in urban driving and 50% in highway driving.

Magnetic FEM Design and Experimental Validation of an Innovative Fail-Safe Magnetorheological Clutch Excited by Permanent Magnets

This paper describes the magnetic design of an innovative fail-safe clutch based on magnetorheological fluid (MRF). A cylindrical arrangement of permanent magnets (PMs) is used to excite the fluid. The suitable distribution of magnetic field inside the MRF and the transmissible torque is obtained by moving the PMs along the axial direction. The device is designed using a magneto/mechanical FEM model, developed on purpose and based on a three-dimensional (3-D) finite-element code, which takes into account the B-H and τ-H functions of the nonlinear materials (e.g., MRF, PM, and ferromagnetic materials). The flux density maps and the shear stress maps inside the fluid are carefully analyzed. Furthermore, in order to validate the FEM model, some preliminary experimental measurements are performed on a prototype. Finally, the magnetic axial force acting on the PM system is investigated.

Analysis of the torque characteristic of a magnetorheological clutch using neural networks

In this paper the dependence of the torque characteristic of a magnetorheological clutch on several working parameters is analyzed by means of a feedforward neural network. The clutch was envisaged to have the possibility to disengage the vacuum pump in diesel engine vehicles, in order to increase the overall vehicle efficiency. A large set of test was carried out following different protocols in order to obtain a detailed characterization of the clutch. Results showed that, due to the characteristics of MR fluids and to the complex mechanism of torque transmission, the torque characteristics (both the yield torque and the torque-slip behavior) are a function of the relative speed between the input and output shafts, of the energy dissipated during the clutch slip and of the rest time between consecutive slippages. The data acquired during all tests were used to train a neural network with five input elements and one output element. The developed neural network proved to satisfactorily reproduce the actual clutch properties and could be used in the future in an engine-vehicle simulator in order to model the torque characteristic of the clutch subjected to different operating cycles.

Analysis of the Experimental Torque Characteristic of a Magnetorheological Clutch Using Neural Networks

In this paper the dependence of the torque characteristic of a magnetorheological clutch on several working parameters is analysed by means of a feedforward neural network. The clutch was envisaged to have the possibility to disengage the vacuum pump in diesel engine vehicles, in order to increase the overall vehicle efficiency.A large set of test was carried out following different protocols in order to obtain a detailed characterization of the clutch. Results showed how, due to the characteristics of MR fluids and to the complex mechanism of torque transmission, the torque characteristics (both the yield torque and the torque-slip behaviour) is function of the relative speed between the primary and secondary clutch groups and also function of the dissipated energy during the clutch slip and of the rest time between consecutive slippages. The data acquired during all tests were used to train a neural network with five input elements and one output element.The developed neural network was proved to satisfactorily reproduce the actual clutch properties and can be used in the future in an engine-vehicle simulator in order to model the torque characteristic of the clutch subjected to different operating cycles.Copyright

Experimental Characterization of a Permanent Magnet Magnetorheological Clutch for Automotive Applications

In this work a magnetorheological clutch prototype with a permanent magnet is presented and the torque transmitted in several operating configurations is obtained by a specifically designed test bench. The clutch prototype was designed in order to have the possibility to disengage the vacuum pump which operates the power brake in diesel engines continuously. Torque transmission and size specifications were suggested by the specific application. A permanent magnet was used in order to obtain a fail-safe operation and particular attention was focused on materials selection in order to maximize torque transmission in the engaged mode and to minimize power consumption when the clutch is disengaged.Tests were carried out on the test bench, in which electric motors apply the driving and braking torques to the primary and secondary shaft of the clutch; the transmitted torque was measured by a torque-meter at several rotational speeds. Experimental results are discussed in the paper with reference to classical literature models. The experimental tests gave also useful indications on possible improvements in the clutch design, especially regarding the seals, which have to prevent leakages at the working fluid pressure and to keep the friction losses low.Copyright

Multibody simulation of a rope-driven automated people mover

In this paper, a multibody model of the automated people mover, PisaMover, is presented. PisaMover is a rope-driven small train, composed of a few cabins, which makes use of train-inspired bogies. The aim of the model was to support the design of the architecture of the suspensions and to select the proper characteristics of the elastic and damping elements in order to fulfill comfort needs of passengers and to resolve the constraints related to the layout of the vehicle and the guide-ways. For this purpose, attention was especially focussed on the definition of the railway path and the modeling of the forces of the supporting and guidance wheels. A simplified model of the rope was implemented, which neglects the rope elasticity and computes the rope force direction taking account of the different positions of the sheaves along the path. The multibody simulation allowed to select the most appropriate suspension system and to properly define the elastic and damping characteristics of the shock absorbers, with respect to the technical constraints. A modal analysis was performed, and several dynamic on-track simulations were carried out to infer the effect of dampers’ design on the comfort of passengers. Within the validity of the simplifying assumptions, the multibody simulation also allowed to obtain a fairly good estimate of the loads necessary for the design of the main structural components.