The reduction of consumption and emissions is a key factor in modern vehicle design. The overall vehicle efficiency is pursued in several ways, including the reduction of consumption of the auxiliary devices (e.g. water pumps, oil pumps, vacuum pumps etc.). In this paper, using two different smart materials (i.e. magnetorheological fluids and shape memory alloys) a device aimed at disengaging the vacuum pump was developed.

The conceived device is composed of a magnetorheological (MR) clutch excited by permanent magnets coaxially manufactured with a sliding spline sleeve moved by shape memory alloys (SMA) springs. In the MR clutch, the magnet can move under the effect of a passive pneumatic system. The magnetic field in the fluid varies with the magnets displacement and two steady positions are possible: the engaged clutch (ON) and the disengaged clutch (OFF). The torque in the ON configuration is high enough to drive the vacuum pump during normal operating conditions, whereas the low torque value in the OFF condition guarantees power saving up to 150 W.

In particular operating conditions (i.e. at low environmental temperatures) the torque necessary to start the vacuum pump may exceed the maximum transmissible torque of the MR clutch. For this reason a sliding spline sleeve, led by two SMA springs which counteract the force of two traditional springs was developed. A dummy plain sliding sleeve with SMA and conventional springs was numerically developed and tested. The fairly good agreement of the results confirmed the feasibility of the combined SMA/MR device.

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