分析和仿真的轉(zhuǎn)矩輔助自動手動變速器Analysis and simulation of a torque assist automated manual transmission
1. Introduction
One of the most challenging issues for the automotive world in recent years has been the improvement of vehicles both in terms of fuel efficiency and longitudinal behaviour. Since transmissions play a fundamental role for energy saving and drivability, many researches have focused on enhancing the performance of existing systems and on developing new technologies.
Among the several types of transmissions currently available, manual transmissions (MT) show the highest efficiency value for any type of transmission (96%), while current production automatics (AT) have been improved to provide an efficiency of about 86% and belt type continuously variable transmissions (CVT) have an overall efficiency of 85%, but their major advantage consists in allowing the engine to operate most fuel efficiently.
A recently developed power-shift automated transmission, i.e. the Dual Clutch Transmission, aims at optimising the advantages of MT and AT, offering high efficiency and excellent shifting quality.
Automated manual transmissions (AMT) are generally constituted by a dry clutch and a multi-speed gearbox, both equipped with electro-mechanical or electro-hydraulic actuators, which are driven by an Electronic Control Unit (ECU). In order to overcome the driving torque interruption that leads to undesired vehicle jerks during gear changes , different devices called torque gap fillers (TGF) can be integrated in AMT driveline architectures. A solution has been developed by Magneti Marelli Powertrain: it mainly consists of an epicyclic gear-set to be added to a conventional AMT allowing to transfer power from the engine to the secondary shaft during gearshifts.
Recently Hitachi Group has proposed an alternative solution, consisting of a friction clutch mechanism – called assist clutch (ACL) – that replaces the fifth gear synchroniser on traditional AMTs. The modulation of the assist clutch allows to shift gears smoothly, without interrupting the driving force; moreover it is a compact and low cost solution that requires relatively little modification to existing layouts.
This paper deals with this ACL-AMT transmission: the analysis will be focused on the system architecture and on the dynamic behaviour.
In particular, the authors, after presenting the kinematic and dynamic model of the transmission, investigate and quantify the power contributions for different engine and ACL interventions arising during various gearshifts in order to highlight the relative weights between available, dissipated and effectively usable power for the vehicle propulsion; finally some simulation results are reported.
2. Transmission layout and features
An ACL-AMT (see Fig. 1) consists of a traditional automated manual transmission with a servo-assisted clutch replacing the fifth gear synchroniser. The system is electronically driven by a central unit that organises the controls of engine, main clutch, gear selectors and assist clutch in order to optimise the gearshift.
The internal combustion engine (E) is linked through the main clutch (CL) to the primary shaft of the gearbox; at the other end of the shaft, the ACL allows the connections between the fifth idle gear and the primary shaft (thus replacing the synchroniser), while the secondary shaft and the differe...
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