Design of a Clutchless Hybrid Transmission for a High-Performance Vehicle

Abstract

There exists the potential for major simplifications to current hybrid transmission architectures, which can lead to advances in powertrain performance. This paper assesses the technical merits of various hybrid powertrains in the context of high-performance vehicles and introduces a new transmission concept targeted at high performance hybrid applications. While many hybrid transmission configurations have been developed and implemented in mainstream and even luxury vehicles, ultra high performance sports cars have only recently begun to hybridize. The unique performance requirements of such vehicles place novel constraints on their transmissions designs. The goals become less about improved efficiency and smoothness and more centered on weight reduction, complexity reduction, and performance improvement. To identify the most critical aspects of a high performance transmission, a wide range of existing technologies is studied in concert with basic physical performance analysis of electrical motors and an internal combustion engine. The new transmission concepts presented here emphasize a reduction in inertial, frictional, and mechanical losses. A series of conceptual powertrain designs are evaluated against the goals of reducing mechanical complexity and maintaining functionality. The major innovation in these concepts is the elimination of a friction clutch to engage and disengage gears. Instead, the design proposes that the inclusion of a large electric motor enables the gears to be speed-matched and torque-zeroed without the inherent losses associated with a friction clutch. Additionally, these transmission concepts explore the merits of multiple electric motors and their placement as well as the reduction in synchronization interfaces. Ultimately, two strategies for speed-matched gear sets are considered, and a speed-matching prototype of the chosen methodology is presented to validate the feasibility of the proposed concept. The power flow and operational modes of both transmission architectures are studied to ensure required functionality and identify further areas of optimization. While there are still many unanswered questions about this concept, this paper introduces the base analysis and proof of concept for a technology that has great potential to advance hybrid vehicles at all levels.

Design of an Electric Motor Transmission System Without Friction Synchronization

“…Clutchless Transmission. Previous research designed a clutchless hybrid transmission system [6]. The clutchless hybrid system, as the name suggests, removes the clutch from the conventional system and uses a second electric motor to help with speed matching during the shift event.…”

System Design and Stress–Strain Analysis for Cranking and Motoring Small-Size Engines

“…A clutch-based solution features the characteristic of the same rpm for the two components, and has the advantage that it ensures the decoupling of the shafts, but it requires a more complex design [18,19]. The literature widely covers its design and structural validation for practical applications [20,21] but shows limited use for engine test benches [22]. As for the belt-coupling configuration, its main advantage comes from the possibility of using pulleys with different gear ratios, thus ensuring the option of combining ICEs and EMs with a different rpm range.…”