CTI Mag: AVL’s Future Hybrid X-Mode

 AVL’s Future Hybrid X-Mode

A modular hybrid transmission family that can be implemented as a conventional AT, 48V or HEV/PHEV system, delivering a new dimensionof safeguarding development efforts and industrial assets in vehicle markets with volatile customer preferences

Ivan Andrasec, Design Engineer Powertrain, AVL List
Bernd Jeitler, Lead Engineer Product Quality Assurance & Production Engineering, AVL List

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Issue: #December 2017

An ongoing effort to reduce fleet CO2 emissions of passenger cars is under way and is shaped by corresponding legislation proposals. Hybrid vehicles offer possible solutions to achieve the ambitious targets. Predictions show that an increase in hybrid vehicles is expected, the volume mix forecasts however are changing very frequently. Such uncertainties also pose challenging questions for future transmissions and related investment decisions. A wide variety of possible concepts already exists and this variety will likely grow bigger. Therefore, there is a high risk of increased research effort in the search for favorable concepts. In addition, the cost of production has to be considered and given resources have to be managed under economic perspectives.

Bearing this in mind, a holistic development approach should be chosen to come up with hybrid transmission concepts or dedicated hybrid transmissions (DHTs) with a focus on those topics.

In this way, AVL’s new Future Hybrid X-Mode is a viable solution that reduces certain risks. The experience gained from the design of the Future Hybrid 7 Mode and 8 Mode DHTs as well as customer demands formed the basis for this development. The additional aspect of economic effectiveness and a refined development process helped to come up with this DHT system concept.

Future Hybrid X-Mode Layout

The Future Hybrid X-Mode is a modular transmission family for transverse application up to E-segment vehicles. Its variants have different characteristics depending on the level of electrification (LoE). The concept revolves around a core transmission and interchangeable component modules. By combining different modules with the core components, one can freely generate different types of transmissions in terms of LoE. It is possible to generate two high-voltage HEV/PHEV systems (HV and HV+), a 48 Volt system (48V) or a 6-speed conventional automated transmission (AT). Their main layout and characteristics can be seen in Figure 1 and Table 1 respectively. The variants differ in number of operation modes and features (hence the name Future Hybrid X-Mode).

Figure 1 Future Hybrid X-Mode Layouts, left: HV, middle: HV+ and 48V, right: AT

Table 1 Main characteristics of Future Hybrid X-Mode variants

An example layout was created for a typical C-segment vehicle with a 105 kW gasoline ICE. The DHT version of the X-Mode (HV) consists of one electric machine with a peak power of 100 kW. The core of the transmission is a Ravigneaux planetary gear set with a two-step helical gear manipulating idler for speed reduction coupled to it. The shift elements are two multi-plate clutches and two brakes with hydraulic actuation (see Figure 1, left).

The layout of the HV variant offers the possibility to generate four parallel hybrid modes (PH) that are forward driving and power-shiftable, two pure electric modes (EV), one torque-split mode (ECVT) and one mode for charging at standstill.

The HV+ variant can be derived when adding another clutch to the HV variant. It is marked blue in the central part of Figure 1. This addition increases the number of operation modes by two more PH modes for forward driving and one reverse PH mode – all of them are powershifted. In addition, the HV+ variant has also one more ECVT mode.

With regard to LoE, this additional clutch enables the transmission to be operated as a 48 Volt system. For the 48V variant it is possible to use an electric machine with up to 25 kW of peak power. Also a conventional 6-speed AT can be realized, if the transmission shall not be electrified (see Table 1 and Figure 1, right).

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