Automotive Alternative Power Systems:
Requirements for Next-Generation Connectors
The following article is an edited reprint courtesy of Tyco Electronics.

There is widespread consensus that internal combustion engines, although continuing to improve, will eventually be replaced by electric drives. The timing for the substitution depends on political motivations and actions, as well as the comparative cost/performance curve of electric drives vs. internal combustion systems.

Viewing rival drive technologies, it becomes clear that although electric drives possess many advantages, the technology will ultimately be adopted in vehicles only through a low-cost reproduction of the complete drivetrain.
 

Figure 2 shows a basic overview of various current and future vehicle drive systems. The applications illustrated already reveal initial leanings towards combining units and components in specific performance classes, potentially contributing to reduced costs.

Electric Drive Train Components

The high voltage onboard power supply is typically a separate supply structure in hybrid or electric vehicles, and consists of the following components (Figure 1).

 

 

 

Electric Connector Requirements

The aforementioned components must be connected to one another electrically. Diverse, specific requirements arise due to the voltage level used. A summary of the main electrical, mechanical, and material-related parameters:

 

 

In addition, specific requirements mirror the increasing complexity inherent in using connectors in high voltage onboard power supplies. These requirements include:

1. Round contacts for optimum ampacity with higher currents

2. Shielding (single and family shield)

3. Protection class (e.g. IP6K9K - dustproof, watertight, contact-protected IPX7 when mated and unmated, contact-protected IP XXB)

4. Interlock safety function, to ensure main contacts mate-first/break-last relative to interlock signal contacts

The many possible combinations of these product requirements can result in a large number of diverse, highly specialized products. Aside from high direct product costs, disadvantages caused by additional approval, certification, and integration costs could also be expected. For this reason, leading German OEMs defined the LV215-1 during the AK 4.3.3. working group. It lists the technical requirements that should be satisfied by new high voltage connectors. This approach will promote standardization and facilitate bundling of the small production volumes expected during the comparatively slow market take-off.

 

With this in mind, Tyco Electronics drafted product proposals that observe this specification.

 

The main feature is the voltage class up to 850 volts DC, and a division into two current categories that cover the most common HV applications. The first category, up to 40 amps, is for conductor cross-sections of 2.5 to 6mm2. In the second category, currents of up to 250 amps are defined for cable cross-sections ranging from 16 to 50mm2. These parameters were intentionally selected to avoid too great a diversity of versions in HV contact systems. Aside from stationary operating points (continuous current), the prescribed dynamic load profiles were assessed, which also permit higher current values for short periods.

 

In order to give designers greater flexibility when using connectors, the same mounting geometry/opening on the aggregate device is applicable to both 90° and 180° cable outlet directions. This means that a 90° or 180° plug coupling can be selected without having to change the aggregate device mounting geometry/opening. All categories are available in 2- and 3-pin versions.

 

The contact protection requirement deserves mention here as only then can comprehensive safety be ensured against potential dangers during assembly, service, or field operation. The 8mm round contact for conductor cross-sections great than 16mm2 (category 2) offer design and space advantages in comparison to flat contacts. The protection level, when mated, is the equivalent of IPX7, IP6k9k, and in unmated applications, IPXXB.

 

The mating condition is detected by an interlock contact integrated in the connector. To facilitate connector integration in automobile production from an ergonomic point of view, insertion and withdrawal forces are reduced to less than 100 N by a lever system. The large conductor cross-sections implemented, and the dead weights thus entailed, result in increased mechanical strain on connectors. This is a particular challenge when fulfilling the relevant vibration classes. Conductors must be effectively bound (strain relief) or their weight minimized in order to reduce strain. In the future, aluminium conductors will play a greater role.

 

Vehicles with electric drives will also have to satisfy high EMC requirements in view of major advances in communication technologies and entertainment electronics. For this reason, these connectors are shielded and designed for shielded conductors.

 

Due to the high voltage onboard power supply topologies and shielding concepts used, induced currents of up to 10 amps, and for short periods, even 25 amps, may occur on the shields.

 

A non-wearing electric drive makes demands on the longevity of connection components. A mating cycle count of up to 50 underscores this demand. With the aim of minimizing accident repair costs, priority was placed on the five-fold replaceability of the housing and contact—a benefit for OEMs to achieve attractive insurance classifications for end users.

 

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For more information about TE’s automotive alternative power products, contact Thomas Grundei at tgrundei@te.com,  or phone +49 6251 133 1382.