DE VELO PMENT BODY

Lightweight Design Door Latch with Integrated Crash Safety System

© Kiekert

AUTHORS

In the event of a passenger car collision, acceleration forces occur that can lead to an unintended opening of the side doors. Although this is reliably prevented today through mass-balancing systems, they come with undesirable additional weight. With its Active Inertia latch system, Kiekert offers a solution based on the acceleration of

Dr.-Ing. Thorsten Nottebaum is Head of Global Product Development at Kiekert AG in Heiligenhaus (Germany).

tiny masses, which takes up very little installation space and saves on cost.

AVOIDING UNINTENDED OPENING OF THE DOOR Dipl.-Ing. Thorsten Bendel is Director Product Development Europe at Kiekert AG in Heiligenhaus (Germany).

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These days, car door latches are generally opened with external door handles that combine the unlatching and opening of the side door in a single movement. Most external door handles are arranged horizontally, fixed to the door on just one edge and pulled away from the door around a single pivot point. This format has established itself among

most cars currently on the market. However, the operating principle behind this function means that the external door handle’s own inertia can lead to the door opening unintentionally in crash scenarios. This typically occurs in side impacts, because the forces are applied exactly opposed to the direction in which the lever opens, but also in any other crash situation in which the external door handle is set in motion with sufficiently high acceleration force.

FUNCTIONAL INTEGRATION FOR WEIGHT REDUCTION

Modern door latches have, however, now reached a level of functional density that permits very little progress in terms of package size and weight as well as further content downscaling. Every single component has a very clear purpose and has been extensively topologically refined. There is only very little potential for savings even in the choice of material, such as the targeted use of polymers or cast and formed metal components [1, 2]. Nevertheless, as is the case throughout the vehicle as a whole, questions are persistently posed about the contribution the locking system can make to weight reduction. The battle to achieve low vehicle weight is now one of the main tasks faced by development engineers in order to reduce CO2 emissions and fleet fuel consumption. This led to the idea of shifting the blocking function in the event of a crash out of the heavy system, consisting of outer door handle and counterweights, and into the compact latch. Obviously, the greatest potential of lightweight design can be realised when a mass balancing system is relocated to wherever the lowest masses have to be moved. The Kiekert development engineers were now faced with new challenges: Because there had been no previous comparable solutions and there was no empirical data to hand, it was necessary to undertake a series of development approaches to investigate and configure the effective inertia inside the latch. 10I2016

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A crash situation cannot be reduced to a simple interaction of two opposing accelerations. In real terms, it is a complex vibration process occurring within a matter of milliseconds, in which the forces work in different directions, potentially reversing multiple times during the event, as it is shown with the different travel curves in FIGURE 1. Acceleration forces of more than 200 g can occur following the initial impact. Now, the tasks were to find a solution for the latch that was as compact as possible with no additional installation space, and to ensure flawless functionality in all physically possible scenarios and in all impact directions. This led to the development of Active Inertia, whereby the protective function is fully integrated into the latch with the lowest possible additional mass. FUNDAMENTAL FUNCTIONALIT Y OF A DOOR LOCKING SYSTEM

A door locking system fundamentally consists of an outer door handle that activates a lever in the latch system. The actuation lever is tasked with releasing the locking mechanism. The locking mechanism consists of at least one pawl and the catch, which, in the locked state, encloses the cotter pin mounted in the door frame. With this configuration, pulling on the outer door handle causes the pawl to release the catch, so that when the door is pulled, it releases the cotter pin and the door can be opened. In order to comply with regulations, an actuation force of around 20 to 50 N is required when opening a passenger

car door. Manual opening lasts approximately 40 to 100 ms, with the smaller value varying the most at between around 40 and 60 ms depending on vehicle configuration. The duration necessarily correlates with the acceleration of the moving masses in the locking system. Acceleration forces of several g can occur in the event of a crash. To avoid unintended opening due to high acceleration of the door handle, the established approach is a locking system in which defined counterweights inside the door prevent the latch from opening. FUNCTIONALIT Y OF ACTIVE INERTIA

The area of application for such systems and for the Active Inertia locking system, too, is normally passenger car side doors as they are the only ones with outer door handles that can be moved by acceleration due to their inertia. These days, most rear latches are actuated electromechanically and the bonnet is unlocked from inside the car. The absence of effective inert mass means the door cannot open unintentionally. In contrast to classic solutions, the functionality of Active Inertia is based not on a simple balance of inertia with the help of large, heavy weights, but a small functional element in the latch itself that responds to speed. Movement of the release lever is therefore not blocked from the outside. Instead, the actuation chain between the release lever and the pawl inside the latch is briefly interrupted by making active use of the behaviour of a small inert mass.

40.0

Travel outside handle [mm]

Unintended opening of the latch through inertia is generally avoided by adding counterweights inside the door. The outer handle and its counterweights thus form a system grouped functionally around the latch itself. The counterweights ensure that in the event of an impact the mass of the overall system is sufficiently well balanced to prevent unintended opening. The external door handle may well move slightly during a crash, but the mass balancing ensures the latch system is not actuated. The downsides of this solution are the large amount of installation space required and the considerable additional weight, both of which pay off purely in the event of a crash. It would therefore be desirable to find an alternative solution that does not involve additional weight.

30.0

20.0

10.0

0.0 0.0

0.015

0.03

Time [s]

0.045

0.06

0.075

FIGURE 1 Different characteristics (coloured curves) of the acceleration forces in a typical side impact crash (© Kiekert)

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across several interacting elements that can be arranged differently depending on installation space and customer preferences. Within this actuation chain, there are therefore a number of options for positioning the functional element of Active Inertia. The main issue is ultimately the functional principle, which is always based on a small mass and its inert mass and a spring. FIGURE 2 In the event of a crash, the actuation chain between the door handle and the locking mechanism is interrupted with the aid of an elastically mounted inertia element (green circle) (© Kiekert)

Specifically, the release lever activated by the outer door handle acts on a transfer lever which rotates around the inertia element, whereby a defined elastic spring connection permits unlatching under normal operating conditions. However, above a defined acceleration, the inertia element can no longer follow the movement of the transfer lever. As a result, the actuation chain is interrupted and the locking mechanism remains engaged, FIGURE 2. Functionality is reversible following a crash, that is, once the acceleration subsides, the system returns to its basic state. Moreover, this also means the blocking function is repeatable in complex crash situations. As long as the latch itself is not damaged, the base function is maintained at all times due to its closed construction. Legislation demands that the latch condition remain unchanged at acceleration forces of up to 30 g. A Kiekert

latch without Active Inertia remains stable up to around 60 g. A Kiekert latch with Active Inertia resists acceleration forces over this level. The limiting element for opening and closing the doors is therefore not the latch, but the condition of the doors and/or body structure following the crash. In this respect, Active Inertia behaves just like any other locking system. However, its compression into a single functional module actually protects in principle against impairment of the closing function caused by deformation of the door. The fundamental function principle behind Active Inertia is always the same, with any variations being in the specific mechanical layout. Different configurations are possible depending on the vehicle application and customer wishes [2, 3, 4]. In practice, the functionality of the release lever and locking mechanism described before is also distributed

FIGURE 3 Full functional integration of the inertia element into the latch module means the counterweights, mounting brackets and, where applicable, crash pads can all be eliminated – thus, a passenger car can be lightened up to 1.2 kg (© Kiekert)

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BENEFITS FOR CAR MANUFACTURERS

In general, it can be said of Active Inertia that, in contrast to conventional solutions, the function is fully integrated into the smallest possible installation space. This has several benefits, one of the most important for the car manufacturers being weight saving. Per latch, the new locking system requires a very small additional mass of around 40 g. However, elimination across the entire system of the counterweights, the mounting brackets and, possibly, large crash pads to protect the locking system means that several hundred grams can be saved in each door, FIGURE 3. Over four doors, the weight benefit can be up to 1200 g depending on the vehicle concept. The locking system thus makes a noticeable contribution on a fleet level to weight reduction and CO2 savings. Further, from a system standpoint, it delivers significant cost benefits due to simplified integration resulting from the elimination of the counterweights and a considerably simpler configuration of the outer actuation lever. The response characteristics, and thus the transition point between closing and opening, can be set entirely through definition of the spring force and the mass of the inertia element. Furthermore, the functionalities of outer actuation and latch are fully decoupled from one another. For car manufacturers, both of these factors simplify vehicle application as, instead of two connected systems, they only have to consider one single, closed functional system that has absolutely no influence on door design. Development, computer simulation of crash behaviour and testing are highly integrated at Kiekert – right through to test rigs developed in-house, including ones for acceleration tests based on specific crash situations. And this is where a further benefit of Active Inertia becomes

evident: Its functionality can be developed and assured on the basis of available crash curves, independent of the external actuation system. Because it is a closed functional unit, a very high level of accuracy can be achieved in simulation work with multi-body simulation and finite-element analysis. In the next development step, testing methods developed in-house enable highly precise validation of behaviour in crash situations. This ultimately reduces the amount of testing required in the later development phases through to entire vehicle crash testing. CONCLUSION

Weight is a major factor in the development of CO2-efficient vehicles. In an ideal

O N

world, additional weight is only acceptable where it contributes to reducing fuel consumption through lower rolling resistance or more efficient powertrain technology. This can lead to conflicts of interest in passive safety. This calls for intelligent solutions that at a minimum retain safety levels while reducing vehicle weight. The Active Inertia locking system by Kiekert integrates the functions for protecting against unintended opening in the event of a crash into the latch itself, thus reducing weight and packaging requirements to a fraction of those for conventional solutions, paired with lower overall system costs. It therefore contributes to lightweight design, costefficient occupant safety and lower fuel consumption.

T H E

R O A D

REFERENCES [1] Bendel, T.: Modern latch development in the area of conflict between continuous comfort improvement and uncompromising crash safety, at concurrent weight and package optimization in the overall side door system. 4 th conference on doors and closures in car body engineering, Bad Nauheim, 13 and 14 November 2013 [2] Bendel, T.: Uncompromising crash safety realized on a side door latch while keeping it light weight and modular to realize a real E-Latch on the same latch platform. 5 th conference on doors and closures in car body engineering, Bad Nauheim, 18 and 19 November 2014 [3] Industrial property right application DE 10 2011 010 815 A1: Vehicle door latch, inverted inertia lock (blocking lever). Kiekert, publication date: 9 August 2012 [4] Industrial property right application DE 10 2011 010 797 A1: Vehicle door latch, inverted inertia lock (release lever). Kiekert, publication date: 9 August 2012

A G A I N

…

THE 2017 AUTOMOTIVE TECHNOLOGY EUROPEAN ROADSHOW In association with

ATZ MTZ

The ATZ/MTZ Automotive Technology Roadshow takes place once again in March 2017 visiting the Major OEM and Tier 1 Organisations across the UK and Germany. This represents an amazing opportunity to come and present your products, services and technologies on board our unique exhibition vehicle directly inside the customers premises. Jaguar Land Rover, Ford (Germany and UK), Aston Martin, Nissan (Sunderland and Cranfield), Toyota, BMW (Germany), Visteon, Continental and others are all on the proposed tour list for 2017.

So if you would like to come and meet the Design/Development/R&D Purchasing and Senior Management Personnel at some of the most strategic European Automotive Facilities then please contact us and we will send you a full information pack by return.  Contact John Aldridge Tel: +44 (0) 1189 886823 Email: [email protected] www.dream-marketing.co.uk

We will provide you with your Exhibition stand with graphic display, power, lighting and cupboard storage and the opportunity to have two of your personnel on the vehicle at each location on the route. 10I2016

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