A company describes its electronic door latching system
The electrification of door latches opens up new opportunities for the exterior vehicle design but also for less complexity and lower weight. Kiekert’s E-latch excellENTRY combines these benefits with a proven mechanical subsystem.
Evolution of Electrically Actuated Door Latches
When the topic of discussion is electrification of the automobile, it refers not only to the powertrain, but also to mechatronic systems and components that generate additional benefits. Modern vehicle networks and electronics are what make it possible to use these systems in the first place by providing them with a reliable power supply and control logic. Electrically actuated side-door latches are attractive to OEMs and car buyers alike because they permit completely new approaches to design, functional configuration and operation. As a mechatronic system, the E-latch enables the best possible combination of the benefits of electronic and mechanical functions.
Electromechanical door latches for side doors have been familiar features since the 1990s. Kiekert presented its first “multifunctional locking system” at the 1995 Frankfurt Motor Show. However, so far, all such products have been conventional latches, electrified retrospectively. The Kiekert E-latch excellENTRY, on the hand, was designed from the outset as a compact mechatronic system. This optimized overall system uses fewer parts and is lighter and more cost-effective from a system standpoint. In contrast to a conventional latch, the excellENTRY has two actuation chains.
In everyday use, the pawl is lifted with the aid of an electric motor. This means the actuation command occurs electrically, be it through a switch, a sensor or triggered by a signal or logic in the vehicle electronics. Like a conventional door latch, the new latch is also equipped with a redundant mechanical subsystem that is only required in the event of an accident and is actuated by purely mechanical means.
Simple Mechanisms, New Design Options
In normal operation, the latch is opened via an electrical impulse delivered, in principle, in any preferred manner. This results in wide-ranging benefits. First, and just like Kiekert’s Active Inertia locking system, the door cannot be opened unintentionally by mechanical forces in the event of a collision. This means that the excellENTRY likewise permits elimination of counterweights in the door. Because the mechanical subsystem has only one redundant function, the components of this actuation path can adopt a more straightforward design. For instance, there would be no need for expensive Bowden cables. Due to their electrical actuation, the external door handles do not require long mechanical travel and therefore do not have to be recessed into the door. As a consequence, the window winder can be positioned a little further outward, adding several centimeters to available space in the interior.
In practice, this might be configured as follows: An almost flush exterior door handle incorporates a sensor element that opens the door in response to touch by releasing the pawl electromechanically. The door can then be pulled open without resistance. There is no spring-back of the door handle and the pawl opens almost silently. Opening, closing and locking can be configured by software. This can even include sound design, whereby an acoustic response could be emitted when a vehicle is unlocked. This provides OEMs with opportunities to develop an operating concept that is not only functional but also attractive to customers.
The possibilities extend even further. Because actuation is via an electrical signal, the signal source could also come from a smartphone. The bottom line is that the E-latch sets no limits on the design of the user interface.
Electronic vs. Mechanical Redundancy
There are individual cases of electrical side-door latches currently in production, although their benefit is currently limited to comfort. The next step is to use an E-latch to achieve safety benefits, too. Functional redundancies will ensure that doors can be opened reliably in the event of a collision – ideally, even more so than with conventional latches.
Purely electronic redundancies are based on the capability to open even in the extreme case of total disconnection from the battery. This calls for a redundant power supply as well as standalone electronics and power supply to ensure function is maintained under all conditions. These electronic components would also have to be 100 percent resistant to external influences such as salt and aging processes. Ultimately, electrical actuation must be able to apply forces that are high enough, even under restraint. This means that the special case of crash redundancy calls for a certain degree of oversizing as regular operation and collision situations use the same actuation chain.
For the Kiekert excellENTRY, the temporary crash redundancy (TCR) is separate and works entirely mechanically. It thus requires no special electronics, no dedicated power storage and offers mechanical actuation redundancy, which can even be optimized for crash situations in terms of the available leverage forces, i.e. it offers more reserves than a conventional latch, despite being mechanically simpler.
Under normal operation of the Kiekert excellENTRY, an integrated electric motor provides travel that acts on the pawl and allows the door to open. It would normally continue to work this way in the event of an accident, as long as there is still power supply from the battery. Nevertheless, TCR is activated as a matter of principle as soon as a crash signal is generated. This causes the actuator to turn in the opposite direction and the subsystem – the mechanical actuation chain – to be activated after five to 10 seconds. If a battery discharge occurs or a pyrotechnic separation of the battery, the car can still be opened mechanically from inside and outside. In most cases, however, the vehicle power supply remains intact in the event of an accident, meaning the door can still be opened electrically. This means the actuator reverses its rotational direction again, relinquishing the redundancy and reactivating normal electromechanical operation.
The functional separation of the electromechanical actuation chain between regular operation and TCR delivers a further benefit: In the case of a conventional latch, exterior and interior door handles must ensure the best possible leverage, while satisfying high demands for comfort. This conflict of interest does not exist with the E-latch. Although the handles, Bowden cables, mounting brackets etc. are more simply configured, they can be optimized for mechanical opening in the event of an accident. For example, the door handle can be designed to provide the best possible lift in exceptional circumstances via an extended travel of 100 mm, which makes it easier to lift the pawl. Electronic redundancy does not offer this option.
A similar principle applies to redundant door operation from inside the car. While a push button or touch sensor provides the electrical means for opening the door, all that is required for mechanical redundancy is a simplified handle of any design – here, too, with an optimized lever configuration. A two-stage function would also be possible for interior operation. One pull on the handle would complete the mechanical actuation chain; the second pull then opens the door. This means the door can be opened from the inside under all circumstances, while purely electronic redundancy would leave occupants shut inside in the event of a power failure.
One fundamental difference from conventional door latches is that the excellENTRY is always mechanically locked except after a collision happens. This means that, in normal operation, there is no mechanical actuation chain from the outside. Opening the door from the outside using the door handle or mechanical manipulation is not possible. Locking and unlocking in everyday use occurs purely electronically and the opening function is electromechanical, triggered by an electronic signal.
“Always locked” also means that the excellENTRY offers the core elements of theft protection without additional cost. Any kind of manipulation of the exterior actuation chain is pointless as the latch can only be unlocked by an electrical impulse. When it comes to a theoretical electronic manipulation while stationary or while driving, there is no difference from current systems. However, if so wished, a further mechanical redundancy would be possible in the form of a small mechanical safety catch that prevents electromechanical unlocking while driving – the so-called ASIL redundancy. This means that even in the theoretical event of an electronic malfunction or manipulation, an unintentional opening of the door is not possible.
In principle, all E-latch functions can be handled with just one servo motor and associated software. Additional child safety locks, for instance, can make sense to prevent the door from being opened by pulling twice on the lever for mechanical redundancy in the event of a theoretical electronic malfunction. More obvious, however, would be to dispense entirely with handles and Bowden cables in the rear doors for mechanical redundancy, and thus remove further complexity from the system. Child locks can be realized through a software function alone. There is no disadvantage compared with a conventional latch with child locks. For children to be released from the rear seats from outside the vehicle in the event of an accident, the door has to be opened from outside anyway. Compared with a mechanical locking device, there is even the distinct benefit that electronic locking and unlocking can be configured freely as required, depending on the situation. This, too, retains the separation of operation and locking function.
The excellENTRY has many benefits for OEMs and consumers alike. It can contribute to reductions in weight, complexity and cost, and help optimize door packaging space, leading to more room in the interior. It also simplifies the development and testing process. It delivers opportunities for flexible, optimized operating concepts and new freedom in the design of exterior and interior operating elements.
Kiekert has also developed purely electronic redundancy, although currently favors a mechanical subsystem, temporary crash redundancy (TCR), in the interests of maximum safety. This solution with a mechanical subsystem obviates risks that could arise from electronics and power supply with purely electrical redundancies. Moreover, operation and available leverage forces can be specifically optimized.
In general, electronic locking and unlocking offers complete freedom when it comes to configuring the actuation concept for normal operation – including remote operation solutions. When paired with the vehicle’s driver assistance systems, entirely new safety concepts are conceivable.
Edited from material supplied by Kiekert