The Mechanism of The Car Door Locking Devices and Its Impacts on The Door Dynamics

1. Introduction

While the car door locking device was optional in the standards prior to EN 81-20 based on the hoistway conditions, with the EN 81-20, it has been the standard equipment for the car doors. This equipment, which meets the requirements of the standard, have a mechanical structure and designed as a subsystem operating within the door mechanism. Although their designs differ based on the manufacturer, almost similar mechanical elements are used on the locking device which may function as required by the standard. Foremost among them comes the compression springs which directly affects the dynamics of the system. Because it has been experimented that the simplest and most common method for making a mechanical structure behave differently under different conditions described by the standard was to use springs in this structure.

2. The requirements for car door locking devices according to EN81-20 Standard

The articles 5.3.9.2 and 5.3.15 of the standard defines how the locking device shall operate. Based on this definition, what is expected form the mechanical system that shall be designed can be summarized as follows:

• The locking device should understand that it is in the locking zone or not.
• It should be locked or unlocked depending on being in the locking zone or not. 

All possible scenarios that could be met in any normal operation should be carefully analyzed in order to conclude if a mechanical locking device meets all the requirements listed above or not.

 3. Operation Mode of the Car Door Locking Device

In general, mechanical locking devices operate directly linked with the door drive system. Many car door locks are designed as an extension of a door element called skate. Skate, which is a mechanism operates in itself, reaches a more complex mechanical structure with the addition of a locking device on it. The function of this structure which operates as a subsystem with the whole door mechanism can be listed as below: :

• To unlock the landing door
• To clutching the locking door and  to provide it to run automatically together with the car door
• To understand if it is in the in the unlocking zone or not,
• To keep the car door locked outside the unlocking door
• If necessary, to allow opening the door manually from the cabin when it is in the unlocking zone.

This subsystem which is called as “skate equipped with locking device” is driven through a trigger directly by the door motor in order to perform the first two items in the list above. The other three functions are performed with the potential energy of the structure as a result of the mechanical features of the structure, without having a need to an external drive system. In many applications, the source of this potential energy with the mechanical structure comes from the compression springs.

4. The Impacts of Locking Devices on Door Dynamics

In order to analyse the impacts of locking devices on door dynamics, a comparison has been made with a car door without a locking device. As seen in Figure 1 (a) and (b), two separate test setups were formed by using “a skate without locking mechanism” and “a skate with a locking device”.

In the test setups, all components that may have an impact on the motor, drive and door dynamics were the same, except the skate. During the test, both setups are run with the same drive parameters and the current that feeds the motor through the drive during the door activations was measured. The measurement results were filtered to include only the skate movement after completing its movement in the direction of the door closing, and the graphics in Figure 2 were obtained.

As seen in the graphic, motor current has increased up to 3.5A for the movement of the skate with a locking device. For the other device, the same value has been measured 1A maximum. It may be concluded that the difference between these two values has been used for the springs that runs the locking device. In other words, electrical energy created by this difference of 2.5A has been transferred to the springs used in the locking device in the form of potential energy. In order to show the difference more tangibly with, the amount of force that should be transferred to the trigger for setting up a locking device has been calculated simply as below: 

5. Conclusion

Based on the measurement results, the difference of 2.5 may be considered as a force of approximately 106N on the motor sheave. According to this data, it may be easily concluded that the measured force is used for providing potential energy to the mechanical elements used in the locking device. However, the measured and calculated numeric values should not be considered as a table that reflects the general condition. These figures may differ depending on many variables such as the mechanical structure of the skate and the locking devices in the setup, the hardness of the springs, the diameter of the motor sheave and driving parameters. The only final judgement could be that the variables of the system should be analyzed in terms of the potential energy need it will create, if a locking device equipped with a skate will be integrated to a car door which was designed without a locking device.