1. Field of the Invention
The present invention relates to a powered vehicle door closing system and specifically to a powered vehicle door closing system suitable for an automotive vehicle such as a van with a sliding door moveable between open and closed positions relative to a vehicle body opening, and more specifically to a system which is capable of forcibly and automatically moving a latch member employed in a lock unit from a half-latched position (a nearly-closed position of the sliding door) to a fully-latched position (a fully-closed position of the sliding door) by powering the final, low-displacement/high-force movement of the sliding door.
2. Description of the Prior Art
Recently, there have been proposed and developed various powered vehicle door closing systems which can automatically move a latch member from a half-latched position to a fully-latched position. One such powered vehicle door closing system has been disclosed in Japanese Patent Provisional Publication (Tokkai Heisei) No. 1-105886. The powered door closing system disclosed in the Japanese Patent Provisional Publication No. 1-105886 is applied to a door lock for an automobile sliding door. The prior art door closing system has three switches, namely a first switch for detection of a half-latched state of the latch member, a second switch for detection of a fully-latched state of the latch member, and a third member for detection of a stand-by position of a moveable drive lever (a portion of a force-transmitting linkage) by way of which the latch member can be shifted from the half-latched position to the fully-latched position. The first switch consists of a pair of electrical contacts, one being a stationary electrical contact provided in the vehicle body and the other being a spring-loaded, plunger-type electrical contact provided onto the door for contact with the stationary contact upon shift to the half-latched position of the latch member via the manual door operation. The first switch is responsive to the movement of the sliding door in such a manner as to rotate the drive lever away from its stand-by position by way of normal rotation (positive rotation) of a drive motor such as a reversible electric motor when the sliding door reaches the half-latched position of the latch member, and as a result the latch member is forcibly moved to its fully-latched position. The second switch is responsive to the movement of the latch member in such a manner as to rotate the drive lever toward the stand-by position by way of reverse-rotation (negative rotation) of the drive motor when the latch member reaches the fully-latched position. The third switch is responsive to the movement of the drive lever in such a manner as to stop the drive motor and consequently to maintain the drive lever at the stand-by position immediately when the drive lever reaches the stand-by position. Each of the second and third switches consists of an ordinary limit switch which is so designed to cut off power automatically at or near the limit of travel of a moving object controlled by electrical means. The conventional system requires an accurate installation of the first, second, and third switches, since respective spring-loaded switching contacts or points of the second and third switches are mechanically operated and additionally the stationary electrical contact (included in the first switch) is provided in the vehicle body, while the other plunger-type electrical contact is provided onto the door for contact with the stationary contact. When installing the three switches on the vehicle, the conventional system requires a complicated wiring harness. This results in an increased assembling time of the respective switches onto the vehicle. Due to a complicated, costly structure of the conventional system, total manufacturing costs of the automotive vehicle with an auto door closing system is increased. Owing to an inherent switching characteristic of the limit switch with the spring-loaded mechanical contact, there is a possibility that a switched-ON operation of the limit switch cannot be completed, particularly during manual quick door closing operation with great momentum. There is a possibility of malfunction of the system.