Bolt drive for motor-vehicle door latch

A drive for a door bolt of a motor-vehicle door latch has a pivot shaft fixed on the bolt offset from the bolt, a motor having a rotary output, a transmission having an input connected to the motor output and an output shaft, and a coupling directly joining the output shaft of the transmission to the pivot shaft for rotation of the bolt by the motor. The transmission output shaft and the pivot shaft are coaxial. The shafts have confronting ends formed with respective sets of axially projecting teeth that axially overlap, engage in each other, and form the coupling. These teeth are of generally triangular cross section and the teeth of the bolt shaft are angularly interleaved with the teeth of the transmission shaft. In addition a star-section element centered on the axes is formed with a plurality of radially open pockets each receiving a respective one of the teeth. This star element is elastomeric.

FIELD OF THE INVENTION 
 The present invention relates to a motor-vehicle door latch. More 
 particularly this invention concerns a bolt drive for such a latch. 
 BACKGROUND OF THE INVENTION 
 A standard motor-vehicle door latch for securing a door edge to a door post
 comprise a latch assembly on the door edge and a bolt on the post. The 
 latch assembly has a pivotal fork that engages around the bolt to retain 
 the door closed, and that can be operated by inside and outside handles 
 and controlled by lock mechanisms. It is standard to provide a central 
 latch system with actuators that control the various functions of the 
 latch. 
 In addition it is known to provide a drive that displaces the door bolt 
 horizontally in the same direction that the latch assembly moves in when 
 the door closes. Thus as described in German patent document 4,210,893 of 
 Szablewski, the bolt itself is centered on a horizontal axis parallel to 
 the normal vehicle travel direction but is mounted at its end in coaxial 
 pivots that define an axis that is parallel to but offset slightly from 
 the bolt axis. A powerful drive such as described in German utility model 
 9,205,765 is connected to the bolt to pivot it about the offset axis 
 through about 180.degree. so as to move the bolt itself through an arc. 
 The purpose of this movement is to pull the door very tightly closed once 
 it has been shut. Thus the door will seat solidly against its seals and 
 sit perfectly flush with the surrounding vehicle body, preventing any 
 annoying air leaks and making the car aerodymanically smooth. The motor is
 employed since closing the door this tightly is not something the vehicle 
 users can be expected to do with ease, so all they have to do is swing the
 door to, whereupon sensors will detect the latched and partially closed 
 position of the door and actuate the drive to pull the door to the fully 
 closed position. 
 The drive for the door bolt is however a complex and expensive piece of 
 equipment. It must be able to apply considerable force to the bolt to 
 perform the desired tight closing operation, and therefore is a rather 
 bulky device. 
 OBJECTS OF THE INVENTION 
 It is therefore an object of the present invention to provide an improved 
 bolt drive for a motor-vehicle door latch. 
 Another object is the provision of such an improved bolt drive for a 
 motor-vehicle door latch which overcomes the above-given disadvantages, 
 that is which is of simple, compact, and reliable construction. 
 SUMMARY OF THE INVENTION 
 A drive for a door bolt of a motor-vehicle door latch has according to the 
 invention a pivot shaft fixed on the bolt offset from the bolt, a motor 
 having a rotary output, a transmission having an input connected to the 
 motor output and an output shaft, and a coupling directly joining the 
 output shaft of the transmission to the pivot shaft for rotation of the 
 bolt by the motor. The transmission output shaft and the pivot shaft are 
 coaxial. 
 In one system according to the invention one of the shafts has a 
 noncylindrical projection and the other of the shafts has a complementary 
 noncylindrical seat receiving the projection and forming therewith the 
 coupling. 
 Alternately in accordance with the invention the shafts have confronting 
 ends formed with respective sets of axially projecting teeth that axially 
 overlap, engage in each other, and form the coupling. These teeth are of 
 generally triangular cross section and the teeth of the bolt shaft are 
 angularly interleaved with the teeth of the transmission shaft. In 
 addition a star-section element centered on the axes is formed with a 
 plurality of radially open pockets each receiving a respective one of the 
 teeth. This star element is elastomeric. 
 The motor output is provided with a worm gear. The transmission input is a 
 bevel gear meshing with the worm gear, and the transmission includes a 
 stepdown gear train between the input and the output shaft. The 
 transmission has a two-part housing enclosing the gear train and the motor
 has a mounting plate to which it is secured and which is secured to the 
 transmission housing. Furthermore the drive further comprises a mounting 
 plate pivotally carrying the bolt, fixed to the transmission housing, and 
 having a hole. The pivot-shaft teeth project along the axis from the hole 
 of the mounting plate and mesh with the teeth of the output shaft. 
 The perfect force transmission from the transmission output shaft to the 
 bolt shaft ensures that the bolt will be rotated accurately. The damping 
 action of the force-transmitting star element gives a quiet action. 
 Furthermore the drive is easy to install since the drive and bolt 
 subassemblies need merely be fitted axially together. The drive is very 
 compact so it can fit easily in a door post

SPECIFIC DESCRIPTION 
 As seen in FIG. 1 a door-bolt drive according to the invention basically 
 comprises a bolt housing 1, a drive motor 2, a transmission 3 having an 
 output shaft 4, and a door bolt 5. The bolt 5 is centered on an axis 5A 
 offset by a distance E from an axis 4A of the transmission output shaft 4.
 More specifically, the motor 2 is fixed to a mounting plate 19 and has an 
 output shaft 28 carrying a pinion gear 20 meshing with a drive gear 29 
 coaxial with a worm gear 12 meshing with a large-diameter gear 13 fixed to
 and coaxial with another smaller gear 14 in turn meshing with another 
 large-diameter gear 15 fixed to and coaxial with another smaller gear 16 
 itself meshing with a drive gear 17 fixed to the shaft 4. This gear train 
 12-17 produces a considerable step down so that the shaft 4 is rotated 
 with substantial torque. The two double gears 13, 14 and 15, 16 are 
 rotatable about respective axes offset from the axis 4A and are contained 
 in a housing having a pair of halves 18a and 18b to which the motor 
 mounting plate 19 is fixed. The output shaft 4 has an end 7 formed as 
 three axially extending teeth 7' projecting through a hole 21 in the 
 housing half 18b. 
 The bolt 5 has centered on the axis 4A a bolt shaft 6 formed with three 
 axially extending teeth 6' that extend through a hole 23 in a mounting 
 plate 22 to which the housing 18a, 18b and the latch plate 1 are both 
 fixed. As shown in FIG. 2 each of the teeth 6' and 7' is of triangular 
 section and they are angularly equispaced about an axis 11 coaxial with 
 the axis 4A. A rubber star element 9 has radially extending arms or vanes 
 10 that form pockets 8 holding the teeth 6' and 7'. Adjacent vanes 10 
 define an angle .alpha. of 60.degree. and snugly receive the teeth 6' and 
 7'. 
 With this system, therefore, the high-speed low-torque motor output at the 
 shaft 28 is reduced to a very low-speed high-torque force transmitted 
 coaxially and directly to the bolt shaft 6. The assembly is very compact 
 and simple and can be counted on to have a long service life. 
 In the arrangement of FIGS. 3 and 4 the coupling parts 8-10 are replaced 
 with a noncylindrical recess 24 formed in a nut 26 on the shaft 5 and a 
 shaft 25 having a complementarily lobed noncylindrical end 27 formed on 
 the shaft 4, although the parts could be reversed. This arrangement also 
 provides for direct coaxial coupling of the transmission output to the 
 bolt shaft.