DE19944133A1 - Vehicle electrical power steering system has motor shaft working in conjunction with worm drive, carrying worm, and forming flexural beam tensioned so worm drive operates with no play - Google Patents

Abstract

The power steering system has drive shaft (6) of an electrical drive motor (2) that works in conjunction with a worm drive, which carries the worm (5), which is in the form of a flexural beam and which is tensioned so that the worm drive operates without any play.

Description

The invention relates to an electrical auxiliary power kung for motor vehicles according to the in the preamble of An Proposition 1 defined art.

Electric power steering systems for motor vehicles, as they are known from the prior art, have a Input shaft on, with a steering handwheel in operative connection and stands for the transfer of one for the steering of torque required to steer wheels. On The output link is in active connection with the wheels to be steered binding. An electric motor, through which directly or indirectly an assistant can be exercised on the output member, is located on the power steering. The input shaft and the output member are via a torsionally elastic member connected in such a way that between the input wel le and the output member a limited twisting movement is possible. For power steering with rack and pinion gear be the output member is designed as a drive pinion and stands over a rack with not shown, steerable ren wheels of a motor vehicle in operative connection. The Rack is above, preferably as a worm gear gears trained reduction gear with an as Electric motor designed servo motor in operative connection. The The output link is via the worm gear with a Electric motor connected. The main components of the electromo tors are a rotor and a stator. The stator is housing firmly, the rotor is connected to a drive shaft Worm gear of the worm gear connected. With help Power steering with ball nut transmission replaces a win despindel the drive pinion.  

When using a worm gear as power transmission supporting mechanism of an electric power steering system, in order to be able to guarantee error-free operation, a sufficient play between the worm shaft and the Worm wheel can be set. If this game is too ge ring is set, so there is tension in the Schnec gearbox, resulting in poor responsiveness expresses. Will the game between worm shaft and Schnec If the gear is too large, the direction of rotation will occur change on the steering handwheel to change the contact surface the tooth flanks. This change of the investment area is from Driver perceived as knocking noise and disturbing find. As gear play increases, so does Ge rush to. Through a suitable selection of the material combination nation between worm shaft and worm wheel can This noise is dampened but not eliminated. By elastic support of one of the components the noises are also dampened.

If the gear backlash is set very low to the Eliminating knocking noises must be very high operating and assembly work.

DE 198 22 478 A1 describes an electric servo Steering device proposed in the case of elastic elements are arranged in a worm gear so that when Contact of the tooth surfaces of the gear parts this elasti elements are deformed so that the collision between between the tooth surfaces can be weakened to to reduce the impact of the tooth surfaces ren.

The disadvantage of the prior art is how he is disclosed in DE 198 22 478 A1, the fact  that additional elements in the worm gear inte need to be grated, which increases assembly and knockout most effort means. The drawback is still disadvantageous The permanent durability of the elastic elements, so that the impact noise after embrittlement and aging of the ela elements can reappear.

The present invention is based on the object represents an electric power steering system for motor vehicles to deliver, in which by play in the worm gear resulting noise can be eliminated without additional Liche components must be used.

The object underlying the invention is achieved by one, also the characteristic features of the main claim having generic electric power steering solved for motor vehicles.

With a slight radial preload between The worm shaft and worm wheel become the game in snail gearbox eliminated.

When designing the radial preload, preload way and preload must be coordinated so that the resulting frictional forces do not jam of the worm gear.

By adjusting the spring length and diameter of the bie beamed worm shaft can reduce rigidity and thus the functionality of the worm gear can be varied.

The worm shaft can also be made in two parts, where a part takes over the function of the bending beam and the other part is used to limit the spring travel. By appropriate dimensioning and material selection from in  internal and external worm shaft part can the characteristic can be determined which the resilient Represents worm shaft under load.

Either the Worm shaft or drive pinion in one, one Adjustable bearing with degree of freedom men.

The worm shaft designed as a bending beam is additional able to act as a torsion spring, and forces if the electric motor suddenly stops, to For example, if you steer to a mechanical stop, weaken, and so the occurring shock load to re reduce.

The radial preload of those designed as bending beams Worm shaft can be done in that in a housing a groove is provided in which the worm shaft is turned on hangs and is thereby biased. With an additional The preload can be increased even further under spring loads. In an extended function variant, the radial one takes place Biasing by a spring-loaded thrust piece that over a set screw is secured in the housing.

Below are various based on the drawings Embodiments of the present invention in principle as described.

Show it:

Fig. 1 shows a first embodiment of an electrically assisted power steering system for motor vehicles with a worm shaft biased by a housing and

Fig. 2 shows a second embodiment of an elec trically assisted power steering system for motor vehicles with a screw biased by a spring-loaded thrust shaft.

Fig. 1 shows an inventive, electrically assisted power steering for motor vehicles, which has a Ge housing 1 , in which an electric drive motor 2 is mounted in bearings 3 and 4 . The housing 1 can be made in one or more parts. In the case of a multi-part design, the individual housing parts are connected to one another via tie rods. A screw 5 is rotatably connected to a drive shaft 6 of the electric drive motor 2 . The drive shaft 6 drives a worm wheel 7 which, in a manner not shown here, is operatively connected to a drive pinion of an auxiliary power steering.

The drive shaft 6 of the electric drive motor 2 is made in two parts. An outer shaft part 8 serves to limit the spring travel and an inner shaft part 9 serves to determine the rigidity of the system. The inner re shaft part 9 is rotatably connected to the screw 5 . The drive shaft 6 acts as a bending and torsion spring, since it can absorb toothing forces and torques that occur.

To set a radial bias, the drive shaft 6 is mounted in the housing 1 so that it only has one degree of freedom. In the embodiment shown in FIG. 1, a groove 10 is provided in the housing 1 for this purpose. However, a spherical bearing could also be used.

Fig. 2 shows another embodiment of a power steering for motor vehicles according to the invention. Here, the radial prestressing of the drive shaft 6 is accomplished in that the worm 5 , which is connected to the inner shaft 9 in a rotationally fixed manner, is connected by a pressure piece 12 loaded with a spring 11 via an intermediate piece 13 . About the dimensioning and material selection of the spring 11 , the bias can be varied.

Reference numerals

1

casing

2nd

electric drive motor

3rd

camp

4th

camp

5

slug

6

drive shaft

7

Worm wheel

8th

outer shaft part

9

inner shaft part

10th

Groove

11

feather

12th

Pressure piece

13

Spacer

Claims (3)

1. Electric power steering system for motor vehicles with an input shaft, which is in operative connection with a steering handwheel and which is used to transmit a torque required for the steering of steering wheels to be steered, an output member which is in operative connection with the wheels to be steered, an electric one Antriebsmo tor ( 2 ) through which an auxiliary force can be exerted on the output member, a torsionally elastic member that binds the input shaft and the output member together such that a limited rotational movement between the input shaft and the output member is possible, and one as a worm gear trained reduction gear, which is in operative connection with the electric drive motor ( 2 ) and the output member, characterized in that a drive shaft ( 6 ) of the electric drive motor ( 2 ) which is in operative connection with the worm gear and carries a worm ( 5 ), trained as a bending beam et is and is biased so that the worm gear works without play. 2. Electric power steering system for motor vehicles according to claim 1, characterized in that the worm ( 5 ) carrying drive shaft ( 6 ) is at least in two parts, with an inner shaft part ( 9 ) the rigidity and part via an outer shaft ( 8 ) the travel can be adjusted. 3. Electric power steering system for motor vehicles according to claim 1, characterized in that the drive shaft ( 6 ) is biased by a pressure piece ( 12 ) loaded with at least one spring ( 11 ).