Abstract:
The invention relates to a power-assisted vehicle steering gear wherein a rotor is mounted directly on the pitman shaft via a coupling. The rotor rotates in a housing inner bore under the influence of circulating magnetic attraction in such a way that it is enabled to supply a torque to the pitman shaft.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a power-assisted steering gear for a vehicle. A power-assisted steering gear of this type is already known (U.S. Pat. No. 2,021,706). 
     In the case of this known device the pitman shaft includes two coupling disks which are designed to mesh with the pinion of an electromotor when power assistance is needed. However, in spite of this simple design, a special coupling and a special electromotor are still needed to produce the additional power and supply it to the pitman shaft. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The power-assisted steering gear set forth herein requires neither a coupling provided with coupling disks nor an electromotor to supply the electrical power to the pitman shaft. A further advantage is that the power-assisted steering gear has a low rotational speed and a high torque. 
     Other objects, features and advantages of the invention are represented in the drawings and will be described hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings show an embodiment of the invention which will be described in more detail hereinafter. 
     FIG. 1 is a diagram of the power-assisted steering device; 
     FIG. 2 is a cross-section through the pitman shaft with coupling and magnetic device; and 
     FIG. 3 is a side view of the rotor and coupling. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A vehicle comprises a steering wheel 1 which is disposed at an upper end of a pitman shaft 2. At its lower end, the pitman shaft 2 is connected to a steering linkage 3 which is used to control the steering wheels 4. The pitman shaft is provided in its middle portion with an equiaxial coupling part 5 to obtain a rotary connection with a rotor 6. 
     As indicated in FIG. 2, the coupling 5 consists of a coupling designed to allow for radial play of the rotor 6 in every direction. The said play is made possible by recesses 7 and by pins 7&#39; cooperating with the side faces of the recesses 7. 
     The rotor has a cylindrical covering surface 8, by which it is inserted in a bore 9 of a fixed housing 10. The diameter of the inner bore 9 is larger than the outer diameter of the rotor 6 and thus a gap 12 is produced between an inner face 11 of the housing bore 9 and the rotor surface 8. Six magnetic poles 13, designated by the capital letters A-F, are uniformly distributed on the periphery of the fixed housing 10. A different number of poles may be provided, but there must be at least three. 
     A torque sensor 14, which monitors the force effective at the steering wheel 1 and supplies it to an electronic switching device 17, is provided on the pitman shaft 2. The electronic switching device 17 receives current from a power source such as a battery and supplies a current to the magnetic poles, magnetic field lines are shown in section C. Sensors of any well known type determine the particular position of the rotor 6 in the housing 10 and supply the information to the electronic device. To begin rotation of the rotor 6, a pulse generator 18 is started. This generator 18 connects the magnetic poles in succession in the circumferential direction according to the position of the rotor 6. The intensity of the current is determined by the torque exerted on the steering wheel. For example, first the magnetic poles D, E and F are connected and the rotor 6 is influenced by these. Then, magnetic pole D is disconnected and magnetic pole A is connected. Thereafter magnetic pole E is disconnected, and so on in the circumferential direction. Therefore, as the trailing magnetic pole of three successive poles is disconnected from the circuit the leading magnetic pole of three successive poles are connected into the circuit. 
     In this manner the surface 8 of the rotor 6 rides on the inner face 11 of the housing 1 and, as the face 8 of the rotor in the circumferential direction is smaller than the inner face 11 of the housing, the rotor 6 functions as an armature and turns about its axis to the left or the right oppositely to the direction of the pulse feed path. The smaller the rotor in relation to the inner surface of the housing, the more rapid the rotation is produced. This rotation is supplied to the pitman shaft 1 via the coupling 5 as power-assisted torque. 
     An advantage of this power-assistance to the pitman shaft 1 according to the invention is that a brushless motor can be used as the steering assist. 
     The device has a low rotational speed and therefore does not require a reduction gear. Furthermore, the low mass moment of inertia of the device allows for rapid starting and stopping. The torque is high and therefore the power assistance especially effective. 
     A further advantage of the device is that the steering without the power assist feature only exhibits slight additional friction since only the rotor 6 must be co-rotated and that only a slight additional mass moment of inertia is produced. 
     The foregoing relates to preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.