Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
2000-05-01
2001-06-26
Johnson, Brian L. (Department: 3618)
Motor vehicles
Steering gear
With electric power assist
C180S444000, C180S446000
Reexamination Certificate
active
06250420
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an electrically assisted power steering system for motor vehicles. The power steering system includes an input shaft, which is operatively connected to a steering and serves to transmit a torque required to steer vehicle wheels that are to be steered. An output member is operatively connected to the wheels to be steered. A servomotor, by which an auxiliary force can be exerted on the input shaft or the output member, is disposed in the power steering system. The input shaft and the output member are connected to one another via a rotationally elastic member in such a way that a limited torsional motion is possible between the input shaft and the output member. For contact-free detection of the direction and intensity of a steering torque acting on the input shaft, a contactless detection unit is used. The detection unit includes one pulse transducer and one sensor each connected to the input shaft and to the output member. The pulse transducers are embodied as magnetic rings, which are provided with magnetic north and south poles in alternating order on their circumferential surfaces.
BACKGROUND OF THE INVENTION
One such power steering system is known from German DE-C2 38 44 578, for instance. In this power steering system, two drums of nonmagnetic material are connected to an input shaft and to an output member, respectively. The drums are provided on their circumference with magnetizable media, in such a way to form magnetic north and south poles in alternation. By measuring the difference in the rotary angles of the two drums, the torque is detected, using magnetoresistive elements.
Detecting the torque makes it possible to regulate the servo assistance of an electric steering system. Regulating the servo assistance in an electric steering system purely as a function of torque feels unaccustomed during driving, because different friction conditions prevail then, compared to a hydraulically assisted power steering system. The “feedback” of the steering speed to the steering moment is missing. To overcome this disadvantage, it is necessary to detect the steering speed. For detecting the steering speed, in known electrical steering systems, for instance in German Patent DE-C2 37 11 854, one additional sensor is provided. The sensor has a direct current tachometer generator, for instance, which generates a direct current with a voltage adapted to the steering speed. This kind of steering speed sensor involves relatively major effort and expense for detecting the steering speed.
BRIEF SUMMARY OF THE INVENTION
The object of the invention is to improve the regulation of an electrically assisted power steering system of this generic type. In particular, it should be possible to detect the steering speed in addition, using simple means.
This object is attained by the power steering system of the present invention. This is accomplished in particular in that, in a power steering system of this generic type, the two magnetic rings are equipped with the same numbers of pole pairs, and that each magnetic ring is assigned one sensor, structurally connected to the housing, by which not only the relative position of the magnetic rings and hence the relative position of the input shaft and of the output member to one another, but also the rotary speed of the input shaft, are detected. By means of this embodiment, it is possible, with two magnetic rings and two sensors assigned to the magnetic rings, to detect both the torque and the rotary speed of the input shaft and thus the steering speed. By detecting the steering speed, the damping of the steering when turning and then straightening out again can be controlled. If an electric motor is used as the servomotor, then the steering speed can also be used as an additional controlled variable for regulating the engine rpm and can then lead to higher-quality regulation.
Expedient and advantageous features of the invention are defined by the dependent claims. For instance, a second magnetic ring, with an associated second sensor, can be disposed on the input shaft for detecting the steering angle. Once the steering angle is detected, the return to steering straight ahead can be actively varied. Furthermore, this makes center damping, to suppress overswings or overshooting, possible as the wheel returns to the center. Straightline stability of the vehicle is also improved.
Further advantages are precise centering on the straight-ahead driving position of the steering and the possibility of designing a characteristic curve as a function of the steering angle. This means that in the position for driving straight ahead, the characteristic curve is different from that in the parking range. In addition, the steering angle signal can be utilized for other vehicle control devices, such as an active chassis or a roll stabilizer.
The two magnetic rings that are disposed on the input shaft expediently have different numbers of pole pairs. With the two magnetic rings and the two associated sensors, an unambiguous determination of steering angle is possible at most in the range of only 180°. If the absolute angle position of the input shaft is to be determined, then the two sensors are assigned an electronic unit, by which, once the straight-ahead position has been determined once and for all, the steering angle traversed at a given time can be detected and stored in memory. To prevent the absolute steering angle from being lost if malfunctions occur, such as a electrical power failure, a third magnetic ring with an associated third sensor can disposed on the input shaft for detecting the absolute steering angle. The third magnetic ring is expediently connected to the input shaft via a speed-reduction gear, which by way of example is embodied in the manner of a “harmonic drive” gear.
REFERENCES:
patent: 4173265 (1979-11-01), Kremer
patent: 4796463 (1989-01-01), Tsals et al.
patent: 4805463 (1989-02-01), Kelledes et al.
patent: 4874053 (1989-10-01), Kimura et al.
patent: 4886137 (1989-12-01), Pawlak et al.
patent: 5226498 (1993-07-01), Gutkowski et al.
patent: 5442956 (1995-08-01), Persson
patent: 5717330 (1998-02-01), Moreau et al.
patent: 6175231 (2001-01-01), Budaker et al.
patent: 37 11 854 (1989-12-01), None
patent: 198 28 513-A1 (1999-12-01), None
patent: 2000055753 (2000-02-01), None
Brenner Peter
Budaker Martin
Loreit Uwe
Nagel Willi
Johnson Brian L.
Larson & Taylor PLC
Yeagley Daniel
ZF Friedrichshafen AG
LandOfFree
Electrically assisted automotive power steering system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrically assisted automotive power steering system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrically assisted automotive power steering system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2513805