Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
1998-03-20
2001-02-13
Hurley, Kevin (Department: 3619)
Motor vehicles
Steering gear
With electric power assist
C180S422000
Reexamination Certificate
active
06186267
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method and an apparatus for operating a steering system for a motor vehicle.
Such a prior art steering system is disclosed in DE-OS 40 31 316 (corresponding to U.S. Pat. No. 5,205,371) and, to the extent that it is relevant to this invention, will be described with reference to
FIGS. 1 and 2
. In such a steering system, the motions of the actuator
13
or
23
, the motor angle &dgr;
M
, are superimposed in the auxiliary drive
12
or
22
on the steering motions imparted by the driver through the steering wheel
11
or
21
, the steering wheel angle &dgr;
L
detected by the sensor
28
. The superimposed motion &dgr;
L
′ thus obtained is transmitted through the steering mechanism
14
and the steering linkage
16
to the steerable wheels
15
a
and
15
b
to set the steering angle &dgr;
V
. The actuator
13
or
23
can be an electric motor. The operating principle of such a servo steering system consists of providing that the steering can be accomplished very indirectly through the transmission i
a
of the auxiliary drive
12
or
22
, and thus low steering wheel moments M
L
can be achieved. Because of this, very large steering wheel angles &dgr;
L
are avoided, inasmuch as suitable motor angles &dgr;
M
are superimposed, so that required output angles &dgr;
L
′ can be set with steering wheel angles of ordinary size according to the equation
&dgr;
L
′=&dgr;
L
/i
a
+&dgr;
M
.
The required motor angle &dgr;
M
required to assist steering, or its desired value, is determined from the steering wheel angle &dgr;
L
. In addition, the motor angle &dgr;
M
can also depend on signals Sm, with these signals Sm representing the vehicle motions detected by the sensors
26
.
In a steering system there are usually one or two universal joints to connect the shafts of the steering mechanism and of the steering wheel with angular and longitudinal displacement. If there is only one universal joint (FIG.
3
), it is well known that with a constant input speed &ohgr;
1
a pulsating output speed &ohgr;
2
is obtained according to the following equation:
ω
2
=
ω
1
⋆
cos
β
1
-
sin
2
β
⋆
cos
2
α
In this equation, &bgr; is the angular offset of the joint and &agr; is the angle of rotation of the input shaft.
It is likewise known that with two universal joints, the nonuniformity of rotation &ohgr;
2
/&ohgr;
1
is smoothed out by a known W- or Z-shaped arrangement, if the two angular offsets &bgr;
1
and &bgr;
2
are of equal magnitude. Other arrangements (
FIG. 4
) lead to nonuniform transmission of rotation, in the same way as a single universal joint.
However, transmission of the rotational steering motion has to be as uniform as possible for good steering precision; this requirement therefore limits the structural possibilities. Because of space limitations and other requirements for the arrangement of units in the engine compartment, under some circumstances no steering shaft design is possible that permits uniform transmission of motion.
The purpose of this invention is to compensate for structurally unavoidable nonuniformity of rotational steering motion.
SUMMARY OF THE INVENTION
This invention relates to a steering system for a motor vehicle with a steering drive train that comprises at least one steerable wheel, one actuator, one auxiliary drive, a steering wheel operable by the driver of the vehicle, as well as a mechanically configured offset device. The offset device has rotating input and output shafts and a predetermined angular orientation between the input and output shafts. The auxiliary drive superimposes the steering motion initiated by the steering wheel and the motion initiated by the actuator to generate the steering motion of the steerable wheel. In accordance with the invention, a control signal is computed dependent on the angular orientation and the rotational motion of the input shaft. The actuator is then controlled dependent at least on the generated control signal, to initiate the motion.
Any structurally unavoidable nonuniformity of rotational motion is compensated for by superimposing an appropriate added angle pursuant to the invention. The invention provides structural simplification and structural space benefits in the engine compartment, since it is possible to more freely choose the arrangement of the joints of the steering shaft. There are also cost benefits since, under some circumstances, a universal joint can be omitted. In the same way, uniform transmission of steering motion is possible from the invention with an unaligned W or Z arrangement (
FIG. 4
) with several, particularly two, offset devices. The invention also provides the possibility of more exact measurements of the actual steering wheel angle, since the steering angle sensor can be placed ahead of the offset device (between the steering wheel and the auxiliary drive), because according to the invention the input and output drive angles of the offset device are the same.
The offset devices can be in the form of cardan or universal joints.
It is also provided in particular that the computation of the control signal depends on whether the offset devices in the steering drive train are located ahead of or beyond the auxiliary drive.
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patent: 4421191 (1983-12-01), Bertin et al.
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patent: 5732379 (1998-03-01), Eckert et al.
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Hackl Matthias
Kraemer Wolfgang
Baker & Daniels
Fischer Andrew J.
Hurley Kevin
Robert & Bosch GmbH
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