The present invention relates to an active anti-roll bar
for the rear suspension of a motor vehicle and to its actuation system. The invention
applies in particular to a rear axle of the type with interconnected wheels.
The dynamic behaviour of the vehicle is determined by the
roll stiffness of the suspensions of the two axles and by their ratio. As is known
to persons skilled in the branch, if the stabilizing roll stiffness of the rear
axle is increased by using a more rigid anti-roll bar, the vehicle is rendered more
oversteering and hence with characteristics of dynamic behaviour that resemble more
those of a sports car.
Since the anti-roll bar acts in conditions of asymmetrical
shimmying on bends, it does not affect the stiffness of the suspension when travelling
in a straight line and hence enables an acceptable travelling comfort to be maintained.
The possibility of adjusting in a continuous or discrete
way the stiffness of the rear anti-roll bar in the suspension of a motor vehicle
enables variation of setting of the attitude of the vehicle between a style of driving
that is more or less sporting.
In state-of-the-art solutions, the possibility of modifying
the torsional rigidity of the anti-roll bar is entrusted to linear or rotational
actuators, which counteract the movement of the bar itself induced by rolling of
the car by applying forces at its ends (in the case of linear actuators), or by
countering the rotation of their central part divided into two portions (in the
case of rotational actuators). These devices have a high cost and are heavy in so
far as the actuators, at the moment of adjustment of the stiffness of the bar, must
counteract the thrust of the bar itself.
Other simpler systems envisage, instead, the possibility
to vary the torsional rigidity of the bar, modifying its path (by variation or replacement
of the median stretch), or to change the position of the twisting section, causing
translation of the bar on its constraints.
Whereas for the solutions described above the variation
in stiffness of the anti-roll bar could be obtained even with the vehicle moving,
in these latter simpler solutions the adjustment is made exclusively with the vehicle
The purpose of the present invention is to overcome the
aforesaid drawbacks by providing a system for adjustment of the stiffness of the
torsion bar that will be of low cost and weight and will enable its actuation even
when the vehicle is moving.
The aforesaid purpose is achieved by the present invention,
the subject of which is an active torsion bar for motor vehicles and a system for
its actuation that present the characteristics specified in Claim 1 and Claim 3,
Further characteristics and advantages will emerge clearly
from the ensuing description, with reference to the annexed plate of drawings, which
are provided purely by way of non-limiting example and in which:
- Figure 1 is a top plan view of a rear suspension of a motor vehicle provided
with the bar according to the invention and its actuating system;
- Figure 2 is a more detailed, enlarged view of one side of the suspension of
- Figure 3 is a schematic front view of the bar according to the invention and
of part of its actuation system; and
- Figure 4 is a schematic side view of part of the torsion bar of the invention
and of its adjustment system.
With general reference to the figures, designated by 1
is the rear suspension of a motor vehicle of the type with interconnected wheels,
constituted by two longitudinal arms 3 connected to one another by a transverse
twisting axle 5, obtained using a metal tube open at its ends. Inserted within the
axle 5 is a torsion bar 7, constituted by a metal plate having a rectangular cross
section. The two ends of the torsion bar 7 are fixed to two cylindrical parts, referred
to herein as rotors 9, which are designed to turn within the axle 5 via the interposition
of bearings 11, preferably smooth or of the roller type, between the rotors and
the internal surface of the axle 5. The rotors each present, facing the ends of
the axle 5, an internal gear 13, the internal teeth of which mesh with a reduction
gear 15 supported in rotation by the respective rotor. The reduction gear 15 meshes
with a driving gear 17 fitted on the output shaft 19 of a rotational actuator 21
for each side of the axle 5 and hence for each end of the torsion bar 7, which,
in the application described, is an electric motor.
The electric actuator can be driven by an electronic control
unit, integrated with other control systems of the vehicle, using for example, as
input signal, the attitude angle of the vehicle or else the angular velocity of
the wheels of the two axles.
In the solution proposed by the invention, the variation
of roll stiffness of the suspension is provided by varying the angular position
of the leaf shaped torsion bar 7. The different torsional rigidity that the rectangular
section makes possible according to the angular position with respect to its longitudinal
axis enables a continuous variation of roll stiffness from a minimum to a maximum,
performing a rotation through 90°of the section of the bar itself.
Of course, numerous variant embodiments of the actuator
device are possible, without thereby departing from the sphere of protection of
the annexed claims. Thus, for example, it will be possible to install hydraulic
actuators instead of electric actuators to provide rotational movement of the bar,
of course by means of a suitable device for transmitting motion, thus enabling an
additional mechanical thrust to be exerted to achieve a higher torsional rigidity
of the bar.
In addition, it will be possible to position the bar outside
the twisting axle in the case where the latter is not made using a tube.