DE102015222761B4 - Counter-steering motor vehicle rear axle - Google Patents

Abstract

Counter-steering motor vehicle rear axle (1), in which a rotary movement of the wheel carrier (10) about a virtual axis (A) in the direction of a Toe-in (δ1) is set, with the virtual axis (A) being inclined in the direction of travel (FR) when projected onto a vehicle longitudinal center plane (FM) and running at an angle (a) to a wheel contact plane (E) and a puncture point (20) with the wheel contact plane (E) which, viewed in the direction of travel (FR), lies behind a wheel contact point (19), characterized in that the virtual axis (A) runs below a wheel center point (M) and the angle (a) is in a range from about 15° to about 60°.

Description

The invention relates to a countersteering motor vehicle rear axle with the features of the preamble of patent claim 1.

Motor vehicle axles are used to implement a wheel guide that is suitable for the motor vehicle. The design of the wheel guide is particularly important for the cornering behavior of the motor vehicle. The motor vehicle axles can be designed as simple, rigid or semi-rigid axles. However, a more complex design in the form of independent wheel suspensions is also possible, with which better driving characteristics can generally be achieved. Here, the design of the motor vehicle rear axle as a multi-link axle, for example as a four-link axle, should be mentioned.

In order to prevent the motor vehicle from swerving at the rear when cornering as far as possible, the wheel guides of the rear wheels are designed in such a way that self-steering behavior occurs in curves, which results in understeering of the motor vehicle and thus overall counteracts a tendency of the motor vehicle to oversteer.

Specifically, to remedy the disadvantage mentioned, it is known to construct rear axles in such a way that a wheel on the outside of the curve is moved into toe-in under the influence of a curve-related lateral force.

This results in understeering of the rear axle when cornering, which contributes to more stable dynamic handling.

From the DE 101 26 192 A1 a rigid rear axle is known in which a rotary movement of the wheel carrier, and thus of the wheel, about a virtual axis in the direction of a toe-in occurs under the action of a lateral force on a wheel attached to the wheel carrier and on the outside of the curve. In concrete terms, the wheel carriers are each connected to the rigid axle via a weakened material offset to the rear in the opposite direction of travel. This results in an approximately vertically arranged, virtual pivot axis about which the respective wheel carrier can be pivoted under the influence of lateral force.

the EP 1 986 873 B1 describes an active vehicle stabilization system for a front and a rear axle. In concrete terms, this system controls stabilizers, which means that the toe and camber angles of the wheels can be changed in a suitable manner.

In the DE 38 26 930 A1 a wheel suspension system for a front axle is disclosed, with which the driving stability is generally improved and in particular a favorable anti-pitch geometry is to be provided.

From the JP 2009 023620 A a rear axle with a steering actuator is known, the virtual axis of which is inclined in the direction of travel to a wheel contact plane and also runs below the wheel center.

Also in the scriptures DE 10 2007 063 545 A1 , U.S. 7,258,355 B2 and EP 0 556 464 A1 Disclosed wheel suspension for the rear wheels of a motor vehicle, in which to stabilize the driving behavior, a virtual axis is inclined in the direction of travel and forms a puncture point with a wheel contact plane, which is at a distance behind a wheel contact point.

Finally, in the DE 10 2008 031 123 A1 a countersteering vehicle rear axle with the features of the preamble of patent claim 1 is described. Specifically, the wheel carriers are each connected to an axle body via a helmet-like support part and reinforcement plates. Several flexible areas and recesses are arranged in the supporting part in such a way that the wheel carrier is pivoted about a virtual axis under the influence of a lateral force when cornering and toe-in.

The virtual axis is inclined on the one hand in the direction of travel and on the other hand in the direction of a longitudinal center plane of the vehicle.

The present invention is based on the object of providing an alternative motor vehicle rear axle with which good driving dynamics properties can be achieved, in particular when cornering.

This object is achieved with the features of patent claim 1. Advantageous embodiments or developments of the invention can be found in the dependent claims.

The invention is based on a counter-steering motor vehicle rear axle in which a rotary movement of the wheel carrier about a virtual axis in the direction of a toe-in occurs under the action of a lateral force on a wheel attached to a wheel carrier and on the outside of the curve. The virtual axis is inclined at an angle in the direction of travel when it is projected onto a longitudinal center plane of the vehicle.

It is proposed that the virtual axis runs below a wheel center point and has a point of intersection with a wheel contact plane which, viewed in the direction of travel, lies behind a wheel contact point.

• • Hohe Eigenfrequenz
• • Hohe Gierdämpfung

It has been shown in simulations and tests by the applicant that good driving behavior of the motor vehicle can be achieved by such a position of the axle. Good driving behavior of a motor vehicle is characterized by the following driving dynamics properties:

• • High natural frequency
• • High yaw damping

A high natural frequency is understood as meaning the ability of the motor vehicle to quickly implement a change in direction desired by a steering movement. In other words, an unstable transitional state (transient cornering behavior) should be run through quickly and replaced by stable cornering (steady-state cornering behavior).

A high yaw damping causes the motor vehicle to oscillate little or not at all during the transient cornering behavior.

In designing the rear axle according to the invention, the applicant started from a precise analysis of the forces occurring on a wheel on the outside of the curve when cornering. For better understanding, the forces that occur are outlined in the last of the attached figures.

$$\text{Mx}=\text{R}\times \text{FyL}$$

und $$\text{Mz}=-\text{nl}\times \text{FyL}$$

mit

FyR =

Radmitten-Seitenkraft

Mx =

Moment um die X-Achse

Mz =

Moment um die Z-Achse

R =

Radradius als Hebelarm

nl =

Reifennachlauf als Hebelarm

FyL =

Latsch-Seitenkraft

According to this, a lateral force acting on the contact patch of the wheel (contact surface lateral force) generates two torques around the wheel center point in addition to a wheel center lateral force occurring at the center point of the wheel, resulting in the following three force components: $$\text{FyR}$$

$$\text{Mx}=\text{R}\times \text{FyL}$$

and $$\text{Mz}=-\text{nl}\times \text{FyL}$$

With

FyR =

wheel center lateral force

M x =

moment about the x-axis

Mz =

moment about the z-axis

R =

Wheel radius as lever arm

nl =

Tire trail as a lever arm

FyL =

Laces lateral force

A contact patch is understood to be a tire contact area that results under normal load conditions, which also entails a corresponding tire trail.

mit

• δ = sich einstellender Spurwinkel
• $\frac{\partial \delta }{\partial FyR}$
  
  = die Änderung des Spurwinkels, bedingt durch die Radmitten-Seitenkraft FyR
• $\frac{\partial \delta }{\partial Mx}$
  
  = die Änderung des Spurwinkels, bedingt durch das Moment Mx
• $\frac{\partial \delta }{\partial Mz}$
  
  = die Änderung des Spurwinkels, bedingt durch das Moment Mz

All three force components mentioned have an influence on or change the toe angle of the wheel on the outside of the curve when cornering, where the following applies: $$\mathrm{\delta =}\frac{\partial \delta }{\partial fyR}\ast \text{FyR}+\frac{\partial \delta }{\partial Mx}\ast \text{Mx}+\frac{\partial \delta }{\partial M\mathrm{e.g}}\ast \text{Mz}$$

With

• δ = resulting toe angle
• $\frac{\partial \delta }{\partial fyR}$
  
  = the change in toe angle caused by the wheel center lateral force FyR
• $\frac{\partial \delta }{\partial Mx}$
  
  = the change in toe angle due to the moment Mx
• $\frac{\partial \delta }{\partial M\mathrm{e.g}}$
  
  = the change in toe angle due to the moment Mz

An additional inertial force FyT acts on the wheel, which depends on the lateral acceleration of the center of the wheel and the mass of the wheel. For example, during stationary cornering, it counteracts the lateral force in the contact area, so that the lateral force in the center of the wheel is smaller than the lateral force in the contact area. This is neglected here, which means that $$\text{FyR}=\text{FyL}$$

und somit $$\frac{\partial \delta }{\partial FyL}=\frac{\partial \delta }{\partial FyR}+\frac{\partial \delta }{\partial Mx}\ast \text{R}-\frac{\partial \delta }{\partial Mz}\ast \text{nl}$$

Substituting (5), (2) and (3) in (4) and dividing by FyL results in the gradient ∂δ/∂FyL, i.e. for the change in the toe angle δ caused by the lateral contact force FyL: $$\frac{\partial \delta }{\partial fyL}=\frac{\partial \delta }{\partial fyR}\ast \frac{fyL}{fyL}+\frac{\partial \delta }{\partial Mx}\ast \text{R}\ast \frac{fyL}{fyL}-\frac{\partial \delta }{\partial M\mathrm{e.g}}\ast \text{nl}\ast \frac{fyL}{fyL}$$

and thus $$\frac{\partial \delta }{\partial fyL}=\frac{\partial \delta }{\partial fyR}+\frac{\partial \delta }{\partial Mx}\ast \text{R}-\frac{\partial \delta }{\partial M\mathrm{e.g}}\ast \text{nl}$$

• 
  = „-Latsch-Seitenkraftlenken“
• 
  = „-Radmitten-Seitenkraftlenken“
• 
  = „-Mx-Lenken“
• 
  = „-Mz-Lenken“

In the following, the gradients shall be denoted as follows:

• 
  = "-Latsch-lateral force steering"
• 
  = "-wheel center lateral force steering"
• 
  = "-Mx-steer"
• 
  = "-Mz-steer"

As already mentioned at the beginning, an overall understeering lateral force steering is aimed at. The applicant has found in tests and simulations that the wheel center lateral force steering surprisingly also has an influence on the driving behavior of the motor vehicle, namely on its yaw damping.

Specifically, the yaw damping of the motor vehicle could be increased by oversteering the center of the wheel lateral force steering. Oversteering wheel center lateral force steering is characterized by a negative sign of the corresponding gradient (see above).

In order to nevertheless achieve a desired, understeering tire-slip lateral force steering, which must have a positive sign overall, the Mx steering must be increased accordingly when designing the rear axle. Due to the larger lever arm (wheel radius R), Mx steering has a greater influence on side-slip lateral force steering than track Mz steering.

In a further analysis, it was determined that the camber stiffness must be as high as possible in order to contribute to high yaw damping. The camber stiffness is characterized by the change in the camber angle y when the lateral force FyL is applied and can be derived analogously to (7) and put into the following formula: $$\frac{\partial g}{\partial fyL}=\frac{\partial g}{\partial fyR}+\frac{\partial g}{\partial Mx}\ast \text{R}-\frac{\partial g}{\partial M\mathrm{e.g}}\ast \text{nl}$$

It has been shown that the desired, partially contradictory properties of the rear axle could be achieved by the position of the virtual axle specified according to the invention.

• • möglichst viel untersteuerndes Latsch-Seitenkraftlenken
• • möglichst viel übersteuerndes Radmitten-Seitenkraftlenken und
• • möglichst hohe Sturzsteifigkeit

nur durch eine umfangreiche, simulationsbasierte Auslegung jeweils einer fahrzeugspezifischen Hinterachse zu erreichen, welche achskennfeldbasierte Fahrdynamiksimulationen, Achssimulationen und eine Bewertung der erreichten Verbesserungen mittels Fahrzeugsimulationen umfasst.Here are the desired properties

• • as much understeering lateral force steering as possible
• • as much oversteering wheel center lateral force steering and
• • Highest possible camber rigidity

can only be achieved through an extensive, simulation-based design of a vehicle-specific rear axle, which includes axle map-based driving dynamics simulations, axle simulations and an evaluation of the improvements achieved using vehicle simulations.

In accordance with the inventive concept, the virtual axis is inclined at an angle ranging from about 15° to about 60° (measured from a horizontal plane). An inclination in such an angle range could contribute to the good driving characteristics of the rear axle.

In particular, it was found that very good values could be achieved with an inclination of the virtual axis at an angle of about 45 degrees.

Finally, simulations showed that it is extremely advantageous for achieving the desired driving dynamics properties if the virtual axis, seen in a front view of the wheel from the outside in the direction of the longitudinal center plane of the vehicle, is roughly a connecting line between an outer connection point of a camber arm and forms an outer connection point of a spring link.

The outer connection point of a link is to be understood as a connection point which, seen in the transverse direction of the vehicle, is further away from the longitudinal center plane of the vehicle than an inner connection point. An outer connection point usually connects the link to a wheel carrier, while an inner connection point usually connects the link to the body or to a subframe connected to the body.

The invention also claims protection for a motor vehicle which is equipped with a rear axle according to the invention.

A preferred embodiment of the invention is shown in the figures and is explained in more detail in the following description. In this case, the same reference symbols refer to identical, comparable or functionally identical components, with corresponding or comparable properties and advantages being achieved even if a repeated description is omitted.

• 1 die Darstellung einer erfindungsgemäßen Hinterachse in Perspektive,
• 2 eine seitliche Darstellung der Hinterachse gemäß Ansicht II aus 1,
• 3 eine Darstellung der Hinterachse von hinten in Fahrtrichtung gemäß Ansicht III aus 1,
• 4 eine Darstellung der Hinterachse von oben gemäß Ansicht IV aus 3,
• 5 eine Darstellung des Spurverhaltens der Hinterachse bei einer angreifenden Latsch-Seitenkraft, vergleichbar mit der Ansicht aus 4, wobei die Hinterachse als Blackbox dargestellt ist,
• 6 eine Darstellung des Spurverhaltens der Hinterachse bei einer angreifenden Radmitten-Seitenkraft, vergleichbar mit der Darstellung gemäß 5,
• 7 eine Darstellung eines Kraftfahrzeugs mit einer erfindungsgemäßen Hinterachse und
• 8 eine allgemeine Darstellung der am kurvenäußeren Rad eines Kraftfahrzeugs wirkenden Kräfte.

Show it, each schematically

• 1 the representation of a rear axle according to the invention in perspective,
• 2 a side view of the rear axle according to view II 1 ,
• 3 a representation of the rear axle from behind in the direction of travel according to view III 1 ,
• 4 a representation of the rear axle from above according to view IV 3 ,
• 5 a representation of the toe-in behavior of the rear axle in the event of an attacking side-slip force, comparable to the view from 4 , where the rear axle is shown as a black box,
• 6 a representation of the tracking behavior of the rear axle in the event of an attacking wheel center lateral force, comparable to the representation in accordance with 5 ,
• 7 a representation of a motor vehicle with a rear axle according to the invention and
• 8th a general representation of the forces acting on the outside wheel of a motor vehicle.

First on the 1 until 4 referenced.

A motor vehicle rear axle 1 can be seen in these figures. The motor vehicle rear axle 1 is designed as a multi-link rear axle, in particular as a four-link rear axle. It has on each side of a wheel R a camber link 11, a toe link 12, a trailing link 13 and a spring link 14.

On the side of each wheel R, each link is connected via a connection point to a wheel carrier 10, to which the wheel R is rotatably attached and which also carries a braking device (not shown). The wheel carrier 10 is shown in an extremely schematic representation as a rigid body with four struts.

A vehicle longitudinal direction, a vehicle transverse direction and a vehicle vertical direction are respectively defined with x, y and z.

Depending on the location of a connection point relative to a vehicle longitudinal center plane FM (cf. 3 and 4 ) or relative to the longitudinal direction x of the vehicle, this is provided with the index a (outside) or i (inside) or v (front) or h (rear).

For example, the camber link 11 has an outer and an inner connection point 11a and 11i, and the toe link 12 has an outer and an inner connection point 12a and 12i accordingly. The trailing arm 13 has a front and a rear attachment point 13v and 13h. The spring link 14 is provided with an outer and an inner connection point 14a and 14i.

A usual direction of travel is numbered with FR.

The camber, toe and spring links 11, 12 and 14 are each attached to the wheel carrier 10 via their outer connection points. The trailing arm 13 is connected to the wheel carrier 10 via its rear connection point 13h.

The camber, toe and spring links 11, 12 and 14 are each connected to a so-called subframe 17 via their inner connection points, the subframe 17 being connectable or connected to a motor vehicle body in a manner not shown.

A stabilizer 18 is also provided to stabilize the rear axle 1 . The stabilizer has a right and a left connection point 18r and 18l, via which it is connected to one of the spring links 14 in each case.

The spring links 14 each also serve to support a shock absorber 16 and a spring 15, the shock absorber 16 being connected in relation to the vehicle vertical axis z to the spring link 14 via a lower connection point 16u and to a body, not shown, via an upper connection point 16o.

Each wheel R rests on a wheel footprint E. In concrete terms, each wheel R rests on the wheel contact plane E at a wheel contact point 19 . The wheel contact point 19 lies on an imaginary vertical connecting line V, which runs through a wheel center point M (cf. 2 ). Under real load conditions, however, there is a wheel contact area (so-called contact patch) L. The wheel R is fastened to the wheel carrier 3 so that it can rotate about the wheel center point M.

From the 2 the special course of a virtual axis A is clearly visible, around which the wheel R is bent in the event of a cornering-related lateral force. This is how the axis A runs, seen in a projection onto a vehicle longitudinal center plane FM (cf. e.g. 3 ), at an angle α to the wheel contact plane E and is inclined in the direction of travel FR. The virtual axis A also runs at a vertical distance a1 below the wheel center M and pierces the wheel contact plane E at a puncture point 20. The puncture point 20 is at a horizontal distance a2 behind the wheel contact point 19 and also behind the laces L, so that the axis A also runs above the lace L.

The angle α is therefore an acute angle between the virtual axis A and a horizontal plane, e.g. the wheel contact plane E. The angle α is preferably in a range from about 15 degrees to about 60 degrees; about 45 degrees.

From the 2 it can also be seen that the axis A in the projection mentioned is approximately a connecting line between the outer connection point 11a of the camber arm 11 and the outer connection point 14a of the spring link 14 forms.

The course of the virtual axis according to the invention can be achieved by a large number of "adjusting screws", which in particular can only be achieved by a vehicle-specific design of the connection points on the one hand (position relative to the vehicle, mutual distances from one another, i.e. further or closer apart) and by vehicle-related design of the bearing of the connection points (softer or harder bearing) are given on the other hand.

Ultimately, the one in the 2 visible, desired course of the virtual axis A can only be determined by extensive vehicle-related, simulation-based design of the rear axle 1. Such a design includes axle map-based vehicle dynamics simulations, axle simulations and an evaluation of the improvements achieved using vehicle simulations.

The described position of the virtual axis A leads to the desired, good driving characteristics, which are characterized when cornering by understeering lateral force steering in the contact area, oversteering wheel center lateral force steering and high camber rigidity.

In the 3 it can also be seen that the wheel longitudinal center plane RM at the top of the wheel R is inclined inward in the direction of the vehicle longitudinal center plane FM. This results in a positive camber angle γ.

In order to better understand the effect of the virtual axis A, its effect is based on the 5 and 6 sketched.

These figures show the wheel longitudinal center plane RM of a wheel on the outside of the curve under the action of a lateral force when cornering.

On the one hand, the position of the virtual axis A has the effect that, seen from above, perpendicular to the direction of travel FR, the longitudinal center plane RM of the wheel moves inward towards the vehicle longitudinal center plane FM under the influence of a lateral force FyL on the front of the tire (cf. RM'). This results in a positive toe angle δ1 (so-called toe-in) or such an angle is increased (cf. 5 ). The laces lateral force FyL thus leads to understeering behavior.

On the other hand, in the same view, the wheel longitudinal center plane RM moves outwards at the front away from the vehicle longitudinal center plane FM (cf. RM') under the influence of a wheel center lateral force FyR, so that a negative toe angle δ2 (so-called toe-out) occurs or one such is enlarged (cf. 6 ). In contrast, the wheel center lateral force FyR leads to an oversteering behavior.

Desired properties of the motor vehicle rear axle 1 can thus be achieved by the design or alignment of the virtual axis A. Overall, this leads to improved handling of a motor vehicle K which is equipped with a motor vehicle rear axle 1 according to the invention (cf. 7 ).

• So ist in dieser Figur ein kurvenäußeres Rad mit einem Radradius R dargestellt. Bedingt durch die Kurvenfahrt greift am Latsch L eine Latsch-Seitenkraft FyL an. Diese überträgt sich zu einem bestimmten Teil auf den Rad-Mittelpunkt M, so dass dort eine Radmitten-Seitenkraft FyR angreift, die der Latsch-Seitenkraft FyL in etwa entspricht.

Finally, to facilitate understanding of the statements made in the introduction to the description based on the 8th the forces occurring on a wheel on the outside of the curve can be briefly outlined:

• A wheel with a wheel radius R on the outside of the curve is shown in this figure. Due to cornering, a lateral force FyL acts on the Latsch L. This is transferred to a certain extent to the center point M of the wheel, so that a lateral force FyR in the middle of the wheel acts there, which roughly corresponds to the lateral force FyL on the contact area.

Due to the wheel radius R and a tire trail nl caused by the contact patch L, which each act as lever arms, the lateral contact force FyL also causes the moments Mx about the x-axis and Mz about the z-axis. All three force components (FyL, Mx and Mz) influence or change the toe angle of the outside wheel when cornering.

Reference List

1

Motor vehicle rear axle

10

wheel carrier

11

camber handlebars

11i

inner connection point

11a

external connection point

12

toe link

12i

inner connection point

12a

external connection point

13

trailing arm

13v

front attachment point

1 p.m

rear attachment point

14

spring link

14i

inner connection point

14a

external connection point

15

Feather

16

shock absorber

16o

upper connection point

4pm

lower connection point

17

subframe

18

stabilizer

18r

right connection point

181

left connection point

19

wheel contact point

20

Intersection point of the virtual axis with the wheel footprint

a1

vertical distance

a2

horizontal distance

A

virtual axis

E

Rad Uprising Plane

FyL

Laces lateral force

FyR

wheel center lateral force

FM

Vehicle longitudinal center plane

FR

driving direction

K

motor vehicle

L

Wheel contact area (Latsch)

M

wheel center

Mx

moment about the x-axis

Mz

moment about the z-axis

nl

tire caster

R

wheel, wheel radius

rm, rm'

wheel longitudinal center plane

V

vertical connecting line

x

x-axis (vehicle longitudinal direction)

y

y-axis (vehicle transverse direction)

e.g

z-axis (vehicle vertical direction)

a

angle

δ1

positive toe angle (toe-in)

δ2

negative toe angle (toe-out)

g

camber angle

Claims (4)

Counter-steering motor vehicle rear axle (1), in which a rotary movement of the wheel carrier (10) about a virtual axis (A) in the direction of a Toe-in (δ1) is set, with the virtual axis (A) being inclined in the direction of travel (FR) when projected onto a vehicle longitudinal center plane (FM) and running at an angle (a) to a wheel contact plane (E) and a puncture point (20) with the wheel contact plane (E) which, viewed in the direction of travel (FR), lies behind a wheel contact point (19), characterized in that the virtual axis (A) runs below a wheel center point (M) and the angle (a) is in a range from about 15° to about 60°. Counter-steering motor vehicle rear axle (1). claim 1 , characterized in that the angle (a) is about 45°. Counter-steering motor vehicle rear axle (1) according to one of Claims 1 until 2 , characterized in that the virtual axis (A), seen in a front view of the wheel (R) from the outside in the direction of the vehicle longitudinal center plane (FM), approximately a connecting line between an outer connection point (11a) of a camber arm (11) and an outer connection point (14a) of a spring link (14). Motor vehicle (K) with a rear axle (1) according to one of the preceding claims.

Images