DE3410115A1 - Passenger car - Google Patents

Abstract

Passenger car whose rear wheels are coupled elasto-kinematically to the body of the vehicle by specifying an advance movement (-nH) (lateral force application before the instantaneous pole of the wheel suspension) in such a way that they are automatically subjected to a wheel lock in the direction of understeering (countersteering) under the effect of lateral forces S engaging on them. The passenger car is equipped with a steering device by means of which rotational movements of the steering wheel are converted via a steering gear or the like into steering movements both of the front wheels and of the rear wheels, the steering movements of the rear wheels which are brought about directly by the steering wheel locks are directed (also steered) opposite to those of the front wheels and the ratio k = (-wH)/wV between the steering angle -wH of the rear wheels and the steering angle wV of the front wheels is constant irrespective both of the size of the steering wheel lock wLK and of the level of the travelling speed. <IMAGE>

Description

Personal Kraftwaoen

The invention relates to passenger cars with a steering device of the type mentioned in the preamble of claim 1.

Passenger cars of the conventional type are front-steered, i. H. Turning movements of the steering wheel are in corresponding via a steering gear and a steering linkage Steering movements of the front wheels implemented; the alignment of the rear wheels is through however, these steering wheel rotations are not directly changed.

The driving behavior of a passenger car is influenced by different Properties determined; z. B. from its behavior during stationary cornering, which are described by the so-called stationary yaw gain factor V. can depend on the size of the slip angle ß that occurs when cornering, d. H. the angle between the longitudinal axis of the vehicle and the direction of movement of the vehicle in the center of gravity, on the speed with which he tiuf steering wheel turns (steering angle jumps) reacts, which is characterized by the so-called yaw reaction time or peak response time as well as its stability behavior, d. H.

on its ability to deal with disruptive factors when driving straight ahead (Lateral forces) to compensate.

The stationary yaw amplification factor Vy gives the ratio of the yaw rate ç to the steering wheel angle 6 LK (steering wheel angle) for stationary cornering, d. H. when driving through a circular path (constant radius) at constant driving speed will. Ultimately, it makes a statement about how strong the steering wheel is when driving through it the Circular path must be taken. Will by average vehicle drivers here yaw intensification factors between about 0.2 to 0.25 l / s at 100 km / h as pleasant and well felt, whereby the steering wheel angle should generally not be too large should in order to keep the steering effort within limits.

Values for the sideslip angle ß are generally perceived as pleasant, those in the case of lateral accelerations between about 0.3 to 0.5 g in the order of magnitude to 20 lie.

The peak response time or yaw reaction time should be as short as possible be. It is the time it takes if the steering wheel is suddenly turned (steering angle jump) passes until the yaw rate ç has reached its maximum value (calculated from the point in time at which the steering angle jump has reached half its value). For conventional vehicles, it is around 0.30 to 0.5 seconds.

Great efforts have been made in the past and much thought has been given to the dynamic behavior of passenger cars, d. H. the speed with which they react to steering wheel turns and you Stability behavior to improve.

For example, arrangements are known in which rotary movements of the steering wheel not only steering movements of the front wheels, but also steering movements of the rear wheels, the transmission ratio between the rear wheel deflection and the front wheel deflection is variable.

In a known arrangement (DE-OS 31 33 985) the transmission ratio between the rear wheel deflection and the front wheel deflection by changing the Size of the rear wheel deflection depending on various operating parameters, such as the driving speed, the lateral acceleration or the yaw changes. For this purpose, an electronic computer is provided, which is supplied on the basis of it Sensor signals etc. an electric motor acting on the steering linkage of the rear wheels controls according to a predetermined program.

Here, not only the size, but also the direction of the rear wheel deflection - relative to the front wheel deflection - changed. In particular, the rear wheels when turning the steering wheel at low Fahrgeschwin speed, as z. B. when turning is common in the opposite direction as the front wheels (co-steering) and at higher driving speeds, as is customary in particular when driving straight ahead are deflected in the same direction as the front wheels (counter-steering). Of the constructive and control engineering effort for this known arrangement is very high.

Further arrangements that are very similar to this are inter alia. known from the German Offenlegungsschriften 29 52 565, 31 24 821 and 31 45 618.

All these known arrangements have in common that the rear wheels by means of in particular electronic control devices at low driving speeds opposite and at higher driving speeds in the same direction as the front wheels are deflected, the control engineering and design effort this is great.

Arrangements are also known (e.g. DE-OS 29 52 566, 31 21 196 or 32 30 036), in which the rear wheels are also deflected when the steering wheel is deflected via a mechanical linkage or the like, which is designed in such a way that that the rear wheels with small steering wheel deflections in the same direction as the Front wheels (counter-steering) are deflected, large turns of the steering wheel, however, one Deflection of the rear wheels opposite to the front wheels (co-steering) or cause no deflection at all. As in general on the one hand at higher driving speeds only smaller turns of the steering wheel are carried out and, on the other hand, larger turns of the steering wheel mainly take place at lower Fahrgeschwindig speeds, is known with these Arrangements, of course, also indirectly a speed-dependent variation given the translation ratio between the rear and front wheel deflection.

The mechanical and structural effort for arrangements of this type is considerably; to get the desired dependency, either be special Cam plates with embedded curved cam tracks, special crank mechanisms with crank discs and crank rods as well as other rod and pin / guide slot arrangements intended.

In another known arrangement (EP-OS 89 631) with steered Front and rear wheels will generally face the rear wheels in the same direction deflected (counter-steering) like the front wheels. About becoming a bearer associated with it of the vehicle (slowing down of the reaction to steering wheel turns, i.e. steering angle jumps) To mitigate, special delay elements are provided that ensure that the rear wheels are always delayed when the steering wheel is turned compared to the front wheels be deflected. In the case of purely hydraulic steering arrangements, in the hydraulic lines leading to the rear wheel steering are not controllable or also arranged depending on driving speed controllable throttles. With electro-hydraulic Rear-wheel steering, on the other hand, electronic delay elements are provided which Control signals taken from the front-wheel steering are delayed to an electronic one Forward control unit to control the hydraulic rear wheel steering.

In this known arrangement, too, the structural and control / Control engineering effort is very high. In addition, the driving behavior appears questionable. The stationary yaw amplification factor V ç is undoubtedly smaller than with conventional ones Vehicles with pure front-wheel drive. Also the speed with which the steering wheel is turned (Steering angle jumps) is responded, worsened compared to conventional Vehicles.

Accordingly, the invention is based on the object without use more expensive, complicated or space-consuming mechanical-constructive or control- or control measures to create a passenger car that at least the same compared to conventional, purely front-steered vehicles good properties for stationary travel and a much better behavior at has dynamic processes, d. H. in particular faster reactions to sudden changes in steering angle shows and has a better stability behavior.

According to the invention, this object is achieved by the characterizing features of claim l solved. Advantageous developments of the invention are in specified in the subclaims.

On the one hand, the rear wheels are set by specifying a lead (-nH) so elasto-kinematically articulated on the vehicle body that it automatically have understeering acting impressed steering effects (counter-steering), and for others are steering wheel rotations by mechanical or equivalent transmission means directly in steering deflections opposite to the steering deflections of the front wheels (Steering) of the rear wheels implemented, the gear ratio between the steering angle of the rear wheels and the front wheels remains constant.

Passenger cars designed in this way can be in a simple manner Way to be dimensioned so that on the one hand it is one of conventional vehicles have the usual excellent behavior during stationary circular travel, d. H. Yaw intensification factors V of about 0.2 to 0.25 l / s at 100 km / h and side slip angle from 10 to 20 with lateral accelerations of 0.3 to 0.5 g, and on the other hand a noticeable have better behavior in dynamic processes, d. H. comparatively low Yaw response times of e.g. B. 0.2 to 0.3 s and very good stability behavior. An essential advantage is that these advantageous properties with proven conventional and trouble-free means are achieved, complicated variable transmission elements or electronic control and computer arrangements however, are not needed.

Based on an embodiment shown in the drawing the invention is explained in more detail below.

The single drawing shows a schematic and basic representation the top view of a passenger car, with only those for understanding The individual parts necessary for the invention are shown and numbered. Basically it can be a front-wheel drive, a rear-wheel drive or a All-wheel-drive company is dealing with the front wheels of the vehicle, numbered with 1 are designed in the usual way as steerable wheels, d. H. they are not at that further illustrated Rad iuhrungsgliedern around a slightly inclined relative to the vertical Axis pivotably articulated and are available via a steering linkage 8, z. B. a rack, with the one to be operated by the driver Steering wheel 7 in connection. In the usual way, a steering wheel rotation by the steering wheel angle 6 bk is thus turned into a corresponding steering movement of the front LK wheels 1 implemented. The front wheel steering angle is numbered with 6 V.

The rear wheels are in the embodiment via a composite or Coupling link axle 4 is pivotably articulated on the vehicle body 3, the two trailing arms with 41 and the one connecting them in the area of the superstructure bearing twistable cross brace are numbered 42. However, the invention is not based on this type of rear suspension is limited. In principle, other known Wheel guide members, e.g. B. semi-trailing arms, double wishbones or struts are used will; it is of course also possible to design the rear axle as a rigid axle.

To the rear wheels 2 with an understeering embossed To provide a steering effect, the rear suspension is so elasto-kinematic executed that the rear wheels under the action of acting on them lateral forces S automatically subject to wheel lock in the direction of understeering (countersteering) are. For this purpose, the steering knuckles or wheel carriers 5 are in a manner known per se (z. B. DE-OS 21 58 931, DE-OS 32 05 783) using elastic elements and default a lead -nH (negative lag) such member on the wheel guide, d. H. on the trailing arm 41, articulated that the - possibly only fictitious - steering axle of the elastic rear wheel movement the roadway behind the vertical wheel center transverse plane penetrates, the lateral force application thus takes place in front of the instantaneous rotational pole of the wheel or the axle.

In the embodiment shown, this type of suspension is through one - in the plan view - at a distance -nH behind the wheel axle lying hinge-like Articulation point 51 between the wheel carrier 5 and trailing arm 41 and by an between Wheel carrier and trailing arm effective elastic element 6 symbolizes. In practice must have the desired elastic or torsionally soft design of the rear suspension cannot be realized by using a mechanical articulated hinge. Decisive is that the - with respect to side force application - torsional stiffness of the rear axle considerably less, d. H. much softer than with conventional rear axles is measured, the so-called axial side force slip angle coefficient C * H larger than is made with conventional vehicles.

The following applies to this axial lateral force slip angle coefficient CH denotes the tire lateral force slip angle coefficient of the rear wheels, LH the torsional rigidity of the rear axle and nH the total caster on the rear axle.

With lead (nH becomes negative) appears in the denominator of this equation thus a minus sign.

In addition, the rear wheels 2 are also like the front wheels 1 with a provided with the steering wheel 7 connected steering device.

Like the front wheels, they are also about a vertical or against the vertical slightly inclined axis is articulated in a steerable manner on its wheel guide members and provided with toe levers attached to a steering linkage, e.g. B.

attack a rack 9. The immediate transmission of the rotary movements of the steering wheel 7 on the rear steering linkage 9 can by means of known mechanical Transmission links take place; their training in detail on the type of used Front axle and rear axle steering depends. In the drawing there is such a mechanical one Transmission element indicated by dashed lines and numbered 10. The mechanical transmission link 10 and the rear steering linkage 9 are designed and arranged in such a way that rotational movements of the steering wheel 7 lead to steering movements of the rear wheels 2, which are opposite (Mitlenken) are directed to the steering movements of the front wheels 1. With an accepted The rear wheels are turned by the steering wheel angle 6 LK in the direction of the arrow 2 thus deflected in the direction of the solid arrow by C'en rear wheel steering angle - 6 H, which is opposite to the front wheel steering angle 6 V.

Especially in those cases where there is a hydraulic power steering exists, i.e. a hydraulic circuit already exists, it may be an advantage, the rear steering mechanism is also hydraulic to operate and in particular the transmission device to the rear axle as a hydraulic line to train.

The gear ratio between the rear wheel steering angle - # H and the front wheel steering angle #V, that is, the ratio is not variable, but constant. It is therefore changed neither as a function of the size of the steering wheel angle 6 LK nor as a function of the level of the driving speed. This ratio is preferably selected so that it is approximately in the order of magnitude between -0.2 and -0.4.

For the lead -nH of the rear axle, a value is selected that is preferably lies in a range between approximately -0.05 m and -0.1 m.

When driving through a left curve, so when the steering wheel 7 as shown is turned to the left by the steering wheel angle ö bk, the LK front wheels 1 turned left by means of the steering linkage 8 by the front wheel steering angle 6 V. the Rear wheels 2, however, are via the V mechanical transmission link 10 and the rear steering linkage 9 immediately around the rear wheel steering angle - 6 H to the right struck. This H of the steering wheel 7 directly caused steering movement of the rear wheels in the direction of oversteering (co-steering) is superimposed due to the provided elasto-kinematic Articulation of the rear wheels under the influence of the wheels when cornering acting lateral force S a counter-directional wheel lock in the direction Understeer (countersteer), which is indicated by a dashed arrow.

By means of the measures according to the invention, taking into account the general vehicle data, it is determined by quantifying the rear axle lead -nH and the ratio Between the rear wheel steering angle and the front wheel steering angle it is possible in a simple manner to determine the driving behavior of the vehicle in such a way that it has better properties than conventional vehicles in dynamic processes and at least as good in stationary processes. It is therefore possible to improve the stability behavior, i.e. the ability of the vehicle to compensate for disturbances when driving straight ahead (lateral forces), and in particular the speed (response behavior) without worsening the steady yaw gain Vgu or w / LK and without worsening (increasing) the side slip angle ß ), with which one reacts to steering wheel turns (steering angle jumps), to increase, ie to reduce the so-called yaw reaction time (peak response time).

In addition, the proposed design of the rear suspension also the turning circle of the vehicle - compared to conventional vehicles - decreased.

Claims (3)

CLAIMS Passenger cars with a steering device through which Rotary movements of the steering wheel via a steering gear or the like in both steering movements the front wheels as well as the rear wheels are implemented, characterized in that that the rear wheels (2) by specifying a lead (-nH) (lateral force attack) the instantaneous wheel suspension pole) is articulated elasto-kinematically on the vehicle body (3) in this way are that they act automatically under the action of side forces (S) acting on them are subject to a wheel lock in the direction of understeering (counter-steering) that the steering movements of the rear wheels directly caused by steering wheel turns (#LK) (2) opposite (steering) to those of the front wheels (1). and that the relationship between the rear wheel steering angle (- #H) and the front wheel steering angle (6 V) is constant regardless of both the size of the steering wheel angle (#LK) and the level of the vehicle speed. 2. Passenger car according to claim 1, characterized in that the ratio lies approximately in a range between -0.2 and -0.4. 3. Passenger car according to claim 2, characterized in that the lead (-nH) of the rear axle in a range between -0.05 m and - 0.1 m lies.