DE19635462A1 - 11 power steering for motor vehicles - Google Patents

Abstract

The invention concerns a servo-assisted steering system for vehicles, the system having at least one steerable, rigid rear axle (1) steered by at least two cylinder-piston units (5, 6) which can be acted on hydraulically. Each of the cylinder-piston units (5, 6) is disposed on one side of the rear axle (1) and is connected in hinged manner at one end to a frame (4) of the vehicle and, at the other, to the rear axle (1). The rear axle (1) is articulated in its upper region on the vehicle frame (4) by means of an A-frame arm (2) in a bearing head (3). The two cylinder-piston units (4, 5) are controlled such that, when the vehicle is travelling in a straight line, both cylinder-piston units (5, 6) are completely retracted and, on cornering, only the cylinder-piston unit (5, 6) on the outside of the curve is adjusted, whilst the cylinder-piston unit (6, 5) on the inside of the curve remains in its retracted position. In this way, the articulation point (7, 8) of the cylinder-piston unit (5, 6) on the inside of the curve forms a swing centre which, together with the bearing head (4) of the A-frame arm (2), forms an axis of rotation for the steering of the rear axle (1). A working circuit (14) and a centring circuit (25) are provided for controlling the cylinder-piston units (5, 6).

Description

The invention relates to power steering for Motor vehicles with at least one steerable, rigid rear teraxle, according to the preamble of claim 1.

For heavy goods vehicles, for example during construction work testify, with more than two axes is often a last one Rear axle designed as a steerable rigid axle. Thereby can the demand for high load capacity and good lap suspension under extreme conditions in heavy Terrain to be met.

The rear axle is steered by at least two hydraulically actuated cylinder-piston units, one of which is attached to one side of the rear axle is arranged. Every cylinder-piston unit is at its one End with a frame of the motor vehicle and at her the end of which is articulated to the rear axle. Additional Lich the rear axle is in its upper area by egg NEN wishbone in a bearing head on the frame of the Motor vehicle articulated.

Such power steering is known from the EP-A2-647 554. This steering requires storage the axis a considerable mechanical effort. The Bo The freedom of the axis is greatly reduced, so that this Arrangement, especially for construction site vehicles, not can be accepted.

The invention has for its object an auxiliary Power steering for motor vehicles with at least one steering  baren rigid rear axle to create a low ren requires construction work and also high functionality security.

This object is characterized by in claim 1 nete power steering solved. For this, the two Zy Linder-piston units controlled so that on a straight line Exit both cylinder-piston units fully retracted are driving and when cornering only the outside of the Zylin the piston unit is adjusted while the inside of the curve Cylinder-piston unit in its retracted position remains. The pivot point of the inside of the curve is Zy linder-piston unit has an instantaneous pole, which together with the bearing head of the wishbone has an axis of rotation for the Steering of the rear axle defined. To control the at the cylinder-piston units are a working group and a Centering circle provided. This results in a simple kine matic structure of the steered rear axle with a hy drastically redundant steering system.

Appropriate and advantageous embodiments of the Er invention are specified in the subclaims. So contains the working group a control valve for the directional tax tion of the two cylinder-piston units and for each cy Linder-piston unit, a check valve and the centering circuit a centering valve for each cylinder-piston unit. Purpose It is moderate if the working group and the centering circle supplied with pressure medium from separate pressure medium sources will. For security reasons, it is advantageous if the Centering contains a pressure accumulator. The control valve of the working group affects everyone directly in a working area Cylinder-piston unit and via a check valve each another working area of each cylinder-piston unit.  

One centering valve of the centering circuit is on one third working area of each cylinder-piston unit closed. Each check valve has a through position and a locking position, the locking position Represents the neutral position of the check valve. In the lock position is a pressure medium flow from the two working clear the cylinder-piston units to the pressure medium container blocked, a pressure medium flow in reverse direction tion is however possible. Each centering valve has one Inlet position and a return position on, the Inlet position represents the neutral position of the centering valve poses. To the straight-ahead position of the steered Hin ensure that the axle is in this straight-ahead position both centering valves in the closed position and both Blocking valves in their blocking position. This will make the two cylinder-piston units each by two independent pending valves in their retracted position that the Straight ahead position corresponds, blocked. The curves driving position of the rear axle is achieved in that the shut-off valve and the centering valve of the inside of the curve Cylinder-piston unit are in their neutral positions, so that this unit locks in its retracted position remains. The check valve of the outer cylinder Piston unit is in its open position and that Centering valve of the cylinder-piston unit on the outside of the curve is in its return position. This allows this cylin the piston unit is adjusted to the desired steering position will.

Because the additional rear axle is steered above a certain speed threshold is no longer necessary agile and no longer desirable, they remain the cylinder-piston units and thus the steering of the  Rear axle above this certain speed threshold, for example 50 km / h, blocked. In the below lying speed range is the steering angle ratio the front axle to the rear axle harmoniously the electronic control changed. So the rear axle steering angle have its maximum size at 0 km / h, while it is zero at, for example, 50 km / h.

In the following the invention is based on one in the Drawing illustrated embodiment explained in more detail tert.

Show it:

Figure 1 shows a cross section through the rear axle with a schematic representation of the Anlen kung.

Figure 2 is a plan view of the rear axle in the straight-out position.

Fig. 3 is a plan view corresponding to Figure 2, but with the axis deflected.

Fig. 4 is a rear axle with schematically shown hydraulic circuits in straight-ahead position of the axis and

Fig. 5 shows the representation of Fig. 4, but with a steered axis.

A steerable, rigid rear axle 1 is attached in its obe ren area by a wishbone 2 in a bearing head 3 on a frame 4 of a motor vehicle shown only indicated. On both sides of the Hinterach se 1 , suitably symmetrical to the bearing head 3 and at a greater distance from it, two cylinder-piston units 5 and 6 are arranged in their lower loading area. The cylinder-piston units 5 and 6 are connected at one end to the frame 4 of the motor vehicle and at their other end in articulation points 7 and 8 with the rear axle 1 .

In FIG. 2, the rear axle 1 is shown in its straight-ahead position. For this purpose, the two cylinder-piston units 5 and 6 are completely retracted.

In Fig. 3, the rear axle 1 is shown in a cornering position. In this case, the lower in Fig. 3 cylin der-piston unit 6, that is, the inner turning cylinder-piston unit, is still fully retracted. The upper in Fig. 3, that is, the outer cylinder-piston unit 5 , is driven according to the desired steering angle. The articulation point 8 of the cylinder-piston unit 6 on the rear axle 1 forms an instantaneous center of the rear axle, together with the bearing head 3 an axis of rotation for the steering of the Hin 1 defined.

In the following, it will be explained in more detail with reference to FIGS . 4 and 5 how the cylinder-piston units 5 and 6 are adjusted. In each case two working spaces 10 and 11 of the cylinder cylinder-piston unit 5 and two working spaces 12 and 13 of the cylinder-piston unit 6 are connected to a hydraulic circuit 14 . The working group 14 contains a servo pump 15 , the pressure medium from a pressure medium container 16 via a control valve 17 in two lines 18 and 20 to the two cylinder-piston units 5 and 6 för changes. From the lines 18 and 20 , a branch line 21 or 22 leads directly to a work space 10 or 12 of the cylinder-piston units 5 or 6 . In each line 18 and 20 , a check valve 23 or 24 is inserted, through which the lines 18 and 20 are closed to the second working space 11 and 13 of the cylinder-piston units 5 and 6 respectively. Each check valve 23 and 24 has a through position and a lock position. In the locked position, a pressure medium flow from the working spaces 11 and 13 of the cylinder-piston units 5 and 6 to the pressure medium container 16 is blocked, but a pressure medium flow in the opposite direction is possible. This blocking position is formed, for example, by a check valve integrated in the blocking valve 23 , 24 . The blocking positions of the blocking valves 23 and 24 represent their neutral position, which is set, for example, by spring force. An adjustment of the check valves 23 and 24 in their passage positions can for example be electromagnetic or hydraulic.

In addition to the working circuit 14 , a centering circuit 25 is connected to the cylinder-piston units 5 and 6 . The centering circuit 25 contains a servo pump 26 which promotes a pressure medium from a pressure medium container 27 into a pressure line 28 . To the pressure line 28 a memory 30 is expediently connected. The pressure line 28 is connected via two branch lines 31 and 32 to a third working space 33 and 34 of the cylinder-piston units 5 and 6 , respectively. Centering valves 35 and 36 are inserted into the branch lines 31 and 32 . Each Zentrierven valve 35 and 36 has an inlet position and a return position, the inlet position being the neutral position of the centering valves 35 and 36 . The centering valves 35 and 36 are actuated in the same way as the control of the check valves 23 and 24 .

In the straight-ahead position, both centering valves 35 and 36 are in their neutral position, ie in their inlet position, and both check valves 23 and 24 are also in their neutral position, ie in their blocking position. In these positions, the working spaces 11 , 13 , 33 and 34 of the two cylinder-piston units 5 and 6 are acted upon with Druckmit tel, thereby blocking the cylinder-piston units 5 and 6 in their retracted position.

In the cornering position, which is shown in Fig. 5, the check valve 24 and the centering valve 36 of the inner cylinder-piston unit 6 remain in their new tral positions. The check valve 23 of the outer cylinder Zylin-piston unit 5 is adjusted in its through position and the centering valve 35 of the outer cylinder-piston unit 5 in its return position. Characterized who the working spaces 11 and 33 of the cylinder-piston unit 5 relieved, so that the cylinder-piston unit 5 can be adjusted via the control valve 17 in the desired position.

By arranging the working group 14 and the additional centering circuit 25 , the cylinder-piston units 5 and 6 are each via two independently acting valves, namely the check valves 23 and 24 and the centering valves 35 and 36 , in their retracted straight-ahead position held or adjusted in their cornering position. This results in a high level of security.

The steering of the rear axle 1 is expediently blocked above a certain speed threshold, for example 50 km / h. It is also expedient if the rear axle 1 is not steered when the brake is actuated due to the large steering roller radius. After releasing the brake, the currently required Len no impact on the rear axle 1 is approached.

Reference list

1 rear axle
2 wishbones
3 bearing head
4 frames
5 cylinder-piston unit
6 cylinder-piston unit
7 articulation point
8 articulation point
9 -
10 work space
11 work space
12 work space
13 work space
14 working group
15 servo pump
16 pressure medium container
17 control valve
18 management
19 -
20 line
21 branch line
22 branch line
23 shut-off valve
24 shut-off valve
25 centering circle
26 servo pump
27 pressure medium container
28 pressure line
29 -
30 memories
31 branch line
32 branch line
33 work space
34 work space
35 centering valve
36 centering valve

Claims (9)

1. Power steering for motor vehicles with at least one steerable, rigid rear axle ( 1 ), the steering of which is carried out by at least two hydraulically actuatable cylinder-piston units ( 5 , 6 ), and with the following further features:

• one of the cylinder-piston units ( 5 , 6 ) is arranged on one side of the rear axle ( 1 ),
• - Each cylinder-piston unit ( 5 , 6 ) is articulated at one end to a frame ( 4 ) of the motor vehicle and at its other end to the rear axle ( 1 ),
• - The rear axle ( 1 ) is articulated in its upper region by a wishbone ( 2 ) in a bearing head ( 3 ) on the frame ( 4 ) of the motor vehicle,

characterized in that the two cylinder-piston units ( 5 , 6 ) are controlled in such a way that when driving straight ahead both cylinder-piston units ( 5 , 6 ) are fully retracted and when cornering only the cylinder-piston unit ( 5 , 6 ) is adjusted while the inside cylinder-piston unit ( 6 , 5 ) remains in its retracted position, so that the articulation point ( 7 , 8 ) of the inside cylinder-piston unit ( 6 , 5 ) forms a momentary pole , the head together with the bearing (4) of the wishbone (2) defining a rotation axis for the steering of the rear axle (1) and that for dently of the cylinder-piston units tion (5, 6) has a working circle (14) and a Centering circle ( 25 ) are provided. 2. Power steering system according to claim 1, characterized in that the working circuit ( 14 ) has a control valve ( 17 ) for the directional control of the two cylinder-piston units ( 5 , 6 ) and for each cylinder-piston unit ( 5 , 6 ) a check valve ( 23 , 24 ) and the Zen trierkreis ( 25 ) for each cylinder-piston unit ( 5 , 6 ) contains a centering valve ( 35 , 36 ). 3. Power steering system according to claim 2, characterized in that the working circuit ( 14 ) a pressure medium source in the form of a servo pump ( 15 ) and a pressure medium container ( 16 ) and that the centering circuit ( 25 ) a pressure medium source in the form of a servo pump ( 26 ) with a Storage ( 30 ) and a pressure medium container ( 27 ) holds ent. 4. Power steering system according to claim 2, characterized in that the control valve ( 17 ) di rectly to a working space ( 10 , 12 ) of each cylinder-piston unit ( 5 , 6 ) and via a check valve ( 23 , 24 ) to egg NEN additional working space ( 11 , 13 ) of each cylinder-piston unit ( 5 , 6 ) is connected and that a centering valve ( 35 , 36 ) to a third working space ( 33 , 34 ) of each cylinder-piston unit ( 5 , 6 ) is connected. 5. Power steering system according to one of claims 2 to 4, characterized in that each blocking valve ( 23 , 24 ) has a passage position and a blocking position, in which a pressure medium flow from the two working spaces ( 11 , 12 ) of the cylinder-piston units ( 5 , 6 ) to the pressure medium container ( 17 ) is blocked, however, a pressure medium flow in the reverse direction is possible, and that each centering valve ( 35 , 36 ) has an inlet position and a return position, the blocking position of the blocking valve ( 23 , 24 ) and the inlet position of the centering valve ( 35 , 36 ) are their neutral positions. 6. Power steering system according to claim 5, characterized in

• - That in the straight-ahead position both Zentrierven tile ( 35 , 36 ) are in their inlet position and both check valves ( 23 , 24 ) in their locked position, in each of two working spaces ( 11 , 33 , 13 , 34 ) of the cylinder-piston Units ( 5 , 6 ) are blocked in their retracted position and
• - That in the cornering position, the check valve ( 23 , 24 ) and the centering valve ( 35 , 36 ) of the respective inner cylinder-piston unit ( 5 , 6 ) are in their neutral positions and the check valve ( 23 , 24 ) of each The outer cylinder-piston unit ( 6 , 5 ) in its through position and the centering valve ( 36 , 35 ) of the outer cylinder-piston unit ( 6 , 5 ) in its return position.

7. Power steering system according to one of claims 1 to 6, characterized in that the steering of the rear axle ( 1 ) is blocked above a certain speed threshold threshold. 8. Power steering system according to one of claims 1 to 7, characterized in that the steering of the rear axle ( 1 ) is held in its straight exit position when the brake is actuated and after releasing the brake the currently required steering angle on the rear axle ( 1 ) is approached.