WO2017001084A1

WO2017001084A1 - Steering system for an automatically driving vehicle

Info

Publication number: WO2017001084A1
Application number: PCT/EP2016/059652
Authority: WO
Inventors: Bastian Witte; Malte ROTHHÄMEL; Felix Kallmeyer
Original assignee: Volkswagen Aktiengesellschaft
Priority date: 2015-06-30
Filing date: 2016-04-29
Publication date: 2017-01-05
Also published as: DE102015212173A1

Abstract

The invention relates to a steering system (1) for an automatically driving vehicle, comprising at least two electrical supply units (2, 3) which are independent of one another, at least one hydraulic circuit and two electric motors (4, 5), wherein the first electric motor (4) is supplied with electrical energy by the first electrical supply unit (2), and the second electric motor (5) is supplied with electrical energy by the second electrical supply unit (3), wherein the electric motors (4, 5) are designed in such a way that they apply a steering torque to at least one component of the steering system (1) and/or actuate a servo valve (8, 21) of the at least one hydraulic circuit.

Description

description

Steering system for an automatically moving vehicle

The invention relates to a steering system for an automatically moving vehicle.

In automatic vehicles, the redundancy in steering and braking is an important feature. In the case of any single fault, they still need to work, with limitations on dynamics or comfort, if necessary. This is because the driver as a fallback for a period of about 10 s after the

Takeover request is not yet available and the entire system has to continue to function.

In contrast, in driver assistance systems brake and steering are executed only one channel. The driver is always present as a fallback level and must take over the vehicle management again at short notice in case of an error.

From WO 2010/125044 A1 a power steering assembly for a hydraulic power steering of motor vehicles is known comprising at least one hydraulic servo valve with an actuator for controlling the steering assistance in dependence of the relative rotation of an input shaft relative to an output shaft, at least two planetary gear

Transmission of the rotational movement of the input shaft or the output shaft to the actuator, wherein in each case a first functional element of a planetary gear with the input shaft or the output shaft and a first functional element of the other planetary gear is rotatably connected to the actuator and a respective second functional element for coupling the planetary gear is provided , and at least one actuator for relative displacement of the actuator relative to the input shaft or the output shaft to the

Steering support characteristic to influence, wherein the at least one actuator is arranged and configured so that it causes the same direction rotation with simultaneous relative rotation of the two respective third functional elements of the planetary gear to each other.

EP 0 856 453 A2 discloses an electrohydraulic steering system for vehicles, which can be activated by manual steering and automatic steering, which can be activated via a switch is included. The steering system has at least one hydraulic steering cylinder

Adjustment of the steerable wheels, wherein preferably two parallel-connected, electrically actuated hydraulic control valves are provided to control the admission of the steering cylinder with hydraulic fluid, each with a control and

Evaluation device for receiving the drive signals are connected. In this case, it is further provided that the control and evaluation device has at least two mutually independent control and evaluation units and an error detection unit, wherein each of the control and evaluation units and the error detection unit, the Lenksignal- set values, the Radeinschlagwinkel actual values and the position of the switch for the automatic steering are supplied. The control and evaluation unit and the error detection unit each have a microcontroller. It is further proposed to provide the microcontroller with independent power supplies and provide a further accumulator for Notpufferung the microcontroller next to the vehicle battery. Finally, an emergency steering pump is provided, which should pump the hydraulic fluid in case of failure of the regular pump.

A disadvantage of the known steering system is that despite some redundancies the

Steering system against single error is insufficiently fault tolerant. For example only, it should be mentioned that the two pumps are hydraulically connected via a common line, so that when a line is interrupted, none of the pumps can pump more hydraulic fluid.

The invention is based on the technical problem of providing a steering system for an automatically moving vehicle, in particular a commercial vehicle, which has a low susceptibility to single defects.

The solution of the technical problem results from a steering system for an automatically moving vehicle with the features of claim 1. Further advantageous embodiments of the invention will become apparent from the dependent claims.

For this purpose, the steering system for an automatically moving vehicle comprises at least two independent electrical supply units, at least one hydraulic circuit and two electric motors. In this case, the first electric motor of the first electrical supply unit and the second electric motor of the second electrical

Supply unit supplied with electrical energy. In this case, the electric motors are designed such that they have a steering torque on at least one component of the steering system apply and / or control a servo valve of the at least one hydraulic circuit. In the case of a single fault in the electronics, it is thus ensured that an electric motor always works and can generate a steering torque (directly via the component or indirectly via the hydraulics). In this case, the electrical supply units are preferably designed as batteries.

In one embodiment, the at least one hydraulic circuit has a pump that can be driven by an electric pump motor or an internal combustion engine. In this case, the electrical supply of the electric pump motor or the control electronics of the internal combustion engine (for example, the engine control unit) from one of the two electrical

Supply units, which is preferably the first supply unit, which will be explained below.

In one embodiment, the rotational movements of the two electric motors are mechanically connected to one another and, for this purpose, preferably dimensioned such that the maximum torque of the second electric motor is a multiple of the first electric motor. The factor is for example 3 to 10, in particular between 6 and 8. Thus, the

less powerful electric motor and the pump motor or the internal combustion engine supplied by the first supply unit. In case of failure then is still the

powerful second electric motor available. Conversely, the less powerful electric motor and the hydraulic together can provide a sufficient

Generate steering torque.

In one embodiment, the first electric motor drives the servo-valve of the hydraulic circuit and the second electric motor applies a steering torque to a steering column or a

Rack of the steering system. Steering column and rack are preferably mechanically coupled.

In an alternative embodiment, the first electric motor applies a steering torque to the steering column and the second electric motor applies a steering torque to the steering column or the rack. In principle, the first electric motor, a steering torque on the

Apply rack. However, if this deliberately designed weaker than the second electric motor, the existing torques for a direct movement of the rack are not enough. In a further embodiment, the two electric motors are arranged on a common shaft, which allows a very compact and inexpensive design. The two electric motors can also be arranged in a common housing, as long as only the electrical separation is ensured.

In a further embodiment, the steering system has two hydraulic circuits, wherein a servo valve of the first hydraulic circuit by the first electric motor and a servo valve of the second hydraulic circuit by the second electric motor can be controlled. Here, too, ensured in a single error of a hydraulic circuit of the other hydraulic circuit sufficient steering torque.

In a further embodiment, the two servo valves are formed as an integrated servo valve, but the two hydraulic circuits are further strictly separated.

In a further embodiment, the at least one electric pump motor can be regulated in such a way that, as the load increases, rotational speed or torque are up-regulated. As a result, in phases where hardly any hydraulic fluid must be pumped, the electric

Energy consumption of the pump motor reduced.

In a further embodiment, the steering system is designed such that a control signal is generated by means of which different brake pressures are set on the front wheels in order to generate a steering movement. Thus, in case of failure of a circle

(regardless of whether one or two hydraulic circuits are used)

additional supporting steering torque for the remaining circle are provided, this embodiment is preferably used in commercial vehicles. This is based on the following consideration. In vehicles with an electric stability program, a spinning vehicle is stabilized again with different brake pressures at the individual wheels. In a car steering is over

Differential brake pressure almost impossible, since the negative steering roller radius initiates the forces in the axis so that the steering is rotated to the opposite side. The

Longitudinal difference due to the brake pressure difference is compensated by the automatic, reverse rotation of the steering again. In the case of commercial vehicles, on the other hand, there is no negative steering wheel radius, but due to their design, only positive ones exist

Scrub radius. Here, therefore, the steering wheel is automatically rotated in the direction of higher braking force. The invention will be explained in more detail below with reference to preferred embodiments. The figures show:

1 is a schematic block diagram of a steering system with a hydraulic circuit in a first embodiment,

2 shows a schematic block diagram of a steering system with a hydraulic circuit in a second embodiment,

3 is a schematic block diagram of a steering system with a hydraulic circuit in a third embodiment,

Fig. 4 is a schematic block diagram of a steering system with two hydraulic circuits in a first embodiment and

Fig. 5 is a schematic block diagram of a steering system with two hydraulic circuits in a second embodiment.

In Fig. 1, a steering system 1 for an automatically moving vehicle is shown schematically. The steering system 1 has a first electrical supply unit 2, which is also referred to as battery A in FIG. 1, wherein it is to be illustrated via the index A which components are electrically supplied by the first supply unit 2.

Accordingly, the steering system 1 to a second electrical supply unit 3, which is also referred to as battery B. The supply units 2, 3 are preferably designed as batteries, but not limited thereto. The steering system 1 further includes a first electric motor 4 (also referred to as M _A ) and a second electric motor 5 (also referred to as M _B ) on. The index A thus makes it clear that the first electric motor 4 (M _A ) is supplied by the first supply unit 2 (battery A). The steering system 1 has a hydraulic circuit formed by a sump 6, a pump 7, a servo valve 8 and a hydraulic cylinder 9. The servo valve 8 has four connections, namely one to the reservoir 6, one to the pump 7 and two to the hydraulic cylinder 9. The servo valve 8 can take three switching positions, namely "forward",

"Backward" and "idle", wherein in the illustration of FIG. 1, the servo valve 8 is in "idle. The pump 7 is driven by an electric pump motor 10 (also referred to as PM _A ), which in turn is electrically supplied by the first supply unit 2. The hydraulic cylinder 9 is connected to a rack 1 1, the steering force on the Wheels 12 transmits. Next, the steering system 1, a steering column 13, at the one

Steering handle 14 (e.g., a steering wheel). The steering column 13 is mechanically coupled to the rack 1 1, for example via a not shown gear. The two electric motors 4, 5 sit on a common shaft 15, which is mechanically connected to the steering column 13 and can transmit a torque to the steering column 13. Furthermore, the servo valve 8 is coupled to the steering column 13, so that the switching position of the

Servo valve 8 changed according to the rotation of the steering column 13. For example, the first electric motor 4 has a maximum torque of 15 Nm, whereas the second electric motor 5 has a maximum torque of 1 10-140 Nm (both values) are related to a steering torque, which the driver has to apply to the steering wheel to achieve the same steering result). The second electric motor 5 is preferably dimensioned such that this is the power steering function in manual

Can carry out driving intervention alone. The steering system 1 is fail-operational in terms of single error and can fully meet the requirements due to the automatic driving and the power steering function with manual intervention, the individual cases of error should be briefly explained.

In case of failure of the hydraulic circuit, the first and second electric motor 4, 5 take over the power steering function with manual driver intervention, the sum of the moments is also sufficient to take over all the requirements of automatic driving.

In the event of a failure of the second electric motor 5, the first electric motor 4 together with the intact hydraulics converts the requirements of automatic driving. The hydraulics provide the power steering function if the driver engages manually.

In the event of failure of the first electric motor 4, the larger second electric motor 5 (possibly together with the intact hydraulic system) converts the requirements of automatic driving. The hydraulic or the second electric motor 5 forms the power steering function, if the driver engages manually.

In case of failure of the first electrical supply unit 2 (battery A), the larger second electric motor 5, the power steering function with manual intervention and the implementation of

Requirements for automatic driving safe. In case of failure of the second electrical supply unit 3 (battery B), the first electric motor 4 and the hydraulic power steering function with manual intervention and the

Implementation of automatic driving safe.

Thus, in a single error always both the power steering function as well as the

ensured automatic driving.

If the first and second electric motors 4, 5 are not located on a common shaft 15, the second electric motor 5 can also act directly on the rack 1 1 via an intermediate gear.

The implementation of at least one hydraulic circuit is energetically cheaper than with two sufficiently large-sized electric motors, which individually could apply the steering torque.

FIG. 2 shows a slightly modified embodiment of FIG. 1, wherein identical elements have the same reference numerals. The only difference is that the pump 7 is driven by an internal combustion engine 16. It is only necessary to ensure that the complete necessary electrical control of the internal combustion engine 16 (such as control units) is provided by the first electrical supply unit 2 (battery A).

FIG. 3 shows a third embodiment, wherein the first electric motor 4 and the second electric motor 5 are not arranged on a common shaft 15. Rather, the first electric motor 4 directly controls the servo valve 8 via its shaft 17. In this case, an additional angle of rotation is added to the twist angle of the torsion bar of the power steering (see WO 2010 / 125044A1). The second electric motor 5 can act as shown with its shaft 18 to the steering column 13 or directly on the rack 1 1 attack. In this case, the first electric motor 4 can be applied extremely small, since this does not have to apply a moment to the steering column 13, but only has to overcome the friction in the adjusting mechanism. Here, the difference between the maximum torques of the two electric motors 4, 5 can be at a factor of 100.

4, an alternative embodiment is shown, wherein, in contrast to the embodiments according to FIGS. 1 to 3, two hydraulic circuits are present. The second hydraulic circuit is formed by a separate reservoir 19, a pump 20, a second servo valve 21 and a second hydraulic cylinder 22. The first one controls Electric motor 4, the first servo valve 8 via its shaft 17 and the second electric motor 5, the second servo valve 21 via its shaft 18 at. The pump 20 of the second hydraulic circuit is controlled by a second electric pump motor 23. Since the first hydraulic circuit completely and exclusively by the first supply unit 2 (battery A) and the second hydraulic circuit completely and exclusively by the second

Supply unit 3 (battery B) is supplied, the steering system is fail-operational against single error.

FIG. 5 shows a modification of the embodiment according to FIG. 4, wherein the two electric motors 4, 5 are again arranged on a common shaft 15. In this case, the two servo valves 8, 21 may also be integrated in a common servo valve that has eight leads and three switch positions, as long as only the complete

Separation of the two hydraulic circuits is guaranteed. Of course, one of the electric pump motors 10, 23 in the embodiments according to FIG. 4 or 5 can also be replaced by the internal combustion engine 16 (see FIG. 2).

Claims

claims

1. Steering system (1) for an automatically moving vehicle, comprising at least two independent electrical supply units (2, 3), at least one hydraulic circuit and two electric motors (4, 5), wherein the first electric motor (4) of the first electrical Supply unit (2) and the second electric motor (5) from the second electrical supply unit (3) is supplied with electrical energy, wherein the electric motors (4, 5) are designed such that this a steering torque on at least one component of the steering system (1) apply and / or control a servo valve (8, 21) of the at least one hydraulic circuit.

2. Steering system according to claim 1, characterized in that the at least one

Hydraulic circuit comprises a pump (7, 20) which is drivable by an electric pump motor (10, 23) or an internal combustion engine (16).

3. Steering system according to claim 1 or 2, characterized in that the two

Electric motors (4, 5) are dimensioned such that the maximum torque of the second electric motor (5) is a multiple of the first electric motor (4).

4. Steering system according to one of the preceding claims, characterized in that the first electric motor (4) controls the servo valve (8) of the hydraulic circuit and the second electric motor (5) a steering torque on a steering column (13) or a

Apply rack (1 1) of the steering system (1).

5. Steering system according to one of claims 1 to 3, characterized in that the first electric motor (4) applies a steering torque to the steering column (13) and the second electric motor (5) a steering torque on the steering column (13) or rack (1 1 ).

6. Steering system according to one of the preceding claims, characterized in that the rotational movements of the two electric motors (4, 5) are mechanically connected to each other.

7. Steering system according to claim 1, 2 or 6, characterized in that the steering system (1) has two hydraulic circuits, wherein a servo valve (8) of the first hydraulic circuit by the first electric motor (4) and a servo valve (21) of the second hydraulic circuit by the second electric motor (5) is controllable.

Steering system according to claim 7, characterized in that the two servo valves (8, 21) are designed as integrated servo valve.

Steering system according to one of claims 2 to 8, characterized in that the at least one electric pump motor (10, 23) is controllable such that with increasing load speed or torque are up-regulated.

0. Steering system according to one of the preceding claims, characterized in that the steering system (1) is designed such that a control signal is generated, by means of which different brake pressures are set to the front wheels to produce a steering movement.