GB2074760A

GB2074760A - Vehicles having servo-steering systems

Info

Publication number: GB2074760A
Application number: GB8112687A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1980-04-25
Filing date: 1981-04-24
Publication date: 1981-11-04
Also published as: GB2074760B; DE3015955A1; SE8102612L; DE3015955C2; SE454029B; IT1135760B; IT8121254A0

Abstract

A vehicle having at least two servo- steering systems (20,21,22 and 23,24,25) is provided with a safety device by which the two steering systems are switched on alternately (26) in a predetermined sequence the function of the two steering systems being continuously monitored and, upon the occurrence of a fault, the trouble-free steering system is switched on or remains switched on. In the case of trackless vehicles guided by a guide cable, continuous monitoring is effected by superimposing on the field of the guide cable a diagnostic field from a diagnostic transmitter (31), and checking whether the steering systems process this diagnostic field correctly with respect to function. For this purpose a microprocessor (30) compares the received diagnostic signal with a reference, and also compares with input to a functioning hydraulic unit (22,25) with its output to the steering gear (13). <IMAGE>

Description

SPECIFICATION Vehicles having servo-steering systems The invention relates to a safety device of the type set forth in the main claim.

When operating vehicles having servo-steering systems, failure of a system component may endanget the vehicle if special measures are not taken.

Therefore complex electronic/hydraulic systems are normally rendered fail-safe by duplication or even triplication.

Three mutually independent individual systems are generally used, their action variables are compared and a majority decision of two out of three is made. That variable of the three variables to be compared which differs from the other two variables is considered to be erroneous by a monitoring unit.

The monitoring unit then renders the corresponding faulty partial system safe by, for example, switching it off.

The problems which have been described are particularly important in the case of electronically guided trackless vehicles, that is to say, systems in which a vehicle which does not run on rails is guided along a wire which is laid along the desired path of travel and which has current flowing therethrough.

Failure of a system component with the attendant failure of a servo-steering system would then cause the vehicle to deviate from the desired path ("derail"). When known concepts are used, a reliable electronic path guide having a steering system rendered fail-safe by triplication requires three servo-steering systems and a monitoring unit. Thus, the reliable electronic path guide is more than three times as extensive as a normal track guide. This implies a considerable increase in cost, particularly the cost of the hydraulic part.

The present invention resides in a safety device for a vehicle having at least two servo-steering systems, the safety device including a control device for switching on the steering systems alternately one at a time in a predetermined manner and for monitoring the function of the steering systems continually, whereby, upon the detection of a fault in a steering system, the fault-free steering system is switched on or remains switched on.

This has the advantage that only two servosteering systems and one control device are required. This renders the safety device considerably less complicated and thus reduces the manufacturing costs.

Thus, in a preferred embodiment of the invention, a particularly simple and advantageous monitoring facility for an electronic part of each servo-steering system is provided by producing a diagnostic field which acts upon the antenna arrangements of a trackless vehicle which is guided by a guide cable laid along the desired path of travel.

The invention is further described, by way of example, with reference to the drawing in which, the single Figure is a block-circuit diagram of an embodiment of a safety device, in accordance with the invention, for a vehicle guided by a guide cable.

In the safety device, illustrated in the Figure, for a vehicle guided by a guide cable laid along the desired path of travel, a drive motor 10 of the vehicle drives two wheels 11,12 by way of a steering gear 13. Two servo-steering systems act on the steering gear 13, the first of which steering systems comprises a first antenna arrangement 20, a first electronic unit 21 and a first hydraulic unit 22, and the second steering system comprises a second antenna arrangement 23, a second electronic unit 24 and a second hydraulic unit 25. The antenna arrangements 20, 23 transmit their signals to the electronic units 21,24 which control the hydraulic units 22, 25 which in turn act upon a multiplexer 26 which is operatively connected to the steering gear 13.The servosteering systems are controlled by a control device 30, preferably a microprocessor, which receives input signals from the electronic units 21,24, the hydraulic units 22, 25 and the output of the multiplexer 26. Furthermore, the control device 30 is triggered by a diagnostic transmitter 31 which is connected to a transmitting antenna 32. Furthermore, the control device 30 has a first indicating element 40 and a second indicating element 41.

Finally, the first hydraulic unit 22 is connected to a first pump 50 which is driven by the drive motor 10, while the second hydraulic unit 25 is connected to a second pump 51 which is driven by the driven wheel 11.

The mode of operation of the device illustrated in the Figure is as follows: The antenna arrangements 20,23 scan the field of the wire which is laid along the desired path of travel and which has current flowing therethrough. The output signals of the antenna arrangements 20,23 are fed to the electronic units 21, 24 which ascertain from the received signals the actual deviation of the vehicle from the guide wire and, in conformity with this deviation, influence the steering gear 13 of the vehicle by way of the hydraulic units 22,25 and the multiplexer 26.

The two servo-steering systems, 20, 21, 22 and 23, 24,25 are operated such that the multiplexer 26 switches on one servo-steering system and switches over to the other servo-steering system after a predetermined short period of time. Preferably, the "on" period of a servo-steering system is dimensioned such that the vehicle can be reliably braked during the "on" period.

In the safety device illustrated in the Figure, the diagnostic transmitter 31 is provided for continuous monitoring of the servo-steering systems. This transmitter produces by way of the transmitting antenna 32 an electromagnetic field which is received by the two antenna arrangements 20, 23 as though it were a field around the guide cable having current flowing therethrough. The individual anten- nae are arranged such that a predetermined deviation "antenna arrangement - apparent cable" is detected in the electronic units 21, 24 by the diagnostic field emitted by the diagnostic transmitter 31.The electronic units 21, 24 ascertain therefrom a diagnostic desired steering angle (3* soll 1 or (3* soll 2 which is fed as an electrical signal to the control device 30. The control device 30 compares the prevailing diagnostic desired steering angle with a predetermined reference value. It is thereby possible continuously to check the function of the electronic units 21,24, that is to say, over the entire period of operation. Checking of the hydraulic units 22,25 is only possible for the servo-steering system which has just been put into operation.If, for example, the first servo-steering system has been put into operation, the output of the electronic unit 21 produces a signal which corresponds to the desired steering angle ss* soll 1 and which serves to control the hydraulic unit 22. This signal is compared with the signal at the output of the multiplexer 26, so that the function of the hydraulic branch of the servosteering system which is operative at any given time is continuously tested by comparing the input and output signals of the said hydraulic branch. If the multiplexer 26 switches over to the second servosteering system, the function of the hydraulic part is monitored in the same manner.

Advantageously, the two hydraulic units are supplied by different drives, namely by the drive motor 10 on the one hand and, on the other hand, by a driven wheel 11. Thus, on the one hand, the servo power can be produced when the vehicle is stationary and when the drive motor 10 is running and, on the other hand, when the vehicle is rolling and when the drive motor 10 is switched off.

If a fault occurs in one of the servo-steering systems, this fault is detected in the manner which is further described above. The detection of a fault in a servo-steering system in the first instance causes the corresponding indicating element 40 or 41 to be switched on for the defective servo-steering system.

Furthermore, the control device 30 causes the trouble-free servo-steering system to be switched on by the multiplexer 26, orto remain switched on.

Finally, in the case of driverless operation, automatic braking of the vehicle is initiated until it comes to rest.

Claims

1. A safety device for a vehicle having at least two servo-steering systems, the safety device including a control device for switching on the steering systems alternatively one at a time in a predetermined manner and for monitoring the function of the steering systems continually, whereby, upon the detection of a fault in a steering system, the fault-free steering system is switched on or remains switched on.

2. A safety device as claimed in claim 1, which is adapted to bring the vehicle to rest in the event of a fault.

3. A safety device as claimed in claim 1 or 2, in which the vehicle is a guided trackless vehicle, and in which each servo-steering system comprises a respective antenna arrangement adapted to detect a wire which is laid along the desired path of travel and which has current flowing therethrough, a respective electronic unit connected to its antenna arrangment and a respective hydraulic unit which is controlled by the electronic unit and which is adapted to act upon the steering gear of the vehicle.

4. A safety device as claimed in claim 3, which further comprises a diagnostic having a transmitting antenna which is operatively coupled with the antenna arrangements for producing diagnostic sig nals in the latter.

5. A safety device as claimed in claim 4, in which each electronic unit contains switching means in which a diagnostic desired steering angle is formed from diagnostic signals received by the respective antenna arrangement, the diagnostic desired steering angle being compared with a predetermined reference value and, upon exceeding a predetermined deviation, an indication for the corresponding servo-steering system is triggered.

6. A safety device as claimed in any preceding claim, in which the servo-power is derived from a drive motor of the vehicle.

7. A safety device as claimed in anyofclaimsl to 5, in which the servo-power for one steering system is derived from a drive motor of the vehicle, and the servo-power for the other steering system is derived from a wheel of the vehicle.

8. A safety device for a vehicle constructed and adapted to operate substantially as herein described with reference to and as illustrated in the drawing.