GB2103161A - Rotational value indicator device - Google Patents

Abstract

A device (10) for indicating relative angular rotation of two shaft portions (5, 6), which is coupled to the two shaft portions and permits any number of revolutions, comprises an output element (17) which is movable in response to relative rotation between the two shaft portions (5, 6). The device is particularly applicable to an assisted steering system with a divided shaft (1) whose portions are connected for limited relative rotation by means of a torsion element (7) between upper and lower shaft portions (5, 6), and wherein a differential gear system (12) with two inputs (23, 24) is provided, with the output of the gear system being coupled to the value indicator (10) which controls the servomotor (8). <IMAGE>

Description

SPECIFICATION Rotational value indicator device This invention relates to a device for indicating differences in angular rotation of two shaft elements which are rotatable relative to one another, and is particularly concerned with the application of such a device to an assisted sterring system for a vehicle.

The invention is particularly concerned with a device for indicating angular rotation when applied to the control of an assisted steering system comprising a shaft divided into upper and lower shaft portions, especially a sterring shaft, where the portions are connected by a torsion element between the upper and lower shaft portions and where there are end stops for limiting the relative rotation of the parts. The shaft portions are coupled together by the device particularly in order to control a servomotor for the lower shaft portion.

Devices for indicating angular rotation and used as assisted steering arrangements are known for example from German published patent specification 26 58 697. There, the torsion element consists of a resilient sleeve which is expansible in the circumferential direction. With this sleeve is associated a diagonal rod in order to limit the extent of the relative rotation between the shaft portions. This diagonal rod which is arranged on one of the shaft portions engages in oversized apertures in the other shaft portion.

It is also known to produce a signal by relative rotation of the shaft portions with respect to one another, for example by means of a magnet on one shaft portion and a differential field plate sensor on the other shaft portion, or, according to German published patent application 26 59 473, by an inductive coupling of a magnet arrangement, and to pick off this signal either by means of a wound conductive strip or by some other conductor. According to German published patent application 14 80 205 it is also known to connect the shaft portions by a hydraulic iinkage by means of which a control valve can be actuated.

All these arrangements have the disadvantage that they require considerable constructional expenditure, and, above all, that the shaft, talking in terms of its parts, can only be rotated through a given arc, since the connection cannot be maintained over a plurality of revolutions. The known connections are subject to the effects of contamination and wear which can vary the function constants. Moreover, error effects can arise in the known, contact-free co-operating elements on the shaft portions due to misalignments.

It is an object of the present invention to improve the type of device first referred to above, in that the shaft portions are able to rotate relative to one another with absolute freedom, and the device responds to only a particularly limited relative rotation between the shaft portions.

Additionally, the device can be made as a robust structure which operates reliably and substantially maintenance-free and with its function constants remaining uniform even over long periods of time.

This is achieved in accordance with the present invention by a value indicator device responsive to the angular rotation of two shaft portions which are rotatable relative to one another, characterised in that the device, which is coupled to both shaft portions and permits any number of rotations, has an output element which is movable in response to a difference in the rotational speeds of the two shaft portions resulting in a limited relative rotation between the shaft portions.

By this means both shaft portions are inelastically coupled to the value indicator device which is arranged to function co-operatively with a signal element in a contact-free manner, with the signal element being moved only in dependence upon the, possible proportional, especially limited relative rotation between the two shaft portions.

In a preferred embodiment of the invention the two shaft portions are coupled by a mechanical coupling to two inputs of a gear system which has its output coupled to the value indicator device and which is movable in dependence upon a differential rotational speed at the two inputs. By means of the mechanical coupling one ensures a reliable connection which does not produce any output indication so long as the rotational speeds at the two inputs remain the same. Consequently, a robust structure can be created. Preferably, a differential gear system is used as the gear system, having planet wheels drivable in opposite senses by the respective shaft portions, with the shafts which carry the planet wheels being mounted rotatably, and with a common shaft for two equalising bevel gears constituting the output element of the indicator device.By the use of a differential gear system one solves the problem with simple means, while also achieving a high operational accuracy.

Preferably, one shaft portion is connected directly to a drive pinion of one planet wheel to drive it in the same rotational sense through a first driving link means, while a drive pinion of the other planet wheel is associated in the framework of the differential gear system with a reversing gear by way of a second driving link means, said second driving link means driving both a pulley on the other shaft portion and also the reversing gear with its one side and driving the pinion of said other planet wheel with its other side. The term "driving link means" used herein is to be understood as including belts, chains or other equivalent link members.It is preferred to use toothed belts, and indeed toothed belts which are formed as double-faced belts with profilings on both the inside and the outside, with the driving pulleys and pin ions being corrrespondingly provided with profilings.

Basically, the mechanical coupling to the two inputs can be simplified by the use of an intermediate gear even when using a differential gear system.

If a rigid connection to the value indicator device is provided, then, according to the preferred embodiment of the invention, the output element is designed to have a contact-free influence on the signal generator of the indicator device. The contact-free effect on the signal generator can be used capacitively or inductively for the servomotor or for something else which responds to measured values. Preferably, a contact-free optical effect is used with a mask arranged on the output element which is movable between two photoelectric diode-transistor pairs which are connected rigidly to the frame. Due to the freedom from contact in the transition movement, oscillations which occur in use can be equalised, whereby the accuracy and sensitivity can be improved. Moreover, influences arising from dirt, contamination and the like are substantially excluded.

In another embodiment of the invention the output element is coupled to an adjusting lever which is mechanically connected to an error indicator of the value indicator. The error indicator may be a potentiometer or a control member for some other operational control circuit, for example with hydraulic operating means.

In order that the invention may be fully understood a preferred embodiment of device in accordance with the invention will now be described by way of example and with reference to the accompanying drawing, in which: Fig. 1 is a schematic side view of the device as applied to a steering shaft; and, Fig. 2 is a plan view of the device shown in Fig. 1.

In Fig. 1 there is shown by way of example a steering shaft 1 which has a manually operated steering wheel 2 at one end and which is connected at the other end to a steering gear mechanism 3 for a steerable wheel 4 of a vehicle.

This steering shaft 1 is divided into an upper shaft 5 and a lower shaft 6, these being connected together by a torsion element 7, for example in the form of a resilient sleeve with an end stop (for example similar to what is shown in West German published patent specification 26 58 697) The lower shaft 6 is driven by a servomotor 8 by way of an operational link 9, for example in the form of a belt drive. The servomotor 8 is controlled by a value indicator 10 by way of an operational link 11.

The value indicator 10 includes a differential gear system 12 in the illustrated embodiment.

This comprises two planet wheels 13, 14 and two equalising bevel gears 15, 1 6 which are mounted on a common shaft 17.

The planet wheels 13 and 14 are mounted on respective shaft 18, 19 which are mounted so as -to be freely rotatable in bearings 21, 22 in a base plate 20. The planet wheel shafts 18, 19 carry respective drive pinions 23, 24 of equal diameter.

Drive pulleys 25, 26 are arranged on the main shaft portions, i.e. the upper shaft 5 and the lower shaft 6, in alignment with the drive pinions 23, 24. Driving belts 27, 28 are guided around these drive pulleys 25, 26, with drive belt 28, which is shown in broken lines in Fig. 2, engaging drive pinion 24, while the other drive belt 27 is guided around a reversing pulley 30 which is mounted on the base plate 20 or on a bearing pad 29 of the base plate, and is thus reversed by its movement around this pulley. Thus, driving belt 27, which is formed as a double driving belt provided with profilings on both sides, has its outer side in cooperating engagement with the drive pinion 23.

If the steering shaft 1 with its shaft positions 5 and 6 is driven at uniform speed, there will be no reaction at the differential gear system 12.

However, as soon as there is a relative rotation between the upper shaft 5 and the lower shaft 6, for example as a result of a movement of the steering wheel 2, the planet wheels 13, 14 are driven in different ways accordingly. As a result, the differential gear system 1 2 pivots as a unit in the bearing 21,22, and the horizontal shaft 17, which functions as a pointer element of the value indicator 10, is moved pivotally to a degree determined by the difference in the angular rotation between the upper shaft 5 and the lower shaft 6.

In connection with this it will be understood that the differential gear system 12, with which there is associated a cage for the gearing in a manner known per se, does not need to be described further.

Furthermore, it will be evident that the starting condition will be maintained for so long as the upper shaft 5 and the lower shaft 6 rotate synchronously at constant speed. The number of revolutions is unlimited. The cage of the differential gear system 12 is not pivotally rotated due to the reversal of the direction of rotation at the planet wheels 13 and 14.

As soon as there is a relative rotation between the upper shaft portion 5 and the lower shaft portion 6, i.e. the rotational speed of the two shaft portions differs for a short time, the differential gear system 12 and its cage are pivotally rotated through an angle /3. This is governed by the following equation.

where d2 is the diameter of pulleys 25 and 26, dl is the diameter of the drive pinions 23 and 24, and a is the angular difference or offset between the upper shaft portion 5 and the lower shaft portion 6.

The value indicator 10 includes a signal generator comprising elements 31 and 32 which, for example, having reference to Fig. 2, may be two photoelectric diode-transistor pairs, indicated at 31, 31' and 32, 32'. The pointer element 17 which carries a mask 33 is movable between these photoelectric elements, so that the transmission of light between the respective pairs of elements is varied, and is wholly freed so far as one pair is concerned with increasing angle /3. The provision of two pairs has the advantage of determining the direction of rotation of the servomotor 8.

It will be appreciated that appropriate measured value signal generators operating in an inductive or capacitive way may be provided in the drive circuit of the servomotor 8, or alternatively, a mechanically coupled ohmic potentiometer may be provided.

If one uses the arrangement of two photoelectric diode-transistor pairs 31,31 and 32, 32' to develop a signal which is dependent on the direction of rotation, then it will be appreciated that the operational link 11 can have two channels with one signal being transmitted in each channel.

Where reference is made to a controlling of the servomotor, it is to be understood in this connection that this includes also a clutch which takes care of the driving of the lower shaft portion only for the case of the assisted drive. The servomotor either drives both shaft portions with synchronous rotation without the introduction of torque, or alternatively it is disconnected from the drive connection to the lower shaft portion 6.

Claims (11)

Claims

1. A value indicator device responsive to the angular rotation of two shaft portions which are rotatable relative to one another, characterised in that the device, which is coupled to both shaft portions and permits any number of rotations, has an output element which is movable in response to a difference in the rotational speeds of the two shaft portions resulting in a limited relative rotation between the shaft portions.

2. A device in accordance with claim 1, adapted for the control of an assisted steering system with a shaft divided into upper and lower shaft portions which are connected by a torsion element and end stop means for limiting relative rotation of the shaft portions in opposite directions, with the value indicator device being coupled to the shaft portions and controlling a servomotor for the lower shaft portion, in which the two shaft portions are coupled by a mechanical coupling to two inputs of a gear system which has its output coupled to the value indicator and which is movable in dependence upon a rotational speed difference at the two inputs.

3. A device in accordance with claim 2, in which the gear system is a differential gear system having planet wheels drivable in opposite senses by the shaft portions, in which the planet wheels are mounted for rotation on respective shafts, and in which the output element of the value indicator comprises a shaft on which two equalising bevel gears meshing with the planet wheels are mounted.

4. A device in accordance with claim 3, in which one shaft portion is connected directly to a driving pinion of one planet wheel to drive it in the same rotational sense through a first driving link means, while a driving pinion of the other planet wheel is associated in the framework of the differential gear system with a reversing gear by way of a second driving link means, said second driving link means driving both a pulley on the other shaft portion and also the reversing gear with its one side and driving the pinion of said other planet wheel with its other side.

5. A device in accordance with claim 4, in which the link means comprise driving belts, the second belt being formed as a double-faced belt with profiled regions on both sides, and in which the driving pulleys on the shaft portions and the driving pinions are correspondingly provided with profiled regions.

6. A device in accordance with any of claims 3 to 5, in which the output element is arranged to have a contact-free influence on the value indicator.

7. A device in accordance with claim 6. in which a mask is provided on the output element and is movable between photoelectric sensors which are connected rigidly to the frame.

8. A device in accordance with any of claims 3 to 5, in which the output element is coupled to a lever which is mechanically connected to an error indicator of the value indicator.

9. A device in accordance with claim 8, in which an ohmic potentiometer is provided as the error indicator.

1 0. A device in accordance with claim 8, in which a hydraulic control circuit comprising a control slide valve is provided as the error indicator.

11. A value indicator device substantially as hereinbefore described with reference to the accompanying drawings.