GB2399325A

GB2399325A - Steering device with simulated reaction force generation

Info

Publication number: GB2399325A
Application number: GB0402406A
Authority: GB
Inventors: Bernhard Goetz
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2003-02-22
Filing date: 2004-02-04
Publication date: 2004-09-15
Anticipated expiration: 2024-02-04
Also published as: JP2004249983A; FR2852567B1; DE10307567A1; FR2852567A1; GB2399325B; GB0402406D0; JP4518379B2

Abstract

A steering device comprises a steering force simulator and a steering handle 1 which is fastened to a rotatably mounted steering shaft 2 which is in operative connection with an electric steering signal sensor. The steering force simulator generates a frictional braking force acting on the steering shaft 2. An axially movable element, such as a piston 4, can be loaded with an axial force to control the surface pressure of at least one pair of friction surfaces 4a,2a which preferably are metallic and conical. An electromagnet 8 is fastened to a housing 3 and acts on the piston 4 via a lever 9. Alternatively hydraulic pressure may be used in combination with a spring 5. Biasing force and operating force generation are provided. The device may be used in a steer by wire industrial truck.

Description

Steering device with a steering force simulator generating a steering

force The invention relates to a steering device with a steering handle which is fastened to a rotatably mounted steering shaft which is in operative connection with an electric steering signal sensor, and with a steering force simulator generating a steering force and acting on the steering shaft, in which the steering force simulator is designed as a friction brake.

In steering devices of this type, there is no mechanical connection between the steering shaft and the wheels of the vehicle to be steered. Instead, an electric or electrohydraulic control device is controlled by electric signals from the steering signal sensor, the control device being coupled to the wheels to be steered. This so- called "by-wire" technology is used for example in industrial trucks.

As in steering devices of this type there is no feedback about a movement of the wheels to be steered, which is detectable as a steering force by the driver at the steering handle, a steering force simulator is used.

A generic steering device is described in DE 100 33 107 A1. The steering force simulator designated there as a "resistance element" has the task of generating a steering force which is changeable and may depend on various operating parameters, for example the driving speed, the actuating speed of the handle (for example steering wheel) and/or the steering angle. In a preferred embodiment, the steering force simulator has an electro-rheological and/or a magneto-rheological fluid. A steering device of this type is relatively complex, however, and therefore expensive.

Furthermore, it is mentioned in said document that, as an alternative, a damper operating on the principle of mechanical friction can be used, in which the friction force can be changed by a biasing of the friction surfaces. Further details about the construction of a steering force simulator of this type cannot be inferred from the document. 2 1

The object of the present invention is based on providing a steering device of the type mentioned at the outset which is constructed in a functionally reliable and simple manner. I Therefore, according to the present invnetion, a steering device comprises a I steering handle which is fastened to a rotatably mounted steering shaft, which is in operative connection with an electric steering signal sensor, and a steering force simulator generating a steering force and acting on the steering shaft, in which the steering force simulator is designed as a friction brake, and in which the steering! force simulator has an axially movable piston which can be loaded with force in the axial direction to control the surface pressure of at least one pair of friction surfaces.

The pair of friction surfaces may, for example, consist of plane friction surfaces. However, according to a configuration of the invention, it may be more advantageous if the pair of friction surfaces is conical in design. With the aid of conical friction surfaces, with targeted design of the conicity, a small operating force of the steering force simulator can be achieved in a space-saving and simple manner with a minimum operating path (piston stroke), a relatively large steering force nevertheless being achievable.

If the friction surfaces are metallic, the steering force simulator is practically wear-free.

The steering force simulator advantageously has an outer cone and an inner cone arranged on the end face in the piston, the inner cone being designed to receive the outer cone. A reversed arrangement with the outer cone formed on the piston is also possible, in principle.

If the outer cone is formed on the lower end of the steering shaft, a separate component does not need to be produced and fastened to the steering shaft.

In a development of the invention, the steering force simulator has means which are in operative connection with the piston to generate a biasing force and means to generate an operating force.

The operating force here may act in the same direction as the biasing force. A certain basic torque is then generated which is always effective when there is a rotational movement of the steering handle (for example steering wheel). An additional torque generated by the operating force, on the other hand, is variable and is controlled as a function of one or more operating parameters.

Reversing this principle, it is also possible for the operating force to act in the opposite direction to the biasing force. In this instance, the steering shaft and therefore the steering handle are initially blocked by a relatively large biasing force.

The operating force removes this blocking in a controlled manner and reduces the steering force to the extent adapted to the respective operating state.

The biasing force can be applied particularly simply by a spring, in particular a pressure spring.

The operating force can be achieved very easily in that the piston can be hydraulically loaded.

However, it is also possible to load the piston mechanically, in particular electromechanically, to generate the operating force.

It is favourable here if an electromagnet which is connected to an openloop and/or closed-loop control mechanism in operative connection with the piston. The operating force can be adjusted in a targeted manner by controlling the electromagnet with the aid of the open-loop and/or closedloop control mechanism.

According to an expedient configuration of the invention, a pressure spring and a piston rod rest on the side of the piston opposing the cone, in which the end of the rod remote from the piston is coupled to a first lever arm of a lever mounted in an articulated manner, the second lever arm of which is connected to the electromagnet. By skilful selection of the lever conditions, a force intensification can be achieved with the result that the electromagnet available to apply the operating force can be relatively small in size.

An advantageous configuration of the invention provides that the steering force generated by the steering force simulator can be controlled as a function of the rotational speed of the steering shaft and/or the angular position of at least one steered wheel.

A plurality of effects can be achieved thereby: when the steering wheel is rotated too rapidly, in other words when the steered wheels cannot follow the rotational movement of the steering handle quickly enough, the steering force can be increased in a manner which can be clearly detected. The driver therefore receives analogous feedback.

It is also possible to increase the steering force if one steered wheel (or both) is located at the stop. Finally, the steering force may also be controlled proportionally to the lock of the steered wheels or to the rotational angle of the steering handle. In this case, the steering force rises continuously for small steering radii (large steering lock) when cornering. Therefore, for example in a fork-lift truck, tipping over is prevented to a greater degree. Additional influencing of the steering force is also possible as a function of the existing driving speed.

If the piston is arranged in a housing in which the steering shaft is mounted, no separate housing is required for the steering force simulator.

The steering signal sensor is also expediently arranged in the housing, for example axially between two rolling bearings provided to mount the steering shaft.

According to a further configuration of the invention the housing is liquid-tight in design at least in the region of the piston. Therefore the piston can be loaded with pressured hydraulic fluid in the simplest manner, the operating force being controlled to the desired degree by pressure modulation. The fluid pressure can be diverted from a system which is present in any case in the vehicle, so the outlay is limited to a suitable pressure modulation mechanism.

The use of the steering device according to the invention is particularly advantageous in an industrial truck since the driving behaviour and the driving safety are favourably influenced.

Further advantages and details of the invention will be described in more detail with the aid of the embodiment shown in the schematic figures, in which: Fig. 1 shows a section through a steering device according to the invention land Fig. 2 shows a section through a variation of the steering device according to the invention.

The steering device has a steering handle 1 designed in the present embodiment as a steering wheel and fastened to the end of a steering shaft 2. The steering shaft 2 is mounted in a housing 3 by rolling bearings not shown in the figures and has an outer cone 2a formed on its end opposing the steering handle 1.

A steering signal sensor, not shown in the figures, is preferably also arranged in the housing 3.

Located below the steering shaft 2 is an axially movable piston 4 secured against rotation in the housing 3, which piston 4 has, on its front end facing the steering shaft 2, an inner cone 4a into which the outer cone 2a of the steering shaft 2 dips. The piston 4 is loaded by a pressure spring 4 in the direction of the steering shaft 2, the pressure spring 5 generating a biasing force. The inner cone 2a, in conjunction with the piston 4 and the incorporated outer cone 4a as well as an actuating mechanism still to be described, forms a steering force simulator.

Depending on how great the surface pressure generated by axial pressure on the piston 4 is between the conical friction surfaces, the steering handle 1 can be turned with more or less ease or difficulty. The steering force can be adjusted in a targeted manner by a master open-loop and/or closed-loop control mechanism which is in operative connection with the actuating mechanism of the piston 4.

The housing 3 which is liquid-tight in design is provided at the lower end with a connection 6 which is connected to a hydraulic line. The piston 4 provided with a sealing ring tpiston ring) 7 can thus be loaded in the same direction as the biasing force of the pressure spring 5 by a hydraulically generated operating force.

Owing to the biasing force and the operating force, a steering force is achieved owing to the effect of the pair of friction surfaces which are preferably metallic and therefore practically wear-free, and formed by the outer cone 2a and the inner cone 4a, the steering force counteracting the actuating force when the steering handle 1 is rotated and bringing about feedback for the operator. The biasing force thus generates a constantly effective small steering force. In addition, an operating force which is dependent on various operating parameters is generated hydraulically.

This may be a steering force fraction, for example, which is dependent on the vehicle speed and/or the steering angle and/or the steering speed (detected by the steering signal sensor). In order to be able to vary the operating force, the hydraulic pressure acting on the piston is modulated by a suitable device.

In the variation shown in Fig. 2 of the steering device according to the invention, the piston 4 is not loaded hydraulically in the direction of the steering shaft 2, but electromechanically, to generate the operating force.

For this purpose, an electromagnet 8 is provided which is fastened outside the housing 3 and is in operative connection with an open-loop and/or closed-loop control mechanism. A first lever arm 9a of a lever 9 mounted in an articulated manner on the housing 3 is coupled to a piston rod 10 which dips axially into the housing 3 and acts there against the piston 4. A second lever arm 9b of the lever 9 is coupled to the electromagnet 8.

The conical configuration of the pair of friction surfaces proves to be of great advantage for the actuation of the piston 4 by the electromagnet 8, as only a minimum operating path (stroke of the piston 4 or the piston rod 10) is required to generate a relatively large surface pressure between the inner cone 4a and the outer cone 2a and therefore a relatively large steering force. The electromagnet 8 therefore only needs to carry out a relatively small stroke and this has a favourable effect on the constructional size thereof and also the production costs.

Claims

Claims 1. A steering device comprising a steering handle which is fastened

to a rotatably mounted steering shaft, which is in operative connection with an electric steering signal sensor, and a steering force simulator generating a steering force and acting on the steering shaft, in which the steering force simulator is designed as a friction brake, and in which the steering force simulator has an axially movable piston which can be loaded with force in the axial direction to control the surface pressure of at least one pair of friction surfaces.
2. A steering device according to claim 1, characterised in that the pair of friction surfaces is conical in design.
3. A steering device according to claim 2, characterised in that the friction surfaces are metallic.
4. A steering device according to claim 2 or 3, characterised in that the steering force simulator has an outer cone and an inner cone arranged on the end face in the piston, the inner cone being designed to receive the outer cone.
5. A steering device according to claim 4, characterised in that the outer cone is formed on the lower end of the steering shaft.
6. A steering device according to any one of claims 1 to 5, characterised in that the steering force simulator has means which are in operative connection with the piston to generate a biasing force and means for generating an operating force.
7. A steering device according to claim 6, characterised in that the operating force acts in the same direction as the biasing force.
8. A steering device according to claim 6, characterised in that the operating force acts in the opposite direction to the biasing force.
9. A steering device according to any one of claims 6 to 8, characterised in that a compression spring is provided as the means to generate the biasing force.
10. A steering device according to any one of claims 6 to 9, characterised in that the piston is hydraulically loaded.
11. A steering device according to any one of claims 6 to 9, characterised in that the piston is electromechanically loaded.
12. A steering device according to claim 11, characterised in that an electromagnet,which is connected to an open-loop and/or closed-loop control mechanism, is in operative connection with the piston.
13. A steering device according to claim 12, characterised in that resting on the side of the piston opposing the friction surfaces, are a pressure spring and a piston rod, in whcih the end of the rod remote from the piston is connected to a first lever arm of a lever mounted in an articulated manner, a second lever arm of which is connected to the electromagnet.
14. A steering device according to any one of claims 1 to 13, characterised in that the steering force generated by the steering force simulator is controlled as a function of the rotational speed of the steering shaft and/or the angular position of at least one steered wheel.
15. A steering device according to any one of claims 1 to 14, characterised in that the piston is arranged in a housing, in which the steering shaft is mounted.
16. A steering device according to claim 15, characterised in that the steering signal sensor is arranged in the housing.
17. A steering device according to claim 15 or 16, characterized in that the housing is liquid-tight in design at least in the region of the piston.
18. A steering device according to any one of claims 1 to 17, characterized by use in an industrial truck.