WO2005028285A1

WO2005028285A1 - Safety coupling for steering systems

Info

Publication number: WO2005028285A1
Application number: PCT/EP2004/008880
Authority: WO
Inventors: Christian Staudenmann; Reto Emmenegger
Original assignee: Thyssenkrupp Automotive Ag
Priority date: 2003-09-06
Filing date: 2004-08-07
Publication date: 2005-03-31
Also published as: DE10341157A1

Abstract

The invention relates to a steer-by-wire steering system comprising a safety coupling (1) interposed between the steering device (20) and the steering actuator (22, 23, 25, 27, 24). Said steering coupling force-couples a driving shaft (3) and a driven shaft (2) with each other when normal operation is disrupted, thereby allowing a direct mechanical actuation of the steering actuator (22, 23, 25, 27, 24) by the steering device (20). The safety coupling (1) comprises an actuating element (5) which, in normal operation, is maintained in an open position by a restoring force. In said open position, the safety coupling (1) is disengaged. Once the restoring force is no longer exerted, the actuator can be restored axially to the closed position by the force of an energy accumulator. The safety coupling is further provided with means (11) which bring form-fit elements (7) in a position that establishes a form fit between the driving shaft (3) and the driven shaft (2).

Description

Safety clutch for steering systems

description

The invention relates to a steering system according to the preamble of patent claim 1.

Such steering systems are known from the prior art (EP 0 981 473 B1; DE 100 15 922 A1). EP 0 981 473 B1 discloses a safety clutch for steering systems which operate according to the "steer-by-wire" principle. In these steering systems, the steering actuator is controlled in normal operation by means of an electronic control unit, ie by the driver via the steering means (For example, a steering wheel) output control signals are given to an electronic control unit, processed there, and then the control unit sends the new control signals received after processing to the steering actuator. "Normal operation" here means operation without disturbing the power supply to the vehicle. It is understood that e.g. in the event of a total failure of the power supply, the “steer-by-wire” steering no longer works. In this case, a mechanical safety coupling must therefore be provided, which becomes effective in the event of a power failure and establishes a mechanical coupling between the steering means and the steering actuator so that the vehicle can be safely controlled even in the event of a power failure.

In the safety clutch proposed for this purpose in EP 0 981 473 B1, it is provided that the clutch is constantly acted upon by a closing force and can be disengaged against the closing force by an actuator which becomes effective by the supply of energy (cf. claim 3; column 2, line 48 to column 3, row 1). The actuator actuating the clutch can be designed as an electromagnetic actuator (cf. claim 4; column 9, lines 2 until 10). However, EP 0 981 473 B1 does not disclose how such an electromagnetic actuator can be constructed. Furthermore, in this document in column 3, line 29, there is the general note that the coupling can work in a force-fitting and / or form-fitting manner, but no embodiment is disclosed in which a form-fitting coupling is used. Instead, only embodiments with a non-positive clutch (claim 9), in particular multi-plate clutch (claim 10), as well as a hydraulic actuator (Fig. 2) are described.

To e.g. in the event of a power failure to ensure safe torque transmission by the force-locking multi-plate clutch disclosed in EP 0 981 473 B1, the spring which acts on the clutch with the permanently effective closing force must be dimensioned so large that its spring force is sufficient to ensure the force closure in the Ensure clutch. However, this means that, during normal operation, a restoring force that counteracts the spring force must be applied, which is greater than the spring force, so that the safety clutch is held in the disengaged, opened state. The energy required to apply this restoring force is therefore very large.

The same disadvantage exists in the steering system known from DE 100 15 922 A1. Here, too, the safety clutch works in a force-locking manner, and the energy required to hold the clutch in the disengaged state is high, since the high spring force required for a force-locking connection has to be overcome.

The invention has for its object to propose a steering system according to the preamble of claim 1, in which the energy expenditure for holding the safety clutch in the disengaged state is minimal during normal operation.

This object is achieved in that means are provided with which positive locking elements can be moved into a position producing a positive locking between the drive shaft and the output shaft, and in that the means are are arranged so that they move the positive locking elements into the position producing the positive locking during the transfer of the actuating element from the open to the closed position.

In the invention, the safety clutch works in a form-fitting manner, so that the spring force required for safe engagement does not have to be as great as in the case of a non-positive coupling. It is sufficient if the spring force is sufficiently large to move the interlocking elements provided according to the invention into a position in which they bring about the interlocking between the input and the output shaft. Since the form-locking elements e.g. can be designed as rolling elements, the force required to move the form-locking elements into the position producing the form-fitting connection is very low compared to the force required to produce a force-fit connection in the case of a force-fit coupling according to the prior art. On the one hand, this has the advantage that the restoring force required for keeping the clutch open during normal operation is also low, as a result of which the energy expenditure required to generate the restoring force is minimal. On the other hand, the spring also requires less installation space, since it can be dimensioned considerably smaller. Such a smaller spring also weighs less, which also saves weight.

In an advantageous embodiment of the invention, the electromagnetic unit with which the restoring force counteracting the spring force is generated is designed as a current-flowable coil which is arranged coaxially with the drive shaft. In this case, in order to achieve a small, compact design of the clutch, it is advantageous if the actuating element is designed as a sleeve arranged coaxially with the drive shaft and thus also with the coil. With this design, the current-carrying coil takes on the function of a lifting magnet and the actuating element that of the armature of the lifting magnet.

In principle, the invention also works when the actuating element is surrounded by the coil, that is to say that the inner diameter of the coil is larger than the outer diameter of the actuating element. In this case, however, one would have to surround the coil with an outer cover (eg made of steel) in order to ensure the magnetic return flow. This would be expensive and would mean that an additional component, namely the outer shell, must be provided. It would also be necessary to manufacture the drive shaft from a special weak magnetic material. This is complex and increases the costs.

It is therefore a preferred embodiment of the invention if the sleeve-shaped actuating element at least partially surrounds the coil. As a result, the actuating element acts as an external armature of a lifting magnet, and the magnetic backflow can take place via the external actuating element. An additional outer shell is no longer required. It is also not necessary to manufacture the drive shaft from a weakly magnetic material. This leads to simpler construction and lower manufacturing costs.

In order to achieve a structurally simple construction of the coupling, it is expedient if the means for moving the interlocking elements are connected directly to the actuating element. As a result, additional connecting parts between the actuating element and the means can be avoided. The structural design is particularly simple if the actuating element and the means form a single integral component.

In order to produce the positive connection for torque transmission between the drive shaft and the driven shaft, the positive-locking elements in a preferred embodiment of the invention are designed as rolling elements which are held in a cage which is connected to the drive shaft in a rotationally fixed manner. At the same time, recesses are provided on the end of the output shaft facing the drive shaft, which recesses serve to receive the rolling elements and for this purpose have a shape that corresponds to the external shape of the rolling elements. If the rolling elements have been moved into the recesses by the actuating element, then the positive connection is established and torques can be introduced from the drive shaft via the cage to the rolling elements and from these then via the recesses into the output shaft. To produce the form-fitting coupling of the input and output shafts, only the Rolling elements are moved by the actuating element into the recesses of the output shaft. For this purpose, a much smaller force is required than would be required to establish a force fit in the case of a force fit clutch. The spring force required for moving the actuating element can therefore be selected to be very low. This in turn means that the restoring force required to hold the clutch in the disengaged state is correspondingly low, so that the energy expenditure for generating the restoring force is minimized.

The cage holding the rolling elements can be designed as a separate component which is non-rotatably connected to the drive shaft, e.g. is screwed. However, a simpler and more robust construction is achieved in that the cage is formed in one piece with the drive shaft.

In a preferred embodiment of the invention, the rolling bodies are designed as balls and the recesses in the output shaft as axially extending, essentially semicircular longitudinal grooves. The radius of these essentially semicircular longitudinal grooves is chosen so large that the rolling elements can penetrate into the recesses at least as far as is necessary to achieve the necessary positive locking for torque transmission.

If the actuating element is designed as an essentially cylindrical sleeve, the means for moving the interlocking elements can be formed simply and in a space-saving manner by the inner contour of a bore arranged in the sleeve at its end facing the output shaft. A suitable bore has at least one cylindrical section, the inside diameter of which is adapted to the outside diameter of the drive shaft. When the clutch is in the engaged state and consequently the form-fitting elements designed as rolling elements are located in the recesses of the output shaft, the cylindrical section of the bore at least partially covers the recesses and thus holds the rolling elements firmly in the recesses. In this way, the rolling elements cannot escape radially from the receptacles and the form fit is ensured. Furthermore, the bore has a section which widens conically from the cylindrical section in the direction of the output shaft. This conical section serves to move the rolling elements into the recesses during the movement of the actuating element from the open to the closed position. Since the rolling elements can roll on the conically inclined surface of this bore section, no canting or other problems can occur and a flow-free movement is guaranteed.

In the simplest case, the actuating element is moved from the open to the closed position by axial displacement, i.e. through a translational movement. However, it is also possible to hold the actuating element on its outer circumference in a screw guide, so that the force exerted by the spring on the actuating element is converted into a guided screw-rotating movement of the actuating element.

As an alternative to the design as a rolling element, the interlocking elements can also be designed, for example, as a toothed ring which is seated on the drive shaft in a manner that is fixed against rotation and axially displaceable. If the actuating element is moved into the closed position, it pushes the ring gear axially in the direction of the output shaft and engages it with a corresponding toothing of the output shaft. In this embodiment, too, the energy expenditure for producing the positive connection is very much lower than the energy expenditure necessary for producing a frictional connection.

Basically, it is not primarily a question of the invention how the form fit is implemented in a constructive manner. There are several options for this, which are known in principle to the person skilled in the art. Rather, the basic principle of the invention is to keep the force required for holding the clutch in the disengaged state during normal operation to a minimum by keeping the spring force required for engaging and permanently acting on the actuating element in normal operation to a minimum. This is achieved according to the invention in that the spring force is only used to produce a positive connection is needed and no longer - as in the prior art - to achieve a frictional connection.

The invention is explained in more detail below with reference to a drawing showing an exemplary embodiment. Show it

1 shows a schematic diagram of a “steer-by-wire” steering system known from the prior art; FIG. 2 axial section of the safety clutch in the disengaged state; FIG. 3 axial section of the safety clutch in the coupled state; FIG. 4 detail “X” of the Fig. 3 (engaged state) in axial section; Fig. 5 detail "X" of Fig. 3 (engaged state) in radial section; Fig. 6 detail "X" of Fig. 2 (disengaged state) in axial section; Fig. 7 detail "X" of Fig. 2 (disengaged state) in radial section.

The schematic structure of a steering device 29 as a “steer-by-wire” arrangement shown in FIG. 1 corresponds to the prior art. It consists, among other things, of a steering wheel 20, a steering column 21, the safety clutch 1, the steering gear 22 and the two Tie rods 24. The tie rods 24 are driven by the toothed rack 23. The drive unit is the drive unit formed from the components servo motor 25, optionally a sensor arrangement (not shown here) and, for example, the ball screw drive 27. The elements 22, 23 and 24 form a kinematic chain , which is referred to in the claims and the description as a "steering actuator".

In normal operation, the driver's request is fed into a control unit 28 by the control wheel 20 via a sensor system (not shown here) as a signal 281. In the control unit 28, the corresponding control voltage 282 for the servo motor or electric motor 25 is determined, possibly with the aid of a sensor signal from the drive unit (not shown here), and is output to the latter.

The invention relates to the safety clutch 1 shown in more detail in axial section in FIG. 2, which in the arrangement according to FIG. direction 29 is provided for a motor vehicle. For normal operation, in which the control unit 28 and the drive unit properly perform the steering function, the safety clutch 1 is disengaged. For this purpose, the signal 8 is output from the control unit to the safety clutch 1. In the event that the normal operating mode mentioned above is disrupted, the signal 8 is interrupted, so that the safety clutch 1 engages automatically and the vehicle is steered in a conventional manner via the mechanical components 22, 23, 24 of the steering system. In the simplest and at the same time most serious case, the fault can consist in a total power failure of the vehicle's on-board voltage.

The main components of the safety clutch 1 shown in FIG. 2 include: a drive shaft 3; an output shaft 2; Rolling elements 7 for torque transmission; a cage 6 non-rotatably connected to the drive shaft 3, in which the rolling elements 7 are held; a surface arranged on, in or on the output shaft 2 with recesses 10 into which the rolling elements 7 can engage in order to produce a positive connection; an actuating element 5 for moving the rolling elements 7 into the position producing the positive connection; a spring 9 for moving the actuator 5; an electromagnetic coil 4, which exerts a restoring force counteracting the spring force of the spring 9 on the actuating element 5 in normal operation.

2 shows the preferred embodiment of the safety coupling 1 in an axial longitudinal section in the disengaged state. 6 and 7, the associated detail sections “X” are shown enlarged. The signal 8, a current flow, is permanently introduced into the coil 4 in normal operation. This generates a magnetic field that the actuating element 5 into the in FIG The open position shown (disengaged state) pulls (to the right in Figure 2.) The actuating element 5 is attracted by the magnetic field, analogous to an iron core of a magnetic coil when current flows, against the spring force of the spring 9. In the exemplary embodiment shown, the spring 9 is a compression spring educated. Due to the rotation of the output shaft 2 and the magnetic force generated by the magnetic field, the rolling elements 7 are pressed or pulled out and come to rest against the inner contour 11 (see FIGS. 6 and 7) of the actuating element 5. As a result, the rolling elements no longer stand in engagement with the recesses 10 of the output shaft 2. The safety clutch 1 is separated and the wheels are adjusted exclusively by the servo motor drive unit 25, 27.

As can be seen from the analogy with the iron core of a magnetic coil, no permanent magnets are required for the construction of the safety clutch 1 in the preferred embodiment.

If a fault occurs in the power supply or in the control unit or in any other way, the current flow 8 is interrupted and the safety clutch engages automatically because then the electromagnetic restoring force is missing, which holds the actuating element 5 against the spring force of the spring 9 in the disengaged position ,

Figures 3, 4 and 5 show the engaged state. The current flow 8 is interrupted. The coil 4 no longer generates a magnetic field. The spring 9 presses the actuating element 5 into the closed position shown in FIG. 3. The rolling elements 7 are pressed by the inner contour 1 (cf. FIGS. 4 and 5) of the actuating element 5 in the direction of the recesses 10 of the output shaft 2. The rolling elements 7 thus engage in the recesses 10 of the output shaft 2. At the same time, the rolling elements 7 are held in the cage 6. The cage 6 is rotatably connected to the drive shaft 3. In the embodiment shown in the figures, the cage 6 and the drive shaft 3 are even formed in one piece.

The torque is correspondingly conducted from the drive shaft 3 via the cage 6 via the rolling elements 7 into the recesses 10 and thus into the output shaft 2. Since the rolling elements 7 roll on the surface of the inner contour 11 in the disengaged state, no spring friction is required by the spring force of the spring 9 during engagement, but only the sliding friction or, in the best case, only the rolling friction can be overcome. The force required for this is many times less than the force that would be required to generate a force fit if the clutch were designed as a force fit clutch as in the prior art. Therefore, the spring 9 can be designed and dimensioned much smaller in the invention, and only a correspondingly small restoring force is required to hold the clutch in the disengaged state. This enables the energy requirement to be kept to a minimum during normal operation.

In the engaged state, the rolling elements 7 are held in the recesses 10 by the surface of the cylindrical part of the inner contour 11 of the actuating element 5. In this way, there is a positive connection between the drive shaft 3 and the output shaft 2, which enables torque transmission. In the coupled state, the rolling elements 7 do not roll.

The invention provides a solution for a safety clutch that fulfills the necessary functions with minimal energy requirements and a technically simple structure. The design according to the invention takes up very little space compared to the prior art. The small space requirement also has advantages in the event of a vehicle crash, since the penetration of components into the passenger compartment can be prevented more easily. In addition, the safety clutch presented in the present invention does not require hydraulic oil, which could leak in the event of a crash and cause environmental damage. This saves costs compared to solutions that require hydraulic oil.

Another advantage of the arrangement according to the invention is that the magnet coil 4 is designed to be stationary, so that there is no need for the power supply transmitting the signal 8 to be rotated. Since the spring 9 only has to be as strong as is necessary to ensure the function under all operating conditions, the energy requirement for keeping the safety clutch open during normal operation is only very low.

In contrast to the prior art, the rotational position of the actuating element 5 does not play in relation to the other components of the safety clutch 1 Role. The safety clutch 1 works in any rotational position. Thus, in the preferred embodiment, the actuating element 5 is not fixed in relation to the rotational position, the actuation is carried out only by a pure translation and the spring 9 is designed as a simple compression spring.

This results in the further advantage of the preferred embodiment of the invention that the safety clutch 1 engages very quickly, since no time-delaying helical movements of the actuating element 5 are required for the engagement. There is also no need to ensure an exact rotational position for producing the positive connection, which increases the security of the system.

Another important advantage of the arrangement according to the invention is the simple structure, which does not require any additional sensors for detecting the engagement or disengagement state of the safety clutch. The tolerances of the individual components can also be relatively generous, since this system should only be used as an emergency system for a short distance. So it is e.g. readily conceivable to couple a signal for a speed limit to the engine management system to the interruption of the signal current for the signal 8.

The embodiment of the invention described here is only one embodiment. However, it is alternatively possible in the same way to arrange the contour with the recesses 10 on the drive shaft 3. Furthermore, the contour with the recesses 10 may not be designed as an inner contour as shown, but rather as an outer contour.

In another embodiment, not shown in the figures, the diameter of the inner opening of the coil 4 is larger than the outer diameter of the actuating element 5, so that the actuating element 5 plunges into the inner opening of the coil 4 in the uncoupled state.

Furthermore, under certain installation space conditions, it may be necessary to design the contour with the recesses 10 and accordingly the cage 6 as a flat circular to form a shaped disk. The form fit can also be ensured without any problems in this case. Accordingly, the 'actuating element 5 in turn closes the clutch by the pressure or rotary movement generated by the spring 9.

A pawl (not shown in the figures) can also be provided, which extends when the actuating element 5 is in the uncoupled state. If the pawl is extended, it axially fixes the actuating element 5 and absorbs the compressive force of the spring 9. It is possible in this way to keep the spring 9 in a compressed state during normal operation, in which the clutch is disengaged. In this case, it is not necessary to generate a permanent restoring force by the electromagnetic coil 4 in order to keep the clutch in the disengaged state. Rather, it is sufficient in this case that a permanent current signal comparable to signal 8 is present at the pawl, which ensures that the pawl is extended. If this signal is lost, for example due to a power failure, the pawl is automatically retracted and the clutch engages as described above. In the solution with the pawl, the energy consumption in normal operation is also very much lower than in the solutions known from the prior art with a non-positive safety coupling, because only as much energy is required as is required to keep the pawl in its extended position to keep.

LIST OF REFERENCE NUMBERS

1 safety clutch 2 output shaft

3 drive shaft

4 spool

5 actuating element

6 cage

7 positive locking elements

8 signal

9 spring

10 recesses

11 inner contour

20 steering means / steering wheel

21 steering column

22 steering gear

23 rack

24 tie rod

25 servo motor / electric motor

27 Ball screw drive

28 control unit

29 steering device

281 Driver request signal

282 control voltage

V cutting plane

X Detail / detail view

Claims

claims

1. Steering system for motor vehicles with steerable vehicle wheels, with a manually operable steering means (20) which acts on a drive unit (25, 27) in normal operation via an electronic control unit (28), and with one between the steering means (20) and the drive unit (25, 27) arranged safety clutch (1), which forcibly couples an input shaft (3) and an output shaft (2) to one another in the event of normal operation, and thus a direct mechanical actuation of a steering actuator (22, 23, 24) by the steering means (20) The safety clutch (1) has an actuating element (5) on which, on the one hand, a permanently effective closing force is exerted by an energy store, through which the actuating element (5) can be moved into a closed position in which the safety clutch (1) is coupled and, on the other hand, in normal operation a reset counteracting the closing force of the energy store L force acts, which is generated by an electromagnetic unit through which current flows during normal operation and which is greater than the closing force of the energy store, so that the actuating element (5) is held in an open position by the restoring force in normal operation, in which the safety clutch (1) is disengaged , and wherein the actuating element (5) can be moved by the force of the energy store in the axial direction in the closed position when the restoring force is omitted, characterized in that means (11) are provided with which form-locking elements (7) fit into a form-fit between the Drive shaft (3) and the output shaft (2) producing position are movable, and that the means (11) are arranged such that during the transfer of the actuating element (5) from the open to the closed position the positive locking elements (7) in the move the positive locking position.

2. Steering system according to claim 1, characterized in that the energy store is designed as a spring (9).

3. Steering system according to claim 1 or claim 2, characterized in that the electromagnetic unit comprises a current-flowing coil (4) which is arranged coaxially to the drive shaft (3).

4. Steering system according to claim 3, characterized in that the actuating element (5) is a coaxial to the drive shaft (3) and the coil (4) arranged sleeve.

5. Steering system according to claim 4, characterized in that the actuating element (5) at least partially surrounds the coil (4).

6. Steering system according to one of claims 1 to 5, characterized in that the means (11) with the actuating element (5) are directly connected.

7. Steering system according to claim 6, characterized in that the actuating element (5) and the means (11) form an integral component.

8. Steering system according to one of claims 1 to 7, characterized in that the interlocking elements (7) are designed as rolling elements which are held in a cage (6) which is connected in a rotationally fixed manner to the drive shaft (3), and that of the drive shaft (3) facing end of the output shaft (2) has recesses (10) for receiving the rolling elements.

9. Steering system according to claim 8, characterized in that the cage (6) is integrally formed with the drive shaft (3).

10. Steering system according to one of claims 8 to 9, characterized in that the rolling bodies as balls and the recesses (10) are designed as axially extending longitudinal grooves with a substantially semicircular cross section.

11. Steering system according to one or more of claims 1 to 10, characterized in that the means (11) is designed as an inner contour of a bore on the side of the sleeve-shaped actuating element (5) facing the output shaft (2), the inner contour of the bore at least has a cylindrical section and a section which widens conically in the direction of the output shaft (2).

12. Steering system according to one of claims 1 to 7, characterized in that the interlocking elements (7) are designed as toothing, which in the coupled state are in engagement with a corresponding toothing on the end of the output shaft (2) facing the drive shaft (3) ,