FORM 2
THE PATENT ACT 1970 {39 of 1970)
&
The Patents Rules, 2003 COMPLETE SPECIFICATION
(See Section 10, and rule 13)
1. TITLE OF INVENTION
SWITCHABLE STABILISER FOR A MOTOR VEHICLE

2. APPLICANT(S)
a) Name
b) Nationality
c) Address

ZF FRIEDRICHSHAFEN AG GERMAN Company 88038 FRIEDRICHSHAFEN GERMANY

3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed : -

Description
The invention relates to switchable stabilisers of the type outlined in the introductory part of claims 1 and 3. Such stabilisers are used in automotive technology.
In principle, each axle of a motor vehicle is provided with a stabiliser, which operates on the basis of the torsion bar principle and is disposed parallel with the vehicle axle, the two ends being secured to a wheel suspension. This stabiliser essentially prevents or reduces the transmission of rocking movements of the wheels caused by road conditions to the vehicle body. Such rocking movements occur in particular when driving round bends or on uneven road surfaces.
One-part stabilisers are designed for a predefined spring characteristic based on their dimensioning and their material properties so that they are able absorb torsional forces to a specific degree only and generate opposing forces accordingly. As a result, however, they are too soft or too hard in their reaction to different loads, which has a detrimental effect on driving comfort. One-part stabilisers are therefore well suited to use on the road. In the case of all-terrain vehicles, on the other hand, they are not suitable due to the higher torsional loads.
To cope with higher torsional loads such as occur when driving off road and where the limited twisting angle of a one-part stabiliser is no longer sufficient, therefore, the stabihsers used are split into two parts which are connected to one another by means of a switchable coupling.
Such a switchable coupling is described in patent specification DE 199 23 100 CI. This switchable coupling has an outer rotating part and an inner rotating part which are rigidly connected to one stabiliser part on the one hand and to the other stabiliser part on the other hand respectively. This being the case, the outer rotating part and the inner rotating part are each fitted with two oppositely lying toothed elements disposed in a common radial plane which form two oppositely lying gaps between them. Also
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disposed in the coupling is an axially displaceable locking piston with locking elements which fit in the gaps of the toothed elements by their end faces and which are biased in the locking direction by a compression spring and in the unlocking direction by a hydraulic pressure. In order to build up the required hydraulic pressure, an appropriate hydraulic system is provided, which primarily comprises a pump, a switchable multi-way valve, a tank and a pressure storage and which is designed as a compact unit. This hydraulic compact unit is disposed in a compartment of the vehicle that is protected against moisture and is connected to the coupling of the two-part stabiliser by means of free lines.
When driving on the road, for example, the hydraulic pressure in the hydraulic coupling is switched off so that the locking piston moves due to the force of the compression spring and the gaps between the toothed elements of the two rotating parts are filled by their locking elements without any clearance. Consequently, the two stabiliser parts are joined so that they, rotate in unison and the two stabiliser parts therefore behave like a one-part stabiliser in this position. When driving off road, for example, the locking piston is biased by a hydraulic pressure, which moves the locking piston against the force of the compression spring and thus opens the locking elements and the radial toothed elements. In this open position, the outer rotating part and the inner rotating part and hence the two stabiliser parts can be rotated relative to one another by a limited rotation angle.
This switchable stabiliser satisfies all the relevant technical requirements. However, it has disadvantages in terms of production and maintenance. For example, the two stabiliser parts, the electric control parts and the hydraulic components must be produced separately and then finished on an assembly line and fitted in the vehicle. The required testing of the system and functioning then takes place in the fitted state. If a fault is found, the defective component then has to be removed from the vehicle again and replaced by a new component.
The underlying objective of the invention is to increase the functional reliability of a
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stabiliser of the generic design, especially with regard to its switching behaviour.
This objective is achieved on the basis of a switchable stabiliser incorporating the characterising features defined in claim 1 and also on the basis of a stabiliser incorporating the characterising features defined in claim 3. Practical embodiments are defined in dependent claims 2 and 4 to 7.
For the purpose of the invention, the hydraulic system of the hydraulic and control system part forms a closed circuit with the piston-cylinder unit of the switchable coupling unit in a switchable stabiliser of the generic design defined in claim 1.
In the case of a switchable stabiliser of a generic design defined in claim 3, the hydraulic and control system part is integrated in the cylindrical housing of the switchable coupling.
The particular advantage of these solutions resides in the fact that because a hydraulic system has an integrated closed hydraulic circuit, there is no need to fit the hydraulic system in a position that is protected from moisture.
Closed hydraulic circuits have no connection to the atmosphere, which means that it is also possible to fit the hydraulic system in an under-floor region of the vehicle. This enables the two-part stabiliser with its switchable coupling and the hydraulic system to be designed as a compact unit. This results in significant cost advantages in terms of production and system testing because work can be carried out on the compact device separately.
Cost savings are also achieved due to the fact that the hydraulic lines that would otherwise have to be run from the hydraulic system to the stabiliser can be dispensed with.
Mounting space is also saved on the vehicle where the hydraulic lines would otherwise
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have to be run and where the hydraulic and control system part would have to be fitted. There is also no need to keep mounting space available for the hydraulic and control system part on vehicles that were not even fitted with a switchable stabiliser.
In one practical embodiment of a stabiliser as defined in claim 1, the hydraulic and control system part is connected to the coupling pressure chamber of the switchable coupling via a pressure line and to the coupling spring chamber of the switchable coupling via a suction line. The pressure line is also connected to an electric pressure switch and the suction line is connected to a pressure storage, and the pressure line and suction line communicate via a bridging line, which bridging line is fitted with an electromagnetically switchable 2/2-way valve which is in the closed position when supplied with power and in the open position when not supplied with power.
In another practical embodiment of the stabiliser defined in claim 3, the hydraulic and control system part is oriented coaxially with the switchable coupling and comprises a cylindrical housing and a valve block disposed in the cylindrical housing, and the cylindrical housing of the hydraulic and control system partis non-rotatably connected to the cylindrical housing of the switchable coupling and the valve block is linked to all the requisite hydraulic elements in a concatenated arrangement.
An interconnecting flange is preferably used as a means of connecting the two cylindrical housings to prevent them from rotating and to increase the strength of the component unit. An interconnecting flange also offers very good conditions for integrating a pressure storage.
In a preferred embodiment of such a stabiliser, the hydraulic and control system part is connected via an internal pressure line to the coupling pressure chamber of the switchable coupling and via an external suction pipe to the coupling spring chamber of the switchable coupling. Furthermore, the pressure lines are connected to an electric pressure switch and the suction line is connected to a pressure storage, and the pressure line and suction line communicate via a bridging line, which bridging line is fitted with
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an electromagnetically switchable 2/2-way valve which is in the closed position when supplied with power and in the open position when not supplied with power.
The pressure storage may also be provided as a single-acting piston-cylinder unit with a storage cylinder, a storage piston and a storage compression spring biasing the storage piston, and the storage cylinder and storage piston are disposed in the interconnecting flange and the storage compression spring with its storage spring chamber is disposed in the first stabiliser part. This being the case, it is of great advantage to provide the pressure storage system as a single-acting piston-cylinder unit because this keeps the radial mounting space to a minimum.
It is generally of advantage if the hydraulic and control system part is oriented coaxially with the mechanical part of the switchable coupling because this enables the radial free space needed on the vehicle for the rotating movement to be kept to a minimum. By using a valve capable of concatenated operation, only a very small amount of mounting space is needed, both in the radial and in the axial direction.
The invention will be described in more detail with reference to an example of an embodiment. Of the drawings:
Fig. 1 is a view of a two-part switchable stabiliser,
Fig. 2 is a diagram in section showing the switchable coupling of the stabiliser and
Fig. 3 is a second diagram in section showing the switchable coupling rotated by 90°.
As illustrated in Fig. 1, the switchable stabiliser comprises a first stabiliser part 1 and a second stabiliser part 2, the two of which are connected to one another via a switchable coupling 3. The two stabiliser parts 1,2 are respectively mounted via a stabiliser bearing 4,5 on the vehicle body and via a pendulum support 6,7 on the wheels of the vehicle. The switchable coupling 3 comprises a mechanical part 8 and a hydraulic and control
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system part 9, and the mechanical part 8 connects the two stabiliser parts 1, 2 to one another in one end position and separates them from one another to permit a limited twisting angle in the other end position.
As may be seen in particular from Figs. 2 and 3, the mechanical part 8 of the switchable coupling 3 has a cylindrical housing 10 and the hydraulic and control system part 9 has a cylindrical housing 11, the two of which are connected to one another by an interconnecting flange 12 to prevent them from rotating. The cylindrical housings 10,11 of this one-part design are in turn connected via a "housing flange 13 to the second stabiliser part 2 so that they are prevented from rotating. On the side of the first stabiliser part 1, the cylindrical housing 10 of the mechanical part 8 is provided with a bearing flange 14, by means of which the end of the first stabiliser part 1 extends through to the interior of the mechanical part 8. Accordingly, the first stabiliser part 1 and the cylindrical housing 10 are radially spaced apart from one another so that an annular chamber 15 is formed across the entire axial length of the cylindrical housing 10. This annular chamber 15 is hydraulically sealed off from the outside in the region of the bearing flange 14 by means of a seal element 16.
At its free end, the first stabiliser part 1 bears a force-transmitting part 17, which is non-rotatably connected to the first stabiliser part 1, and which is designed to slide relative to the internal wall of the cylindrical housing 10 and is axially supported on the interconnecting flange 12, supporting the first stabiliser part 1. As illustrated in Fig. 3, this force-transmitting part 17 has an axially extending toothed element 18 with preferably conically extending tooth sides. As also illustrated in Fig. 3, a matching toothed element 19 is non-rotatably inserted in the cylindrical housing 10 in the axial region of this toothed part 18. The two toothed elements 18, 19 therefore form two oppositely lying gaps between them, in which the two appropriately shaped locking elements 20 of an axially displaceable locking piston 21 engage. To this end, this locking piston 21 is able to slide relative to the first stabiliser part 1 and relative to the internal wall of the cylindrical housing 10 and is designed axially and in terms of its delimitation so that a coupling spring chamber 22 is formed in the annular chamber 14 between the
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locking piston 21 and the bearing flange 14 on the one hand and a coupling pressure chamber 23 is formed between the locking piston 21 and the interconnecting flange 12 on the other hand. In order to isolate the coupling pressure chamber 23 and the coupling spring chamber 22 hydraulically, the locking piston 21 has an inner seal element 24 to isolate the first stabiliser part 1 and an outer seal element 25 to isolate the cylindrical housing 10. Inserted in the coupling spring chamber 22 is a coupling compression spring 26, which is supported on the bearing flange 14 and biases the locking piston 21 in the direction of the force-transmitting part 18. In the opposite direction, the locking piston 21 is biased by the force of a hydraulic pressure in the coupling pressure chamber 23. The two toothed elements 18, 19 of the force-transmitting part 17 and the cylindrical housing 10 as well as the two locking elements 20 of the locking piston 21 are adapted to one another so that they engage under the force of the coupling compression spring 26 and establish a clearance-free connection between the first stabiliser part 1 and the cylindrical housing 10, and disengage across an axially limited path due to the force of the hydraulic pressure in the coupling pressure chamber 23, thereby permitting a limited twisting angle between the first stabiliser part 1 and the cylindrical housing 10.
The hydraulic and control system part 9 essentially comprises a hydraulic valve block 27 disposed inside the cylindrical housing 11 in the spatial vicinity of the mechanical part 8, which is connected to the co-operating hydraulic elements in a concatenated arrangement. These hydraulic elements form a closed hydraulic circuit for driving the mechanical part 8 of the switchable coupling 3.
Accordingly, this hydraulic circuit is provided with an electric motor 28 which is linked to a pump 29. This pump 29 communicates with the coupling pressure chamber 23 of the hydraulic coupling 3 via a pressure line 30 extending through the interconnecting flange 12 and with the coupling spring chamber 22 of the switchable coupling 3 via a suction line 31, a suction connector 32 and an externally lying suction pipe 33. To this end, the pressure line 30 and the suction line 31 are connected. via a bridging line 34, which is fitted with an electromagnetically switchable 2/2-way valve 35. The suction
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line 30 is also connected to a pressure storage 36 comprising a storage cylinder 37 and a storage piston 39 biased by a storage compression spring 38. In spatial terms, the storage cylinder 37 and the storage piston 39 are disposed in the interconnecting flange 12, whilst the storage compression spring 38 extends through an axially extending storage spring chamber 40. This storage spring chamber 40 is integrated in the first stabiliser part 1. Disposed in the suction line 31 is a non-releasable check valve 41 opening in the direction of the pump 29, whilst a non-releasable check valve 42 closing in the direction of the pump 29 is provided in the pressure line 30. The pressure line 30 also has a connection to an electric pressure switch 43.
As illustrated in Fig. 1, the hydraulic and control system part 9 also has a hydraulic filling connector 44 on the interconnecting flange 12 and two electric terminals 45 and 46 for the 2/2-way valve 35 and the electric motor 28 on the housing flange 13.
To render the system operational, the entire hydraulic system including the coupling spring chamber 22, the coupling pressure chamber 23 and the pressure storage 36 are filled via the filling connector 44 with a quantity of hydraulic oil which is enough to generate sufficient pressure to operate the switchable coupling 3.
Under normal road conditions, the electric motor 28 is switched off and the 2/2-way valve 35 is left without power. This being the case, the 2/2-way valve 35 assumes its open through-flow position so that the pressure line 30 and the suction line 31 communicate with one another via the bridging line 34 and the 2/2-way valve 35. The pressure line 30 and the suction line 31 are therefore at the same pressure, which is transmitted to the coupling pressure chamber 23 and the coupling spring chamber 22 and biases the locking piston 21 with the same pressure at both ends. Due to the fact that the surfaces are of identical size, the hydraulic forces on the locking piston 21 cancel each other out and the force of the coupling compression spring 26 therefore pushes the locking piston 21 in the direction of the force-transmitting part 17. The conical locking elements 20 therefore move between the toothed element 18 of the first stabiliser part 1 and the toothed element 19 of the cylindrical housing 10 until the locking elements 20
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and the toothed elements 18,19 lie against one another by their lateral cone surfaces without any clearance. The switchable coupling 3 is locked in this state and the two stabiliser parts 1 and 2 connected in this manner act like a one-part stabiliser. The force of the coupling compression spring 26 and the cone surfaces of the toothed elements 18, 19 and locking elements 20 are adapted to one another so that the force of the coupling compression spring 26 predominates over the axially acting twisting forces of the switchable coupling 3 and the closed state of the switchable coupling 3 is kept closed across the entire load width.
Under abnormal road conditions such as occur off road, for example, the spring characteristic of the mutually coupled stabiliser parts 1 and 2 is no longer sufficient to compensate for the rocking movements of the wheels. In order to obtain a bigger twisting angle of the two stabiliser parts 1,2, a central control signal is triggered, which supplies the 2/2-way valve 35 and the electric motor 28 with power. As result, the 2/2-way valve 35 switches into its closed position, whilst the electric motor 28 starts up and activates the pump 29. The pump 29 thus draws hydraulic oil out of the coupling spring chamber 22 via the internal suction line 31 and the external suction pipe 33 and conveys it via the internal pressure line 30 into the coupling pressure chamber 23. As a result, a higher pressure prevails in the coupling pressure chamber 23 than the pressure in the coupling spring chamber 22. The pressure difference acts on the locking piston 21 and generates a force which opposes the force of the coupling compression spring 26 and which pushes the locking piston 21 in the direction of the bearing flange 14 into an end position. This locks the switchable coupling 3 and the free ends of the toothed elements 18,19 on the one hand and the locking elements 20 on the other hand remain in an axially overlapping position. Due to the conical shape of the lateral cone faces, however, a predefined radial pivoting angle is left free between the toothed elements 18,19 and the locking elements 20. When the locking piston 21 is in this end position, a predefined pressure is established in the coupling pressure chamber 23, which is transmitted via the internal pressure line 30 and activates the pressure switch 43. With this control signal, the electric motor 28 is switched off and the pressure conditions in the pressure line 30 and hence in the coupling pressure chamber 23 as well as in tine
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suction line 31 and hence in the coupling spring chamber 22 remain unchanged. The switchable coupling 3 is maintained in the opened position as a result.
As road conditions improve, a central control signal is transmitted to the hydraulic and control system part 9 again, as a result of which the power to the 2/2-way valve 35 is switched off. As a result, the 2/2-way valve 35 moves back into its opened position so that the pressure line 30 and the suction line 31 communicate again and a pressure compensation is established at the locking piston 21. The locking piston moves due to the force of the coupling compression spring 26 and locks the switchable coupling.
Possible changes in volume which might occur due to temperature fluctuations or due to leakage losses are compensated by the pressure storage 36 biased by the storage compression spring 38.
If the electrical control part of the hydraulic and control system part 9 suffers damage, the 2/2-way valve 35 always assumes the through-flow position so that at least the locked function range of the switchable coupling 3 is maintained.
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List of reference numbers

1 First stabiliser part
2 Second stabiliser part
3 Switchable coupling
4 Stabiliser bearing
5 Stabiliser bearing
6 Pendulum support
7 Pendulum support
8 Mechanical part
9 Hydraulic and control system part
10 Cylindrical housing
11 Cylindrical housing
12 Interconnecting flange
13 Housing flange
14 Bearing flange
15 Annular chamber
16 Seal element
17 Force-transmitting part
18 Toothed element of the stabiliser part
19 Toothed element of the cylindrical housing
20 Locking element
21 Locking piston
22 Coupling spring chamber
23 Coupling pressure chamber
24 Inner seal element
25 Outer seal element
26 Coupling compression spring
27 Valve block
28 Electric motor
29 Pump
30 Pressure line
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31 Suction line
32 Suction connector
33 Suction pipe
34 Bridging line
35 2/2-way valve
36 Pressure storage
37 Storage cylinder
38 Storage compression spring
39 Storage piston
40 Storage spring chamber
41 Non-releasable check valve
42 Non-releasable check valve
43 Pressure switch
44 Filling connector
45 Electric terminal
46 Electric terminal

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WE CLAIM:
1. Switchable stabiliser for a motor vehicle comprising a first stabiliser part (1) and a second stabiliser part (2), the two of which are connected to one another by means of a switchable coupling (3), which switchable coupling (3) is designed as a single-acting piston-cylinder unit and is connected to a hydraulic and control system part (9), characterised in that the hydraulic system of the hydraulic and control system part (9) forms a closed circuit with the piston-cylinder unit of the switchable coupling unit (3).
2. Switchable stabiliser as claimed in claim 1, characterised in that the hydraulic and control system part (9) is connected to the coupling pressure chamber (23) o( the switchable coupling (3) via a pressure line (30) and to the coupling spring chamber (22) of the switchable coupling (3) via a suction pipe (33), the pressure line (31) is connected to an electric pressure switch (43) and the suction line (31.) is connected to a pressure storage (36), and the pressure line (30) and suction line (31) communicate via a bridging line (34), which bridging line (34) is fitted with an electromagnetically switchable 2/2-way valve (35) which is closed in the position supplied with power and open in the position without power.
3. Switchable stabiliser for a motor vehicle, comprising a first stabiliser part (1) and a second stabiliser part (2), the two of which are connected to one another by means of a switchable coupling (3), which switchable coupling (3) is designed as a single-acting piston-cylinder unit and is connected to a hydraulic and control system part (9), characterised in that the hydraulic and control system part (9) is integrated in the cylindrical housing (10) of the switchable coupling (3).
4. Switchable stabiliser as claimed in claim 3, characterised in that the hydraulic and control system part (9) is oriented coaxially with the switchable coupling (3) and comprises a cylindrical housing (11) and a valve block (27) disposed in the cylindrical housing (11), and the cylindrical housing (11) of the hydraulic and control system part (9) is non-rotatably connected to the cylindrical housing (10)
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of the switchable coupling (3), and the valve block (27) is linked in a concatenated arrangement to all the requisite hydraulic elements.
5. Switchable stabiliser as claimed in claim 4, characterised in that an interconnecting flange (12) is used to connect the two cylindrical housings (10, 11) so that they do not rotate.
6. Switchable stabiliser as claimed in claim 3, characterised in that the hydraulic and control system part (9) is connected to the coupling pressure chamber (23) of the switchable coupling (3) by means of an internal pressure line (30) and to the coupling spring chamber (22) of the switchable coupling (3) via an external suction pipe (33), the pressure line (31) is connected to an electric pressure switch (43) and the suction line (31) is connected to a pressure storage (36), and the pressure line (30) and suction line (31) communicate via a bridging line (34), which bridging line (34) is fitted with an electro magnetically switchable 2/ 2-way valve (35) which is closed in the position supplied with power and open in the position without power.
7. Switchable stabiliser as claimed in claim 6, characterised in that the pressure storage (36) is provided in the form of a single-acting piston-cylinder unit with a storage cylinder (37), a storage piston (39) and a storage compression spring (38) biasing the storage piston (39), and the storage cylinder (37) and storage piston (39) are disposed in the interconnecting flange (12) and the storage compression spring (38) with its storage spring chamber (40) is disposed in the first stabiliser part(l).
Dated this 20th day of March, 2007

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ABSTRACT
The objective is to design a switchable stabiliser as a compact unit. To this end, it is proposed that the hydraulic system of the hydraulic and control system part (9) form a closed circuit with the piston-cylinder unit of the switchable coupling unit (3) and the hydraulic and control system part (9) is integrated in the cylindrical housing (10) of the switchable coupling (3).
To,
The Controller of Patents,
The Patent Office,
Mumbai
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Figure 1