BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention pertains to a clutch device for a retarder according to the preamble of claim 1 , a vehicle comprising such a clutch device according to the preamble of claim 17, and a method for the connection of a retarder according to the preamble of claim 18.

A retarder is used to brake a driving source, such as a vehicle. Often the retarder consists of an auxiliary brake, which complements the wheel brakes of the vehicle. Thus, excessive wear of the wheel brakes is avoided. The retarder is connected to the vehicle's gearbox or propeller shaft via a transmission. In order to reduce energy losses and thus reduce the vehicle's fuel consumption, the transmission and the retarder are disconnected from the gearbox or the propeller shaft when the retarder is disengaged and does not have to brake the vehicle. The retarder shaft is at a standstill or near standstill when the retarder is not activated. The retarder's rotor and stator form a torus, which must be filled with a fluid as soon as a braking effect from the retarder is desired. In the event that a clutch device, which is used for the connection and disconnection of the retarder with the gearbox or the propeller shaft, comprises a synchronisation device with synchronisation rings, the connection and disconnection of the transmission with the gearbox or the propel- ler shaft is more difficult, since the torus of the retarder contains a certain amount of water, resulting in a non-negligible torque called a residual torque. In other words, a residual torque is required in order to keep the retarder rotating because of the amount of liquid remaining therein. During the entire connection sequence, including gliding into the synchronisation by revving and subsequently locking, the synchroni- sation device must cope with keeping down the rotational speed difference even though the residual torque remains. If the rotational speed difference becomes too great, the synchronisation device may be damaged. In order to counteract this, the synchronisation device may be dimensioned to cope with said residual torque, with the result that another type of synchronisation must be used. Document DE 1600243 A1 shows a retarder for a vehicle, in which a stator may be connected with a plate clutch on the one hand, and a form-locking clutch on the other hand. When the retarder is not activated, both the rotor and the stator will rotate. In order to activate the retarder when braking, the stator must be braked to a standstill and to a locked position with the help of the plate clutch and the form-locking clutch.

Document WO2013083322 A1 pertains to a drive train for a motor vehicle, comprising two clutches for connection of a retarder. The document DE10305239 A1 pertains to a driving device for a connectible retarder, which is equipped with a synchronisation and a dog clutch.

The document WO2004048167 A1 shows a retarder for a vehicle, where the stator has been braked to a standstill and to a locked position with the help of a plate clutch and the form-locking clutch.

The document US 3777860 A shows a retarder for vehicles with a rotor and a stator, wherein the rotor is installed to connect and disconnect the vehicle's driving shaft with a clutch device, which is controlled automatically depending on the activation of the vehicle brake.

SUMMARY OF THE INVENTION

Despite prior art solutions, there is a need to further develop a clutch device for a re- tarder which does not significantly encumber a driving source when it is disengaged, but which has a low weight and which is engaged when the retarder shall exert a braking effect on the driving source.

Another objective of the invention is to provide a clutch device for a retarder, which exerts a substantially zero braking torque on the driving source when disengaged.

Another objective of the invention is to provide a clutch device for a retarder, which reduces the fuel consumption of a vehicle. Another objective of the invention is to provide a clutch device for a retarder, which clutch device comprises a compact control element with a small number of interacting components. Another objective of the invention is thus to provide a clutch device with increased life and reliability for a retarder.

These objectives are achieved with a retarder of the type specified at the beginning, which is characterised by the features specified in patent claim 1 .

Such a clutch device is subjected to low wear and tear, which results in an increased service life and reliability of the clutch device. The clutch device entails that the retarder in a disengaged state exerts a substantially zero braking torque on the driving source, which thus reduces the fuel consumption of a vehicle. Since the control ele- ment is compact and comprises a small number of components, the clutch device's complexity and weight will be less, which reduces the vehicle's fuel consumption and increases the reliability of the clutch device. The two clutch elements interact and are integrated in each other and are engaged with a common power source, which entails that only one communication between the power source and the clutch devices is required.

The objectives specified above are also achieved with a vehicle of the type mentioned above, which is characterised by the features specified in patent claim 1 7. The retarder exerts a substantially zero torque on the vehicle, in order to thus reduce the fuel consumption. The controlled connection and disconnection of the retarder via the clutch device also entails that its service life and reliability increases.

The above objectives are also achieved with a method for the connection of a retarder of the type specified at the beginning, which is characterised by the features specified in patent claim 1 8.

Other advantages of the invention are set out in the detailed description below. BRIEF DESCRIPTION OF THE DRAWINGS

Below is a description, as an example, of a preferred embodiment of the invention with reference to the enclosed drawings, on which:

Fig. 1 shows a schematic side view of a vehicle with a clutch device for a retarder according to the present invention,

Fig. 2 shows a cross-sectional view of a first embodiment of a clutch device for a re- tarder, according to the present invention, in a disconnected state,

Fig. 3 shows a cross-sectional view of the first embodiment of the clutch device for a retarder, according to the present invention, in a connected state, Fig. 4 shows a flow chart of a method for the connection of a retarder according to the present invention, and

Fig. 5 shows a graph of different pressure levels. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Fig. 1 shows a schematic side view of a vehicle 1 , which vehicle 1 is equipped with a retarder 2, which is connected and disconnected with a clutch device 4 according to the present invention. The vehicle 1 is also equipped with a gearbox 6, which is con- nected to a combustion engine 8, which drives the driving wheels 10 of the vehicle 1 via the gearbox 6 and a propeller shaft 1 2. The driving wheels 10 are equipped with wheel brakes 1 1 . A control device 16 is arranged to control the retarder 2. The retarder 2 comprises a rotatable first shaft 18, which is equipped with a first rotational speed sensor 9 to detect the speed of the first shaft 1 8. The rotational speed sensor 9 is connected to the control device 16.

Fig. 2 shows a cross-sectional view of a clutch device 4 for a retarder 2, according to one embodiment of the present invention, in a disconnected state. The first shaft 1 8 is connected with a rotor 20 of the retarder 2, and a second shaft 22 is arranged to engage with a driving source. According to the embodiment shown in Fig. 2, the driving source constitutes the vehicle 1 , wherein the connection of the retarder 2 with the vehicle 1 is carried out via the gearbox 6. In Fig. 2 the gearbox 6 is displayed schematically. The second shaft 22 is equipped with teeth 24 for engagement with a transmission 26 arranged at the gearbox 6, which transmission comprises a cogwheel 28 between the output shaft 30 and the second shaft 22 of the gearbox 6. The transmission 26 may be arranged in the gearbox 6. On the output shaft 30 of the gearbox the propeller shaft 1 2 is also arranged. The cogwheel 28 entails that the output shaft 30 of the gearbox always drives the second shaft 22 when the propeller shaft 12 rotates. Preferably, a gearing in the ratio 3:1 occurs through the transmission 26, but other gearings are also possible, e.g. 1 :1 . A second rotational speed sensor 31 is arranged at the second shaft 22, or on the cogwheel 28, in order to measure the speed of the second shaft 22 or the cogwheel 28. The second rotational speed sensor 31 is suitably connected to the control device 16 (Fig. 1 ).

The first shaft 18 is preferably mounted with a bearing 36 in a gearbox housing 38, and in a retarder housing 40. On the first shaft 18 the rotor 20 is arranged, which in a connected state rotates with a speed which is proportionate to the speed of the output shaft 30 of the gearbox 6. A stator 42 is connected to the retarder housing 40 and will therefore not rotate.

The rotor 20 and the stator 42 jointly form a toroidally shaped hollow space, called torus 44, which is filled with a fluid 46, such as water, through an opening 47, when the retarder 2 carries out a braking torque on the output shaft 30 of the gearbox 6, in order to brake the vehicle 1 to thus reduce the vehicle's 1 speed. The braking effect arises since the rotor 20 and the stator 42 are equipped with blades or shovels 48, creating a flow of fluid in the torus 44 when the rotor 20 rotates. The flow of fluid creates, in interaction with the shovels 48 of the rotor 20 and the stator 42, a reaction force which forms the braking effect. The higher the rotational speed of the rotor 20, and the greater the amount of fluid in torus 44, the greater the reaction force, and thus the torque, becomes. On the occasions when the retarder 2 does not have to brake the vehicle 1 , the torus 44 is drained of fluid 46 that is partly replaced with steam, entailing that the shovels 48 of the rotor 20 and the stator 42 primarily will create a steam flow in the torus 44. The steam flow causes an undesirable reaction force on the first shaft 18, which generates a braking torque on the output shaft 30 of the gearbox 6. The braking torque from the retarder 2 entails that the fuel consumption of the vehicle 1 increases when the combustion engine 8 of the vehicle 1 exerts a torque. The friction from the bearings of the first shaft 18 emits a reaction force, which entails an increased fuel consumption. For this reason, the first shaft 1 8 may be disconnected from the output shaft 30 of the gearbox 6, when the retarder 2 is not used to brake the vehicle 1 . The fuel consumption of the vehicle 1 may thus be reduced. Filling and draining of torus 44 with fluid 46 is done via a fluid circuit. The torus 44 must be filled with fluid 46 as quickly as possible when a braking effect from the retarder 2 is desired. A slow filling initially entails a lack of a braking effect from the retarder 2, leading to an exaggerated use of the wheel brakes of the vehicle 1 , which will be exposed to unnecessary wear. The clutch device 4 according to the invention entails that the first shaft 18, and thus the retarder 2, may be disconnected from the gearbox 6, entailing that the retarder 2 does not have a braking effect on the vehicle 1 when the retarder 2 is disengaged. When the retarder 2 is to be engaged, the retarder 2 must be connected mechanically with the output shaft 30 of the gearbox 6 in a quick and efficient manner. In or- der to achieve this, a first and a second clutch element 54, 56 are arranged between the first and second shafts 18, 22. The first clutch element 54 consists of a friction clutch of the plate type, and the second clutch element 56 consists of a form-locked clutch of the dog clutch type. The first clutch element 54 comprises an inner sleeve 57, shiftable on the first shaft, which though the first splines 59 is rotationally locked with the first shaft. The inner sleeve 57 is arranged to connect and disconnect the first clutch element 54 during axial shifting. The second clutch device 56 comprises an axially shiftable sleeve 58, equipped with teeth 60, adapted to engage with corresponding teeth 62 on a carrier 61 of the second shaft 22. The second shaft 22 is arranged co-axially with the first shaft 18, and the second shaft 22 is preferably mounted with rolling bearings 63 on the first shaft 18. The axially shiftable outer sleeve 58 is axially shiftable on the inner sleeve 57, and is rotationally locked with the inner sleeve 57 through second splines 67.

When the retarder 2 is to be engaged in order to brake the vehicle 1 , the clutch de- vice 4 is thus engaged, so that the first shaft 1 8 is connected with the second shaft 22 via the first clutch element 54. Since the second shaft 22 rotates from the start and the first shaft 18 stands still, the first clutch element 54 will make the first shaft 1 8 rotate. The first clutch element 54 is, according to the embodiment, a plate clutch, connecting the first and the second shafts 18, 22 through friction. The plate clutch will, however, not be able to transmit the braking torque which arises when the retarder 2 is to brake the vehicle 1 . For this reason, the second clutch element 56, which consists of a form-locked clutch such as a dog clutch, is connected. The second clutch element 56 is dimensioned to be able to transfer the large braking torque which is exerted by the retarder 2.

Fig. 3 shows a cross-sectional view of the clutch device 4 for a retarder 2, according to the present invention, in a connected state. The outer sleeve 58 has been shifted on the inner sleeve in a direction towards the carrier 61 , so that the teeth 60, 62, which are formed on the outer sleeve 58 and on the carrier 61 , engage with each other with the result that the outer sleeve 58 and the carrier 61 connect the first and the second shaft 18, 22 in a form-locked manner.

As shown in Figs. 2 and 3, the first shaft 18 is equipped with a first and a second central bore 64, 66. The first bore 64 leads lubricant to bearing 63 and to the clutch device 4 for friction reducing, lubricating and cooling purposes. The second bore 66 leads pressurised air from a power element 91 , which is preferably a pressurised air compressor, and further through a pressurised air channel 70, in order to control the clutch device 4. The inner sleeve 57 is equipped with a first piston section 72 and the outer sleeve 58 is equipped with a second piston section 74. The first and the second piston sections 72, 74 are circular and designed to be shifted axially in a first and second cylinder section 76, 78, respectively, which are circular and arranged on the first shaft 18. The cylinder sections 76, 78 may be rotationally locked in relation to the shaft with a form locking 90. The pressurised air is led, via the pressurised air channel 70, to the respective first and second cylinder sections 76, 78, in order to shift the first and second piston sections 72, 74. The connection of the first cylinder section 76 with the pressurised air channel 70 has a smaller surface than the connection of the second cylinder section 78 with the pressurised air channel 70. Accordingly, the connection of the first cylinder section 76 with the pressurised air channel 70 will function like a throttle 79, entailing that the air flow and the pressure equalisation between the cylinder section 76 and the pressurised air channel 70 is delayed.

A first return spring 80 is arranged between the first shaft 1 8 and the inner sleeve 57. The first return spring 80 strives to return the inner sleeve 57 to a position where the inner sleeve 57 does not engage the first clutch element 54. A second return spring 82 is arranged between the first shaft 18 and the outer sleeve 58. The second return spring 82 strives to return the outer sleeve 58 to a position where the outer sleeve 58 does not engage the second clutch element 56. The first clutch element 54 is arranged with a first set of plates 84 arranged on the first shaft 18, and with a second set of plates 86 arranged on the carrier 61 . When the inner sleeve 57 is shifted axially in a direction towards the plates 84, 86, these are compressed, so that the friction between the first and the second sets of plates 84, 86 results in a reaction torque arising between the first and the second shaft 18, 22. The reaction torque entails that the first shaft 18 will be dragged along by the second shaft 22, so that the second shaft 22 drives the first shaft 18.

When the retarder 2 is to be engaged in order to brake the vehicle 1 , the clutch device 4 is thus engaged, so that the first shaft 1 8 is connected with the second shaft 22 via the first clutch element 54. Since initially, the second shaft 22 rotates and the first shaft 18 stands still, the first clutch element 54 will make the first shaft 1 8 rotate. Pressurised air is applied to the clutch element 54 from a valve 88, or a switch connected to the first power element 91 . The valve 88 or the switch connected to the power element 91 in the form of a pressurised air compressor is controlled by the control device 16 (Fig. 1 ). Since the first clutch element 54 is a plate clutch, it will not be able to transmit the braking torque which arises when the retarder 2 is to brake the vehicle 1 . The reason for this is that the plate clutch is too small, and if it were to be dimensioned to transfer the entire braking torque it would be very large and bulky. For this reason, the second clutch element 56 is connected when the first and the second shafts 18, 22 have reached substantially the same rotational speed. The second clutch element 56 is dimensioned to be able to transfer the large braking torque which is exerted by the retarder 2 when the torus is filled with fluid. By arranging the first return spring 80, the piston section 72 and its area on which the air pressure acts, and the return spring 82, the piston section 74 and its area on which the air pressure acts, the first return spring's 80 spring force will be overcome by an air pressure from the valve 88 or the switch connected with the power element 64 in the form of a pressurised air compressor, lower than the spring force of the second return spring 82. In other words, a higher air pressure is required to overcome the spring force of the second return spring 82 than what is required to overcome the spring force of the first return spring 80.

When the clutch device 4 is connected at a first point in time t1 , pressurised air is supplied through the pressurised air channel 70 at a first pressure level p1 , which impacts both the first and the second piston section 72, 74 with a first force. The first pressure level p1 is adapted in such a manner, that the spring force of the first return spring 80 is overcome, but the spring force of the second return spring 82 is not overcome. Thus, the first piston section 72 and the inner sleeve 57 will be shifted in an axial direction towards the first clutch element 54 and compress the first second plates 84, 86 so that the first clutch element 54 is engaged. During the same time period, the external sleeve 58 is not displaced axially by the air pressure. When the first clutch element 54 is engaged, the first shaft 1 8 will be dragged along by the rotation of the second shaft 22. By measuring the rotation of the first and second shafts 18, 22 with the first and second rotational speed sensors 9, 31 , it is possible to determine when the first shaft 1 8 has reached the same or substantially the same rotational speed as the second shaft 22. When the first shaft 18 has reached the same or substantially the same rotational speed as the second shaft 22, the air pressure is increased through the valve 88 to a second pressure level p2 at a second point in time t2, so that the external sleeve 58 overcomes the spring force of the second return spring 82 through a second force. Thus, the outer sleeve 58 will be shifted axially in a direction towards the carrier 61 , via the pressurised air acting on the second piston section 74. When the outer sleeve 58 reaches the carrier 61 , the teeth 60 of the outer sleeve 58 will engage with the corresponding teeth 62 of the carrier 61 . When the second clutch element 56 is connected, the torus 44 of the retarder 2 is filled with fluid 46, which entails that the retarder 2 will exert a braking action on the vehicle 1 , as described above. According to the above, the retarder 2 is described as being arranged in a vehicle 1 in order to brake the vehicle 1 , but it is also possible to use the retarder 2 according to the present invention for other applications. According to the above, the vehicle 1 , the combustion engine 8, the gearbox 6 or the propeller shaft 12 may constitute a driving source, which is connected directly or indirectly to the retarder 2. Other driving sources may, however, be connected to the retarder 2. In the event the teeth 60, 62 of the outer sleeve 58 and the carrier 61 should end up in a position where the teeth 62 of the carrier 61 prevent the outer sleeve 58 from being shifted axially, and thus prevent the teeth 60 of the outer sleeve 58 from engaging with the teeth 62 of the carrier 61 , they will engage with each other when the torus 44 is filled with fluid, since the large braking torque from the retarder 2 will overcome the friction force in the first clutch element 54 and twist the first and second plates 84, 86 relative to each other. When the second shaft 22 is twisted relative to the first shaft 18, the carrier 61 will be twisted in relation to the outer sleeve 58, and as a result the teeth 62 of the carrier 61 no longer prevent the outer sleeve 58 from being shifted axially, so that the teeth 60 of the outer sleeve 58 will engage with the teeth 62 of the carrier 61 . In order to be able to lock the second clutch element 56 without the locking torque increasing too much in the first clutch element 54, a throttle 79 may be inserted between the air pressure channel 70 and the first cylinder section 76. The increase of the air pressure is then delayed in the first cylinder section 76 in relation to the second cylinder section 78. The insertion of the throttle 79 entails, in the event the teeth 60 and 62 face each other and the rotational speeds of the shafts 22 and 18 are synchronous, that the second shaft 22 may more easily be twisted relative to the first shaft 18 when the retarder's braking torque increases, and accordingly the teeth 60 of the outer sleeve 58 may engage more easily and faster with the teeth 62 of the carrier 61 . The insertion of the throttle 79 entails, in the event the rota- tional speeds of the shafts 22 and 18 are not synchronous or nearly synchronous, that the rotational speed of the shaft 1 8 is not able to increase too much before the second clutch element 56 has engaged with the teeth 62 of the carrier 61 . This is advantageous in cases where a controlled rotational speed difference must be reached in order for the second clutch element 56 to engage with the teeth 62 of the carrier 61 .

When the retarder 2 is disconnected, the torus 44 is emptied of fluid, and subse- quently the air pressure is reduced to the first pressure level p1 , so that the spring force of the second return spring 82 is no longer overcome by the air pressure. Thus, the second return spring 82 will move the teeth 60 of the outer sleeve 58 out of their engagement with the teeth 62 of the carrier 61 . Subsequently the valve 88 is closed, so that the air pressure is reduced to atmospheric pressure, whereupon the spring force of the first return spring 80 is no longer overcome by the air pressure. Thus, the first return spring 80 will move the inner sleeve 57 at a distance from the plates 84, 86 of the first clutch element 54, so that the first clutch element 54 is disconnected and the first shaft 18 is no longer driven by the second shaft 22. Thus, the first shaft 18 will no longer rotate or will rotate very slowly, which results in the impact of the first shaft 18 on the second shaft 22 becoming minimal. Instead of reducing the air pressure in two steps, it is possible to reduce the air pressure continuously from the second pressure level p2 to atmospheric pressure.

A method for connection of the retarder 2 will be explained with the help of Figures 4 and 5. The flow chart in Fig. 4 shows that in a first step a), a first force achieved by a first air pressure is applied to the first clutch element 54, so that the second shaft 22 brings the first shaft 18 to rotate with substantially the same speed as the second shaft 22. In a second step b), a second force achieved by a second air pressure, which is larger than the first air pressure, is applied to the second clutch element 56, so that the first and second shafts 18, 22 are connected with each other. In a third step c), the retarder 2 is activated through the supply of fluid 46 to the torus 44 of the retarder 20.

The graph in Fig. 5 shows how the first force in step a) is generated with pressurised air at the first pressurised air level p1 at the point in time t1 , and that the second force in step b) is generated with pressurised air at the second pressurised air level p2 at the point in time t2, the pressurised air level p2 being greater than the pressurised air level p1 . The components and features specified above may, within the framework of the invention, be combined between different embodiments specified.