BACKGROUND AND PRIOR ART

The present invention pertains to a retarder according to the preamble of patent claim 1, a vehicle, which comprises such a retarder according to the preamble to patent claim 7, and a method for the engagement and disengagement of a retarder according to the preamble to patent claim 8.

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 engaged 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 is disengaged and the retarder is disengaged from the gearbox or the propeller shaft when the retarder is deactivated and does not have to brake the vehicle. The retarder shaft is then immobile, which entails that the oil pump, which is driven by the retarder shaft, is not able to fill the retarder oil circuit and the torus, which is formed by the rotor and stator of the retarder, with retarder oil.

The torus must be filled with retarder oil as quickly as possible when a braking effect from the retarder is sought. A slow filling initially entails a lack of a braking effect from the retarder, which entails an exaggerated use of the vehicle's wheel brakes which will be exposed to unnecessary wear.

In order to expedite the filling of the torus, the retarder may be equipped with an oil accumu- lator, which is filled with retarder oil and which, with the power from a piston impacted by hydraulic oil, leads the retarder oil via an accumulator circuit and a retarder oil circuit into the torus. The oil accumulator's contribution to quickly filling the torus is not sufficient, however, in all operating conditions and especially not in close connection to starting the vehicle, as the retarder oil in the retarder is then cold and viscous and has not yet filled the retarder oil cir- cuit, since the retarder shaft and thus the oil pump on the retarder shaft have been immobile for a longer period. The engagement of the transmission on the gearbox or the propeller shaft may also be more difficult where the vehicle's combustion engine and gearbox have not achieved a predetermined working temperature. In the event that a clutch device, which is used for the engagement and disengagement of the transmission on the gearbox or the propeller shaft, comprises a synchronisation device with synchronisation rings, the engagement and disengagement of the transmission on the gearbox or propeller shaft is more difficult when the clutch device is cold. Thus the retarder's braking effect may be delayed or altogether absent. The document US-A-3777860 shows a retarder for vehicles with a rotor and stator, at which 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, there is a need to further develop a retarder which does not significantly encumber a driving source when it is deactivated, but which is activated for a very short period of time when it exerts a braking effect on the driving source. The objective of the present invention is thus to provide a retarder with a short activation period.

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

Another objective of the invention is to provide a retarder which reduces the fuel consumption of a vehicle.

Another objective of the invention is to provide a retarder with increased service life and reli- ability.

These objectives are achieved with a retarder of the type specified at the beginning, which is characterised by the features specified in the patent claim 1. Such a retarder reduces the activation time significantly on engagement of the retarder. When the driving source is started, the retarder and the driving source are engaged, so that the retarder shaft drives the oil pump in order to fill the retarder oil circuit with retarder oil. A ta- chogenerator is arranged to measure the retarder shaft's revolutions in order to determine, based on knowledge about the capacity of the oil pump, when the retarder oil circuit is filled with retarder oil. Thus, the retarder is prepared for disengagement from the driving source in order to exert, when disengaged, substantially zero braking torque on the driving source and at a later stage to be engaged with a very short activation time. When the retarder oil circuit is filled, the retarder is disengaged from the driving source through the clutch.

When the retarder's associated clutch device operates at a predetermined working temperature, the retarder and the driving source are, according to one embodiment of the invention, engaged so that the retarder shaft drives the oil pump in order to fill the retarder oil circuit with retarder oil. When the clutch device for engagement and disengagement of the retarder shaft to and from the driving source, has achieved the predetermined working temperature, the retarder is disengaged from the driving source via the clutch device.

According to another embodiment of the invention, the retarder is permitted to be disengaged only if the conditions specified above are met and if the driving source emits a positive torque for the first time. When the driving source emits a positive torque for the first time, an indication that the retarder should not brake the driving source is thus obtained, so that the retarder may be disengaged.

The above objectives are achieved also with a vehicle of the type specified at the beginning, which is characterised by the features specified in the patent claim 7. The retarder permits a brief activation time and, when deactivated, exerts substantially zero braking torque on the vehicle in order thus to reduce the fuel consumption. The controlled engagement and disengagement of the retarder also entails that its service life and reliability increases. The above objectives are achieved also with a method for the engagement and disengagement of a retarder specified at the beginning, which is characterised by the features specified in the patent claim 8.

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

Below is a description, as an example, of preferred embodiments of the invention with refer- ence to the enclosed drawings, on which:

Fig. 1 shows a schematic side view of a vehicle with a retarder according to the present invention, Fig. 2 shows a cross section view of a retarder according to the present invention, and

Fig. 3 shows a flow chart of a method for the engagement and disengagement of a retarder according to the present invention. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Fig. 1 shows a schematic side view of a vehicle 1, vehicle 1 which is equipped with a retarder 2 according to the present invention. The vehicle 1 is also equipped with a gearbox 4, which is connected to a combustion engine 6, which drives the driving wheels 8 of the vehicle 1 via the gearbox 4 and a propeller shaft 10. The combustion engine 6 is equipped with a temperature sensor 12 in order to measure the temperature of the coolant 14 of the combustion engine 6. The temperature sensor 12 may also be placed in the gearbox 4 or in the retarder 2, in order to measure the temperatures of the gearbox oil 16 and the retarder oil 18, respectively. A torque sensor 20 is arranged on the combustion engine 6 in order to detect the torque emitted from the combustion engine 6. The temperature sensor 12 and the torque sensor are engaged to a control device 22, which is arranged to control the retarder 2.

Fig. 2 shows a cross section view of a retarder 2 according to the present invention. The retarder 2 is equipped with a retarder shaft 24, which is engaged to an output shaft 26 of the gearbox 4 via a cog gear 28, comprising a first and second cogwheel 30, 32 engaged with each other. The first cogwheel 30 is arranged on the output shaft 26 of the gearbox 4 and the second cogwheel 32 is arranged on the retarder shaft 24. The first cogwheel 30 may be engaged and disengaged to the output shaft 26 of the gearbox 4 via a clutch device 34. Prefera- bly, a gearing through the cog gear 28 in the ratio of 3: 1 occurs, but other gearings are also possible, e.g. 1: 1.

The retarder shaft 24 is preferably journalled in the gearbox and in a retarder housing 38 via a bearing 36. A rotor 40 and an oil pump 42 are arranged on the retarder shaft 24, which rotate at revolutions which are proportionate to the output shaft 26 of the gearbox 4. A stator 44 is connected to the retarder housing 38 and may therefore not rotate. The retarder housing 38 comprises an oil pump 46, which is filled with retarder oil 18 to a predetermined level. An oil filter 50 filters away any potential particles in the retarder oil 18.

The rotor 40 and the stator 44 jointly form a toroidal cavity, referred to as a torus 52, which is filled with retarder oil 18 when the retarder 2 is to exert a braking torque on the output shaft 26 of the gearbox 4 in order to brake the vehicle 1 to thus reduce the speed of the vehicle 1. The braking effect arises since the rotor 40 and the stator 44 are equipped with blades or shovels 54, which create an oil flow in the torus 52 when the rotor 40 rotates. The oil flow creates a reaction force jointly with the shovels 54 of the rotor 40 and the stator 44, which forms the braking effect. The greater the revolutions of the rotor 40, the greater the reaction force. On occasions when the retarder 2 does not have to brake the vehicle 1, the torus 52 is drained of retarder oil 18, which entails that the shovels 54 of the rotor 40 and the stator 44 will create an air flow in the torus 52. The air flow causes an undesirable reaction force on the retarder shaft 24, which generates a braking torque on output shaft 26 of the gearbox 4. The braking torque from the retarder 2 entails that the fuel consumption of the vehicle 1 increases when the combustion engine 6 of the vehicle 1 exerts a torque. The friction from the bearings and the oil pump 42 of the retarder shaft 24, which is driven by the retarder shaft 24, also ex- ert a reaction force which causes an increased fuel consumption. For this reason the first cogwheel 30 may be disengaged from the output shaft 26 of the gearbox 4 when the retarder 2 is not used to brake the vehicle 1. Thus the fuel consumption of the vehicle 1 may be reduced.

Filling and draining of the torus 52 with retarder oil 18 takes place with a retarder oil circuit 56, which comprises a primary and a secondary oil circuit 58, 60. When the retarder 2 is activated in order to brake the vehicle 1, the first cogwheel 30 is engaged to the output shaft 26 of the gearbox 4. Thus, the retarder shaft 24 rotates, which causes the retarder shaft 24 to drive the oil pump 42, which pumps retarder oil 18 from the oil sump 46 via the oil filter 50. The oil pump 42 thus fills the primary oil circuit 58 with retarder oil 18. The primary oil circuit 58 is connected with the torus 52, which causes the torus 52 to be filled with retarder oil 18. In order for the torus 52 to be filled with retarder oil 18, however, a safety valve 62 must be closed, which occurs with the help of hydraulic oil 64, which is added via a first regulation valve 66. The safety valve 62 is also a drainage valve, which opens and closes a drainage channel 68, connecting the torus 52 and the oil sump 46. The drainage channel 68 is also engaged with the oil sump 46.

When the torus 52 is filled and the retarder 2 brakes the vehicle 1, the retarder oil 18 will be heated by the flow effects generated by the shovels 54 of the rotor 40 and the stator 44. The retarder oil 18 will thus be led further to the secondary circuit 60, which is engaged with an oil cooler 70. After the retarder oil 18 has passed the oil cooler 70, the retarder oil 18 is then led further through the secondary oil circuit 60, which is engaged downstream of the oil cooler 70 with the torus 52. Thus the secondary oil circuit 60 returns the retarder oil 18 into the torus 52. Downstream of the oil cooler 70, the secondary oil circuit 60 is connected with the oil sump 46 via a control valve 72, which is opened and closed by hydraulic oil 64 via a proportional valve 74. When the retarder 2 is engaged and brakes the vehicle 1, the control valve 72 is closed. Thus the retarder oil 18 in the secondary oil circuit 60 will be returned to the torus 52. In order to expedite the filling of the torus 52 at low revolutions of the output shaft 26 of the gearbox 4, and thus low revolutions of the retarder shaft 24, when the oil pump 42 is unable to achieve a sufficiently large oil flow, an oil accumulator 76 may be activated with hydraulic oil 64 via a second regulation valve 78. The oil accumulator 76 is filled with retarder oil 18 which, with pressure from a piston impacted by the hydraulic oil 64, leads retarder oil 18 via an accumulator circuit and the secondary oil circuit 60 into the torus 52.

In order to drain the torus 52, the safety valve 62 and the control valve 72 are opened, so that the retarder oil 18 leaves the torus 52 via the drainage channel 68 and via the control valve 72. The torus 52 must be filled with retarder oil 18 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, which entails an exaggerated use of the wheel brakes of the vehicle 1, which will be exposed to unnecessary wear. The contribution of the oil accumulator 76 to quickly filling the torus 52 is not sufficient, however, in all operating conditions and especially not in close connection with starting the vehicle 1, as the retarder oil 18 in the retarder 2 is then cold and viscous and has not yet filled the retarder oil circuit 56, since the retarder shaft 24 and thus the oil pump 42 on the retarder shaft 24 have been immobile for a longer period. The engagement of the first cogwheel 30 on the output shaft 26 of the gearbox 4 may also be more difficult where the combustion engine 6 and gearbox 4 of the vehicle 1 have not achieved a predetermined working temperature. In the event the clutch device 34 for engagement and disengagement of the first cogwheel 30 on the output shaft 26 of the gearbox 4 comprises a synchronisation device with synchronisation rings 80, and if the clutch device 34 is lubricated by the gearbox oil 16 in the gearbox 4, the engagement of the first cogwheel 30 on the output shaft 26 of the gearbox 4 may be more difficult when the gearbox oil 16 is cold. Thus the braking effect of the retarder 2 may be delayed or altogether absent.

The present invention resolves the above stated problem by connecting the first cogwheel 30 to the output shaft 26 of the gearbox 4 when the vehicle is started. In this start-up phase of the vehicle 1 and the combustion engine 6 of the vehicle 1, the torus 52 and the primary and secondary oil circuits 58, 60 are drained of retarder oil 18, which means that the retarder 2 does not exert a full brake torque on the vehicle 1. However, the retarder 2 acts with an undesirable reaction force on the retarder shaft 24 when the torus 52 is drained, which results in an increased fuel consumption, as mentioned above. This entails that it is desirable to disconnect the first cogwheel 30 from the output shaft 26 of the gearbox 4 as soon as possible.

When the combustion engine 6 is started up, the control valve 72 is closed according to the invention, while the safety valve 62 is opened. Thus, the primary and the secondary oil circuits 58, 60 will be filled with retarder oil 18 by the oil pump 42 activated by the retarder shaft 24. However, torus 52 is not filled with retarder oil 18, since the safety valve 62 is open and the drainage channel 68 is thus also open. By determining the volume in the primary and secondary oil circuits 58, 60 and at the same time knowing the capacity of the oil pump 42 at different revolutions, the duration required to fill the primary and the secondary oil circuits 58, 60 may be calculated if the revolutions of the output shaft 26 of the gearbox 4 are meas- ured, which is carried out with a tachogenerator 82. The retarder oil circuit 56 is deemed filled when sufficient time has lapsed with a flow exceeding a certain minimum level. The retarder oil flow is assessed based on the revolutions of the output shaft 26 of the gearbox 4, which at a certain speed is proportionate to the flow. The tachogenerator 82 is according to the embodiment displayed in Fig. 2 arranged on the output shaft 26 of the gearbox 4, but it is also possible to arrange the tachogenerator 82 on the retarder shaft 24 in order to directly measure the speed of the retarder shaft 24.

According to the invention, the temperature of the coolant 14 of the combustion engine 6, the temperature of the gearbox oil 16 in the gearbox 4 and/or the temperature of the retarder oil 18 in the retarder 2 are also measured. When one or all of these temperatures have reached a predetermined limit value, while it has been concluded at the measured time that the primary and the secondary oil circuits 58, 60 in the retarder have been filled with retarder oil 18, which is described above, the first cogwheel 30 will be disengaged from the output shaft 26 of the gearbox 4. In engagement with the temperature measuring, it is also possible to measure and take into consideration the temperature surrounding the vehicle 1. The temperature of the coolant 14 in the combustion engine 6, the temperature of the gearbox oil 16 in the gearbox 4 and/or the temperature of the retarder oil 18 in the retarder 2 are proportionate to the temperature of the clutch device 34 and give an indication of the temperature of the clutch device 34.

During the above disengaged state of the retarder 2, the retarder oil circuit 56 is filled with retarder oil 18 and the temperature of the clutch device 34 for the first cogwheel 30 has achieved a temperature which enables a quick and effective engagement of the first cogwheel 30 on the output shaft 26 of the gearbox 4.

According to one embodiment of the invention, the retarder 2 is permitted to be disengaged only provided that the conditions described above are met and if the combustion engine 6 emits a positive torque for the first time. If the combustion engine 6 of the vehicle 1 is started and its coolant 14 reaches the predetermined temperature and the time for the filled retarder oil circuit 56, the first cogwheel 30 will be disengaged from the output shaft 26 of the gearbox 4 when the combustion engine 6 emits a positive torque.

When the retarder 2 is to be activated to brake the vehicle 1, the clutch device 34 is thus activated, so that the first cogwheel 30 is connects to the output shaft 26 of the gearbox 4. At the same time, the safety valve 62 is closed, so that the draining channel 68 is closed. This entails that the torus 52 will quickly be filled with retarder oil 18, since the retarder shaft 24 rotates and drives the oil pump 42, which pumps retarder oil 18 from the oil sump 46 and further along to the retarder oil circuit 56. Since the retarder oil circuit 56 is already filled with retarder oil 18 before the retarder 2 is activated, the retarder oil 18 from the secondary oil circuit 60 will flow into torus 52 and fill this, which entails that the retarder 2 will exert a braking effect on the vehicle 1, as described above. According to the above, the retarder 2 is described as being arranged at 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, combustion engine 6, gearbox 4 or propeller shaft 10 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.

The method according to the present invention will be described below jointly with the flow chart in Fig. 3, the method of which comprises the steps to:

a) engage the retarder shaft 24 to the driving source 1, 4, 6, 10 with the clutch device 34; b) with the oil pump 42 fill the retarder oil circuit 56 with retarder oil 18; and

c) with the clutch device 34 disengage the retarder shaft 24 from the driving source 1, 4, 6, 10 when the retarder oil circuit 56 is filled with retarder oil 18.

The method also comprises the additional step:

d) that a safety valve of the retarder 2 is controlled to an open position to open a draining channel 68 engaged to the torus 52 and thus to drain the torus 52 of retarder oil 18. The method also comprises the additional step:

e) to measure the revolutions of the retarder shaft 24 in order to determine when the retarder oil circuit 56 is filled with retarder oil 18.

The method also comprises the additional step:

f) to determine the temperature of the clutch device 34 and to disengage the retarder shaft 24 from the driving source 1, 4, 6, 10 with the clutch device 34 when the temperature of the clutch device 34 has reached a predetermined temperature.

The method also comprises the additional step:

g) that the temperature of the clutch device 34 is determined by measuring the temperature of the driving source 1, 4, 6, 10.

The method also comprises the additional step: h) to measure a torque emitted by the driving source 1, 4, 6, 10 and to disengage the retarder shaft 24 from the driving source 1, 4, 6, 10 with the clutch device 34 when the driving source 1, 4, 6, 10 emits a torque. The method also comprises the additional steps:

i) after the disengagement of the retarder shaft 24 from the driving source 1, 4, 6, 10 to engage the retarder shaft 24 to the driving source 1, 4, 6, 10 with the clutch device 34; and j) to control the safety valve 62 to a closed position in order to close the draining channel 68 engaged with the torus 52, so that the torus 52 is filled with retarder oil 18 from the retarder oil circuit 56 filled with retarder oil 18 and so that the retarder 2 acts with a braking torque on the driving source 1, 4, 6, 10.

The components and features specified above may within the framework of the invention be combined between different embodiments specified.