Hydrodynamic brake

A hydrodynamic brake which comprises a stator and a rotor, arranged to form a toroidal space, and blades on the rotor and the stator extend into the space. A medium which is intended to be supplied to the toroidal space to effect a braking action. A first pipe circuit for transferring the medium from an outlet from the toroidal space to an inlet to the toroidal space. A second pipe circuit for transferring the medium from a storage space to the toroidal space. The second pipe circuit transfers the medium to the toroidal space via a second inlet which is arranged separately relative to a corresponding first inlet to the first pipe circuit.

BACKGROUND TO THE INVENTION, AND STATE OF THE ART

The invention relates to a hydrodynamic brake including a rotor and a stator in shell form which together define an annular working space, and respective blades on the stator and the motor and projecting into the shell. The invention particularly concerns inlet and outlet of working medium to the space.

Oil is commonly used as a working medium of hydrodynamic brakes such as retarders in motor vehicles. The oil is supplied to the toroidal space defined by the stator and rotor of the retarder. The oil exerts in the toroidal space a braking action on the rotor and hence on the vehicle's driveline which is connected to the rotor. During the resulting braking process, the oil's kinetic energy is converted to thermal energy. Upon leaving the toroidal space, the oil is led via a pipe circuit to a heat exchanger before the cooled oil is led back to the toroidal space. To prevent overheating of the oil it is important to maintain a large flow through the toroidal space. With a large oil flow it is also possible to achieve effective cooling of the retarder in association with the toroidal space by means of the circulating oil. A simple way of achieving a large flow of oil through the toroidal space is to utilise the pressure differences which arise in the toroidal space during the operation of the rotor.

WO 02/04835 corresponding to U.S. Pat. No. 6,918,471, commonly owned herewith, describes advantageous positioning of an inlet and an outlet for the oil in the toroidal space whereby the aforesaid pressure differences are utilised to provide a large oil flow through the toroidal space. To that end, the inlet incorporates a multiplicity of input holes arranged on surfaces of the stator where low pressure occurs during operation of the retarder. The outlet incorporates output holes arranged on surfaces of the stator where relatively high pressure occurs during operation of the retarder. The oil is thus easily led into the toroidal space via the input holes and pushed out at high pressure from the toroidal space via the output holes to the pipe circuit which is intended to recirculate the oil to the toroidal space after cooling. Oil from an oil sump is also supplied continuously to the toroidal space during retarder braking. This entails the oil from the oil sump being pumped up to the high pressure which prevails in the pipe circuit which recirculates the oil to the toroidal space after cooling. The pump is thus subject to severe requirements in that it must have sufficient capacity to impart to the oil from the oil sump at least as high a pressure as the oil in said pipe circuit. Severe requirements also apply in this case to the pipe circuit adjacent to the pump to prevent the occurrence of leakage.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a hydrodynamic brake which allows a supply of the medium from the storage space to the toroidal space of the hydrodynamic brake via a relatively simple and hence less expensive pipe circuit.

This object is achieved with the hydrodynamic brake of the kind mentioned in the introduction which is characterised by the invention. The present invention relates to a hydrodynamic brake which comprises a stator and a rotor, arranged to form a toroidal space, and blades on the stator and the rotor extend into the space. A medium is intended to be supplied to the toroidal space to effect a braking action on the rotor via the blades. A first pipe circuit transfers the medium from an outlet from the toroidal space to an inlet to the toroidal space. A second pipe circuit transfers the medium from a storage space to the toroidal space. The second pipe circuit transfers the medium to the toroidal space via a second inlet which is arranged separately relative to a corresponding first inlet to the first pipe circuit.

Using a separate second pipe circuit for the medium which extends from the storage space to a separate second inlet to the toroidal space means that there is no need to impart to the medium in the second pipe circuit the same high pressure of medium as prevails in the first pipe circuit. The risk of leakage in such a second separate pipe circuit whereby the medium is transferred at a relatively moderate positive pressure is considerably less than in a pipe circuit in which a high pressure of medium prevails. This means that the second pipe circuit can be of relatively simple design and be provided at relatively low cost.

According to a preferred embodiment of the present invention, the second inlet incorporates at least one input hole situated in a region where the pressure during a braking process is substantially always lower than the pressure of the medium in the first pipe circuit. The lower the pressure in the toroidal space adjacent to the second inlet, the smaller the capacity required for leading the medium from the storage space, in which atmospheric pressure usually prevails, to the toroidal space. With advantage, the pressure in said region of the toroidal space corresponds substantially to atmospheric pressure during most braking processes. There is substantially no pressure difference between the toroidal space inlet and the storage space. This means that a relatively small capacity is required for transferring the medium to the toroidal space and that the risk of leakage in the second pipe circuit is therefore slight.

According to another preferred embodiment of the present invention, said input holes are situated substantially centrally in the toroidal space. The central region of the toroidal space usually exhibits a pressure which does not differ substantially from atmospheric pressure. It is therefore advantageous that the second pipe circuit should supply the medium to the toroidal space in said central region. The second inlet may be situated adjacent to a free end portion of a blade. The blades of the stator and rotor have a free end portion which extends substantially to a centrally situated plane which extends through the toroidal space between the stator and the rotor. The second inlet is preferably situated in the stator. As the stator, unlike the rotor, is stationary, it is less complicated to arrange the second pipe circuit so that it extends through a stator blade than through a rotor blade.

According to another preferred embodiment of the present invention, the second pipe circuit incorporates a pump for transferring the medium to the toroidal space. Such a pump requires a relatively small capacity and may be of relatively simple design because the difference between the pressure of the medium in the storage space and in the region adjacent to the second inlet of the toroidal space is comparatively small. Such a pump may therefore be provided at relatively limited cost. Said pump is with advantage a gear pump. Gear pumps are of relatively simple design with a small number of constituent parts. Gear pumps are used conventionally in hydrodynamic brakes such as retarders in motor vehicles. In the case here concerned, the gear pump is connected to and is driven by the same shaft as the rotor. The gear pump is thus connected to the vehicle's driveline, runs continuously with the vehicle and pumps the medium continuously from the storage space during vehicle operation. The gear pump pumps the medium to the toroidal space when the retarder is activated, but pumps the medium past the toroidal space back to the storage space when the retarder is not activated.

According to another preferred embodiment of the present invention, the first inlet to the toroidal space incorporates at least one input hole situated in a radially outer region of the stator. Such positioning of the first inlet obviates the need for the portion of the first pipe circuit which is adjacent to the inlet having to extend radially internally about the toroidal space. The outlet from the toroidal space is also preferably situated in a radially outer region of the stator. Such positioning of the outlet likewise obviates any need for the portion of the first pipe circuit which is adjacent to the outlet to have an extent radially internally about the toroidal space. The hydrodynamic brake with both the inlet and the outlet of the first pipe circuit situated in a radially outer region of the stator can be made to occupy less space.

FIG. 1depicts a hydrodynamic brake in the form of a retarder of a powered vehicle. The retarder comprises a stator1and a rotor2. The stator1has an annular shell3with a multiplicity of blades4arranged at uniform spacing along the annular shell3. The rotor2is of corresponding design with an annular shell5which incorporates a multiplicity of blades6likewise arranged at uniform spacing along the annular shell5. The respective shells3,5of the stator1and rotor2are coaxially arranged with respect to one another so that they together form a toroidal space7. The rotor2incorporates a shaft portion8which is firmly connected to a rotatable shaft9. The rotatable shaft9is itself connected to an appropriate driveshaft of the vehicle's driveline. The rotor2will thus rotate together with the vehicle's driveline.

The retarder depicted inFIG. 1incorporates a housing which comprises a first element10and a second element11. The first element10incorporates a body in which inter alia the stator1and the rotor2are arranged. The second element11is of cover-like design and can be fitted detachably along a connecting region12to the first element10so that in a fitted state they form a closed housing. In the connecting region12, a gasket13is arranged so that the housing forms a sealed enclosure. The first element10incorporates a multiplicity of recesses14–23which each have an opening in a substantially common plane A represented by the broken line A—A inFIG. 1. The connecting region12of the first element10and second element11also has an extent in said plane A.

The recesses14–23are each designed to accommodate a component which forms part of the retarder. The shape and size of the recesses14–23are adapted to the respective specific components which they accommodate. A first such recess14accommodates a first check valve24. A second recess15accommodates an outlet check valve25. A third recess16accommodates a gear pump26. A fourth recess17accommodates a second check valve27. A fifth recess18accommodates a dump (rapid emptying) valve28. A sixth recess19accommodates a regulating valve29. A seventh recess20accommodates an inlet check valve30. An eighth recess21accommodates a filling valve31. A ninth recess22accommodates an intake valve32for filling an accumulator33. A tenth recess23accommodates said accumulator33. The first element10and the second element11thus form a sealed housing which incorporates an oil sump34for storage of oil.

The retarder incorporates a first pipe circuit35with a first portion35awhich leads the oil from an outlet from the toroidal space7to the outlet check valve25. A second portion35bof the first pipe circuit leads the oil from the outlet check valve25to a heat exchanger36to cool the oil. A third portion35cof the first pipe circuit leads the cooled oil to the inlet check valve30or alternatively to the regulating valve29, depending on whether the retarder is or is not activated. A fourth portion35dof the first pipe circuit leads the oil to an inlet to the toroidal space7. The retarder incorporates a second pipe circuit37with a first portion37avia which the oil is drawn from the oil sump34to the gear pump26. A second portion37bof the second pipe circuit37leads the oil to the first check valve24and the second check valve27. When the retarder is not activated, the oil is led via the first check valve24and a third portion37cof the second pipe circuit to the second portion35bof the first pipe circuit. If the retarder is activated, the oil is led instead via the second check valve27and a fourth portion37dof the second pipe circuit to an inlet to the toroidal space7. The retarder also incorporates a third pipe circuit38which connects the accumulator33to a fourth portion35dof the first pipe circuit. The third circuit38incorporates the filling valve31and the accumulator's intake valve32. The first element10of the housing incorporates, adjacent to the recesses14–23, occupied ducts which form part of the aforesaid pipe circuits35,37,38.

A first control valve39is intended to control, by means of a control pressure, the operation of the safety valve18so that the toroidal space7can be quickly emptied of oil when necessary. A proportional valve40is intended to control, by means of a control pressure, the operation of the regulating valve19in order to activate the retarder and regulate the retarder's braking action. A second control valve41is intended to control, by means of a control pressure, the operation of the accumulator33so as to fill the toroidal space quickly with oil in order to effect a rapid braking action of the retarder. All of these three control valves39,40,41and the heat exchanger36are situated outside the housing.

When the vehicle's driver does not require the vehicle to be subjected to any braking action, the proportional valve40supplies no control pressure to the regulating valve29, which opens fully so that any oil in the third portion37cof the first pipe circuit drains away, via a passage42, to the oil sump34. This means that no oil runs past the inlet check valve30, which requires relatively high oil pressure for it to open and lead oil to the toroidal space7. As in this situation no oil is led to the toroidal space7, substantially no braking action is effected other than a minor undesired braking action due to a so-called no-load loss caused by the rotor circulating the air present in the toroidal space7.

The driveshaft9also drives the gear pump26which continuously pumps oil from the oil sump34during operation of the vehicle. From the gear pump26, the oil is led at a positive pressure to the second portion37bof the second pipe circuit. The first check valve24here has a spring with preloading such that it opens at a positive pressure of about 0.5 bar. The second check valve27has a spring with preloading such that it opens at a positive pressure of about 2 bar. When the regulating valve29is open, there is substantially no positive pressure in the first pipe circuit35. This means that in the second portion35bof the first pipe circuit there is no positive pressure which would otherwise increase the opening pressure for the first check valve24. As the first check valve24opens at a lower pressure than the second check valve27, the oil transferred from the oil sump34by the gear pump26is only led via the first check valve24and the third portion37cof the second pipe circuit to the second portion35bof the first pipe circuit, which is thus situated after the toroidal space7in the direction of flow of the oil. Thereafter the oil is led back to the oil sump34via the heat exchanger36, the third portion35cof the first pipe circuit, and the regulating valve29.

When the vehicle's driver requires the vehicle to be subjected to a braking action, the proportional valve40supplies the regulating valve29with a control pressure which is greater than the preloading of the inlet check valve30. The second control valve41activates the accumulator33so that the latter, via the third pipe circuit38and the filling valve31, leads oil at high pressure to the fourth portion35dof the first pipe circuit and to the toroidal space7. The accumulator33initiates oil supply by means of a positive pressure to bring about rapid filling of the toroidal space7and thereby effect a corresponding rapid braking action of the retarder. After the circulation of the oil in the toroidal space7, the oil is led out at high pressure via an outlet from the stator1to the first portion35aof the first pipe circuit. The outlet check valve25is opened by the high oil pressure and the oil is led to the second portion35bof the first pipe circuit. At this stage the oil is at a positive pressure of at least 5 bar. The oil in the second portion35bof the first pipe circuit is also led into the third portion37cof the second pipe circuit and exerts there a pressure action urging the first check valve24towards a closed position. The opening pressure required for the first check valve24will thus be higher than the corresponding opening pressure for the second check valve27which had a preloading of about 2 bar. This means that all of the oil transferred by the gear pump26from the oil sump34will be led via the second check valve27and the fourth portion37dof the second pump circuit to an inlet to the toroidal space7.

The inlet to the toroidal space7is with advantage arranged centrally in the toroidal space7. In the central part of the toroidal space a relatively low pressure prevails in substantially all operating states. Using a separate pipe portion37dto supply the oil from the oil sump34at atmospheric pressure to the toroidal space7means that this oil need not be pumped up to the high pressure which prevails in the fourth portion35dof the first pipe circuit. A less expensive gear pump26with a smaller pump capacity can therefore be used. The fourth portion37dof the second pipe circuit may also be of relatively simple design since it need only be dimensioned to carry oil at a relatively small positive pressure.

The oil is led from the second portion35bof the first pipe circuit to the heat exchanger36, in which it is cooled. The braking action of the retarder is regulated by the control pressure from the proportional valve40. The position of the regulating valve29is adjusted by means of the control pressure from the proportional valve40so that a certain proportion of the cooled oil after the heat exchanger36is led back to the oil sump34, while the remainder is led past the inlet check valve30to the toroidal space7. The result is regulation of the amount of oil circulating in the toroidal space7so as to effect a desired braking action.

FIG. 2depicts a stator1with an annular shell3which incorporates a multiplicity of blades4arranged at uniform spacing along the annular shell3. The fourth portion35dof the first pipe circuit ends with a first inlet to the toroidal space7, which inlet incorporates a multiplicity of input holes42situated in a radially outer region of the stator1on the side of the blades4where a relatively low pressure prevails. In a likewise radially outer region of the stator1, but on the opposite side of the blades4, output holes43are incorporated in an outlet to allow oil to leave the toroidal space7. On this side of the blades4a high oil pressure prevails. The oil is thus supplied to the toroidal space7in low-pressure regions and leaves it via high-pressure regions. This pressure difference results in a large oil flow though the toroidal space7. A large oil flow through the toroidal space7has a positive effect in that the oil is not overheated and that there is effective cooling of the retarder in association with the toroidal space7.

The second pipe circuit37thus caters for transfer of the oil from the oil sump34to a second inlet to the toroidal space7when the retarder is in its active state. The second inlet incorporates an input hole44arranged separately relative to the input hole42of the first inlet. Using a completely separate second pipe circuit37to supply the cold oil from the oil pan34to the toroidal space7obviates the need to pump the oil up to the pressure which prevails in the first pipe circuit35. The positive pressure in the first pipe circuit35is usually greater than 5 bar. The input hole44of the second inlet discharges at a free end portion of one of the blades4of the stator1. The input hole44of the second inlet thus provides a supply of oil in a central region of the toroidal space7. Here a substantially atmospheric pressure prevails substantially independently of the operating state of the retarder. The pressure difference between the oil sump34and the central region of the toroidal space7to which the oil from the oil sump is supplied is thus marginal. A relatively simple gear pump26with a smaller pumping capacity can therefore be used. The second pipe circuit37which transfers the oil to the input hole44of the second inlet may therefore as a whole be of relatively simple design, since there is no need to convey oil at a large positive pressure. The risk of leakage in the second pipe circuit37is thus considerably reduced.

FIG. 3depicts a section though a portion of the stator1inFIG. 2. The fourth portion37dof the second pipe circuit leads here into an input hole44which extends through a blade4of the stator1. The input hole44discharges adjacent to a free end portion substantially in the middle of the blade4. The oil is thus supplied to a relatively centrally situated region of the toroidal space7.

The invention is in no way limited to the described embodiment but may be varied freely within the scopes of the claims.