BACKGROUND TO THE INVENTION AND PRIOR ART

The present invention relates to an arrangement for counteracting cooling of an exhaust treating component in a vehicle according to the preamble of claim 1.

Exhaust lines of combustion engines such as diesel engines may comprise a plurality of exhaust treating components, e.g. a particulate filter DPF (diesel particulate filter) and an SCR (selective catalytic reduction) catalyst. A particulate filter captures from the exhaust gases soot particles which subsequently burn in a regeneration process. To remove nitrogen oxides from the exhaust gases, a urea solution is injected into the exhaust line at a point upstream of the SCR catalyst. The urea solution is vaporised by the warm exhaust gases in the exhaust line, resulting in the formation of ammonia. The ammonia and the nitrogen oxides in the exhaust gases react with one another in the SCR catalyst, resulting in the formation of nitrogen gas and water vapour. For an SCR catalyst to have a high degree of efficiency, it needs to be at a temperature above a lowest value which may be of the order of 200°C. The SCR catalyst should nevertheless not be at too high a temperature, since its efficiency will decrease above a certain value and there will also be risk of the active layers in the catalyst being damaged by too hot exhaust gases.

Heavy vehicles are commonly provided with a hydrodynamic brake in the form of a hydraulic retarder which takes care of braking on downhill runs. When a retarder is activated, no fuel will normally go to the engine. In this situation the engine will pump cold air through the exhaust treating components in the exhaust system during the braking process. If the downhill run is long, an SCR catalyst may well be cooled to a lower temperature than that required for being able to inject urea solution into the exhaust line. In such cases the catalyst may take a not negligible period of time to revert to a temperature at which the SCR catalyst can reduce the nitrogen oxides content of the exhaust gases in an optimum way.

GB 2 058 911 refers to a heat exchanger for cooling of oil used in a hydraulic retarder. The heat exchanger is situated in a bypass line to an inlet line which leads air to a combustion engine. By means of a valve the inlet air may be led through the bypass line and cool the oil in the heat exchanger before going to the engine. The retarder oil may thus undergo cooling while at the same time the warmed inlet air will counteract the cooling of the engine which occurs when the retarder is activated. EP 1 547 842 refers to a method for recovering brake energy in a hybrid vehicle which is powered by a combustion engine and an electrical machine. During a braking process the electrical machine serves as a generator and generates electrical energy which is normally stored in a battery. During a lengthy braking process a very large amount of brake energy is developed. The capacity of the battery will not always be sufficient to store all of the electrical energy generated during such a braking process. In such cases, electrical energy generated is led to an electrical warming device for direct or indirect warming of exhaust gases in an exhaust line. Exhaust treating components in the exhaust line may thus undergo warming during the braking process of the hybrid vehicle.

SUMMARY OF THE INVENTION

The object of the present invention is to maintain a desired operating temperature of an exhaust treating component in an exhaust line in operating situations where a hydraulic retarder is activated in a vehicle.

This object is achieved with the arrangement of the kind mentioned in the introduction which is characterised by the features indicated in the characterising part of claim 1. A liquid medium led through a hydraulic retarder undergoes powerful warming when the retarder brakes the vehicle's powertrain. The liquid medium is with advantage an oil which has the characteristic that it can be warmed to a high temperature without affecting its characteristics. The warm liquid medium leaving the retarder needs in all circumstances to be cooled before it can be used again in the retarder. When the retarder is activated, the vehicle is engine-braked and cold air is pumped through the exhaust line, with consequent risk of exhaust treating components in the exhaust line being cooled to a temperature at which they cannot clean the exhaust gases in a desirable way. The exhaust treating components therefore need to be warmed while at the same time the liquid medium in the retarder' s brake system needs to be cooled. According to the invention the brake system comprises a first line which leads the warm liquid medium from the activated retarder to a first heat exchanger situated in the exhaust line at a point upstream of the exhaust cleaning component. The air pumped through the exhaust line thus undergoes warming while at the same time the liquid medium undergoes cooling. The exhaust cleaning component can thus maintain a relatively high temperature throughout the period when the retarder is activated and the vehicle is engine -braked, and therefore begin to clean the exhaust gases in a substantially optimum way as soon as the retarder is inactivated and fuel is again injected into the engine.

In one embodiment of the present invention the exhaust line is divided into two parallel lines in a section situated between the engine and the exhaust treating component, and the first heat exchanger is situated in one of said parallel lines. The arrangement may comprise a first flow element adapted to distributing the gas flow in the exhaust line between the two parallel lines. This means that the whole exhaust flow from the engine can be led through the parallel line which has no heat exchanger when the retarder is not activated. The heat exchanger will thus not act upon the exhaust gases during operation of the engine. The whole or parts of the air flow can be led through the other parallel line which has the heat exchanger when the retarder is activated and the vehicle is engine-braked. Thus the air pumped through the exhaust line in operating situations where the retarder is activated can be warmed by the warm liquid medium from the retarder.

In one embodiment of the present invention the arrangement has in the brake system a second flow element adapted to leading a variable flow of the liquid medium to the heat exchanger. The heat transfer in a heat exchanger is related to the temperatures and flows of the heat transfer media. The air in the exhaust line may be warmed to a variable temperature by, for example, varying the flow of the liquid medium through the first heat exchanger.

The arrangement may comprise a control unit adapted to controlling the first flow element and/or the second flow element and hence the heat transfer in the heat exchanger when the retarder is activated, so that the gas led to the exhaust treating component will be at a temperature within a range in which the exhaust cleaning component has an optimum exhaust treatment capacity. Such a control makes it possible for the exhaust treating component to maintain an optimum operating temperature throughout the period when the retarder is activated and the vehicle is engine -braked. The exhaust treating component will thus also be at an optimum temperature for treating exhaust gases as soon as the engine braking process ends and exhaust gases begin to flow through the exhaust treating component again. In this case a warming period with deficient exhaust cleaning after an engine braking process has ended is eliminated. In one embodiment of the present invention the control unit is adapted to conducting the control of the heat transfer in the heat exchanger on the basis of information from at least one sensor which monitors a parameter related to the temperature of the exhaust treating component. This is a simple way of providing feedback as to whether the exhaust treating component is at an acceptable temperature. If said sensor indicates that the exhaust treating component is at too low a temperature, the heat transfer in the heat exchanger will be adjusted so that the air pumped through the exhaust line assumes a raised temperature. If the sensor indicates that the exhaust treating component is at too high a temperature, the heat transfer in the heat exchanger will be adjusted so that the air pumped through the exhaust line assumes a lower temperature.

In one embodiment of the present invention the control unit is adapted to receiving information from a sensor which monitors the gas temperature within the exhaust line at a point close to the exhaust treating component. It is usually not appropriate to fit a sensor within an exhaust treating component in order to directly monitor the temperature of the exhaust treating component. Exhaust treating components have an active surface layer which is in contact with the gas flowing through and which will therefore relatively quickly assume substantially the same temperature as the gas. Measuring the gas temperature close to the exhaust treating component is

uncomplicated and provides a good indication of the temperature of the exhaust treating component. Other sensors may also be used to control the warming of the air in the heat exchanger. Such sensors may for example monitor the air flow in the exhaust line and the temperature and flow of the liquid medium in the brake system. In another embodiment of the present invention the brake system comprises a second heat exchanger in which the liquid medium is cooled. In a conventional brake system the liquid medium in a heat exchanger is cooled by coolant from the engine's cooling system. In this case it is also appropriate to use such a heat exchanger to subject the liquid medium to a second step of cooling after it has undergone a first step of cooling in the first heat exchanger. The fact that in this case the liquid medium is also cooled in two heat exchangers results in a reduced cooling requirement in the second heat exchanger and hence the load on the engine's cooling system which is normally subject to great stresses when it has to cool away the large amount of thermal energy which may be generated during a lengthy braking process with a hydraulic retarder. In one embodiment of the invention the arrangement comprises a WHR system adapted to absorbing thermal energy from the gases in the exhaust line at a point downstream of the exhaust treating component. This means that the thermal energy which the air acquires in the first heat exchanger can be recovered and be reused or be stored as electrical energy. The stored electrical energy may be used on a later occasion for operation of the vehicle or its components. A WHR system makes it possible for the exhaust treating component to be provided with warming in a very energy economising way.

In another embodiment of the present invention the exhaust treating component is an SCR catalyst. For an SCR catalyst to be able to reduce nitrogen oxides in exhaust gases, a urea solution needs to be injected into and vaporised in the exhaust line at a point upstream of the catalyst. The arrangement according to the invention enables an SCR catalyst to maintain a temperature which corresponds to a desired operating temperature during retarder braking processes. The exhaust gases may thus be provided with urea solution and undergo optimum reduction of nitrogen oxides in the catalyst immediately after the retarder braking process ceases. The exhaust treating component need not be an SCR catalyst but may be substantially any exhaust treating component in an exhaust line which requires a certain temperature for it to function in an optimum way. Such other exhaust treating components might be an oxidation catalyst or an ammonia slip catalyst.

In another embodiment of the present invention the brake system comprises flow components adapted to leading cooled liquid medium to the heat exchanger, and to cooling of exhaust gases which are led through the heat exchanger in operating situations where the retarder is not activated. Exhaust treating components usually require a relatively high exhaust temperature for them to function in an optimum way. If the temperature of the exhaust gases becomes too high, the degree of efficiency of the exhaust treating components will usually decline while at the same time active surface layers of the exhaust treating components risk being damaged by too hot exhaust gases. In this case the heat exchanger and the liquid medium may be used to cool the exhaust gases in operating situations where the exhaust gases are too hot. This means that optimum cleaning of the exhaust gases may be achieved in an exhaust treating component even in operating situations with very high exhaust temperatures. It also means that the service life of the exhaust treating components will not be reduced by damage which might occur through contact with very hot exhaust gases.

In another embodiment of the present invention the exhaust line comprises a particle filter situated upstream of the SCR catalyst, and said first heat exchanger is situated in the exhaust line at a point between the particle filter and the catalyst. Exhaust gases from diesel engines contain soot particles, so exhaust lines for diesel engines are provided with a particle filter which captures soot particles from the exhaust gases. The particle filter does however need to be regenerated at regular intervals. The regeneration process involves the exhaust gases being subjected to such a high temperature that the soot particles burn in the filter. This may be achieved by heavy load upon the engine or by injecting unburnt fuel into the exhaust line. In a regeneration process it is appropriate to use the liquid medium to cool the exhaust gases in the heat exchanger. An SCR catalyst may thus assume a lower temperature than that prevailing in the particle filter during the regeneration process. The catalyst may thus maintain optimum reduction of nitrogen oxides during the regeneration process. The cooling of the exhaust gases in the first heat exchanger prevents the catalyst's active surface layers from coming into contact with too hot exhaust gases.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below by way of examples with reference to the attached drawings, in which

Fig. 1 depicts an arrangement according to a first embodiment of the present

invention, and

Fig. 2 depicts an arrangement according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Fig. 1 depicts a combustion engine 1 adapted to powering a vehicle. The engine 1 may for example be intended to power a heavy vehicle. The engine is provided with an exhaust line 2, only part of which is depicted. The exhaust line may initially be provided with an undepicted turbine of a turbo unit to compress inlet air which is led to the engine, and with an undepicted return line for recirculation of exhaust gases. The exhaust line comprises a section which is divided into two parallel lines 2a, 2b. A valve 3 is provided at a point where the exhaust line divides into the parallel lines 2a, 2b. The valve, here exemplified in the form of a damper 3, makes it possible for the gas flow in the exhaust line to be directed to either of the two parallel lines 2a, 2b. It is also possible to distribute the gas flow in a variable way between the two parallel lines. The parallel lines join together again at a point upstream of a number of the exhaust cleaning components 4-7.

The exhaust cleaning components are in this case an oxidation catalyst 4, a particle filter 5, an SCR catalyst 6 and an ammonia slip catalyst 7. In the oxidation catalyst, part of the nitrogen monoxide in the exhaust gases is oxidised to nitrogen dioxide. Substantially equal proportions of nitrogen dioxide and nitrogen monoxide may thus be achieved in the exhaust gases. The exhaust gases should preferably contain equal amounts of nitrogen monoxide and nitrogen dioxide when they reach the SCR catalyst 6 situated downstream, to make it possible to achieve optimum reduction of nitrogen oxides. After the oxidation catalyst 4, the exhaust gases are led to the particle filter 5 in which soot particles are caught and burnt. An undepicted injection device is provided to inject a urea solution into the exhaust line at a point upstream of the SCR catalyst 6. The urea solution is vaporised by the warm exhaust gases, resulting in the formation of ammonia in the exhaust gases. The exhaust gases need to be at a relatively high temperature to vaporise the ammonia. The ammonia and the nitrogen oxides in the exhaust gases react with one another when they reach the SCR catalyst, resulting in the formation of nitrogen gas and water vapour. For the nitrogen oxides to be reduced in an effective way in an SCR catalyst, they need to be at a temperature of at least 200°C. The exhaust temperature should however not be too high, since the degree of efficiency of the catalyst will drop at too high temperatures, at which there will also be more risk of damage to its active layers. Any remaining ammonia in the exhaust gases is eliminated in the ammonia slip catalyst 7 situated downstream of the SCR catalyst 6.

The exhaust line 2 is provided, at a point downstream of the exhaust treating components 4-7, with a WHR (waste heat recovery) system 8 for recovery of thermal energy from the gases in the exhaust line. The WHR system 8 comprises a closed line circuit with a circulating medium whose vaporisation and condensation temperatures at the pressures which occur in the line circuit during operation are appropriate for the purpose. The medium may be water. The medium is circulated in the line circuit by a pump 8a. The WHR system comprises a heat exchanger in the form of an evaporator 8b situated in the exhaust line 2. The medium in the evaporator is warmed by the gases in the exhaust line to a temperature at which it vaporises. The WHR system comprises an expander in the form of a turbine 8c in which the medium expands. The turbine is thus provided with rotary motion which can drive a generator 8d to generate electrical energy which is stored in a battery 8e. Alternatively, the turbine's rotary motion may be converted, via a mechanical transmission, to driving motion for the vehicle's powertrain. The WHR system comprises a condenser 8f in which the medium is cooled to a temperature at which it condenses. The WHR system may of course also comprise further components, e.g. a recuperator and a warming device for ensuring that all of the medium vaporises before going to the turbine. A possible alternative is a WHR system which comprises a thermal electric generator.

The engine 1 is adapted to driving the vehicle via a powertrain. The powertrain comprises inter alia a rotatable shaft 9 and a driveshaft which supports a pair of tractive wheels 10. The vehicle is provided with a hydrodynamic brake system 11 which comprises a retarder 11a. The retarder consists of a stator element which is stationary and a rotor element which rotates with the rotatable shaft 9 in the powertrain. The rotatable shaft may be situated in or close to a gearbox of the vehicle. The stator element and the rotor element form together a toroidal space. When the retarder is activated, a liquid medium in the form of retarder oil is led through the toroidal space. The stator element and the rotor element are provided in the toroidal space with blades which in conjunction with the retarder oil induce a braking process of the rotor element relative to the stator element and hence relative to the powertrain and the vehicle. The retarder oil undergoes powerful warming when it passes through the toroidal space during a retarder braking process. The brake system 11 comprises a container 1 lb for retarder oil. The retarder oil is led from the container to the retarder 11a via an inlet line 11c provided with a valve l id by which the retarder is activated. When the valve 1 Id is open, oil is drawn from the container to the retarder' s toroidal space and the retarder is thereby activated. When the valve 1 Id is closed, no oil is led to the retarder, which is therefore not activated. When the retarder is activated, oil is led out from the toroidal space to a first heat exchanger 1 If via an outlet line 1 le. The first heat exchanger is situated in the second parallel line 2b of the exhaust line. The warm oil from the retarder undergoes a first step of cooling in the first heat exchanger 1 If by gases which flow through the exhaust line's second parallel line 2b. The oil is thereafter led to a second heat exchanger 1 lg in which it undergoes a second step of cooling by coolant which circulates in a cooling system which cools the engine. The oil thus reaches the container 1 lb in a cooled state and can thereafter be reused in the retarder so long as the valve 1 Id is kept open. A control unit 12 is adapted to controlling the valve Hi and hence the activation of the retarder. The brake system 11 comprises a first bypass line 1 lh and a valve 1 li by which part of the oil may be led past the first heat exchanger 1 If. The control unit is also adapted to controlling the valve Hi and hence the oil flow through the first heat exchanger.

The control unit 12 receives information from a brake control 13 which is used by a driver to activate the retarder 11a. The control unit regulates the gas flow through the parallel lines 2a, 2b by means of the damper 3. In operating situations where the retarder is not activated, the damper 3 will usually be in a first position which completely closes an inlet aperture to the second parallel line 2b, in which case the whole exhaust flow is led through the first parallel line 2a. In operating situations where the retarder is activated, the control unit puts the damper 3 into a second position, represented by a dotted line in Fig. 1, in which case the whole gas flow is led through the second parallel line 2b and the first heat exchanger 1 If. When the retarder is activated, the engine will pump air through the exhaust line 2. The air will be warmed by the warm oil from the retarder in the first heat exchanger. The air warmed in the first heat exchanger passes thereafter through the exhaust treating components 4- 7. The warmed air may be used to prevent the exhaust treating components from cooling when the retarder is activated. A sensor 14 monitors the gas temperature at a point substantially immediately upstream of the exhaust treating components.

In operating situations where the vehicle reaches a long downhill run, the driver activates the retarder via the brake control 13. Alternatively the retarder may be activated automatically. When the control unit 12 receives this information, the valve 1 Id opens, whereupon retarder oil is drawn from the container 1 lb to the retarder 1 la via the inlet line 1 lc. The flow of retarder oil through the retarder causes the vehicle to be braked. The supply of fuel to the engine ceases, while at the same time the retarder is activated and the engine pumps air through the exhaust line 2. The control unit receives information from the sensor 14 concerning the gas temperature in the exhaust line close to the exhaust treating components 4-7. As soon as the gas temperature drops below a lower threshold value, the control unit puts the damper 3 into the second position so that the air in the exhaust line is led through the second parallel line 2b. The air is warmed by the retarder oil in the first heat exchanger 1 If. The sensor 14 monitors the temperature of the air before it passes through the exhaust treating components. The control unit receives information substantially continuously from the sensor 14 concerning the temperature of the air. If the sensor indicates that the air is at too low a temperature, the control unit operates the valve 1 li in such a way that the oil flow through the first heat exchanger 1 If increases. If the sensor indicates that the air is at too high a temperature, the control unit operates the valve 1 li in such a way that the oil flow through the first heat exchanger 1 If decreases. Such a control enables the exhaust treating components 4-7 and, in particular, the SCR catalyst 6 to maintain a temperature within a range in which the catalyst achieves optimum oxidation of nitrogen oxides. The warm air leaving the exhaust treating components is led through the evaporator 8b in which it vaporises the medium which circulates in the WHR system 8. The thermal energy with which the air is provided via the first heat exchanger 1 If may thus also be utilised and converted to electrical energy or mechanical energy in the WHR system. The WHR system can therefore also generate electrical energy or mechanical energy at times when the vehicle is engine-braked.

When the vehicle has reached the end of the hill, the control unit 12 closes the valve 1 Id so that the flow of oil to the retarder 1 la ceases. The injection of fuel into the engine commences and exhaust gases flow again through the exhaust line 2. The control unit puts the damper 3 into the first position so that the whole exhaust flow passes through the first parallel line 2a. The injection of urea solution commences and the SCR catalyst can immediately start oxidising the exhaust gases in an optimum way, since it will have maintained its optimum operating temperature throughout the period when the retarder was activated. The period of deficient oxidation of nitrogen oxides which might occur if the SCR catalyst cooled down during a retarder braking process is thus eliminated. Moreover, this improved exhaust cleaning ability provides the retarder oil with a first step of cooling in the first heat exchanger 1 If. This makes it possible for the second heat exchanger 1 lg to have a smaller capacity. It may be made smaller and represent a smaller load on the ordinary cooling system for cooling the engine when the retarder is activated. Alternatively the retarder may have more braking power. Fig. 2 depicts an alternative embodiment. The arrangement in this embodiment comprises substantially all the components of that in Fig. 1 and a number of further components. It thus has the same ability as the arrangement in Fig. Ito warm the air in the exhaust line 2 and maintain the temperature of the SCR catalyst situated downstream at times when the retarder 1 la is activated, so that the catalyst can clean the exhaust gases immediately after the braking process has ended. It likewise has a WHR system 8 which is able to utilise the thermal energy in the warmed air at a point downstream of the exhaust treating components at times when the retarder is activated. In this alternative embodiment, however, the parallel lines 2a, 2b are situated between the particle filter 5 and the SCR catalyst 6. The brake system 11 comprises in this case a second bypass line 1 lj which extends between the inlet line 1 lc and the outlet line 1 le. The brake system comprises a three-way valve 1 lk which can assume three different positions, viz. a first position which is closed, a second position which leads cooled retarder oil from the tank 1 lb to the retarder 11a, and a third position which leads cooled retarder oil from the tank to the bypass line 1 lj. A control unit 12 is adapted to putting the three-way valve into the respective positions in different operating situations and to controlling the activation of the pump 11m. During operation of the engine, the particle filter 5 needs regenerating at regular intervals. To this end, the engine may be activated so that the exhaust temperature is raised to such a high level that the soot particles caught in the filter burn.

Alternatively, unburnt fuel may be injected into the exhaust gases to raise the exhaust temperature. The efficiency of the SCR catalyst 6 is reduced at very high

temperatures. Its active layers might also be damaged by too hot exhaust gases, with consequent shortening of its service life. The control unit 12 receives information which indicates when the particle filter should be regenerated. The control unit receives information substantially continuously from the sensor 14 concerning the temperature of the exhaust gases in the exhaust line close to the catalyst. When the temperature of the exhaust gases rises beyond an upper threshold value, the control unit puts the valve 1 lk into the third position, followed by the pump 1 lm being started. Cooled retarder oil is thus conveyed from the container 1 lb to the first heat exchanger 1 If via the outlet line 1 le. The control unit adjusts the position of the damper 3 so that the exhaust gases in the exhaust line pass through the second parallel line 2b. The exhaust gases are cooled by the oil in the first heat exchanger 1 If. The control unit receives information substantially continuously from the sensor 14 concerning the temperature of the exhaust gases close to the catalyst. The control unit controls the valve Hi and hence the oil flow through the first heat exchanger in such a way that the exhaust gases entering the catalyst will substantially never be at a higher temperature than the upper threshold value. The catalyst is thus also enabled to maintain optimum reduction of nitrogen oxides even in operating situations where the particle filter 5 is being regenerated. Even in operating situations where the engine is under heavy load and the exhaust gases are at a higher temperature than the upper threshold value, the control unit will be able to direct cooled retarder oil to the first heat exchanger 1 If and control the valve 1 li in such a way that the temperature of the exhaust gases is reduced to a level below the threshold value.

The invention is in no way restricted to the embodiment to which the drawing refers but may be varied freely within the scopes of the claims. The exhaust treating component need not be an SCR catalyst but may be any kind of exhaust treating component which requires a relatively high temperature for it to achieve optimum treatment of exhaust gases.