Abstract:
The invention relates to a method and a device for increasing the use of the braking moment of a retarder in an automobile. According to this method, the heat produced by the retarder during braking is dissipated using a coolant. The method is characterized in that at least one auxiliary consumer and/or at least one of the following devices of the cooling system—a connected fan, a connected thermostat, a coolant pump, a bypass-valve—is controlled in dependence on the mode of the operation of the retarder.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method for increasing the utilization of the braking torque of a retarder in a motor vehicle. The invention further relates to conducting away heat generated in the retarder during the braking operation using a coolant. The invention also relates to operating secondary loads in a cooling system even if not required. 
     In order to cool vehicle components, for example hydrodynamic brakes, internal combustion engines, etc., use is generally made today of coolant circuits comprising a coolant, preferably water with appropriate antifreeze additives. In such circuits, a specific quantity of coolant per time unit flows through the component to be cooled. The coolant absorbs heat that is to be conducted away from the component and conveys the heat to a radiator, for example a ribbed radiator, or to a heat exchanger. The radiator or exchanger outputs the absorbed and conveyed quantity of heat into the environment or to another coolant circuit. The cooling power of such a system is determined essentially by the efficiency of the individual system components, for example the delivery capacity of the coolant pump. 
     In order to protect the engine cooling system against overheating when a retarder is switched on, it has therefore been proposed in 
     WO 94/27845 
     to reduce the retarder braking power as a function of the engine speed, and thus the speed of the coolant pump. 
     A disadvantage with this method or this control system is that the retarder braking torque is reduced very early, and as a result the braking power of the retarder is utilized only insufficiently. 
     SUMMARY 
     The object of the present invention is therefore to specify a method and a device for carrying out the method with which the disadvantages of the prior art are avoided and the retarder braking torque can be utilized better than hitherto, that is to say the retarder availability is increased. 
     This object is achieved according to the invention in that at least one secondary load and/or at least one of the following devices of the cooling system in the vehicle: 
     a switched fan 
     a switched thermostat 
     a coolant pump 
     a bypass valve in the cooling circuit 
     is actuated as a function of the instantaneous or future braking requirement. 
     It is particularly advantageous if at least the following retarder operating states: 
     switching on the retarder 
     requested or actually selected braking level of the retarder 
     are distinguished. In terms of actuation, the following variants are conceivable: 
     everything depends on the engine control system. It controls the engine, the fan and the retarder; or 
     each of the aforesaid assemblies has its own control system and these communicate with one another; or 
     retarder and fan have a common control system. 
     A particularly interesting variant consists in not sensing the instantaneous braking requirement or not exclusively sensing the instantaneous braking requirement, but also the future braking requirement in terms of predictive driving. The future braking requirement can be defined here by means of a navigation system in which the route ahead is examined by means of, for example, a satellite system (so-called global positioning system). 
     According to the invention, the retarder availability with respect to the maximum possible level of braking torque can be increased by virtue of the fact that a switched fan, for example that of the vehicle radiator, is connected into the circuit by the retarder electronics when the retarder switch-on instruction is present, as a result of which the efficiency of the cooling system is increased. 
     In order to avoid fuel being used unnecessarily by the fan which is connected into the circuit when the retarder is switched off, there is provision that when the retarder is OFF instruction is present, the fan is enabled again or switched off. Actuation takes place then only by means of the sensors of the engine cooling system. As an alternative to switching off or enabling the fan when the retarder is switched off, there may also be provision to switch off or enable the fan when the retarder braking torque drops below a specific value that is predefined at a low level. 
     In addition to a pure on/off logic system as described above, it is advantageously provided that in the case of multi-step fans or infinitely adjustable fans the actuation of the fan is carried out as a function of the requested retarder braking power, for example the selected retarder braking level. In principle, the fan according to the invention operates with a high rotational speed at high retarder braking levels, whereas at low retarder braking levels the fan is either entirely enabled or runs with only a reduced rotational speed. 
     In a further, developed embodiment of the invention, there may be provision for the thermostat which is preferably embodied as a 2/3-way valve in, for example, the coolant circuit of the vehicle cooling system to be switched as a function of retarder operating states. 
     There may be provision that if the cooling system is running in the bypass mode, i.e. the coolant fluid is being conducted past the vehicle radiator, the 2/3-way valve is actuated, after the retarder is switched on, in such a way that coolant fluid flows through the vehicle radiator in order to increase the cooling power of the cooling system. 
     The retarder availability can be increased further if not only the fan and the bypass valve are actuated as a function of the braking requirement but also a coolant pump, if said pump is one whose rotational speed can be actuated or regulated. In such embodiments there may be provision that the rotational speed of the coolant pump is increased when the retarder is switched on and decreased to the normal level when the retarder is switched off. With a coolant pump whose rotational speed can be adjusted, it is also possible to select the rotational speed as a function of the selected retarder braking level. 
     So that the heat generated by the retarder can be conducted away better than hitherto and not exclusively by means of the cooling system and from there into the environment, there is provision that secondary loads in the vehicle which do not have to be permanently in use are switched on if the retarder is switched on, in order to convert the braking work into useful work, with the result that the energy can be utilized more appropriately. 
     If the retarder is a secondary retarder, and there is no need whatsoever to restrict the invention to this, a separate heat exchanger is generally assigned to said secondary retarder. If the heat exchanger circuit has, like the engine cooling system, a bypass, in a particular refinement of the invention it is possible to operate the bypass similarly to the operation of the radiator bypass valve. The heat exchanger bypass in this instance is connected in a way analogous to the radiator bypass valve. That is, coolant is conducted through the heat exchanger when relevant for the braking mode of the retarder, and past the heat exchanger when the retarder is switched off. 
     In addition to the method described above, the invention also makes available a control device for carrying out the method. According to the invention there is provided a control or regulating system that comprises means, for example sensors, for sensing the retarder operating states or the instantaneous or future braking state. The system further comprises a control/regulating device that actuates vehicle assemblies such as secondary assemblies and/or devices of the cooling system as a function of the retarder braking states detected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An example of the invention will now be explained with reference to the drawings, in which: 
     FIG. 1 is a schematic view of a vehicle cooling system according to the invention with a retarder which operates as a primary retarder. 
     FIG. 2 is a schematic view of a vehicle cooling system according to the invention with a retarder which operates as a secondary retarder. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 represents a drive unit composed of an engine  1  and a cooling circuit  3 . The cooling circuit  3  comprises a radiator  5 , a coolant pump  7 , which is configured here as a coolant pump regulated whose rotational speed is regulated, and an equalization vessel  9 , which always ensures that there is adequate overpressure on the pump intake side. The embodiment illustrated in FIG. 1 is a primary retarder  13  which is arranged in the cooling circuit. By means of the switch-over valve  11  it is possible to conduct coolant past the vehicle when the retarder is switched off. The invention is, however, not restricted in any way to primary retarders which, as in FIG. 1, are arranged in the coolant circuit of the engine. The invention can also be applied even if the coolant circuit is separated from the engine and retarder. 
     A bypass line  40  leads past the radiator and branches at the point  42 . At the point  42 , a switch-over valve or thermostat  44  is arranged which can be configured as a 3/2-way valve. The 3/2-way valve has the function of controlling the coolant flow in such a way that it can be conducted either through the radiator or else through the bypass line  40  past the radiator. It is generally the case that the 3/2-way valve conducts the coolant stream to the radiator  5  partially or for the greater part in operating phases in which a large amount of heat is conducted away. In the phase in which a small amount of heat is conducted away, the 3/2-way switch-over valve  44  directs the coolant to the engine  1  or to the pump  7  via the bypass line. The 3/2-way valve can be embodied as an expansible-material-regulated valve or as an electrical or pneumatic continuously variable valve. 
     The fan  15  is arranged downstream of the vehicle radiator  5  as a further assembly of the cooling system. The fan  15  is preferably of switchable design. The retarder operating state, i.e. switched-on retarder, switched-off retarder, braking level of the retarder, is detected, for example, by the sensor  22  or by the retarder operator lever which is not illustrated here, tapped and transmitted to the control/regulating unit  24 . 
     As a function of the sensed or transmitted signal, the control/regulating unit  24  controls the various assemblies of the cooling system such as the fan, 3/2-way valve or else vehicle secondary assemblies which are not continuously in use and via which heat can be conducted away. 
     For example, the fan  15  can be activated when the retarder is switched on, and the cooling power of the vehicle cooling system can thus be increased. As a result, the full braking power or the maximum braking torque of the retarder is available immediately when the retarder is switched on. 
     If the switch-over valve  44  is in the bypass position and the heat is being conducted past the radiator via the bypass  40 , said switch-over valve  44  can, like the fan  15 , be activated so that the coolant is conducted through the radiator  5 . Of course, in a particular advantageous refinement, it is possible to co-ordinate the activation of the switch-over valve  44  and thus the fan  15 . In this way, for example, the switch-over valve  44  can be switched to a setting in which there is a flow through the radiator  5  and the rotational speed of the fan  15  is then increased. If the requested braking power of braking torque drops below a specific value, the fan  15  can firstly be switched off. The switch-over valve  44  is not switched to bypass mode again unit the retarder is completely switched-off. 
     In one developed embodiment, there may be provision for the rotational speed of the fan to be controlled as a function of the respective retarder braking level. For example, the rotational speed of the fan can be increased at a high retarder braking level, i.e. high braking torque request, and thus a requirement for a large amount of heat to be conducted away, while it is reduced when low braking torque is requested. 
     In addition to the fan  15  and the switch-over valve  44 , a rotational-speed-regulated coolant pump  7  is provided in the embodiment of a vehicle cooling system illustrated in FIG.  1 . 
     The rotational-speed-regulated coolant pump  7  is also actuated by the control/regulating device  24 . It is possible, for example when a retarder ON instruction is present, to adjust the rotational speed of the coolant pump to a predetermined, significantly higher value than during normal driving mode. The delivery capacity in the coolant circuit is increased and more heat can be conducted away than during the normal mode. 
     If the braking torque or the requested braking power drops below a specific value, the rotational speed of the pump  7  can be reduced to the value required solely by the engine cooling system when the retarder is switched off. By reducing both the rotational speed of the pump  7  and that of the fan  15  and switching over the bypass valve  44  when the retarder OFF instruction is present, it is possible to minimize the fuel consumption in the driving mode because components which are not required do not operate at the same time. 
     On the other hand, by connecting into the circuit the above-mentioned assemblies when a retarder ON instruction is present or at a predefined braking level, the retarder availability is increased in comparison with the previously known control/regulating systems. 
     FIG. 2 illustrates an alternative embodiment of the invention. The coolant circuit  3  of the engine  1  is illustrated again. 
     In contrast with the, retarder illustrated in FIG. 1, the retarder  13  in FIG. 2 is a so-called secondary retarder which is preferably arranged on the vehicle transmission or on the output shaft. The conduction away of heat in such a system is preferably carried out by means of a separate retarder coolant circuit  50  which outputs the heat to the vehicle cooling system  3  via the heat exchanger  52 . 
     As in FIG. 1, the fan  15 , the switch-over valve  44  and the rotational-speed-regulated coolant pump  7  are actuated by means of the control/regulating device  24  given specific retarder operating states which are communicated to the control/regulating device  24  either by the sensor  22  or, for example, the retarder control operating lever. 
     In addition to this, in the embodiment according to FIG. 2 there may be provision that a switch-over valve  54  is also actuated in the retarder cooling circuit  50 , specifically when the retarder is switched on, in such a way that the coolant is not conducted via the bypass  56  but rather via the-heat-exchanger  52 . 
     In addition to the actuation of the assemblies of the cooling system which have been described in detail above, there may be provision that secondary assemblies in the vehicle which do not have to be continuously used are also actuated in order to promote the conduction away of heat. This measure can further increase the retarder availability. 
     The invention thus discloses for the first time a system with which the braking effect of a retarder can be utilized to a maximum degree directly after switching on by virtue of the fact that additional assemblies of the cooling system or secondary assemblies of the vehicle are actuated.