Method for regulating the temperature of the coolant in an internal combustion engine using an electrically operated coolant pump

The present invention relates to a method of regulating the temperature of a coolant in an internal combustion engine which is connected to a radiator by at least one forward and return line and to a coolant pump.

Methods and equipment for cooling the coolant in an internal combustion engine are already known in principle. For example, German Patent No. 37 05 232 describes a method of regulating the temperature of the coolant where a sensor operates a motor actuator as a function of individual engine map characteristics, e.g., rpm and/or engine load, to open or close a bypass valve or the like to achieve a predetermined temperature in the engine coolant circuit. To control the motor actuator, the sensor is heated by a heating device according to the given characteristic data, so it can deliver a suitable signal to the motor actuator. Such a device seems relatively expensive in terms of energy required, because the drive motor for the coolant pump runs constantly, regardless of whether a small amount of waste heat needs to be removed when the internal combustion engine is idling or a large amount when the engine is running.

The method according to the present invention for regulating the temperature of a coolant in an internal combustion engine, however, has the advantage that the speed of the coolant pump is itself regulated or controlled so that its speed corresponds only to the heat to be dissipated.

It is especially advantageous for the speed control to be determined from the temperature difference between the setpoint and the instantaneous temperature of the internal combustion engine, because significant operating states of the engine are detected in this temperature difference.

By preselecting the setpoint temperature as a function of time, the warmup phase of the engine can be controlled easily in an advantageous manner.

It seems especially advantageous to select the setpoint temperature on the basis of a time table, because an especially easy adjustment to different types of engines and their coolant circuits is possible in this way.

The control signal for the coolant pump can be regulated especially easily and advantageously by using a PID controller.

Another advantage is that in addition to controlling the coolant pump, other valves such as the thermostatic valve, the heating valve or an engine fan can also be controlled to optimize the cooling capacity. This additional influence on the coolant circuit can be used either to make the engine warm up more quickly in the cold start phase or to remove excess heat more rapidly at a high load and when the engine is turned off. This reduces exhaust emissions and prevents overheating of the engine.

It also seems advantageous that a suitable display appears when the engine temperature is exceeded, allowing the driver to react appropriately and thus prevent damage.

It is also advantageous that the parameters are linked in stages in the manner of fuzzy logic to guarantee optimal temperature conditions for the internal combustion engine.

By linking the various parameters such as rpm, engine load, vehicle speed and intake temperature or outside temperature, it is possible to form a control signal for the coolant pump which takes into account all the operating conditions that occur.

FIG. 1 shows a schematic diagram of a coolant circuit of an internal combustion engine.

FIG. 2 shows a block diagram of the temperature control.

In the schematic diagram of the coolant circuit in FIG. 1, internal combustion engine 1 is connected to a radiator 4 via an electrically operated coolant pump M and a thermostatic valve 2 by a forward line 7 . At a suitable location, a forward sensor 6 a for detecting the forward temperature is installed on the forward line 7 . In addition, the instantaneous temperature of internal combustion engine 1 is measured with a temperature sensor 6 . A return line 8 connects radiator 4 to the coolant circuit of internal combustion engine 1 via a heating valve 3 . Heating valve 3 is also connected to heater 5 of the passenger compartment. Likewise, thermostatic valve 2 is connected to return line 8 through another valve and bypass line 9 . For the sake of thoroughness, it should also be pointed out that the radiator is thermally connected to one or more engine fans 10 , where engine fan 10 may be designed for multiple speeds. According to FIG. 1, valves 2 , 3 are designed as 3-way valves.

The functioning of this arrangement is explained in greater detail below on the basis of the block diagram in FIG. 2 . Item 11 is a setpoint generator for the engine temperature, which is preselected as a function of time or in the form of a table, for example. The instantaneous engine temperature measured with temperature sensor 6 is processed in a suitable manner in block 12 and sent to summing unit 14 . The differential signal between setpoint generator 11 and block 12 forms a correction quantity for the control signal for coolant pump M in block 13 . Then the PID controller signal of block 13 is added up in summing unit 15 , taking into account other parameters supplied by block 16 for control of the coolant pump. The other parameters include, for example, values for the engine rpm, the instantaneous engine load of the internal combustion engine, vehicle speed, intake temperature or outside temperature, the engine temperature itself and/or the on-board voltage. This is represented symbolically by the parallel arrows at block 16 . After linking the signals to the PID controller signal, the control signal for coolant pump M is formed in block 15 . Depending on this value, coolant pump M runs at a corresponding speed, thus causing a corresponding change in rate of coolant flow in forward line 7 and/or return line 8 . If this control algorithm is not sufficient to adjust the setpoint temperature for the engine, thermostatic valve 2 or multiple-speed engine fan 10 is controlled or a warning display on the dashboard is activated in block 17 after a suitable analysis of the instantaneous engine temperature (block 12 ) and the control signal for the coolant pump. These elements are represented symbolically by the parallel output arrows of block 17 .

Since special functions for control of coolant pump M may be needed for maintenance jobs or in the workshop, a device is provided in block 18 to allow a separate drive for coolant pump M. This block 18 therefore contains suitable devices, e.g., for connecting a workshop tester which drives coolant pump M in filling and venting the cooling system. As an alternative, the internal combustion engine can also be warmed up over this line by using an auxiliary heater (not shown in the figure). Furthermore, operation of coolant pump M to prevent overheating after turning off a hot internal combustion engine 1 can also be controlled over this line.

The blocks shown in FIG. 2 are designed as known components (e.g., PID controllers, temperature sensors, etc.). The simplest linkage is through an appropriate program.

Rules for adjusting the cooling capacity can be taken from Tables 1 and 2. For example, if engine temperature tmot is >85° C. according to Table 1, and if the forward temperature of coolant pump tvkmp is >90%, then thermostatic valve 2 is operated, for example, to coolant over forward line 7 to radiator 4 and then return it over return line 8 . If there is a further increase in engine temperature tmot, and if it is >95° C. at the same relative capacity of coolant pump M, then fan speed 1 is activated. Then when the engine temperature rises further to more than 100° C., fan speed 2 is activated. When the temperature of the internal combustion engine increases further to above 110° C., the “overheating” warning is displayed on the dashboard.

Table 2 shows as an example the measures taken to reduce the cooling capacity. If engine temperature tmot is <105° C. and the cooling capacity is <80%, then the “overheating” warning is deactivated. Accordingly, when the engine temperature is <97° C. and the cooling capacity is <80% or <60%, fan speeds 2 and 1 , respectively, are turned off. If the temperature drops further, e.g., tmot <83° C. and a cooling capacity <40%, valve 2 is switched so that radiator 4 is turned off and bypass line 9 handles the return flow to internal combustion engine 1 . Thermostatic valve 2 also closes at temperatures <75° C., so the engine heats up rapidly according to the given temperature curve. Rapid heating of internal combustion engine 1 has the advantage that the noxious exhaust during the warmup phase can be reduced as rapidly as possible.

Since commercially available electronic components (ICs) are often used for control operations, a further embodiment of the present invention provides for this control to be established according to the principles of fuzzy logic.