EP0731260B1 - Control method for a cooling circuit of an internal combustion engine - Google Patents

Description

The invention relates to a method for regulating a cooling circuit Internal combustion engine, in particular for motor vehicles, with at least one Coolant pump for setting a coolant flow, a cooler module in which a Heat exchange between an air flow adjustable by means of a fan and the coolant, possibly a temperature-dependent valve for adjustment a mixing ratio between that passed through the cooler module Coolant flow and a guided over a second flow branch Coolant flow and a control unit that is at least that of the coolant pump generated coolant flow and controls the air flow generated by the fan.

A device for controlling the cooling of a device is known Internal combustion engine that uses a coolant pump to generate the Flow of the coolant in an internal combustion engine and a radiator guided coolant circuit, a fan for generating an air flow through the Cooler and a control device depending on a temperature setpoint of the coolant controls the air flow generated by the fan. The Coolant pump is driven by an organ of the internal combustion engine and thus a function of the speed of the internal combustion engine Coolant flow generated, especially in the warm-up phase after the start of Internal combustion engine requires too much energy and the Warm-up phase of the internal combustion engine unnecessarily extended.

In the case of the one described in German laid-open specification DE 38 10 174 A1 Device for controlling the coolant temperature of an internal combustion engine is indeed in addition to the blowers that generate the air flow through the cooler, also those from one Electric motor driven coolant pump depending on a temperature setpoint controlled, but the temperature setpoint is dependent on the engine load and Engine speed specified so that the warm-up phase through the Operating point-dependent control of the coolant pump and fan is unnecessary is extended.

WO-A-84 00578 describes a control method according to the preamble of Claim 1 known. According to this document, only the Coolant pump operated, the speed of the coolant pump being regulated in such a way that the temperature difference between the inlet and outlet temperature of the Motor is below a certain limit. Has the temperature at the outlet of the Motors reaches a certain threshold, the temperature difference between the temperature at the inlet and outlet of the motor in relation to the aforementioned Limit value and also the temperature at the output of the motor in relation to one certain temperature limit regulated by the speed of the coolant pump and if necessary, the fan speed is also set accordingly. For Determination of the temperature difference between the temperature at the inlet and the The temperature at the output of the motor becomes two separate temperature sensors used, however, the circuitry complexity is relatively high and Operation carried out continuously and two separate temperature measurements must be evaluated.

The present invention is therefore based on the object of a method for To provide control of a cooling circuit for an internal combustion engine, in which with the simplest possible means, the power consumption of the coolant pump and the Air flow through the cooler module producing blower kept low Warm-up phase of the internal combustion engine by generating too high Coolant flow is not unnecessarily extended.

This object is achieved by the characterizing part of claim 1 specified features solved. The subclaims define advantageous ones Refinements and developments of the invention.

According to the invention, by specifying a temperature limit of the coolant between the warm-up phase after the start of the internal combustion engine and one Operation of the internal combustion engine with operating temperature differentiated. Below of the temperature limit is both that generated by the coolant pump Coolant flow and the air flow generated by the fan through the cooler module in Regulated depending on a differential temperature setpoint. After reaching the The temperature limit value controls the coolant pump and the blower both as a function of the differential temperature setpoint and a temperature setpoint of the coolant at the engine outlet.

With the help of the invention thus a rapid heating of the internal combustion engine and a shortening of the warm-up phase achieved, but by adhering to the Differential temperature setpoint between engine inlet and engine outlet no hot spots can arise on individual components of the internal combustion engine.

According to an advantageous development of the invention, it is provided below the Temperature limit only the coolant flow generated by the coolant pump in Regulate dependence of the differential temperature, but no air flow through the Generate cooler module.

A further shortening of the warm-up phase is achieved if below one Initial coolant temperature that is less than the temperature limit and one defined period of time after starting the internal combustion engine neither Coolant flow from the coolant pump still generates an air flow from the blower. The time period in which neither the coolant pump nor the blower are activated, is determined so that no hot spots can occur on the internal combustion engine.

Because of the thermal inertia of the internal combustion engine for a short time Changes in engine load and engine speed for heat flow from Internal combustion engine in the coolant does not matter, according to another Formation of the invention provided that the control of the coolant pump and / or the fan generating the air flow as a function of the heat flow in the coolant occurs. This is done by creating those from the control unit Control signals with a delay to the coolant pump and / or the fan to get redirected. The size of the delay is chosen so that the Time behavior of the coolant pump and the blower the dynamic behavior of the Heat flow of the coolant corresponds.

After the temperature limit is reached, a minimum Energy use after an embodiment of the invention by the coolant pump generated coolant flow and the air flow adjustable by the fan in Dependence of a time comparison of the efficiency of the coolant pump and Fan for heat dissipation controlled by the cooler module.

The temperature setpoint of the coolant for the control at least the Coolant pump and blower is preferred depending on one for each Operating point of the internal combustion engine optimal engine temperature determined.

According to the invention it is provided for the regulation depending on the Differential temperature setpoint necessary differential temperature actual value from the Heat flow from the internal combustion engine into the coolant and the coolant flow determine. The at least from the operating point of the internal combustion engine and from The coolant flow predetermined heat flow is stored as a map in the control unit.

Figur 1

eine schematische Darstellung eines Kühlmittelkreislaufes,

Figur 2

ein Ablaufdiagramm für das gesamte Regelverfahren,

Figur 3

ein Ablaufdiagramm für die Regelung in der Warmlaufphase des Verbrennungskraftmotors und

Figur 4

ein Ablaufdiagramm für die Regelung der Betriebstemperatur.

The invention will be described in more detail below using an exemplary embodiment. The associated drawings show:

Figure 1

1 shows a schematic illustration of a coolant circuit,

Figure 2

a flow diagram for the entire control process,

Figure 3

a flowchart for the control in the warm-up phase of the internal combustion engine and

Figure 4

a flow chart for the regulation of the operating temperature.

The coolant circuit shown in FIG. 1 for an internal combustion engine 2 of a motor vehicle consists of several line branches a to f, the opening cross sections of which are controlled by a temperature-dependent valve 6 (thermostat). The direction of rotation of the coolant flow, which is driven by the coolant pump 3, is indicated by arrows. The line branch a is guided via a cooler module 1 for cooling the coolant emerging from the internal combustion engine 2. Air is drawn in from outside the motor vehicle by the fan 4 arranged behind the radiator module 1. When flowing through the cooler module 1, a heat exchange takes place between the air flow m ˙ _l adjustable by the blower 4 and the coolant flow m ˙ _w . Furthermore, a line branch b is provided, the cross section of which can be controlled by the temperature-dependent valve 6 in order to influence the coolant temperature. The line branch c has an expansion tank 7 and serves to regulate the pressure in the entire coolant circuit. A heat exchanger 8 for the interior heating of the motor vehicle and a cooler 9 and 10 for cooling the engine oil and the transmission oil are arranged in the additional line branches d to f. These line branches d to f are optional. The corresponding cooling or heating functions can also be solved in other ways. Furthermore, the coolant circuit includes a control unit 5, for example the control unit of the internal combustion engine, which receives the output signal S _sen of the coolant temperature ϑ _w as an input signal _{, is} detected at the engine outlet temperature sensor 11 and via the output signals S _pump , S _air and S _therm both the speed of the Coolant pump 3 and the fan 4 and the temperature-dependent valve 6 controls.

Furthermore, the control method of the coolant circuit to be carried out by the control unit 5 should are described in more detail. Figures 2 to 4 show flow diagrams for explanation this control procedure.

As illustrated in FIG. 2, three cases are distinguished in the method according to the invention; the warm-up V1 of the internal combustion engine, the driving mode V2 at the operating temperature of the coolant and the run-on V3. In the first method step A1, it is checked whether the internal combustion engine 2 has been started. If this is the case, the coolant temperature ϑ _{w is} compared (output signal S _{sen from} the temperature sensor 11) at the engine outlet with a temperature limit value ϑ _w characterizing the end of the warm-up phase V1 _{, warm.} At a coolant temperature ϑ _w, below this temperature limit, warm-up V1 is detected. If the coolant temperature ϑ _w, the temperature _limit ϑ _{w, warml has been} reached, the coolant circuit is controlled according to the algorithm for driving mode V2 at operating temperature.

If the internal combustion engine 2 is not started, it is checked whether the coolant temperature θ _{w, is} a temperature limit value θ _w, exceeds _by, that the internal combustion engine 2 has to be further cooled. In this case, the coolant circuit is controlled using an algorithm for the run-on V3. If the coolant temperature ϑ _{w is} below the temperature limit ϑ _w, the control stops _after the internal combustion engine 2 is restarted.

In the warm-up phase V1, the sequence of which is shown in FIG. 3, the first step is to compare the coolant temperature ϑ _w, at the engine outlet, with a coolant _start temperature ϑ _{w, start} . If the coolant temperature is below the coolant _start value ϑ _{w, start} , the coolant pump 3 starts with a delay of the time period t _start in order to keep the heat flow from components of the internal combustion engine 2 into the coolant as low as possible and thus to achieve a faster heating of the components . After the time period t _start or when the temperature _start value ϑ _{w, start} has been reached, the coolant flow m ˙ _w generated by the coolant pump 3 is continuously increased until, for the first time, the minimum coolant flow m ˙ _{w , min} for maintaining the differential temperature setpoint Δϑ _{w, Mot is intended} between Motorein- reaches and exits. The control signal S _{pump, min} for the coolant _pump 3 is calculated in the control unit 5 from the minimum coolant flow m ˙ _{w , min} . When the minimum coolant flow m ˙ _{w , min} is reached for the first time, the coolant _{pump 3 is} controlled to maintain the differential temperature setpoint Δϑ _{w, Mot,} coolant with a control _signal S _{pump, warml} . The actual differential temperature Δϑ _{w, Mot,} required for the control results from the heat flow Q ˙ _Mot from the internal combustion engine into the coolant, which in turn is calculated from the current coolant flow m ˙ _w , the current engine load L _Mot and the engine speed n. The heat flow Q ˙ _Mot is preferably stored as a map in the control unit 5 for the special internal combustion engine 2.

After reaching the minimum coolant flow m ˙ _{w , min} , the reaction of the coolant pump 3 to short-term engine load and speed changes should be prevented. Since, due to the thermal inertia of the internal combustion engine 2, brief changes in the engine load L _Mot and the engine speed n play no role for the heat flow Q ˙ _Mot in the coolant, carrying the speed of the coolant pump 3 would represent unnecessary energy consumption. The control signal S _pump for the coolant _pump is therefore assigned a dynamic transmission behavior, the time constant T _{stg of} which is chosen so that the time behavior of the coolant _pump roughly corresponds to the behavior of the heat flow Q ˙ _Mot from the internal combustion engine into the coolant. It follows from this that the speed change of the coolant pump 3 follows the change in the heat flow Q Q _mot into the coolant.

The blower 4 is not activated during the warm-up phase V1, ie no airflow m ˙ _{l is} generated by the cooler module 1. The warm-up phase V1 has ended when the current coolant temperature ϑ _w, the temperature _{limit value den w, warml is} reached for the first time.

When the temperature _{limit value} ϑ _{w, warml} (FIG. 4) is reached, in addition to the control as a function of the differential temperature setpoint Δϑ _{w, Mot,} the coolant temperature _is also controlled as a function of a temperature setpoint ϑ _w, according to the algorithm for driving mode V2 at operating temperature instead. To do this, the temperature setpoint ϑ _{w, set is first} calculated. For this purpose, there is a map in the control unit 5 in which the optimum temperature setpoint ϑ _w, for the specified engine temperature with variable engine load L _Mot , engine speed n and coolant flow m ˙ _w , is stored. From this variable temperature setpoint ϑ _w, at the engine outlet, the coolant flow m ˙ _w and the heat flow Q ˙ _Mot from the internal combustion engine 2 into the coolant, the control temperature ϑ _{w, therm} results for the temperature-dependent valve 6, from which the control signal S _therm is determined for the temperature-dependent valve 6. As in a conventional cooling circuit, the valve 6 regulates the coolant temperature ϑ _w via the coolant flow conditions between the line branch a led via the cooler module 1 and the line branch b.

From the calculation of the minimum coolant flow m ˙ _{w, min} results in the required minimum speed of the coolant pump 3 and thereby the optimum drive signal S _{pump, min.} If the current coolant temperature exceeds ϑ _w, the temperature setpoint is ϑ _{w, and} if the engine outlet is _hot by a differential value Δϑ _w, either the speed of the coolant pump 3 and thus the coolant flow m ˙ _w or the speed of the fan 4 and thus the air flow m ˙ _l increased. Whether it makes more sense in terms of energy to change the speed of the coolant pump 3 or of the blower 4 is determined by comparing their efficiency for heat dissipation at the cooler module 1 over time. The heat dissipation or the heat flow Q ˙ _{w , k} at the cooler module 1 depends on the heat transfer coefficient k, which results from the heat transfer coefficients coolant-cooler module and cooler module-air and according to the formula: k = 1 A k · 0.8 m l · m w a k · m w 0.8 + b k · m l 0.8 + c k 0.8 m l · m w is calculated, where A _{k is} the area on the cooler module 1 and a _k , b _k and c _{k are} constants for the calculation of the heat transfer coefficient.

In order to assess the effectiveness of the change in the air flow m ˙ _l and the coolant flow m ˙ _w , the partial derivatives are formed:

For each operating point of the cooler module, the size of the increase in heat dissipation per unit mass of the substances involved is thus obtained. If these values are now related to the energy input P _L , P _wapu , which is required for the provision of the coolant flow or air flow, a comparison value K _{η is obtained} to assess the most favorable change in the operating point. K η = η k, l · 1 P L η k, wapu · 1 P wapu

If the characteristic value K _η > 1, it is more efficient to increase the air flow m ˙ _l . For K _η <1, the coolant flow m ˙ _{w should be} increased.

If, as shown in FIG. 1, the coolant circuit is simultaneously used to cool the engine oil via a cooler 9, the current oil temperature ϑ _{oil can be} monitored with a sensor (not shown). Exceeds the current oil temperature θ _{oil has} a temperature limit value θ _{oil, cross} so the coolant temperature is gradually θ _{w, is} lowered until the oil temperature θ _oil drops below this limit temperature value. The coolant temperature required for the selected engine temperature is then set again.

The dynamic behavior of the control in the event of brief changes in the engine load L _Mot and the engine speed n is different for compliance with the differential temperature setpoint Δϑ _{w, Mot,} setpoint and the temperature setpoint ϑ _w, setpoint. The control according to the differential temperature setpoint Δϑ _{w, Mot, soll} corresponds in its dynamics to that of warming up V1. The regulation according to the temperature setpoint ϑ _{w, should} be done faster by varying the valve current S _term and the speeds of the coolant pump 3 and blower 4. When designing, a compromise must be found between an energetic optimum and the temperature constancy of the components of the internal combustion engine 2. For energy purposes, it makes sense to allow brief temperature changes in the components, such as those that occur during the overtaking process. If one optimizes in the direction of constant temperature of the components of the internal combustion engine, then by reacting to changes in the engine load, a precontrol against the change in the coolant temperature ϑ _{w, ist} or the heat flow Q ˙ _mot into the coolant can be achieved. If an engine operating point is set which would result in an increased heat flow Q ˙ _Mot into the coolant, 6 cooler coolant can be pumped into the internal combustion engine by controlling the temperature-dependent valve, which results in a higher heat flow Q ˙ _Mot in the coolant and thus lower component temperature fluctuations Episode. Furthermore, the coolant flow m ˙ _w or the air flow m ˙ _l can be increased in advance. This is particularly recommended if the valve 6 is not able to follow rapid changes due to its design.

REFERENCE SIGN LIST

1

Cooler module

2nd

Internal combustion engine

3rd

Coolant pump

4th

fan

5

Control unit

6

temperature dependent valve

7

surge tank

8th

Heat exchanger

9

cooler

10th

cooler

11

Temperature sensor

a - f

Line branches

m ˙ _{w ,} min

minimal coolant flow

m ˙ _w

Coolant flow

m ˙ _l

Airflow

ϑ _{w, warm}

Temperature limit for warm-up

Δϑ _{w, Mot, is}

Differential temperature actual value

Δϑ _{w, Mot, should}

Differential temperature setpoint

ϑ _{w, should}

Temperature setpoint

ϑ _{w, after}

Temperature limit for the wake

t _start

Duration of the delay

ϑ _{w, start}

Initial temperature value

ϑ _{w, therm}

Control temperature of the temperature-dependent valve

Δϑ _{w, hot}

Difference value

ϑ _{w, is}

Current temperature of the coolant at the engine outlet

L _Mot

Engine load

n

Engine speed

REFERENCE SIGN LIST

Q ˙ _{w, k}

Heat flow at the cooler module

Q ˙ _Mot

Heat flow

V1

Warm up

V2

Driving operation at operating temperature

V3

trailing

S _sen

Output signal of the temperature sensor

S _pump

Control signal for the coolant pump

S _{pump, min}

Control signal for the minimum coolant flow

S _{pump, warm}

Control signal for the coolant pump in the warm-up phase

S _therm

Control signal for the valve

S _air

Control signal for the fan

T _stg

Time constant

ϑ _oil

Oil temperature

ϑ _{oil, limit}

Limit temperature value

k

Heat transfer coefficient

A _k

Surface on the cooler module

a _k, b _k, c _k

Constants

P _L

Energy use for the blower

P _wapu

Use of energy for the coolant pump

K _η

Comparative value

η _{k, wapu}

Efficiency of the coolant pump

η _{k, l}

Fan efficiency

Claims (10)

1. Method for controlling a cooling circuit of an internal combustion engine, in particular of a motor vehicle,

   having at least one cooling medium pump (3) for controlling a cooling medium flow,

   having a cooler module (1) in which a heat exchange takes place between an air flow, which can be adjusted by means of a fan (4), and the cooling medium, and

   having a control device (5), which controls at least the cooling medium flow produced by the cooling medium pump (3) and the air flow produced by the fan (4),

   wherein the cooling medium flow produced by the cooling medium pump (3), and the air flow produced by the fan (4) through the cooler module (1) is controlled below a temperature limit value (ϑ_w,warml) of the cooling medium in dependence upon a differential temperature set value (Δϑ_{w,Mot, soll}) of the cooling medium between the engine inlet and the engine outlet, and after reaching the temperature limit value (ϑ_w,warml) is controlled in dependence upon both the differential temperature set value (Δϑ_{w,Mot, soll}) and on a temperature set value (ϑ_w,soll),
   characterised in that
   a differential temperature actual value (Δϑ_{w, Mot,ist}) required for the control in dependence upon the differential temperature set value (Δϑ_w,Mot,soll) is determined from the heat flow (Q ˙_Mot ) from the internal combustion engine (2) into the cooling medium and from the cooling medium flow (m ˙_w ).
2. Method according to claim 1, characterised in that the differential temperature set value (Δϑ_{w,Mot, soll}) and/or the temperature set value (ϑ_w,soll) are dependent upon the operating point (L_{Mot, n}) of the internal combustion engine (2).
3. Method according to claim 1 or 2, characterised in that the temperature limit value (ϑ_w,warml) characterises the end of the warm-up phase (V1) of the internal combustion engine (2).
4. Method according to one of claims 1 to 3, characterised in that below the temperature limit value (ϑ_w,warml) only the cooling medium flow (m ˙_w ) produced by the cooling medium pump (3) is controlled in dependence upon the differential temperature (Δϑ_{w,Mot, soll}), but no air flow (m ˙_l ) is produced by the fan (4).
5. Method according to one of claims 1 to 4, characterised in that after starting the internal combustion engine (2) below a cooling medium initial temperature (ϑ_w,start), which is lower than the temperature limit value (ϑ_w,warml), and during a predetermined period of time (t_start) no cooling medium flow (m ˙_w ) is produced by the cooling medium pump (3) nor is an air flow (m ˙_l ) produced by the fan (4).
6. Method according to claim 5, characterised in that the length of the predeterminable period of time (t_start) is defined in dependence upon the operating points which have occurred since starting the internal combustion engine.
7. Method according to one of claims 1 to 6, characterised in that the cooling medium pump (3) and/or the fan (4) is actuated with a delay, of which the time constants (T_stg,wapu; T_stg,l) are selected in such a way that the behaviour of the cooling medium pump (3) and/or of the fan (4) with respect to time corresponds to the behaviour of the heat flow (Q ˙_Mot) from the internal combustion engine (2) L_in the cooling agent at high engine speeds (n).
8. Method according to one of claims 1 to 7, characterised in that after reaching the temperature limit value (ϑ_w,warml) and the cooling medium flow (m ˙_w ) produced by the cooling medium pump (3) and the air flow (m ˙_l ) which can be adjusted by the fan (4) are controlled in dependence upon a comparison, with respect to time, of the operating efficiency (η_k,wapu;k,l) of the cooling medium pump and fan for the dissipation of heat at the cooler module (1).
9. Method according to one of claims 1 to 8, characterised in that the temperature set value (ϑ_w,soll) is determined in dependence upon an engine temperature which is optimal for each operating point (L_mot,n) of the internal combustion engine (2).
10. Method according to one of claims 1 to 9, characterised in that the heat flow (Q ˙_Mot ) from the internal combustion engine (2) into the cooling medium is stored in the control device (5) in dependence upon the operating point (L_mot,n) of the internal combustion engine (2) and upon the cooling medium flow (m ˙_w ).

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