EP0731260A1 - Control method for a cooling circuit of an internal combustion engine - Google Patents

Abstract

The regulation system has a control device (5) for adjusting the revs of the coolant circulation pump (3) and the fan (4) directing air through the radiator, in dependence on the required temp of the engine coolant. The heating-up phase for the engine is shortened by reducing the output of the circulation pump and the fan after starting the engine until the engine coolant reaches a given temp threshold, above which the regulation for maintaining the required coolant temp is brought into operation.

Description

The invention relates to a method for regulating a cooling circuit of an internal combustion engine, in particular for motor vehicles, with at least one coolant pump for setting a coolant flow, a cooler module in which heat exchange takes place between an air flow that can be set by means of a blower and the coolant, and possibly a temperature-dependent valve for setting a mixing ratio between the coolant flow led via the cooler module and a coolant flow led via a second flow branch and a control device which controls at least the coolant flow generated by the coolant pump and the air flow generated by the fan.

German published patent application DE 44 08 078 A1 describes a device for controlling the cooling of an internal combustion engine, which has a coolant pump for generating the flow of coolant in a coolant circuit guided via the internal combustion engine and a cooler, a blower for generating an air flow through the cooler and a control device which controls the air flow generated by the fan as a function of a temperature setpoint of the coolant. The coolant pump is driven by an organ of the internal combustion engine and thus generates a coolant flow which is dependent on the speed of the internal combustion engine and which, particularly in the warm-up phase after the start of the internal combustion engine, requires too much energy and unnecessarily extends the warm-up phase of the internal combustion engine.

In the device for regulating the coolant temperature of an internal combustion engine described in German Offenlegungsschrift DE 38 10 174 A1, the coolant pump driven by an electric motor is controlled as a function of a temperature setpoint in addition to the blowers that generate the air flow through the cooler, but the temperature setpoint is dependent on the Engine load and engine speed specified, so that here too, the warm-up phase is unnecessarily extended by the operating point-dependent control of the coolant pump and the fan.

The object of the invention is therefore to provide a method for regulating a cooling circuit for an internal combustion engine, in which the power consumption of the coolant pump and the fan producing the air flow through the cooler module is kept low and the warm-up phase of the internal combustion engine by generating an excessively high coolant flow is not extended unnecessarily.

The object is achieved by the features of the patent claim. Advantageous refinements and developments are presented in the subclaims.

According to the invention, by specifying a temperature limit value of the coolant, a distinction is made between the warm-up phase after the start of the internal combustion engine and an operation of the internal combustion engine at operating temperature. Below the temperature limit, both the coolant flow generated by the coolant pump and the air flow generated by the blower are regulated by the cooler module as a function of a differential temperature setpoint. After the temperature limit has been reached, the coolant pump and the blower are regulated depending on the differential temperature setpoint and a temperature setpoint of the coolant at the engine outlet.

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

According to an advantageous development of the invention, it is provided that only the coolant flow generated by the coolant pump is regulated as a function of the differential temperature below the temperature limit, but no air flow is generated by the cooler module.

A further shortening of the warm-up phase is achieved if neither a coolant flow from the coolant pump nor an air flow from the blower is generated below a coolant start temperature that is lower than the temperature limit value and a defined period of time after the internal combustion engine is started. The time period in which neither the coolant pump nor the blower are controlled is determined so that no hot spots can occur on the internal combustion engine.

Since, due to the thermal inertia of the internal combustion engine, short-term changes in the engine load and the engine speed are irrelevant for the heat flow from the internal combustion engine into the coolant, it is provided according to a further embodiment of the invention that the control of the coolant pump and / or the fan producing the air flow is dependent of the heat flow into the coolant. This is done by forwarding the control signals generated by the control unit to the coolant pump and / or the blower with a delay. The size of the delay is chosen so that the time behavior of the coolant pump and the fan corresponds to the dynamic behavior of the heat flow of the coolant.

After the temperature limit value has been reached, the coolant flow generated by the coolant pump and the air flow adjustable by the blower are controlled as a function of a time comparison of the efficiencies of the coolant pump and blower for heat dissipation from the cooler module for a minimal use of energy.

The temperature setpoint of the coolant for the control of at least the coolant pump and the blower is preferably determined as a function of an optimal engine temperature for each operating point of the internal combustion engine.

According to an advantageous embodiment, provision is further made to determine the actual differential temperature value required for the control as a function of the differential temperature setpoint from the heat flow from the internal combustion engine into the coolant and the coolant flow. The heat flow predetermined at least by the operating point of the internal combustion engine and by the coolant 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 ṁ _l adjustable by the fan 4 and the coolant flow ṁ _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} a coolant temperature ϑ _w as an input signal, temperature sensor 11 _{which is} detected at the engine outlet 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.

The control method of the coolant circuit to be carried out by the control unit 5 will be described in more detail below. FIGS. 2 to 4 show flow diagrams of this control method for explanation.

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 step A1, it is checked whether the internal combustion engine 2 was started., This is the case, a comparison is made of the coolant temperature θ _{w, (output} signal S _sen of the temperature sensor 11) at the engine outlet to a termination of the warm-up phase θ V1 characterizing temperature limit value _{w , 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 coolant temperature ϑ _{w is} compared in a first method step _{, is} 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 ṁ _w generated by the coolant pump 3 is continuously increased until, for the first time, the minimum coolant flow ṁ _{w , min} for maintaining the differential temperature setpoint Δϑ _{w, Mot, should} between engine and outlet is reached. The control signal S _{pump, min} for the coolant _pump 3 is calculated in the control unit 5 from the minimum coolant flow ṁ _{w, min} . When the minimum coolant flow ṁ _{w , min} is reached for the first time, the coolant _{pump 3 is} regulated to maintain the differential temperature setpoint Δϑ _{w, Mot,} coolant with a control _signal S _{pump, warml} . The differential temperature actual value Δϑ _{w, Mot,} required for the control results from the heat flow Q̇ _Mot from the internal combustion engine into the coolant, which in turn is calculated from the current coolant flow ṁ _w , the current engine load L _Mot and the engine speed n. The heat flow Q̇ _Mot is preferably stored as a map in the control unit 5 for the special internal combustion engine 2.

After the minimum coolant flow ṁ _{w , min has been reached} , 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 Q̇ _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 selected such that the time behavior of the coolant pump roughly corresponds to the behavior of the heat flow Q̇ _Mot from the internal combustion engine into the coolant. It follows that the speed change of the coolant pump 3 follows the change in the heat flow Qestr _Mot in the coolant.

The blower 4 is not activated during the warm-up phase V1, ie no airflow ṁ _{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 ṁ _w , is stored. From this variable temperature setpoint ϑ _w, at the engine outlet, the coolant flow ṁ _w and the heat flow Q̇ _Mot from the internal combustion engine 2 into the coolant, the control temperature ϑ _{w, therm} for the temperature-dependent valve 6 results, from which the control signal S _therm for the temperature-dependent valve 6 is determined. 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.

berechnet wird, wobei A_k die Fläche am Kühlermodul 1 und a_k, b_k und c_k Konstanten für die Berechnung des Wärmedurchgangskoeffizienten sind.From the calculation of the minimum coolant flow ṁ _{w, min} , the required minimum speed of the coolant _pump 3 and thus the optimal control 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 difference value Δϑ _w, either the speed of the coolant pump 3 and thus the coolant flow ṁ _w or the speed of the fan 4 and thus the air flow ṁ _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 Q̇ _{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: $$\mathit{\text{k}}\text{=}\frac{\text{1}}{{\mathit{\text{A}}}_{\mathit{\text{k}}}}\text{·}\frac{{\left({\dot{\mathit{\text{m}}}}_{\mathit{\text{l}}}\text{·}{\dot{\mathit{\text{m}}}}_{\mathit{\text{w}}}\right)}^{\text{0.8}}}{{\mathit{\text{a}}}_{\mathit{\text{k}}}\text{·}{\dot{\mathit{\text{m}}}}_{\mathit{\text{w}}}{}^{\text{0.8}}\text{+}{\mathit{\text{b}}}_{\mathit{\text{k}}}\text{·}{\dot{\mathit{\text{m}}}}_{\mathit{\text{l}}}{}^{\text{0.8}}\text{+}{\mathit{\text{c}}}_{\mathit{\text{k}}}{\left({\dot{\mathit{\text{m}}}}_{\mathit{\text{l}}}\text{·}{\dot{\mathit{\text{m}}}}_{\mathit{\text{w}}}\right)}^{\text{0.8}}}$$

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 Kühl _l and the coolant flow die _w , the partial derivatives are formed: $$\begin{array}{c}\begin{array}{c}\frac{\text{ϑ}\mathit{\text{k}}\text{·}{\mathit{\text{A}}}_{\mathit{\text{k}}}}{\text{ϑ}{\dot{\text{m}}}_{\mathit{\text{l}}}}\text{=}\frac{\text{0.8}{\dot{\mathit{\text{m}}}}_{\mathit{\text{l}}}{}^{\text{-0.2}}}{{\left({\mathit{\text{a}}}_{\mathit{\text{k}}}\text{+}\left(\frac{{\mathit{\text{b}}}_{\mathit{\text{k}}}}{{\dot{\mathit{\text{m}}}}_{\mathit{\text{w}}}{}^{\text{0.8}}}\text{+}{\mathit{\text{c}}}_{\mathit{\text{k}}}\right)\text{·}{\dot{\mathit{\text{m}}}}_{\mathit{\text{l}}}{}^{\text{0.8}}\right)}^{\mathrm{2nd}}}{\text{= η}}_{\mathit{\text{k}}\text{,}\mathit{\text{l}}}\\ \frac{\text{ϑ}\mathit{\text{k}}\text{·}{\mathit{\text{A}}}_{\mathit{\text{k}}}}{\text{ϑ}{\dot{\mathit{\text{m}}}}_{\mathit{\text{w}}}}\text{=}\frac{\text{0.8}{\dot{\mathit{\text{m}}}}_{\mathit{\text{w}}}{}^{\text{-0.2}}}{{\left({\mathit{\text{b}}}_{\mathit{\text{k}}}\text{+}\left(\frac{{\mathit{\text{a}}}_{\mathit{\text{k}}}}{{\dot{\mathit{\text{m}}}}_{\mathit{\text{l}}}{}^{\text{0.8}}}\text{+}{\mathit{\text{c}}}_{\mathit{\text{k}}}\right)\text{·}{\dot{\mathit{\text{m}}}}_{\mathit{\text{w}}}{}^{\text{0.8}}\right)}^{\mathrm{2nd}}}{\text{= η}}_{\mathit{\text{wapu}}}\end{array}\end{array}$$

For each operating point of the cooler module, the size of the increase in heat dissipation per unit mass of the substances involved is 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. $$\text{Kη =}\frac{\text{η}{}_{\mathit{\text{k}}\text{,}\mathit{\text{l}}\text{·}\frac{\text{1}}{{\mathit{\text{P}}}_{\mathit{\text{L}}}}}}{{\text{η}}_{\mathit{\text{k}}\text{,}\mathit{\text{wapu}}}\text{·}\frac{\text{1}}{{\mathit{\text{P}}}_{\mathit{\text{wapu}}}}}$$

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

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 gradually the coolant temperature ϑ _{w is} reduced until the oil temperature ϑ _oil drops below this limit temperature value again. 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 dynamics to that of warm-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 Q̇ _Mot into the coolant can be achieved. If an engine operating point is set that would result in an increased heat flow Q̇ _Mot into the coolant, 6 coolant coolant can be pumped into the internal combustion engine by controlling the temperature-dependent valve, which would result in a higher heat flow Q̇ _Mot in the coolant and thus lower component temperature fluctuations . Furthermore, the coolant flow ṁ _w or the air flow ṁ _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

ṁ _{w ,} min

minimal coolant flow

ṁ _w

Coolant flow

ṁ _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

Q̇ _{w, k}

Heat flow at the cooler module

Q̇ _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 (11)

Method for regulating a cooling circuit of an internal combustion engine, in particular a motor vehicle, with at least one coolant pump for setting a coolant flow, a cooler module in which heat exchange takes place between an air flow which can be set by means of a blower and the coolant, possibly a temperature-dependent valve for setting a mixing ratio between the two coolant flow led via the cooler module and a coolant flow led via a second flow branch, and a control device which controls at least the coolant flow generated by the coolant pump and the air flow generated by the fan,
characterized in that the coolant flow ( ṁ _w ) generated by the coolant pump (3) and the air flow ( ṁ _l ) generated by the blower (4) through the cooler module (1) as a function of a temperature _{limit value} (ϑ _{w, warml} ) of the coolant a differential setpoint (Δϑ _{w, Mot, set} ) of the coolant between the engine inlet and the engine outlet and after reaching the temperature _limit (ϑ _{w, warml} ) depending on both the differential temperature setpoint (Δϑ _{w, Mot, set} ) and a temperature Setpoint (ϑ _{w, should} ) is regulated. Method according to claim 1, characterized in that the differential temperature setpoint (Δϑ _{w, Mot, set} ) and / or the temperature setpoint (ϑ _{w, set} ) are dependent on the operating point (L _{Mot, n} ) of the internal combustion engine (2) . Method according to Claim 1 or 2, characterized in that the temperature _{limit value} (ϑ _{w, warml} ) _indicates the end of the warm-up phase (V1) of the internal combustion engine (2). Method according to one of claims 1 to 3, characterized in that below the temperature limit value (θ _{w, warml)} only the flow of coolant generated by the coolant pump (3) (M _w) in dependence of the temperature difference _{(w Δθ, Mot, soll)} is controlled , but no air flow ( ṁ _l ) is generated by the fan (4). Method according to one of claims 1 to 4, characterized in that after starting the internal combustion engine (2) below a coolant _start temperature (ϑ _{w, start} ) which is less than the temperature _limit (ϑ _{w, warml} ) and for a predetermined period of time (t _start ) neither a coolant flow ( ṁ _w ) from the coolant pump (3) nor an air flow ( ṁ _l ) from the fan (4) is generated. Method according to Claim 5, characterized in that the length of the predeterminable time period (t _start ) is defined as a function of the operating points which have occurred since the start of the internal combustion engine. Method according to one of claims 1 to 6, characterized in that the control of the coolant pump (3) and / or the blower (4) takes place with a delay, the time constants (T _{stg, wapu;} T _{stg, l} ) are selected so that that the time behavior of the coolant pump (3) and / or the fan (4) corresponds to the behavior of the heat flow ( Q̇ _Mot ) from the internal combustion engine (2) L _into the coolant at high engine speeds (n). Method according to one of claims 1 to 7, characterized in that after reaching the temperature _limit (ϑ _{w, warml} ) and the coolant flow ( ṁ _w ) generated by the coolant _pump (3) and the air flow ( ṁ _l ) are controlled as a function of a time comparison of the efficiencies (η _{k, wapu; k, l} ) of the coolant pump and fan for heat dissipation on the cooler module (1). Method according to one of claims 1 to 8, characterized in that the temperature setpoint (ϑ _{w, set} ) is determined as a function of an optimum engine temperature for each operating point (L _{Mot, n} ) of the internal combustion engine (2). Method according to one of claims 1 to 9, characterized in that an actual differential temperature value (Δϑ _{w, Mot, ist} ) required for the control as a function of the differential temperature setpoint (Δϑ _{w, Mot, soll} ) from the heat flow ( Q̇ _Mot ) is determined by the internal combustion engine (2) into the coolant and the coolant flow ( ṁ _w ). A method according to claim 10, characterized in that the heat flow ( Q̇ _Mot ) from the internal combustion engine (2) into the coolant from the operating point (L _{Mot, n} ) of the internal combustion engine (2) and the coolant flow ( ṁ _w ) is stored in the control unit (5) is.

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