DE19644535C1 - Automobile accessory heater switching method - Google Patents

Abstract

The switching method switches in the auxiliary heating in dependence on the detected temperature of the coolant at the exit from the engine, with at least two successive measured temperature values used for calculation of the temperature at a later point via an exponential temperature increase characteristic for a constant engine load. The calculated temperature is compared with the required value for the coolant, with the auxiliary heating switched in when the calculated temperature is below the required value.

Description

The invention relates to a method for switching on a vehicle auxiliary heater on the Based on a measurement of the coolant temperature at the engine outlet.

A known method of this type sees an alternative to manually switching on the Vehicle heater a control unit with two bimetallic switches, the switching position of is dependent on the ambient and coolant temperature. The disadvantage, however, is that if the temperature falls below a specified ambient temperature and if it is cold Coolant the auxiliary heater is switched on each time the engine is started, even if for example, because of a research driving style, high vehicle load or "cold" settings Heating controller the coolant temperature quickly assumes values that an additional heating operation do not make necessary. Such unnecessary heating events have a negative impact on the Fuel consumption and reduce due to the relatively high frequency of short heating times the service life of the auxiliary heater.

DE 30 24 983 A1 describes a preheating system in which a heater for a predicted and set time before the intended time of use is switched on. The maximum preheating time is typically one hour. Becomes for the time of use, for example for the intended departure time of the Motor vehicle, a relatively high outside temperature is suspected, based on experience set much shorter preheat time, which is the correct assessment of the switch-on time requirement. In order to remedy this deficiency, this document proposes not the  Switch-on time but the time when the preheater is put into use pre-program, then within an appropriate maximum time limit of, for example, one hour based on a value previously empirically determined, the Preheat so that the target temperature at the prevailing temperature is reached at the time of use.

The invention is based on the object of a method for switching on a vehicle door heater of the type mentioned in the preamble of claim 1, the one Switching on the auxiliary heater as required is guaranteed.

This object is achieved by the features of claim 1. Advantageous embodiments of the invention can be found in the subclaims.

In other words, the method according to the invention produces a switch-on as required of the auxiliary heater based on a temperature prediction based on a current temperature measurement, being when the predicted temperature becomes a the additional heater falls below a temperature setpoint in the future is switched on. The need to switch on the auxiliary heater in this way can be achieved the advantage of a longer burner life, results in less smoke formation and lower glow plug load. Reduced fuel consumption is also achieved.

A preferred point in time for the coolant temperature expected value is in claim 2 or 3 called.

A practical calculation of the expected coolant temperature is in claim 4 called.

As indicated in claim 5, the detection of the coolant temperatures is carried out Determination of the coolant temperature expected value, which is compared with the target value, at even time intervals.  

According to a further development of the invention mentioned in claims 6 and 7, the Coolant temperature setpoint from the vehicle interior air temperature or from the Position of the cold / warm valve in the vehicle interior derived to the conditions Location, namely to be optimally taken into account in the vehicle interior.

The advantageous development of the invention mentioned in claim 8 allows an optimal Adaptation of the temperature forecast to the respective engine of the with the additional heater equipped vehicle.

The invention is explained in more detail below by way of example with reference to the drawing. The only Figure of the drawing shows the exponential course of the coolant temperature at a constant Motor load and measured values plotted in this exponential curve, including a Expected value, to which reference is made below.

The invention is based on the finding that the coolant temperature at the engine outlet at constant motor load follows an exponential function. The coolant temperature can be in can be measured in a known manner with an integrated sensor in a control unit. The measured temperature values can be used to calculate the exponential course of the Use the coolant temperature in order to anticipate a later one Predict coolant temperature at engine outlet. From this prediction of the temperature at a later time can be compared to a temperature setpoint Determine the criterion as to whether heating is necessary or not.

The exponential course of the coolant temperature at the engine outlet with a constant engine load is an exponential function of the form:

ϑ _i = ϑ _end . (1-e⁻ ^{k * i} ) (1)

shown as an example for a discrete sampled signal with i = measuring point (the For example, measuring points are set evenly every 30 seconds), whereby different measurement curves are characterized by different coefficients k.  

An expected value ϑ _{i + tx of} the coolant temperature at a future point in time can be represented, for example, as follows using formula (1):

ϑ _{i + 10} = ϑ _end . (1-e⁻ ^{k * (i + 10)} (1a)

in this example tx is assumed to be 10, which is the case with a sequence of measuring points an expected value of 30 seconds after 5 minutes starting from the last one Measuring point means.

With the currently recorded temperature and the current temperature gradient, formed from the temperature between the currently measured time ϑ _i and the temperature ϑ _i-1 previously measured, the temperature at the point in time "10 measuring points later" can be determined using a constant C ₁₀ ( as an example of the constants C _tx of claim 4) can be calculated as follows:

ϑ _{i + 10} = ϑ _i + C _10. (ϑ _i -ϑ _i-1 ) (2)

For the sampled function, the following applies to the derivation according to measuring points:

ϑ _i -ϑ _i-1 = ϑ _i '(i) = ϑ _end .ke⁻ ^{k * i} (3)

By inserting formula (1) and formula (3) into formula (2) and equating formula (1a) and formula (2), one obtains:

ϑ _end . (1-e⁻ ^{k * (i + 10)} ) = ϑ _end . (1-e⁻ ^{k * i} ) + C ₁₀ .ϑ _end .ke⁻ ^{k * i} (4)
1-e⁻ ^{k * (i + 10)} = 1-e⁻ ^{k * i} + C ₁₀ .ke⁻ ^{k * i} (5)

e⁻ ^{k * (i + 10)} = e⁻ ^{k * i} -C ₁₀ .ke⁻ ^{k * i} (6)

e⁻ ^{k * 10} = 1-C ₁₀ .k (7)

By changing formula (7) you get:

With k = 0.16 this results in C ₁₀ = 4.99 ∼ 5. This means that by multiplying the difference between the last two temperature measurements by the factor C ₁₀ = 5, the coolant temperature can be calculated, which is expected to be ten measuring steps of 30 s , so it will rule 5 minutes later.

The expected temperature ϑ _{i + 10} calculated in this way is compared with a predetermined limit value or setpoint value, with the vehicle auxiliary heater being switched on when the expected value is below the setpoint value, otherwise not.

According to an advantageous development of the invention, the position of the hot / cold slide in the interior of the vehicle is a variable that can be used to assess whether the vehicle heater should be switched on according to the method according to the invention, ie from the position of this slide a coolant temperature required to heat the vehicle can be calculated. The decision "to heat or not" is derived from a comparison between this required temperature and the expected coolant temperature ϑ _{i + tx} .

In the exemplary embodiment shown in the figure, the measured curve profile for a factor C ₁₀ according to formula (8), which corresponds approximately to a value of 5, is entered with the line provided with crosses (x).

For the embodiment designated with a thick point, starting from a temperature δ _i of 40.4 ° C. measured at measuring point i = 7 and a temperature δ _i-1 of 37 measured at the previous measuring point (i-1) = 6, 02 ° C a pre-calculated temperature δ _{i + 10} = δ ₁₇ = 40.4 + 5. (40.4 - 37.02) = 57.3 ° C.

If a comparison of this calculated expected temperature δ ₁₇ with a predetermined target value, that the former is smaller, the vehicle auxiliary heater is switched on, which otherwise does not occur.

Claims (8)

1. A method for switching on a vehicle auxiliary heater on the basis of a measurement of the coolant temperature at the engine outlet, characterized in that from at least two chronologically successive coolant temperature measured values ϑ _i-1 and ϑ _i, a coolant temperature occurring at a predetermined point in time t _x later Expected value ϑ _{i + tx is} calculated on the basis of the exponential course of the coolant temperature at constant engine load, therefore:
ϑ _i = ϑ _end . (1-e⁻ ^{k * i} ) (1)
where ϑ _end <ϑ _{i + tx} , which occurs when the heating mode is stable, and where k is a coefficient that determines the course of the exponential curve,
that this expected value is compared with a coolant temperature setpoint,
and that the auxiliary heater is switched on when the expected value is below the setpoint. 2. The method according to claim 1, characterized in that the coolant temperature-Er maintenance value between one and 10 minutes later than the second or last one Coolant temperature reading is. 3. The method according to claim 2, characterized in that the coolant temperature-Er maintenance value about 5 minutes later than the second or last one Coolant temperature reading is. 4. The method according to claim 1, 2 or 3, characterized in that the coolant temperature expected value δ _{i + tx} with the aid of a constant C _tx from the formulas
ϑ _{i + 10} = ϑ _i + C _10. (ϑ _i -ϑ _i-1 ) (2),
and
ϑ _i -ϑ _i-1 = ϑ ' _i (i) = ϑ _end .k _* e⁻ ^{k * i} (3)
as
is calculated. 5. The method according to any one of claims 1 to 4, characterized in that the Coolant temperature is detected at regular time intervals. 6. The method according to any one of claims 1 to 5, characterized in that the Coolant temperature setpoint derived from vehicle interior air temperature becomes. 7. The method according to claim 6, characterized in that the coolant temperature target value obtained from the position of the cold / warm valve in the vehicle interior becomes. 8. The method according to any one of claims 1 to 7, characterized in that the Coefficient k is selected depending on the engine type of the vehicle.