DE4007699A1 - Fuel-fired auxiliary heater for motor vehicle - has with pulse-operated blower and burner controlled by variable pulse lengths - Google Patents

Abstract

The fuel fired heater has a solenoid-operated fuel pump and an electric motor-powered blower. The pump and blower are driven by a square pulse signal, with the relative pulse lengths and spacings adjustable to generate different heating effects. The heater warms the engine coolant system and is controlled by temp. sensors. A process (MC) is linked to pulse generators (ST1, ST2) to generate the pulse and pause periods. The battery voltage is also monitored and variations in voltage are corrected to obtain controlled heating. ADVANTAGE - Variable heating control with optimum efficiency.

Description

The invention relates to a fuel-fed Additional heating device for motor vehicles, with one Electric motor for driving a combustion air blower, with a control device for the electric motor, with a electromagnetic fuel pump, with a Control device for the fuel pump, with a Temperature sensor, which is arranged in the heat transfer medium, and with a control device that depends on Output signal of the temperature sensor Combustion air flow rate and the fuel flow rate influenced. Such additional heaters are in Motor vehicles used to even when the Vehicle and when the engine stops Heating of the motor vehicle interior and / or the Coolant of the internal combustion engine, especially in winter to enable.

Such an additional heating device is from DE-OS 36 39 172 previously known. The additional heating device points there a combustion air blower, which is usually by an electric motor is driven. The electric motor is usually connected to a control device. Furthermore, a fuel supply device is provided, usually as an electromagnetic fuel pump is trained and also by a Control device is controllable. A temperature sensor is in the heat transfer medium in the case of this additional heating device in an air duct for measuring the heating air temperature arranged and connected to a control device which in Dependence on the output signal of the temperature sensor Combustion air flow rate and the fuel flow rate influenced.  

However, this previously known additional heating device has Disadvantages. On the one hand, this additional heating device only to regulate the heating output to a maximum Generable value provided. With these measures, though the efficiency of the additional heating device is optimized will. However, these measures do not succeed Temperature control of the heat carrier temperature in the sense of a To keep constant.

The previously known additional heating device has the other Disadvantage that it is not further described with what technical means the combustion air flow rate and the fuel delivery rate is to be influenced.

From DE-PS 26 19 478 is an additional heating device known in which the supply voltage of Additional heating device is measured and the Fuel delivery rate of a clocked electromagnetic fuel pump, depending on the Supply voltage is affected. An influence the combustion air flow rate is not there, however provided, especially not in the sense of a Keeping the heat transfer medium constant.

The invention has the task of an additional heating device to create, in a simple and inexpensive way the heat transfer medium temperature to a constant value can be regulated, this regulation if possible should take place with little loss.

This object is achieved in that the Control device have clock generators, which in generate substantially rectangular clock signals, and that the control device the pulse-pause ratio of the Clock signals depending on the signal of the Temperature sensor in the sense of keeping the Heat carrier temperature affected.  

The fact that the control device clock generators has the substantially rectangular signals generate, the delivery rate of both Combustion air blower via the electric motor as well electromagnetic fuel pump with very low electrical losses occur. It is special here advantageous if the clock signals essentially Have a rectangular shape. The control device affects then the pulse-pause ratio of the clock signals and thus the combustion air flow rate and the Fuel delivery rate. This influencing the clock signals takes place depending on the signal from the temperature sensor in the In order to keep the heat transfer medium constant.

The additional heating device according to the invention has the previous advantage that simple and inexpensive way the temperature of the Heat transfer medium by influencing the Combustion air flow rate and the fuel flow rate can be kept constant. The invention Additional heating device is comparatively simple because no additional clock generators Furnishing parts are required. Such Clock generators are simple and simple inexpensive to build.

The additional device according to the invention has the further Advantage that the regulation of the heat carrier temperature in is carried out with low losses because of the power control for rectangular clock signals by simple change of the pulse-pause ratio can take place without one Power loss must be generated at reactive loads.

Advantageous refinements and developments of additional heater according to the invention go from the Sub-claims emerge. It is particularly beneficial if the control device has a memory which  Pulse-pause ratios depending on the signal from the Temperature sensors are filed, on the one hand, with regard to the dependence of the pulse-pause ratios on Temperature sensor signal almost any freedom to have. On the other hand, a linear pulse-pause ratio depending on Temperature sensor signal must be stored.

The control device can determine the duration of the pulse widths influence. However, it is also influencing the Duration of the pulse breaks possible.

A temperature-dependent, electrical resistance, especially with negative Temperature coefficients (NTC) can be used. Such electrical resistors are easy to find in stores procure and inexpensive. The heat transfer medium can advantageous water, especially the engine cooling water Internal combustion engine, because then both with the heated Engine cooling water in the winter before the engine Tempering can be warmed as well Motor vehicle interior can be heated.

But in the event of brief drops in the supply voltage even when the supply voltage slowly drops Battery with a longer operating time a change in the Combustion air flow and fuel flow to prevent it is particularly advantageous if a Supply voltage sensor is provided, and if the Control device, depending on the measured Supply voltage, the pulse-pause ratio of the Clock signals influenced so that the Combustion air flow rate and the fuel flow rate remain constant. That means that when the Supply voltage, e.g. B. at a Influencing the pulse width, the pulse width increased so far will that the time average of the electric motor of the  Combustion air blower and the electromagnetic Electrical power supplied to the fuel pump is the same remains.

In this context, the supply voltage sensor advantageously an electrical voltage divider consisting of Resistors, the control device being the voltage taps at the center tap of the voltage divider. Through this Measure the measured supply voltage easily and be implemented cost-effectively to a value that for example, by an analog-digital converter Microcomputer can be processed without further measures.

Voltage stabilization can also be provided be, the temperature sensor in series with a Series resistor in the stabilized supply circuit is switched. The control device can then control the voltage at the connection point of the series resistor and temperature sensor tap. In this case too, the series resistor and the temperature sensor uses an ohmic voltage divider which the total voltage drop of the stabilized Supply voltage corresponds. The partial voltage drops depend on the electrical resistance values of Series resistor and temperature sensor, the electrical resistance of the series resistor is constant, the electrical resistance of the temperature sensor itself however depending on the temperature of the heat transfer medium changes. From the tension at the center tap this The regulator can be a voltage divider Pulse-pause ratios calculate the current Take the temperature of the heat transfer medium into account.

To not only indirectly give clues about the Combustion air flow rate of the combustion air blower too , it is particularly advantageous if a Measuring device for the speed of the electric motor (M) is provided. Without this measuring device, due to  Preliminary tests in the construction of the invention Additional heater assumed that a certain predetermined pulse-pause ratio of one corresponds to the specific speed of the electric motor. However, to for example, locking states of the electric motor too detect or slow down the speed of the Combustion air blower due to increased age-related bearing friction is the speed measurement of the Electric motor advantageous.

In this context, the measuring device can Have motor voltage sensors. This motor voltage sensor can be a voltage divider consisting of electrical Resistors, the control device the voltage taps at the center tap of the voltage divider. The Voltage divider is z. B. with the negative Supply voltage of the power source and on the other hand with a pole of the fan electric motor connected, this Pol preferably the of the control device with the negative supply voltage connected pole of the Electric motor is. Using these measures is an easy one Adaptation of the measured motor voltage to the measurable Input voltages e.g. B. an analog-digital converter of a microcomputer possible.

It is special when using a motor voltage sensor advantageous if the measuring device in the Clock pulse breaks the electromotive force of the Electric motor measures by taking the difference from the Forms supply voltage and motor voltage. The Electric motor generates in the event of its rotation without a Supply voltage is present, a so-called electromotive force, the size of which depends on the current speed of the electric motor. The size of the Supply voltage is when the motor circuit is closed known. The motor voltage can in the clock pulse pauses Electric motor can be measured. By forming the difference  receives from the supply voltage and the motor voltage one the electromotive force which is a measure of that Speed of the electric motor is.

In this context, the control device advantageously have comparisons that the measured electromotive force with a signal from the Temperature sensor corresponding electromotive force compares. The pulse-pause ratio can then be in the sense keeping the speed of the electric motor constant to be influenced.

To simplify the invention Additional heater, it is particularly advantageous if the control devices and / or the regulating device and / or the measuring device are parts of a microcomputer. In this case, the effort required to set up the additional heating device according to the invention on the use a microcomputer instead of some discrete electronic ones and electrical components.

An embodiment of an inventive Additional heating device is shown in the drawings and will be explained in more detail below with reference to the drawings explained.

Show it

Fig. 1 is a block diagram of an auxiliary heating device according to the invention,

Fig. 2 is a voltage timing chart of the control of the electric motor of the combustion air blower,

Fig. 3 is a flowchart for a method as it can run as part of the microcomputer (MC) in Fig. 1 and

FIGS. 4a to d show various time diagrams for explaining the control principle of the auxiliary heating device according to the invention of FIG. 1.

In Fig. 1, an electrical resistor (RV) is a series resistor with an electrical resistor (RT) with negative temperature coefficients (NTC) with the positive pole of a stabilized voltage supply and the negative pole (-) of a power source or automotive battery (B) conductive connected. The stabilized, positive supply voltage is generated by a voltage stabilization circuit (SS). For reasons of power supply, a microcomputer (MC) is connected to the negative pole (-) on the one hand and to the positive pole of the stabilized voltage supply of the motor vehicle battery (B) via a second input (E 2 ).

The microcomputer (MC) receives the voltage at the center handle of the voltage divider via a first input (E 1 ), formed from the electrical resistance (RV) and the electrical resistance (RT). A third input (E 3 ) of the microcomputer (MC) is conductively connected to a center tap of a voltage divider, formed from a third resistor (R 3 ) and a fourth resistor (R 4 ), which on the one hand is connected to the negative supply voltage of the current source (B ) and on the other hand is connected to a pole of an electric motor (M) of a combustion air blower. The pole of the electric motor (M) is a pole which can also be conductively connected to the negative supply voltage (-) via a first control device (ST 1 ). Furthermore, the microcomputer (MC) is conductively connected via a fourth input (E 4 ) to the center tap of a further voltage divider, formed from a first resistor (R 1 ) and a second resistor (R 2 ), which on the one hand is connected to the positive pole ( +) of the supply voltage source (B) and on the other hand is conductively connected to the negative pole (-) of the supply voltage source (B). Via this voltage divider, formed from the resistors (R 1 , R 2 ) and the fourth input (E 4 ), the microcomputer (MC) can measure a voltage that corresponds to the unstabilized supply voltage, that is, the supply voltage upstream of the stabilization circuit (SS) is proportional. The voltage divider, formed from the resistors (R 3 , R 4 ), enables the microcomputer to measure a voltage via the input (E 3 ), which voltage is proportional to the connection point between the electric motor (M) and the first control device (ST 1 ) and is a measure on the one hand for supplying the electric motor (M) with voltage when the first control device (ST 1 ) is switched through and on the other hand is a measure for the rotation of the electric motor (M) by generating an electromotive force. Via a first output (A 1 ), the microcomputer (MC) controls a second control device (ST 2 ), which is also conductively connected in series with an electromagnetic fuel pump (BP) to the poles of the motor vehicle battery.

The microcomputer (MC) delivers essentially rectangular clock signals at its outputs (A 1 , A 2 ), which are fed to the control devices (ST 1 , ST 2 ). The shape of the rectangular clock signals is explained in FIG. 2 using the example of the control of the electric motor (M) via the first control device (ST 1 ) and the output (A 2 ). A voltage (U) is plotted against time (t) in FIG. 2. The supply voltage at the motor vehicle battery (B), which is measured via the voltage divider, consisting of the resistors (R 1 , R 2 ), is shown with (UB). Between the voltage value 0 and the positive supply voltage (UB) now moves the potential of a voltage on the electric motor (M), as it is at the center tap between the electric motor (M) and the first control device (ST 1 ) or the voltage divider, consisting of the Resistors (R 3 , R 4 ) can be measured via the third input (E 3 ). The potential at this input (E 3 ) essentially depends on whether the first control device (ST 1 ) is switched through or not and whether the electric motor (M) is rotating or not. The switching state of the first control device (ST 1 ) determines the rectangular clock signal with which the electric motor (M) is supplied. The difference (EMF) shown in FIG. 2 between the positive supply voltage (UB) and a motor voltage (UM) results when the first control device (ST 1 ) is switched off, so that the electric motor is not supplied with voltage from the motor vehicle battery at this time . Due to the inertia of the electric motor, however, the electric motor continues to rotate and generates the motor voltage (UM) shown in FIG. 2.

The difference between the battery voltage (UB) and the motor voltage (UM) then results in the electromotive force (EMF), which is a measure of the speed of the electric motor (M). The pulse duration of the rectangular clock signal is identified by (T 1 ) in FIG. 2. The interval duration of the rectangular clock signal is identified by (T 2 ) and (T 3 ) indicates the period duration of a clock cycle of the rectangular clock signal.

In Fig. 3 is the sequence of a method for controlling the heat transfer temperature, as z. B. can run in the microcomputer (MC), explained in more detail. After starting a microcomputer program, a water temperature of the engine cooling water serving as the heat transfer medium is first measured by determining the voltage value of the NTC resistor (RT). This is done in process step 1.

After this process step 1, the supply voltage (UB) is measured in a process step 2, for example in the case of an electrical resistance divider (R 1 , R 2 ).

Then in a process step 3 from the measured water temperature a setpoint for the speed of the electric motor (M), with the setpoint here instead of the speed, the value of one immediately electromotive force read out from a table can be.

To control the fuel pump is also from a table z. B. the value of the previously measured EMF of the electric motor (M) is taken out. With this table value for the pulse-pause ratio of the rectangular clock signal for the fuel pump (BP), the fuel pump (BP) is then controlled for the second control device (ST 2 ). This takes place in method step 5. After these pulse-pause ratios of the two clock signals have been set in the form described, the method returns to method step 1 with the measurement of the water temperature and the method steps described are repeated cyclically.

In parallel to the procedure described, e.g. B. in a step 6, the engine (M) of Combustion air blower can already be switched on, whereby because of the not yet available at this time Information about water temperature and supply voltage the motor with a constant pulse-pause ratio of one Clock signal is supplied. In a process step 7 the motor voltage is then measured. Next is done in a step 8 the calculation of the back emf from the difference of supply voltage (UB) and Motor voltage (UM). Then in one step 9 by comparison of the measured electromotive force, with that calculated according to method steps 3 and 4 electromotive force determined whether the electromotive force and thus the speed of the Electric motor (M) corresponds to the desired value.  

If this is not the case, then in one process step 9 the electric motor (M) to that of the water temperature readjusted the corresponding setpoint. After this Process steps return the process for engine control and to keep the speed of the electric motor (M) constant to step 7 with measurement of the motor voltage (UM) back. These processes are also repeated cyclically.

In FIG. 4, various operations in the auxiliary heating device according to the invention are shown in FIG. 1 through 3 in response to a time (t).

In Fig. 4a the supply voltage (UB) is plotted in function of time (t). This voltage-time diagram assumes that at a first point in time (t 1 ) the supply voltage (UB), e.g. B. breaks briefly by interrupting a supply voltage line. After a longer period of time, the voltage (UB) should have dropped to a value at a second point in time (t 2 ) due to, for example, the gradual draining of the motor vehicle battery (B), which is less than the voltage value (UB) when the motor vehicle battery is fully charged (B ).

FIG. 4b shows the course of the heat transfer medium temperature (TW), measured on the temperature-dependent resistance (RT) in FIG. 1, over time (t). It was assumed that at time 0 the supply voltage (UB) was switched on, for example via the ignition starter switch of a motor vehicle, and that a cold motor vehicle with a cold internal combustion engine was to be heated by the additional heating device according to the invention. Accordingly, the heat transfer temperature, the z. B. the temperature of the cooling water on an internal combustion engine can be at a lower temperature at time 0. As time (t) progresses, the heat transfer medium heats up so that the temperature of the heat transfer medium (TW) rises until it reaches the value specified by the control device at a third point in time (t 3 ).

Keeping the temperature (TW) of the heat transfer medium constant is possible with the measures according to FIGS. 4c and 4d. In Fig. 4c, the speed of the fan motor (M) is the combustion air blower as a function of time (t) is applied. It can be seen that when the additional heating device according to the invention is switched on by the control device, a pulse-pause ratio is predetermined, which leads to a comparatively high speed (s) of the electric motor (M). With the heating of the heat transfer medium by increasing the heat transfer medium temperature (TW), the speed (n) of the electric motor (M) then gradually decreases as the time progresses. At a point in time (t 3 ) at which the heat carrier reaches its desired temperature (TW), the electric motor (M) then also reaches its continuous speed (n) which it needs to keep the temperature of the heat carrier constant. As previously explained, a voltage dip takes place at a first point in time (t 1 ) which, as shown in FIG. 4c, is shown as a small dip in the speed-time curve of the electric motor (M). However, this slight change in the electric motor speed (n) when the voltage drops at the first point in time (t 1 ) does not lead to a change in the heat temperature (TW) because the time period is too short on the one hand and because only one is adjusted by adjusting the pulse-pause ratio accordingly there is a slight change in the electric motor speed (n) at this point in time, although the voltage drop, as shown in FIG. 4a, is almost complete. Likewise, due to the gradual decrease in the operating voltage (UB) at time t <t 2, there is no reduction in speed, since this is counteracted by readjusting the pulse-pause ratio.

In Fig. 4d, the delivery rate (MBP) of the fuel pump (BP) is plotted against time (t). It can also be seen here that, in analogy to the sequence according to FIG. 4c, at the beginning of the function of the additional heating device according to the invention, the delivery rate of the fuel pump (BP) is comparatively large in accordance with the high speed (s) of the electric motor (M). As the heat transfer medium heats up and the heat temperature (TW) increases, the delivery rate (MBP) of the fuel pump drops to lower values, in a manner similar to the speed of the electric motor (M). At the point in time (t 3 ) at which the advertising medium reaches its desired heat carrier temperature (TW), the delivery rate (MBP) is also set to a quasi-stationary value, which on the one hand is at the desired heat carrier temperature (TW) and on the other hand at the preset speed (n ) of the electric motor (M) correlated.

Claims (15)

1. Fuel-fed additional heating device for motor vehicles, with an electric motor for driving a combustion air blower, with a control device for the electric motor, with an electromagnetic fuel pump, with a control device for the fuel pump, with a temperature sensor which is arranged in the heat transfer medium, and with a control device which influences the combustion air flow rate and the fuel flow rate as a function of the output signal of the temperature sensor, characterized in that the control devices (ST 1 , ST 2 ) have clock generators which generate essentially rectangular clock signals and that the control device (MC) controls the pulse Pause ratio of the clock signals as a function of the signal from the temperature sensor (RT) in the sense of keeping the heat transfer medium constant. 2. Additional heating device according to claim 1, characterized characterized in that the control device (MC) one Memory in which pulse-pause ratios in Dependence on the signal from the temperature sensor (RT) are filed. 3. Additional heating device according to claim 1, characterized in that the control device (MC) influences the duration of the pulse widths (T 1 ). 4. Additional heating device according to claim 1, characterized in that the control device (MC) influences the duration of the pulse pauses (T 2 ). 5. Additional heating device according to claim 1, characterized  characterized in that the temperature sensor (RT) temperature-dependent electrical resistance, especially with negative temperature coefficients (NTC). 6. Additional heating device according to claim 1, characterized characterized in that the heat transfer medium is water, especially the engine cooling water Internal combustion engine is. 7. Additional heating device according to claim 1, characterized characterized in that a voltage divider is provided, and that the control device (MC) depending on the Supply voltage the pulse-pause ratio of the Clock signals affected so that the ratio of Combustion air flow rate and the The fuel delivery rate remains constant. 8. Additional heating device according to claim 7, characterized in that the supply voltage sensor is a voltage divider consisting of resistors (R 1 , R 2 ), and that the control device (MC) the voltage at the center tap of the voltage divider (R 1 , R 2 ) taps. 9. Additional heating device according to claim 5, characterized characterized that a voltage stabilization (SS) it is provided that a series resistor and Temperature sensors (RT) in series in the stabilized Supply circuit are switched, and that the Control device (MC) the voltage at the connection point of series resistor (RV) and temperature sensor (RT) taps. 10. Additional heating device according to claim 1, characterized characterized in that a measuring device for the Speed of the electric motor (M) is provided.   11. Additional heating device according to claim 10, characterized characterized in that the measuring device a Has motor voltage sensor. 12. Additional heating device according to claim 11, characterized in that the motor voltage sensor is a voltage divider consisting of resistors (R 3 , R 4 ), and that the control device (MC) the voltage at the center tap of the voltage divider (R 3 , R 4 ) taps. 13. Additional heating device according to claim 11, characterized characterized in that the measuring device in the Clock pulse breaks the electromotive force (EMF) of the Electric motor (M) measures by taking the difference Supply voltage (UB) and motor voltage (UM) forms. 14. Additional heating device according to claim 14, characterized characterized in that the control device (MC) one Comparator has the measured electromotive force (EMF) with a signal from the Corresponding temperature sensor (RT) compares electromotive force (EMF), and that the Control device of the pulse-pause ratio in the sense keeping the speed of the electric motor constant (M) influenced. 15. Additional heating device after one or more of the preceding claims, characterized in that the control device and / or the measuring device Are part of a microcomputer (MC).