WO1996018848A1 - Control circuit for a fan drive motor - Google Patents

Abstract

The invention concerns a control circuit for a vehicle heater fan drive motor. The control circuit comprises a voltage divider which emits a signal (S) representative of the supply voltage to a microcomputer (12) where the measuring signal is converted into a digital value which is used as the address signal for a table memory which stores compensated signals which are used to form a PWM signal which is emitted to the control input of a semiconductor switch (6) in the circuit of the motor (2). In this way a relatively constant rotational speed of the motor (2) is attained, even when the supply voltage (UB) fluctuates.

Description

Control circuit for a blower drive motor

The invention relates to a control circuit for a blower or pump drive motor.

In particular, the invention relates to a control circuit for a blower or pump drive motor of a vehicle heater or a burner for regenerating a particle feeder for diesel engines.

Burners for regenerating particle feeders for diesel engine exhaust systems as well as (auxiliary) vehicle heaters, often referred to as "auxiliary heaters", have a drive motor which drives a combustion air blower and, if appropriate, a heating air blower. A combustion air blower is also present in vehicle heaters with water as the heat carrier, but instead of a heating air blower, a water pump serves as a means for circulating the heat carrier.

In the case of the blowers mentioned above, an electric motor provides the blower drive, just as an electric motor provides the drive for a pump.

Both the vehicle heaters in question and the devices for regenerating particle feeding for diesel engines use the on-board battery as the operating voltage source. The usual voltages of these batteries are e.g. 12 or 24 volts, these

Voltages, however, are subject to considerable fluctuations.

Do you want e.g. If a vehicle heater is operated with a constant output, this means that the rotational speed of the combustion air blower (also of the heating air blower, the

Motors for the water pump, the fuel pump) required. If the nominal voltage of the on-board battery drops from 24 V to 22 V or even further, the blower motor turns correspondingly slower, so that the vehicle heater does not deliver the desired output and significantly less favorable exhaust gas values arise.

One can now think of providing a speed control for the electric motor, which ensures that, regardless of voltage fluctuations in the supply voltage, the desired SoU speed of the motor and, consequently, the fan coupled therewith is always achieved.

However, if the entire device is not to exceed a certain price, regulation may not be possible, among other things, because measuring the motor voltage and the speed (eg by means of a tachogenerator) directly on the motor and the required regulating device are associated with some effort .

The present invention is intended to provide a control circuit for a blower or pump drive motor, which is placed between the poles of a DC voltage source, which can be implemented relatively cheaply and nevertheless has a good agreement between the engine speed and the desired or desired speed reached.

This is achieved according to the invention by the control circuit specified in claim 1 for a blower or pump drive motor which is placed between the poles of a DC voltage source, in which

Circuit of the motor is a semiconductor switch controlled with a PWM signal (pulse width modulation signal), in that use is made of a voltage sensor which gives a measurement signal representative of the DC voltage of the DC voltage source to a controller which compensates for the measurement signal Signal that is used to form the PWM signal.

The semiconductor switch in the circuit of the motor, which is e.g. is a MOSFET, is driven by the PWM signal with a frequency in the kilohertz range. The behaves

Motor as if it were powered by a DC voltage that is coming out the pulse duty factor of the PWM signal can be calculated. The duty cycle indicating the ratio of pulse length to pulse pause (alternatively: pulse length to pulse period duration) must be greater in order to achieve a specific target speed, the lower the voltage of the DC voltage source.

When the DC voltage source supplies the nominal voltage, the control system outputs a PWM signal, which can depend on an adjustable target speed value and ensures that the motor rotates at the desired speed. If the potential of the DC voltage source now fluctuates, for example drops by a few volts, such a change in the supply voltage is detected by the voltage sensor. The control then forms a compensated measurement signal from this measurement signal, which is then used to form the PWM signal. If the supply voltage drops, this means that the compensated measurement signal has the consequence that the pulse duty factor of the PWM signal is increased, so that in the end the motor behaves as if the DC voltage of the DC voltage source had not changed. By varying the duty cycle, the motor always receives an "effective" DC voltage that is independent of the voltage of the DC voltage source (the voltage of the on-board battery).

The motor can be operated at a constant speed, but the motor speed can also be increased or decreased in accordance with certain, predetermined functions, for example in accordance with a ramp function. In all of these control processes, a change in the voltage of the DC voltage source is taken into account in the manner described above, in that a compensated measurement signal is formed from the measurement signal formed by the voltage sensor, which is used to generate the PWM signal.

The voltage sensor can be a simple voltage divider with two resistors. If the control is also designed as a microcontroller (μC = microcontroller), which is usually used to control the vehicle heaters in question, not even the two resistors are the only ones additional components for the control circuit, since these are already used for other purposes (in control units in vehicle heaters).

In a special embodiment of the invention it is provided that the

Control is designed as a μC, which contains an analog-to-digital converter (ADC), the input of which is supplied with the measurement signal, and the output signal of which is used as an address signal for a table memory (ROM) in which the compensated values associated with certain actual voltage values are stored are, which form the compensated signal.

The ADC integrated in the μC converts the analog signal representative of the battery voltage into a digital value. This digital value forms the address of a table memory contained in a ROM. The

The content of the table memory can be determined by calculation, but it can also - preferably - be determined by tests, for example by specifying a constant motor speed, the PWM signals required to achieve this constant motor speed and the digital values to be determined such PWM

Signals belong. This process is repeated for different values of the DC voltage queue, so that a specific table storage value is obtained for each of these different values. If one of these values is then determined during actual operation of the voltage sensor, the table memory converts this value into a compensated signal, with the result that this compensated signal leads again to the desired speed.

An exemplary embodiment of the invention is explained in more detail below with reference to the drawing. Show it:

1 shows a block diagram of a control circuit according to the invention for a blower motor of a vehicle heater, and

FIG. 2 shows a characteristic curve that shows the dependence of the duty cycle of a PWM signal on the supply voltage for a large and illustrated for a low speed at a certain load torque.

As stated above, this is specifically about controlling a blower or pump drive motor of a vehicle heater.

The invention is equally applicable to burners for regenerating PartikelfUtem for diesel engines.

FIG. 1 shows a direct current motor 2 between a direct voltage source U _B and ground, with a freewheeling diode 4 connected to it, with a MOSFET 6 connected in series with the motor 2 as a beautiful semiconductor switch. The semiconductor switch 6 operates at a frequency in the range of more than 20 kHz. If the direct voltage voltage has a voltage of U _B = 24 V and the pulse duty factor, here the ratio of pulse length to pulse period, that of

Is the semiconductor switch 6 opening and closing PWM signal 50 percent, the motor 2 behaves as if it were operated with a DC voltage of about 12V. This does not take into account the voltage at the semiconductor switch 6 caused by a certain forward resistance and the reverse voltage of the

Free-wheeling diode 4. In fact, the effects of these voltages on the operation of the circuit can be eliminated within certain limits, for example by designing the winding of the motor, mathematical routine, comparing the motor / control device, so that only the level of the DC voltage of the motor 2 is required for operation of the motor Voltage queue U _{B is} decisive.

The voltage source U _{B is} connected via a measuring line 6 'to a voltage controller 8 which is formed from two resistors R1 and R2 and serves as a voltage sensor. A measurement signal S is tapped at the connection node 10 between the two resistors R1 and R2, which is proportional to the current supply voltage U _B.

The measurement signal S is applied to the A / D input of a controller 12 designed as a microcontroller (μC). The μC is baked in a manner known per se. It contains an analog-to-digital converter the mentioned input A / D. The measurement signal S is thus converted into a digital value.

The μC 12 also contains a read-only memory ROM 14, the address input of which is supplied with the digital signal coming from the A / D input. In the ROM 14, compensated measuring signals kS are stored in tabular form, which are output with a specific clock cycle not shown here, each compensated signal kS depending on the measuring signal S. The compensated signal kS is applied to an input of a PWM circuit 16, which in a manner known per se supplies a PWM signal (pulse-width-modulated signal) which is dependent on the signal kS to the control input of the semiconductor switch 6.

The PWM signal not only depends on the compensated signal kS, but can also depend on a further signal which depends on an input n, ^ (SoU speed value).

FIG. 2 shows the dependence of the pulse duty factor t on the supply voltage V, specifically for a FaU with a high speed i ^ and the FaU with a relatively low speed n _κ at a certain load torque. Only the low speed n _{κ of} the motor 2 is considered as a representative. With a supply voltage of 5V, the duty cycle t _{v is} 100 percent. If the pulse duty factor is defined as the ratio of pulse length to pulse pause, direct current has a pulse duty factor of infinite. If the pulse duty factor is defined as the ratio of the pulse length to the pulse period, a pulse duty factor of 1 or 100 percent means that there are practically no pulse pauses. A duty cycle and 50 percent means that the pulse length is the same as the associated pulse pause.

In Figure 2, the speed n _κ at a voltage of 5 V is only achieved with a duty cycle of 100 percent. If the supply voltage is 15 volts, a pulse duty factor of 30 percent is sufficient. The characteristic curves shown qualitatively in FIG. 2 can be used to form the values for the table memory in the μC according to FIG. 1. Ie: For a series of supply voltage values, an associated set of duty cycle values is stored, and this duty cycle range then forms the compensated signal kS.

Alternatively, the table memory can also be used with empirically determined values.

If, for example, the supply voltage U _B drops somewhat during operation, this does not affect the measurement signal S as a reduction in the amplitude. Accordingly, the digital value supplied to the address input of the ROM 14 has a smaller value. Such a compensated signal kS is stored under the address associated with this smaller value, which leads to a PWM signal with an increased pulse duty factor. This increased duty cycle opens the semiconductor switch 6 for a somewhat longer period of time with each pulse, so that the motor 2 effectively receives a higher voltage. The value of the compensated signal kS is preset such that the speed of the motor 2 is kept constant.

As is also indicated in FIG. 1, the PWM circuit can also receive a SoU speed signal in addition to the compensated signal kS. This allows the speed of the motor 2 to be changed.

As mentioned above, the pulse duty factor can be defined as the ratio of the pulse length to the pulse period. This also corresponds to the following relationship:

uu _^ ,,

with l = duty cycle UU _ggll == NNeennnn - GSleichichichririrwert the motor U ,,,. = current supply voltage If the nominal rectification value of the motor corresponds to the current supply voltage, then there is a duty cycle of 1 or 100%, which corresponds to the FaU of the DC power supply. A pulse duty factor of 0.5 or 50 percent corresponds to a nominal rectification value of the motor that is half as large as the current supply voltage.

From this it is clear that the duty cycle can be varied in order to obtain certain speed curves, for example speed ramps or constant speeds.

In addition to constant speeds and (linear) ramps, non-linear speed curves can also be achieved.

If the circuit according to FIG. 1 is considered, the following relationship can be derived for the above formula for the pulse duty factor t:

, = (new - U _D ) / (U - I _L ^• Ros - U _D )

with U ^ = terminal voltage on the motor U _D = barrier layer voltage. the Freüaufdiode

U _BAT = supply voltage (measured voltage)

I _L = load current at the operating point

Ros = resistance of the semiconductor switch in the live FaU

The forward resistance of the semiconductor switch has the greatest influence on the speed control. However, this influence can be minimized by suitable winding design. Since the scatter of the other parameters is largely known, and because the respective supply voltage U _{BAT is available} as the measured voltage, the value for can be calculated using mathematical formulas. In this case, a table memory can be dispensed with, but instead the parameter values mentioned must be taken into account.

Claims

claims 1. Control circuit for a blower or pump drive motor (2) which is placed between the poles of a DC voltage source (U _B ), a semiconductor switch (6) driven by a PWM signal being present in the circuit of the motor (2), comprising a voltage sensor (8, R1, R2), which gives a measurement signal (S) representative of the DC voltage of the DC voltage source to a controller (12), which converts the measurement signal into a compensated measurement signal (kS), which is used to load the PWM signal is used. 2. Control circuit according to .Anspruch 1, characterized in that the voltage sensor is built by a voltage controller (Rl, R2). 3. Control circuit according to claim 1 or 2, characterized in that the controller has a microcontroller (C12) which contains an analog-to-digital converter, the input of which is supplied with the measurement signal, and the output signal of which as an address signal for a clock signal. beUenspeicher (ROM 14) is used, in which associated compensated values are stored for certain actual voltage values, which would burden the compensated signal (kS). 4. Control circuit according to claim 1 or 2, characterized in that the pulse duty factor of the PWM signal is calculated according to the following formula: , = (Ua - U _D ) / (U _BAT - I _L ^* Ros - U _D ) with U ^ = terminal voltage on the motor U _D = barrier layer the Freüaufdiode U _BA τ ⁼ supply voltage (measured voltage) I _L = load current at the operating point R _DS = resistance of the semiconductor switch in the live FaU 5. Control circuit according to claim 4 for a vehicle heater or a burner of a particle feed for diesel engines, characterized gekenn¬ characterized in that the pulse duty factor (is set to set linear or non-linear ramp functions for the speed curve, which are chosen such that the operating behavior of the Brenner, for example with regard to the exhaust gas values, is optimized.