Abstract:
The present invention concerns a control system for an electric motor, wherein an operating mode with predetermined value assignments is selected for a parameter set for controlling an electric motor and the pulse frequency of a control signal for the electric motor is set in accordance with the selected operating mode in order thereby to signal to the electric motor the selected value assignments for the parameter set.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 USC §119 to German Patent Application No. 10 2013 019 666.3 filed on Nov. 22, 2013, which application is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention concerns a control apparatus, a motor regulator and a control method for controlling an electric motor, in particular a ventilator fan for motor vehicles, by means of a pulsed control signal. 
     BACKGROUND OF THE INVENTION 
     The standard “Local Interconnect Network” (LIN) was developed as a specification for a serial communication system as a new de-facto standard in particular for inexpensive communication of intelligent sensors and actuators in motor vehicles. The LIN serves in particular for inexpensive communication and is based on a one-wire bus which can be associated with the field buses. The LIN is composed of a master device and one or more slave devices. The master device has knowledge about the temporal sequence of all data to be transmitted. Those data are transmitted by the corresponding slave devices when they are required to do so by the master device. That is effected by sending out a message header characterised by a given message address. Subsequently the slave device connects its data output to the bus. 
     The new LIN standard is also intended for communication between control devices and motor regulators for electric motors in motor vehicles. Thus for example voltages or currents in radiator cooling fan regulators and interior fan regulators are regulated by means of corresponding signals or messages by way of various interfaces like for example pulse width modulation (PWM) and LIN. In that case an LIN interface has the advantage of greater flexibility over a PWM interface as various messages can be communicated while the PWM interface can only deliver a signal frequency and a pulse duty cycle. In the case of the PWM interface, it was possible to achieve a certain degree of flexibility by a variation in the pulse duty cycle, for example between 0% and 100%. 
       FIG. 2  shows a diagrammatic time graph of a PWM signal in pulse form, showing the period duration T, the pulse duration t PD  and the pulse pause t PP . In this case the frequency of the PWM signal occurs as the inverse of the period duration, that is to say f=1/T. 
     As many control systems are based on a PWM-based control there is a need for backward compatibility so that conventional PWM-based devices can communicate with more recent LIN-based devices, that is to say the information which can be transmitted by means of the LIN can also be transmitted by way of a PWM-interface. 
     SUMMARY OF THE INVENTION 
     Therefore the object of the present invention is to improve a PWM-based control system to the effect that use is possible in conjunction with more recent control components which expect LIN-specific information. 
     That object is attained by a control apparatus as set forth in claim  1 , a motor regulator as set forth in claim  7  and a control method as set forth in claim  11 . 
     Accordingly a parameter set for controlling the electric motor is defined by an operating mode which in turn is linked to the pulse frequency of the pulsed control signal so that the selected value assignment for the parameter set can be signaled to the electric motor by means of the pulsed control signal. The signaled pulse frequency of the control signal is communicated to the motor regulator of the electric motor and detected there, wherein the parameter set for operation of the electric motor is determined in dependence on the detected pulse frequency. 
     It is also possible to provide different frequencies or frequency ranges (frequency windows) for a plurality of operating modes so that parameter values like for example overcurrent thresholds, overvoltage thresholds, fan switching frequencies, current rise and fall limits and so forth can be signaled. 
     Switching over to another parameter set is thus possible by simply changing the frequency of the control signal. 
     In addition the proposed signaling method can also be used for selecting between a normal mode and a test mode. Adjustment of the pulse frequency can be effected directly by way of a frequency-determining element or a frequency-determining circuit or by changes to the period duration by means of suitable time-determining element or a suitable time-determining circuit. 
     Establishing the parameter set in accordance with the operating mode can also be implemented in dependence on a predetermined motor manufacturer so that the control system can be adapted to different manufacturers of electric motors like for example ventilator fans or the like. 
     Further advantageous developments are recited in the appendant claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in greater detail hereinafter by means of embodiments by way of example with reference to the accompanying drawings in which: 
         FIG. 1  shows a schematic block circuit diagram of a control system according to the first embodiment, 
         FIG. 2  shows a time graph of a PWM-control signal, 
         FIG. 3  shows a table with a first assignment specification between frequencies and parameter-determining operating modes, and 
         FIG. 4  shows a second table with assignment specifications between frequencies and parameters. 
     
    
    
     DETAILED DESCRIPTION 
     Set out hereinafter is a description of a preferred embodiment by way of example with reference to a control system of a ventilator fan motor in a motor vehicle. 
       FIG. 1  shows a schematic block circuit diagram of the control system in which a motor regulator  20  (here: fan regulator) for an electric motor (here: fan motor (M))  30  is controlled by way of a PWM signal provided in a control device  10 . General regulation of the fan motor  30  is effected by way of a control input signal  200  which is passed to a PWM-control unit (PS)  16 , the PWM-control unit  16  generating a PWM-signal whose pulse duration or duty cycle is altered in dependence on the control signal  200 . The PWM-control signal is passed to a fan control (LS)  29  in the fan regulator  22 , which then controls the fan motor  30  in accordance with the control input signal  200 . The control input signal  200  can also involve a control signal  200  generated in dependence on a feed-back signal from the fan motor  30  so that a closed control loop is formed for regulating the fan motor  30 . 
     In accordance with the embodiment the control device has an additional input for the selection of an operating mode or a parameter set, by way of which a parameter control signal  100  can be input. The parameter control signal  100  can be input manually by a user or can be generated automatically by the control system in dependence on environmental conditions and/or other system-relevant properties. The control device  10  includes a selection unit (A)  12  which receives and evaluates the parameter control signal  100  and, in dependence on the parameter control signal  100 , selects an assigned operating mode and/or an assigned parameter set. That can occur in dependence on a storage table, an address memory or other link or logic circuits. The selection of the operating mode or the parameter set is passed to a frequency selection unit (F)  14  which feeds the pulse control unit  16  with a suitable control signal for establishing the frequency of the PWM-control signal. That conversion of the operating mode or the parameter set into a frequency in respect of the control signal can also be implemented on the basis of a storage table, an addressable memory, a selection circuit or a logic circuit. Conversion of the parameter control signal  100  into the frequency selection signal of the frequency selection unit  14  can also be implemented by a one-time conversion in an individual storage table, an individual addressable memory, an individual selection circuit or an individual selection logic means. 
     As can be seen from  FIG. 1  therefore, besides the pulse width or pulse duty cycle information in respect of the PWM-control signal, additional information in regard to the operating mode or the parameter set can be transmitted by the frequency of the PWM-control signal to the fan regulator  20 . As shown in  FIG. 1  firstly an operating mode B 1  at a lower frequency in respect of the PWM-signal is transmitted and later a second operating mode B 2  at a higher frequency in respect of the PWM-signal is transmitted. 
     At the fan regulator  20  the PWM-signal is passed to an interface (SS)  22  which feeds the PWM-control signal to the fan control  29 . In addition the PWM-signal or at least a signal corresponding to the frequency of the PWM-control signal is passed on to a detection unit (E)  24  which detects the frequency of the PWM-control signal and passes the result of the detection step to an adjusting unit (S)  26 . The adjusting unit  26  performs corresponding parameter setting in dependence on the signaled parameter set or the signal operating mode and stores the signaled parameter set in a first parameter memory (P)  28 . 
     The fan control  29  can thus access the parameter memory  28  and acquires the parameter set desired for the currently prevailing operating mode or the currently prevailing parameter choice, for control of the fan motor  30 . 
     The blocks of the control device  10  and the fan regulator  20  shown in  FIG. 1  can be in the form of discrete hardware circuits, logic digital circuits, gate arrays or programmable logic circuits (PLDs) or software-controlled processors. 
     In a first practical example of the embodiment, corresponding to the table shown in  FIG. 3 , it is possible to select between a test operating mode and a normal mode for example by way of the frequency of the PWM-control signal. Thus for example at a frequency f=50 Hz, it is possible to set a normal mode B N  of the fan regulator  20  while at a frequency f=120 Hz of the PWM-control signal the fan regulator  20  is put into a test operating mode B T . Specific values can be assigned to predetermined parameters as further frequencies or frequency windows with additional operating modes, in which case the parameters can be for example overcurrent thresholds, overvoltage thresholds, fan switching frequencies, current rise and current fall limits and so forth. 
     Referring to  FIG. 3  for example in addition to the normal operating mode and the test operating mode at a frequency f=300 Hz of the PWM-control signal, an operating mode B 25-16  is set, in which case the overcurrent threshold is  25 A, the fan switching frequency is 16 kHz, the current rise is at a maximum 7 A/s and the current fall is at a maximum 20 A/s. In addition an operating mode B 32-20  is signaled by a frequency f=400 Hz of the PWM-control signal, in which case then the overcurrent threshold is  32 A, the fan switching frequency is 20 kHz, the current rise is at a maximum 10 A/s and the current fall is at a maximum 30 A/s. 
     Different operating modes or parameters can then also be transmitted by switching over between different frequencies of the PWM-signal. Thus for example after the expiry of a predetermined period of time (for example a second) another frequency (and thus another parameter set and thus another operating mode) could be signaled. It will be appreciated that, instead of establishing the frequency, it is also possible to apply the period duration of the PWM-control signal. 
     To reduce the tolerance in respect of frequency or period measurement it is also possible to use a reference frequency (or reference period). Thus for example a frequency f=500 Hz can be transmitted as a fixed frequency while all other frequencies can be established proportionally thereto. The time until all parameters are transmitted and the first parameter occurs again can also be predetermined as the reference. As a further practical example, various frequencies of the PWM-signal can also be signaled for signaling respective users or manufacturers and correspondingly predetermined required characteristics of the control system, in which case another frequency of the PWM-signal is associated with various users or manufacturers. 
       FIG. 4  shows a table of a further practical example in which a range-dependent linear control of the maximum current of the fan regulator  20  or the switching frequency of the fan regulator  20  can be signaled. As shown in  FIG. 4  in a frequency range of between f=50 Hz and f=150 Hz control is implemented linearly or successively from a maximum current I max =10 A to a maximum current of I max =30 A, while between a frequency f=170 Hz and a frequency f=250 Hz of the PWM-control signal a switching frequency of between 17 kHz and 25 kHz can be signaled. Thus continuous or successive current limitation to 10 A (at f=50 Hz) to 30 A at (f=150 Hz) and continuous or successive regulation of the switching frequency of the fan regulator  20  is accordingly possible. 
     It will be appreciated that any other links between the frequency of the PWM-control signal and predetermined parameters, operating modes or parameter sets can readily be envisaged and are comprehensible to the man skilled in the art. Thus different types of fan motors or ventilating blowers from the same or different manufacturers can also be signaled by different frequencies of the PWM-control signal. 
     The present invention is not limited to the fan motor control in accordance with the above-described embodiment but can be used for the most widely varying motor control and regulating situations in dependence on pulsed control signals in order thereby in addition to pulse width control also to permit a transmission of operating modes or parameter sets. The fan regulator  20  shown in  FIG. 1  can be separate from the fan motor  30  or can be integrated thereinto.