Method for checking the functions of a plurality of fans The present invention relates to a method for checking the func ^¬ tions of fans within an ensemble of a plurality of fans. Fur ^¬ ther, the present invention relates to an apparatus for control ^¬ ling and detecting the functions of fans within an ensemble of a plurality of fans. Moreover, the present invention relates to a domestic appliance with an ensemble of a plurality of fans. Ad ^¬ ditionally, the present invention relates to a computer program stored in a computer usable medium, comprising computer readable program means for causing a computer to perform a method for checking the functions of fans within an ensemble of a plurality of fans.

Fans for cooling and venting purposes are used in different types of appliances. For example, a cooking hob, a cooking oven and a hood may comprise one or more fans. In some cases, safety standards require the detection of faults on the fans. In par ^¬ ticular, a lock or disconnection of the fan may occur. It is desired that the detection of faults on the fans does not signifi ^¬ cantly disturb the operation of the fans. It is an object of the present invention to provide a method for checking the functions of fans within an ensemble of a plurality of fans, wherein the time of deactivating the fans is minimized.

The object is achieved by the method according to claim 1.

According to the present invention the method for checking the functions of fans within an ensemble of a plurality of fans, said method comprises the following steps:

starting a normal operation mode, detecting or evaluating a common fan monitoring signal depending on the speeds of the fans,

starting a dynamic fan checking routine, in which the fan monitoring signal is compared with a lock threshold value, if the fan monitoring signal is smaller than the lock threshold value, then the dynamic fan checking routine is finished and the normal operation mode is set forth, if the fan monitoring signal is bigger than the lock threshold value, then the dynamic fan checking routine is finished and a multiple-fan checking routine is started, and

consecutive fan tests corresponding with one single fan in each case are performed during the multiple-fan checking routine, wherein

during each fan test the corresponding fan is activated for a predetermined time period, while the other fans are deac ^¬ tivated during said time period,

during each fan test the fan monitoring signal is compared with the lock threshold value and a disconnecting threshold value,

if the fan monitoring signal is bigger than the lock threshold value, then the corresponding fan is locked and an error is detected, and

if the fan monitoring signal is smaller than the disconnecting threshold value, then the corresponding fan is disconnected and an error is detected.

The core of the present invention is the combination of the dy ^¬ namic fan checking routine and the subsequent possible multiple- fan checking routine. If no locked fan is detected during the dynamic fan checking routine, then the multiple-fan checking routine is not necessary. Preferably, the speed of each fan is controlled by a correspond ^¬ ing pulse-width modulation signal, while the fans are enabled and disabled by a common fan enabling signal.

For example, the predetermined time period for the fan test is between ten and twenty seconds, preferably thirteen seconds.

In particular, the fan monitoring signal bases on an analogue signal, preferably on a current signal amplitude of the fans, sampled and averaged by an analogue-digital converter system.

In this case, the samples of the analogue signal are taken dur ^¬ ing the last part of the predetermined time period of the fan test, in particular during the last third of the predetermined time period, preferably during the 9th to the 12th seconds of the time period of thirteen seconds.

For example, between 20 and 50 samples, preferably 30 samples, of the fan monitoring signal are taken within the last part of the predetermined time period of the fan test.

Further, the lock threshold value may be adapted or adaptable to the number of enabled and disabled fans during the dynamic fan checking routine.

Moreover, during the dynamic fan checking routine between 20 and 50 samples, preferably 30 samples, of the fan monitoring signal may be taken within a time period of between two seconds and five second, preferably three seconds.

Preferably, during the dynamic fan checking routine the speed of the fan is at its maximum value. In contrast, during the fan test, the speed of the fan may be between 40% and 80% of its maximum value, preferably 60% of its maximum value. In particular, the fan monitoring signal is represented by a bi ^¬ nary coded number, preferably by an eight-bit number.

For example, the multiple-fan checking routine is periodically activated after a predetermined time interval once an error has been detected, wherein said time interval is between three and five minutes, preferably four minutes.

Alternatively, the multiple-fan checking routine is immediately activated, if an error has been detected.

Further, the present invention relates to an apparatus for con ^¬ trolling and detecting the functions of fans within an ensemble of a plurality of fans, wherein the apparatus is provided for a method mentioned above.

Additionally, the present invention relates to a domestic appli ^¬ ance with an ensemble of a plurality of fans, wherein the domes ^¬ tic appliance comprises the apparatus for controlling and de ^¬ tecting the functions of fans and/or the domestic appliance is provided for the method mentioned above.

At last, the present invention relates to a computer program stored in a computer usable medium, comprising computer readable program means for causing a computer to perform the method de- scribed above.

Novel and inventive features of the present invention are set forth in the appended claims. The present invention will be described in further detail with reference to the drawing, in which

FIG 1 illustrates a schematic block diagram of an apparatus for controlling and detecting the functions of a plurality of fans according to a preferred embodiment of the present invention,

FIG 2 illustrates a schematic block diagram of a system for

controlling and detecting the functions of a plurality of fans according to the preferred embodiment of the present invention,

FIG 3 illustrates a schematic flow chart diagram of an algo ^¬ rithm for detecting the functions of a plurality of fans according to the preferred embodiment of the present in ^¬ vention,

FIG 4 illustrates a schematic flow chart diagram of a multiple- fan checking routine according to the preferred embodi ^¬ ment of the present invention, and

FIG 5 illustrates a schematic diagram of a fan monitoring sig ^¬ nal as function of the time t during the multiple-fan checking routine according to the preferred embodiment of the present invention.

FIG 1 illustrates a schematic block diagram of an apparatus for controlling and detecting the functions of a plurality of fans 12, 14 and 16 according to a preferred embodiment of the present invention. The apparatus includes a control unit 10, a driver and sensing device 20, a first fan driver 22, a second fan driver 24 and an Nth fan driver 26. The apparatus may be adapted for controlling and detecting the functions of two up to N fans 12, 14 and 16. The apparatus is connected to the fans 12, 14 and 16.

The first fan driver 22 is connected via a unidirectional line to a first fan 12. In a similar way, the second fan driver 24 is connected via a unidirectional line to a second fan 14. Moreo ^¬ ver, an Nth fan driver 26 is connected via a unidirectional line to an Nth fan 16. The control unit 10 is connected to the N fan drivers 22, 24 and 26 via separate unidirectional lines. Fur- ther, the control unit 10 is connected to the driver and sensing device 20 via a unidirectional line. Contrary, the driver and sensing device 20 is connected to the control unit 10 via an ^¬ other unidirectional line. At last, the driver and sensing de ^¬ vice 20 is connected to the N fan drivers 22, 24 and 26 via a common unidirectional line.

A first pulse-width modulation signal 32 is sent from the control unit 10 to the first fan driver 22. In a similar way, a second pulse-width modulation signal 34 is sent from the control unit 10 to the second fan driver 24. Moreover, an Nth pulse- width modulation signal is sent from the control unit 10 to the Nth fan driver 26. A fan enabling signal 28 is sent from the control unit 10 to the driver and sensing device 20. Further, said fan enabling signal 28 is sent from the driver and sensing device 20 to the fan drivers 22, 24 and 26. A fan monitoring signal 30 is sent from the driver and sensing device 20 to the control unit 10.

FIG 2 illustrates a schematic block diagram of a system for con- trolling and detecting the functions of the plurality of fans

12, 14 and 16 according to the preferred embodiment of the pre ^¬ sent invention. The system comprises an input-output device 38, a fan speed monitoring device 40 and a sensing and control sys ^¬ tem 42. The sensing and control system 42 includes an analogue- digital converter system 44 and a fan control system 46. In this example, the input-output device 38 is realized by hardware, while the sensing and control system 42 is realized by software. The analogue-digital converter system 44 includes an analogue- digital converter 48 and averaging means 50. The fan control system 46 includes a fan control unit 52 and a look-up table 54.

An analogue signal 56 is sent from the input-output device 38 to the analogue-digital converter 48. The analogue signal 56 corre- sponds with the speed of the fan 12, 14 or 16. The analogue-dig ^¬ ital converter 48 samples and converts the analogue signal 56 into a sampled digital signal 58. The averaging means 50 aver ^¬ ages the sampled digital signals 58 and generates a fan monitor ^¬ ing signal 60. The fan monitoring signal 60 is sent from the av- eraging means 50 of the analogue-digital converter system 44 to the fan control unit 52 of the fan control system 46.

The fan control unit 52 generates the pulse-width modulation signals 32, 34 and 36 and the fan enabling signal 28 on the ba- sis of the fan monitoring signal 60 from the averaging means 50 and one or more threshold values 64 provided by the look-up ta ^¬ ble 54.

The fan speed monitoring device 40 may send a speed request 62 to the fan control unit 52, so that the current speed of the fans 12, 14 and 16 is indicated by said fan speed monitoring de ^¬ vice 40.

FIG 3 illustrates a schematic flow chart diagram of an algorithm for detecting the functions of three fans 12, 14 and 16. The al ^¬ gorithm comprises an initial step 68 and a running mode 70. The running mode 70 includes the states of deactivated fans 72 and activated fans 74. The transition from the states of deactivated fans 72 to the states of activated fans 74 is performed, if the fan speed F_S is bigger than zero. In contrast, the transition from the states of activated fans 74 back to the states of deac ^¬ tivated fans 72 occurs, if the fan speed F_S is zero. Further, the state of activated fans 74 includes a normal operation mode 76, a dynamic fan checking routine 78 and a multiple-fan checking routine 80. In this example, the multiple-fan checking rou ^¬ tine 80 is a three-fan checking routine.

When the fans 12, 14 and 16 are activated, then the normal oper- ation mode 76 is obtained. When the number of samples N_S ex ^¬ ceeds a threshold value of samples THR_S sufficient for averag ^¬ ing the monitoring signal F, then the dynamic fan checking routine 78 is activated. If the fan monitoring signal F is smaller than a lock threshold value THR_L, then the algorithm changes from the dynamic fan checking routine 78 to the normal operation mode 76 again. However, if the fan monitoring signal F is bigger than the lock threshold value THR_L, then the algorithm changes from the dynamic fan checking routine 78 to the multiple-fan checking routine 80. If a fan timer signal FT exceeds a fourth fan timer threshold value THR3, then the algorithm changes from the multiple-fan checking routine 80 back to the dynamic fan checking routine 78.

There are two ways for entering the three-fan checking routine 80. The first way is a periodic activation of the three-fan checking routine 80, wherein the three-fan checking routine 80 is activated periodically once a fault has been detected. For example, every four minutes a reactivation attempt and a check of all fans 12, 14 and 16 is performed. The second way is a con- ditional activation of the three-fan checking routine 80, wherein the pulse-width modulation signals 32, 34 and 36 are fixed at 100%. If a fault is detected, then the three-fan check ^¬ ing routine 80 is immediately triggered. During the running mode 70 the three-fan checking routine 80 is possible, if at least one fan 12, 14 or 16 is locked. In this example, the three-fan checking routine 80 requires 41 seconds.

The dynamic fan check routine 78 is called periodically. In this example, the dynamic fan check routine 78 is called every 100 milliseconds. A predetermined number of sampled digital signals 58 from the analogue-digital converter are averaged. In this ex ^¬ ample, thirty sampled digital signals 58 are averaged, so that every three seconds a dynamic fan lock evaluation is performed.

During the dynamic fan check routine 78 the pulse-width modula ^¬ tion signals 32, 34 and 36 of the fans 12, 14 and 16 are con ^¬ stantly at 100%. There are conditions, in which a locked fan 12, 14 or 16 may be detected. If all fans 12, 14 and 16 are enabled, i.e. no fan 12, 14 or 16 is disabled by the three-fan checking routine 80, then a three-fan threshold value D3_THR is used to detect that at least one of the fans 12, 14 and 16 is locked. If at least one fan 12, 14 and/or 16 is disabled by the three-fan checking routine 80, then a two-fan threshold value D2_THR is used to detect that at least one of the fans 12, 14 and 16 is locked .

FIG 4 illustrates a schematic flow chart diagram of the multi ^¬ ple-fan checking routine 80 according to the preferred embodi- ment of the present invention. In this example, the multiple-fan checking routine is the three-fan checking routine 80. The three-fan checking routine 80 comprises an initial step 82, a first fan test 84, a second fan test 86, a third fan test 88 and a final step 90.

In the initial step 82 the initialization of all variables of the algorithm is executed. When the fan timer signal FT exceeds a first fan timer threshold value THRO, then the first fan test 84 is activated. In a similar way, when the fan timer signal FT exceeds a second fan timer threshold value THR1, the second fan test 86 is activated. Moreover, when the fan timer signal FT ex ^¬ ceeds a third fan timer threshold value THR2, then the third fan test 88 is activated. At last, when the fan timer signal FT ex- ceeds the fourth fan timer threshold value THR3, the final step 90 is activated.

During the first fan test 84 only the first fan 12 is enabled for a predetermined time. In this example, the first fan 12 is enabled for 13 seconds. Further, the fan speed is set at a pre ^¬ determined level, in this example at 60%. From the 9th to the 12th seconds the analogue signal 56 is sampled in order to sta ^¬ bilize the speed of the first fan 12. In a similar way, only the second fan 14 is enabled during the second fan test 86 for 13 seconds and the fan speed is set at 60%. From the 9th to the 12th seconds the analogue signal 56 is sampled in order to stabilize the speed of the second fan 14. In a uniform manner, only the third fan 14 is enabled during the third fan test 88 for 13 seconds and the fan speed is set at

60%. From the 9th to the 12th seconds the analogue signal 56 is sampled in order to stabilize the speed of the third fan 16.

In each fan test 84, 86 and 88, thirty samples of the analogue signal 56 are acquired from the 9th to the 12th seconds and av ^¬ eraged, so that the fan monitoring signal 60 is obtained. Then the fan monitoring signal 60 is compared with the lock threshold value THR_L and a disconnecting threshold value THR_D. If the fan monitoring signal 60 is above the lock threshold value THR_L, then the activated fan 12, 14 or 16 is locked. If the fan monitoring signal 60 is below the disconnecting threshold value THR_D, then the activated fan 12, 14 or 16 is disconnected . During the final step 90 the total number of locked and/or dis ^¬ connected fans 12, 14 and 16 is calculated. Each locked and/or disconnected fan 12, 14 and 16 is disabled until the next acti- vation of the three-fan check routine 80. For example, the next three-fan check routine 80 is activated after four minutes. At last, the final step finishes the three-fan checking routine 80.

FIG 5 illustrates a schematic diagram of the fan monitoring sig- nal F as function of the time t during the multiple-fan checking routine 80 according to the preferred embodiment of the present invention. In this example, the multiple-fan checking routine is the three-fan checking routine 80.

The fan monitoring signal F is represented as an eight-bit value. The disconnecting threshold value THR_D is 30. The lock threshold value THR_L is 168. During a first phase 92 of about thirteen seconds the fan monitoring signal F has a value of about 100, wherein the fan monitoring signal F is between the disconnecting threshold value THR_D and the lock threshold value THR_L . During a second phase 94 of about further thirteen seconds the fan monitoring signal F has a value of slightly more than zero, wherein the fan monitoring signal F is smaller than the disconnecting threshold value THR_D. During a third phase 96 of about further thirteen seconds the fan monitoring signal F has a value of about 220, wherein the fan monitoring signal F is bigger than the lock threshold value THR_L .

During the first phase 92 the first fan 12 is running normally. The fan monitoring signal F during the second phase 94 indicates that the second fan 14 is disconnected. The fan monitoring sig ^¬ nal F during the third phase 96 indicates that the third fan 16 is locked. As result the second fan 14 and the third fan 16 are disabled. The multiple-fan checking routine 80 causes a delay of about 240 seconds.

The algorithm of the present invention has the advantage that the multiple-fan checking routine 80 is not necessary, if during the dynamic fan checking routine 78 the fan monitoring signal F is smaller than the lock threshold value THR_L . In this example, the maximum time for deactivating the locked fan 12, 14 and/or 16 is about 41 seconds. This results in a low heating of the windings of the fan 12, 14 and/or 16. The algorithm of the pre ^¬ sent invention is suitable for two up to N fans.

Although an illustrative embodiment of the present invention has been described herein with reference to the accompanying draw- ing, it is to be understood that the present invention is not limited to that precise embodiment, and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the in ^¬ vention. All such changes and modifications are intended to be included within the scope of the invention as defined by the ap ^¬ pended claims.

List of reference numerals

10 control unit

12 first fan

14 second fan

16 Nth fan

20 driver and sensing device

22 first fan driver

24 second fan driver

26 Nth fan driver

28 fan enabling signal

30 fan monitoring signal

32 first pulse-width modulation signal

34 second pulse-width modulation signal

36 Nth pulse-width modulation signal

38 input-output device

40 fan speed monitoring device

42 sensing and control system

44 analogue-digital converter system

46 fan control system

48 analogue-digital converter

50 averaging means

52 fan control unit

54 look-up table

56 analogue signal

58 sampled digital signal

60 fan monitoring signal

62 speed request

64 threshold value

68 initial step

70 running mode

72 state of deactivated fans

74 state of activated fans

76 normal operation mode 78 dynamic fan checking routine

8 0 multiple-fan checking routine, three-fan checking routine

82 initial step

8 4 first fan test

86 second fan test

8 8 third fan test

9 0 final step

92 first phase

9 4 second phase

96 third phase

F fan monitoring signal

FT fan timer signal

F_S fan speed

THRO first fan timer threshold value

THR1 second fan timer threshold value

THR2 third fan timer threshold value

THR3 fourth fan timer threshold value

D2_THR two-fan threshold value

D3_THR three-fan threshold value

N_S number of samples

THR_S threshold value of samples

THR_L lock threshold value

THR_D disconnecting threshold value

time