Patent Publication Number: US-6661195-B1

Title: Starting motor for an internal combustion engine, having a safety device

Description:
BACKGROUND INFORMATION 
     It is known to ascertain the thermal loading of the starting motor (abbreviated as starter) by measuring the armature current or the temperature of the carbon brushes, using appropriate sensors. However, the known devices have the disadvantage of being relatively costly, since additional sensors are needed. For example, an appropriate temperature sensor is needed to measure temperature, the sensor having to be in proximity to the carbon brushes, in order that it can essentially detect their temperature. The known methods for measuring current also require a measuring element, e.g. a shunt in the measuring line or, in the case of a contactless measurement, e.g. a Hall sensor. Both methods exact costs for the sensors, wiring, as well as their installation, and are an additional risk to the reliability of the starting motor. Furthermore, a circuit arrangement for electric starting motors is known from German Patent No. 2700982, which evaluates the time-related current variations or voltage variations of the current supplied to the starting motor. If the variation over time falls below a predefined threshold value, this is interpreted as sustained operation of the internal combustion engine, and the starting motor switches off, since the voltage variations are smaller during sustained engine operation than during starting. 
     SUMMARY OF THE INVENTION 
     The starting motor of the present invention has the advantage of the installation not requiring additional hardware such as sensors, wiring, possibility for control, etc., since these functions can be implemented by the components already present in the control circuit. It is considered to be especially advantageous that, from the measurement of the voltage ripple, e.g. by simulation or empirical measurement, one can easily derive local temperature peaks, e.g. at the carbon brushes, or derive the load of the starting motor. In certain operational situations, such as “cranking” for a long time after a cold winter night, or running by means of the starter, without the support of the motor, while a ship is being loaded (because the tank is empty), the starter can experience overloading which would result in it being damaged or destroyed. This is advantageously prevented by the subject matter of the present invention. 
     It is particularly advantageous that the induction flux to the internal combustion engine is immediately interrupted by switching off the primary current, and therefore, the starting motor cannot be heated any further. The starting motor can then only be used again after it cools off, in order to prevent it from being damaged. 
     It is also favorable that the armature current of the starting motor can be ascertained indirectly from the data already existing for a corresponding reference starter. It is often necessary to determine the armature current, since the temperature of the starting motor carbon brushes can be ascertained, using this value. A high armature current results in a correspondingly high temperature, due to the heating of the starting motor, as well as the heating of the sparking brush, while the temperature is lower at a lower armature current. 
     A further advantage is that, for purposes of control, the measured voltage-ripple values can be read off at a corresponding output. For purposes of servicing, this simplifies the discovery of a possible error source. Errors can then be read out during the next maintenance inspection of a motor vehicle. 
     Since the control circuit is normally equipped with a small microcomputer chip, the existing control circuit can be advantageously expanded, using a corresponding, supplementary software program as a control program for the starting motor. The improvement of the control-circuit reliability is also particularly advantageous, since the unneeded components mean that no risk of error can arise. Furthermore, every type of starting motor can easily be accommodated by a simple modification of the control program. 
     It is also regarded as an advantage that the limiting load for the starting motor can be appropriately adjusted by taking the ambient temperature into account. For example, the limiting value can be correspondingly reduced at a high ambient temperature since, in this case, it is possible for damage to occur earlier. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a block diagram as an overall view, according to the present invention. 
     FIG. 2 indicates a flow chart, according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     The block diagram of FIG. 1 shows a starting motor  1  having a gear box  9 , whose power take-off shaft, which is not shown, is arranged through a pinion  3  in such a manner that pinion  3  meshes with the teeth of a gear rim  4  during the starting phase of internal combustion engine  6 , and thus, sets the crankshaft of internal combustion engine  6  into the intended angular motion. Attached to starting motor  1  is an electrically operated meshing relay  2 , by means of which the closed linkage between starting motor  1  and internal combustion engine  6  is ensured during the starting operation. Meshing relay  2  is electrically connected, via its control input, to the output of a control circuit  5  (ESC), to which a control output of a motor control unit  8  is connected. A comparator  10  and a measurement input are connected to further inputs of control circuit  5 ; the measurement input being wired, via terminal  30  of the starter circuit, between a battery  7  and a terminal on meshing relay  2 . In addition, control circuit  5  is connected to an error storage means  19 , as well as to a safety device  20 . It also follows from FIG. 1 that all of the mentioned devices are connected to the negative pole of the battery. 
     The alternative of installing individual devices  10 ,  19 ,  20  in a housing, together with control circuit  5 , is provided. 
     The method of functioning of control circuit  5 , along with safety device  20 , is now explained in detail, referring to FIG.  2 . It must be pointed out in advance that control circuit  5  normally includes elements already, which control meshing relay  2  prior to the starting of starting motor  1 , in such a manner that pinion  3  is first slid into gear rim  4  before the angular motion begins. After the pinion of starting motor  1  meshes with gear rim  4  of internal combustion engine  6 , the meshing relay therefore switches on the starter current, so that the starting motor starts and drives the crankshaft of the internal combustion engine by means of mentioned pinion  3  and gear rim  4 . Because of the friction and the compression of the pistons in the individual cylinders, internal combustion engine  6  generates a braking torque at gear rim  4 , which is not constant, but largely periodic. Starter current I (primary current of the starter) is a function of the torque to be applied. Because the periodic moment causes starting motor  1  to draw a periodic current from battery  7 , periodic voltage dips occur at terminal  30 , which are measured by control circuit  5 , in that, e.g. an analog-digital converter (AD converter) digitizes the voltage at terminal  30 , and supplies it to a computer chip in control circuit  5 . The program, which is used to control the computer chip in control circuit  5 , and whose purpose is to control meshing relay  2  or the entire starting operation, is already well-known, and must therefore not be explained in further detail. It is regarded as novel and inventive that control circuit  5  includes an additional program routine, by which the voltage ripple simultaneously measured at terminal  30  is subsequently processed to the effect that the period duration and the ripple frequency are calculated as a function of the starter type and combined with the voltage values, to obtain the current flow through the starting motor. Then, the heating at various points in the starting motor, especially at the carbon brushes, is calculated therefrom. For example, the calculation parameters for the warming of starting motor  1  or its carbon brushes are derived from empirical comparison measurements, which were previously acquired at a reference starter. This calculated value is supplied to safety device  20 , which compares this value to a corresponding value of a comparator  10 . If this limiting value is exceeded or undershot, the starter current for starting motor  1  is preferably limited or switched off. 
     This operation is explained again in principle in the flow chart of FIG. 2, in which the further program routine is set up. 
     As already mentioned above, the battery-voltage ripple is measured at terminal  30 , by an AD converter  19 . In position  12 , control circuit  5  forms a differential value from the average value of the last converter values, this differential value being subtracted from the current converter value. In position  13 , the time between the zero crossings is measured, and in position  14 , the starter rotational speed is calculated therefrom. Taking into consideration the type of starting motor  1 , starter current I is calculated (position  15 ) from the digitized voltage value of AD converter  19 , and from the starter rotational speed. Taking the ambient temperature into account, the heating of starting motor  1  is then calculated in position  16 , from the existing data, by comparing them to the values stored for the separate temperatures. In position  17 , the starting operation is interrupted by safety device  20 , e.g. in response to the allowable limit temperature being exceeded, in order to protect starting motor  1  from possible damage. 
     Of course, other known methods for measuring the voltage ripple can also be used in place of the AD converter. 
     Furthermore, it must be pointed out that the control circuit has an error storage means  19 , in which the error messages of the safety device are stored after the predefined limit value is exceeded. For example, these error messages are saved in the long term, along with the date, time, temperature, etc. of starting motor  1 , until the next service check, at which time this error message can be read out and, if necessary, the cause can be investigated.