Abstract:
A method and apparatus for detecting slippage of a coolant pump drive belt on an internal combustion engine having a generator driven by the belt. The method comprises monitoring electrical output of the generator and determining that coolant belt slippage has occurred when the electrical output is reduced below a normal electrical output level.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to auxiliary power units and, in particular, to apparatuses and methods for detecting slippage of coolant belts thereof.  
         [0002]     This invention relates to auxiliary power units and, in particular, to apparatuses and methods for detecting slippage of coolant belts thereof.  
         [0003]     Auxiliary power units are used for various purposes and may be installed, for example, on diesel-engined vehicles to maintain certain functions when the main engine is off. These units include a smaller internal combustion engine, usually diesel-fueled, and an alternator or some other type of electrical generator to power such things as the air-conditioning system.  
         [0004]     Various safety and diagnostic systems are incorporated into such an auxiliary power unit to monitor its operation and, in some cases, to shut down the auxiliary power unit when certain contingencies arise. These auxiliary power units may include a coolant pump and an alternator or other type of generator, both conventionally being driven by a common drive belt, usually a V-belt. If the V-belt slips or breaks, the coolant pump no longer operates and the engine is subject to overheating and potential damage to the engine. As a result it is common to incorporate a safety device which shuts down the engine in the event that the belt breaks.  
         [0005]     One way of detecting belt slippage or breakage in the prior art is to incorporate a temperature sensor in the coolant system of the engine. If the coolant pump stops, then, in theory, the temperature of the coolant increases. The temperature sensor senses this increase in temperature and shuts down operation of the engine. However, in actual fact, an air pocket often forms adjacent to the temperature sensor when the coolant pump stops and this air pocket prevents the temperature sensor from accurately measuring the temperature of the coolant. As a result, the belt potentially can slip or break and yet the engine will not be disabled because the temperature sensor does not sense the resulting temperature rise in the coolant.  
         [0006]     U.S. Pat. No. 2,809,224 discloses an arrangement where electric current for the ignition system of an engine is supplied solely by the generator (and not the battery) after the engine has started. Fan belt breakage accordingly causes the engine to stop and prevents overheating. The voltage however is not actually monitored and apparently the engine would only stop if the belt actually breaks or slips a very significant amount. Thus it provides no early warning of the problem and results in abrupt shutting off of the engine.  
         [0007]     U.S. Pat. No. 3,877,003 discloses a system for detecting fan belt slippage which may result in overheating. This is done by comparing the rotation of a member rotated by the fan belt with the rotation of the engine shaft. However the device is relatively complicated.  
         [0008]     Various other patents do not specifically discuss cooling system alarms or monitoring as an objective, but deal with an analysis of power output from an alternator or generator to diagnose drive belt slippage. U.S. Pat. No. 6,029,512, for example, detects the speed of the alternator from the frequency of the ripple in the output voltage.  
         [0009]     Japanese Patent JP 54160908 uses a counter to detect slip rate and provides a warning lamp to indicate an alarm to recognize slip of the belt.  
         [0010]     Japanese Patent JP 60151445 uses a pulse signal and the ratio of alternator rotational speed to engine speed to detect slip. A charge lamp indicates abnormality.  
       SUMMARY OF THE INVENTION  
       [0011]     According to a first aspect of the invention, there is provided a method for detecting slippage of a coolant pump drive belt on an internal combustion engine having a generator driven by said belt. The method comprises monitoring electrical output of the generator and determining that coolant belt slippage has occurred when the electrical output is reduced below a normal electrical output level.  
         [0012]     According to a second aspect of the invention, there is provided an auxiliary power unit having an internal combustion engine with a coolant pump, a generator and a drive belt operatively engaging the coolant pump and the generator. A coolant belt slip detector comprises an electrical output monitor coupled to the generator, reduced electrical output indicating coolant belt slippage.  
         [0013]     According to a third aspect of the invention, there is provided a power unit having an internal combustion engine with means for disabling the engine. There is an alternator, the alternator including means for providing a first signal when the alternator output is below a specified level. A drive belt operatively connects the alternator to the engine. A controller is connected to the alternator for receiving the first signal and providing a second signal to the means for disabling the engine, whereby the engine is disabled when the alternator output is below the specified level.  
         [0014]     According to a fourth aspect of the invention, there is provided a method of disabling an engine having an alternator operatively coupled to the engine by a drive belt, when slippage of the drive belt or breakage of the drive belt occurs. The method comprises providing a first signal from the alternator to a controller when output of the alternator is below a specified level and providing a second signal from the controller to a means for disabling the engine when the controller receives the first signal from the alternator, thereby disabling the engine.  
         [0015]     The invention offers significant advantages compared to prior art. Early detection of belt slippage is possible by monitoring the output of the alternator and thus the engine of the auxiliary power unit can be stopped before damage has occurred due to overheating. In addition, the method and apparatus require the addition of few components to a conventional auxiliary power unit, thus resulting in a relatively inexpensive safety feature. Moreover, compared to prior art systems using coolant temperature sensors, air or gas pockets in the coolant system do not adversely affect operation of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0016]     Referring to the drawing:  
         [0017]      FIG. 1  is a simplified, partly diagrammatic view of an auxiliary power unit incorporating a coolant belt slippage detection system according to an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]     Referring to the drawing, this shows an auxiliary power unit  10  which is generally conventional and includes an internal combustion engine  12 , a diesel engine in this particular example. The engine has a sheave  14  mounted on the crankshaft  13  of the engine in the conventional manner. A continuous drive belt  16 , a V-belt in this example, extends about the sheave  14  as well as sheave  20  on alternator  22  and sheave  24  on coolant pump  26 . These components are conventional and thus are not described in more detail.  
         [0019]     There is an APU controller  30  connected to the output of the alternator  22  by conductors  32  and  34 . The alternator is a conventional type and includes a regulator  40 , a three-phase armature winding  42  and a field winding  44 . There is an NPN transistor Q 1  with a base connected to the regulator, an emitter connected to ground and a collector connected to the conductor  34 . Alternatively, in other embodiments of the invention, Q 1  can be a PNP transistor, an n-channel MOSFET or a p-channel MOSFET transistor. The transistor operates as a switch and, in conventional installations, turns on a “check engine” light on the dashboard of a vehicle to indicate that alternator output is below a specified level and the battery is not being charged. This could indicate that the alternator is not functioning properly or that the belt  16  has broken. However the light also typically comes on when the engine is starting. Thus conventionally the power supplied to the light would not indicate necessarily that the belt has broken or slipped and could not be used to disable the engine since this could prevent the engine from starting. The invention utilizes the signal provided by transistor Q 1  to indicate that the belt has broken or is slipping, but ignores the signal when the engine is starting since that would not indicate a problem with the belt.  
         [0020]     Specifically, microcontroller  50  of the APU controller provides signals to operate two switches S 1  and S 2 . In normal operation switch S 2  is closed and battery voltage V BATT  is supplied to fuel solenoid  52  of engine  12  so the engine is supplied with fuel. At the same time, switch S 1  is closed and the alternator supplies current for the battery. Alternator feedback ALT_FB provides a high signal via conductor  34  during normal operation.  
         [0021]     If the belt  16  breaks or slips, the base of transistor Q 1  receives power from the regulator  40  and turns on, changing ALT_FB to a low state which is sensed by the microcontroller  50  which opens switch S 2 , thereby shutting off power to the fuel solenoid  52 , thereby shutting off fuel to the engine and causing the engine to shut down. It should be understood that the invention is applicable to other means for shutting down the engine such as an ignition cut off.  
         [0022]     During the engine starting sequence, the microcontroller  50  first closes switch S 1 , providing power to the regulator  40  which provides power to the base of transistor Q 1  because the regulator does not receive power from the alternator windings. Transistor Q 1  turns on, changing ALT FB to a low state. However, the microcontroller  50 , sensing that this is the starting sequence, ignores the ALT_FB signal.  
         [0023]     When the engine starts, the alternator starts producing power, the transistor Q 1  turns off and ALT_FB goes to a high state. This indicates to microcontroller  50  that the engine has started successfully. Thereafter, if Q 1  turns on and, ALT_FB goes low, the engine shuts down if ALT_FB stays low for a predetermined period of time, five seconds in this example. That is taken as an indication that the belt  16  has broken, the belt slipping or that the alternator is faulty. In any of these cases the engine  12  is shut down by cutting off the fuel supply via solenoid  52 .  
         [0024]     It will be understood by someone skilled in the art that many of the details provided above are by way of example only and are not intended to limit the scope of the invention which is to be determined with reference to the following claims.