Patent Publication Number: US-2004046517-A1

Title: Electric system of a vehicle

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates to an electric system of a vehicle, and more particularly, to an electric system of a vehicle for utilizing a voltage higher than the conventional 14V, and for determining rotational speed of a motor of the vehicle.  
       BACKGROUND OF THE INVENTION  
       [0002] Recently, the number of electric components consuming electric power in vehicles has been increasing and, accordingly, strategies for supplying stable and sufficient electric power for such components are being considered. For example, raising the voltage used for such electric components has been proposed. However, to raise the voltage level of an electric vehicle, the electric systems used by the vehicle must also be modified.  
       [0003] A motor for an electric generator usually includes a stator and rotor. The stator and rotor, collectively referred to herein as a motor-generator unit, can be combined to selectively function as an electric generator when the motor-generator unit is being mechanically driven, or as a motor when being electrically driven, as is well-known in the art. A motor-generator unit functions more efficiently when the applied voltage is higher.  
       [0004] The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention, and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.  
       SUMMARY OF THE INVENTION  
       [0005] In a preferred embodiment, an electric system of a vehicle having an engine and a transmission includes: a battery unit, a motor-generator unit, and a control unit. The battery unit is of a voltage higher than 14V. The motor-generator unit, disposed between the engine and the transmission, is for selectively functioning as a motor for driving the engine, and as an electric generator driven by the engine. The control unit is for recharging the battery unit by controlling output electric power of the motor-generator unit, and for driving the motor-generator unit with electric power of the battery unit.  
       [0006] In another preferred embodiment, the battery unit further comprises a plurality of battery units, including at least one low-voltage battery unit and at least one high voltage battery unit. Low-voltage electric components of the vehicle receive power substantially from the at least one low-voltage battery unit, and high-voltage electric components of the vehicle receive power substantially from the at least one high-voltage battery unit.  
       [0007] In a further preferred embodiment of the present invention, the motor-generator unit includes: a stator fixed to the engine body, and a rotor fixed to at least one of a crankshaft of the engine and an input rotating element of the transmission. Preferably, the transmission is an automatic transmission equipped with a torque converter, and the input rotating element of the transmission is the torque converter.  
       [0008] In another further preferred embodiment of the present invention, the electric system of a vehicle further includes: a toothed wheel having a plurality of teeth and rotating with the rotor; and a magnetic sensor, fixed at a stationary portion of at least one of the engine and the transmission, for generating pulse signals corresponding to rotation of the toothed wheel. The control unit calculates rotation speed of the rotor based on signals from the magnetic sensor. Preferably, the plurality of teeth are formed on an exterior circumference of the toothed wheel, and the magnetic sensor is disposed to the exterior of the plurality of teeth with a predetermined gap therebetween. Also, preferably, the transmission is an automatic transmission equipped with a torque converter, and the toothed wheel preferably is disposed at a side of the torque converter toward the motor-generator unit. Additionally, preferably, the plurality of teeth preferably are configured in a resolution of approximately 3 degrees, and the distance between adjacent teeth of the plurality of teeth is preferably approximately 14 mm.  
       [0009] The control unit of a preferred embodiment of the present invention calculates a rotation speed of the motor-generator unit by counting a number of pulses sequentially received from the magnetic sensor for a predetermined period, and by subsequently calculating a rotation speed of the motor-generator unit based at least in part on a value obtained by dividing the number of the received pulses by the predetermined period.  
       [0010] In yet another preferred embodiment of the present invention, a method for determining the rotational speed of a motor in a vehicle is presented. The method includes driving a motor that rotates a rotor, the rotor including a toothed wheel having a plurality of teeth; generating pulses by magnetically sensing rotation of the plurality of teeth of the toothed wheel with a magnetic sensor, the magnetic sensor being fixed at a stationary portion of at least one the engine and a transmission; and calculating rotational speed of the motor, in a control unit, based at least part on the pulses from the magnetic sensor.  
       [0011] Preferably, the step of calculating rotational speed of the motor further comprises: counting a number of pulses sequentially received from the magnetic sensor for a predetermined period; and calculating a rotation speed of the motor based at least in part on a value obtained by dividing the number of the received pulses by the predetermined period.  
       [0012] Also, preferably, the transmission is an automatic transmission equipped with a torque converter, and the toothed wheel is disposed at a side of the torque converter toward the motor. In addition, the plurality of teeth preferably are configured in a resolution of approximately 3 degrees. The distance between adjacent teeth of said plurality of teeth is preferably approximately 14 mm. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0013] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of the invention:  
     [0014]FIG. 1 is a schematic diagram of an electric system of a vehicle according to a preferred embodiment of the present invention;  
     [0015]FIG. 2 is an enlarged perspective view of portion A in FIG. 1; and  
     [0016]FIG. 3 is a flowchart showing a method for calculating rotation speed of a motor-generator unit according to a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0017] A preferred embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings.  
     [0018] As shown in FIG. 1, the electric system includes a battery unit  170 , a motor-generator unit  120 , and a control unit  160 . The battery unit  170  has a voltage higher than 14V. The motor-generator unit  120 , disposed between an engine  110  and a transmission  140 , is for selectively functioning as a motor for driving the engine  110 , and as an electric generator driven by the engine  110 . The control unit  160  is for recharging the battery unit  170  by controlling output electric power of the motor-generator unit  120 , and for driving the motor-generator unit  120  by electric power of the battery unit  170 .  
     [0019] Note that the transmission  140  can be a manual transmission or an automatic transmission equipped with a torque converter. However, preferably, the transmission  140  is hereinafter described as an automatic transmission equipped with a torque converter  142 . The torque converter  142  is connected to a transmission input shaft  146  protruding from a transmission body  144  of the transmission  140 .  
     [0020] For purposes of the description below, the expression “motor-generator unit” is hereinafter abbreviated as “IGS” (Integrated Generator and Starter). The word “Starter” abbreviated in “IGS” is adopted to note that the IGS  120  can function as a starter of the engine  110 , but it should be understood that the scope of the motor-generator unit  120  is not limited to this embodiment.  
     [0021] More specifically, the IGS  120  includes a stator  122  and a rotor  124 . The stator  122  is fixed to an engine body  112 , and the rotor  124  is fixed to both a crankshaft  114  of the engine  110 , and to an input rotating element, i.e., the torque converter  142  of the transmission  140 . For example, as shown in FIG. 1, the rotor  124  is fixed to the crankshaft  114  on the left, and fixed to the torque converter  142  on the right by fixing members  128 .  
     [0022] The battery unit  170  connected to the control unit  160  includes a 12V battery  174  connected to the control unit  160 , and to an additional 36V battery  172 , through a DC-DC converter  165 . As described above, batteries of different voltages are separately included in the preferred embodiment of the present invention. Electric components  184  with small electric loads, for example, a radio and/or turn signals, are connected to the 12V battery  174 . Components  182  with high electric loads are connected to the 36V battery  172 . The high electric load components may include a compressor in an air conditioning system and/or a water pump of the engine  110 , which are normally belt-driven, but can be changed to be electrically-driven.  
     [0023] The control unit  160  can be implemented as one or more processors activated by predetermined software, and the predetermined software can be programmed by a person of ordinary skill in the art to perform each step performed by the control unit  160  as described herein. The control unit  160  may also contain other necessary hardware and software components, as will be understood by persons skilled in the art, to permit the control unit to communicate with sensors and to execute the control function as described herein.  
     [0024] The control unit  160  starts the engine  110  by controlling the IGS  120  as a motor using electric power supplied from the batteries  172  and  174 . When the engine  110  is running, the control unit  160  controls the IGS  120  as an electric generator, such that the batteries  172  and  174  are recharged by electric power generated by the IGS  120 .  
     [0025] Additionally, the electric system of a vehicle according to a preferred embodiment of the present invention further includes a sensor unit  130  for detecting a rotation speed of the rotor  124 . The sensor unit  130  includes: a toothed wheel  134  having a plurality of teeth  210  (shown in further detail in FIG. 2) and rotating with the rotor  124 ; and a magnetic sensor  132 , fixed at a stationary portion of the engine  110  and/or the transmission  140 , for generating pulse signals corresponding to rotation of the toothed wheel  134 .  
     [0026] The control unit  160  calculates rotation speed of the rotor  124  based on signals received from the magnetic sensor  132 . The rotation speed of the rotor  124  can be used for controlling the engine  110  and/or the IGS  120 . For example, the rotation speed can be used as a parameter for controlling electric power generation of the IGS  120 , and can be used as a precise measurement of engine speed, i.e., rotation speed of the crankshaft  114 , because the rotor  124  is fixed thereto.  
     [0027] Referring now to FIG. 2, which is an enlarged perspective view of portion A of FIG. 1, mechanical features of the toothed wheel  134  and the magnetic sensor  132  are illustrated. The plurality of teeth  210  are formed on an exterior circumference of the toothed wheel  134 , and the toothed wheel  134  is disposed at a distal end of a side of the torque converter  142 , toward the IGS  120 .  
     [0028] The magnetic sensor  132 , which generates electric signals from magnetic interaction with the teeth  210 , is fixed in a transmission housing  220  as an example of the stationary portion of the engine  110  and/or the transmission  140 . The magnetic sensor  132  is disposed toward an exterior of the plurality of teeth  210 , with a predetermined gap therebetween.  
     [0029] Specifications of the teeth  210 , such as teeth distance, are implementation details that may be determined by a person skilled in the art. As an example, when the diameter of the torque converter  142  is about 27 cm, forming more than 120 teeth on the exterior circumference of the torque converter  142  is found to result in substantial noise in pulses generated at the magnetic sensor  132 . Therefore, it is preferable that the plurality of teeth  210  are configured in a resolution of about 3 degrees and, more specifically, that the distance between adjacent teeth of the plurality of teeth  210  is about 14 mm.  
     [0030] Referring to FIG. 3, to calculate rotation speed of the IGS  120 , according to a preferred embodiment of the present invention, the control unit  160  receives pulses sequentially from the magnetic sensor  132  for a predetermined period (S 310 ), and then counts the number of the received pulses (S 320 ). Subsequently, the control unit  160  calculates the rotation speed of the IGS  120  on the basis of a value obtained by dividing the number of the received pulses by the predetermined period (S 330 ). In a preferred embodiment, the value obtained at step S 330  is in “pulses per second” units, but this value can be converted to a variety of units of rotational speed.  
     [0031] The above-explained method for calculating rotation speed of the IGS  120  is programmed and implemented in the control unit  160 .  
     [0032] According to a preferred embodiment of the present invention, the mechanism for starting an engine and generating electricity is simplified over the prior art where a starter motor and an electric generator are separately equipped. Furthermore, rotation speed of the motor-generator unit (i.e., the engine speed) can be precisely determined, which enables precise control of the engine and the motor-generator unit.  
     [0033] While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Throughout this specification and the claims which follow, unless explicitly described to the contrary, the word “comprise” or variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.