Abstract:
A hybrid vehicle includes a reciprocating internal combustion engine having intake and exhaust poppet valves which are controlled so as to minimize the amount of power required to motor the engine during regenerative braking, so as to maximize energy stored within an energy storage device recharged by a rotating reversible machine operatively connected with the engine, the vehicle&#39;s road wheels, and the energy storage device.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a hybrid vehicle having an internal combustion engine, a rotating reversible machine coupled to the engine for selectively providing both power to road wheels and regenerative braking capability enhanced by operating the engine cylinder valves so as to minimize the motoring horsepower of the engine during regenerative braking. 
         [0003]    2. Disclosure Information 
         [0004]    Hybrid vehicles have taken many forms. A common form of the so-called “mild” hybrid includes an internal combustion engine driving road wheels through a transmission. With a mild hybrid, a rotating reversible machine, such as an electric motor/generator or hydraulic pump/motor, is coupled to the engine for rotation with the engine&#39;s crankshaft. Accordingly, the reversible machine rotates whenever the engine is rotating. Because the engine rotates in synchronicity with the reversible machine, regenerative braking of the vehicle requires not only that the rotating machine be motored by the vehicle road wheels, but also that the engine be motored by the road wheels during regenerative braking. This is an undesirable situation from the standpoint of maximizing regenerative capability, because the power absorbed by the engine cannot be captured regeneratively. 
         [0005]    It would be desirable to minimize the motoring horsepower of an engine in a hybrid vehicle in which the engine and rotating machine are coupled together, so as to maximize regenerative battery, or hydraulic accumulator, charging capability of the vehicle. 
       SUMMARY OF THE INVENTION 
       [0006]    According to an aspect of the present invention, a hybrid vehicle includes a reciprocating internal combustion engine having a crankshaft and a plurality of power cylinders, with each cylinder having a piston reciprocably housed therein. At least one intake poppet valve and at least one exhaust poppet valve services each engine cylinder. A transmission is coupled to the engine. The transmission is connected to at least one road wheel. A rotating reversible machine, operatively connected with the engine, the transmission, and with an energy storage device such as a traction battery, provides power to the transmission and regeneratively charges the traction battery or other storage device during braking of the vehicle. An engine controller disables at least some of the power cylinders during regenerative braking of the vehicle, by operating at least some of the poppet valves such that the valves open and close at points which are approximately symmetrical about rotational positions of the crankshaft at which the directions of motion of the pistons change. 
         [0007]    According to another aspect of the present invention, a hybrid vehicle may include a number of intake port throttles, with one of the throttles being mounted in proximity to each of the intake valves, with the engine controller closing the port throttles of the cylinders being disabled. 
         [0008]    According to another aspect of the present invention, an engine controller operates not only exhaust valves, but also intake valves of the cylinders being disabled, such that both the intake valves and the exhaust valves open and close at points which are symmetrical about rotational positions of the crankshaft at which directions of motion of each of the pistons change. 
         [0009]    According to another aspect of the present invention, the present poppet valves are operated by a camshaft, with the engine controller further including a cam phaser for powering the camshaft and for adjusting the rotational position of the camshaft with respect to the engine&#39;s crankshaft. Multiple camshafts and cam phasers may be used for intake and exhaust valves. 
         [0010]    According to another aspect of the present invention, a rotating electrical machine of the present invention is coupled to the vehicle&#39;s transmission through the engine at a fixed gear ratio. 
         [0011]    According to another aspect of the present invention, a method for operating a reciprocating internal combustion engine in a hybrid vehicle during regenerative braking of the vehicle includes operating a rotating reversible machine, such as an electrical or fluid power machine, coupled to the engine and to at least one road wheel through a transmission, as a power absorber, and operating intake and exhaust poppet valves associated with the power cylinders of the engine such that all said valves open and close at points which are approximately symmetrical about rotational positions of the engine&#39;s crankshaft at which the directions of motion of the engine&#39;s pistons change, whereby the power required to motor the engine during regenerative braking will be minimized. 
         [0012]    According to another aspect of the present invention, a method for motoring a reciprocating internal combustion engine in a hybrid vehicle during regenerative braking, such that power required to motor the engine is reduced and regenerative charging of the traction battery is maximized, includes operating a rotating reversible machine, coupled to at least one road wheel and to the engine, as a generator connected to a storage battery or other energy storage device, while operating intake and exhaust poppet valves associated with the power cylinders of the engine such that the valves open and close at points which are approximately symmetrical about rotational positions of the engine&#39;s crankshaft at which the directions of motion of the engine&#39;s pistons change. 
         [0013]    It is an advantage of a method and system according to the present invention that regenerative capability may be improved for a hybrid vehicle in which the engine and generator/motor are locked together rotationally. 
         [0014]    It is yet another advantage of a method and system according to the present invention that increased fuel economy associated with regeneration may be achieved without the need for cylinder valve actuation hardware capable of completely deactivating valves in one or more cylinders of the engine. This advantage results from the present invention because deactivation may be achieved either through a combination of intake port throttling and exhaust valve timing adjustment, or by adjusting the timing of both the intake and exhaust valves. Neither technique requires that the valves be prevented from moving periodically. 
         [0015]    Other advantages, as well as features of the present invention, will become apparent to the reader of this specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a schematic representation of a hybrid vehicle according to various aspects of the present invention. 
           [0017]      FIG. 2  is a schematic representation of a portion of an internal combustion engine used in the vehicle of  FIG. 1 . 
           [0018]      FIG. 3  is a diagram showing cylinder pressure and crankshaft position with an engine having a cylinder valve control system according to the present invention. 
           [0019]      FIG. 4  is a second diagram showing cylinder pressure and crankshaft position of an engine having an alternative timing arrangement according to the present invention. 
           [0020]      FIG. 5  is a third diagram showing cylinder pressure and crankshaft position of an engine having an alternative timing arrangement according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    As shown in  FIG. 1 , vehicle  10  has a number of road wheels  12 , which are operated by means of a powertrain including engine  14 , motor/generator  18 , and transmission  22 . Road wheels  13  are unpowered. Engine  14  and motor/generator  18  are coupled together rotationally such that engine  14  generally rotates in unison with motor/generator  18 . This arrangement is found in a so-called “mild” hybrid vehicles which offer the advantage of lower initial cost, albeit at the expense of reduced regenerative capability. As noted above, the present invention is intended to increase the regenerative capability which would otherwise be available with vehicle  10 . 
         [0022]    As its name implies, motor/generator  18  functions not only as a traction motor receiving power from traction battery  26  and powering road wheels  12  through transmission  22 ; motor/generator  18  also functions as a generator during regenerative braking so that kinetic energy associated with vehicle  10  may be transferred through transmission  22  to motor/generator  18 , where the energy is converted to electrical power stored within storage battery  26 . Because engine  14  and motor/generator  18  are coupled together, engine  14  also rotates during regenerative braking. As a result, some of the energy which could otherwise be converted to stored energy within traction battery  26  is dissipated by motoring friction within engine  14 . As discussed above, motor/generator  18  may be replaced with a hydraulic or pneumatic pump/motor; in either case, traction battery  26  would be replaced by a hydraulic or pneumatic storage tank or accumulator. Thus, as used herein the term “motor/generator” refers to a reversible rotating machine such as an electrical motor/generator, a hydraulic motor/pump or a pneumatic motor/compressor, and the term “traction battery” refers to an energy storage device which could be embodied as an electrical storage battery, or a fluid accumulator, or yet other types of energy storage devices known to those skilled in the art, suggested by this disclosure, and suitable for use as an electrical, hydraulic, or pneumatic energy storage device. 
         [0023]    Controller  30  operates camshaft phaser  38  and, optionally, port throttles  34 , to maximize regenerative capability of motor/generator  18  by reducing the power required to motor engine  14 . The verb “motor” is used herein in the conventional sense that motoring refers to rotation of engine  14  by motor/generator  18 , transmission  22 , and road wheels  12 . Controller  30  operates at least one camshaft phaser  38  which controls the position of at least exhaust camshaft  46  shown in  FIG. 2 . 
         [0024]      FIG. 2  illustrates various details of engine  14 . Thus, crankshaft  66  is connected with piston  74  by means of connecting rod  70 . Intake valve  50  and exhaust valve  54  control the ingress and egress of air and fuel and exhaust gases, respectively, from the engine&#39;s cylinders. Air enters by means of intake port  58  and exhaust gasses leave by means of exhaust port  62 . Intake camshaft  42  operates intake valve  50  and exhaust camshaft  46  operates exhaust valve  54 . Port throttle  34  is shown as being positioned in intake port  58 . 
         [0025]    Controller  30  operates camshaft phaser  38  and port throttles  34  during regenerative operation of vehicle  10  by operating exhaust valve  54  in a first instance such that exhaust valve  54  opens and closes at points which are approximately symmetrical about rotational positions of crankshaft  66  at which the direction of motion of piston  74  is changing. This is shown in  FIGS. 3 and 4 . 
         [0026]    In  FIG. 3 , exhaust valve  54  is shown as opening and closing approximately symmetrically about top dead center (TDC) of the exhaust stroke of a particular cylinder of engine  14 . In  FIG. 3 , pressure within the engine cylinder changes from a negative value at bottom dead center (BDC) on the expansion stroke to roughly atmospheric pressure during the exhaust stroke. As a result, the atmospheric pressure which is reached on the exhaust stroke is maintained through a portion of the intake stroke until the exhaust valve closes. Thereafter the pressure within the cylinder decreases to a sub-atmospheric pressure at BDC of the intake stroke, (because port throttles  34  are closed), and once again increases during the compression stroke to a super-atmospheric value which is then reduced during the expansion stroke following the compression stroke. Because the pressure buildup from sub-atmospheric to atmospheric, which occurs as piston  74  moves from BDC to TDC on the exhaust stroke is reduced to the same sub-atmospheric pressure during the subsequent expansion to BDC on the intake stroke, the net effect is that the work required to compress the gases within the cylinder is extracted during expansion of the intake stroke, and very little energy is dissipated within the engine cylinder. 
         [0027]    If camshaft phaser  38  is used only on the exhaust valve, port throttles  34  should be employed to minimize engine motoring torque. However, in some configurations it may be possible to use phasers on both camshafts, so as to permit greater flexibility in the controlling of valve timing and thus avoid any need for port throttles  34 . 
         [0028]    In  FIG. 4 , exhaust valve  54  is shown as opening and closing approximately symmetrically about bottom dead center (BDC) of the expansion stroke of a particular cylinder of engine  14 , while intake valve  50  is shown as opening and closing approximately symmetrically about bottom dead center (BDC) of the intake stroke. As a result, atmospheric pressure is maintained for most of the cycle, as gases are pulled in an out through the open intake or exhaust valves. Near each TDC the intake and exhaust valves are both closed and pressure builds up, but the net effect is that the work required to compress the gases within the cylinder is extracted during expansion, and very little energy is dissipated within the engine cylinder. 
         [0029]    With some engines, such as single overhead cam (SOHC) or so-called OHV engines having valves actuated by pushrods, it may not be feasible to control exhaust cam phasing separately from intake cam phasing, as described in connection with  FIGS. 3 and 4 . In such case, engine motoring torque may be minimized by phasing intake and exhaust events equally. In  FIG. 5 , intake valve  50  is sown as opening and closing approximately symmetrically about bottom dead center (BDC) of the intake stroke, similarly to  FIG. 4 . Without separate control, the exhaust opening and closing are not symmetric about TDC or BDC, and negative work at the end of the expansion stroke is only partially recovered during the beginning of the exhaust stroke. Accordingly, the method of  FIG. 5  is not as efficient as the methods of  FIGS. 3 and 4 . However, this method is more efficient than use of an unmodified engine, and has the added advantage of being less expensive and more feasible to implement than the other illustrated methods. 
         [0030]    Those skilled in the art will appreciate in view of this disclosure that a variety of camshaft phaser mechanisms could be employed for the purpose of providing camshaft phaser  38 . For example, U.S. Pat. No. 5,107,804 discloses a camshaft phaser mechanism suitable for use according to an aspect of the present invention. 
         [0031]    During regenerative braking, controller  30  operates camshaft phaser  38  and port throttles  34 , if engine  14  optionally includes the port throttles, so as to minimize the power required to motor engine  14 , either by changing the exhaust valve phasing while closing port throttles  34  in the embodiment of  FIG. 3 , or alternatively, by changing both the intake valve and exhaust valve phasing in the manner shown in  FIGS. 4 and 5 . In this manner, because engine  14  is more easily motored, or rotated, by road wheels  12  motor/generator  18 , less energy is lost to motoring friction and concomitantly more of the kinetic energy in vehicle  10  may be captured within traction battery  26  by operating motor/generator  18  as a generator. 
         [0032]    Although the present invention has been described in connection with particular embodiments thereof, it is to be understood that various modifications, alterations, and adaptations may be made by those skilled in the art without departing from the spirit and scope of the invention set forth in the following claims.