Abstract:
A control system for a hybrid drive unit, in which an assist prime mover is connected through a transmission mechanism to an output member, to which a torque outputted by a main prime mover is transmitted, comprises gear shift controller for switching a shift control condition of said transmission in accordance with the action state of said main prime mover. A gear shift is inhibited in case a vehicle is run by an assist prime mover, and the gear shift is inhibited also in case the assist prime mover outputs a torque in connection with starting the main prime mover. A transmission is operated into a state just before starting the shifting operation in case the gear shift is inhibited in connection with starting the main prime mover.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a hybrid drive unit provided with a plurality of prime movers as a power source for driving a vehicle, and more particularly, to a control system for a hybrid drive unit, wherein a second prime mover is connected through a transmission to an output member, to which a power is transmitted from a first prime mover.  
           [0003]    The present invention relates to the subject matter contained in Japanese Patent Application No.2003-178163, filed on Jun. 23, 2003, which is expressly incorporated herein by reference.  
           [0004]    2. Description of the Related Art  
           [0005]    One example of this kind of hybrid drive unit is disclosed in JP-A-2002-225578. In the hybrid drive unit described in this publication, an engine and a first motor generator are connected to each other through a synthesizing/distributing mechanism composed of a single pinion type planetary gear mechanism, an output member is connected to the synthesizing/distributing mechanism in a torque a torque transmittable manner, and a second motor generator is connected through a transmission mechanism to the output member.  
           [0006]    According to the hybrid drive unit described in JP-A-2002-225578, therefore, a torque synthesized from an output torque of an engine and a torque of the first motor generator in accordance with a gear ratio of the single pinion type planetary gear mechanism appears on an output shaft, and an engine speed can be controlled by the first motor generator. Therefore, it is possible for the engine to be driven for the optimum fuel consumption thereby to improve a fuel consumption of a vehicle. Moreover, the torque can be applied to the output shaft, by generating an electric power (i.e., regeneration of energy) by the first motor generator so as to drive the second motor generator by the electric power generated, when the engine is being driven at the optimum fuel consumption. Therefore, sufficient driving force can be obtained without deteriorating the fuel consumption. Moreover, the torque outputted by the second motor generator can be raised and transmitted to the output shaft, by having an gear ratio to be set by the transmission greater than “1”. And in case the gear ratio is reduced (e.g., in case the transmission is set in a high speed stage), a speed of the second motor generator can be decreased so that the second motor generator can be changed into a low power type or a small size type.  
           [0007]    In Japanese Published Examined Application 47-31773, moreover, there is disclosed the hybrid drive unit, in which a low brake is released and a high brake is applied in case of switching to a high gear stage, and in which the high brake is released and the low brake is applied in case of switching to a low gear stage. Thus, the interchange between the high gear stage and the low gear stage can be achieved by switching a connection of the brakes.  
           [0008]    According to the invention disclosed in the aforementioned JP-A-2002-225578, the engine is started by driving the first motor generator connected to the engine through the synthesizing/distributing mechanism. However, since the first motor generator is also connected to the output shaft, it is necessary for the torque not to appear on the output shaft during a startup of the engine, by countervailing the output torque of the first motor generator by driving the second motor generator. Therefore, ordinarily, a gear shift is inhibited during the startup of the engine, and is carried out after the startup of the engine is completed. Moreover, since a shifting preparatory control such as a play reducing of a transmission mechanism is required before executing a shifting operation, a time-lag occurs during the period from an instant when a shifting command is outputted until the instant when the shifting operation is substantially started. Because of this, there arises a problem that a rise of the driving force is delayed at the starting time of driving a vehicle, in case the shifting preparatory control is carried out after the engine is started completely.  
           [0009]    According to the invention disclosed in the aforementioned Japanese Published Examined Application 47-31773, moreover, there is a problem such that the shocks occur if a timing of switching between the high brake and the low brake is off.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention has been conceived noting the technical problems thus far described and its object is to provide a control system which can prevent a delay in a rise of driving force by carrying out a shifting preparatory control prior to an instant when a startup of a prime mover is completed.  
           [0011]    In order to achieve the above-specified objects, this invention is constructed to switch a shift control condition in accordance with an action state of a main prime mover such as an engine. Specifically, according to this invention, there is provided a control system for a hybrid drive unit in which an assist prime mover is connected through a transmission mechanism to an output member, to which a torque is outputted by a main prime mover is transmitted, wherein the shift control condition is switched in accordance with the action state of said main prime mover. The action state of said main prime mover includes the action state in the course of starting the main prime mover.  
           [0012]    According to the invention, therefore, a control condition of the transmission accords to the action state of the main prime mover so that the effects of behaviors of the transmission and the assist prime mover on the output torque can be suppressed.  
           [0013]    Moreover, according to the invention, the gear shift of the transmission is inhibited unless the startup of an internal combustion engine, which constructs the main prime mover, is not completed. Therefore, fluctuation in an output shaft torque at the startup of the internal combustion engine can be prevented or suppressed. In addition, the shifting operation is carried out after the startup of the internal combustion engine is completed, so that the vehicle starts moving smoothly.  
           [0014]    Furthermore, according to the invention, the assist prime mover is so controlled as to reduce the torque which is transmitted from the main prime mover to the output member in connection with starting of the main prime mover. Therefore, a situation of a startup control of the main prime mover can be known on the basis of a control condition of the assist prime mover, and the shifting operation of the transmission is inhibited during the startup control.  
           [0015]    The above and further objects and novel features of this invention will more fully appear from the following detailed description when the same is read with reference to the accompanying drawings. It is to be expressly understood, however, that the drawings are for purpose of illustration only and are not intended as a definition of the limits of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a schematic flow chart explaining a control example by a control system of this invention.  
         [0017]    [0017]FIG. 2 is a block diagram schematically showing one example of a hybrid drive unit to which this invention is applied.  
         [0018]    [0018]FIG. 3 is a skeleton diagram showing the hybrid drive unit more specifically.  
         [0019]    [0019]FIG. 4(A) is a nomographic diagram concerning a planetary gear mechanism shown in FIG. 3, and FIG. 4(B) is a nomographic diagram concerning a Ravignaux type planetary gear mechanism shown in FIG. 3 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    This invention will be described in connection with its specific examples. The first description is made on a hybrid drive unit, to which this invention is applied. The hybrid drive unit or an application target of this invention is mounted on a vehicle, for example. As shown in FIG. 2, the torque of a main prime mover (i.e., a first prime mover)  1  is transmitted to an output member  2 , from which the torque is transmitted through a differential  3  to drive wheels  4 . On the other hand, there is provided an assist prime mover (i.e., a second prime mover)  5 , which can make a power running control to output a driving force for a drive and a regenerative control to recover an energy. This assist prime mover  5  is connected through a transmission  6  to the output member  2 . Between the assist prime mover  5  and the output member  2 , therefore, the transmission torque is increased/decreased according to a gear ratio to be set by the transmission  6 .  
         [0021]    This transmission  6  can be constructed to set the gear ratio at “1” or higher. With this construction, at the power running time for the assist prime mover  5  to output the torque, this torque can be raised and transmitted to the output member  2  so that the assist prime mover  5  can be made to have a low capacity or a small size. However, it is preferred that the running efficiency of the assist prime mover  5  is kept in a satisfactory state. In case the speed of the output member  2  rises according to the vehicle speed, for example, the gear ratio is lowered to decrease the speed of the assist prime mover  5 . In case the speed of the output member  2  drops, on the other hand, the gear ratio may be raised.  
         [0022]    The aforementioned hybrid drive unit will be described more specifically hereafter. As shown in FIG. 3, the main prime mover  1  is mainly constructed to include an internal combustion engine (as will be called the “engine” hereinafter)  10 , a motor generator (as will be tentatively called the “first motor generator” or “MG  1 ”)  11 , and a planetary gear mechanism  12  for synthesizing or distributing the torque between those internal combustion engine  10  and first motor generator  11 . The engine  10  is a well-known power unit such as a gasoline engine or a diesel engine for outputting a power by burning a fuel, and is so constructed that its running state such as the throttle opening (or the air intake amount), the fuel feed amount or the ignition timing can be electrically controlled. This control is made by an electronic control unit (E-ECU)  13  composed mainly of a microcomputer, for example.  
         [0023]    On the other hand, the first motor generator  11  is exemplified by a synchronous electric motor and is constructed to function as an electric motor and a dynamo. The first motor generator  11  is connected through an inverter  14  with an accumulator device  15  such as a battery. By controlling the inverter  14 , moreover, the output torque or the regenerative torque of the first motor generator  11  is suitably set. For this control, there is provided an electronic control unit (MG1-ECU)  16 , which is composed mainly of a microcomputer. Here, a stator (not shown) of the first motor generator  11  is so fixed that it cannot rotate.  
         [0024]    Moreover, the planetary gear mechanism  12  is a well-known one for establishing a differential action with three rotary elements: a sun gear  17  or an external gear; a ring gear  18  or an internal gear arranged concentrically with the sun gear  17 ; and a carrier  19  holding a pinion gear meshing with those sun gear  17  and ring gear  18  such that the pinion gear may rotate on its axis and revolve around the carrier  19 . The engine  10  has its output shaft connected through a damper  20  to the carrier  19  as a first rotary element. In other words, the carrier  19  acts as an input element.  
         [0025]    On the other hand, the rotor (not shown) of the first motor generator  11  is connected to the sun gear  17  as a second rotary element. Therefore, this sun gear  17  is the so-called “reaction element”, and the ring gear  18  as a third rotary element is the output element. And, this ring gear  18  is connected to the output member (i.e., the output shaft)  2 .  
         [0026]    In the example shown in FIG. 3, on the other hand, the transmission  6  is constructed of one set of Ravignaux type planetary gear mechanisms. These planetary gear mechanisms are individually provided with external gears, i.e., a first sun gear (S 1 )  21  and a second sun gear (S 2 )  22 , of which the first sun gear  21  meshes with a short pinion  23 , which meshes with an axially longer long pinion  24 , which meshes with a ring gear (R)  25  arranged concentrically with the individual sun gears  21  and  22 . Here, the individual pinions  23  and  24  are so held by a carrier (C)  26  as to rotate on their axes and to revolve around the carrier  26 . Moreover, the second sun gear  22  meshes with the long pinion  24 . Thus, the first sun gear  21  and the ring gear  25  construct a mechanism corresponding to a double-pinion type planetary gear mechanism together with the individual pinions  23  and  24 , and the second sun gear  22  and the ring gear  25  construct a mechanism corresponding to a single pinion type planetary gear mechanism together with the long pinion  24 .  
         [0027]    There are also provided a first brake B 1  for fixing the first sun gear  21  selectively, and a second brake B 2  for fixing the ring gear  25  selectively. These brakes B 1  and B 2  are the so-called “frictional engagement devices” for establishing applying forces by frictional forces, and can adopt a multi-disc engagement device or a band type engagement device. The brakes B 1  and B 2  are constructed to change their torque capacities continuously according to the engaging forces of oil pressures or electromagnetic forces. Moreover, the aforementioned assist prime mover is connected to the second sun gear  22 , and the carrier  26  is connected to the output shaft  2 .  
         [0028]    In the transmission  6  thus far described, therefore, the second sun gear  22  is the so-called “input element”, and the carrier  26  is the output element. The transmission  6  is constructed to set high gear stages of gear ratios higher than “1” by applying the first brake B 1 , and to set low gear stages of gear ratios higher than those of the high gear stages by applying the second brake B 2  in place of the first brake B 1 . The shifting operations between those individual gear stages are executed on the basis of a running state such as a vehicle speed or a drive demand (or the accelerator opening). More specifically, the shifting operations are controlled by predetermining gear stage regions as a map (or a shifting diagram) and by setting any of the gear stages according to the detected running state. For these controls, there is provided an electronic control unit (T-ECU)  27 , which is composed mainly of a microcomputer.  
         [0029]    Here, in the example shown in FIG. 3, there is adopted as the assist prime mover  5  a motor generator (as will be tentatively called the “second motor generator” or “MG 2 ”), which can have the power running mode to output the torque and the regenerative mode to recover the energy. A rotor (not shown) of the second motor generator  5  is connected to the second sun gear  22 . Moreover, the second motor generator  5  is connected through an inverter  28  to the battery  29 . The power running mode, the regenerative mode and the torques in the individual modes are controlled by controlling the inverter  28  by an electronic control unit (MG2-ECU)  30  composed mainly of a microcomputer. Here, the battery  29  and the electronic control unit  30  can also be integrated with the inverter  14  and the battery (the accumulator device)  15  for the aforementioned first motor generator  11 . Here, a stator (not shown) of the second motor generator  5  is so fixed that it cannot rotate.  
         [0030]    A nomographic diagram of the single pinion type planetary gear mechanism  12  as the aforementioned torque synthesizing/distributing mechanism is present at (A) in FIG. 4. When the reaction torque by the first motor generator  11  is inputted to the sun gear (S)  17  against the torque to be inputted to the carrier (C)  19  and outputted by the engine  10 , a higher torque than that inputted from the engine  10  appears at the ring gear (R)  18  acting as the output element. In this case, the rotor of the first motor generator  11  is rotated by the torque, and the first motor generator  11  functions as a dynamo. With the speed (or the output speed) of the ring gear  18  being constant, on the other hand, the speed of the engine  10  can be continuously (or without any step) changed by increasing/decreasing the speed of the first motor generator  11 . Specifically, the control for setting the speed of the engine  10  at a value for the best fuel economy can be made by controlling the first motor generator  11 .  
         [0031]    As indicated by a chain line in FIG. 4(A), moreover, the first motor generator  11  rotates backward when the engine  10  is halted while the vehicle is running. In this state, if the torque is outputted in a forward direction by operating the first motor generator  11  as the electric motor, the torque acts on the engine  10  connected to the carrier  19  to rotate it in the forward direction. As a result, the engine  10  can be started (i.e., motored or cranked) by the first motor generator  11 . In this case, the torque acts on the output shaft  2  in the direction to stop the rotation of the output shaft  2 . Therefore, the driving torque for running can be maintained by controlling the torque outputted from the second motor generator  5 , and at the same time, the startup of the engine  10  can be executed smoothly. Here, the hybrid type of this kind is called “mechanical distribution type” or “split type”.  
         [0032]    On the other hand, a nomographic diagram of the Ravignaux type planetary gear mechanism constructing the transmission  6  is presented at (B) in FIG. 4. When the ring gear  25  is fixed by the second brake B 2 , a low gear stage L is set so that the torque outputted from the second motor generator  5  is amplified according to the gear ratio and applied to the output shaft  2 . When the first sun gear  21  is fixed by the first brake B 1 , on the other hand, there is set a high gear stage H having a lower gear ratio than that of the low gear stage L. The gear ratio at this high gear stage H is higher than “1” so that the torque outputted by the second motor generator  5  is augmented according to that gear ratio and applied to the output shaft  2 .  
         [0033]    Here, in the state where the individual gear stages L and H are steadily set, the torque to be applied to the output shaft  2  is such one as is augmented from the output torque of the second motor generator  5  according to the gear ratio. In the shifting transitional state, however, the torque is such one as is influenced by the torque capacities at the individual brakes B 1  and B 2  and by the inertia torque accompanying the speed change. On the other hand, the torque to be applied to the output shaft  2  is positive in the drive state of the second motor generator  5  but negative in the driven state.  
         [0034]    The hybrid drive unit thus far described comprises two prime movers such as the main prime mover  1  and the assist prime mover  5 , so that the vehicle runs with low fuel consumption and low emission by making good use of those prime movers. Even in case of driving the engine  10 , the speed of the engine  10  is controlled for the optimum fuel consumption by the first motor generator  11 . Moreover, inertia energy of the vehicle is regenerated as an electric power at the coasting time. In case the torque is assisted by driving the second motor generator  5 , the torque to be added to the output shaft  2  is increased by setting the transmission  6  at the low gear stage L when the vehicle speed is low, and the speed of the second motor generator  5  is relatively lowered to reduce the loss by setting the transmission  6  at the high gear stage H when the vehicle speed is raised. As a result, the torque assist is executed efficiently.  
         [0035]    The gear shift of the second motor generator  5  is inhibited during the cranking of the engine is being carried out by the first motor generator  11 , because it is necessary to countervail the output of the torque to the output shaft by the second motor generator  5 . Therefore, it is necessary to output the shifting command after the cranking is ended in case of carrying out the gear shift at the startup of the engine  10 , as the case of starting to move the vehicle under the state where the high gear stage H is set at the startup of the engine  10 . This causes a problem such that a rise of the driving force is delayed at the starting time of driving a vehicle. Following controls are executed in order to avoid this problem.  
         [0036]    One example of a flowchart of the control is shown in FIG. 1. First of all, it is decided (at Step S 01 ) whether or not a current status is in EV running. The “EV running” means the state in which the vehicle is being driven by the second motor generator  5 . This running state is automatically selected by considering a drive demand, a charging amount of the batteries  15  and  29 , the action state of the entire hybrid drive unit and so on. Here, the EV running does not include the case in which the control to startup the engine  10  is carried out, but includes the case in which the control to halt the engine  10  is carried out.  
         [0037]    In case the answer of Step S 01  is YES, a gear shift inhibiting flag is turned ON and the gear shift is inhibited (at Step S 09 ). As a result of this, the gear shift is inhibited and fluctuation in the torque is suppressed in case the mechanism is driven by the second motor generator  5 .  
         [0038]    In case the answer of Step S 01  is NO, specifically, in case the driving is not executed by the second motor generator  5 , it is decided (at Step S 02 ) whether or not the startup control of the engine  10  is being carried out. In case the answer of Step S 02  is NO, specifically, in case the running state is in a steady running state established by the engine  10 , the gear shift inhibiting flag is turned OFF and the gear shift is allowed (at Step S 07 ).  
         [0039]    In case the answer of Step S 02  is YES, specifically, in case neither the driving is executed by the second motor generator  5  nor the engine  10  is started, in short, in case the vehicle is not running, it is decided (at Step S 03 ) whether or not the shifting command is outputted. In case the answer of Step S 03  is NO, the gear shift is inhibited (at Step S 09 ).  
         [0040]    Since the engine startup control is started, the cranking of the engine  10  by the first motor generator  11  is started. On the other hand, the first motor generator  11  is connected also to the output shaft  2 , so that the torque generated by the first motor generator  11  has to appear also on the output shaft  2 . Therefore, it is necessary to countervail this torque by the second motor generator  5 . In order to avoid unnecessary fluctuation in the torque of the second motor generator  5  resulting from the shifting operation, therefore, the gear shift is inhibited.  
         [0041]    In case the answer of Step S 03  is YES, it is decided (at Step S 04 ) whether or not the shift control is currently being executed. In case the answer of Step S 04  is YES, the shifting operation currently in execution is continued (at Step S 08 ). In case the answer of Step S 04  is NO, specifically, in case the engine  10  is in the startup control and the shift control has not yet been carried out, it is decided (at Step S 05 ) whether or not the cranking of the engine  10  is ended. Here, a definition of the “cranking” is a period during the countervailing of the torque is executed by the second motor generator  5 . For example, the “cranking” includes the period during a damping control to suppress a startup vibration of the engine  10  is executed by the second motor generator  5 .  
         [0042]    In case the answer of Step S 05  is YES, specifically, in case a necessity to countervail the torque by the second motor generator  5  is eliminated, the shift control is carried out (at Step S 08 ). In case the answer of Step S 05  is NO, specifically, in case of cranking currently, a shifting preparatory action is started (at Step S 06 ). The shifting preparatory action is an action to carry out so-called “play reducing” at a switching time between brakes B 1  and B 2  activated by an oil pressure, which is carried out prior to the actual shifting operation.  
         [0043]    When processes are ended at Steps S 06  and S 08 , a gear shift inhibiting flag is turned OFF and the gear shift is allowed (at Step S 07 ). Then, wait until the cranking is ended, and the gear shift is carried out or continued when the next or later routine is executed.  
         [0044]    The shifting preparatory action (at Step S 06 ) prior to the shifting operation is carried out in case a decision result of Step S 05  is NO, in other words, in the state where the cranking is not completed. Specifically, the cranking action and the shifting preparatory action are executed concurrently. Therefore, the period from an output instant of the shifting command to a starting instant of the gear shift is shortened, so that the driving force can rise quickly.  
         [0045]    Moreover, in each of the states such as the EV running state, the engine startup state, the cranking state, and a cranking ending state, the action state of the main prime mover  1  is switched to the shift control conditions such as a gear shift inhibiting condition, a gear shift allowing condition, a gear shift preparatory condition, and a gear shift executing condition. Specifically, the condition of the shift control is changed in accordance with the action state of the main prime mover  1 . Therefore, the driving force can rise properly in accordance with each action states.  
         [0046]    Furthermore, in case the main prime mover  1  is being cranked, it is necessary to countervail the torque appearing on the output shaft  2  during the cranking by the second motor generator  5 . Therefore, the gear shift is inhibited and is allowed at an ending instant of the cranking or after the cranking. Specifically, an inhibition or an allowance of the gear shift is made in accordance with the action state of the second motor generator  5 . Therefore, unnecessary fluctuation in the torque can be prevented.  
         [0047]    Here will be briefly described the relation between the aforementioned individual examples and the present invention. The means for executing the individual controls of Steps S 06  to S 09  shown in the aforementioned FIG. 1 correspond to the gear shift control means of the invention, the means for executing the control of Step S 06  correspond to the means for executing the shifting preparatory control, and the means for executing the control of Step S 08  correspond to the means for executing the gear shift after the completion of the startup. Also, the means for executing the control of Step S 07  correspond to the means for executing the gear shift, and the means for executing the control of Step S 09  correspond to the gear shift inhibiting means. In addition, the second motor generator  5  corresponds to the assist prime mover of the invention.  
         [0048]    Here, this invention should not be limited to the specific examples thus far described. The hybrid drive unit, to which this invention is applied, is properly exemplified by the so-called “mechanical distribution type” hybrid drive unit in which the torque of the internal combustion engine and the torque of the first motor generator (or the electric motor) are transmitted to the output member through the synthesizing/distributing mechanism composed mainly of the planetary gear mechanism, as shown in FIG. 3, and in which the torque of the second motor generator (or the electric motor) is transmitted to the output member through the transmission.  
         [0049]    However, the hybrid drive unit of the invention may have another construction. In short, the hybrid drive unit, in which the second prime mover is connected to the output member to which the torque is transmitted from the first prime mover. Moreover, the transmission of the invention may be not only the transmission having the construction to shift the gear stage between high and low, but also a multiple-stage type transmission or a continuously variable transmission.  
         [0050]    Here will be synthetically described the advantages to be attained by this invention. According to the invention, the transmission can be controlled properly in accordance with the action state of the main prime mover. Therefore, the driving force can be raised properly at the starting time of driving.  
         [0051]    Moreover, according to the invention, the shifting preparatory control is carried out prior to the shift control when the internal combustion engine constructing the main prime mover is started by an external force. Therefore, the vehicle can be started moving by executing the gear shift immediately at the instant when the startup of the internal combustion engine is completed. Accordingly, the driving force can be raised quickly at the starting time of driving.  
         [0052]    Still moreover, according to the invention, the control subsequent to the shifting preparatory control is started at the instant when the startup of the main prime mover is completed. Therefore, the gear shift can be executed with a good response.  
         [0053]    Furthermore, according to the invention, the gear shift is inhibited or allowed in accordance with the action state of the assist prime mover. Therefore, the torque can is prevented from fluctuating unnecessarily so that the driver can drive the vehicle without any uncomfortable feeling.