Patent Publication Number: US-2011059824-A1

Title: Mode changing device for a power branching transmission

Description:
The invention relates to the field of devices for changing transmission mode, particularly in power distribution transmissions for motor vehicles. 
     Application FR 2 859 669 (RENAULT) discloses a power distribution transmission connecting the combustion engine in parallel to the wheels of the vehicle using two mechanical power transmission paths. The transmission described comprises two electrical machines forming an electrical power transmission path by converting mechanical power into electrical power and vice versa. One of the mechanical power paths comprises a mode change device. This device comprises a mode change epicyclic geartrain in which two inputs of the epicyclic geartrain are inserted along said mechanical path. The third input to the mode change epicyclic geartrain is connected by a component either to another input or to the casing of the transmission. In one of the modes, the third input is connected to the casing so that the velocity ratio applied to the mechanical transmission path can be adjusted by varying the tooth sets of the mode change epicyclic geartrain. In the other mode, the third input is connected to another input of this same epicyclic geartrain so that the latter rotates en masse. The velocity ratio applied to the mechanical path is set at unity. The disadvantage with a mode change device such as this is that only one of the modes can be adjusted independently of the other. 
     The invention proposes a mode change device for a power distribution transmission and the corresponding transmission, which overcome the aforementioned disadvantages and which notably allow greater flexibility in adapting each of the transmission modes. According to one embodiment, the mode change device for a power distribution transmission comprises a casing intended to be fixed to the transmission, an epicyclic geartrain with three inputs, a blocking means for immobilizing a first input with respect to the casing, that can be actuated selectively in order to establish a first mode of operation of the transmission, and a drivechain equipped with a lock-up means which, when the lock-up means is actuated, connects the first input to a second input so as to establish a second mode of operation of the transmission. The drivechain comprises at least one intermeshing of two pinions. 
     The applicant has noticed that for each of the two modes of operation of the transmission, the proportion of power passing along the electrical path is at a minimum for a given range of transmission ratios. This range is the range in which the transmission exhibits the best energy efficiency. The applicant has particularly noticed that overall optimization of the transmission involves getting the optimum range of ratios for the second mode to follow on from the optimum range of ratios for the first mode. By virtue of the intermeshing ratio introduced in the drivechain between the two inputs of the mode change epicyclic geartrain, it is possible to adjust each of the modes independently of one another. That makes it possible, by acting on the two pinions of the drivechain, to modify the optimum range of the second mode in such a way that it follows on from the optimum range of ratios for the first mode, and to do so without having to alter the other parts of the transmission. That may make it possible, for example, for one and the same transmission to be adapted to suit various drives. 
     According to an alternative form, the first input of the epicyclic geartrain is a planet carrier and the second input is an annulus gear. 
     According to another alternative form, the lock-up means comprises a dog-type synchronizer. 
     According to one embodiment, the synchronizer is coaxial with the epicyclic geartrain. 
     According to another embodiment, the device comprises a countershaft on which there are mounted a first and a second intermediate pinion and the dog-type synchronizer able to lock the rotation of the two intermediate pinions; the first intermediate pinion meshing with a first main pinion that is fixed with respect to the first input; the second intermediate pinion meshing with a second main pinion that is fixed with respect to the second input. This drivechain has two successive intermeshings. That further improves the flexibility of the transmission. In addition, it allows the synchronizer, that has to be actuated by a fork, to be resited at a more accessible point in the transmission. This is particularly advantageous when the components mounted on the axis of the mode change epicyclic geartrain are of significant radial bulk which they are in transmissions mounted transversally in the vehicle, for example when a chain is fitted around the annulus gear of the mode change epicyclic geartrain. 
     Advantageously, the synchronizer comprises a body capable of translational movement and collaborating with longitudinal splines of the countershaft. The first intermediate pinion is mounted fixedly on the countershaft. That makes it possible to have a synchronizer that is particularly compact in a radial direction. 
     Advantageously, the synchronizer is able to synchronize the first intermediate pinion either with the casing alone, or with the casing and with the second intermediate pinion simultaneously, or with the second intermediate pinion alone. The transition between the two modes of operation of the transmission occurs when the mechanical path in which the mode change device is inserted has a zero velocity. The transmission ratio inserted in said mechanical path can then be changed without making the vehicle jolt. In addition, that makes it possible to switch from one transmission mode to the other without at any moment opening the mechanical power transmission path in which the mode change device is inserted. 
     According to an alternative form, the blocking means directly connects the first input to the casing in such a way that components contributing to the second mode actuating drivechain do not transmit torque when the first mode is actuated. The applicant company has noticed that the torque transmitted by the mechanical path in which the mode change device is inserted is lower in the second mode than in the first mode. Not using the second mode drivechain for the first mode allows the size of the components in this drivechain to be reduced. That for example makes it possible to reduce the diameter of the shafts or the width of the tooth sets, and to reduce the space occupied by the transmission. 
     Advantageously, the blocking means comprises a sliding gear, guided in axial translation in the casing, and a flange fixed to the first input. The sliding gear is equipped with lateral dogs able to collaborate with dogs belonging to the flange. 
     Advantageously, the blocking means can be actuated independently of the lock-up means. That makes it possible for the region of overlap between the two modes to be adjusted more simply, and that decreases the mechanical tolerances on the actuators. 
    
    
     
       Other features and advantages of the invention will emerge from reading the detailed description of a number of embodiments taken by way of nonlimiting examples and illustrated by the attached drawing in which: 
         FIG. 1  is an overview of the power distribution transmission according to the invention; 
         FIG. 2  is a detailed diagram of the transmission showing a device according to one embodiment of the invention; 
         FIG. 3  is a longitudinal section through the device according to the embodiment of  FIG. 2 ; and 
         FIG. 4  is a longitudinal section through another embodiment of the invention. 
     
    
    
     As illustrated in  FIG. 1 , the power distribution transmission is connected to a combustion engine MT, to a first electrical machine ME 1 , to a second electrical machine ME 2  and to wheels  1 . The actual transmission proper comprises an input shaft  2 , a first epicyclic geartrain G 1 , a second epicyclic geartrain G 2  and a mode change device  4 , which comprises a third epicyclic geartrain G 3  together with a blocking means  5  and a lock-up means  6 . The transmission also comprises four transmission devices  7 ,  8 ,  9  and  10  exhibiting a fixed transmission ratio and interposed between the second epicyclic geartrain G 2  and, respectively, the combustion engine MT, the mode change device  4 , the second electrical machine ME 2  and the wheels  1 . Another fixed ratio transmission device  6   a  is mounted in series with the lock-up means  6  between two inputs of the third epicyclic geartrain G 3 . 
     The torque transmitted to the input shaft  2  is split by a common rotation power combination device  2   a , between the transmission device  7  and the first epicyclic geartrain G 1 . The driving torques from the transmission devices  8  and  9  are added together by a first common rotation power combination device  1   a . The transmission has one power transmission electrical path and two power transmission mechanical paths. The electrical path comprises the electrical machines ME 1  and ME 2 . A first mechanical path connects the first epicyclic geartrain G 1  to the first common rotation power combination device  1   a . A second mechanical path connects the second common rotation power combination device  2   a  to the second epicyclic geartrain G 2 . 
     The transmission works on a power distribution basis. The power of the combustion engine MT is transmitted to the wheels  1  via the mechanical paths and via the electrical path. When one of the machines ME 1  or ME 2  is operating as an alternator, the other is operating as a motor. The difference between the electrical energy supplied by the alternator and that consumed by the motor is stored or provided by a battery B of the vehicle. 
     When the blocking means  5  of the mode change device  4  is actuated and the lock-up means  6  is unlocked, the transmission ratio between the first epicyclic geartrain G 1  and the transmission device  8  exhibits a fixed given ratio. This configuration corresponds to a first mode of operation of the transmission, suited to low vehicle speeds. 
     When the lock-up means  6  is actuated and the blocking means  5  is unblocked, the mode change device  4  exhibits another transmission ratio allowing the power distribution transmission to be operated in a way that is optimized for high vehicle speeds. The change in mode occurs when no mechanical power is passing through the mode change device  4 , that is to say when the three inputs of the third epicyclic geartrain G 3  are stationary. The mode change instant is not manifested by any vehicle torque change jolt. In addition, the change in mode may be effected using dog-type systems which have the advantage that they can be actuated mechanically and do not give rise to any dispersion of energy once they are in the engaged position. 
     All the gearings in the transmission are optimized so that, in the first mode of operation (blocking means  5  activated), the proportion of energy transmitted through the electrical path is minimal for a range of transmission ratios between the engine MT and the wheels M 1  that correspond to low vehicle speeds. Thanks to this optimization, the transmission has an infinitely variable ratio while at the same time minimizing energy losses due to the conversion of mechanical energy into electrical energy and vice versa. The device  6   a  makes it possible to introduce a degree of freedom allowing the second mode of operation of the transmission to optimize the proportion of energy transmitted through the electrical path for a range of transmission ratios that is a continuous progression from the optimized range for the first mode. The presence of a transmission device with a fixed ratio  6   a  in the mode change device  4  allows the entire transmission to be optimized from an energy standpoint for a very wide range of transmission ratios. 
       FIG. 2  will now be used to describe in greater detail a particular structure that can be used to achieve a power distribution transmission corresponding to  FIG. 1 . 
     The transmission mainly comprises two axes, one comprising the combustion engine MT and the first electrical machine ME 1  and the other comprising the second machine ME 2 . On the first axis, from left to right, the transmission comprises a drive shaft  11  for the first electrical machine ME 1 , about which there are mounted, so that they can rotate, a first hub  12  and a second hub  13 . An input shaft  14  is equipped with a dynamic damper device  15 , connected to the combustion engine MT in axial alignment with the drive shaft  11 . 
     The first and third epicyclic geartrains G 1 , G 3  are coaxial with the first axis. Each of the epicyclic geartrains G 1 , G 3  comprises a sun gear P 1 , P 3 , planet pinions S 1  and S 3 , a planet carrier PS 1 , PS 3  and an annulus gear C 1 , C 3 . The first hub  12  is equipped with a fixed main pinion  16 , with a free main pinion  17  and is fixed to the planet carrier PS 3 . The sun gear P 3  and the planet carrier PS 1  are fixed to the second hub  13 . The free main pinion  17  is fixed to the annulus gear C 3  and meshes with an intermediate pinion  18  mounted free to rotate on a countershaft  19 . The countershaft  19  comprises a double dog-type synchronizer  20  and a fixed intermediate pinion  21  in a mesh with the fixed main pinion  16 . The synchronizer  20  is able, under the action of a fork  22 , to lock the fixed pinion  21  either to the intermediate pinion  18 , or to dogs  23  that are fixed with respect to a casing  24  of the transmission. 
     The blocking means  5  consists of the main pinion  16 , the intermediate pinion  18 , the synchronizer  20  and the fixed dog  23 . 
     A description of the second axis of the transmission will now be given. A drive shaft  30  for the second electrical machine ME 2  and an intermediate shaft  31  are aligned with one another. Two coaxial epicyclic geartrains G 2  and G 4  respectively each comprise a sun gear P 2 , P 4 , planet pinions S 2  and S 4 , a planet carrier PS 2 , PS 4  and an annulus gear C 2 , C 4 . The sun gear P 4  is mounted on the drive shaft  30 . A wheel  32  mounted free to rotate comprises the annulus elements C 4  and C 2  and is connected to the annulus gear C 3  in terms of rotation by a chain  33 . The sun gear P 2  is made to rotate by the intermediate shaft  31  and by a wheel  34  connected by a chain  35  to the annulus gear C 1 . The planet carrier PS 2  is mounted on a hub  36   a  free to rotate about the intermediate shaft  31  and connected to the wheels via a differential  36 . 
     The fixed-ratio transmission device  9  consists of the epicyclic geartrain G 4  in which the planet carrier PS 4  is fixed. That allows a transmission ratio to be introduced between the drive shaft of the second electrical machine ME 2  and the annulus gear C 2  of the second epicyclic geartrain G 2 . 
     The first common rotation power combination device  1   a  is a ternary device consisting of the annulus gear C 2  made to rotate by the chain  33 , the planets of the second and fourth epicyclic geartrains G 2  and G 4 . The second common rotation power combination device  2   a  is a ternary device consisting of the annulus gear C 1  made to rotate by the input shaft  14 , the chain  33  and the planets of the first epicyclic geartrain G 1 . In an alternative form, any kind of common rotation power combination device would be suitable. All that is required is for this device to consist of a wheel made to rotate by at least three different rotational-drive means. The rotational speed is common to the three means and the sum of the torques exerted by the means on the common wheel is zero. 
       FIG. 3  will now be used to describe the space-saving advantage afforded by the fact that the synchronizer  20  is located on the countershaft  19  when the annulus gear C 3  of the mode change epicyclic geartrain G 3  has the chain  33  passing around it. Indeed, in the case of a transmission intended to be mounted transversally in a vehicle, the space requirement that needs to be optimized is the lengthwise size.  FIG. 3  illustrates the fact that the function of synchronization between the planet carrier PS 3  and the annulus gear C 3  occupies, in the axial direction, only the width of the main pinions  16  and  17 . 
     The intermediate pinion  19  is mounted on two rolling bearings in the casing  24 . The free intermediate pinion  18  is blocked against translational movement along the countershaft  19  by axial thrust rolling bearings  40 . The shaft  19  is equipped with longitudinal splines  41  that act as synchronizer bodies for the synchronizer  20 . The synchronizer  20  has a sliding gear  42  which comprises a guide hub  43  collaborating directly with the splines  41  of the guide shaft  19 . The sliding gear comprises a skirt  44  extending axially around the shaft  19  and connected at one end to a wheel  45  extending radially and at the other end to the guide hub  43 . The wheel is equipped with a dog  46  able to collaborate either with dogs  18   a  of the free intermediate pinion  18  or with the dogs  23  fixed to the casing  24 . The axial distance between the dogs  23  and  18   a  is less than the axial length of the dog  46 . 
     During translational movement of the sliding gear  42 , the dog  46  moves from a position in which it collaborates only with the fixed dog  23 , as illustrated in  FIG. 3 , then into a common position in which the dog  46  collaborates simultaneously with the dogs  23  and  18   a , then finally into a position in which the dog  46  collaborates only with the dog  18   a . In the position of engagement with the pinion  18 , the skirt  44  of the sliding gear  20  surrounds the axial thrust rolling bearing  40  and part of the hub of the pinion  18 . Thanks to this arrangement of the skirt  44 , the dogs  46  and  18   a  can have a diameter greater than the empty radial space between the chain  33  and the shaft  19 . In addition, the skirt  44  allows the fork  22  to be able to move axially in an axial region situated on the other side of the chain  33  with respect to the intermediate pinion  18 . Thus, a construction such as this allows simultaneously synchronizing between the planet carrier  3  and the annulus gear  3  needed for the mode change and introduction of a meshing ratio into the drivechain between these two elements, and does so while at the same time minimizing the axial space requirement and the additional radial space required. 
       FIG. 4  will now be used to describe an improvement to the previous device, in which the immobilizing device  5  can be actuated independently of the lock-up means  6 , while at the same time retaining all of the abovementioned advantages. A flange  50  extends radially out from the planet carrier PS 3  and is connected to that portion of the planet carrier PS 3  that lies between the first and third epicyclic geartrains G 1  and G 3 . The flange  50  at its periphery has dogs  51 . A sliding gear  53  in the form of an annulus surrounds the annulus gear C 1  of the first epicyclic geartrain G 1 . The sliding gear  53  has axial splines  52  collaborating with complementary splines belonging to the casing  24 . The sliding gear  53  has dogs  54  extending laterally in the axial direction so that they can collaborate with the peripheral dogs  51  of the flange  50 . The sliding gear  53  can be actuated by a system of forks, not depicted, situated in the same axial portion of the transmission as the forks  22 , that is to say between the chains  33  and  35 . 
     In an alternative form of embodiment, the sliding gears  53  and  42  are actuated not independently of one another but simultaneously by one and the same actuator. The fact of having moved the immobilizing means  5  upstream of the drivechain linking the planet carrier PS 3  to the annulus gear C 3  makes it possible to have main and intermediate pinions  16 ,  17 ,  18  and  21  with tooth set widths that are narrower, because they have a lower torque to transmit. In addition, the wheel  45  may also be narrower, because the dog  46  has to collaborate only with the dog  18   a . These two factors make it possible further to reduce the axial size of the transmission.