Abstract:
A method is provided for preselecting gear in a double-clutch transmission that includes, but is not limited to measuring at least two types of transmission speed of the double-clutch transmission, evaluating the at least two types of transmission speed, determining a next gear of the double-clutch transmission and preselecting the next gear.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to British Patent Application No. 1003675.4, filed Mar. 5, 2010, which is incorporated herein by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The technical field relates to a double clutch transmission for pre-selection of gear. It also relates to a method of preselecting gear for the double-clutch transmission. 
       BACKGROUND 
       [0003]    A double-clutch transmission comprises two input shafts that are connected to and actuated by two clutches separately. The two clutches are often enclosed by a housing to form a single device. The two clutches are connected to the two input shafts separately for transmitting driving torque from an engine to any of the two input shafts at a time. Typical double clutch transmissions suffer from poor fuel efficiency although many fuel-saving techniques have been adopted. Both car manufacturers and motorists require new techniques to further improve the fuel efficiency at low cost. 
       SUMMARY 
       [0004]    The present application provides a method for preselecting gear in a double-clutch transmission. The method comprises a step of measuring two or more types of transmission speed of the double-clutch transmission. The types of transmission speed includes an input speed of the double-clutch transmission, an output speed of the double-clutch transmission, a change of speed at one or more input shafts of the double-clutch transmission and a change of speed at one or more output shaft of the double-clutch transmission. The transmission speed further includes various speeds of gearwheels and shafts of the double-clutch transmission. 
         [0005]    Usually, measuring a speed or an acceleration of a vehicle that is installed with the double-clutch transmission is equivalent to measuring the output speed of the double-clutch transmission and the acceleration at the output of the double-clutch transmission respectively. The method also comprises a step of evaluating the two or more transmission speeds. The step of evaluating comprises comparing the transmission speed against predetermined thresholds. The step of evaluating also comprises a step of comparing multiple transmission speeds for judging whether the transmission speed increases or decreases over time. The step of evaluating further comprises a step of comparing multiple transmission speeds for calculating rates of the increase or decrease. 
         [0006]    The method further comprises a step of determining a next gear of the double-clutch transmission. The next gear is based on evaluating the transmission speed so that predictions of the next-to-engage gear are put forward. Scheme of predictions can be programmed on in a transmission control unit for selecting gear. Additionally, the method comprises a step of preselecting the next gear. The step of preselecting comprises engaging components of the next gear train. For example, the preselecting comprises locking an idler of the next gear to its weight-carrying layshaft. Preselected idler does not receive driving torque from an engine because a clutch disc of the next gear is not yet connected to the engine. The act of pre-selection reduces the number of engaging components so that there is less number of couplings and loss of momentum when the next gear is selected for driving. 
         [0007]    The method that causes the pre-selection of next gear based on two more types of transmission speed, which is more accurate and reliable for gear pre-selection. For example, the double-clutch transmission causes the pre-selecting a higher gear when both an input speed and an output speed of the transmission increases, which provides more reliable prediction for the next gear. The pre-selection of the higher gear can be wrong if the pre-selection depends on the input speed alone. This is because the increase of input speed may be due to a driver&#39;s stepping on an acceleration pedal of the transmission when driving uphill, but the driver actually intends driver slower. 
         [0008]    The two or more types of transmission speed can comprise an input speed of the double-clutch transmission, or an acceleration speed at an output of the transmission. The two or more types of transmission speed can also comprise an output speed of the transmission, or an acceleration speed at an input of the transmission. 
         [0009]    The step of evaluating can comprise a step of gauging or quantifying a change of the transmission speeds of the double-clutch transmission. The transmission speeds can be picked up one or more sensors that send electrical signals to the transmission control unit via cables. The transmission control unit processes the electrical signals so that the transmission control unit detects speeds or toques of an input, an output or other parts of the double-clutch transmission. Together with inputs from an engine control unit, the transmission control unit regulates the parts of the double-clutch transmission. The change of the transmission speeds may be known as acceleration or deceleration, although the deceleration is another form of acceleration in a negative direction. 
         [0010]    The step of measuring can comprise a step of sensing a speed change of a vehicle that is installed with the double-clutch transmission. The step of measuring can be implemented by attaching sensors to moving parts of the double-clutch transmission or on a frame of the vehicle. The speed change of the vehicle, which is acceleration, is detected by sensors for observing movements of the vehicle. Speed sensors can be readily adopted for checking the speed change of the vehicle at low cost. 
         [0011]    The step of measuring can comprise a step of detecting an input speed of the double-clutch transmission. The double-clutch transmission receives the input speed at its two input shafts that are connected to an engine via a double clutch. The input speed reflects an output speed of the engine. Since the output speed of the engine is directly controlled by a driver of the vehicle, the detection of the input speed of the double-clutch transmission gives clear indication on whether the driver intends to speed up or slow down, thus provide reliable indication for controlling the double-clutch transmission. 
         [0012]    The step of determining can comprise a step of predicting a higher gear if the double-clutch transmission accelerates or predicting a lower gear if the double-clutch transmission decelerates. Once the input speed of the double-clutch transmission increases, there is an indication that the driver wants to accelerate. Similarly, there is an indication that the driver wishes to decelerate if the input speed of the double-clutch transmission decreases. Accordingly, gear can be appropriately selected for moving the vehicle at suitable speed and efficiency. 
         [0013]    The step of determining can further comprise a step of predicting a higher gear if the engine accelerates, or predicting a lower gear if the engine decelerates. The technique of predicting next gear can be programmed into the transmission control unit. Once the transmission control unit or the engine control unit senses that the engine increases its speed, the transmission control unit or the engine control unit predicts that the next gear is a higher gear. A lower gear is predicted if the transmission control unit or the engine control unit senses that the engine decreases its speed. The engine speed is regulated by an acceleration pedal, which is directly controlled by the driver. 
         [0014]    The step of determining can further comprise a step of predicting a higher gear if the input speed of the double-clutch transmission exceeds a speed threshold or predicting a lower gear if the input speed of the double-clutch transmission is lower than the speed threshold. Since the double-clutch transmission receives a stable input speed and the driving torque from the engine, fluctuations of the input speed and the driving torque are linked to the driver&#39;s intensions for speeding. Once the input speed of the double-clutch transmission drops below a threshold or goes beyond a set value, the transmission control unit predict indications of acceleration or deceleration accordingly, in response to the driver&#39;s actions. 
         [0015]    The step of determining further comprises a step of predicting a higher gear if both the double-clutch transmission accelerates and the input speed of the double-clutch transmission increases. Once both an input speed of the double-clutch transmission and the vehicle&#39;s speed increase, the transmission control unit has a higher confidence level of predicting a higher gear for the next. This avoids an error of predicting a next gear to be higher where the vehicle increases its speed, but the engine speed is still low. Such situation happens when the vehicle moves down a slope with an increase in speed, but the engine speed is still low. Therefore, the arrangement of predicting a next gear depending on both the acceleration of the double-clutch transmission and the input speed of the engine gives the prediction of a next gear with more accuracy. 
         [0016]    The step of determining further can comprise a step of predicting a lower gear if both the double-clutch transmission decelerates and the input speed of the double-clutch transmission decreases. When the vehicle drives up a hill, the double-clutch transmission reduces its output speed, but the engine speed is still rather high. The prediction of the next gear to be higher will be wrong if the transmission control unit only takes the input speed of the double-clutch transmission  1  into account. Watching both the deceleration of the double-clutch transmission at its output end and output end provides more reliable and accurate prediction of the next gear. 
         [0017]    The present application provides a powertrain for preselecting gear. The powertrain comprises a speed sensor mounted on the powertrain, a transmission control unit that is connected to the speed sensor and a double-clutch transmission that is controlled by the transmission control unit. 
         [0018]    The double-clutch transmission further comprises an inner input shaft and an outer input shaft. The outer input shaft encloses a portion of the inner input shaft. An inner clutch disc is connected to the inner input shaft whilst an outer clutch disc is connected to the outer input shaft. The inner clutch disc and the outer clutch disc are parts of a double clutch that has a clutch housing for enclosing the two clutch discs. The double-clutch transmission also comprises a first layshaft and a second layshaft that are spaced apart from each other in parallel to the input shafts. A pinion of the double-clutch transmission is mounted on one of the layshafts for outputting drive torque. 
         [0019]    Gearwheels of the double-clutch transmission are arranged on the first layshaft, on the second layshaft, on the inner input shaft and on the outer input shaft. The gearwheels comprises a first gearwheel train, a second gearwheel train, a third gearwheel train, a fourth gearwheel train and a fifth gearwheel train for providing five sequentially increasing forward gears respectively. 
         [0020]    The first gearwheel train comprises a gearwheel first gear on one of the input shafts, meshing with an idler first gear on one of the layshafts. The third gearwheel train comprises a gearwheel third gear on one of the input shafts, meshing with an idler third gear on one of the layshafts. The fifth gearwheel train comprises a gearwheel fifth gear on one of the input shafts, meshing with an idler fifth gear on one of the layshafts. The second gearwheel train comprises a gearwheel second gear on the other input shaft, meshing with an idler second gear on the other layshaft. The fourth gearwheel group comprises a gearwheel fourth gear on the other input shaft, meshing with an idler fourth gear on the other layshaft. Each gearwheel train comprises one or more coupling devices on one of the layshafts to selectively engage one of the idler gearwheels for providing one of the five gears. 
         [0021]    The double-clutch transmission further comprises an output gearwheel on an output shaft for meshing with the pinion. The transmission control unit is configured to control the double-clutch transmission for preselecting a next gear depending on two or more types of transmission speed of the double-clutch transmission. In the double-clutch transmission, an idler gearwheel and a coupling device can replace a fixed gearwheel or a gearwheel. A fixed pinion is also possible to be replaced by an idler pinion with a coupling device. The double-clutch transmission can further have more gear trains for providing more gears. For example, the double-clutch transmission can include sixth gear train that has a gearwheel sixth gear on the input shaft of even gears, meshing with an idler sixth gear on the layshaft of high gears. Additionally, the double-clutch transmission can include seventh gear train that has a gearwheel seventh gear on the input shaft of odd gears, meshing with an idler seventh gear on the layshaft of high gears. 
         [0022]    The powertrain can select suitable gears in response to various speeds and acceleration conditions. The selected gears can maximise fuel utilisation efficiency and speed performance of a vehicle with the power train. The suitable gears also enable improvements on noise, vibration, and harshness. The powertrain can comprise an engine that is connected to the input shafts via the two clutch discs, a crankshaft of the engine being connected to the vehicle speed sensor for measuring an engine speed. In other words, the two input shafts are connected to a gearbox by the double clutch such that the engine provides driving torque to one of the two input shafts at a time. Shifts between the input shafts thus become swift and efficient for minimising disruption in torque transmission. 
         [0023]    The engine can comprise an internal combustion engine, an electric motor, a hybrid engine or a combination of any of these engines. These various types of engines make the powertrain more versatile for a variety of energy sources. For example, the powertrain with the electric motor has an excellent speed performance with little emission. 
         [0024]    The double-clutch transmission can further comprise a third layshaft arranged in parallel to the input shafts, the first layshaft and the second layshaft. The double-clutch transmission can also comprise a pinion and other gearwheels on the third layshaft for outputting the drive torque. The other gearwheels comprising a reverse gearwheel train for providing a reverse gear. The reverse gear train comprises an idler reverse gear on the third layshaft that meshes with the gearwheels on one of the first layshaft and the second layshaft. The reverse gearwheel train also comprises a coupling device on the third layshaft to engage the idler reverse gear to the third layshaft for providing the reverse gear. The reverse gear enables the vehicle with the double-clutch transmission to be more manoeuvrable for parking. 
         [0025]    The idlers of low gears and idlers of high gears are mounted on separate layshafts. The idlers of low gears can include idlers of the first gear, the second gear, and the third gear. The idlers of high gears can include idlers of the fourth gear, the fifth gear, the sixth gear and the seventh gear. Alternatively, the fourth gear can also belong to the group of low gears. Gearwheels of high gears typically have smaller diameters than those of low gears. A layshaft that carries the gearwheels of high gears can have a distance to the input shafts that is shorter than a distance from the input shafts to a layshaft with low gears. This arrangement makes the double-clutch transmission compact. 
         [0026]    The present application provides a vehicle with the powertrain for preselecting gears. A linear speed sensor is installed on a body of the vehicle for measuring driving speed of the vehicle. The linear speed sensor sends electrical signals to the transmission control unit for regulating the double-clutch transmission in response to the speed of the vehicle. Automatic selections of gears become feasible for fuel efficiency, low noise of gear shifting and comfort for passengers of the vehicle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and: 
           [0028]      FIG. 1  illustrates an expanded view of a double-clutch transmission; and 
           [0029]      FIG. 2  illustrates a vehicle installed with the double clutch transmission. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    The following detailed description is merely exemplary in nature and is not intended to limit application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or summary or the following detailed description. 
         [0031]    In the following description, details are provided to describe an embodiment of the application. It shall be apparent to one skilled in the art, however, that the embodiment may be practiced without such details.  FIG. 1  and  FIG. 2  illustrate the embodiment of the present application. These figures comprise parts that have same reference numbers. Description of these parts is hereby incorporated by reference. 
         [0032]    In particular,  FIG. 1  illustrates an expanded view of a double-clutch transmission  1 . The double clutch transmission  1  comprises shafts, gearwheels and a double-clutch  6 . The gearwheels are mounted on the shafts that are further connected to an engine  3  via the double clutch  6 . According to the  FIG. 1 , the double clutch transmission  1  comprises following shafts, from top to bottom, an output shaft  14 , an upper layshaft  40 , two input shafts  20 ,  22 , a lower layshaft  50  and a reverse gear shaft  38 . The input shafts  20 ,  22  comprise a solid input shaft  20  and a hollow input shaft  22 . The hollow input shaft  22  encloses the solid input shaft  20  in its core and the solid input shaft  20  protrudes outside the hollow input shaft  22  at its opposite ends. The two input shafts  20 ,  22  are coaxial. 
         [0033]    The hollow input shaft  22  is mounted onto the solid input shaft  20  by a pair of solid shaft bearings  71  that are disposed between the solid input shaft  20  and the hollow input shaft  22  at two ends of the hollow input shaft  22 . As a result, the two input shafts  20 ,  22  are coupled coaxially such that the solid input shaft  20  is free to rotate inside the hollow in-put shaft  22 . The assembly of the input shafts  20 ,  22  is supported by a solid shaft bearing  71  at a protruding end of the solid shaft  20  on the left and by a hollow shaft bearing  72  on the right on the hollow input shaft  22 . 
         [0034]    As shown in  FIG. 1 , gearwheels are mounted onto the solid input shaft  20  and the hollow input shaft  22  coaxially. There are two gearwheels mounted on the left exposed portion of the solid input shaft  20 . These two gearwheels, from left to right, are a fixed wheel fourth gear  31  and a fixed wheel second gear  30 . The fixed wheel second gear  30  also serves as a fixed wheel sixth gear  32 . On the hollow input shaft  22 , which surrounds a right portion of the solid input shaft  20 , there are mounted with a fixed wheel third gear  25 , a fixed wheel seventh gear  27  and a fixed wheel first gear  24 , from left to right. The fixed wheel third gear  25  also serves as a fixed wheel fifth gear  26 . 
         [0035]    The lower layshaft  50  is provided below both the solid input shaft  20  and the hollow input shaft  22 . There are a number of gearwheels and coupling devices mounted on the lower layshaft  50 , which include, from left to right, an idler fourth gear  63 , a double-sided coupling device  82 , an idler second gear  61 , an idler third gear  62 , a double-sided coupling device  83 , an idler first gear  60  and a lower pinion  51 . One lower layshaft bearing  76  is provided between the lower pinion  51  and the idler first gear  60 . Another layshaft bearing  73  is provided on a left side of the idler fourth gear  63  at an end of the lower layshaft  50 . The lower pinion  51  is fixed onto the lower layshaft  50 . The idler first gear  60 , the idler third gear  62 , the idler second gear  61  and the idler fourth gear  63  are mounted on the lower layshaft  50  by bearings separately such that these gearwheels become idlers, being free to rotate around the lower layshaft  50 . In other words, gearwheels of low gears  60 ,  61 ,  62 ,  63  (e.g., 1st, 2nd, 3rd &amp; 4th gears) are installed on the same lower layshaft  50  coaxially. In particular, one of the lower layshaft bearings  76  is installed next to the gearwheel of the lowest gear (i.e. idler first gear  60 ) and the lower pinion  51 . Both the double-sided coupling devices  82 ,  83  are configured to move along the lower layshaft  50  such that they can either synchronise a gearwheel on their left or right to the lower layshaft  50  respectively. The idler first gear  60  meshes with the fixed wheel first gear  24 . The idler third gear  62  meshes with the fixed wheel third gear  25 . The idler second gear  61  meshes with the fixed wheel second gear  30 . The idler fourth gear  63  meshes with the fixed wheel fourth gear  31 . 
         [0036]    The upper layshaft  40  is installed above the input shafts  20 ,  22 . Gearwheels and coupling devices are mounted onto the upper layshaft  40 , including, from left to right, a park-lock gearwheel  39 , a single-sided coupling device  81 , an idler sixth gear  65 , an idler fifth gear  64 , a double-sided coupling device  80 , an idler seventh gear  66  and an upper pinion  41 . One upper layshaft bearing  73  is positioned between the upper pinion  41  and the idler seventh gear  66 . Another layshaft bearing  73  is positioned at an end of the upper layshaft  40 , next to the park-lock gearwheel  39 . In other words, gearwheels of high gears  64 ,  65 ,  66  (e.g. 5th, 6th &amp; 7th gears) reside on the same upper layshaft  40 . The idler seventh gear  66 , the idler fifth gear  64 , and the idler sixth gear  65  are mounted on the upper layshaft  40  by bearings respectively such that these gearwheels are free to rotate around the upper layshaft  40 . The double-sided coupling device  80  is configured to move along the upper layshaft  40  to engage or disengage any of the idler seventh gear  66  and the idler fifth gear  64  to the upper layshaft  40 . The single-sided coupling device  81  is configured to move along the upper layshaft  40  to engage or disengage the idler sixth gear  65  to the upper layshaft  40 . The idler seventh gear  66  meshes with the fixed wheel seventh gear  27 . The idler fifth gear  64  meshes with the fixed wheel fifth gear  26 . The idler sixth gear  65  meshes with the fixed wheel sixth gear  32 . 
         [0037]    The park-lock gearwheel  39  comprises a park-lock on the upper layshaft  40  that carries a final drive pinion  41 . The park-lock is a wheel which is provided with a ratchet device, with a click device having a rack element, a claw or similar. The park-lock keeps the upper layshaft  40 , the upper pinion  41  and the output shaft  14  from rotating, which stops a vehicle  5  with the double-clutch transmission  1  from running when parked. Detailed structure of the park-lock is not shown in  FIG. 1 . 
         [0038]    The output shaft  14  is situated above the upper layshaft  40 . The output layshaft  14  has an output gear wheel  12  fixed onto it in the middle. Two opposite ends of the output shaft  14  are attached and supported by two output shaft bearings  75  respectively. The output gearwheel  12  meshes with the upper pinion  41  and the lower pinion  51 . 
         [0039]    In contrast to the output shaft  14 , the reverse gear layshaft  38  is located below the lower layshaft  50 . The reverse gear layshaft  38  carries a second idler reverse gear  36 , a double-sided coupling device  84 , an idler reverse gear  35  and a reverse pinion  53 , from left to right. One reverse gear shaft bearing  74  that supports the reverse gear layshaft  38  is installed between the idler reverse gear  35  and the reverse pinion  53 . Another reverse gear shaft bearing  74 , which also supports the reverse gear shaft  38 , is attached to a left end of the reverse gear shaft  38 . The reverse pinion  53 , the idler reverse gear  35 , the double-sided coupling device  84 , and the second idler reverse gear  36  are mounted onto the reverse gear shaft  38  coaxially. The idler reverse gear  35  and the second idler reverse gear  36  are installed onto the reverse gear layshaft  38  by bearings such that the idler reverse gear  35  and the second idler reverse gear  36  can freely rotate around the reverse gear shaft  38 . The double-sided coupling device  84  is configured to move along the reverse gear shaft  38  to synchronise either the idler reverse gear  35  or the second idler reverse gear  36  with the reverse gear shaft  38 . The idler reverse gear  35  meshes with the idler first gear  60 . The second idler reverse gear  36  meshes with the idler fourth gear  63 . The reverse pinion  53  meshes with the output gearwheel  12 . 
         [0040]    In the double clutch transmission  1 , there are three double-meshing features and one triple-meshing feature. A first double meshing feature comprises that the fixed wheel third gear  25  meshes with both the idler third gear  62  and the idler fifth gear  64  separately. A second double meshing comprises that the fixed wheel second gear  30  meshes with the idler second gear  61  and the idler sixth gear  65  separately. A third double meshing feature comprises that the idler first gear  60  meshes with the fixed wheel first gear  24  and the idler reverse gear  35 . The triple-meshing feature comprises that the output gearwheel  12  meshes with the upper pinion  41 , the lower pinion  51  and the reverse pinion  53 . 
         [0041]    A distance  56  between the input shafts  20 ,  22  and the upper lay-shaft  40  is smaller than a distance  58  between the input shafts  20 ,  22  and the lower layshaft  50 . The distance  56  between the input shafts  20 ,  22  and the upper layshaft  40  is measured from a common longitudinal axis of the input shafts  20 ,  22  to a longitudinal axis of the upper layshaft  40 . Similarly, the distance  58  between the input shafts  20 ,  22  and the lower layshafts  50  is measured from the common longitudinal axis of the input shafts  20 ,  22  to a longitudinal axis of the lower layshaft  50 . The difference exists because the gearwheels of high gears  64 ,  65 ,  66  have smaller diameters than the diameters of the gearwheels of low gears  60 ,  61 ,  62 ,  63 . In other words, the upper layshaft  40  is brought to be closer to the input shafts  20 ,  22  than the lower layshaft  50 . 
         [0042]    The double clutch  6  has an inner clutch disc  8  and an outer clutch disc  10 , which are fixed to the solid input shaft  20  and the hollow input shaft  22  respectively. The two clutch discs  8 ,  10  are enclosed by a clutch housing  4 . The clutch housing  4  and the two clutch discs  8 ,  10  are connected to each other by other components that are not shown. The other components enable the clutch housing  4  to engage any of the two clutch discs  8 ,  10  at a time for torque transmission. The inner clutch disc  8  and the clutch housing  4  are parts of an inner clutch of the double-clutch transmission  1 , whilst the outer clutch disc  10  and the clutch housing  4  are parts of an outer clutch of the double-clutch transmission  1 . 
         [0043]    The clutch housing  4  is attached to the engine  3 . Specifically, a crankshaft  2  is fixed to the clutch housing  4  at an end. The clutch housing  4  thus receives torque from the engine  3  for driving any of the two input shafts  20 ,  22 . The clutch housing  4  has a larger outer diameter around the inner clutch disc  8  than that around the outer clutch disc  10 . Correspondingly, the inner clutch disc  8  has a larger outer diameter than that of the outer clutch disc  10  inside the clutch housing  4 . The fact that the larger inner clutch disc  8  on the solid input shaft  20  drives the first gear makes the double clutch transmission  1  robust. 
         [0044]    The engine  3  encloses the crankshaft  2  inside an engine block although the engine block is omitted from  FIG. 1 . Another end of the crankshaft  2  is installed with a vehicle speed sensor  90 . The vehicle speed sensor  90  is also known as an output speed sensor that sends varying frequency signal to the transmission control unit  98  via cables to determine the rotational speed of the engine  3 . The transmission control unit  98  evaluates the signals and determines rotational speeds and rotational acceleration of the crankshaft  2 . The rotational speed of the crankshaft  2  corresponds to the engine speed, whilst the rotational acceleration of the crankshaft  2  is engine acceleration. In short, the transmission control unit  98  assesses engine speed and engine acceleration of the double clutch transmission  1 . The vehicle speed sensor  90  may also be known as an output speed sensor (OSS). The vehicle speed sensor  90  sends the speed and acceleration information to the transmission control unit  98  to determine when a gear change should take place. 
         [0045]      FIG. 2  illustrates a vehicle  5  that is installed with the double clutch transmission  1 . The vehicle  5  has two front wheels and two rear wheels at bottom. The double-clutch transmission  1  is installed into a body of the vehicle  5 . The vehicle  5  has two front wheels  7  and two rear wheels  9 . The two rear wheels  9  receive the torque from the double clutch transmission  1  via a differential (not shown) that is further coupled to the output gearwheel  12 . 
         [0046]    A wheel speed sensor  94  is attached to a shaft  88  that joins the rear wheels. The wheel speed sensor determines a speed of the vehicle  5  and sends electrical signals of the vehicle speed to the transmission control unit  98 . The wheel speed sensor  94  is also connected to the engine control unit via cables. The wheel speed sensor  94  senses rotational speed variations of the shaft such that the engine control unit can assess accelerations of the vehicle based on received electrical signals from the wheel speed sensor  94 . 
         [0047]    A linear speed sensor  96  is mounted on the body of the vehicle. The linear speed sensor  96  is linked to the transmission control unit  98  by cables. The linear speed sensor  96  detects respective movements between the body and ground such that speeds of the vehicle are obtained for calculation by the engine control unit. 
         [0048]    In the present specification, the expressions “mesh” and “comb” with respect to geared wheels or engaged gearwheels are provided as synonyms. The solid input shaft  20  is alternatively termed as an inner input shaft  20 , while the hollow input shaft  22  is alternatively termed as an outer input shaft  22 . The solid input shaft  20  is alternatively replaced by a hollow shaft that is disposed inside the hollow input shaft  22 . The term “coupling device” is alternatively termed as “shifting mechanism” or “synchroniser” for engaging or disengaging its adjacent gearwheels to a shaft. The coupling device enables a gearwheel and its weight-carrying shaft that rotates at different speeds to be adjusted to the same speed and then locked together for torque transmission. The double-clutch transmission is alternatively termed as twin-clutch double-clutch transmission, double-clutch, double clutch transmission or dual clutch transmission. “Wires” may replace the term “cable” that serves the function of making electrical connections. The tern “gear” is a short form of “gear speed” or “gear speeds”. 
         [0049]    The fixed wheel first gear  24  is also known as the first fixed gearwheel  24 . The fixed wheel third gear  25  is also known as the third fixed gearwheel  25 . The fixed wheel fifth gear  26  is also known as the fifth fixed gearwheel  26 . The fixed wheel seventh gear  27  is also known as the seventh fixed gearwheel  27 . The fixed wheel second gear  30  is also known the second fixed gearwheel  30 . The fixed wheel fourth gear  31  is also known as the fourth fixed gearwheel  31 . The fixed wheel sixth gear  32  is also known as the sixth fixed gearwheel  32 . The idler first gear  60  is also known as the first gear idler gearwheel  60 . The idler second gear  61  is also known as the second gear idler gearwheel  61 . The idler third gear  62  is also known as the third gear idler gearwheel  62 . The idler fourth gear  63  is also known as the fourth gear idler gearwheel  63 . The idler fifth gear  64  is also known as the fifth gear idler gearwheel  64 . The idler sixth gear  65  is also known as the sixth gear idler gearwheel  65 . The idler seventh gear  66  is also known as the seventh gear idler gearwheel  66 . The idler reverse gear  35  is also known as a reverse gear idler gearwheel  35 . Any of the input shafts  20 ,  22 , the layshafts  38 ,  40 ,  50  and the output shaft  14  can be supported by more than two bearings. 
         [0050]    In figures of the present application, dash lines represent combing relationship between gearwheels that are linked to the dash lines. 
         [0051]    The double clutch transmission  1  permits gearshift operations with less loss of driving torque. This is because the gearshift operations can be achieved by selectively connecting one of the two clutch discs  8 ,  10  of the double-clutch transmission  1 . Therefore, an associated additional main drive clutch can be avoided. The selective connection between the two clutches also enables the realization of an automatic transmission that can be operated without interruptions in propulsive power. The propulsive power comprises momentum derived from the rotating gearwheels and shafts inside the double-clutch transmission  1 . Such a transmission is similar in design to a mechanical manual transmission and it has correspondingly very low friction losses. The double-clutch transmission  1  further provides a parallel manual transmission that can be used for transverse installation in a front-wheel drive vehicle. 
         [0052]    The double-clutch transmission  1  can be connected similar to a known manual transmission, such as a parallel manual transmission. In the known that a manual transmission, a drive shaft for a front axle of the vehicle  5  extends outward from its double-clutch transmission case, and parallel to the output shaft  14  of the double-clutch transmission  1 . The arrangement of the known manual transmission provides little space left for actuation of the manual transmission and clutch, and for an optional electric motor. The optional electric motor can act as a starter device for the internal combustion engine  3 , as an energy recuperation device for brake operation or as an additional drive means in hybrid vehicles. Having such little space presents a number of difficulties that are solved or at least alleviated by the application. The double-clutch transmission  1  has two clutches  8 ,  10  for connecting to an electrical motor and the manual transmission in a compact manner. 
         [0053]    The double-clutch transmission  1  provides a compact structure of a parallel transmission. The parallel transmission includes two input shafts  20 ,  22 , each of which can be non-rotatably coupled via its own clutch discs  8 ,  10  to the engine  3 . The double-clutch transmission  1  further provides the output shaft  14  that is parallel to the input shafts  20 ,  22 . The double-clutch transmission  1  is particularly well suited for transverse installation in front-wheel drive vehicles, in which the front differential, for example, is positioned below the pinions  41 ,  51 ,  53 . A short overall length of the power train for transmitting torques can be achieved. The double-clutch transmission  1  provides three relatively small pinions  41 ,  51 ,  53  on three intermediately arranged layshafts  40 ,  50 ,  38  that combs with one relatively big output gearwheel  12  that in turn is connected with the output shaft  14 . This arrangement provides a compact and lightweight double-clutch transmission  1 . 
         [0054]    The double-clutch transmission  1  further allows a design in which the output gearwheel  12  is integrated into a transmission differential device without providing an intermediate output shaft  14 . This allows a very dense packaging situation for the double-clutch transmission  1 . 
         [0055]    It is further advantageous to provide fixed wheels of the even gearwheels on one input shaft and fixed wheels of the odd gears on another input shaft. This arrangement provides the above-mentioned power-shift operation in a smooth and efficient manner when gearshift is performed sequentially. This is because the double-clutch transmission  1  can alternatively engage one of the two clutches to select gearwheels of the two input shafts  20 ,  22  during the speed escalation. For example, the power-shift operation from the first gear to the fourth gear causes the hollow input shaft  22  and the solid input shaft  20  being engaged alternatively, which is energy efficient and fast for switching the driving torque between the two input shafts  20 ,  22 . 
         [0056]    The double-meshing feature of the idler third gear  62  and the idler fifth gear  64  via the intermediate fixed wheel third gear  25  (i.e., fixed wheel fifth gear  26 ) provides swift and efficient gearshifts between the third gear and the fifth gear. No input shaft or clutch change is required for the direct gearshift between the two gears. Since the fixed wheel third gear  25  is the same as the fixed wheel fifth gear  26 , no additional gearwheel is required for providing each of the third and fifth gears. Weight of the double-clutch trans-mission  1  is reduced as comparing to having two separate gearwheels (i.e. fixed wheel third gear  25  &amp; fixed wheel fifth gear  26 ). 
         [0057]    In a similar manner, the other double meshing feature of the idler second gear  61  and the idler sixth gear  65  via the intermediate fixed wheel second gear  30  (i.e. fixed wheel sixth gear  32 ) also provides fast and efficient gearshifts. Weight of the double-clutch transmission  1  is further reduced as comparing to having two separate gearwheels (i.e. fixed wheel second gear  30  &amp; fixed wheel sixth gear  32 ). 
         [0058]    Gearwheels  60 ,  61 ,  62 ,  63  of the low gears (i.e., 1st, 2nd, 3rd &amp; 4th) that are provided on the same lower layshaft  50  are advantageous. This is because the lower layshaft  50  has lower rotational speed with larger size for transmitting stronger torque, as compared to that of the upper layshaft  40 . This arrangement eliminates the need of providing multiple layshafts with larger size for carrying those heavy load gearwheels  60 ,  61 ,  62 ,  63  of the low gears (i.e., 1st, 2nd, 3rd &amp; 4th) separately. Therefore, the double-clutch trans-mission  1  can be made light at less cost. 
         [0059]    Lower layshaft bearings  76  on the lower layshaft  50  are mounted adjacent to the gearwheel  60  of low gears (e.g. 1st gear) and the lower pinion  51 . This arrangement provides stronger mechanical support to the lower layshaft  50  for less shaft deflection. Similarly, the layshaft bearing  73 ,  76  and the idler shaft bearing  74  are provided next to the pinions  41 ,  51 ,  53  for stronger support. As a result, the layshafts  40 ,  50  and the reverse gear shaft  38  can be reduced in weight for lower cost. 
         [0060]    A variant of the embodiment with two double-shared gearwheels on two different input shafts  20 ,  22  has the advantage of providing a higher ratio-flexibility and less dependency. In the current example of double-clutch transmission  1 , gearshifts between the third and fifth gears can be faster because both the idler fifth gear  64  and the idler third gear  62  are engaged to the same fixed wheel third gear  25  all the time, thus readily available for the selection. It is beneficial to provide the gearwheels of the first gear, of the reverse gear, of the output gear wheel  12  and of the pinions  41 ,  51 ,  53  close to the bearings for sturdy supporting. These gearwheels undergo bigger forces than those of the higher gears (e.g., idler fifth gear  64 ) because the drive ratio is higher for the lower gears and the reverse gear. Therefore, their shafts must take up higher driving forces. If those forces are taken up close to the support points of the shafts, a reduced shaft bending will occur. 
         [0061]    The double-clutch transmission  1  is configured to transmit seven forward gears and two reverse gears. The double-clutch transmission  1  provides a first gear when the clutch housing  4  engages the outer clutch disc  10  and the double-sided coupling device  83  locks the idler first gear  60  to the lower layshaft  50 . The clutch housing  4  is detached from the inner clutch disc  8 . A torque of the first gear is transmitted from the crankshaft  2 , via the clutch housing  4 , via the outer clutch disc  10 , via the hollow input shaft  22 , via the fixed wheel first gear  24 , via the idler first gear  60 , via the double-sided coupling device  83 , via the lower layshaft  50 , via the lower pinion  51 , via the output gear wheel  12 , to the output shaft  14 . The number of tooth engagements or engaged gear pairs for the torque transfer of the first gear is three. 
         [0062]    The double-clutch transmission  1  provides a second gear when the clutch housing  4  engages the inner clutch disc  8  and the double-sided coupling device  82  locks the idler second gear  61  to the lower layshaft  50 . The clutch housing  4  disengages the outer clutch disc  10 . A torque of the second gear is transmitted sequentially from the crankshaft  2 , the clutch housing  4 , the inner clutch disc  8 , the solid input shaft  20 , the fixed wheel second gear  30 , the idler second gear  61 , the double-sided coupling device  82 , the lower layshaft  50 , the lower pinion  51 , the output gear wheel  12 , to the output shaft  14 . The number of tooth engagements or engaged gear pairs for the torque transfer of the first gear is again three. 
         [0063]    The double-clutch transmission  1  provides a third gear when the clutch housing  4  engages the outer clutch disc  10  and the double-sided coupling device  83  locks the idler third gear  62  to the lower layshaft  50 . The clutch housing  4  further disengages the inner clutch disc  8 . A torque of the third gear is transmitted sequentially from the crankshaft  2 , the clutch housing  4 , the outer clutch disc  10 , the hollow input shaft  22 , the fixed wheel third gear  25 , the idler third gear  62 , the double-sided coupling device  83 , the lower layshaft  50 , the lower pinion  51 , the output gear wheel  12 , to the output shaft  14 . The number of tooth engagements or engaged gear pairs for the torque transfer of the first gear is also three. 
         [0064]    The double-clutch transmission  1  provides a fourth gear when the clutch housing  4  engages the inner clutch disc  8  and the double-sided coupling device  82  locks the idler fourth gear  63  to the lower layshaft  50 . The clutch housing  4  disengages the outer clutch disc  10  for transmitting the fourth gear. A torque of the fourth gear is transmitted sequentially from the crankshaft  2 , the clutch housing  4 , the inner clutch disc  8 , the solid input shaft  20 , the fixed wheel fourth gear  31 , the idler fourth gear  63 , the double-sided coupling device  82 , the lower layshaft  50 , the lower pinion  51 , the output gear wheel  12 , to the output shaft  14 . The number of tooth engagements or engaged gear pairs for the torque transfer of the first gear is three. 
         [0065]    The double-clutch transmission  1  provides a fifth gear when the clutch housing  4  engages the outer clutch disc  10  and the double-sided coupling device  80  locks the idler fifth gear  64  to the upper layshaft  40 . The clutch housing  4  further disengages the inner clutch disc  8 . A torque of the fifth gear is transmitted sequentially from the crankshaft  2 , the clutch housing  4 , the outer clutch disc  10 , the hollow input shaft  22 , the fixed wheel fifth gear  26 , the idler fifth gear  64 , the double-sided coupling device  80 , the upper layshaft  40 , the upper pinion  41 , the output gear wheel  12 , to the output shaft  14 . The number of tooth engagements or engaged gear pairs for the torque transfer of the first gear is also three. 
         [0066]    The double-clutch transmission  1  provides a sixth gear when the clutch housing  4  engages the inner clutch disc  8  and the single-sided coupling device  81  locks the idler sixth gear  65  to the upper layshaft  40 . The clutch housing  4  disengages the outer clutch disc  10  for transmitting the sixth gear. A torque of the sixth gear is transmitted sequentially from the crankshaft  2 , the clutch housing  4 , the inner clutch disc  10 , the solid input shaft  20 , the fixed wheel sixth gear  32 , the idler sixth gear  65 , the single-sided coupling device  81 , the upper layshaft  40 , the upper pinion  41 , the output gear wheel  12 , to the output shaft  14 . The number of tooth engagements or engaged gear pairs for the torque transfer of the first gear is three. 
         [0067]    The double-clutch transmission  1  provides a seventh gear when the clutch housing  4  engages the outer clutch disc  10  and the double-sided coupling device  80  locks the idler seventh gear  66  to the upper layshaft  40 . The clutch housing  4  further disengages the inner clutch disc  8 . A torque of the seventh gear is transmitted sequentially from the crankshaft  2 , the clutch housing  4 , the outer clutch disc  10 , the hollow input shaft  22 , the fixed wheel seventh gear  27 , the idler seventh gear  66 , the double-sided coupling device  80 , the upper layshaft  40 , the upper pinion  41 , the output gear wheel  12 , to the output shaft  14 . The number of tooth engagements or engaged gear pairs for the torque transfer of the first gear is also three. 
         [0068]    As illustrated above, the double-clutch transmission  1  provides two reverse gears. The vehicle  5  moves with a first reverse gear when the clutch housing  4  engages the outer clutch disc  10  and the double-sided coupling device  84  locks the idler reverse gear  35  to the reverse gear layshaft  38 . The clutch housing  4  also disengages the inner clutch disc  8 . A torque of the first reverse gear is transmitted from the crankshaft  2 , via the clutch housing  4 , via the outer clutch disc  10 , via the hollow input shaft  22 , via the fixed wheel first gear  24 , via the idler first gear  60 , via the idler reverse gear  35 , via the double-sided coupling device  84 , via the reverse gear layshaft  38 , via the reverse pinion  53 , via the output gear wheel  12 , to the output shaft  14 . 
         [0069]    The vehicle  5  moves with a second reverse gear when the clutch housing  4  engages the inner clutch disc  8  and the double-sided coupling device  84  locks the second idler reverse gear  36  to the reverse gear layshaft  38 . The clutch housing  4  also disengages the outer clutch disc  10 . A torque of the second reverse gear is transmitted from the crankshaft  2 , via the clutch housing  4 , via the inner clutch disc  8 , via the solid input shaft  20 , via the fixed wheel fourth gear  31 , via the idler fourth gear  63 , via the second idler reverse gear  36 , via the double-sided coupling device  84 , via the reverse gear layshaft  38 , via the reverse pinion  53 , via the output gear wheel  12 , to the output shaft  14 . 
         [0070]    The above-mentioned nine torque flow paths not only provide viable solutions to generate nine gears of the double-clutch transmission  1 , but also offer possibilities of switching from one gear to the other efficiently. For example, gear jumps from the second gear to the sixth gear is efficiently provided by the double-meshing of the idler second gear  61  and the idler sixth gear  65  via an intermediate gearwheel, namely the fixed wheel second gear  30 . The gear jump from the second gear to the sixth gear does not require stopping the solid input shaft  20 . Furthermore, the double-meshing of the idler second gear  61  and the idler sixth gear  65  avoids the need of providing two separate fixed gearwheels on an input shaft. In other words, less space is required on the solid input shaft  20  because two fixed gearwheels  30 ,  32  are combined into a single one. The double-clutch transmission  1  can thus be made lighter and cheaper by the reduction of one gearwheel. The other double meshing of the idler third gear  62  and the idler fifth gear  64  via the fixed wheel third gear  25  provides similar benefits. 
         [0071]    The double meshing features further provide additional gear changes at high efficiency. Any gear of the first double meshing feature can be switched to another by selecting one of the input shafts  20 ,  22 . For example, gear changing from the sixth gear to the third gear can be achieved by deselecting the solid input shaft  20  and selecting the hollow input shaft  22 . When using the park-lock, the park-lock gearwheel  39  on the upper layshaft  40  can be easily engaged to lock the output shaft  14 , via the upper layshaft  40 , via the upper pinion  51 , via the output gear wheel  12 . 
         [0072]    In providing gear meshing or combing for torque transmission, less number of gear tooth engagement (i.e., gear engagement) is preferred. The less number of gear tooth engagement provides lower noise and more efficient torque transmission. Examples of the less number of gear tooth engagement are found in some of the above-mentioned torque flow paths. The double-clutch transmission  1  enables pre-selection of gears as a function of vehicle acceleration. The pre-selection is also known as pre-synchronisation. The pre-selection causes an idler gearwheel of a next-expected gear to be engaged to its weight-carrying layshaft. The acceleration comprises increase or decrease in speed of the vehicle  5 . 
         [0073]    In a process of acceleration, the wheel speed sensor  94  detects acceleration of rotational speed of the vehicle  5 . The linear speed sensor  96  also sends electrical signals to the transmission control unit  98  indicating that the vehicle  5  is increasing its speed. The vehicle  5  is accelerated from the first gear such that the double-sided coupling device  83  engages the idler first gear  60  to the lower layshaft  50 . The driving torque from the engine  3  is transmitted to the output gearwheel  12  via the clutch housing  4 , via the outer clutch disc  10 , via the hollow input shaft  22 , via the fixed wheel first gear  24 , via the idler first gear  60 , via the double-sided coupling device  83 , via the lower layshaft  50 , via the lower pinion  51 , to the output gearwheel  12 . In the mean time, the double-sided coupling device  82  also engages the idler second gear  61  because the transmission control unit  98  expects the next gear of the acceleration is the second gear. Due to the pre-selection of the second gear, the inner clutch disc  8 , the solid input shaft  20 , the fixed wheel second gear  30 , the idler second gear  61 , and the double-sided coupling device  82  are driven by the lower layshaft  50 . In other words, the solid input shaft  20  is freewheeling. Once the clutch housing  4  switches its connection from the outer clutch disc  10  to the inner clutch disc  8 , the vehicle immediately drives at the second gear. 
         [0074]    When the transmission control unit  98  receives signals from the wheel speed sensor  94  and the linear speed sensor  96  indicating that the vehicle  5  continues the acceleration, the double-sided coupling device  83  detaches the idler first gear  60  from the lower layshaft  50  and subsequently the double-sided coupling device  83  engages the idler third gear  62 . At this moment, the hollow input shaft  22  is freewheeling. As the vehicle continues to accelerate, an idler gearwheel of a next-expected gear is engaged, but receiving no driving torque for the moment. 
         [0075]    In a process of deceleration, the wheel speed sensor  94  detects deceleration of rotational speed of the vehicle  5 . The linear speed sensor  96  also gives electrical signals to the transmission control unit  98  signifying that the vehicle  5  is decreasing its speed. The vehicle  5  is decelerated from the seventh gear such that the double-sided coupling device  80  engages the idler seventh gear  66  to the upper layshaft  40 . The driving torque from the engine  3  is transmitted to the output gearwheel  12  via the clutch housing  4 , via the outer clutch disc  10 , via the hollow input shaft  22 , via the fixed wheel seventh gear  27 , via the idler seventh gear  66 , via the double-sided coupling device  80 , via the upper layshaft  40 , via the upper pinion  41 , to the output gearwheel  12 . In the mean time, the single-sided coupling device  81  also connects the idler sixth gear  65  because the transmission control unit  98  expects the next gear of the deceleration is the sixth gear. Due to the pre-selection of the sixth gear, the inner clutch disc  8 , the solid input shaft  20 , the fixed wheel sixth gear  32 , the idler sixth gear  65 , and the single-sided coupling device  81  are driven by the upper layshaft  40 . In other words, the solid input shaft  20  is freewheeling. Once the clutch housing  4  switches its engagement from the outer clutch disc  10  to the inner clutch disc  8 , the vehicle  5  promptly cruises at the sixth gear. 
         [0076]    When the transmission control unit  98  receives signals from the wheel speed sensor  94  and the linear speed sensor  96  indicating that the vehicle  5  continues the deceleration, the double-sided coupling device  80  detaches the idler seventh gear  66  from the upper layshaft  40  and subsequently the double-sided coupling device  80  engages the idler fifth gear  64 . At this moment, the hollow input shaft  22  is freewheeling. As the vehicle continues to decelerate, an idler gearwheel of a next-expected gear is engaged, but receiving no driving torque for the moment. 
         [0077]    The double clutch transmission  1  also enables the pre-selection of gears as a function of engine speed. The vehicle speed sensor  90  that is mounted on the crankshaft  2  measures the engine speed. The transmission control unit  98  receives electrical signals from the vehicle speed sensor  90  for deciding speed of the engine  3 . When the engine  3  runs at 4000 RPM (round per minute), the vehicle  5  drives at the third gear such that the double-sided coupling device  83  engages the idler third gear  62  to the lower layshaft  50 . Once the vehicle speed sensor  90  detects that the rotational speed of the engine  3  increases, the double-sided coupling device  82  engages the idler fourth gear  63  to the lower layshaft  50  such that the solid input shaft  20  and the inner clutch disc  8  are freewheeling. In other words, the escalation of engine speed causes the transmission control unit  98  to preselect the fourth gear. 
         [0078]    As a driver continue to press an acceleration pedal down, the clutch housing  4  disconnects the outer clutch disc  10  and locks onto the inner clutch disc  8 . Thus, the vehicle  5  immediately runs at the fourth gear because the output gearwheel  12  receives the driving torque from the engine  3  via the idler fourth gear  63 . The idler third gear  62 , the fixed wheel third gear  25  and the hollow input shaft  22  are freewheeling, also driven by the lower layshaft  50 . Shortly after, the double-sided coupling device  80  locks the idler fifth gear  64  to the upper layshaft  40 . The upper pinion  40 , the upper layshaft  40 , the idler fifth gear  64 , the double-sided coupling device  80 , the fixed wheel fifth gear  26  and the hollow input shaft  22  then follow the rotation of the output gearwheel  12  for freewheeling. 
         [0079]    The clutch housing  4  disengages the inner clutch disc  8  and engages the outer clutch disc  10  when the engine speed keeps increasing. Consequently, the vehicle  5  runs at the fifth gear. In the mean time, the double-sided coupling device  82  detaches from the idler fourth gear  63  and the single-sided coupling device  81  attaches the idler sixth gear  65  to the upper layshaft  40 . Accordingly, the sixth gear is preselected when the engine speed increases. 
         [0080]    Pre-selection of gear also applies when the engine speed decreases. When the vehicle  5  drives at the fifth gear, the double-sided coupling device  82  connects the idler fourth gear  63  to the lower layshaft  50  although the driving torque is transferred from the engine  3  to the idler fifth gear  64  and the double-sided coupling device  80  for driving. The pre-selection of fourth gear is controlled by the transmission control unit  98  that predicts the next gear of speed to be the fourth gear based on knowledge of lowering engine speed at the fifth gear. 
         [0081]    As the driver moves his foot away from the acceleration pedal, the engine speed further reduces. The further reduction of engine speed is sensed by the vehicle speed sensor  90  such that the transmission control unit  98  brings the double-sided coupling device  80  away from the idler fifth gear  64 . Shortly afterwards, the double-sided coupling device  82  engages the idler fourth gear  63  to the lower layshaft  50  for driving at the fourth gear. Subsequently, the double-sided coupling device  83  locks the idler third gear  62  to the lower layshaft  50  for preselecting the third gear. Further pre-selections of lower gears follow similar steps that are described for engine speed reduction from the fifth gear to the fourth gear. 
         [0082]    The double-clutch transmission  1  further enables the pre-selection of gear as a combined function of vehicle acceleration and engine speed. A pre-selection of a lower gear is performed when the transmission control unit  98  identifies vehicle&#39;s deceleration and reduction of engine speed. A pre-selection of a higher gear is carried out when the transmission control unit  98  confirms vehicle&#39;s acceleration and increase of engine speed. These schemes are programmed in the transmission control unit  98 . 
         [0083]    In a case of pre-selection of a lower speed, the vehicle  5  firstly drives at the fifth gear. The diving torque is transmitted from the engine  3  to the output gearwheel  12  via the idler fifth gear  64 . The vehicle&#39;s acceleration is monitored by the transmission control unit  98  that receives electrical signals from the linear speed sensor  96  and the wheel speed sensor  94 . The engine speed is also checked by the transmission control unit  98  by taking electrical signals from the vehicle speed sensor  90 . 
         [0084]    Once the transmission control unit  98  determines that the vehicle  5  is decelerating and the engine  3  is reducing its speed, the fourth gear is pre-selected such that the double-sided coupling device  82  connects the idler fourth gear  63  to the lower layshaft  50 . At this moment, the vehicle  5  still drives at the fifth gear and the outer clutch disc  8  is attached to clutch housing  4  for transmitting the driving torque from the engine  3  to the idler fifth gear  64  via the hollow input shaft  22 . However, the inner clutch disc  10  is detached from the clutch housing  4 . 
         [0085]    When a trend of vehicle&#39;s deceleration and the engine&#39;s reduction in speed persists, the clutch housing  4  switches its connection from the outer clutch disc  10  to the inner clutch disc  8 . Immediately, the vehicle  5  moves at the fourth gear. Afterwards, the double-sided coupling device  80  moves away from the idler fifth gear  64  whilst the double-sided coupling device  83  locks the idler third gear  62  to the lower layshaft  51 . The driving torque is transferred from the crankshaft  2  to the idler fourth gear  63  via the solid input shaft  20 , whilst the hollow input shaft  22  is freewheeling. 
         [0086]    As the vehicle  5  continues to decelerate and the engine  3  resists the reduction in speed, the double-clutch transmission  1  shifts its gear from the fourth gear to the third gear. The pre-selection of gear also becomes the second gear when the vehicle  5  cruises at the third gear. The shifting to the third gear and the pre-selection of the second gear follow similar fashion that are descried above for the shifting to the fourth gear and the pre-selection of the third gear. 
         [0087]    In a case of pre-selection of a higher speed, the vehicle  5  firstly drives at the fifth gear. The driving torque is transmitted from the engine  3  to the output gearwheel  12  via the idler fifth gear  64 . Once the transmission control unit  98  notices that the vehicle  5  is accelerating and the engine  3  is increasing its speed, the sixth gear is pre-selected that the single-sided coupling device  81  connects the idler sixth gear  65  to the upper layshaft  40 . At this moment, the vehicle  5  still drives at the fifth gear and the outer clutch disc  10  is attached to clutch housing  4  for transmitting the driving torque from the engine  3  to the idler fifth gear  64  via the hollow input shaft  22 . However, the inner clutch disc  8  is detached from the clutch housing  4 . 
         [0088]    When a trend of vehicle&#39;s acceleration and the engine&#39;s increase in speed persist, the clutch housing  4  switches its connection from the outer clutch disc  10  to the inner clutch disc  8 . Immediately, the vehicle  5  moves at the sixth gear when the singe-sided coupling device  81  locks the idler sixth gear  65  to the upper layshaft  41 . Afterwards, the double-sided coupling device  80  moves away from the idler fifth gear  64 . The driving torque is transferred from the crankshaft  2  to the idler sixth gear  65  via the solid input shaft  20 , whilst the hollow input shaft  22  is freewheeling. The seventh gear is preselected that the double-sided coupling device  80  locks the idler seventh gear  66  to the upper layshaft  40 . 
         [0089]    As the vehicle  5  continues to accelerate and the engine  3  resists the increase in speed, the double-clutch transmission  1  shifts its gear from the sixth gear to the seventh gear. Further pre-selection of a higher gear no longer exists. 
         [0090]    The double-clutch transmission  1  provides gear pre-selection as a functional of vehicle acceleration, of engine speed or in combination of both. When pre-selection is a function of vehicle acceleration, the double-clutch transmission  1  engages a gear that is high than the currently using gear if the vehicle  5  accelerates. The double-clutch transmission  1  selects a gear that is lower than the currently using gear if the vehicle  5  decelerates. By adding vehicle acceleration to pre-selection strategy, a precise preselecting point is determined for enhance performance and riving experience of the vehicle  5 . 
         [0091]    When pre-selection is a function of engine speed, the double-clutch transmission  1  engages a gear that is high than a currently using gear if the engine  3  runs faster than a predetermined engine speed. The double-clutch transmission  1  selects a gear that is lower than the currently using gear if the engine  3  runs slower than the predetermined engine speed. By adding engine speed to pre-selection strategy, a precise preselecting point is determined for enhance performance and riving experience of the vehicle  5 . 
         [0092]    When pre-selection is a function of both the vehicle acceleration and the engine speed, the double-clutch transmission  1  engages a gear that is high than a currently using gear if the vehicle  5  accelerates and the engine  3  runs faster than a predetermined engine speed. The double-clutch transmission  1  selects a gear that is lower than the currently using gear if the vehicle  5  decelerates and the engine  3  runs slower than the predetermined engine speed. 
         [0093]    The pre-selection function that depends on both the engine speed and the vehicle acceleration is used in different driving modes. In a normal or an economy-driving mode, the transmission control unit  98  selects a neutral gear to be a preselected gear most of the time for high gearbox efficiency. In a manual mode where the driver determines a present gear, however, the transmission control unit  98  will preselect a gear that is higher than the present gear most of the time because up-shift of gear is normally slower than downshift of gear. Since the pre-selection function depends on both the engine speed and the vehicle acceleration, it is easy to recalibrate the transmission control unit  98  for the various driving modes. 
         [0094]    In the scheme, that the pre-selection of gear depending on both the vehicle acceleration and the engine speed, the transmission control unit  98  eliminates potential confusions on preselecting a high or lower gear when the vehicle  5  decelerates but the engine  3  escalates in speed. Such situation occurs when the vehicle  5  climbs a slope. This scheme thus gives more accurate predictions for preselecting next gear. 
         [0095]    The pre-selections of gear enable the double clutch transmission  1  to have lower fuel consumption. The pre-selection reduces chances of abrupt changes of rotation speeds in gearwheels such that momentums of the gearwheels are preserved during gearshifts. The lower fuel consumption facilitates less emission of pollution when the engine  3  uses fossil fuel. 
         [0096]    The pre-selections of gear reduce response time when changing between different gears. With the pre-selection, passengers of the vehicle  5  experience less sudden breaks during gearshifts. The vehicle  5  that has the gear pre-selection functions become sporty, but has less discomfort in speeding. 
         [0097]    Up-shifting synchronising speed will also be lowered if the pre-selection is performed on a lower vehicle speed. In a synchronising process, synchronisation energy and temperature rise of synchronising parts change depending on a speed differences between synchronising parts (e.g. gearwheel, lay shaft) and a duration of the synchronising process. The synchronisation energy and the temperature rise will be lower if the synchronising process is performed at the lower vehicle speed. The pre-selection function at the lower vehicle speed minimises an amount of the synchronisation energy and the temperature rise. 
         [0098]    The pre-selection of gear improves the vehicle&#39;s performance on noise, vibration, and harshness (NVH). Since an idler gearwheel of a next gear is pre-selected, less number of parts require locking during an actual engagement step of the next gear. The vehicle  5  with the double-clutch transmission  1  thus experiences reduced noise, vibration and harshness for driving efficiency and comfort. Life span of the double-clutch transmission  1  is extended with lower amount of maintenance required. 
         [0099]    While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.