Abstract:
Transmissions in which the mechanical gear shift arrangements are replaced by electro-hydraulic operated shift mechanisms that have to be able to be neutralised positively to ensure a proper operation. An arrangement and method are provided to determine the position of the shift rail so a shift can be made only if the conditions are right. To prevent engagement of two shift members at the same time and consequent damage in case of electronic failure, mechanical safety features such as detents are included.

Description:
TECHNICAL FIELD  
       [0001]     The present disclosure relates to the field of automated manual transmissions. More specifically but not exclusively the present invention relates to an automated manual transmission and a method of controlling at least part of the gearshifts of an automated manual transmission.  
       BACKGROUND  
       [0002]     Conventional manual transmissions use gearshift systems whereby the driver manually selects the desired gear by shifting a gear stick into a certain position in the gearbox. The gear stick is in direct connection with an internal shift mechanism usually comprising some form of shift rails, shift forks and shift collars. One disadvantage of such a system is that the gearbox and the gear stick have to be arranged in such a configuration that all components can easily be interconnected by a mechanical linkage. To allow for a more flexible installation, systems have been developed wherein the mechanical linkage has been replaced by a system wherein electro-hydraulic solenoids direct oil to and from pistons mounted at the end of the shift rails to control the position of the shift rail. A well known problem associated with such a system is the locating and securing of this shift mechanism in a neutral position. The positive neutralisation of a mechanism is essential to prevent erroneous gear engagement and multiple gear sets being engaged simultaneously. A failure to do so could result in uncontrolled machine behaviour and severe mechanical damage. Previous arrangements, such as for example the 5-speed Power Synchro gearbox of Turner Powertrain, Wolverhampton, UK, utilise a multiple piston set-up whereby a set of compound pistons operate on hydraulic principles to neutralise the shift rail. This arrangement has certain disadvantages such as the complexity of the components and machining procedures and hence cost.  
         [0003]     It is an aim of the present invention to solve one or more of the problems set forth above.  
       SUMMARY OF THE INVENTION  
       [0004]     It is an object of the present disclosure to provide a gearshift arrangement with a first and a second shift member as part of respectively a first and second mechanism. The arrangement further has a sensing arrangement adapted to monitor the position of the first shift member relative to a neutral position and an actuating arrangement operable to position the first shift member into the neutral position based on at least one signal from the sensing arrangement. A mechanical arrangement is included and is adapted to prevent movement of the second shift member if the first shift member is not in a neutral position.  
         [0005]     A second object of the disclosure is to provide a method of operating a gearshift arrangement having a first and a second shift member as part of respectively a first and second shift mechanism. The method includes the steps of electronically determining the position to a neutral position of the first shift member, positioning the first shift member into a neutral position based on at least one determination from the previous step and mechanically preventing movement of the second shift member if the first shift member is not in the neutral position. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a schematic vertical section through a gearbox according to the present invention;  
         [0007]      FIG. 2  is a schematic cross sectional view of a detent mechanism which may be used in the gearbox of  FIG. 1 ; and  
         [0008]      FIG. 3   a,    3   b  and  3   c  are schematic views of a shift fork as used in the gearbox of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION  
       [0009]     Referring to  FIGS. 1 and 2 , gearbox  10  has a first shift mechanism  11  for the engagement of first and second gear and a second shift mechanism  111  for the engagement of third and fourth gear. More gears and/or gear mechanisms may be added. For simplicity, as both first shift mechanism  11  and second shift mechanism  111  are substantially similar, only shift mechanism  11  will be described in detail. Like numbers in first shift mechanism  11  and second shift mechanism  111  indicate like structures.  
         [0010]     The first shift mechanism includes three shift members, namely a shift rail  12 , a shift collar  16  and a shift fork  14 . Shift fork  14  is rigidly connected to shift rail  12 , but is in a floating engagement with shift collar  16 .  FIGS. 3   a - 3   c  shows shift fork  14  with two prongs  17  that engage with a counterpart such as circumferential groove  19  on shift collar  16 . Although in this example shift fork  14  is of the two prong type and engages shift collar  16  via groove  19  in a floating fashion, the principle is applicable to other types of shift fork and collar arrangements. Shift collar  16  is for this disclosure considered to include the actual gear engagement clutch, for example a synchroniser clutch.  
         [0011]     Connected to opposite ends of shift rail  12  are single acting pistons  18  and  20  ( 20  is not shown,  120  is shown instead) as part of an actuating arrangement  21 . However one dual acting piston (not shown) may be used instead of two single acting pistons  18  and  20  if preferred. Pistons  18  and  20  may be pressurised by a fluid such as air or like in this case oil, the oil flow being generated by a pump (not shown) and directed to and from pistons  18  and  20  by solenoid valves  22  and  24  respectively. Alternatively, shift rail  12  may be actuated by an electronic solenoid (not shown) rather than an electro-hydraulic system. Other electro-hydraulic solenoid arrangements may also be possible, whereby one or multiple electro-hydraulic solenoids may operate together with directional valves or mechanical linkages to simplify the system or reduce the number of components or cost.  
         [0012]     Specifically now referring to  FIG. 2 , interlocking device  30  is in this example a kind of detent arrangement with a series of balls  32   a,    32   b,    32   c  and  32   d,  preferably made of metal, of which balls  32   a  and  32   d  at both extremes of the series each may engage with a recesses  33  and  133  in shift rails  12  and  112 . Recesses  33  and  133  in shift rails  12  and  112  are located on the rails in a position corresponding to neutral positions when the recess is lined up with the corresponding balls  32   a  or  32   d.  A neutral position for shift rails  12  and  122  is defined as the position in which shift collars  16  and  116  are in a position where no gears are engaged or being engaged. The overall length of the series of balls  32   a - d  is greater than the distance between the two nearmost outer surfaces of shift rails  12  and  112 . This prevents in normal operation the engagement of a multiple of any of 1 st , 2 nd , 3 rd  and 4 th  gears. A different number of balls such as  32   a - d  or different arrangements having cylindrical or other shapes or non-metal components may be used.  
         [0013]     Shift rail  12  further has a series of adjacent recesses  34   a,    34   b  and  34   c,  substantially similar to shift rail  112  with recesses  134   a,    134   b  and  134   c.  This is the same principle for both shift rails, so for simplicity only shift rails  12  with recesses  34   a - c  will be discussed in the following paragraph. Recesses  34   a - c  may engage with a detent mechanism such as ball  37  and spring  38  to define three discrete positions as part of a mechanical arrangement  36 . The first position may correspond to shift mechanism  11  engaging first gear. The second position may correspond to shift mechanism  11  being in a neutral position, whilst the third position may correspond to shift mechanism  11  engaging second gear. The biased detent aids in locating shift rails  12  into any of the three positions and keeping it in that position. Ball  37  is preferably made of metal, but other materials as well as other shapes may be used.  FIG. 1  shows a variation  35  of this detent mechanism, whereby the principle is the same, but the position of the mechanism is different.  
         [0014]     Furthermore there are sensing arrangements  39  and  139 . Again for simplicity only one such arrangement is discussed here, because the principles and components are substantially similar for both shift mechanisms  11  and  111 . Sensor  40  may be fitted to a location in gearbox  10 , or for ease of servicing external whilst at least partially protruding through a wall of gearbox  10 . The sensing part is preferably located in a position adjacent to shift fork  14 , because sensor  40  is responsive to activator  42  which is either fitted to or an integral part of shift fork  14 . One possible type of sensor and activator arrangement is a non-contact linear position sensor together with a ferrous activator. The sensor may for example be a blade sensor as manufactured by Gill Technology, Lymington, Hampshire, UK. Sensor  40  is preferably a proportional and adjustable sensor to give a wider range of detection and to enable a calibration procedure. However, other suitable sensing arrangements may be used, for example contact sensors. If some type of activator is required it may also be fitted in a different position, for example on the shift rail or the shift collar. As shift rail  12 , shift fork  14  and shift collar  16  all have fixed relative positions to one another, it is not significant which component is used for activation of the sensor, because in normal operation the positions of all other components may be determined once one has been sensed.  
         [0015]     The signal generated by sensor  40  is sent preferably to an electronic control unit (ECU)  44 . ECU  44  may be programmed to monitor and control a wide variety of transmission and other functions, but is able to process the signal sent from sensor  40 . ECU  44  further may receive an input from for example a vehicle driver and may process the signals to than send a signal to control solenoid valves  22  and  24 . An alternative may be to have a system without ECU  44 , wherein solenoid valves  22  and  24  are activated directly or indirectly by signals from sensor  40  or a multiplicity of similar sensors. ECU  44  may be able to control both shift mechanisms  11  and  111 .  
       INDUSTRIAL APPLICABILITY  
       [0016]     During normal operation gearbox  10  and hence shift mechanisms  11  and  111  may be in a neutral position. The vehicle driver selects a desired gear, which is signaled to ECU  44 . ECU  44  further receives signals from sensors  40  and  140 . If all parameters are acceptable ECU  44  may activate one of solenoid valves  22 ,  24 ,  122  and  124  to direct a flow of oil from a pump (not shown) onto one of pistons  18 ,  20 ,  118  and  120  to shift one of shift mechanisms  11  and  111 . The oil pressure acting on the piston may during a shift be varied by for example the solenoid valve to give smooth gear engagement and disengagement.  
         [0017]     For example, the vehicle driver wishes to engage first gear from neutral. Via an input device his selection is signalled to ECU  44 . ECU  44  has also detected the neutral positions of shift mechanisms  11  and  111  via sensors  40  and  140 . If all conditions are met, ECU  44  sends a signal to solenoid valve  24  to direct oil from a pump (not shown) to piston  20  and a signal to solenoid valve  22  to create a return connection for the oil displaced by piston  18 . The oil acting on piston  20  moves shift rail  12  and hence shift collar  16  to a position wherein shift collar  16  engages first gear. Once the gearshift is completed both solenoid valves  22  and  24  open up the oil connection from pistons  18  and  20  to a return line, so all pistons are depressurised. During this shift the oil pressure acting on piston  18  has to be high enough to overcome the resistance of the actual gear engagement and to lift ball  37  out of recess  34   b.  Once first gear engagement is completed or near completion, ball  37  engages with recess  34   c.  Because shift rail  12  is in an out of neutral position, interlocking device  30  prevents shift rail  112  from movement as ball  32   d  is now firmly engaged with recess  133 .  
         [0018]     If the driver decides to shift to a gear that can only be engaged by shift mechanism  112 , for example 3 rd  gear, the following actions will take place. Before shift mechanism  112  can be activated, shift mechanism  12  has to be put into the neutral position. Under normal operating conditions, ECU  44  will not activate shift mechanism  112  before it receives a signal from sensor  40  that shift mechanism  12  is in the neutral position. However, in case that an electronic failure or error happens and ECU  44  attempts to engage shift mechanisms  12  and  112  simultaneously, interlocking mechanism  30  prevents this from happening. This mechanical interlocking feature is extremely important to avoid serious damage to gearbox  10 . To neutralise shift mechanism  12 , ECU  44  signals solenoid valve  22  to direct oil onto piston  18  and solenoid valve  24  to create a return connection for the oil displaced by piston  20 . Shift rail  12  will then move towards the neutral position. Activator  42  is continuously sensed by sensor  40  which signals to ECU  44  a signal corresponding to the position of  42  and hence shift mechanism  11 . Once shift rail  12  is close to reaching the neutral position, ECU  44  may signal solenoid valve  22  to reduce the flow of oil to piston  18  to reduce the speed of shift rail  12  and so prevent an overshoot condition wherein shift rail  12  passes the neutral position. When shift rail  12  is substantially in the neutral condition, ECU  44  may signal on or both solenoid valve  22  and  24  to stop all flow to and from pistons  18  and  20 . In approximately the same period detent mechanism  36  engages with recess  34   b  to aid shift rail  12  to settle in the neutral position and to give positive retention of shift rail  12  in that neutral position.  
         [0019]     Because of both shift rails  12  and  112  now being in the neutral position, neither of shift rails  12  and  112  are prevented from movement by interlocking device  30 .  
         [0020]     The following step is where shift mechanism  112  has to engage 3 rd  gear. ECU  44  receives or has received a signal from sensor  40  about the neutral position of shift rail  12 . ECU  44  signals solenoid valve  124  to direct oil onto piston  120  and solenoid valve  122  to open a return connection for the oil displaced by piston  118 . The remainder of the shift is substantially similar as the engagement of first gear as described in paragraph  14  onwards. Although some of the steps as described have to be performed in a certain order, this is not essential for all steps. Also some of the steps may at least partially overlap.  1