The invention relates to a method for operating a transmission system for a vehicle. The method further relates to a transmission system for a vehicle.

BACKGROUND TO THE INVENTION

There is a trend in the automotive industry towards more efficient, more comfortable and cleaner vehicles. The control strategy for shifting plays an important role for the transmission of a vehicle such as an electric vehicle, hybrid vehicle or combustion engine vehicle. The handling of the gear shifting mechanism greatly influences both the drivability, perceived comfort and the efficiency of the vehicle.

Transmission systems, such as automatic transmission systems for vehicles generally have an input arranged for connection to a drive source, such as an internal combustion engine, and an output arranged for connection to a load, such as a drive train of the vehicle. For a vehicle it is desired to provide a transmission with a limited number of gear ratios between the drive source(s) and the load, e.g. obtained by a limited number of switchable speed transforming gears, so as to have the drive source(s) function during operation in a working area where a more advantageous energy consumption is achieved. One type of transmission system includes a transmission comprising a first gear input shaft, a first gear output shaft connected to the output, and a first speed transforming gear between the first gear input shaft and the first gear output shaft, and a second gear input shaft, a second gear output shaft connected to the output, and a second speed transforming gear between the second gear input shaft and the second gear output shaft. Hence, different gears, such as first gear, second gear, third gear, etc. can be associated with the first gear input shaft or the second gear input shaft, and can be individually selected by the transmission system.

Gear synchronization in a vehicle transmission (e.g. friction transmission system) can be performed by a synchronizer mechanism. Drag torque depends on many variables which may not easily be measurable or which may be subject to a high degree of variation under standard operation conditions. This may significantly influence the engagement of synchronizers in a vehicle transmission. During transient engagement the drag torque may vary nonlinear ly and/or unexpectedly, which may cause the engagement mechanism to fail and/or the synchronization process to fail, which in turn may cause damage to friction surfaces of the synchronizer. Furthermore, variables such as speed and operating temperature of the transmission may also play an important role for the drag. The temperature variation influences the viscosity of the transmission fluid which can have considerable effect on the drag torque. The drag torque can be significantly higher at low temperature, resisting the synchronization process and/or increasing the likelihood of failure of the synchronizer mechanism to engage correctly. The engagement of the mechanism can be significantly extended at low temperatures, which may have the potential to lead to ring overheating and persistent damage to friction surfaces.

Drag torque typically results from both slipping clutch speed and absolute gear speed. During the synchronizer engagement process torques are applied to the mechanism, wherein a cone clutch torque is used to match speeds between the target gear and shaft, and an indexing chamfer torque is used to align and interlock the mechanism after speeds have been matched. Typically, the process is resisted by the drag torque when the target gear has to be accelerated to a higher speed, wherein both drag associated with gear and clutch slip speeds will resist engagement.

In some situations, a high drag torque may even desynchronize the synchronizer mechanism or even in the long term lead to permanent damage of critical components of the synchronizer. There is a need to increase reliability during the engagement process when downshifting from a higher gear to a lower gear.

SUMMARY OF THE INVENTION

It is an object of the invention to provide for a method and a system that obviates at least one of the above mentioned drawbacks. More in general it is an object to provide an improved, or at least alternative, transmission system and/or a method for downshifting a transmission.

Alternatively or additionally, it is an object of the invention to improve the shifting strategy of a transmission of a vehicle.

Alternatively or additionally, it is an object of the invention to increase reliability during an engagement process when downshifting from a higher gear to a lower gear.

Alternatively or additionally, it is an object of the invention to reduce wear and tear when performing a downshifting operation in a transmission.

Alternatively or additionally, it is an object of the invention to improve the transmission system of a vehicle and/or a vehicle comprising said transmission system.

Thereto, the invention provides for a method for downshifting a transmission from a higher gear to a lower gear. The transmission comprises an input shaft, an output shaft, a first transmission path relating to a higher gear of the transmission and a second transmission path relating to a lower gear of the transmission. The first and second transmission paths are arranged in parallel with respect to each other between the input shaft and the output shaft. The first transmission path includes a first gear reduction and a first coupling member, including a force closed coupling. The second transmission path includes a second gear reduction and a second coupling member, including a form closed coupling. The first coupling member is engaged (or closed) and the second coupling member is disengaged when the transmission is operating at the higher gear. The downshifting includes synchronizing an output and an input of the second coupling member by at least partially disengaging the first coupling member resulting in an increasing rotation speed of the input shaft, and (subsequently) engaging the second coupling member when the output and input of the second coupling member are, at least sufficiently, synchronized.

Advantageously, a pre- selection of the second coupling member is not required during the shifting method. It is possible to synchronize torque paths by means of the first coupling member instead of performing a pre-selection by means of the second coupling member embodied as a synchronizer. Furthermore, in this way, the second coupling member (e.g. synchronizer) may no longer require a dual cone. Alternatively or additionally, the second coupling member can be smaller in diameter. This may advantageously render the transmission more simple and cost effective. By employing the advantageous shift strategy method, the cost of the transmission may also be reduced (e.g. use of a single cone synchronizer in the transmission system). Also the reliability of the shifting method can be enhanced. Moreover, wear and tear when performing a downshifting operation in a transmission can be reduced.

Optionally, at least partially disengaging the first coupling member resulting in an increasing rotation speed of the input shaft, involves slipping of the first coupling member. The resulting increased speed of the input shaft can be the result of transmission flaring or a shift flare. As a result of at least partially disengaging the first coupling member, the coupling member can be operated in a slipping fashion when downshifting from a higher gear of the transmission to a lower gear of the transmission. Advantageously, in this way, it is possible to switch between the higher gear to the lower gear (i.e. downshifting) without interruption of the torque transfer from the input shaft to the output shaft or vice versa, e.g. from the drive to the load or vice versa. Additionally, as a result of operating the first coupling member in a slipping fashion, shocks involved with changing gears can be reduced or prevented in an advantageous manner during downshifting.

Optionally, the first coupling member is arranged between the input shaft and the first gear reduction. Optionally, the first coupling member includes a force closed friction coupling. In an example, the first coupling member may be a friction clutch or a brake which may be operated in a slipping manner.

Optionally, the second coupling member is arranged between the second gear reduction and the output shaft. Advantageously, the second coupling member can include a form closed coupling such as a dog clutch and/or keyed coupling.

It is appreciated that a gear reduction may form an accelerating or decelerating gear reduction from its input to its output (cf. up/down). Herein the term gear reduction may be understood as a speed transforming gear which is used to denote a combination, e.g. a pair, of gear wheels transforming a rotational speed at a respective input shaft into a (lower, equal or higher) rotational speed at a respective output shaft. The transmission system allows the vehicle to be operated in different gears, such as reverse gear, first gear, second gear, third gear, fourth gear, fifth gear, etc. Each gear reduction or speed transforming gear is associated with one or more transmission gears. Herein a transmission gear denotes a combination, e.g. pair, of gear wheels causing the transmission to operate in a predetermined gear. E.g. a first transmission gear causes the transmission to operate in first gear. It will be appreciated that it is possible that different transmission gears share one or more gear wheels.

When the transmission is operating at the higher gear, wherein the first coupling member is engaged and the second coupling member is disengaged, the input shaft can have a rotation speed substantially corresponding to the first input rotation speed.

The output and input of the second coupling member may be sufficiently synchronized for example at a speed difference chosen in the range of 0-200 rpm, 0- 100 rpm, 0-50 rpm, 0-20 rpm or 0-10 rpm. Other relative differences may also be used, such as a speed difference of 0 rpm, or such as for example a relative speed difference between the output and the input of the second coupling member chosen in the range of 0-20%, 0-10%, 0-5%, 0-3% or 0-1%.

When the transmission is operating in the higher gear (e.g. third gear) of the transmission, the second coupling member is disengaged and the first coupling member is engaged. Hence, the first transmission path will be coupled to the output shaft 4. However, the rotational speed at the output of the second coupling member may not correspond to the rotational speed at the input of the second coupling member, requiring synchronization before the second coupling member cab be engaged. When switching to the lower gear (e.g. second gear) of the transmission, the first coupling member is at least partially disengaged, preferably allowing slip, such that the input and output of the second coupling member can become synchronized. As a result of the at least partial disengagement of the first coupling member, the rotational speed at the input of the second coupling member is allowed to change. In this way, the speed difference between the input of the second coupling member and the output of the second coupling member can be reduced (e.g. until it becomes zero). When the speed difference between the output and the input becomes zero (or close to zero), the second coupling member can be sufficiently synchronized so that it can be (subsequently) engaged. In an example, a gear reduction is formed by a planetary gear set comprising at least three rotational members, wherein a first rotational member is connected to an input of the gear reduction and a second rotational member is connected to an output of the gear reduction.

Optionally, the second transmission path further includes a third coupling member between the input shaft and the second gear reduction. The downshifting can further include engaging the third coupling member.

Optionally, the second coupling member includes a synchronizer.

A synchronizer may comprise a plurality of elements. In an example, a synchronizer comprises two elements, namely a friction element arranged for synchronizing torque paths and a dog clutch arranged for engaging torque paths.

Optionally, the second coupling member includes, or is, a dog clutch.

Optionally, the method further includes determining an operating temperature of the transmission, and/or determining the drag at the third coupling member, and carrying out an alternative downshifting method when the temperature is above a predetermined temperature threshold and/or when the drag is below a predetermined drag threshold.

The first coupling member and/or the second coupling member can be controlled by a controller of the transmission system utilizing measurements related to temperature and/or clutch drag. As indicated above, a synchronizer may comprise a friction element arranged for synchronizing torque paths and a dog clutch arranged for engaging torque paths. Advantageously, in an example in which the second coupling member is embodied as a synchronizer, a dog clutch of the synchronizer is used when shifting at lower temperatures (and/or higher drag), wherein, optionally, when shifting at higher temperatures (and/or lower drag), both the friction element and the dog clutch of the synchronizer are used.

Optionally, in case the temperature is above the predetermined temperature threshold and/or when the drag is below the predetermined drag threshold, the downshifting is carried out by performing the steps of: with the first coupling member (fully) engaged synchronizing the output and the input of the second coupling member; engaging the second coupling member; at least partially disengaging the first coupling member; and engaging the third coupling member when an output and input of the third coupling member are sufficiently

synchronized. Optionally, the steps are carried out consecutively.

Optionally, the output and the input of the second coupling member are synchronized with the first coupling member engaged, using the synchronizer of the second coupling member.

Advantageously, the second coupling member can comprise a dog clutch.

Optionally, determining of the operating temperature of the transmission and/or the drag at the third coupling member is based on a model.

For example, the operating temperature and/or drag at the third coupling member may be estimated calculated based on other parameters using a model. The model may be a computational model comprising one or more input parameters.

Optionally, determining of the operating temperature of the transmission and/or the drag at the third coupling member is based on

measurements.

The measurements can be carried out directly, wherein one or more sensors are used. Additionally or alternatively, the measurements may be carried out indirectly for determining the operating temperature of the transmission and or the drag at the third coupling member. In case of an indirect measurements, the quantities may be calculated based on other measurements. For example, the drag at the third coupling member may be calculated based on at least the operating temperature of the transmission. Other parameters may also be used for calculating the drag at the third coupling member.

Optionally, the temperature threshold is between -30 °C and 100 °C, preferably between -20 °C and 60 °C, more preferably between -10 °C and 30 °C.

Typically, the resulting drag at the third coupling member depends on the temperature. Particularly, at lower temperatures, for example when the transmission is not yet operating at normal operating temperatures, the drag at the third coupling member is higher. A higher drag may cause detrimental effects on synchronization during conventional shifting.

According to a further aspect, is provided a transmission system for a vehicle. The transmission system includes an input shaft, an output shaft, a first transmission path relating to a higher gear of the transmission and a second transmission path relating to a lower gear of the transmission. The first and second transmission paths are arranged in parallel with respect to each other between the input shaft and the output shaft. The first transmission path includes a first gear reduction and a first coupling member, including a force closed coupling. The second transmission path includes a second gear reduction and a second coupling member, including a form closed coupling. The first coupling member is engaged and the second coupling member is disengaged when the transmission is set for operating at the higher gear. For downshifting, a controller of the transmission system is arranged for synchronizing an output and an input of the second coupling member by at least partially disengaging the first coupling member resulting in an increasing rotation speed of the input shaft, and engaging the second coupling member when the output and input of the second coupling member are, at least sufficiently, synchronized.

Optionally, engaging the second coupling member when the output and input of the second coupling member are synchronized is performed subsequently after at least partially disengaging the first coupling member resulting in an increasing rotation speed of the input shaft.

Optionally, the first coupling member is arranged between the input shaft and the first gear reduction. Optionally, the first coupling member includes a force closed friction coupling.

Optionally, the second coupling member is arranged between the second gear reduction and the output shaft. Advantageously, the second coupling member can include a form closed coupling such as a dog clutch and/or keyed coupling.

The output and input of the second coupling member may be sufficiently synchronized for example at a speed difference of smaller than 200 rpm, 100 rpm or 50 rpm. Other relative differences may also be used, such as for example a relative difference between the output and the input of the second coupling member of smaller than 20%, 10%, 5% or 2%. Other ranges may also be employed.

In case the first coupling member is at least partially disengaged (e.g. engaged in a slipping manner), a speed difference between the input and the output of the second coupling member can change, which may allow

synchronization. Optionally, the second transmission path further includes a third coupling member between the input shaft and the second gear reduction.

Optionally, the first coupling member is embodied as planetary gear set with a friction member. The friction member may comprise a friction brake.

Optionally, an output of the first and third coupling members is connected via a fourth coupling member. Optionally, the fourth coupling member comprises a form closed element and/or a force closed element (e.g. synchronizer and dog clutch).

Optionally, the second transmission path is free from a further coupling member between the input shaft and the second gear reduction. For example, the third coupling member may not be required and therefore may be omitted from the transmission system. In this way, the complexity of the system may be reduced.

Optionally, the second coupling member includes, or is, a synchronizer. Optionally, the second coupling member includes, or is, a dog clutch. Optionally, the controller is arranged for determining an operating temperature of the transmission, and/or determining the drag at the third coupling member, and carrying out an alternative downshifting method when the temperature is above a predetermined temperature threshold and/or when the drag is below a predetermined drag threshold.

The shifting strategy can be changed/selected on the basis of the operating temperature of the transmission. At lower temperatures (e.g. <50 °C) the drag losses tend to be higher, possibly causing synchronization problems for the second coupling member, when downshifting from the higher gear to the lower gear of the transmission. Hence, an operating temperature of the transmission can provide a measure for possible drag losses which may lead to synchronization problems. For example, if the transmission system includes a third coupling member, alternatively or additionally, the shifting strategy can be selected based on the drag at the third coupling member. It is appreciated that temperature and/or drag may be measured or estimated. Also other system parameters or measured quantities can be employed relating to the temperature or drag.

Optionally, the controller is arranged for, in case the temperature is above the predetermined temperature threshold and/or when the drag is below the predetermined drag threshold, carrying out the downshifting by with the first coupling member engaged synchronizing the output and the input of the second coupling member, engaging the second coupling member, and disengaging the first coupling member. Optionally the steps of synchronizing the output and the input of the second coupling member, engaging the second coupling member, and disengaging the first coupling member are carried out consecutively in that order. Optionally, with the first coupling member engaged synchronizing the output and the input of the second coupling member is carried out using the third coupling member.

According to a further aspect, is provided a vehicle comprising a transmission system according to the present invention.

According to a further aspect, is provided a computer program product for operating a transmission system for a vehicle. The transmission comprises an input shaft, an output shaft, a first transmission path relating to a higher gear of the transmission and a second transmission path relating to a lower gear of the transmission. The first and second transmission paths are arranged in parallel with respect to each other between the input shaft and the output shaft. The first transmission path includes a first gear reduction and a first coupling member, including a force closed coupling. The second transmission path includes a second gear reduction and a second coupling member, including a form closed coupling. The first coupling member is engaged and the second coupling member is disengaged when the transmission is operating at the higher gear so that the output shaft has a rotation speed corresponding to the first output rotation speed. For downshifting, the computer program product comprises instructions for causing a controller to synchronize an output and an input of the second coupling member by at least partially disengaging the first coupling member resulting in an increasing rotation speed of the input shaft, and (subsequently) engaging the second coupling member when the output and input of the second coupling member are, at least sufficiently, synchronized.

Optionally, the first coupling member is arranged between the input shaft and the first gear reduction. Optionally, the first coupling member includes a force closed friction coupling. Optionally, the second coupling member is arranged between the second gear reduction and the output shaft. Advantageously, the second coupling member can include a form closed coupling such as a dog clutch and/or a keyed coupling.

Engaging the second coupling member can be carried out when the output and the input of the second coupling member are sufficiently synchronized (e.g. when the speed difference is smaller than a threshold, e.g. smaller than 200 rpm, 100 rpm or 50 rpm). Other relative value differences may also be employed.

The transmission may be suitable for a vehicle comprising an combustion engine, electric drive or hybrid drive. Further, the gear reductions may have a non-1 gear ratio. With the transmission it is possible for a transmission gear ratio at the output to be changed while a torque is maintained.

It will be appreciated that any of the aspects, features and options described in view of the method apply equally to the vehicle and the described transmission system. It will also be clear that any one or more of the above aspects, features and options can be combined.

BRIEF DESCRIPTION OF THE DRAWING

The invention will further be elucidated on the basis of exemplary embodiments which are represented in a drawing. The exemplary embodiments are given by way of non-limitative illustration. It is noted that the figures are only schematic representations of embodiments of the invention that are given by way of non-limiting example.

In the drawing:

Fig. 1 shows a schematic diagram of an embodiment of a transmission system;

Fig. 2 shows a schematic diagram of an embodiment of a transmission system;

Fig. 3 shows a schematic diagram of an embodiment of a transmission system;

Fig. 4 shows a schematic diagram of an embodiment of a transmission system;

Fig. 5 shows a schematic diagram of an embodiment of a transmission system; Fig. 6 shows a schematic diagram of an embodiment of a transmission system;

Fig. 7 shows a schematic block diagram of a method for operating a transmission system; and

Fig. 8 shows a schematic block diagram of a method for operating a transmission system.

DETAILED DESCRIPTION

Figure 1 shows a schematic diagram of an embodiment of a transmission system 1 for a vehicle. The transmission system 1 includes an input shaft 2, an output shaft 4, a first transmission path 6 relating to a higher gear of the transmission and a second transmission path 8 relating to a lower gear of the transmission. The first and second transmission paths 6, 8 are arranged in parallel with respect to each other between the input shaft 2 and the output shaft 4. Here an input of the first transmission path 6 is connected to an input of the second transmission path 8. Here an output of the first transmission path 6 is connected to an output of the second transmission path 8. The first transmission path 6 includes a first gear reduction 10 and a first coupling member 12, including a force closed coupling, e.g. comprising friction element. The second transmission path 8 includes a second gear reduction 14 and a second coupling member 16, including a form closed coupling, e.g. comprising dog clutch. The first coupling member 12 is engaged and the second coupling member 16 is disengaged when the transmission is set for operating at the higher gear. For downshifting, a controller (not shown) of the transmission system 1 is arranged for synchronizing an output 18 and an input 20 of the second coupling member 16 by partially disengaging the first coupling member 12. Disengaging the first coupling member 12 results in an increasing rotation speed of the input shaft 2. Then the second coupling member 16 can be engaged when the output 18 and input 20 of the second coupling member 16 are, at least sufficiently, synchronized. The second coupling member 16 can comprise a synchronizer.

In this example, the first coupling member 12 is a friction clutch. The friction clutch 12 can be partially disengaged such that it can be operated in slipping manner. Partially disengaging the first coupling member 12 results in an increasing rotation speed of the input shaft 2. This may allow switching from one speed transforming gear (higher gear) to the other speed transforming gear (lower gear), by engaging the second coupling member when sufficiently synchronized, while retaining the torque transfer from the input shaft to the output shaft or from the output shaft to the input shaft in the transmission system. Furthermore, by operation of the first coupling member in a slipping fashion, shocks involved with changing gears may be substantially prevented during downshifting.

Further, in the shown embodiment, the second transmission path 8 is free from a further coupling member between the input shaft 2 and the second gear reduction 14.

The second coupling member 16 can be engaged when the rotational speed difference at the input 20 and the output 18 of the second coupling member is smaller than a speed difference threshold Vthreshoid. The output and input of the second coupling member may be sufficiently synchronized for example at a speed difference of smaller than 200 rpm, 100 rpm or 50 rpm. Other relative differences may also be used, such as for example a relative difference between the output 18 and the input 20 of the second coupling member 16 of smaller than 20%, 10%, 5% or 2%. For determining whether the output 18 and input 20 of the second coupling member 16 are sufficiently synchronized, the rotational speed at the input 20 and the output 18 of the second coupling member 16 can be measured. Hence, the output 18 and input 20 of the second coupling member 16 can be sufficiently synchronized when a rotational speed difference exists between the output 18 and input 20.

As, partially, disengaging the first coupling member 12 allows the rotational speed of the input 2 to increase, the second coupling member 16 can be engaged, or engagement can be initiated, just before the rotational speed difference between the input 20 and the output 18 of the second coupling member 16 becomes zero. In such a case, the output 18 and input 20 of the second coupling memberl6 are sufficiently synchronized.

The first transmission path 6 may for example relate to a third gear and the second transmission path 8 may for example relate to a second gear. Hence, downshifting in this example implies shifting from third gear to second gear. Other gear combinations may also be used. Figure 2 shows a schematic diagram of an embodiment of a

transmission system 1. The transmission system 1 further comprises a third coupling member 22 between the input shaft 2 and the second gear reduction 14. In this embodiment, downshifting further includes engaging the third coupling member 22. The first coupling member is arranged between the input shaft 2 and the first gear reduction 10. The second coupling member 16 is arranged between the second gear reduction 14 and the output shaft 4. The second coupling member 16 can be a form closed coupling member, such as a dog clutch and/or keyed coupling. The first coupling member 12 can be a force closed friction coupling.

Preferably, the second coupling member 16 comprises a dog clutch. In this example, the third coupling member 22 is a force closed friction coupling. The third coupling member 22 may have drag losses at lower temperatures (e.g. lower than 50 °C).

When the transmission system 1 is operating at the higher gear, the first coupling member 12 is engaged and the second coupling member 16 is disengaged. The downshifting can be performed by performing the steps of synchronizing an output and an input of the second coupling member 16 by at least partially disengaging the first coupling member 12 resulting in an increasing rotation speed of the input shaft 2, engaging the third coupling member 22 and subsequently engaging the second coupling member 16 when the output and input of the second coupling member 16 are sufficiently synchronized.

The first coupling member 12 may be allowed to slip when being partially disengaged. In this way, advantageously, shocks can be avoided during gear downshifting. Also, it may be possible to maintain torque at the output shaft 4 during downshifting operation.

The controller of transmission system 1 may further be arranged for determining an operating temperature of the transmission and/or determining the drag at the third coupling member 22. Alternatively, instead of measuring a temperature and/or drag, a parameter indicative of the temperature and/or drag may also be determined and used by the controller. Measurements and/or a

(predictive) computational model can be employed for determining a temperature and or drag. The controller of the transmission system 1 may further be configured to carry out an alternative downshifting method when the temperature is above a predetermined temperature threshold and/or when the drag is below a

predetermined drag threshold.

In case the temperature is above the predetermined temperature threshold and/or when the drag is below the predetermined drag threshold, the controller of the transmission system 1 can be configured for carrying out the downshifting by (consecutively) with the first coupling member 12 fully engaged synchronizing the output and the input of the second coupling member 16 by at least partially engaging the third coupling member 22. Once the output and the input of the second coupling member 16 are sufficiently synchronized, the second coupling member 16 is engaged, and the first coupling member 12 is disengaged. Advantageously, an improved shifting can be obtained at lower temperatures, such as for example below 48 °C. Other temperature thresholds may also be used.

Alternatively or additionally, improved shifting can be obtained while having (higher) clutch drag (losses).

Figure 3 shows a schematic diagram of an embodiment of a transmission system 1. The transmission system 1 comprises an input shaft 2 connectable to a drive source 24, such as an electromotor/generator or an internal combustion engine, which forms a main drive, and an output shaft 4 which can be connected to a load 26, such as at least one wheel of the vehicle. In this

embodiment, the drive source 24 is an electromotor/generator 24 which is connected to an accumulator 28 via power electronics 30. The transmission system 1 comprises two parallel transmission paths 6, 8 between the input shaft 2 and output shaft 4. The first coupling member 12 is arranged in the first transmission path 6 and the second coupling member 16 is arranged in the second transmission path 8. A gear reduction 10, 14 with mutually different gear ratios is arranged in each of the transmission paths 6, 8, respectively. The first and second transmission paths can be as described in relation to figures 1 and 2. The load 26 can for example be connected to the output shaft 4 by means of a differential gear. The transmission system 1 includes a transmission which may be housed in a transmission housing.

Figure 4 shows a schematic diagram of an embodiment of a transmission system 1. A third coupling member 22 is arranged between the input shaft 2 and the second gear reduction 14. Further, the first coupling member 12 in the first transmission path 6 is embodied as a planetary gear set with a friction member (e.g. brake). A planetary gear set can comprise three rotational members of which a first rotational member is connected to the input shaft 2, a second rotational member is connected to the output shaft 7 and a third rotational member is connected to a friction brake 12a, forming the first coupling member. The first rotational member can be formed by a planet gear carrier. The second rotational member can be formed by a sun gear. The third rotational member can be formed by an annulus. It will be appreciated that the first coupling member 12 in the examples of figures 1-3 can also include a planetary gear set.

Figure 5 shows a schematic diagram of an embodiment of a

transmission system 1. As shown in the embodiment of figure 5, the first coupling member 12 is embodied as a planetary gear set with a friction member, and the third coupling member 22 is arranged between the input shaft 2 and the second gear reduction 10. Further, an output of the first coupling member 12 and an output of the third coupling member 22 are connected via a fourth coupling member 32.

Figure 6 shows a schematic diagram of an embodiment of a

transmission system 1, wherein the second transmission path 8 is free from a further coupling member between the input shaft 2 and the second gear reduction 14. Advantageously, the second coupling member 16 is embodied as a dog clutch 16.

Here it is also the case that when the transmission is operating in the higher gear (e.g. third gear) of the transmission, the second coupling member is disengaged and the first coupling member is engaged. Hence then the first transmission path 6 is coupled to the output shaft 4. The rotational speed at the output 18 of the second coupling member 16 will not correspond to the rotational speed at the input 20 of the second coupling member 16. When switching to the lower gear (e.g. second gear) of the transmission, the first coupling member 12 is at least partially disengaged, preferably allowing slip, such that the input 20 and output 18 of the second coupling member 16 can become sufficiently synchronized. The rotational speed at the input 20 of the second coupling member 16 can then change as a result of at least partially disengaging the first coupling member 12. In this way, the speed difference between the input 20 of the second coupling member 16 and the output 18 of the second coupling member 16 can decrease (possibly until it becomes zero, or even passes zero). When the speed difference between the output and the input becomes zero (or within a range near a zero speed difference), the second coupling member will be sufficiently synchronized so that it can be (subsequently) engaged. Thus, the second coupling member 16 can also be engaged when the relative speed difference between the output and the input is sufficiently small. Also, in this way, the second coupling member 16 may be embodied as a dog clutch, e.g. instead of a synchronizer. Furthermore, operating the first coupling member in slipping fashion enables maintaining torque during shifting. Also shocks resulting from shifting from the higher gear to the lower gear may be prevented or reduced.

Figure 7 shows a schematic block diagram of a method 1000 for shifting a transmission system 1 from a higher gear to a lower gear. The transmission system comprises an input shaft 2, an output shaft 4, a first transmission path 6 relating to a higher gear of the transmission and a second transmission path 8 relating to a lower gear of the transmission. The first and second transmission paths 6, 8 are arranged in parallel with respect to each other between the input shaft 2 and the output shaft 4. The first transmission path 6 includes a first gear reduction and a first coupling member 12, including a force closed coupling. The second transmission path 8 includes a second gear reduction and a second coupling member 16, including a form closed coupling. The first coupling member 12 is engaged and the second coupling member 16 is disengaged when the transmission is operating at the higher gear. For downshifting an output 18 and an input 20 of the second coupling member 16 are synchronized. In a first step 1001, the first coupling member 12 is at least partially disengaged resulting in an increasing rotation speed of the input shaft (cf. 'flaring'). In a second step 1002, the second coupling member 16 is engaged when the output 18 and input 20 of the second coupling member 16 are, sufficiently, synchronized. In an embodiment, the second step 1002 is carried out subsequently. Optionally, the second transmission path may further comprise a third coupling member 22 between the input shaft and the second gear reduction, and wherein downshifting further includes engaging the third coupling member 22.

When the first coupling member 12 is engaged in a slipping manner, a speed difference between the input 20 and the output 18 of the second coupling member 16 may vary or change, allowing synchronization. The speed difference can be monitored for determined the moment on which sufficient synchronization is reached so that the second coupling member 16 can be engaged (in sufficient synchronization). The first coupling member 12 is operated in a slipping fashion when the first coupling member 12 is at least partially disengaged for

synchronizing the output 18 and the input 20 of the second coupling member 16. In this way, it is possible to switch from one speed transforming gear (cf. higher gear) to another speed transforming gear (cf. lower gear) while retaining the torque transfer from the input to the output or from the output to the input in a transmission. Additionally, as a result of operating the first coupling member in a slipping fashion, shocks involved with changing gears can be reduced or prevented during downshifting.

Figure 8 shows a schematic block diagram of a method 2000 for shifting a transmission system 1 as described above. The first coupling member 12 is engaged and the second coupling member 16 is disengaged when the transmission is operating at the higher gear. In a first step 2001, an operating temperature T of the transmission is determined. Alternatively or additionally, the drag D at the third coupling member is determined in the first step 2001. The temperature T or drag D, or a measure related to these quantities, can be determined using measurements . Additionally or alternatively a (computational) model can be employed for calculating values for the T or D based on other parameters. For example, the values T or D can be estimated taking into account various parameters in an computational estimation model. In a second step 2002, it is determined whether the temperature T is above a predetermined temperature threshold Threshold and/or whether the drag is below a predetermined drag threshold Dthreshoid. In case the temperature T is above the predetermined temperature threshold Threshold and/or the drag is below the predetermined threshold Dthreshoid, the downshifting is carried out by performing steps 2003-2006. In the third step 2003, the output and the input of the second coupling member 16 are synchronized with the first coupling member, e.g. fully, engaged. For this purpose a synchronizer of the second coupling member 16 may be utilized. In a fourth step 2004, the second coupling member is engaged. The second coupling member may comprise, or be, a dog clutch. In a fifth step 2005, the first coupling member 12 is at least partially disengaged. In a sixth step 2006, the third coupling member 22 is engaged when an output and input of the third coupling member are sufficiently synchronized. The above mentioned steps can be carried out

consecutively in the order given above. In case the temperature T is below or equal to the predetermined temperature threshold Threshold and/or the drag is above or equal to the predetermined threshold Dthreshoid, the downshifting is carried out by performing alternative steps 2050, 2051. As in the embodiment of figure 7, an output 18 and an input 20 of the second coupling member 16 are synchronized for downshifting, wherein in a first alternative step 2050, the first coupling member 12 is at least partially disengaged resulting in an increasing rotation speed of the input shaft and in a second alternative step 2002, the second coupling member 16 is engaged when the output 18 and input 20 of the second coupling member 16 are, sufficiently, synchronized. The second alternative step 2051 can also be carried out consecutively.

Hence, the first coupling member and/or the second coupling member can be controlled by a controller of the transmission system utilizing

measurements related to temperature and/or clutch drag. A synchronizer may comprise a friction element arranged for synchronizing torque paths and a dog clutch arranged for engaging torque paths. In an example in which the second coupling member is embodied as a synchronizer, a dog clutch of the synchronizer can be used when shifting at lower temperatures (and/or higher drag), wherein, optionally, when shifting at higher temperatures (and/or lower drag), both the friction element and the dog clutch of the synchronizer are used. The second coupling member can be synchronized using the first coupling member, at lower temperatures. At higher temperatures, the second coupling member can be synchronized by means of a synchronizer, for example utilizing a synchro-ring.

Generally, the shifting strategy can be changed selected based on the operating temperature of the transmission. It can be expected that at lower temperatures, the drag losses are higher, possibly causing synchronization problems when downshifting from the higher gear to the lower gear. Therefore, the temperature can be a measure for possible drag losses influencing the shifting strategy employed in the transmission system 1. If the transmission system 1 includes a third coupling member 22, alternatively or additionally, the shifting strategy can be changed selected based on the determined drag at the third coupling member 22 (measurement, estimation or prediction). Additionally or alternatively, other quantities, variables or parameters relating to the temperature and/or drag are used for changing/selecting the shifting strategy..

Herein, the invention is described with reference to specific examples of embodiments of the invention. It will, however, be evident that various

modifications and changes may be made therein, without departing from the essence of the invention. For the purpose of clarity and a concise description features are described herein as part of the same or separate examples or embodiments, however, alternative embodiments having combinations of all or some of the features described in these separate embodiments are also envisaged.

The transmission system may be implemented in a vehicle, such as cars, recreational vehicles, trucks, buses, bicycles, motorcycles, lawn mowers, agricultural vehicles, construction vehicles, golf carts, trolleys and robotic vehicles. Other vehicles are possible as well. The shown embodiments involved vehicles comprising four wheels, however vehicles with a different number of wheels can be utilized. It also perceivable that a plurality of transmission systems are included in a vehicle.

Actuation of the coupling members may be performed by means of a hydraulic actuation system. However other embodiments may include actuation by means of mechanical, electromechanical or electro-hydraulic systems. A

combination of actuation systems for the different components of the transmission are also envisaged.

The motor or engine of the vehicle comprising the transmission system according the current invention may be or include any combination of an internal combustion engine and an electric motor. Other motors and engines are possible as well such as a fuel-cell motor. In some embodiments, the motor is a hybrid engine and/or could include multiple types of engines and/or motors. For instance, a gas- electric hybrid car could include a gasoline engine and an electric motor. Other examples are possible.

It will be appreciated that the method may include computer implemented steps. All above mentioned steps can be computer implemented steps. Embodiments may comprise computer apparatus, wherein processes performed in computer apparatus. The invention also extends to computer programs,

particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of source or object code or in any other form suitable for use in the implementation of the processes according to the invention. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a ROM, for example a semiconductor ROM or hard disk. Further, the carrier may be a transmissible carrier such as an electrical or optical signal which may be conveyed via electrical or optical cable or by radio or other means, e.g. via the internet or cloud.

Some embodiments may be implemented, for example, using a machine or tangible computer-readable medium or article which may store an instruction or a set of instructions that, if executed by a machine, may cause the machine to perform a method and/or operations in accordance with the embodiments.

Various embodiments may be implemented using hardware elements, software elements, or a combination of both. Examples of hardware elements may include processors, microprocessors, circuits, application specific integrated circuits (ASIC), programmable logic devices (PLD), digital signal processors (DSP), field programmable gate array (FPGA), logic gates, registers, semiconductor device, microchips, chip sets, et cetera. Examples of software may include software components, programs, applications, computer programs, application programs, system programs, machine programs, operating system software, mobile apps, middleware, firmware, software modules, routines, subroutines, functions, computer implemented methods, procedures, software interfaces, application program interfaces (API), methods, instruction sets, computing code, computer code, et cetera.

Herein, the invention is described with reference to specific examples of embodiments of the invention. It will, however, be evident that various

modifications, variations, alternatives and changes may be made therein, without departing from the essence of the invention. For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments, however, alternative embodiments having combinations of all or some of the features described in these separate embodiments are also envisaged and understood to fall within the framework of the invention as outlined by the claims. The specifications, figures and examples are, accordingly, to be regarded in an illustrative sense rather than in a restrictive sense. The invention is intended to embrace all alternatives, modifications and variations which fall within the spirit and scope of the appended claims. Further, many of the elements that are described are functional entities that may be implemented as discrete or distributed components or in conjunction with other components, in any suitable combination and location.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word 'comprising' does not exclude the presence of other features or steps than those listed in a claim. Furthermore, the words 'a' and 'an' shall not be construed as limited to 'only one', but instead are used to mean 'at least one', and do not exclude a plurality. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to an advantage.