COMMERCIAL VEHICLE

Description

[0001] The invention relates to commercial vehicles, e.g. mobile excavators, wheel loaders, telehandlers, dumpers, etc.

[0002] Such commercial vehicles are often electrically or hydrostatically powered. The transmissions are designed in such a way that they cannot be shifted while driving, but only when the vehicle is stationary. In particular, shifting between gears with different ratios is only possible when the vehicle is stationary. The transmissions often do not have a dedicated reverse gear, but rather only two or more gear ratios. Moving the commercial vehicle forward or backward can then usually be achieved by reversing the direction of rotation of the drive motor.

[0003] A typical mechanical transmission for a commercial vehicle has two gear ratios, each with a pair of meshing gears. A shifting device is provided on a shaft carrying two gears, i.e., one gear from each gear ratio pair, with which the torque flow can be directed from the shaft to one of the two gears and thus to one of the two gear pairs (shift ratios).

[0004] The two gears each have a clutch body on the side with teeth on the circumference, over which a shift sleeve with a corresponding matching counter toothing can be pushed.

[0005] To establish the flow of power or torque, the shift sleeve can be moved axially on the shaft, e.g., into three different positions. In a central position, the shift sleeve is separated from the coupling bodies of the two gears and thus from the two gear ratios, allowing neutral operation. From the neutral position, the shift sleeve can be moved axially either to one or the other coupling body to create a positive coupling between the respective gear on the one hand and the shaft on which the shift sleeve is movable on the other.

[0006] The teeth on the shift sleeve and the teeth on the clutch body of the gear in question often have bevels on their axial end faces to allow the teeth to slide into each other during a shifting operation.

[0007] Fig. 1 shows schematically such a switching process under optimal conditions.

[0008] A section of a tooth of a shift sleeve 1 is shown in relation to a tooth of a clutch body 2. Several teeth are arranged side by side on the circumference of the shift sleeve 1 as shown, each spaced apart from the other by gaps.

[0009] Similarly, the clutch body 2 has several teeth spaced apart around its circumference. The clutch body 2 is associated with a gear (not shown), which in turn is part of a gear pair and thus a gear of the transmission.

[0010] To create the desired positive connection between the shift sleeve 1 and the clutch body 2, the shift sleeve 1, which is axially displaceable on a transmission shaft (not shown), must be able to be displaced with its teeth into the spaces between the teeth of the clutch body 2. Fig. 1 The direction of displacement is indicated by an arrow A and the desired end position is indicated by a dashed line.

[0011] Fig. 2 shows a situation with a non-optimal relative position of the teeth of the shift sleeve 1 and the clutch body 2. Here, the bevelled end faces of the teeth are in front of each other, so that a relative rotation between the teeth in the circumferential direction U is required in order to bring the teeth into a relative position analogous to Fig. 1 Only then can the shift sleeve 1 be moved further towards the clutch body 2 so that the teeth slide into the mutual gaps.

[0012] Although the shift sleeve 1 is subjected to an actuating force, e.g., from an actuator, this actuating force is not sufficient, particularly in commercial vehicle transmissions, to achieve the desired relative rotation between the shift sleeve 1 and the clutch body 2.

[0013] In commercial vehicle transmissions, the shifting process occurs when the vehicle is stationary. This is usually done by applying the brake to prevent the vehicle from rolling away. The operator can use a button or switch to send a shift command in the form of an electrical signal to the control unit to initiate the shifting process.

[0014] The shifting is typically unsynchronized, and the drivetrain is not torque-free during the shifting process. Therefore, it can only be shifted while stationary, and the strained drivetrain makes shifting difficult for the reasons mentioned above.

[0015] In such commercial vehicles, the drive motor (traction motor) is positively connected to the transmission. Due to the rigid connection between the transmission and the drive motor, every movement in the transmission also causes a movement in the drive motor. In hydrostatic drives with a hydraulic drive motor, the drive motor is connected to a drive pump (hydraulic pump) via hydraulic hoses, which, however, is in a neutral position when the vehicle is stationary and the gearshift is being carried out. This means that the drive pump cannot take in any oil when the drive motor moves and thus blocks the drive motor. The motor cannot rotate, which ultimately also blocks the required relative rotation of the shift sleeve 1 relative to the clutch body 2 of the relevant gearwheel. In this situation, changing gears is either not possible or only possible with difficulty.The gearshift remains unsuccessful and can only be remedied by restarting the commercial vehicle and moving it a certain distance, then attempting to shift again. With a bit of luck, the transmission will then shift. Otherwise, the driver must attempt several times to achieve a more favorable gear position during operation by starting the engine and moving the vehicle.

[0016] DE 10 2008 054 635 A1, on which the two-part claim is based, discloses a method for operating an electric machine of a drive train with a positive-locking switching element comprising two switching element halves. The electric machine can rotate the switching element halves relative to each other in both directions of rotation.

[0017] DE 10 2005 043 700 A1 describes a shift-dog transmission and a shifting method. A countershaft of the transmission can be rotated by means of an electric motor.

[0018] From DE 10 2017 206 375 A1 a transmission arrangement for a travel drive is known in which a hydrostatic transmission and a manual transmission are provided coupled in series.

[0019] The invention is based on the object of providing a commercial vehicle in which the success rate for gear changes at a standstill can be significantly improved and can reach almost 100%.

[0020] The object is achieved according to the invention by a commercial vehicle having the features of claim 1. Advantageous embodiments are specified in the dependent claims.

[0021] A commercial vehicle is specified, comprising a mechanical transmission with at least two gear stages; a drive motor coupled to the transmission for transmitting a torque from the drive motor to the transmission; an axially displaceable shift sleeve for shifting the gears between two gear stages; an actuating device for generating an actuating force acting on the shift sleeve for axially displacing the shift sleeve and thus shifting the gears; and a control device for activating the actuating device and thus generating the actuating force on the shift sleeve and, in parallel, for controlling the drive motor such that the drive motor changes its direction of rotation at least once while the actuating force acts on the shift sleeve.

[0022] An electric, pneumatic or hydraulic actuator or a control actuator can be used as an actuating device to move the shift sleeve axially at least between the two gear steps and thereby to create a force or torque flow between a gear step and a shaft carrying the shift sleeve.

[0023] The actuating device generates the actuating force for moving the shift sleeve. If the teeth of the shift sleeve and the teeth of the respective gear (clutch body of the corresponding gear) are in an optimal relative position to each other, the teeth can slide into the gaps between each other to easily create the desired positive connection so that the torque can be transmitted (see above explanations on Fig. 1 ).

[0024] However, if the teeth of the shift sleeve and the teeth of the corresponding gear collide, i.e. cannot slide into the gaps between each other, the above-mentioned Fig. 2 The blocking described above takes place. In this case, the drive motor is automatically activated and its direction of rotation is changed at least once, while the actuating force continues to act on the shift sleeve.

[0025] The control of the actuator and the reversal of the drive motor's rotational direction by the control device can be implemented as an assistance function that is performed automatically with each gear change, without requiring separate activation by the operator. The operator simply needs to input their gear change request while the vehicle is stationary. The actual switching, including the single or multiple reversal of the drive motor's rotational direction, is performed by the assistance function.

[0026] The shift sleeve can have a toothing, wherein the gear stages that can be switched by the shift sleeve or that are assigned to the shift sleeve each have a toothing corresponding to the toothing of the shift sleeve, and wherein the shift sleeve can be moved into a switching position with a gear stage, in which the toothing of the shift sleeve and the toothing of the gear stage in question engage with one another and thereby form a positive connection, via which a torque flow between the gear stage and the shift sleeve is made possible.

[0027] An operating device can be provided for inputting a shift command by an operator when the operator wishes to shift a gear. Upon receipt of the shift command, the control device can activate the actuating device and effect a change in the direction of rotation of the drive motor. The operator thus initiates the shifting process by inputting the shift command. The control device can then activate the actuating device and effect the change in the direction of rotation. The change in the direction of rotation should occur at least once. If unsuccessful, the change in the direction of rotation can also occur multiple times, effectively creating a pulsation of the direction of rotation by changing the direction of rotation more frequently in a short period of time.

[0028] A gear change monitoring device can be provided for monitoring a successful gear change and generating a control signal when a successful gear change has been detected. When the gear change command is present, the control device can initially only activate the actuating device, but not the change in direction of rotation. The change in direction of rotation of the drive motor can only be effected if, after a predetermined period of time has elapsed since the actuating device was activated, no control signal is present. This means that after the operator has entered the gear change command, an attempt is first made to change the gear without any further measures by simply applying the actuating force to the shift sleeve. If the teeth of the shift sleeve and the teeth of the corresponding gear orwhose clutch body are in the optimal position relative to each other, the gear can then be changed without any further action being necessary.

[0029] However, if the gear shift could not be completed successfully after a certain period of time, the control signal cannot be generated. In this case, the control device can begin to assist the gear shift by changing the direction of rotation once or several times. The actuating force continues to be applied to the shift sleeve, allowing the teeth of the shift sleeve to eventually slide into the spaces between the teeth of the clutch body.

[0030] During driving operation, the drive motor can generate a driving torque. During activation of the actuator and, if applicable, during the change of rotation of the drive motor, the drive motor can generate a switching torque, whereby the switching torque is smaller than the driving torque, in particular much smaller than the driving torque.

[0031] The driving torque is present in a driving mode when the commercial vehicle is operating according to its intended use. The shifting torque, on the other hand, represents an upper limit or threshold range that must not be exceeded during a shifting operation. The torque acting during a shifting operation changes, so the actual torque varies with the change in direction of rotation. However, exceeding the shifting torque limit should be prevented to prevent damage to the transmission, and in particular damage to the gearing on the shift sleeve or clutch body.

[0032] The values ​​for the driving torque and the shifting torque do not need to be precisely defined. Rather, they can be ranges of values, but they must differ significantly from each other. In particular, as stated above, the shifting torque must be significantly lower than the driving torque. In particular, the shifting torque can be less than 50% of the driving torque, in particular less than 20%, in particular less than 10%, and in particular less than 5% of the driving torque.

[0033] The torque limitation for the switching process is important to prevent damage to the gearing, which can otherwise be caused by excessive local surface pressure on the teeth, as described above with reference to Fig. 2 has already been explained.

[0034] The switching torque or the torque during a switching process can be monitored, for example, by pressure sensors, so that the specified switching torque is not exceeded and the desired torque limitation can be achieved.

[0035] A torque limiting device can be provided to monitor and limit the shifting torque. The torque limiting device can thus ensure that the shifting torque limit is not exceeded, thus preventing damage to the shifting mechanism or the transmission.

[0036] According to the present invention, the drive motor is a hydrostatic drive motor, wherein switchable hydraulic valves are provided by which a reversal of the direction of rotation of the drive motor can be effected, and wherein the torque limiting device can have a pressure control device for controlling the hydraulic pressure applied to the drive motor in such a way that the switching torque does not exceed a limit value.

[0037] The hydraulic valves allow hydraulic pressure to be applied alternately to the two ports of the hydrostatic drive motor. This creates alternating pressure pulsations on the drive motor, enabling rapid reversal of rotation. However, the best possible pressure control is required to achieve the most precise torque for the gearshift. In particular, exceeding the limit value must be avoided for the reasons mentioned above. Thus, controlled control of the drive motor can be provided to prevent damage to the transmission.

[0038] The torque limiting device can have at least one pressure sensor for monitoring the hydraulic pressure applied to a pressure side of the drive motor by switching the hydraulic valves. In particular, the torque limiting device can have, for example, two pressure sensors, each of which monitors the hydraulic pressure at an input of the drive motor. A typical hydrostatic drive motor for a commercial vehicle has two hydraulic pressure inputs that can be alternately actuated to drive the motor in both directions of rotation.

[0039] The pressure sensors enable control and thus regulation of the hydraulic pressure so that the switching torque does not exceed the specified limit.

[0040] These and other advantages and features of the invention are explained in more detail below using examples with the aid of the accompanying figures. They show: Fig. 1 a schematic representation of a switching process with optimal switching position of the switching sleeve and clutch body; Fig. 2 a gearshift operation in which the teeth of the shift sleeve and clutch body are not in an optimal position; Fig. 3 a switching process in a commercial vehicle according to the invention; Fig. 4 the schematic design of a commercial vehicle transmission with a hydrostatic drive; and Fig. 5 the schematic structure of a commercial vehicle transmission not belonging to the invention with an electric drive.

[0041] Based on the Fig. 1 und 2 The problem that can occur when switching commercial vehicle transmissions at a standstill if the respective teeth of the shift sleeve and the corresponding gear (clutch body) are not in the optimal switching position has already been explained above in connection with the state of the art ( Fig. 2 ).

[0042] According to the invention, in addition to applying an actuating force to the shift sleeve, a change in the direction of rotation is carried out by the drive motor, which enables a relative movement of the teeth involved on the circumference, so that finally an optimal switching position can be achieved in which the teeth involved can slide into one another.

[0043] This relationship is illustrated by Fig. 3 explained.

[0044] There, a tooth of a shift sleeve 1, shown as an example, is in front of a tooth of a clutch body 2, also shown as an example. The two teeth are each shown as part of a toothing extending over the circumference of the shift sleeve 1 or the clutch body 2.

[0045] The shift sleeve 1 and thus also the tooth shown is acted upon by an actuating force S with the aid of an actuating device (not shown) in the direction of the clutch body 2. Since the tooth of the shift sleeve 1 is located in front of the tooth of the clutch body 2, it cannot slide freely into the space between the teeth of the clutch body 2. In this respect, this initial position corresponds to the above-mentioned Fig. 2 .

[0046] Parallel to the application of the actuating force S or starting somewhat later (e.g. after a predetermined period of time), a drive motor (not shown) is automatically activated for a short time, so that a relative rotation can take place between the teeth (toothing) of the shift sleeve 1 and the teeth (toothing) of the clutch body 2. In particular, as in Fig. 3 shown - the tooth of the shift sleeve 1 shown there is moved in the circumferential direction U and finally slides in the axial direction A into the space next to the tooth of the clutch body 2 in order to achieve the desired positive switching position, which has already been described above with reference to Fig. 1 was explained.

[0047] Fig. 4 shows an embodiment of the invention for a hydrostatic drive in a commercial vehicle.

[0048] For this purpose, a hydrostatic drive motor 5 is provided, which is driven by a hydraulic drive pump 6 in a conventional manner. Pressure sensors 7 are provided to monitor the hydraulic pressure applied to the drive motor. These sensors are arranged on both pressure sides of the drive motor.

[0049] The two pressure sensors 7 can, in particular, ensure that the hydraulic pressure generated by the drive pump 6 during a gearshift and applied to the drive motor 5 is significantly lower than that required for regular driving operation. During driving operation, the full torque that can be provided by the hydrostatic drive can be generated. However, during gearshifting, only a significantly lower torque may be applied to prevent damage to the teeth on the shift sleeve 1 and the clutch body 2. The torque values ​​during the gearshift should, for example, be less than 20% or less than 10% of the driving torque values. For example, the torque values ​​can range from 0.5% to 5% of the driving torque value.

[0050] By changing the valve positions using hydraulic valves (not shown), the direction of rotation of the drive motor can be changed. During a switching operation, the hydraulic valves can be switched relatively quickly in succession to effect brief changes in the direction of rotation of the drive motor 5. This creates pressure pulsations that can support the switching process.

[0051] The drive motor 5 is connected to a transmission 9 via a drive shaft 8. In the example shown, the transmission 9 is two-stage and has a first gear 10 and a second gear 11, each with paired gears for transmitting the torque of the drive motor 5 to an output shaft 12. The output shaft 12 can be connected, for example, to wheels of the commercial vehicle.

[0052] For switching between gear stages 10 and 11, an axially movable shift sleeve 1 is provided, which is axially movable on a guide sleeve 13. The guide sleeve 13 is positively connected to the output shaft 12 in a conventional manner.

[0053] The shift sleeve 1 has - as already explained several times above - a toothing on the circumference, e.g. an internal toothing, which can be pushed over an external toothing on the clutch body 2 of a respective gear wheel of one of the gear stages 10 or 11. This results in the switching situations, which are already based on the Fig. 1 bis 2 were explained.

[0054] The axial position of the shift sleeve 1 can be adjusted using two actuators 14.

[0055] The generation of the actuating force by the actuators 14 as well as the switching of the direction of rotation of the drive motor 5 by controlling the hydraulic valves (not shown) and regulating the hydraulic pressure to a low value can be implemented in the form of an assistance function that is automatically activated with each gear change.

[0056] In particular, the assistance function can initially monitor whether the gear change is easy because the gears are in the optimal position (see Fig. 1 ). However, if it is determined that direct switching is not possible because the teeth of the gears are in front of each other (cf. Fig. 2 ), the assistance function can bring about the desired pressure pulsation or change in direction of rotation to support the switching process.

[0057] Fig. 5 shows as a variant to the hydrostatic drive of Fig. 4 an electric drive not part of the invention.

[0058] Instead of the hydrostatic drive motor 5 of Fig. 4 an electric drive motor 20 is provided, which can be controlled by a suitable motor control 21, e.g. a converter with additional control electronics.

[0059] The drive motor 20 drives the gear 9 via the drive shaft 8, which is essentially identical in construction to the gear 9 of Fig. 4 can be, so that further explanation is unnecessary.

Claims

1. Commercial vehicle, comprising - a mechanical transmission (9) with at least two gear ratios; - a drive motor (5) which is coupled to the transmission (9) in order to transmit a torque from the drive motor (5) to the transmission (9); - an axially displaceable shift collar (1) which is adapted to shift the gears between two gear ratios; - an actuating device (14) which is adapted to generate an actuating force, which acts upon the shift collar (1), in order to axially displace the shift collar (1) and thus shift the gears; and comprising - a control device which is adapted to activate the actuating device (14) and thus generate the actuating force on the shift collar (1) and, in parallel therewith, to energise the drive motor (5) such that the drive motor (5) changes its direction of rotation at least once while the actuating force acts upon the shift collar (1); characterised in that - the drive motor (5) is a hydrostatic drive motor; and that - switchable hydraulic valves are provided which are adapted to alternately provide hydraulic pressure to connections of the hydrostatic drive motor (5) in order to effect an alternating pressure pulsation at the drive motor (5) and thus a rapid reversal of the direction of rotation.

2. Commercial vehicle as claimed in claim 1, wherein - the shift collar (1) has a toothing arrangement; - the gear ratios which can be shifted by the shift collar (1) each have a toothing arrangement which corresponds to the toothing arrangement of the shift collar (1); and wherein - the shift collar (1) can be displaced to a shift position with a gear ratio, in which the toothing arrangement of the shift collar (1) and the toothing arrangement of the respective gear ratio engage with one another and thereby form a form-fitting connection which permits a torque flow between the gear ratio and the shift collar (1).

3. Commercial vehicle as claimed in any one of the preceding claims, wherein - an operating device is provided which is adapted to input a shift command by an operator when the operator wishes to shift a gear ratio; and wherein - when the shift command is present, the control device activates the actuating device (14) and effects the change in the direction of rotation of the drive motor (5).

4. Commercial vehicle as claimed in any one of the preceding claims, wherein - a gear change monitoring device is provided which is adapted to monitor a successful gear change and generate a control signal when a successful gear change has been established; - when the shift command is present, the control device is adapted to initially activate only the actuating device but not to effect the change in the direction of rotation; and wherein - the control device is adapted to effect the change in the direction of rotation of the drive motor (5) only when no control signal is present after a specified period of time has elapsed after activation of the actuating device.

5. Commercial vehicle as claimed in any one of the preceding claims, wherein - the commercial vehicle is designed to generate a driving torque by means of the drive motor (5) during a driving operation; - the commercial vehicle is designed to generate a shift torque by means of the drive motor (5) during the activation of the actuating device (14) and the change in the direction of rotation of the drive motor (5); and wherein - the shift torque is smaller than the driving torque.

6. Commercial vehicle as claimed in any one of the preceding claims, wherein a torque limiting device is provided which is adapted to monitor the shift torque and to limit the shift torque.

7. Commercial vehicle as claimed in claim 6, wherein - the torque limiting device has a pressure regulating device which is adapted to regulate the hydraulic pressure applied to the drive motor (5) such that the shift torque does not exceed a limit value.

8. Commercial vehicle as claimed in claim 7, wherein the torque limiting device has at least one pressure sensor (7) which is adapted to monitor a hydraulic pressure applied to a pressure side of the drive motor (5) by switching the hydraulic valves. motor (5) by switching the hydraulic valves.