Switching method and device for carrying out the switching method

Abstract

Method for shifting gears in a powershift transmission (2) driven by an internal combustion engine (3), which has at least four powershift gears and at least four synchronous gears, wherein a powershift gear and a synchronous gear are assigned to each gear, characterized in that when shifting down a synchronous gear and when an engine load threshold is exceeded, the lowest powershift gear is selected.

Description

[0001] The invention relates to a method for shifting gears according to the preamble of patent claim 1 and to a device for carrying out the method according to the preamble of patent claim 2.

[0002] The invention is based on a powershift transmission, which is manufactured by the applicant and is available on the market under the designation TPT 16 to 20. This powershift transmission, which is used particularly for tractors, is designed as a group transmission and has a main transmission designed as a synchronized transmission and a pre-transmission gear designed as a splitter transmission, which is driven by the internal combustion engine of the vehicle. The main transmission comprises five synchronized gears, and the splitter transmission has six powershift gears or powershift stages. Each synchronized gear can be combined with a powershift gear, resulting in a total of thirty gears. A problem when shifting gears can arise when the engine load is high, iedownshifting at high drive torque: During such a pull-down shift, the vehicle's speed can drop significantly, so that due to the loss of speed, the lower gear to be shifted no longer matches the current driving speed. This can impair the downshift process.

[0003] The invention comprises the features of independent patent claims 1 and 2. Advantageous embodiments emerge from the subclaims.

[0004] According to a first aspect of the invention, a method for shifting gears in a powershift transmission comprises the following method step: When the engine load is high, i.e. when the drive torque is high, when shifting down from a higher to a lower gear, a lower, preferably the lowest powershift stage is first preselected. If, for example, the vehicle is traveling with the fourth synchronized gear in the highest powershift stage, e.g. stage 6, and a shift is to be made from the fourth synchronized gear to the third synchronized gear, the lower, e.g. stage 5, or preferably the lowest powershift stage, e.g. stage 1, is first selected. The third synchronized gear is then engaged. The advantage of this method step is that the drive torque of the engine is reduced by the lower or lowest powershift stage, thus making it easier to move off after engaging the clutch.This can also prevent the engine from stalling.

[0005] According to a further aspect of the invention, a powershift transmission is provided as a device for implementing the method. This transmission is designed as a group transmission and comprises a splitter transmission as the primary transmission and a synchronized transmission as the main transmission. The splitter transmission is thus arranged between the drive engine and the main transmission and reduces the drive torque across the various powershift stages. All synchronized gears of the synchronized transmission can thus be combined with different powershift stages.

[0006] According to a preferred embodiment, the splitter transmission has at least four, preferably six, powershift gears. This allows for a finely gradual reduction of the drive torque.

[0007] According to a further preferred embodiment, the synchronous transmission has at least four, preferably five synchronous gears, each of which can be combined with the individual powershift stages.

[0008] According to a further preferred embodiment, the powershift transmission has a transmission control system capable of detecting the level of engine load, i.e., the drive torque. Thus, the transmission control system can issue the command to preselect the lowest powershift gear when downshifting under high engine load.

[0009] The first engine load threshold defines a preset value of engine load, which, when interrupted by a synchronized gear shift, reduces the vehicle speed by approximately 25% due to the interruption of the engine load required to maintain speed. This can be the case, for example, when driving uphill.

[0010] Alternatively, the value for the first engine load threshold can be set completely freely, depending on how comfortable the vehicle's shifting should be. In principle, and based on the inventive concept, any value between 1% and 99% of the expected speed reduction is possible.

[0011] The second engine load threshold defines another preset value for the engine load, which preferably lies at a higher engine load than the value of the first engine load threshold. Accordingly, the vehicle speed would be reduced by a correspondingly greater amount by interrupting this comparatively higher engine load.

[0012] An embodiment of the invention is illustrated in the drawing and is described in more detail below, wherein further features and / or advantages may emerge from the description and / or the drawing.

[0013] The single figure shows a schematic representation of the drive train of a vehicle, preferably a tractor, which has a driven rear axle 1. A powershift transmission 2 is driven by an internal combustion engine 3 of the vehicle and drives the rear axle 1 via an axle drive 4. The powershift transmission 2 comprises a main transmission 5, which is designed as a synchronous transmission 5 with five synchronous gears, and an upstream splitter transmission 6, which has six powershift stages, also called powershift gears. The engine 3 drives the splitter transmission 6, the latter drives the main transmission 5, and this drives the axle drive 4. The powershift transmission 2 forms a preferred device for carrying out the method according to the invention for shifting gears (shifting method), which is described below.

[0014] As mentioned above, a synchronous gear of the synchronous transmission 5 can be combined with a powershift gear of the splitter transmission 6, with the powershift stage being engaged first and then the synchronous gear. When downshifting gears under high engine load, i.e. a high drive torque of the engine 3, the speed of the vehicle can reduce significantly so that the speeds of the gear to be disengaged and the gear to be engaged no longer match one another, which can impair the gear shifting process. According to the invention, it is therefore provided that when downshifting a synchronous gear under high engine load, the lowest powershift stage is preselected before the synchronous gear is engaged. This reduces the drive torque of the engine so that the synchronous gear shifting process can be carried out smoothly and without interruption.

[0015] The invention will be explained using two gearshift examples: When the engine load is low, the vehicle is to shift down from the fourth synchronous gear in the highest powershift stage (stage 6) to the third synchronous gear. During this downshift, the vehicle speed, which was, for example, 22.5 km / h before the shift, drops only slightly during the shift, i.e., to 18.3 km / h, for example. The downshift therefore takes place as standard in the same, i.e., the highest powershift stage (stage 6). If, on the other hand, the vehicle is to shift down from the fourth synchronous gear in the highest powershift stage (stage 6) to a lower gear, i.e., the third synchronous gear, when the engine load is high, the vehicle speed would drop sharply from, for example, 22.5 km / h, i.e., to 11.1 km / h.For this downshift, a transmission control unit (not shown), which detects the engine load, preselects the lowest powershift gear (gear 1). The third synchronized gear is then engaged. The lowest powershift gear (gear 1) reduces the engine's drive torque to a minimum, preventing the synchronized shifting process from being blocked by the engine. Reference symbol 1 rear axle 2 powershift transmissions 3 Engine 4 axle transmission 5 synchronous transmissions 6 splitter gearboxes

Claims

[1] Method for shifting gears in a powershift transmission (2) driven by an internal combustion engine (3), which has at least four powershift gears and at least four synchronous gears, wherein one powershift gear and one synchronous gear are assigned to each gear, characterized by that when a synchronous gear is shifted down and an engine load threshold is exceeded, the lowest powershift gear is selected. [2] Device for carrying out the method according to claim 1, characterized by that the powershift transmission (2) is designed as a group transmission (2) which comprises a synchronous transmission (5) as the main transmission (5) and a splitter transmission (6) as the primary transmission (6). [3] Device according to claim 2, characterized by that the splitter gearbox (6) has at least four powershift gears. [4] Device according to claim 2 or 3, characterized by that the synchronous transmission (5) has at least four synchronous gears. [5] Device according to claim 2, 3 or 4, characterized by that the powershift transmission (2) has a transmission control which detects the level of the engine load.

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