Engine braking function for continuously variable transmission

Abstract

The invention relates to a method for adjusting a transmission ratio (105) of a continuously variable transmission contained in a drive train of a vehicle; wherein the transmission ratios (105) are set in the traction mode in such a way that the absolute value of the torque applied to the shaft of the drive train does not exceed a first boundary function (101) which associates each transmission ratio (105) of the transmission with a boundary torque (107) applied to the shaft during the maximum torque load of the drive train in the traction mode; wherein the transmission ratio (105) is set in the coasting mode in such a way that the absolute value of the torque applied to the shaft does not exceed the second boundary function (103). A second boundary function (103) associates each transmission ratio of the transmission with a boundary torque (107) exerted on the shaft at a maximum torque load of a drivetrain part downstream of the engine of the drivetrain during coasting operation.

Description

Field of the Invention

[0001] The present invention relates to a method according to the preamble of claim 1 and a computer program according to the preamble of claim 6. Background Art

[0002] In the prior art, the adjustment of an automatic transmission for implementing engine braking is known. For example, the corresponding adjustment is disclosed in document JP61146645A2. In order to achieve the engine braking effect, gear upshifts of the transmission are prohibited at this time.

[0003] The adjustment is subject to torque limitations. This is to prevent overloading of the drive train. To limit the torque, the maximum engine torque and the torque load capacity of the downstream drive train are taken into account. Summary of the Invention

[0004] The object of the present invention is to improve the braking effect of a drive train having a continuously variable transmission. This object is solved by the method according to claim 1 and the computer program according to claim 6. Preferred refinements of the present invention are specified in the dependent claims.

[0005] The method is used to adjust the transmission ratio of a continuously variable transmission comprised in the drive train of a vehicle. A continuously variable transmission, also known as a CVT, is a transmission in which the transmission ratio between the input shaft and the output shaft can be adjusted steplessly. The continuously variable transmission can be, for example, a power-split continuously variable transmission used in construction machinery.

[0006] In addition to the transmission, the drive train also includes all torque transmission components in the torque flow extending from the engine to the driven wheels of the vehicle. Thus, the engine, one or more drive shafts, and one or more axle differentials also belong to the drive train.

[0007] The drive train can operate in traction or in coasting. In traction, the engine generates a driving torque that provides propulsion. In coasting, the drive train is loaded with a torque flow in the opposite direction. This torque flow acts as a brake and thus counteracts the propulsion of the vehicle.

[0008] In traction, the transmission ratio is adjusted such that the torque applied to the shaft of the drive train does not exceed a first boundary function in absolute value. Specifically, the transmission ratio is adjusted such that the torque applied to the shaft does not exceed the boundary torque of the first boundary function assigned to the corresponding transmission ratio of the transmission. This shaft can be a shaft in the drive train for which the torque can be determined. Preferably, this shaft is a shaft provided with a torque sensor.

[0009] The first boundary function assigns each transmission ratio of the transmission to a boundary torque applied to the shaft. This boundary torque is applied when the entire drive train is subjected to the maximum possible torque during traction operation. Thus, when the drive train is subjected to the maximum possible torque load during traction operation, the above-mentioned boundary torque is applied to the shaft.

[0010] During coasting operation, the transmission ratio of the transmission is similarly adjusted by means of a second boundary function. Specifically, the transmission ratio is adjusted such that the torque applied to the shaft does not exceed, in absolute value, the boundary torque assigned to the corresponding transmission ratio of the transmission by the second boundary function.

[0011] According to the invention, the second boundary function assigns each transmission ratio of the transmission to a boundary torque corresponding to the maximum possible torque load of the part of the drive train downstream of the engine during coasting operation. This boundary torque is applied to the shaft when the above-mentioned part of the drive train is subjected to the maximum torque load during coasting operation. According to the invention, the maximum braking effect that the part of the drive train downstream of the engine can withstand without damage is utilized. In this way, the braking effect of the engine can be maximized while taking into account the load capacity of the downstream part of the drive train.

[0012] The downstream part of the drive train refers to the part of the drive train located between the engine and the driven wheels of the vehicle. The transmission, one or more drive shafts and / or one or more axle differentials can belong to this part of the drive train.

[0013] In a preferred refinement, for at least one transmission ratio of the transmission, the first boundary function is different from the second boundary function. Specifically, the boundary torque assigned to at least one transmission ratio of the transmission by the first boundary function is different from the boundary torque assigned to the same transmission ratio by the second boundary function.

[0014] According to the refinement, the difference between the first boundary function and the second boundary function corresponds to the different load capacities of the drive train during traction operation and coasting operation. Thanks to the refinement, it is possible to take these differences into account when adjusting the transmission ratio.

[0015] In another preferred refinement, for at least one transmission ratio of the transmission, the second boundary function is greater than the first boundary function. Specifically, the boundary torque assigned to at least one transmission ratio of the transmission by the second boundary function is greater than the boundary torque assigned to the same transmission ratio by the first boundary function. This means that, according to the refinement, a greater torque can be transmitted during coasting operation than during traction operation.

[0016] In another preferred improvement, the engine is adjusted such that the engine can exert an increased braking torque. This can be achieved, for example, by means of variable valve control. During coasting operation, the movement of the piston can be made difficult by closing the valves in a targeted manner. Accordingly, this improvement is configured such that, for at least one rotational speed, the torque loaded on the driveline part downstream of the engine during coasting operation is greater in absolute value than the torque loaded during traction operation.

[0017] In another preferred improvement, if the torque applied to the shaft during coasting operation exceeds the second boundary function or the boundary torque of the respective transmission ratio assigned to the second boundary function in absolute value, the vehicle's brakes are automatically activated. This supports the engine braking according to the present invention.

[0018] A computer program according to the present invention executes the method according to the present invention or a preferred improvement. The computer program is configured to implement the method according to the present invention or a preferred improvement of the method. This means that the computer program includes instructions for implementing the method according to the present invention or a preferred improvement. When the computer program is implemented by the transmission control device, the computer program causes the transmission control device to implement the method according to the present invention or a preferred improvement.

[0019] The computer program can be included in the transmission control device, stored on a storage medium, or encoded in one or more transmitted or transmissible signals. The computer program can in particular be presented as a computer program product, i.e., a tradable unit or a unit for transferring the ownership of the computer program. The computer program can be presented not only as software but also in the form of hardware-based circuit logic. Description of the Drawings

[0020] In Figure 1 a preferred embodiment of the present invention is shown. In the figure:

[0021] Figure 1 two boundary functions are shown. Detailed Description

[0022] Figure 1 The first boundary function 101 and the second boundary function 103 are shown. The two boundary functions 101, 103 respectively assign to each transmission ratio or inverse transmission ratio 105 of the continuously variable transmission a maximum output torque 107.

[0023] The first boundary function 101 corresponds to the maximum torque load capacity of the entire driveline during traction operation. The engine also belongs to the driveline. This limits the maximum load capacity of the driveline at higher inverse transmission ratios 105.

[0024] The second boundary function 103 corresponds to the maximum torque load capacity of the part of the drive train downstream of the engine during coasting operation. Accordingly, the second boundary function 103 does not include an engine-based limitation. Thus, the second boundary function 103 allows for a greater torque load at a larger inverse transmission ratio.

[0025] Denote the operating state during coasting operation as A. The output torque 107 in state A exceeds the boundary torque allowed according to the first boundary function 101 at the corresponding inverse transmission ratio 105. If the first boundary function is used to adjust the transmission ratio during coasting operation, the inverse transmission ratio 105 must be increased accordingly. However, this results in a reduced braking effect.

[0026] To make full use of the maximum load capacity of the drive train, the second boundary function 103 is used instead. This allows for a higher output torque 107 at the inverse transmission ratio 105 in operating state A. Thereby, the achievable braking torque is increased.

[0027] List of reference numerals

[0028] 101 Boundary function

[0029] 103 Boundary function

[0030] 105 Inverse transmission ratio

[0031] 107 Output torque

Claims

1. A method for adjusting the transmission ratio (105) of a continuously variable transmission included in a drive train of a vehicle; wherein, the transmission ratio (105) is adjusted in traction operation such that the torque applied to the shaft of the drive train does not exceed, in absolute value, a first boundary function (101) that assigns to each transmission ratio (105) of the transmission a boundary torque (107) applied to the shaft at the maximum torque load of the drive train in traction operation; and wherein, the transmission ratio (105) is adjusted in coasting operation such that the torque applied to the shaft does not exceed, in absolute value, a second boundary function (103); characterized in that, the second boundary function (103) assigns to each transmission ratio of the transmission a boundary torque (107) applied to the shaft at the maximum torque load of the part of the drive train downstream of the engine of the drive train in coasting operation.

2. The method according to claim 1, characterized in that, for at least one transmission ratio (105) of the transmission, the first boundary function (101) is different from the second boundary function (103).

3. The method according to the preceding claim, characterized in that, for at least one transmission ratio of the transmission, the second boundary function (103) is greater than the first boundary function (101).

4. The method according to the preceding claim, characterized in that, for at least one rotational speed, the torque with which the part of the drive train downstream of the engine is loaded in coasting operation is greater, in absolute value, than the torque with which it is loaded in traction operation.

5. The method according to any one of the preceding claims, characterized in that, when the torque (107) applied to the shaft in coasting operation exceeds, in absolute value, the second boundary function (103), the brakes of the vehicle are automatically activated.

6. A computer program; characterized in that, it has instructions for causing a transmission control device of a vehicle to adjust the transmission ratio (105) of a continuously variable transmission included in the drive train of the vehicle according to the method according to any one of the preceding claims.

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