DE-102018109417-B4 - METHOD AND SYSTEM FOR CONTROLLING ENGINE BRAKES

Abstract

Vehicle operating procedures, comprehensive: Operating a continuously variable transmission (CVT) via a control unit to adjust the engine speed according to a first engine speed-to-vehicle speed profile in response to a request for engine braking; and Changing the operation of the CVT via the control to adjust the engine speed according to a second engine speed-to-vehicle speed profile in response to a vehicle speed error and brake pedal position.

Inventors

• Carol Louise Okubo
• Kent HANCOCK
• Jacob DOAN
• Bryan Whitney D. Belt

Assignees

• FORD GLOBAL TECHNOLOGIES, LLC

Dates

Publication Date

20260513

Application Date

20180419

Priority Date

20170421

Claims (15)

1. Vehicle operating procedures, comprising: Operating a continuously variable transmission (CVT) via a controller to adjust the engine speed according to a first engine speed-to-vehicle speed profile in response to a request for engine braking; and changing the operation of the CVT via the controller to adjust the engine speed according to a second engine speed-to-vehicle speed profile in response to a vehicle speed error and a brake pedal position.
2. Procedure according to Claim 1 , where operating the CVT involves adjusting the torque of an electric machine to adjust the motor speed.
3. Procedure according to Claim 2 , where the second engine speed-to-vehicle speed profile includes a first threshold engine speed that must not be exceeded.
4. Procedure according to Claim 3 , furthermore, comprehensively modifying the operation of the CVT via the control to adjust the engine speed according to a third engine speed-to-vehicle speed profile in response to a vehicle speed error and brake pedal position.
5. Procedure according to Claim 4 , wherein the third engine speed-to-vehicle speed profile includes a second threshold engine speed that must not be exceeded, where the second threshold engine speed is greater than the first threshold engine speed.
6. Procedure according to Claim 1 , furthermore, comprehensive provision of engine braking while the CVT adjusts the engine speed according to the second engine speed-to-vehicle speed profile.
7. Procedure according to Claim 1 , furthermore, comprehensively modifying the operation of the CVT via the control to adjust the engine speed according to a second engine speed-to-vehicle speed profile in response to vehicle acceleration and brake pedal position.
8. Procedure according to Claim 7 , furthermore, comprehensively increasing the engine pumping work in response to increasing vehicle speed while the vehicle speed is higher than a threshold speed and while the CVT adjusts the engine speed according to the second engine speed-to-vehicle speed profile.
9. Procedure according to Claim 8 , furthermore, comprehensively reducing engine pumping work in response to decreasing vehicle speed while the vehicle speed is higher than a threshold speed and while the CVT adjusts the engine speed according to the second engine speed-to-vehicle speed profile.
10. Procedure according to Claim 7 , where the first engine speed-to-vehicle speed profile provides a lower engine speed for a given vehicle speed than the second engine speed-to-vehicle speed profile provides for the given vehicle speed.
11. Procedure according to Claim 10 , where the second engine speed-to-vehicle speed profile provides a greater degree of engine braking for a given vehicle speed than the first engine speed-to-vehicle speed profile provides for that vehicle speed.
12. Procedure according to Claim 7 , wherein the CVT is a belt- or chain-driven CVT, and further comprising: requiring a threshold duration to adjust the engine speed according to the first engine speed-to-vehicle speed profile prior to adjusting the engine speed according to the second engine speed-to-vehicle speed profile.
13. Procedure according to Claim 7 , wherein the CVT includes a planetary gear set and a generator, and further comprising: changing the operation of the CVT via the control to adjust the engine speed according to the first engine speed-to-vehicle speed profile after adjusting the engine speed according to the second engine speed-to-vehicle speed profile in response to vehicle acceleration and brake pedal position.
14. Procedure according to Claim 7 , furthermore, comprehensively changing the operation of the CVT via the control to set the engine speed according to a third engine speed-to-vehicle speed profile after setting the engine speed according to the second engine speed-to-vehicle speed profile in response to vehicle acceleration and brake pedal position.
15. Procedure according to Claim 1 , furthermore, comprehensively increasing the engine pumping work in response to the vehicle speed being higher than a threshold speed, while the CVT adjusts the engine speed according to the second engine speed-to-vehicle speed profile.

Description

AREA This description relates to a method and a system for operating the powertrain of a vehicle that includes a continuously variable transmission (CVT). The method and system can be particularly useful for operating a vehicle on roads with negative gradients. GENERAL STATE OF THE ART AND BRIEF OVERVIEW A vehicle may incorporate a CVT to improve fuel economy and reduce vehicle weight. In some examples, the CVT might couple an engine to wheels via a belt or chain, with the belt or chain positioned between a continuously variable drive pulley and a continuously variable driven pulley. The radius of the continuously variable drive pulley (e.g., a pulley in the CVT closest to the engine along a torque path in the power transmission arrangement) can be increased or decreased to change the CVT's input-to-output ratio. Similarly, the radius of the continuously variable driven pulley (e.g., a pulley in the CVT furthest from the engine along the torque path in the power transmission arrangement) can be increased or decreased to change the CVT's input-to-output ratio (e.g., the CVT gear ratio). The belt or chain can transmit engine torque from the engine to the vehicle's wheels when the driver demands positive torque. Conversely, if the driver demands little or no torque and the vehicle is traveling on a downhill slope, the belt or chain can transfer some of the vehicle's kinetic energy to the engine. Friction and pumping work within the engine (e.g., compression and expansion of gases) can counteract the torque transmitted from the vehicle's wheels to the engine, thus reducing the vehicle's acceleration. In other examples, the CVT can take the form of a planetary gear set and a generator. The generator's torque can be adjusted to control the motor speed independently of the wheel speed. The motor's torque, along with the torque of an electric motor positioned downstream of the generator in a vehicle power transmission, can be used to propel the vehicle when driver demand is high. Conversely, at least some of the vehicle's kinetic energy can be transferred through the planetary gear set and to the motor by adjusting the generator's torque when driver demand is low and engine braking is required. However, when a CVT transfers torque from the vehicle wheels to an engine for engine braking, transmission noise and vibration can increase to undesirable levels because the CVT can be controlled to limit the engine speed to less than a single threshold. For example, the CVT might control the engine speed to remain below a maximum, and the transmission can generate a significant amount of noise when the engine is running near its maximum speed. Therefore, it may be desirable to provide a means of utilizing engine braking while limiting the exposure of vehicle occupants to transmission noise and vibration. Engine control units for such CVTs are from the EP 0 180 916 B1 known, while a drive control from the DE 601 10 519 T2 is known. The inventors of the present invention have recognized the aforementioned problems and have developed a vehicle operating method comprising: operating a continuously variable transmission (CVT) via a control unit to adjust the engine speed according to a first engine speed-to-vehicle speed profile in response to a request for engine braking; and changing the operation of the CVT via the control unit to adjust the engine speed according to a second engine speed-to-vehicle speed profile in response to a vehicle speed error and a brake pedal position. By adjusting the engine speed via a CVT according to one of a variety of engine speed-to-vehicle speed profiles, it may be possible to provide a desired level of engine braking without generating more noise and vibration in the powertrain than is desired. One or more of the many engine speed-to-vehicle speed profiles can maintain a constant engine speed while the vehicle speed increases after the vehicle reaches a threshold speed. Additionally, the engine speed can be reduced to less than a threshold engine speed for each engine speed-to-vehicle speed profile. The engine speed-to-vehicle speed profile can be limited, and each profile can have a different upper threshold or maximum engine speed than other profiles. The different profiles can have different upper engine speed thresholds, allowing engine noise to be adjusted to the severity of the road gradient. In this way, the power transmission noise can change proportionally to the gradient, providing an enhanced driving experience. Furthermore, limiting the frequency of changes between different profiles can improve handling. The present description can offer several advantages. In particular, for a vehicle incorporating a CVT, the approach can provide desirable levels of powertrain noise and vibration during engine braking. Furthermore, the approach can provide conditions useful for limiting powertrain noise according to the severity of the road gradient, so that a driver experiences a powertrain noi