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.

Description

AREA

[0001] 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

[0002] 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.

[0003] 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.

[0004] 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.

[0005] Engine control units for such CVTs are known from EP 0 180 916 B1, while a drive control unit is known from DE 601 10 519 T2.

[0006] 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.

[0007] 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 drivetrain noise and vibration than desired. One or more of the numerous 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 limited to less than a threshold engine speed for each engine speed-to-vehicle speed profile, and each engine speed-to-vehicle speed profile can have a different upper threshold or maximum engine speed than other engine speed-to-vehicle speed profiles.The different engine speed-to-vehicle speed 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, the conditions for switching between the different engine speed-to-vehicle speed profiles can provide improved vehicle handling by limiting the frequency of these transitions.

[0008] 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 noise level more appropriate for the driving conditions. Additionally, the approach can provide supplemental engine braking after the engine reaches a threshold speed, allowing vehicle speed to be controlled without switching to a different engine speed-to-vehicle speed profile.

[0009] The aforementioned advantages, as well as further advantages and features of the present description, will readily become apparent from the following detailed description, whether considered on its own or in conjunction with the accompanying drawings.

[0010] It is understood that the foregoing summary is provided to present, in simplified form, a selection of concepts that are described in more detail in the full description. It is not intended to mention important or essential features of the claimed subject matter, the scope of which is defined solely in the claims following the full description. Furthermore, the claimed subject matter is not limited to implementations that address the disadvantages mentioned above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The advantages described here become more fully apparent from reading an example of an embodiment, referred to here as the detailed description, either on its own or with reference to the drawings, in which the following applies: Fig. Figure 1 is a schematic representation of an engine; Fig. 2A is a schematic representation of a first exemplary vehicle power transmission; Fig. 2B is a schematic representation of a second exemplary vehicle power transmission; Fig. Figure 3 shows exemplary engine speed-to-vehicle speed profiles of a CVT, which provide a basis for setting the drive-to-output ratio of the CVT; Fig. Figure 4 shows a likely operational sequence according to the procedure from Fig. 5A and Fig. 5B; and Fig. 5A and Fig. Section 5B shows an exemplary procedure for operating a vehicle's power transmission system. DETAILED DESCRIPTION

[0012] This description concerns the operation of a vehicle's power transmission. The power transmission may include an engine, a torque converter, and a CVT. The vehicle's engine can be configured as shown in... Fig. 1 shown, designed to be. The engine off Fig. 1 can be in a like in Fig. 2A and Fig. The power transmission shown in Figure 2B is included. The CVT can be operated as shown in Figure 2B. Fig. Three engine speed-to-vehicle speed profiles are provided. The systems consist of Fig. 1, Fig. 2A and Fig. 2B can determine the operational sequence from Fig. 4. Provide the procedure from Fig. 5A and Fig. 5B can be used in the system from Fig. 1, Fig. 2A and Fig. 2B must be included to determine the operational sequence from Fig. 4 to provide.

[0013] It will be on Fig. 1 Referenced in which an internal combustion engine 10 comprising a plurality of cylinders, one of which is in Fig. As shown in Figure 1, the electronic engine control unit 12 controls the engine. The engine 10 consists of the cylinder head 35 and the block 33, which includes the combustion chamber 30 and the cylinder walls 32. The piston 36 is positioned within the block and moves back and forth via a connection to the crankshaft 40. The flywheel 97 and the ring gear 99 are coupled to the crankshaft 40. The starter 96 (e.g., a low-voltage electric machine (operated at less than 30 volts)) comprises the pinion shaft 98 and the pinion 95. The pinion shaft 98 can selectively drive the pinion 95 so that it engages the ring gear 99. The starter 96 can be mounted directly on the front or rear of the engine. In some examples, the starter 96 can selectively supply torque to the crankshaft 40 via a belt or chain. In one example, the starter motor 96 is in a basic state when it is not engaged with the engine crankshaft.The combustion chamber 30 is shown communicating with the intake manifold 44 and the exhaust manifold 48 via an intake valve 52 and an exhaust valve 54, respectively. Each intake and exhaust valve can be actuated by an intake cam 51 and an exhaust cam 53. The position of the intake cam 51 can be determined by the intake cam sensor 55. The position of the exhaust cam 53 can be determined by the exhaust cam sensor 57. The opening and closing time of the intake valve 52 can be adjusted relative to the position of the crankshaft 40 via the valve phase adjustment device 59. Similarly, the opening and closing time of the exhaust valve 54 can be adjusted relative to the position of the crankshaft 40 via the valve phase adjustment device 58.

[0014] It is shown that the fuel injection device 66 is positioned such that it injects fuel directly into the cylinder 30, a process known to those skilled in the art as direct injection. The fuel injection device 66 dispenses liquid fuel proportionally to the pulse width of the signal from the controller 12. The fuel is supplied to the fuel injection device 66 by a fuel system (not shown) comprising a fuel tank, a fuel pump, and a fuel distributor (not shown). In one example, a two-stage high-pressure fuel system can be used to generate higher fuel pressures.

[0015] Additionally, it is shown that the intake manifold 44 communicates with the turbocharger compressor 162 and the engine air intake 42. In other examples, the compressor 162 may be a supercharger. The shaft 161 mechanically couples the turbocharger turbine 164 to the turbocharger compressor 162. The optional electronic throttle 62 sets a position of the throttle valve 64 to control the airflow from the compressor 162 to the intake manifold 44. The pressure in the charge chamber 45 can be referred to as a throttle inlet pressure, since the inlet of the throttle 62 is located within the charge chamber 45. The throttle outlet is located in the intake manifold 44. In some examples, the throttle 62 and the throttle valve 64 may be positioned between the intake valve 52 and the intake manifold 44 such that the throttle 62 acts as an intake port throttle.The compressor return valve 47 can be selectively adjusted to a variety of positions between fully open and fully closed. The wastegate 163 can be adjusted via the control 12 to allow exhaust gases to selectively bypass the turbine 164 in order to control the speed of the compressor 162. The air filter 43 cleans the air entering the engine air intake 42.

[0016] The distributorless ignition system 88 provides a spark to the combustion chamber 30 via the spark plug 92 in response to the control unit 12. The wideband lambda sensor (Universal Exhaust Gas Oxygen sensor - UEGO sensor) 126 is shown coupled to the exhaust manifold 48 upstream of the catalytic converter 70. Alternatively, the UEGO sensor 126 can be replaced by a binary lambda sensor.

[0017] In one example, catalyst 70 can contain multiple catalyst modules. In another example, multiple emission control devices, each containing multiple modules, can be used. Catalyst 70 can also be a three-way catalyst in one example.

[0018] Control 12 is in Fig. Figure 1 shows a conventional microcomputer comprising: microprocessor unit 102, input / output ports 104, read-only memory 106 (e.g., non-volatile memory), random access memory 108, keep-alive memory 110, and a conventional data bus.It has been shown that, in addition to the signals already discussed, the control unit 12 receives various signals from sensors coupled to the motor 10, including the following: an engine coolant temperature (ECT) from the temperature sensor 112, which is coupled to the cooling sleeve 114; a position sensor 134, coupled to an accelerator pedal 130, to detect a force exerted by the foot 132; a position sensor 154, coupled to the brake pedal 150, to detect a force exerted by the foot 152; a measurement of the engine manifold pressure (MAP) from the pressure sensor 122, which is coupled to the intake manifold 44; an engine position from a Hall effect sensor 118, which detects the position of the crankshaft 40; and a measurement of the mass of air entering the engine from the sensor 120. and a measurement of the throttle position from sensor 68.Atmospheric pressure can also be detected for processing by the controller 12 (sensor not shown). In a preferred aspect of the present description, the engine position sensor 118 generates a predetermined number of evenly spaced pulses at each revolution of the crankshaft, from which the engine speed (RPM) can be determined.

[0019] During operation, each cylinder within the engine 10 typically undergoes a four-stroke cycle: The cycle includes the intake stroke, the compression stroke, the power stroke, and the exhaust stroke. During the intake stroke, the exhaust valve 54 generally closes and the intake valve 52 opens. Air is drawn into the combustion chamber 30 via the intake manifold 44, and the piston 36 moves toward the bottom of the cylinder to increase the volume within the combustion chamber 30. The position at which the piston 36 is near the bottom of the cylinder and at the end of its stroke (e.g., when the combustion chamber 30 has reached its maximum volume) is typically referred to by those skilled in the art as bottom dead center (BDC).

[0020] During the compression stroke, the inlet valve 52 and the exhaust valve 54 are closed. The piston 36 moves towards the cylinder head to compress the air within the combustion chamber 30. The point at which the piston 36 is closest to the cylinder head at the end of its stroke (e.g., when the combustion chamber 30 has its smallest volume) is typically referred to by those skilled in the art as top dead center (TDC). In a process referred to below as injection, fuel is introduced into the combustion chamber. In a process referred to below as ignition, the injected fuel is ignited by known ignition means, such as the spark plug 92, resulting in combustion.

[0021] During the power stroke, the expanding gases push the piston 36 back to bottom dead center (BDC). The crankshaft 40 converts piston movements into torque of the crankshaft. Finally, during the exhaust stroke, the exhaust valve 54 opens to release the burnt air-fuel mixture to the exhaust manifold 48, and the piston returns to top dead center (TDC). It should be noted that the above is merely an example and that the timing of the opening and / or closing of the intake and exhaust valves can vary, for example, to provide positive or negative valve overlap, late closing of the intake valve, or various other examples.

[0022] Fig. 2A is a block diagram of a vehicle 225, which includes a powertrain or transmission 200. The powertrain consists of Fig. 2A includes the one in Fig. The powertrain 200 is shown in Figure 1, which includes the vehicle system controller 255, the engine controller 12, the CVT controller 254, and the brake controller 250. The controllers can communicate via the Controller Area Network (CAN) 299. Each controller can provide information to other controllers, such as torque output limits (e.g., maximum torque output of the controlled device or component), torque input limits (e.g., maximum torque input of the controlled device or component), torque output of the controlled device, sensor and actuator data, and diagnostic information (e.g., information regarding a malfunctioning CVT, information regarding a malfunctioning engine, information regarding malfunctioning brakes).Furthermore, the vehicle system control 255 can provide commands to the engine control 12, the CVT control 254 and the brake control 250 to meet driver input requests and other requirements based on vehicle operating conditions.

[0023] For example, in response to a driver releasing the accelerator pedal, the vehicle control unit 255 can request a desired wheel torque or wheel power level based on the vehicle speed to provide a desired rate of vehicle deceleration. The desired wheel torque can be provided by the vehicle control unit 255 requesting a braking torque from the brake control unit 250.

[0024] In other examples, the control of powertrain devices may be divided differently than in Fig. Figure 2A shows this. For example, a single controller can replace the vehicle system controller 255, the engine controller 12, the CVT controller 254, and the brake controller 250. Alternatively, the vehicle system controller 255 and the engine controller 12 can be a single unit, while the CVT controller 254 and the brake controller 250 are separate controllers.

[0025] In this example, the drive train 200 can be driven by the motor 10. The motor 10 can be equipped with a Fig. The engine start system shown in Figure 1 can be started. An engine output torque can be transmitted to the pump impeller 285 of the torque converter 206. The output of the torque converter is transmitted by the turbine impeller 286 to the CVT 208. The torque converter 206 also includes the torque converter bypass lock-up clutch 212 (TCC). The torque is transmitted directly from the pump impeller 285 to the turbine impeller 286 when the TCC is locked. The TCC is electrically operated by the control unit 12. Alternatively, the TCC can be hydraulically locked. In this example, the torque converter can be considered a component of the transmission.

[0026] When the torque converter lock-up clutch 212 is fully disengaged, the torque converter 206 transmits engine torque to the CVT 208 via fluid transfer between the torque converter's turbine wheel 286 and pump wheel 285, thus enabling torque amplification. Conversely, when the torque converter lock-up clutch 212 is fully engaged, the engine output torque is transmitted directly to the CVT 208 via the torque converter clutch. Alternatively, the torque converter lock-up clutch 212 can be partially engaged, allowing adjustment of the amount of torque transmitted directly to the CVT.The CVT control 254 can be designed to adjust the amount of torque transmitted by the torque converter 212 by adjusting the torque converter lock-up clutch in response to different engine operating conditions or based on a driver-based engine operating request.

[0027] The CVT 208 can include the drive, neutral, and reverse gear set 230, the drive pulley or driving pulley 237, the driven pulley or driven pulley 234, and the driven gear set 238. The actuators 231 can extend and retract the drive pulley rollers 236 and the driven pulley rollers 235 to vary the ratio of the actual total number of revolutions of the CVT drive pulley to the actual total number of revolutions of the CVT driven pulley (e.g., CVT ratio). The belt or chain 232 transmits torque between the drive pulley 237 and the driven pulley 234. By adjusting the CVT ratio, the engine speed can be adjusted relative to the vehicle speed, allowing the engine to operate under efficient conditions. The CVT controller 254 can command the actuators 231 to set the positions of the rollers 236 and rollers 235.The output disc 234 can transmit engine torque to the vehicle wheel 216 via the output gear set 238. The CVT control 254 can adjust the positions of the road wheels 236 and 235 in response to engine load, engine speed, vehicle speed, CVT temperature, and other operating conditions.

[0028] The rotational speed of the wheels 216 can be determined via the wheel speed sensor 221. Furthermore, a frictional force can be exerted on the wheels 216 by engaging the friction wheel brakes 218. For example, the friction wheel brakes 218 can be engaged in response to the driver pressing a brake pedal (not shown) and / or in response to instructions within the brake control unit 250. The brake control unit 250 can also actuate the brakes 218 in response to information and / or requests from the vehicle system control unit 255. Likewise, a frictional force on the wheels 216 can be reduced by disengaging the wheel brakes 218 in response to the driver releasing their foot from a brake pedal, as well as in response to instructions from the brake control unit and / or instructions and / or information from the vehicle system control unit.For example, as part of an automated engine stopping process, the vehicle brakes can exert a frictional force on the wheels 216 via the control unit 250.

[0029] In response to a request to accelerate the vehicle 225, the vehicle control unit can receive a driver-demand torque or power request from an accelerator pedal or other device. The vehicle control unit 255 then requests engine torque from the engine control unit 12. The CVT 254 selectively engages the torque converter clutch 212 and establishes a CVT ratio via the drive pulleys 236 and output pulleys 235.

[0030] In response to a request to decelerate the vehicle 225 and provide engine braking, the vehicle control system can terminate or reduce the amount of fuel injected into the engine 10 and request an engine speed to vehicle speed ratio as prescribed by one of the many engine speed to vehicle speed profiles that are defined in Fig. Figure 3 shows that, alternatively, the CVT control unit 254 can adjust the CVT ratio to provide an engine speed-to-vehicle speed ratio, as prescribed by one of the many engine speed-to-vehicle speed profiles, in response to an engine braking request from the vehicle system control unit 255. The engine braking request can be provided in response to the brake pedal position. The vehicle system control unit 255 can also request braking via the friction brakes 218.

[0031] Now, with reference to Fig. Figure 2B shows an alternative power transmission 200b. The power transmission 200b includes the motor 10 and the torque actuator 204, as shown in Figure 2B. Fig. 1 and Fig. 2A. The motor 10 provides torque to the planetary gear set 280, and the generator 288 can operate in a torque control mode, whereby the torque of the generator 288 is adjusted so that the speed of the motor 10 is controlled to a desired speed via the planetary gear set 280. The motor torque output from the planetary gear set 280 can be fed to the switching system via a transmission 289. The electrical output from the generator 288 provides electrical energy to the energy storage device 285 and the electric motor 286. The energy storage device 285 can supply electrical current to the electric motor 286 via the variable voltage control 281 when the motor 10 is not operating.The electrical energy storage device 285 can be a battery, a capacitor, or another electrical energy storage device, and the electrical energy storage device 285 can be selectively electrically coupled to the stationary power grid (not shown). Under certain conditions, the electric motor 286 can also be operated in generator mode for regenerative braking. Torque from the motor 10 and electric motor 286 can be combined in the switching system with a transmission 289 to provide torque to the vehicle wheels 216 via a mechanical power path. The controller 12 controls the operation of the motor 10, the generator 288, and the electric motor 286 to adjust the power supplied to the vehicle wheels 216. Thus, the power transmission from... Fig. 2B no gearbox with multiple fixed gear ratios for delivering power from the engine and electric motor to the vehicle wheels.

[0032] The speed of motor 10 can be set to a speed independent of the speed of electric motor 286 and wheels 216, so that the power transmission 200b operates as a CVT, which is electrically controlled by setting a torque of generator 288. In particular, a ratio of an actual total number of motor revolutions supplied to the planetary gear set to an actual number of revolutions input to the gear set with a gear ratio or to the vehicle wheels (e.g., CVT gear ratio) can be set by adjusting the torque of generator 288.

[0033] In one example, the motor 10 is mechanically coupled to a planet carrier of the planetary gear set 280. The generator 288 is mechanically coupled to a sun gear of the planetary gear set 280, and a ring gear of the planetary gear set 280 is mechanically coupled to a gear set with a ratio 289. The electric motor 286 is also coupled to the gear set with a ratio 289. The planetary gear set 280 allows the motor 10 to rotate at a speed that differs from the wheel speed and the electric motor speed. There does not need to be a speed difference with a fixed ratio between the motor 10 and the wheels 216 or the electric motor 286. Instead, the motor speed can be set to a speed that is independent of the wheel speed by adjusting the torque of the generator 288.For example, the engine speed can be varied with the speed of the wheels 216, the engine speed can be varied while the wheel speed is constant, or the engine speed can be kept constant while the speed of the wheels 216 varies.

[0034] Now, with reference to Fig. Figure 3 shows an exemplary sequence of engine speed-to-vehicle speed profiles for operating a CVT to control engine braking. The vertical lines VS1 and VS2 represent vehicle speeds at which one or more of the engine speed-to-vehicle speed profiles provide, or provide, a constant engine speed as the vehicle speed increases. The in Fig. The 3 engine speed-to-vehicle speed profiles shown (e.g., engine braking profiles) can be stored in non-volatile memory from one or more in the system. Fig. 1, Fig. 2A and Fig. The controls shown in 2B may be stored. Furthermore, one or more of the controls shown in Fig. The 3 engine speed-to-vehicle speed profiles shown form the basis for operating a CVT, as described in the procedure from Fig. 5A and Fig. 5B is described.

[0035] The course from Fig. Figure 3 includes a vertical axis representing engine speed and a horizontal axis representing vehicle speed. Each of the engine speed-to-vehicle speed profiles 302-308 provides a different level of engine braking. Profile 308 provides a lower level of engine braking than profiles 306, 304, and 302. Profile 302 provides the highest level of engine braking. Profile 308 can provide a desired rate of vehicle deceleration when the vehicle is traveling on a road with a slight negative gradient (e.g., -0.5% gradient). Profile 302 can provide the desired rate of vehicle deceleration when the vehicle is traveling on a road with a steeper negative gradient (e.g., -2% gradient).

[0036] It can be observed that profile 308 begins with a constant engine speed at lower vehicle speeds. The engine speed then increases linearly as the vehicle speed increases. Engine braking torque can increase as the engine speed follows profile 308 because engine friction increases with engine speed. The engine may receive no fuel and can be turned using the vehicle's kinetic energy when the CVT is operating to provide the engine speed-to-vehicle speed profile 308. The CVT's gear ratio can be adjusted in response to the vehicle speed so that the engine speed follows the relationship with vehicle speed shown in profile 308.

[0037] Profile 306 provides a higher level of engine braking (e.g., more resistance to engine and vehicle movement) than profile 308. This higher level of engine braking is due to the higher engine speeds relative to vehicle speeds compared to profile 308. Additionally, profile 306 provides a constant engine speed for increasing vehicle speeds above VS2. Section 306a is a constant engine speed section of profile 306, which can be described as the minimum engine speed for profile 306. By maintaining a constant engine speed for vehicle speeds above VS2, power transmission noise and vibration can be kept below a threshold level when the absolute value of the road gradient is below a certain threshold.Thus, for slight negative road gradients, the noise and vibration of the vehicle powertrain can be limited to less than a first threshold level. Conversely, for steeper negative road gradients, it can be permitted for the noise and vibration of the vehicle powertrain to increase to a second threshold level during a more extreme driving condition, where a human driver might tolerate elevated levels of vehicle noise. In some examples, the engine pumping work can be increased when the engine speed is maintained in profile section 306a while the vehicle speed increases, by adjusting the engine valve timing. Increasing the engine pumping work can further increase engine braking even when the engine speed is kept constant, so that the vehicle speed can be maintained or reduced at higher vehicle speeds.In some examples, the engine pumping work cannot be increased for profile 306 at vehicle speeds below VS2.

[0038] Profile 304 provides an even higher level of engine braking than profile 306. Profile 304 can be activated, and the CVT can control the engine speed according to profile 306 when descending steeper negative gradients, allowing the vehicle speed to be controlled with lower levels of wheel friction braking. Similar to profile 306, profile 304 provides a constant engine speed for vehicle speeds above VS1. Profile section 304a, with constant engine speed above vehicle speeds of VS1, is larger than the constant engine speeds for vehicle speeds above VS2 provided by profile 306. The larger constant engine speed shown in profile 304 for vehicle speeds above VS1 allows for higher levels of powertrain noise and vibration, thus enabling higher levels of engine braking.Furthermore, a human driver of the vehicle may tolerate higher levels of noise and vibration when engine braking is activated for steeper gradients. Thus, the higher constant engine speed above vehicle speed VS1 can limit power transmission noise and vibration while providing higher levels of engine braking. Section 304a is a constant engine speed section of profile 304 that can be described as the maximum engine speed to be exceeded for profile 304. In some examples, the engine pumping work cannot be increased at vehicle speeds below VS1 for profile 304.

[0039] Profile 302 provides the highest level of engine braking in this example. For a given vehicle speed (e.g., VS1), it provides a maximum engine speed, thus delivering the highest level of engine braking at that vehicle speed. Furthermore, profile 302 provides a maximum constant engine speed for increasing vehicle speeds, allowing for a high level of engine braking without excessive noise and vibration in the power transmission. Section 302a is a constant engine speed section of profile 302, which can be described as the maximum engine speed to be exceeded for profile 302. In some examples, the engine pumping work cannot be increased for profile 302 at vehicle speeds below VS1.

[0040] Depending on vehicle operating conditions, a vehicle can provide engine braking according to profile 308 and then increase engine braking according to profiles 306, 304, and 302. Furthermore, vehicle braking can be provided at a higher level according to profile 302 and then reduced according to profile 308. Engine speeds at vehicle speeds that do not correspond to profiles 302 to 308 are avoided during engine braking.

[0041] It should be noted that Fig. Figure 3 shows four exemplary engine speed-to-vehicle speed profiles. However, a smaller or larger number of engine speed-to-vehicle speed profiles may be provided. Additionally, engine speed-to-vehicle speed profiles do not necessarily have to conform to the shapes shown in Figure 3. Fig. The profiles shown in the three examples follow this pattern. For instance, engine speed-to-vehicle speed profiles can follow an exponential trajectory.

[0042] Now, with reference to Fig. 4 a likely operational sequence according to the procedure from Fig. 5A and Fig. 5B shown. The one in Fig. The vehicle operating sequence shown in section 4 can be implemented via the procedure from Fig. 5A and Fig. 5B together with the one in Fig. 1, Fig. 2A and Fig. The system shown in 2B will be provided. Fig. The four processes shown occur simultaneously and are aligned in time.

[0043] The first course from the top Fig. Figure 4 shows the vehicle speed over time. The vertical axis represents the vehicle acceleration, which increases in the direction of the arrow on the vertical axis. The horizontal axis represents time, and time increases from the left side of the figure to the right side.

[0044] The second course from the top Fig. Figure 4 shows the motor speed over time. The horizontal axis represents time, which increases from the left to the right side of the figure. The vertical axis represents the motor speed, which increases in the direction of the arrow on the vertical axis.

[0045] The third course from the top Fig. Figure 4 shows the work done by the engine pump over time. The vertical axis represents the work done by the engine pump, and this work increases in the direction of the arrow on the vertical axis. The horizontal axis represents time, and time increases from the left side of the figure to the right side.

[0046] The fourth course from the top Fig. Figure 4 shows the vehicle speed over time. The vertical axis represents the vehicle speed, and the vehicle speed increases in the direction of the arrow on the vertical axis. The horizontal axis represents time, and time increases from the left side of the figure to the right side.

[0047] The fifth path from the top Fig. Figure 4 shows the state of the vehicle brake pedal over time. The vertical axis represents the state of the vehicle brake pedal, and the brake pedal is depressed when curve 402 is at a higher level near the arrow of the vertical axis. The vehicle brake pedal is not depressed when curve 402 is at a lower level near the horizontal axis.

[0048] The sixth course from the top Fig. Figure 4 shows the active engine braking profile over time. The vertical axis represents which engine braking profile (e.g., as in Fig. (3 profiles shown) is active, and engine braking increases as the number of the active engine braking profile increases. For example, an engine braking profile with a value of one can be engine braking profile 308. Fig. 3. An engine braking profile that has a value of four can be engine braking profile 302. Fig. 3. The horizontal axis represents time, and time increases from the left side of the figure to the right side of the figure.

[0049] At time T0, the vehicle is not accelerating and the engine speed is constant. The engine pumping work and vehicle speed are also constant. The brake pedal is not depressed and no engine braking profile is active.

[0050] At time T1, the brake pedal is applied and the vehicle acceleration is at a low level. The engine speed remains at its previous level, and the engine pumping work also remains at its previous level. The vehicle speed does not increase, and the first engine braking profile is activated in response to the application of the vehicle brakes.

[0051] Between time T1 and time T2, the vehicle accelerates when traveling downhill (not shown). The engine speed increases as the vehicle speed increases to enhance engine braking. The engine pumping work remains constant as the vehicle speed increases. The brake pedal remains depressed, and the first engine braking profile remains active. The engine speed is adjusted in response to the vehicle speed by the CVT selecting a gear ratio.

[0052] At time T2, the vehicle reaches an acceleration level that causes the CVT to activate the second engine braking profile. The engine speed relative to the vehicle speed is adjusted by the CVT according to this second engine braking profile. The brakes remain applied, and the vehicle speed continues to increase. The engine speed also continues to increase, and the engine pumping work remains constant.

[0053] Between time T2 and time T3, the vehicle continues to accelerate and the engine speed continues to increase. The engine pumping work remains constant and the vehicle speed continues to increase as the vehicle accelerates. The brake pedal remains depressed and the second engine braking profile remains active. These conditions may indicate that the vehicle is traveling on a road with a negative gradient that is becoming steeper.

[0054] At time T3, the vehicle speed reaches a threshold speed, at which point the engine pumping work increases. In one example, the closing of the engine intake valve is advanced or retarded to near bottom dead center of the intake stroke, and the timing of the exhaust valve is advanced so that the opening of the exhaust valve moves towards top dead center of the power stroke. In this way, the amount of air entering and being compressed in the engine cylinders increases, while the exhaust valves open earlier to release air that expands in the cylinders, thus increasing the engine pumping work. By increasing the engine pumping work after the engine speed reaches a threshold speed, engine braking can be increased without increasing the engine speed, thereby reducing engine noise and / or vibration.

[0055] Between time points T3 and T4, the vehicle speed continues to increase, while the engine speed is kept constant by the CVT. The CVT maintains the constant engine speed by varying the CVT ratio. The engine pumping work increases with the increasing vehicle speed. The vehicle continues to accelerate, and the brake pedal remains depressed. The second engine braking profile remains active.

[0056] At time T4, the vehicle begins to decelerate, and the engine speed remains at its previous constant value as the vehicle speed decreases. The engine pumping work begins to decrease, and the brake pedal remains depressed. The second engine braking profile remains active. Such conditions can occur when a vehicle decelerates in response to a road gradient.

[0057] Between time T4 and time T5, the vehicle continues to decelerate, and the engine slows down from its previous constant speed. The engine pumping work is reduced to the level it was at before time T3. The vehicle brakes remain applied.

[0058] At time T5, in response to a vehicle speed error falling below a threshold, the active engine braking profile switches from the second profile to the first profile. The vehicle continues to decelerate, and the engine speed continues to decrease. The engine pumping work remains constant, and the brake pedal remains depressed.

[0059] In this way, engine braking can be adjusted by setting a CVT's gear ratio according to a variety of profiles that relate engine speed to vehicle speed. Additionally, engine pumping work can be increased or decreased to adjust engine braking under conditions where increasing engine speed could raise powertrain noise and vibration beyond acceptable levels.

[0060] Now, with reference to Fig. 5A and Fig. Figure 5B shows an exemplary flowchart for a method of operating a vehicle power transmission. The method from Fig. 5A and Fig. 5B can be integrated into the systems from Fig. 1, Fig. 2A and Fig. 2B be included and interact with them. Furthermore, at least sections of the procedure from Fig. 5A and Fig. 5B may be included as executable instructions stored in non-volatile memory, while other sections of the procedure may be carried out via a controller that translates operating states of devices and actuators in the physical world. It should be noted that Fig. 5A and Fig. 5B illustrates a flowchart, but a state machine represents the process from Fig. 5A and Fig. 5B can be carried out without deviating from the scope of the invention.

[0061] In procedure 502, procedure 500 assesses whether hill start assist and engine braking are requested. In one example, a human driver might select hill start assist via a user interface to slow the vehicle using less wheel friction braking. Engine braking and hill start assist can be activated or requested in response to a driver releasing the accelerator pedal or requesting less than a threshold amount of torque from the power transmission. The vehicle speed at the time the accelerator pedal is released is used as the desired vehicle speed, and hill start assist attempts to maintain the vehicle speed at the desired speed.Initially, the hill start assist can rely on regenerative braking to maintain vehicle speed, but it can also add engine braking, as described here, if regenerative braking capacity is insufficient to maintain the desired speed. Hill start assist can be useful for extending the service life of wheel friction brakes and maintaining vehicle speed while driving on a road with a negative gradient.

[0062] If procedure 500 determines that hill start assist is active and engine braking is requested, the answer is yes, and procedure 500 proceeds to 504. Otherwise, the answer is no, and procedure 500 terminates. If procedure 500 terminates during vehicle deceleration conditions, the engine may be turned without fuel supply if the vehicle brakes are applied. Alternatively, the engine speed may be reduced to an idle speed, while the engine continues to turn after termination.

[0063] In procedure 504, procedure 500 adjusts the engine speed in response to an engine braking profile CVTfn1, which relates the engine speed to the vehicle speed. The engine braking profile CVTfn1 can be configured as in engine braking profile 308. Fig. Figure 3 shows that this engine braking profile can provide a lower level of engine braking compared to other engine braking profiles. The CVTfn1 function describes a relationship between engine speed and vehicle speed that provides a desired level of engine braking. The CVT ratio is set according to the CVTfn1 engine braking profile to provide a specific engine speed at a given vehicle speed. Additionally, fuel flow to the engine can be cut off during engine braking. Procedure 500 transitions to 506.

[0064] At 506, procedure 500 reassesses whether hill start assist and engine braking are requested. Procedure 500 reassesses whether hill start assist and engine braking are requested in the event that it may be desirable to terminate engine braking in response to a human driver pressing the accelerator pedal or to any other condition that may indicate a desire to terminate engine braking. If procedure 500 assesses that hill start assist and engine braking are not requested, the answer is No, and procedure 500 terminates. Otherwise, the answer is Yes, and procedure 500 proceeds to 508.

[0065] In procedure 508, procedure 500 assesses whether the vehicle speed error (Vspd_er) is greater than the output of function (fun1) or whether the vehicle acceleration (Acc) is greater than the output of function (fun2). If either condition is true and the engine speed has been set above a threshold (cal1) for a duration (Tim1) in response to the engine braking profile CVTfn1, then the answer is yes, and procedure 500 proceeds to 510. Otherwise, the answer is no, and procedure 500 returns to 504. The conditions in 508 can be expressed mathematically as follows: If ((Vspd_er > fun1 or Acc > fun2) and Tim1 > cal1), then procedure 500 proceeds to 510. Otherwise, procedure 500 returns to 504.In one example, the function fun1 is a table stored in non-volatile memory referenced by the current vehicle speed error (desired vehicle speed minus actual vehicle speed) and the brake pedal input. The fun1 table contains empirically determined vehicle speed error values ​​against which the vehicle speed error is compared. The function fun2 is a second table stored in non-volatile memory referenced by the current vehicle acceleration and brake pedal position. The fun2 table contains empirically determined vehicle acceleration values ​​against which the vehicle acceleration is compared. In one example, values ​​from fun1 are provided such that procedure 500 requires a smaller vehicle speed error to transition to 510 as the brake pedal position increases (e.g.,(for a command for higher braking torque). Tim1 is a value of a timer that tracks a duration during which the engine speed is adjusted in response to CVTfn1, and cal1 is a predetermined threshold duration.

[0066] In procedure 500, method 510 adjusts the engine speed in response to an engine braking profile CVTfn2, which relates the engine speed to the vehicle speed. The engine braking profile CVTfn2 can be configured as in engine braking profile 306. Fig. 3 is shown, and the engine braking profile can provide a higher level of engine braking compared to the CVTfn1 engine braking profile. The CVTfn2 function describes a relationship between engine speed and vehicle speed that provides a desired level of engine braking. The CVT ratio is set according to the CVTfn2 engine braking profile to provide an engine speed at a specific vehicle speed. For example, if, as in Fig. As shown in Figure 3, if the vehicle speed is greater than VS2 and engine braking profile 306 is activated, the CVT ratio is adjusted to provide an engine speed equal to the engine speed in line segment 306a. Additionally, fuel flow to the engine can be deactivated during engine braking. Procedure 500 then proceeds to 512.

[0067] In 512, method 500 can adjust the motor pump work depending on the engine speed and vehicle speed. In particular, if the engine speed is in a range where the engine speed is kept constant as the vehicle speed increases (e.g., segment 306a in Fig. 3) The engine pumping work can be increased as vehicle speed increases by adjusting the intake and exhaust valve timing. For example, the intake valve closing time can be adjusted (e.g., advanced or retarded) to increase the cylinder air charge, while simultaneously the exhaust valve opening time can be advanced to release compressed gas earlier, thus increasing engine pumping work as vehicle speed increases while engine speed remains constant. Similarly, the intake valve closing time can be adjusted (e.g., advanced or retarded) to decrease the cylinder air charge, while simultaneously the exhaust valve opening time can be retarded to retain compressed gas longer, thus reducing engine pumping work as vehicle speed decreases while engine speed remains constant.In this way, the engine pumping work can be adjusted in response to the vehicle speed while keeping the engine speed constant, so that appropriate levels of engine braking can be provided even when an engine braking profile limits the engine speed to reduce noise and vibration of the power transmission. Method 500 transitions to 514.

[0068] At 514, procedure 500 reassesses whether hill start assist and engine braking are requested. Procedure 500 reassesses whether hill start assist and engine braking are requested if it might be desirable to terminate engine braking in response to a human driver pressing the accelerator pedal or to any other condition that might indicate a desire to terminate engine braking. If procedure 500 assesses that hill start assist and engine braking are not requested, the answer is no, and procedure 500 terminates. Otherwise, the answer is yes, and procedure 500 proceeds to 516.

[0069] At 516, procedure 500 assesses whether the vehicle speed error (Vspd_er) is lower than a predetermined threshold (thr1) and whether the vehicle acceleration (Acc) is lower than the output of the function (fun3). If both conditions are true and the engine speed has been set above a threshold (cal2) for a duration (Tim2) in response to the engine braking profile CVTfn2, then the answer is yes and procedure 500 returns to 504. Otherwise, the answer is no and procedure 500 proceeds to 518. The conditions at 516 can be expressed mathematically as follows: If ((Vspd_er<thr1 und Acc> If fun3) and Tim2>cal2), then procedure 500 returns to 504. Otherwise, procedure 500 transitions to 518. In an example, thr1 is a predetermined threshold variable stored in non-volatile memory.The function fun3 is a table stored in non-volatile memory that references the current vehicle acceleration and brake pedal position. The fun3 table contains empirically determined vehicle acceleration values ​​against which the current vehicle acceleration is compared. Tim2 is a value from a timer that tracks the duration during which the engine speed is adjusted in response to CVTfn2, and cal2 is a predetermined threshold duration.

[0070] In procedure 518, procedure 500 assesses whether the vehicle speed error (Vspd_er) is greater than the output of function (fun4) or whether the vehicle acceleration (Acc) is greater than the output of function (fun5). If either condition is true and the engine speed has been set above a threshold (cal3) for a duration (Tim3) in response to the engine braking profile CVTfn2, then the answer is yes, and procedure 500 proceeds to 520. Otherwise, the answer is no, and procedure 500 returns to 510. The conditions in 518 can be expressed mathematically as follows: If ((Vspd_er > fun4 or Acc > fun5) and Tim3 > cal3), then procedure 500 proceeds to 520. Otherwise, procedure 500 returns to 510.In one example, the function `fun4` is a table stored in non-volatile memory that references the current vehicle speed error (desired vehicle speed minus actual vehicle speed) and the input brake pedal position. The `fun4` table contains empirically determined vehicle speed error values ​​against which the current vehicle speed error is compared. In one example, values ​​for `fun4` are provided such that procedure 500 requires a smaller vehicle speed error to transition to 520 as the brake pedal position increases (for example, for a command for higher braking torque). The function `fun5` is a second table stored in non-volatile memory that references the current vehicle acceleration and brake pedal position.The fun5 table contains empirically determined vehicle acceleration values ​​against which the vehicle's acceleration is compared. Tim3 is a value from a timer that tracks a duration during which the engine speed is adjusted in response to CVTfn2, and cal3 is a predetermined threshold duration.

[0071] At 520, procedure 500 adjusts the engine speed in response to an engine braking profile CVTfn3, which relates the engine speed to the vehicle speed. The engine braking profile CVTfn3 can be configured as in engine braking profile 304. Fig. 3 is shown, and the engine braking profile can provide a higher level of engine braking compared to the engine braking profile CVTfn2. The function CVTfn3 describes a relationship between engine speed and vehicle speed that provides a desired level of engine braking. The CVT ratio is set according to the engine braking profile CVTfn3 to provide an engine speed at a specific vehicle speed. Additionally, the fuel flow to the engine can be shut off during engine braking. Procedure 500 transitions to 522.

[0072] In the case of 522, the method 500 can adjust the motor pumping work depending on the motor speed and vehicle speed. In particular, if the motor speed is in a range where the motor speed is kept constant as the vehicle speed increases (e.g., motor speed greater than VS1 in Fig. 3) The engine pumping work can be increased as vehicle speed increases by adjusting the intake and exhaust valve timing. Likewise, the intake valve closing timing can be adjusted (e.g., advanced or retarded) to reduce cylinder air charge, while simultaneously the exhaust valve opening timing can be retarded to retain compressed gas longer, thereby reducing engine pumping work as vehicle speed decreases while maintaining a constant engine speed. In this way, engine pumping work can be adjusted in response to vehicle speed while maintaining a constant engine speed, thus providing appropriate levels of engine braking even when an engine braking profile limits engine speed to reduce powertrain noise and vibration. Method 500 transitions to 524.

[0073] At 524, procedure 500 reassesses whether hill start assist and engine braking are requested. Procedure 500 reassesses whether hill start assist and engine braking are requested in the event that it may be desirable to terminate engine braking in response to a human driver pressing the accelerator pedal or to any other condition that may indicate a desire to terminate engine braking. If procedure 500 assesses that hill start assist and engine braking are not requested, the answer is no, and procedure 500 terminates. Otherwise, the answer is yes, and procedure 500 proceeds to 526.

[0074] At 526, procedure 500 assesses whether the vehicle speed error (Vspd_er) is lower than a predetermined threshold (thr2) and whether the vehicle acceleration (Acc) is lower than the output of the function (fun6). If both conditions are true and the engine speed has been set above a threshold (cal4) for a duration (Tim4) in response to the engine braking profile CVTfn3, then the answer is yes and procedure 500 returns to 510. Otherwise, the answer is no and procedure 500 proceeds to 528. The conditions at 526 can be expressed mathematically as follows: If ((Vspd_er<thr2 und Acc> If fun6) and Tim4>cal4), then procedure 500 returns to 510. Otherwise, procedure 500 transitions to 528. In one example, thr2 is a predetermined threshold variable stored in non-volatile memory.The function fun6 is a table stored in non-volatile memory that references the current vehicle acceleration and brake pedal position. The fun6 table contains empirically determined vehicle acceleration values ​​against which the current vehicle acceleration is compared. Tim4 is a value from a timer that tracks the duration during which the engine speed is adjusted in response to CVTfn3, and cal4 is a predetermined threshold duration.

[0075] At 528, procedure 500 assesses whether the vehicle speed error (Vspd_er) is greater than the output of function (fun7) or whether the vehicle acceleration (Acc) is greater than the output of function (fun8). If either condition is true and the engine speed has been set above a threshold (cal5) for a duration (Tim5) in response to the engine braking profile CVTfn3, then the answer is yes, and procedure 500 proceeds to 530. Otherwise, the answer is no, and procedure 500 returns to 520. The conditions at 528 can be expressed mathematically as follows: If ((Vspd_er>fun7 or Acc>fun8) and Tim5>cal5), then procedure 500 proceeds to 530. Otherwise, procedure 500 returns to 520.In one example, the function `fun7` is a table stored in non-volatile memory that references the current vehicle speed error (desired vehicle speed minus actual vehicle speed) and the input brake pedal position. The `fun7` table contains empirically determined vehicle speed error values ​​against which the current vehicle speed error is compared. In one example, values ​​from `fun7` are provided such that procedure 500 requires a smaller vehicle speed error to transition to 530 as the brake pedal position increases (for example, for a command for higher braking torque). The function `fun8` is a second table stored in non-volatile memory that references the current vehicle acceleration and brake pedal position.The fun8 table contains empirically determined vehicle acceleration values ​​against which the vehicle's acceleration is compared. Tim5 is a value from a timer that tracks a duration during which the engine speed is adjusted in response to CVTfn3, and cal5 is a predetermined threshold duration.

[0076] At 530, procedure 500 adjusts the engine speed in response to an engine braking profile CVTfn4, which relates the engine speed to the vehicle speed. The engine braking profile CVTfn4 can be configured as in engine braking profile 302. Fig. 3 is shown, and the engine braking profile can provide a higher level of engine braking compared to the engine braking profile CVTfn3. The function CVTfn4 describes a relationship between engine speed and vehicle speed that provides a desired level of engine braking. The CVT ratio is set according to the engine braking profile CVTfn4 to provide an engine speed at a specific vehicle speed. Additionally, the fuel flow to the engine can be shut off during engine braking. Procedure 500 transitions to 532.

[0077] In the case of 532, the method 500 can adjust the motor pumping work depending on the motor speed and vehicle speed. In particular, if the motor speed is in a range where the motor speed is kept constant as the vehicle speed increases (e.g., motor speed greater than VS1 in Fig. 3) The engine pumping work can be increased as the vehicle speed increases by adjusting the intake and exhaust valve timing. Likewise, the intake valve closing timing can be adjusted (e.g., advanced or retarded) to reduce the cylinder air charge, while simultaneously the exhaust valve opening timing can be retarded to retain compressed gas longer, thereby reducing engine pumping work as the vehicle speed decreases while maintaining a constant engine speed. In this way, the engine pumping work can be adjusted in response to the vehicle speed while maintaining a constant engine speed, thus providing appropriate levels of engine braking even when an engine braking profile limits the engine speed to reduce powertrain noise and vibration. Method 500 transitions to 534.

[0078] At 534, procedure 500 reassesses whether hill start assist and engine braking are requested. Procedure 500 reassesses whether hill start assist and engine braking are requested in the event that it may be desirable to terminate engine braking in response to a human driver pressing the accelerator pedal or to any other condition that may indicate a desire to terminate engine braking. If procedure 500 assesses that hill start assist and engine braking are not requested, the answer is no, and procedure 500 terminates. Otherwise, the answer is yes, and procedure 500 proceeds to 536.

[0079] At 536, procedure 500 assesses whether the vehicle speed error (Vspd_er) is lower than a predetermined threshold (thr3) and whether the vehicle acceleration (Acc) is lower than the output of the function (fun9). If both conditions are true and the engine speed has been set above a threshold (cal6) for a duration (Tim6) in response to the engine braking profile CVTfn4, then the answer is yes and procedure 500 returns to 520. Otherwise, the answer is no and procedure 500 returns to 530. The conditions at 536 can be expressed mathematically as follows: If ((Vspd_er<thr3 und Acc> If fun9) and Tim6>cal6), then the procedure returns 500 to 520. Otherwise, the procedure returns 500 to 530. In an example, thr3 is a predetermined threshold variable stored in non-volatile memory.The function fun9 is a table stored in non-volatile memory that references the current vehicle acceleration and brake pedal position. The fun9 table contains empirically determined vehicle acceleration values ​​against which the current vehicle acceleration is compared. Tim6 is a value from a timer that tracks the duration during which the engine speed is adjusted in response to CVTfn4, and cal6 is a predetermined threshold duration.

[0080] Procedure 500 can begin supplying fuel to the engine and operating the engine without engine braking when Procedure 500 ends. Thus, the engine can begin propelling the vehicle again after Procedure 500 ends.

[0081] Thus, the procedure is Fig. 5A and Fig. 5B provides a vehicle operating procedure that includes: 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. The procedure includes, where the first engine speed-to-vehicle speed profile is a linear relationship between engine speed and vehicle speed. The procedure includes, where the second engine speed-to-vehicle speed profile includes a first threshold engine speed that is not to be exceeded.The method further includes modifying the operation of the CVT via the control unit to adjust the engine speed according to a third engine speed-to-vehicle speed profile in response to a vehicle speed error and a brake pedal position. The method includes, wherein the third engine speed-to-vehicle speed profile incorporates a second threshold engine speed that must not be exceeded, and the second threshold engine speed is greater than the first threshold engine speed. The method further includes providing engine braking while the CVT adjusts the engine speed according to the second engine speed-to-vehicle speed profile.

[0082] The procedure from Fig. 5A and Fig. 5B further provides a vehicle operating procedure that includes: 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 vehicle acceleration and brake pedal position. The procedure further includes increasing the engine pumping work in response to increasing vehicle speed while the vehicle speed is above a threshold speed and while the CVT is adjusting the engine speed according to the second engine speed-to-vehicle speed profile.The procedure further includes reducing the 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.

[0083] In some examples, the method involves the first engine speed-to-vehicle speed profile providing a lower engine speed for a given vehicle speed than the second engine speed-to-vehicle speed profile providing for that vehicle speed. The method involves the second engine speed-to-vehicle speed profile providing a greater degree of engine braking for a given vehicle speed than the first engine speed-to-vehicle speed profile providing for that vehicle speed. The method involves the CVT being a belt- or chain-driven CVT and further involves requiring a threshold duration to set the engine speed according to the first engine speed-to-vehicle speed profile before setting the engine speed according to the second engine speed-to-vehicle speed profile.The method includes, wherein the CVT comprises a planetary gear set and a generator, and further comprises changing the operation of the CVT via the control unit to set the engine speed according to the first 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. The method further comprises changing the operation of the CVT via the control unit 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.

[0084] The procedure from Fig. 5A and Fig.5B provides a vehicle operating procedure that includes: 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; 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 brake pedal position; and 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. The procedure involves increasing the engine pumping work by adjusting the intake and exhaust valve timing of an engine.The method involves the CVT being coupled to an engine. The method involves the CVT adjusting the engine speed by setting a gear ratio between the CVT's input and output. The method involves ensuring that the engine pumping work is not increased while the vehicle speed is below the threshold speed, while the CVT adjusts the engine speed according to the second engine speed-to-vehicle speed profile. The method further involves stopping the fuel flow to an engine while the engine speed is being adjusted according to the second engine speed-to-vehicle speed profile.

[0085] It should be noted that the exemplary control and estimation routines contained herein can be used with various engine and / or vehicle system designs. The control methods and routines disclosed herein can be stored as executable instructions in non-volatile memory and executed by the control system, including the controller, in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein can represent one or more from any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Accordingly, various illustrated actions, processes, and / or functions can be performed in the illustrated sequence or in parallel, or in some cases, omitted.Similarly, the processing sequence is not strictly necessary to achieve the features and advantages of the exemplary embodiments described here, but is provided to facilitate illustration and description. One or more of the illustrated actions, processes, and / or functions can be performed repeatedly, depending on the specific strategy employed. Furthermore, at least some of the described actions, processes, and / or functions can graphically represent code that is to be programmed into non-volatile memory of the computer-readable storage medium in the control system.Furthermore, the control actions can transform the operating state of one or more sensors or actuators in the physical world when the described actions are performed by executing the instructions in a system that includes the various motor hardware components in combination with one or more controllers.

[0086] This concludes the description. A person skilled in the art will recognize many changes and modifications upon reading this description, without altering its spirit or scope. For example, this description could be advantageously used for I3, I4, I5, V6, V8, V10, and V12 engines running on natural gas, gasoline, diesel, or alternative fuel designs.

Claims

[1] Vehicle operating procedures, including: 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. [2] Method according to claim 1, wherein operating the CVT includes adjusting the torque of an electric machine to adjust the motor speed. [3] Method according to claim 2, wherein the second engine speed-to-vehicle speed profile includes a first threshold engine speed that is not to be exceeded. [4] Method according to claim 3, further comprising changing 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 a brake pedal position. [5] Method according to claim 4, wherein the third engine speed-to-vehicle speed profile includes a second threshold engine speed not to be exceeded, wherein the second threshold engine speed is greater than the first threshold engine speed. [6] Method according to claim 1, further comprising providing engine brakes while the CVT adjusts the engine speed according to the second engine speed-to-vehicle speed profile. [7] Method according to claim 1, further comprising 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 vehicle acceleration and brake pedal position. [8] Method according to claim 7, further comprising increasing the engine pump 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] Method according to claim 8, further comprising reducing the engine pump 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] Method according to claim 7, wherein the first engine speed-to-vehicle speed profile provides a lower engine speed for a vehicle speed than the second engine speed-to-vehicle speed profile provides for the vehicle speed. [11] Method according to claim 10, wherein the second engine speed-to-vehicle speed profile provides a greater degree of engine braking for a vehicle speed than the first engine speed-to-vehicle speed profile provides for the vehicle speed. [12] Method according to claim 7, wherein the CVT is a belt- or chain-driven CVT, and further comprising: Requires a threshold duration to adjust the engine speed according to the first engine speed-to-vehicle speed profile before adjusting the engine speed according to the second engine speed-to-vehicle speed profile. [13] The method of 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 set the engine speed according to the first 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. [14] Method according to claim 7, further comprising changing the operation of the CVT via the control to adjust the engine speed according to a third 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. [15] Method according to claim 1, further comprising increasing the engine pump work in response to the fact that the vehicle speed is higher than a threshold speed, while the CVT adjusts the engine speed according to the second engine speed-to-vehicle speed profile.

Images