Hydraulic turbocharged engine with automatic start-stop function

Abstract

The present invention relates to a hydraulic turbocharged engine with automatic start-stop functionality. Systems and methods are provided for a vehicle engine including a turbocharger coupled to a hydraulic pump and a hydraulic accumulator. In one example, a method can include supplying pressure from an accumulator coupled to a hydraulic pump to a hydraulic braking system of a vehicle in response to the vehicle coming to a stop, the hydraulic pump being coupled to a shaft of a turbocharger of an engine mounted within the vehicle and automatically shutting down the engine when the vehicle is stopped.

Description

TECHNICAL FIELD

[0001] The present invention relates generally to methods and systems for hydraulic brake systems that allow for the use of automatic engine start-stop technology on a hydraulic hybrid vehicle. BACKGROUND

[0002] As emission regulations continue to be enacted, there is an increasing demand for more fuel efficient vehicles. To improve fuel economy, the popularity of technologies such as automatic start-stop systems is on the rise. These start-stop systems automatically shut down the engine by stopping the delivery of fuel to the combustion chamber when the vehicle is stopped and idling, a major source of fuel waste. Long idling conditions are typical for delivery vehicles, taxis, and commuter vehicles in heavy traffic situations. During the temporary engine shutdown, once the vehicle controller receives an indication of a torque demand from the operator or other engine parameter requiring engine power (e.g., low battery charge), the engine restarts and resumes normal operation. Many hybrid vehicles have automatic engine start-stop systems that utilize an auxiliary electric motor to run auxiliary systems when the engine is off. Many hybrid vehicles employ an integrated starter motor in place of a traditional starter motor and alternator for harvesting regenerative braking energy and to withstand the frequent start-stop cycles inherent to these systems.

[0003] Hydraulic hybrid vehicles (HHVs) can store pressurized fluid in a reservoir (e.g., accumulator) during engine operation. One example of a hydraulic hybrid vehicle is shown in U.S. Patent No. 7,146,266 to Teslak et al. Therein, a reversible pump uses braking energy to direct hydraulic fluid into a nitrogen-charged high pressure accumulator. When the vehicle controller receives a torque demand from the operator, the pump is reversed and uses the pressurized fluid to accelerate the vehicle. However, the inventors have recognized potential problems with such systems. In one example, hydraulic brake systems associated with a compression ignition engine are typically supplied with hydraulic pressure from a main engine source (e.g., power steering system) that is not functional when the engine is off. To maintain the functionality of the brake system during engine off conditions, these systems tend to include a supplemental electric pump motor.

[0004] Attempts to integrate automatic start-stop systems into compression ignition engine systems include well-known full hybrid vehicles, in which a hydraulic pump motor is coupled to the engine for starting and stopping both the vehicle and the engine. Beaty et al. illustrate an example method in U.S. Patent No. 7,104,920. In this method, a hydraulic hybrid powertrain includes an engine coupled to a hydraulic pump motor, which is coupled to the vehicle's transmission and hydraulic accumulator. The transmission can be operated via the hydraulic pump motor or via both the engine and the hydraulic pump motor. However, the inventors have recognized the potential problems with such full hybrid systems. In one example, the aforementioned system requires the addition of a very large hydraulic pump motor, which significantly increases the cost, weight, and complexity of the vehicle system, making its implementation impractical in most passenger vehicles. Summary of the Invention

[0005] In one example, the problem described above can be addressed by a method for a vehicle that includes: supplying pressure to the vehicle's hydraulic braking system from an accumulator coupled to a hydraulic pump coupled to the shaft of a turbocharger (e.g., a hydraulic turbocharger) mounted in the vehicle, in response to the vehicle coming to a stop, and automatically shutting off the engine when the vehicle stops. In this way, the hydraulic pressure accumulator coupled to a hydraulic hybrid engine can be used as a source of braking energy to enable the use of automatic start-stop technology, thereby improving fuel economy and reducing emissions.

[0006] As an example, during engine operation, when the pressure in the accumulator is below a threshold, a hydraulic pump coupled to the rotating shaft of the turbocharger charges the accumulator (e.g., a hydraulic accumulator) with hydraulic pressure. When the vehicle stops for a duration exceeding the threshold and the pressure in the accumulator is above the threshold, the brake fluid supplied to the braking components coupled to the vehicle's wheels switches from being sourced from the main engine to being sourced from the hydraulic accumulator. Unlike typical hydraulic braking systems associated with compression-ignition engines (where the main engine source loses power and thus hydraulic pressure when the engine is off), the hydraulic accumulator maintains hydraulic pressure even when the engine is off. Because pressurized hydraulic brake fluid can be supplied to the braking system using the accumulator, automatic engine start-stop for compression-ignition engines can be achieved. In this way, the use of expensive pump motors to maintain hydraulic pressure can be avoided, thus maintaining low manufacturing costs and improving fuel efficiency.

[0007] It should be understood that the above overview is provided to introduce some concepts in a simplified form, which are further described in the specific embodiments. This is not intended to identify the key or essential features of the claimed subject matter, the scope of which is uniquely defined by the appended claims. Furthermore, the claimed subject matter is not limited to embodiments that address any shortcomings mentioned above or in any part of this disclosure. Attached Figure Description

[0008] Figure 1 An example embodiment of an engine system is shown, which includes a hydraulic turbocharger coupled to the engine.

[0009] Figure 2 An example embodiment of a hydraulic braking system, including a hydraulic turbocharger and a hydraulic accumulator, coupled to an engine configured to start and stop automatically is shown.

[0010] Figures 3A-3B A flowchart illustrating a procedure that can be implemented to operate a turbocharger to charge a hydraulic accumulator and operate a hydraulic braking system coupled to the hydraulic accumulator.

[0011] Figure 4 A flowchart illustrating a procedure for automatically starting and stopping a diesel engine with a hydraulic braking system is shown.

[0012] Figure 5 An example operation of a turbocharged engine coupled to a hydraulic braking system including a hydraulic accumulator is shown. Detailed Implementation

[0013] The following description relates to systems and methods for hydraulic braking systems that allow the use of automatic start-stop technology in hydraulic hybrid vehicles. An example of such a system includes a turbocharged engine, wherein the turbocharger is coupled to a hydraulic pump and an accumulator, such as... Figure 1 As shown. The accumulator can also be coupled to the vehicle's hydraulic braking system, and the hydraulic braking system can be configured to operate using hydraulic braking pressure from the main engine source or from the hydraulic accumulator, such as... Figure 2 As shown. In one example, the engine could be a diesel (e.g., compression ignition) engine, where the main engine source can supply hydraulic pressure only to the hydraulic braking system during engine start-up and operation. During engine operation, the control program (e.g., ...) can be configured according to the control program. Figures 3A-3B The example program shown controls the hydraulic turbocharger. The vehicle controller can be configured to execute programs (such as...) in response to vehicle braking conditions and accumulator hydraulic pressure levels. Figure 4 The example program shown will be used to implement automatic start and stop. Figure 5The diagram illustrates an example operation of a turbocharged engine coupled to a hydraulic pump and an accumulator. By coupling the hydraulic braking system of the compression ignition engine system to a hydraulic accumulator pressurized by a hydraulic pump coupled to the turbocharger, hydraulic pressure can be supplied at any time even when the engine is off, thereby enabling the use of automatic start-stop technology in the compression ignition engine system.

[0014] Figure 1 Aspects of an example engine system 100 are schematically illustrated. Engine system 100 may be included in a propulsion system such as road vehicle system 98. In one example, road vehicle system 98 is a hydraulic hybrid vehicle. Engine system 100 includes an engine 10, which may be a compression ignition (e.g., diesel) engine. In other embodiments, engine 10 may be an internal combustion engine or other suitable type of engine. Engine 10 is coupled to a booster. In the depicted example, the booster is a hydraulic turbocharger 20, which includes an exhaust-driven turbine 22 located in an exhaust passage 56 coupled to a compressor 26 via a shaft 28. Compressor 26 is located in an intake passage 38 upstream of a boost air cooler (e.g., CAC 32). A hydraulic pump 34 is also coupled to turbocharger 20 such that hydraulic pump 34 can be driven by the turbocharger. In the depicted example, hydraulic pump 34 is shown directly coupled to shaft 28, which is directly coupled to turbine 22 and compressor 26. However, it should be understood that the hydraulic pump can be coupled to a separate shaft selectively driven by shaft 28. Hydraulic pump 34 can be hydraulically coupled to hydraulic accumulator 36, so that driving hydraulic pump 34 can direct hydraulic energy to hydraulic accumulator 36 (e.g., a reservoir) for storage. Hydraulic pump 34 can also be fluidly coupled to... Figure 1 The source of the hydraulic brake fluid (e.g., oil pan) is not shown. This brake fluid source may be related to the information below. Figure 2 The main engine source is shared, or it can be separate and independent from the brake fluid source of the main engine source. In one example, the hydraulic accumulator 36 can be a bladder-type accumulator, which includes a resilient bladder filled with nitrogen fitted in a rigid-walled pressure vessel. In another example, the hydraulic accumulator 36 can be a piston-type accumulator, which includes a driven piston to compress and pressurize the introduced hydraulic fluid. In yet another example, the hydraulic accumulator 36 can be a diaphragm-type accumulator, which includes a rubber plate (e.g., a diaphragm) serving as a separating element between the nitrogen chamber and the hydraulic chamber.

[0015] In this manner, the hydraulic accumulator 36 can be charged by the operation of the turbocharger (e.g., by the rotation of shaft 28). Although the current embodiment uses a hydraulic turbocharger, it should be appreciated that other combinations and configurations of the booster device are possible. In one embodiment, the turbocharger may be a twin-scroll device. In another embodiment, the turbocharger may be a variable geometry turbocharger (VGT), wherein the turbine geometry changes actively according to engine operating conditions. In yet another embodiment, the engine system 100 may include a supercharger and a turbocharger. In embodiments including a supercharger, the compressor 26 may be at least partially driven by electromechanical and / or engine 10.

[0016] Engine 10 receives air along intake passage 38 through airbox 40 including air purifier 42. The air is compressed by compressor 26 and delivered via CAC 32 for cooling before entering intake manifold 30, where it enters engine 10. In some examples, CAC 32 may be an air-to-air heat exchanger or a water-to-air heat exchanger. Figure 1 In the embodiment shown, the pressure of the air filling in the intake manifold 30 is detected by the manifold air pressure (MAP) sensor 72.

[0017] like Figure 1 As shown, one or more sensors can be coupled to the inlet of compressor 26. For example, temperature sensor 74 can be coupled to the inlet to estimate the compressor inlet temperature. As another example, pressure sensor 76 can be coupled to the compressor inlet to estimate the pressure of the air entering the compressor. Other sensors may include, for example, an air-fuel ratio sensor, a humidity sensor, etc. In other examples, one or more of the compressor inlet conditions (such as humidity, temperature, etc.) can be inferred based on engine operating conditions. Sensors can estimate the intake air received at the compressor inlet from the intake passage and the air recirculated upstream from CAC 32. One or more sensors may also be coupled upstream of compressor 26 to intake passage 38 to determine the composition and condition of the air entering the compressor. These sensors may include, for example, a mass airflow (MAF) sensor 78.

[0018] The intake manifold 30 is coupled to a series of combustion chambers 44 via a series of intake valves (not shown). The combustion chambers are further coupled to an exhaust manifold 46 via a series of exhaust valves (not shown). In the depicted embodiment, a single exhaust manifold 46 is shown. However, in other embodiments, the exhaust manifold may include multiple exhaust manifold sections. A configuration with multiple exhaust manifold sections allows exhaust gases from different combustion chambers to be directed to different locations within the engine system 100.

[0019] In one embodiment, each of the exhaust valve and the intake valve can be electronically actuated or controlled. In another embodiment, each of the exhaust valve and the intake valve can be cam-actuated or controlled. Whether electronically or cam-actuated, the opening and closing timing of the exhaust valve and the intake valve can be adjusted according to the desired combustion and emission control performance. Alternatively, a variable cam timing device (not shown) can be driven to adjust the timing of the intake valve and the exhaust valve (not shown) to provide reduced positive intake to the exhaust valve overlap. That is, the intake valve and the exhaust valve will be open for a shorter duration and will move away from being simultaneously open for a portion of the intake stroke.

[0020] In some examples, compressor 26 may include a compressor recirculation valve (CRV) 48 spanning compressor 26. The depicted example shows a recirculation passage 50 with CRV 48 for recirculating (hot) compressed air from the compressor outlet back to the compressor inlet. In some embodiments, the compressor recirculation system may alternatively or additionally include a recirculation passage for recirculating (cooled) compressed air from the compressor outlet downstream of the boost air cooler to the compressor inlet or compressor bypass to dissipate the compressed air into the atmosphere. CRV 48 may be a continuously variable valve, wherein the valve position is continuously variable from a fully closed position to a fully open position. In some embodiments, compressor recirculation valve 48 may typically be partially open during boost engine operation to provide some surge margin. In this document, the partially open position may be the default valve position. Increasing the opening of the compressor recirculation valve may include an actuating (or energizing) solenoid of the valve. Example CRV operation will be discussed further herein.

[0021] Exhaust gas from one or more exhaust manifold sections is directed to turbine 22 to drive the turbine. When reduced turbine torque is desired, some exhaust gas may instead be directed through wastegate passage 54, bypassing turbine 22. Wastegate valve 52 may be actuated to open to relieve at least some of the exhaust pressure from upstream to downstream of turbine 22 through wastegate passage 54. By reducing the exhaust pressure upstream of turbine 22, turbine speed can be reduced. In one embodiment, wastegate valve 52 may be vacuum-actuated, that is, it may be actuated by applying a vacuum by the engine or other source. The mixed flow from turbine 22 and wastegate passage 54 then flows through an emission control device (not shown) before all or part of the treated exhaust gas is released to the atmosphere through exhaust passage 56. However, depending on the operating conditions, some exhaust gas may instead be directed to the intake passage through an EGR passage (not shown), which includes an EGR cooler and an EGR valve. In one example, EGR may be recirculated to the inlet of compressor 26. Various sensors, including exhaust temperature sensor 80 and exhaust pressure sensor 82, can be included in exhaust passage 56. In some examples, oxygen sensor 79 can be coupled to exhaust manifold 46 to estimate the proportion of oxygen in the exhaust gas.

[0022] The depicted embodiments include compression ignition engines that can operate using diesel or biodiesel. Diesel engines typically operate using direct injection, which involves injecting fuel directly into the combustion chamber. However, it should be recognized that other fuels, such as gasoline, alcohol-blended fuels, compressed natural gas, etc., can be used. Engines using these fuels can supply fuel to the combustion chamber via direct injection, port injection, throttle body injection, or any combination thereof. Port injection delivers a fuel spray into the intake manifold and mixes it with the intake air at the intake manifold before it enters the combustion chamber. This example may include multiple direct fuel injectors 58. As previously described, the described embodiments are compression ignition engines, and therefore combustion can be initiated by compression ignition; however, it should be recognized that spark ignition may also be used in alternative embodiments. Additionally, example embodiments including spark ignition engines may also include a throttle valve with a variable-actuated throttle plate (not shown).

[0023] In situations where the driver's torque demand increases instantaneously, such as during accelerator pedal depressing, when transitioning from non-boosted to boosted engine operation, the opening of the wastegate valve 52 can be reduced to limit the wastegate passage 54, thereby reducing the amount of exhaust gas bypassing the turbine. By increasing the exhaust flow through turbine 22, the turbocharger speed increases, thereby increasing the amount of compressed intake air delivered to the engine combustion chamber. In one example, wastegate valve 52 can be closed. The increased turbine speed can drive compressor 26, thereby increasing the pressure of the intake air entering engine 10. Additionally, the increased turbine speed, and thus the increased turbocharger shaft speed 28, can drive the speed of hydraulic pump 34, thereby increasing the volume and / or pressure of hydraulic fluid (e.g., hydraulic energy) stored (e.g., charged) in accumulator 36. Reference will be made herein. Figures 2-5 Further details regarding the control of the hydraulic pump and accumulator were disclosed.

[0024] During periods when the driver's torque demand decreases, such as when releasing the accelerator pedal, when transitioning from boosted to deboosted engine operation, CRV 48 can be opened to prevent the higher speeds of turbine 22 from overwhelming compressor 26 and causing compressor surge. In one example, if the accumulator pressure level is above a threshold pressure level, the opening of wastegate 52 can be increased to increase the flow of exhaust gas bypassing turbine 22 and reduce turbine speed. This allows excess boost pressure to be relieved substantially immediately. However, in another example, if the accumulator pressure level is below a threshold pressure level during accelerator pedal release, wastegate 52 can remain closed, allowing turbine 22 to continue rotating, thereby rotating hydraulic pump 34 to direct hydraulic fluid into accumulator 36, thus charging the accumulator. The opening of CRV 48 can be increased to provide some surge margin. See below for reference. Figures 3A-3B The operation of the example turbocharger will be discussed further.

[0025] Engine torque from engine 10 can be transmitted to vehicle wheels 60 via one or more powertrain shafts 62. The motor vehicle can have any number of wheels 60. Specifically, engine torque can be transmitted from crankshaft 61 to transmission 64, and thereon to wheels 60 via one or more powertrain shafts 62. Transmission 64 can be a fixed-ratio transmission including multiple gear ratios to allow engine 10 to rotate at speeds different from those of the wheels 60. Transmission 64 can be automatic, where operating conditions determine the transmission gear, or it can be manual, where an operator selects the transmission gear. A clutch (not shown) can be provided between engine crankshaft 61 and transmission 64. By changing the torque transmission capability of the clutch (e.g., clutch slip), the amount of engine torque transmitted to the wheels via the powertrain shafts can be adjusted.

[0026] Engine system 100 may also include control system 14. Control system 14 is shown as receiving information from a plurality of sensors 70 (various examples of which are described herein) and sending control signals to a plurality of actuators 90 (various examples of which are described herein). As an example, sensors 70 may include a MAP sensor 72, a compressor inlet temperature sensor 74, a MAF sensor 78, a compressor inlet pressure sensor 76, an exhaust temperature sensor 80, and an exhaust pressure sensor 82. Controller 12 may generate an engine speed signal RPM based on a surface ignition sensing signal (PIP) from a Hall effect sensor or other type of sensor (not shown) coupled to crankshaft 61. The manifold air pressure signal MAP from manifold pressure sensor 72 may be used to provide an indication of vacuum or pressure in the intake manifold. Other sensors, such as additional pressure, temperature, air-fuel ratio, and composition sensors, may be coupled to various locations within engine system 100. Actuators 90 may include, for example, a compressor recirculation valve 48, an exhaust valve 52, and a fuel injector 58.

[0027] The control system 14 may further include a controller 12. The controller may receive input data from various sensors 70, process the input data, and employ various actuators 90 based on the received signals and instructions stored in the controller's memory. The controller 12 may respond to the processed input data based on one or more programs programmed therein (such as those described herein). Figure 3A , Figure 3B and Figure 4 The controller may use instructions or code in the example control program described to employ actuator 90. As an example, the controller may send signals to the actuator of exhaust valve 52 to increase or decrease the opening of the exhaust valve, thereby decreasing or increasing the rotational speed of exhaust turbine 22 and turbocharger shaft 28, which drives compressor 26 of turbocharger 20.

[0028] The control system 14 may also include a display device (not shown) for enabling an operator to input (e.g., a keyboard or touchscreen) and transmit instructions and messages to the operator. In one example, the display device may be coupled to a controller. The controller can receive operator input via the display device and / or send instruction sets from the controller 12 to the operator via the display device. In one example, the operator can disable the engine's automatic start-stop function by indicating a request via the display device.

[0029] In addition to using turbocharger 20 to provide instantaneous boost pressure, a hydraulic pump coupled to the turbocharger can advantageously be used to generate a hydraulic energy source temporarily stored in hydraulic accumulator 36. Therefore, the hydraulic turbocharger 20 can provide a reliable onboard hydraulic energy source. In one example, hydraulic energy can be stored in hydraulic accumulator 36, which provides a readily available hydraulic energy source that can be used to maintain braking pressure in the hydraulic braking system during engine shutdown. Due to the reliable hydraulic energy source in the engine-off state, automatic engine start-stop can be achieved.

[0030] Turn now Figure 2 , Figure 2 Shown in Figure 1 A more detailed schematic diagram of the hydraulic braking system and automatic start-stop system of the engine system 100 described herein is provided. The controller 12, coupled to the engine system 100, is shown as a microcomputer, which includes a microprocessor unit (CPU) 106, input / output ports (I / O) 108, electronic storage media for executable programs and calibration values ​​(shown in this particular example as a read-only memory chip (ROM) 110), random access memory (RAM) 112, keep-alive memory (KAM) 114, and a data bus. The controller 12 can receive various signals from sensors coupled to the engine 10, in addition to those previously described. Figure 1 In addition to the signals discussed, these include, but are not limited to, measurements of intake mass airflow (MAF) from mass airflow sensor 78, manifold absolute pressure (MAP) from sensor 72, and accumulator pressure from pressure sensor 216. Controller 12 receives... Figure 1 and Figure 2 The various sensors shown receive signals and employ... Figure 1 and Figure 2The various actuators shown adjust engine operation based on received signals and instructions stored in the controller's memory. In one example, the controller 12 may receive a signal from the pressure sensor 216 indicating that the internal pressure of the hydraulic accumulator 36 is below a first pressure threshold, and in response, adjust the operation of the pump control valve 210 to direct hydraulic fluid from the hydraulic pump 34 into the accumulator.

[0031] Engine 10 can be coupled to engine starting system 246, which includes a starter motor. In one example, the starter motor can be coupled to an energy storage system (e.g., a battery), wherein the starter motor is driven by energy from the battery. In another example, the starter motor can be a crankshaft integrated starter generator (CISG). In yet another example, the starter motor can be a belt-driven integrated starter generator (BISG). In yet another example, the starter can be a powertrain drive motor, such as a hybrid power generation device connected to the engine via a coupling device. The coupling device can include a transmission, one or more gears, and / or any other suitable coupling device. The starter can be configured to support engine restart at a predetermined near-zero threshold speed (e.g., below 50 or 100 rpm), which is indicated by a signal (ST) from controller 12. In other words, by operating the starter motor of starting system 246, engine 10 can be rotated and started to turn.

[0032] The engine 10 shown has four cylinders 44, but it should be appreciated that the engine 10 may include more or fewer cylinders. One fuel injector 58 is shown coupled to each cylinder 44, but it should be appreciated that more than one fuel injector may be coupled to each cylinder. Fuel from the fuel system 202 can be delivered to the engine 10 via fuel line 203 and distributed to the fuel injectors 58 via fuel rail 204. Actively controlled compression ignition engine fuel rail injection (e.g., common rail direct injection) systems ensure optimal fuel combustion and distribution. In one example, the fuel rail 204 may operate under elevated pressure to enhance fuel atomization. In other examples, the controller 12 may send a signal to inject a small amount of fuel into the combustion chamber (e.g., cylinder 44) prior to the main injection event to reduce engine noise. It should be appreciated that specific fuel rail 204 configurations, fuel injection timing, and fuel injection quantity can vary to meet design engine constraints and desired performance parameters.

[0033] Fuel system 202 may include one or more of a storage tank (e.g., a fuel tank), a fuel pump, and a control valve (not shown) to store and manage the fuel supply. As previously described, the example described is a compression ignition engine, so the fuel system can operate using diesel or biodiesel, but in other engine configurations, other fuels may be used. One or more fuel pumps and one or more fuel control valves of fuel system 202 may be controllably actuated to adjust the amount of fuel delivered to fuel injector 58 of engine 10. In some examples, the fuel control valve may be an electromechanically actuated solenoid valve. In the depicted example, fuel system 202 is actively controlled in response to a fuel signal (FS) from controller 12. In one example, in response to receiving a first FS signal, fuel system 202 may be controlled to reduce the fuel delivery to engine 10 by decreasing the opening of the fuel control valve or by decreasing the operation of the fuel pump. In another example, in response to a second FS signal, fuel system 202 may be controlled to increase the fuel delivery to combustion chamber 440 of engine 10 by increasing the opening of the fuel control valve or by increasing the operation of the fuel pump. It should be recognized that the fuel injector 58 can also be actively controlled to regulate the fuel delivered to the cylinders, including during engine start-stop events.

[0034] like Figure 1 As shown, turbine 22 is coupled to compressor 26 via turbocharger shaft 28. In one example, hydraulic pump 34 may be coupled to turbocharger shaft 28. In other examples, hydraulic pump 34 may be located on a different shaft separate from shaft 28, but still be driven by rotation of shaft 28. Alternatively, hydraulic pump 34 may be configured to be separate from turbocharger shaft 28. Hydraulic pump 34 is fluidly coupled to hydraulic accumulator 36. In the depicted embodiment, the hydraulic pump may be driven by the rotating turbocharger, directing pressurized hydraulic fluid into accumulator 36. In some cases, the accumulator may reach a first pressure threshold (e.g., maximum pressure) when additional hydraulic pressure is not required in accumulator 36. In one example, the first pressure threshold may be determined based on recommendations from the accumulator manufacturer or design limitations of hydraulic braking system components. In other examples, the first pressure threshold may be determined based on the possible uses of the stored hydraulic pressure, thereby avoiding increased costs associated with storing excessive pressurized hydraulic fluid.

[0035] Some embodiments of the hydraulic system may include a pump control valve 210 coupled between a hydraulic pump 34 and a hydraulic accumulator 36. When the hydraulic pressure stored in the accumulator 36 has reached a first pressure threshold indicated by the accumulator pressure sensor 216, the pump control valve 210 can be actuated to control the destination of hydraulic fluid leaving the hydraulic pump 34. The controller 12 may send a control signal (PCV) to actuate the pump control valve 210. In one example, in response to the accumulator pressure falling below the first pressure threshold indicated by the accumulator pressure sensor 216, the pump control valve 210 can be actuated to a first position. In this position, hydraulic fluid from the outlet of the hydraulic pump 34 can be directed to the accumulator 36, thereby filling the accumulator 36. In another example, in response to the accumulator pressure exceeding the first pressure threshold indicated by the accumulator pressure sensor 216, the pump control valve 210 can be actuated to a second position. In this position, hydraulic fluid from the outlet of the hydraulic pump 34 can be directed through a recirculation passage 212 to the inlet of the hydraulic pump 34 or, as previously described, to the hydraulic sump (not shown). In some examples, the pump control valve 210 may optionally be adjusted in response to engine operating parameters (e.g., turbocharger speed or operator torque demand), in addition to adjustments in response to accumulator pressure.

[0036] In some examples, the hydraulic pump 34 can be configured to be disconnected from the turbocharger 20. A decoupling mechanism 214 or other suitable device can be coupled between the hydraulic pump and the turbocharger shaft. In one example, the decoupling mechanism 214 can be a clutch. In some embodiments, the controller 12 can send a control signal (DM) to drive the decoupling mechanism 214. The decoupling mechanism 214 can be driven to a first position in response to the accumulator pressure falling below a first pressure threshold indicated by the accumulator pressure sensor 216. In this position, the decoupling mechanism 214 couples the hydraulic pump 34 to the turbocharger 20 such that the hydraulic pump 34 is driven by the rotation of the turbocharger 20, thereby directing hydraulic fluid to the accumulator 36 (e.g., charging the accumulator). The decoupling mechanism 214 can also be driven to a second position in response to the accumulator pressure being equal to or higher than the first pressure threshold indicated by the accumulator pressure sensor 216. Hydraulic pump 34 is disconnected from turbocharger 20, so that hydraulic pump 34 is not driven by turbocharger 20, thereby reducing (e.g., stopping) the flow of hydraulic fluid from hydraulic pump 34 to accumulator 36. It should be recognized that additional signals or engine operating parameters may help determine whether the hydraulic pump is disconnected from the turbocharger.

[0037] In other examples, the hydraulic pump 34 can be configured to be disconnected from the accumulator 36. In one example, the hydraulic pump 34 can be disconnected from the accumulator by driving the pump control valve 210 to direct hydraulic fluid through the recirculation passage 212 instead of into the accumulator 36. In some examples, the recirculated hydraulic fluid can re-enter the oil pan (from which the hydraulic pump draws fluid) or enter the hydraulic pump inlet. Another possible method of disconnecting the hydraulic pump from the accumulator includes stalling the hydraulic pump.

[0038] It should be recognized that some embodiments may include one or more of mechanisms for disconnecting the hydraulic pump 34 from the turbocharger 20 and for disconnecting the hydraulic pump 34 from the accumulator 36. Other embodiments may include another suitable method that keeps the turbocharger running without diverting hydraulic fluid from the hydraulic pump into the accumulator when this is not desired. It should be recognized that, additionally or alternatively, the hydraulic pump 34 may also be disconnected from the compressor 26.

[0039] In some embodiments, when the hydraulic pressure stored in accumulator 36 is equal to or higher than a first pressure threshold and there is a boost demand from the operator exceeding a first boost demand threshold, hydraulic fluid (e.g., energy) can be directed from accumulator 36 to hydraulic pump 34 to assist the turbocharger's acceleration spin. In this way, the likelihood of turbo lag can be reduced. In some embodiments, pump control valve 210 can be driven by sending a PCV signal to complete the delivery of hydraulic fluid from accumulator 36 to the turbocharger to assist boost pressure, such that the hydraulic fluid can flow from accumulator 36 through recirculation channel 212 and then return upstream of the hydraulic pump or enter the oil pan upstream of the hydraulic pump to drive the hydraulic pump, thereby also driving the turbocharger. In an alternative embodiment, a separate recirculation channel can be used to direct hydraulic fluid from accumulator 36 to the turbocharger to assist boost pressure. In a further embodiment, the pump can be flipped to provide boost torque to turbocharger 20. It should be appreciated that the hydraulic pressure stored in accumulator 36 can also be advantageously used to power other vehicle systems, including, for example, an alternator or drive shaft. In some examples, the hydraulic accumulator 36 may also be coupled to a power take-off (PTO) 239, which may or may not be coupled to a vehicle drive shaft such as the powertrain shaft 62. In this way, hydraulic energy from the accumulator 36 can be used to drive the PTO 239 to power various auxiliary components. Some non-limiting examples of auxiliary units powered by the PTO include air compressors, generators, liquid transfer pumps, pneumatic blowers, and vacuum pumps (not shown).

[0040] Vehicle wheels 60 are nominally fitted with braking assemblies 238, which may include brake calipers. In the depicted example, the braking system is a hydraulic braking system, which includes a main engine source 220 that provides hydraulic braking energy (e.g., pressurized hydraulic braking fluid, brake fluid, or hydraulic fluid), but it should be recognized that other types of braking systems may be used. In some examples, the main engine source 220 may be a power steering system. In this way, the hydraulic fluid of the power steering system can also be used as the main engine source 220 to supply hydraulic fluid to the braking system. In one example of a hydraulic braking system, when operator 230 depresses brake pedal 232, a pushrod (not shown) drives a piston in a reservoir (e.g., a master cylinder), causing brake fluid to flow through a port into a chamber. This increases the pressure in the hydraulic system, forcing the fluid to flow through hydraulic brake lines 236, where the hydraulic fluid drives the braking system to apply braking force to the wheels 60 (e.g., by actuating the brake calipers).

[0041] Other examples of hydraulic braking systems include brake-by-wire, common in modern hybrid vehicles. In brake-by-wire, brake pedal position sensor 234 measures the hydraulic pressure generated when operator 230 depresses brake pedal 232, and a signal BPP is sent to controller 12. Additional sensor inputs can be used to determine the appropriate brake control signal (BCS) sent to main engine source 220. In some examples, additional sensor inputs may include wheel speed sensors, yaw sensors, steering wheel angle, and accelerator position. Based on the sensor inputs, as may be indicated by the actuation of the brake pedal, controller 12 receives a request from the operator to stop the vehicle. Therefore, the controller generates a BCS signal that can drive a pump (not shown) coupled to main engine source 220 to pressurize the hydraulic system and drive brake assemblies 238 coupled to wheels 60 to apply appropriate braking force to wheels 60. In one example, the actuation of brake assembly 238 may include the actuation of brake calipers. It should be recognized that brake assemblies are typically mounted on all vehicle wheels, but for simplicity... Figure 2 Only one wheel and the braking components coupled to it are shown in the diagram.

[0042] The brake-by-wire system can assist the main braking system or can be an independent braking system. In one example, the vehicle operator 230 may wish to bring the vehicle to a sudden stop at a red light and quickly and fully depress the brake pedal 232. The brake pedal position sensor 234 senses that the brake pedal 232 is fully depressed, thereby indicating to the controller 12 that the operator has requested a high braking force (BPP) signal. In response to the BPP signal and possibly signals from the vehicle speed sensor, the controller can send a brake control signal (BCS) to the main engine source 220 to drive the braking system to apply immediate high braking force to the wheels, thereby stopping the vehicle as requested by the operator.

[0043] In the depicted example, the hydraulic system can be configured to operate using hydraulic fluid (e.g., energy) from the main engine source 220 and / or the hydraulic accumulator 36. In one example, a brake source control (BSC) valve 240 can be coupled to the hydraulic braking system such that the brake assembly 238 can be fluidly coupled to either the main engine source 220 or the accumulator 36 via a hydraulic brake line 236. In this way, actuation of the brake source control valve 240 can govern whether the brake assembly 238 receives brake fluid from the main engine source 220 or from the accumulator 36. It should be appreciated that, in some embodiments, hydraulic fluid can also be supplied from the hydraulic accumulator 36 to the main engine source 220 during engine automatic stop. Thus, if the main engine source 220 is a power steering system, hydraulic fluid from the hydraulic accumulator can also provide power steering during engine automatic stop. The brake source control valve 240 can be actuated based on a brake source control valve signal (BSC) generated by the controller. In one example, the BSC valve 240 can be driven to a first position via a first BSC signal, wherein the first position of the BSC valve directs hydraulic fluid from the main engine source 220 to supply the brake assembly 238. In another example, the BSC valve 240 can be driven to a second position via a second BSC signal, wherein driving the BSC valve 240 to the second position stops the flow of hydraulic fluid from the main engine source 220 and begins directing hydraulic fluid from the hydraulic accumulator 36 to the brake assembly 238. In one example, the BSC signal can be determined based on feedback from various engine sensors, including a vehicle speed sensor, an accumulator pressure sensor 216, and a brake control signal, which is at least partially based on a brake pedal position sensor. Additionally, the position of the brake source control valve 240 can be indicated to the controller 12 via a signal BSCP coupled to the BSC valve 240.

[0044] Braking assembly 238 may include a hydraulic return line 242 that provides a conduit for returning hydraulic brake fluid to the hydraulic braking system when braking force is no longer required. In some examples, the hydraulic accumulator and the main engine source may have a common oil source (e.g., an oil pan), with all hydraulic fluid from the hydraulic return line entering the shared oil pan. Alternatively, the hydraulic accumulator and the main engine source may be separate hydraulic systems with separate and distinct return lines and oil pans. For the commonly used oil pan configuration, a return control valve 244 can be actuated to govern the destination of the returning hydraulic fluid. In some examples, the return control valve 244 can be controlled based on a hydraulic return (HR) signal from a controller, the HR signal responding to pressure levels in the main engine source 220 and the accumulator 36. For example, if the hydraulic pressure in the main engine source 220 drops below a predetermined threshold pressure, the return control valve 224 can be actuated to a first position to direct returning hydraulic fluid to the main engine source 220, thereby increasing the pressure in the main engine source 220. Alternatively, in the same example, if the hydraulic pressure in accumulator 36 drops below a predetermined threshold pressure, the return control valve 224 is actuated to a second position to direct the return hydraulic fluid to accumulator 36.

[0045] Under normal operating conditions (e.g., when the vehicle is being propelled and / or when the engine is running), the main engine source 220 can be used to supply hydraulic fluid to the brake assembly 238. In some examples, the main engine source 220 can be coupled to the engine crankshaft 61, and power can be supplied to the main engine source 220 by the movement of the crankshaft 61. In some embodiments, the main engine source 220 can be coupled to the crankshaft 61 via a coupling connection 243 (e.g., a timing belt or timing chain). However, when the engine is off, the crankshaft 61 does not continue to rotate, and the main engine source will not be able to continue to supply power by the movement of the crankshaft 61. Therefore, when the engine is off, the main engine source 220 may not be available to supply pressurized hydraulic fluid to the brake assembly 238. By configuring the braking system to operate using the accumulator 36 as an additional source of pressurized hydraulic brake fluid, a source of pressurized hydraulic brake fluid can be available at any time during the engine-off state. Therefore, vehicles equipped with the aforementioned system can also be configured to operate using automatic start-stop technology, thereby improving fuel economy without the need for an expensive auxiliary electric motor.

[0046] Turn now Figure 3A The example program 300 for operating a turbocharger coupled to a hydraulic pump is shown. The hydraulic pump is also coupled to a hydraulic accumulator and configured to charge the accumulator with hydraulic fluid under suitable operating conditions. This is based on instructions stored in the controller's memory and in conjunction with data from sensors in the engine system (such as those referenced above). Figure 1The signals received by the described sensors, and the instructions for executing program 300 and other programs and methods included herein, can be executed by the controller. According to the method described below, the controller can employ the engine actuator of the engine system to adjust engine operation.

[0047] At point 302, the procedure includes estimating and / or measuring the engine (e.g., Figure 1 and Figure 2 The engine operating conditions of the turbocharged engine shown are as follows. Engine operating conditions may include, but are not limited to, engine speed (Ne), desired engine torque (Tq), brake pedal position (BPP), manifold absolute pressure (MAP), manifold air temperature (MAT), engine coolant temperature (ECT), ambient humidity, and accumulator (e.g., Figure 1 and Figure 2 The pressure in the accumulator 36 shown. At 304, it is determined whether a boost demand has been received (e.g., a boost level exceeding the currently provided boost level or a required boost pressure exceeding atmospheric pressure). In one example, the operator may have already actuated the accelerator pedal to indicate a demand for increased boost. If no boost demand is received, at 306, the procedure includes continuing current engine operation and adjusting the exhaust valve (e.g., ...) based on operator demand before continuing monitoring for the accelerator pedal release status at 322. Figure 1 and Figure 2 The exhaust valve 52). In one example, no boost demand may include a coasting condition where the vehicle can be pushed down a hill without needing boost. The exhaust valve may remain closed, as indicated by mapping data for a given operating condition. It should be appreciated that, in one embodiment, unless controlled by a controller (e.g., Figure 1 and Figure 2 The controller 12) indicates that otherwise the engine's hydraulic pump (e.g., Figure 1 and Figure 2 The hydraulic pump 34) and the turbocharger (e.g., Figure 1 and Figure 2 The turbochargers 20 can be coupled to each other.

[0048] If a boost demand is received, at point 308, the controller sends a signal to the actuator coupled to the wastegate valve to reduce the opening of the wastegate valve (e.g., close the wastegate valve). To meet the boost demand, the wastegate valve can be completely closed to prevent exhaust gas from bypassing the turbine. The increased exhaust flow through the turbine increases the turbine speed, which in turn increases the speed of the hydraulic pump and compressor coupled to the turbine. By increasing the compressor speed, the intake air is compressed and delivered to the engine, thereby increasing its boost capacity.

[0049] At 310, the procedure includes determining the hydraulic accumulator (e.g.,Figure 2 and Figure 1 The procedure involves checking whether the pressure in the hydraulic accumulator 36) is less than a first pressure threshold. In one example, the first threshold may be the maximum expected hydraulic pressure that can be stored in the accumulator. The first pressure threshold may be determined based on the accumulator manufacturer's recommendations or based on the permissible pressure of the hydraulic lines coupled to the hydraulic braking system. If the accumulator pressure is less than the first pressure threshold, at 312, the procedure includes continuing turbocharger operation while keeping the wastegate closed until monitoring for accelerator pedal release at 322. It should be understood that the hydraulic pump and turbocharger remain coupled, and the rotation of the turbine will cause the hydraulic pump to charge the accumulator with pressurized hydraulic fluid. It should be understood that charging the hydraulic accumulator means that hydraulic fluid is entering the hydraulic accumulator, thereby increasing the pressure applied to the hydraulic fluid within the accumulator by the compression mechanism. As previously mentioned, the compression mechanism may be a pre-charged inert compressible gas (e.g., nitrogen) within the accumulator, or it may be a driven piston. Therefore, the amount of hydraulic energy stored in the accumulator (e.g., in the form of pressurized hydraulic fluid) also increases.

[0050] If the accumulator pressure is greater than the first threshold, the procedure continues to step 314, where the procedure includes keeping the exhaust valve closed. The procedure then continues to step 316 to determine if the boost pressure demand is greater than the threshold boost pressure demand.

[0051] If the accumulator pressure is greater than a first pressure threshold, but the boost demand is not greater than the threshold boost demand, then at 318, the procedure may include disengaging the hydraulic pump from the accumulator or turbocharger. A boost demand less than the threshold boost demand may occur when the boost demand is insufficient to be met using the accumulator's boost assistance. For example, if the boost demand is not greater than the threshold, this may indicate that the turbocharger is rotating fast enough for the current boost demand and no additional rotational energy from the accumulator is required to achieve the desired boost level (e.g., a boost demand determined based on the torque level required by the operator). In one example, disengaging the hydraulic pump may include disconnecting the hydraulic pump from the turbocharger. Disengaging the hydraulic pump from the turbocharger may include driving a decoupling mechanism (e.g., Figure 2 (Decoupling mechanism 214). In another example, the hydraulic pump can be decoupled from the accumulator. Decoupling the hydraulic pump from the accumulator may include a pump control valve (e.g., Figure 1 and Figure 2 (Pump control valve 210). Actuation of the pump control valve allows hydraulic fluid from the pump to be recirculated from downstream to upstream of the pump, instead of continuing to the hydraulic accumulator. In other examples, the hydraulic pump can operate in stall mode to prevent excessive pressure from entering the accumulator.

[0052] If the boost demand at 316 exceeds the threshold boost, this can represent a higher boost demand, such as the boost demand from pressing the accelerator pedal. The boost demand exceeding the threshold boost level at 316 can be greater than the initial boost demand received at 304. In one example, the threshold boost level at 316 can be based on the turbocharger's current speed. For example, if the boost demand exceeds this threshold, the turbocharger may not be able to boost quickly enough to provide the required boost. Therefore, if the boost demand exceeds this threshold, the procedure continues to 320. At 320, the procedure includes advantageously providing the stored energy from the accumulator to the turbocharger to meet the increased boost demand. In one example, hydraulic fluid from the accumulator can be directed to a hydraulic pump to increase the pump's speed. Because the hydraulic pump and turbine can be connected via one or more shafts (e.g., Figure 3B and Figure 1 The hydraulic pump is coupled to shaft 28, so increasing the speed of the hydraulic pump can also increase the speed of the turbocharger and increase the boost pressure delivered to the engine. In another example, the hydraulic pump can be flipped to supply stored energy from the accumulator to the turbocharger. In this way, the stored hydraulic energy can be used to provide engine boost pressure and reduce the likelihood of turbo lag.

[0053] At 322, it is determined whether an accelerator pedal release condition exists. An accelerator pedal release condition occurs when the operator cancels actuation of the accelerator pedal (e.g., removes their foot from the accelerator pedal), resulting in a relatively sharp drop in torque demand. In one example, accelerator pedal release could occur when the operator commands the vehicle to stop abruptly in response to approaching an obstacle in the road. If no accelerator pedal release condition occurs (e.g., the controller receives a pedal position signal greater than a threshold from the accelerator pedal position sensor), the procedure continues to 324, where the procedure includes continuing to... Figure 2 The current engine continues to operate before step 332 shown. Continuing to operate the current engine may include continuing to deliver stored energy from the accumulator to the turbocharger to meet boost demand.

[0054] If the accelerator pedal has been released, the procedure continues to 326, where it determines whether the accelerator pressure is less than a first pressure threshold. As previously mentioned, the first pressure threshold for the accelerator is the pressure at which additional hydraulic pressure is not required in the accelerator (e.g., the accelerator's maximum pressure or energy storage level). In one example, the first pressure threshold may be determined based on the accelerator manufacturer's recommendations or design limitations of the hydraulic braking system components. In other examples, the first pressure threshold may be determined based on the possible uses of the stored hydraulic pressure, thereby avoiding the increased costs associated with storing excessive pressurized hydraulic fluid. If the accelerator pressure is greater than the first pressure threshold, the procedure continues to 328, where it may include one or more of the following steps as previously described: opening the exhaust valve, disengaging the hydraulic pump from the turbocharger, and disengaging the hydraulic pump from the hydraulic accumulator. In one example, opening the exhaust valve may include the controller signaling the actuator of the exhaust valve to increase the valve opening to increase the amount of exhaust bypassing the turbine. In another example, disengaging the hydraulic pump and turbocharger may include a controller signaling an actuator of a decoupling mechanism (e.g., a clutch) to disengage the hydraulic pump and turbocharger. In yet another example, disengaging the hydraulic pump from the hydraulic accumulator may include opening a pump control valve to recirculate hydraulic fluid leaving the pump, rather than directing it to the accumulator. In other examples, the pump may operate in stall mode. In some examples, engine operating parameters such as turbocharger speed or accumulator pressure level may be used to determine how the hydraulic pump should disengage from the accumulator using one or more of the methods described above. In this way, continuous operation of the turbocharger will not lead to overcharging of the accumulator.

[0055] If the accumulator pressure is less than a first pressure threshold, the procedure continues to 330, where the procedure includes closing the passage coupled to the exhaust valve (e.g., Figure 3B and Figure 2 The exhaust valve (54) is coupled to both sides of the exhaust turbine. Because the exhaust valve is closed, exhaust gas may not bypass the turbine. Instead, the exhaust gas travels through the turbine, causing it to rotate, and consequently, a hydraulic pump coupled to the turbine. By keeping the exhaust valve closed during accelerator pedal release, the hydraulic pump can continue to rotate during accelerator pedal release, thus charging the accumulator as needed.

[0056] After 330, the program proceeds to... Figure 4 As shown at 332, at 332, an assessment is made as to whether the vehicle brakes are being applied. Applying the brakes may include the vehicle operator actuating the brake pedal (e.g., Figure 4The brake pedal 232 is used to indicate the desired deceleration of the vehicle. If the vehicle brakes are not applied, the procedure continues to 334, where the procedure includes continuing the current engine operation before ending the procedure.

[0057] If the vehicle brakes are applied, the procedure continues to step 336, where the procedure includes starting as follows before ending the procedure. Figure 3B The braking is described further in the text. Now turn. Figure 2 The illustrated program 400 can automatically start and stop a diesel engine with a hydraulic braking system. Program 400 can be... Figure 2 The procedure 300 shown continues at 336. At 402, the procedure includes supplying braking pressure to the braking system using the main engine source in response to the application of the vehicle brakes (while the engine is running). For example, since the brake pedal is actuated, a BPP signal can be transmitted to the controller based on parameters such as vehicle speed and brake pedal position (BPP) signals, and a brake control signal (BCS) can be indicated. The main engine source (e.g., Figure 1 The main engine source 220 shown can receive BCS signals from the vehicle controller to determine the direction of braking components coupled to the vehicle wheels (e.g., coupled to...). Figure 2 The amount of braking force (e.g., hydraulic fluid) of the braking assembly 238 of the wheel 60 shown is used to decelerate the vehicle.

[0058] At 404, the procedure includes determining whether the vehicle has stopped (e.g., is no longer being propelled). In one example, when the light is about to turn red, the vehicle operator may actuate the brake pedal to apply the vehicle brakes, thereby stopping the vehicle at the red light. If the vehicle has not stopped, the procedure continues to 406, where it includes continuing to run the engine and supplying braking pressure through the main engine source before ending. If it is determined at 404 that the vehicle has stopped, the procedure continues to 408 to determine whether the pressure in the hydraulic accumulator is greater than a second pressure threshold. In one example, the second pressure threshold may be sufficient to allow the vehicle engine (e.g., Figure 2 and Figure 1 The hydraulic pressure level at which the engine 10) automatically stops. In some examples, a second pressure threshold may be determined based on an estimated hydraulic pressure required to maintain braking pressure during a typical engine automatic stop event. In other examples, the second pressure threshold may be determined based on mapping data.

[0059] If the hydraulic pressure stored in the accumulator is not greater than the second pressure threshold, the procedure continues to 406, where it includes continuing to run the engine according to the operator's torque demand and supplying braking pressure from the main engine source before ending. If the hydraulic pressure stored in the accumulator is greater than the second pressure threshold, the procedure continues to 410, where it includes determining whether the vehicle has stopped for the threshold duration. If the vehicle has stopped before the threshold duration, the procedure continues to 406, where it includes continuing to run the engine according to the operator's torque demand and supplying braking pressure from the main engine source before ending. By ensuring that the threshold duration has elapsed before changing the source of the hydraulic brake fluid and activating the engine's automatic start-stop function, this helps avoid frequent engine stops and starts under certain operating conditions when the operator tends to "pump and release" the brakes or allow the vehicle to slowly "creep," which would cause unnecessary engine wear and inconvenience to the operator. In one example, the threshold duration could be a set duration, such as two to three seconds.

[0060] In other examples, the controller can identify driving patterns to "learn" about traffic conditions around the vehicle. In one example, if the controller identifies that the vehicle is moving slowly with frequent, very short stops, it can compare this data with mapped data and assert that the vehicle is in stop-and-go traffic and that the short duration of the stops may not be suitable for switching braking sources and activating automatic start-stop. Alternatively, if the controller identifies that the vehicle is traveling at a relatively constant speed of 35 mph, interspersed with stops of 20 seconds or longer, it can compare this data with mapped data and assert that the vehicle may be traversing a town with regular traffic lights and that the duration of the stops is suitable for switching braking sources and activating automatic start-stop. In other examples, GPS or vehicle-to-everything (V2X) functionality can remotely assess driving conditions to determine whether traffic and other driving conditions are suitable for switching braking sources and activating automatic start-stop. In this way, in response to deceleration and / or braking indications and inferences about traffic conditions and / or driving patterns, the controller can predict future conditions that may be suitable for automatic engine start-stop. In one example, in response to a predicted upcoming automatic start-stop condition, the controller can actuate the exhaust valve and / or decoupling mechanism to increase the available pressure in the accumulator, thereby increasing the potential duration of the upcoming start-stop and further improving fuel economy.

[0061] In one example, the controller can send a brake control signal (BCS) to drive the brake source control valve (e.g., Figure 2The brake source control valve 240 selectively switches between sources of hydraulic fluid supplied to the braking assembly. In one example, the brake source control valve can be actuated to a first position, wherein the main engine source is fluidly coupled to the braking assembly, while the hydraulic accumulator is not coupled to the braking assembly. In this position, hydraulic fluid can be supplied from the main engine source to the braking assembly. In another example, the brake source control valve can be actuated to a second position, thereby switching the source of hydraulic braking fluid from the main engine source to the hydraulic accumulator. Specifically, the hydraulic accumulator (e.g., Figure 2 and Figure 1 The accumulator 36 can be fluidly coupled to the braking assembly, while the main engine source is not coupled to the braking assembly. Hydraulic fluid can be supplied from the hydraulic accumulator to the braking assembly. If the vehicle has stopped for a threshold duration, at 412, the procedure includes supplying braking pressure via the hydraulic accumulator and automatically cutting off the engine. In one example, supplying braking pressure via the hydraulic accumulator can be achieved by actuating the brake source control valve to a second position, where the hydraulic accumulator is fluidly coupled to the braking assembly, while the main engine source is not coupled to the braking assembly.

[0062] In some examples, the controller can also send signals to drive a power steering control valve (not shown) to selectively switch between sources of hydraulic fluid supplied to the power steering system, which can also be used as a main engine source (e.g., Figure 2 The main engine source 220). In one example, the brake source control valve can operate as a power steering control valve. The power steering control valve can be actuated to a first position, wherein the power steering system is not fluidly coupled to the hydraulic accumulator. In this position, hydraulic fluid can be supplied solely by the power steering system to provide power steering. In another example, the power steering control valve can be actuated to a second position, thereby switching the source of hydraulic fluid from the power steering system to the hydraulic accumulator. Specifically, the hydraulic accumulator (e.g., ...) Figure 1 and Figure 2The accumulator 36 can be fluidly coupled to the power steering system, and hydraulic fluid can be supplied from the hydraulic accumulator to provide power steering. It should be recognized that if the hydraulic accumulator is used to supply hydraulic power to both the hydraulic braking system and the power steering system during automatic start-stop, then supplying power to the braking system has a higher priority than supplying power to the power steering system. Specifically, if the hydraulic charge in the hydraulic accumulator decreases, hydraulic fluid can be supplied to the braking system before supplying hydraulic fluid to the power steering system. Similarly, if both systems are powered via the hydraulic accumulator and the accumulator's charge level drops below a third pressure threshold, the engine can be started to maintain braking pressure. Automatic engine start-stop can be achieved because braking pressure is supplied from the hydraulic accumulator to the braking components. Because the pressure in the hydraulic accumulator is independent of the running engine, pressurized hydraulic braking fluid in the accumulator remains available to maintain appropriate braking pressure during engine shutdown. Automatic engine shutdown can include stopping the refueling of the engine. In one example, the controller can supply hydraulic fluid to the combustion chamber (e.g., Figure 2 and Figure 2 The fuel injector in the combustion chamber 44) (e.g., Figure 1 The fuel injector 58 sends a signal to stop supplying fuel to the combustion chamber. In another example, the controller can send a signal to the engine's fuel system (e.g., Figure 2 The fuel system 202 sends a signal to stop fuel delivery to the engine's fuel injectors. Specifically, the controller may command the opening of the fuel control valve to decrease (e.g., close the fuel control valve) or command the fuel pump to stop pumping fuel to the engine. By preventing fuel from entering the engine's combustion chamber, the engine will automatically shut down. In other examples, the controller may use other suitable means to stop fuel delivery to the combustion chamber.

[0063] At 414, the procedure includes determining whether the hydraulic accumulator pressure is less than a third pressure threshold. The third pressure threshold is less than a second pressure threshold. The third pressure threshold may be the minimum hydraulic pressure within the accumulator capable of supplying sufficient braking pressure to the braking components. In one example, the third pressure threshold may be based on the minimum hydraulic braking pressure used to maintain vehicle braking, and may include a threshold margin. In other examples, the third pressure threshold may be based on mapping data or determined to avoid vacuuming in the braking system. If the hydraulic accumulator pressure is less than the third pressure threshold, at 416, the procedure includes restarting the engine and also includes stopping the supply of hydraulic braking pressure from the hydraulic accumulator to the braking components. At this point, the hydraulic braking pressure to the braking components returns to the state where hydraulic braking pressure is supplied by the main engine source. In one example, switching the hydraulic braking source from the accumulator to the main engine source may include the controller sending a BSC signal to drive the brake source control valve to a first position, in which the main engine source is fluidly coupled to the braking components, while the hydraulic accumulator is not coupled to the braking components. Hydraulic fluid may be delivered from the main engine source to the braking components. Additionally at 416, the procedure includes restarting the engine, which may include the controller sending a signal to a starter motor coupled to the engine to start and rotate (e.g., spin) the engine. Restarting the engine may also include sending a control signal to the engine fuel system to reintroduce fuel into the engine's combustion chamber via fuel injectors. Because the engine is started and rotated and fuel is reintroduced into the combustion chamber, combustion resumes and the engine restarts. It should be understood that this restart is not in response to an operator's request for torque or other auxiliary systems, but rather in response to accumulator pressure relative to a threshold.

[0064] It should be understood that in some embodiments, battery charge can also be monitored during automatic engine shutdown, and the engine can be restarted if the battery charge drops below a threshold charge level. The threshold charge level can be determined based on maintaining an appropriate charge level to sustain vehicle operating systems, including the starter motor, and vehicle assistance systems.

[0065] If the hydraulic accumulator pressure exceeds the third pressure threshold, at point 418, the procedure includes maintaining the engine off. Maintaining the engine off may include continuing to block fuel delivery from the engine combustion chamber. Additionally, maintaining the engine off may include continuing to use the hydraulic braking pressure from the accumulator to actuate the braking components and prevent the vehicle from being propelled.

[0066] At 420, the procedure includes determining whether a request to end the vehicle stop condition has been received. In one example, the red traffic light that would cause the operator to stop the vehicle has turned green, and the operator has indicated that they wish to move the vehicle. This could be because the operator has already actuated the accelerator pedal or engaged the clutch to disengage the vehicle's transmission (e.g., ...). Figure 5 and Figures 1-2 The transmission (64) shifts gears, indicating its intention to propel the vehicle. If a request to end the vehicle's stopped state has been received, the procedure proceeds to 416, the engine restarts, and the controller stops supplying hydraulic braking pressure to the braking system via the hydraulic accumulator. Specifically, the main engine source supplies braking pressure to the braking components.

[0067] Turn now Figure 5 Example mapping diagram 500 illustrates exemplary operation of a turbocharged engine coupled to a hydraulic braking system, which includes a hydraulic accumulator (e.g., ​ (The engine system shown). The horizontal axis (x-axis) represents time, and the vertical markers t1-t8 mark key moments in the turbocharger's operation. (Refer to...) ​ Curve 502 shows the change in accelerator pedal position over time. Curve 504 shows the change in vehicle speed over time. Curve 506 shows the coupling status of the hydraulic pump (e.g., coupled to the turbocharger and / or accumulator). Curve 508 shows the change in the position of the wastegate valves coupled to both sides of the exhaust turbine of the turbocharger. Curve 510 shows the engine on / off status. Curve 512 shows the rotational speed of the turbocharger with a hydraulic pump coupled to the engine. Curve 514 shows the change in accumulator internal pressure over time relative to a first pressure threshold (curve 513), a second pressure threshold (curve 515), and a third pressure threshold (curve 517).

[0068] Before time t1, the accelerator pedal position (curve 502) indicates that the accelerator pedal is depressed, for example, when accelerating on an entrance ramp to enter the highway. Therefore, as shown in curve 504, the vehicle speed increases. Because the accumulator pressure is below a first pressure threshold 513, the hydraulic pump is coupled to the turbocharger and the hydraulic accumulator, so that rotation of the turbocharger also rotates the hydraulic pump, thereby filling the accumulator (e.g., increasing the pressure inside the hydraulic accumulator), as shown in curve 514. As shown in curve 508, the wastegate valve remains closed, and the engine starts as the vehicle is being propelled (curve 510). As shown in curve 512, due to depressing the accelerator pedal, the turbocharger speed is observed to increase.

[0069] At time t1, the accelerator pedal finds a stable position indicating a steady acceleration request, as shown in curve 502. The vehicle speed follows a similar trajectory (curve 504). As shown in curve 514, before time t2, the hydraulic pump remains coupled to the turbocharger and hydraulic accumulator because the accumulator pressure remains below the first pressure threshold 513 (curve 506). The wastegate across the exhaust turbine remains closed (curve 508) to guide exhaust gas through the turbine. The engine remains on while the vehicle is being propelled, as shown in curve 510. After time t1, the turbocharger speed stabilizes, as shown in curve 512.

[0070] Unless the pressure in the accumulator reaches the first pressure threshold 513, the engine operating conditions remain essentially unchanged at time t2, as shown by curve 514. As shown by curve 506, as previously mentioned, the hydraulic pump can be disconnected from the turbocharger and / or the hydraulic accumulator to avoid overcharging the accumulator. After time t2, the pressure in the hydraulic accumulator remains constant because it is no longer being charged by the hydraulic pump.

[0071] As shown in curve 502, at time t3, the accelerator pedal is released. As shown in curve 504, the vehicle speed decreases accordingly. Since the accumulator pressure remains at the first pressure threshold 513, as shown in curve 514, the hydraulic pump and turbocharger can remain disconnected, as shown in curve 506. Additionally, as shown in curve 508, the exhaust valve can open to avoid compressor surge. Because the rate of exhaust flow through the turbine also decreases, the turbocharger speed decreases. It should be recognized that the vehicle brake (not shown) can be applied between t3 and t4 to bring the vehicle to a stop.

[0072] At time t4, the vehicle is no longer propelled (e.g., the vehicle stops), but subsequently, in response to an operator's torque request (e.g., pressing the accelerator pedal), as shown in curve 502, the vehicle is immediately propelled again, as shown in curve 504. The duration of the stop at t4 may not exceed a threshold duration, so the brake fluid source does not switch from the main engine source to the hydraulic accumulator, and the automatic engine stop is not activated or initiated. As a result, the engine remains running, as shown in curve 510. At t4, the accumulator pressure is at a first pressure threshold (curve 513), and to meet the increased torque demand, the accumulator can be used to provide additional boost pressure to the engine. As a result, the hydraulic pump is again coupled to the turbocharger and the accumulator (curve 506) to direct hydraulic fluid to the accumulator and further to the turbocharger. As a result, the accumulator pressure can decrease, as shown in curve 514. During the accelerator pedal depressing at t4, the wastegate remains closed (curve 508).

[0073] Continue pressing the accelerator pedal until time t5, at which point release the accelerator pedal, as shown in curve 502. During the release of the accelerator pedal, because the accelerator pressure is below the first pressure threshold 513, the hydraulic pump and turbocharger remain coupled (curve 506) and the wastegate remains closed (curve 508), allowing the turbocharger to continue operating and thus recharge the accelerator, as shown in curve 514. It should be understood that the operator may also apply the brakes (not shown) to bring the vehicle to a stop between t5 and t6.

[0074] At time t6, as shown by vehicle speed curve 504, the vehicle stops again and remains stopped until t8. As shown by curve 514, the accumulator pressure is above the second pressure threshold 515, and since the vehicle remains stopped for a duration exceeding the threshold, the hydraulic braking source can be switched from the main engine source to the hydraulic accumulator, and automatic engine shutdown can be enabled and initiated. As shown by curve 510, the engine can automatically shut off after the threshold duration has elapsed following t6. As shown by curve 508, the exhaust valve remains closed; when the vehicle stops, the accelerator pedal (curve 502) remains at zero between t6 and t8. The hydraulic pump can be coupled to the turbocharger and the accumulator (curve 506).

[0075] Between t6 and t7, after t6 the vehicle remains stationary as the engine quickly shuts off automatically, and the accumulator can lose pressure as it supplies hydraulic pressure to the vehicle's braking components (curve 514). As shown in curve 514, at t7, the accumulator pressure drops to the third pressure threshold 517. In response to the accumulator pressure reaching the third pressure threshold, the engine restarts at t7 and remains running until t8, as shown in curve 510. At time t7, the source of hydraulic braking pressure for the braking components can be switched from the hydraulic accumulator to the main engine source.

[0076] In this way, a hydraulic turbocharger can be advantageously used to generate a hydraulic energy source for temporary storage in an accumulator. Therefore, a hydraulic turbocharger can provide a reliable onboard hydraulic energy source. In one example, hydraulic energy can be stored in a hydraulic accumulator, which provides a readily available hydraulic energy source that can be used to maintain braking pressure in the hydraulic braking system during engine shutdown. As mentioned above, the diesel engine can use the main engine source to provide hydraulic braking pressure to the vehicle brakes; however, this main source is unavailable when the engine is off. Because of the hydraulic energy source available during engine shutdown, automatic start-stop can be enabled.

[0077] The advantage of coupling a hydraulic pump to a turbocharger is that pressurized hydraulic fluid from the pump can be stored for subsequent use by the hydraulic braking system, including when the engine is off. The advantage of providing a brake fluid pressurization source during engine-off conditions is the ability to use automatic start-stop technology in vehicles equipped with hydraulic brakes. Specifically, the advantage of supplying pressure to the vehicle's hydraulic braking system from an accumulator coupled to a hydraulic pump (which is coupled to the shaft of a turbocharger mounted in the vehicle's engine) and automatically shutting off the engine when the vehicle stops is that while the engine (e.g., a diesel engine) is stopped, the hydraulic braking pressure is maintained at hydraulic pressure, thereby improving fuel economy and reducing engine emissions.

[0078] A method for a vehicle includes: supplying pressure from an accumulator coupled to a hydraulic pump coupled to a shaft of a turbocharger of an engine mounted in the vehicle to a hydraulic braking system in response to the vehicle stopping; and automatically shutting off the engine when the vehicle stops. In a first example of the method, the method further includes: supplying pressure from a main engine source to the hydraulic braking system in response to a request to reduce the vehicle speed while the vehicle is not stopped during engine operation. A second example of the method optionally includes the first example and further includes: wherein the automatic shutdown of the engine is in response to a pressure in the accumulator exceeding a threshold pressure level. A third example of the method optionally includes one or more of the first and second examples and further includes: wherein the automatic shutdown of the engine is further in response to the vehicle stopping for a threshold duration. A fourth example of the method optionally includes one or more of the first to third examples and further includes: not shutting off the engine when the vehicle stops in response to a pressure in the accumulator falling below a threshold pressure level. A fifth example of the method may optionally include one or more of the first to fourth examples, and further includes: wherein supplying pressure from the accumulator to the hydraulic braking system comprises driving a valve via a controller to allow hydraulic pressure from the accumulator to be transmitted to the hydraulic braking system. A sixth example of the method may optionally include one or more of the first to fifth examples, and further includes: during engine operation, when the vehicle is in motion, adjusting the position of an exhaust valve disposed in a bypass passage surrounding the turbine of the turbocharger based on a pressure level stored at the accumulator. A seventh example of the method may optionally include one or more of the first to sixth examples, and further includes: wherein adjusting the exhaust valve comprises opening the exhaust valve in response to a pressure level stored at the accumulator being higher than an upper threshold level. An eighth example of the method may optionally include one or more of the first to seventh examples, and further includes: wherein adjusting the exhaust valve comprises closing the exhaust valve in response to a pressure level stored at the accumulator being lower than an upper threshold level and in response to deceleration of the vehicle. A ninth example of the method may optionally include one or more of the first to eighth examples, and further includes: disengaging the hydraulic pump from the shaft of the turbocharger in response to the pressure level stored at the accumulator reaching an upper threshold level. A tenth example of the method may optionally include one or more of the first to ninth examples, and further includes: during engine operation, when the vehicle is in motion, driving the turbocharger via the hydraulic pump in response to depressing the accelerator pedal and a required boost level exceeding the threshold level, utilizing the hydraulic pressure stored at the accelerator. An eleventh example of the method may optionally include one or more of the first to tenth examples, and further includes: wherein the engine is a diesel engine.

[0079] Another method for a vehicle including a diesel engine includes: during a first braking condition, supplying hydraulic pressure to a hydraulic braking system of the vehicle via a main hydraulic pressure source of the diesel engine; and during a second braking condition, supplying hydraulic pressure to the hydraulic braking system of the vehicle via an accumulator coupled to a hydraulic pump coupled to the shaft of a turbocharger of the diesel engine. In a first example of the method, the method further includes: wherein the first braking condition includes braking and stopping the vehicle while the diesel engine remains running, and wherein the second braking condition includes automatically shutting off the diesel engine in response to the vehicle braking and stopping. A second example of the method optionally includes the first example and further includes: wherein the second braking condition further includes when a pressure level stored at the accumulator is higher than a threshold pressure level. A third example of the method optionally includes one or more of the first and second examples and further includes: adjusting the position of an exhaust valve disposed in a bypass passage surrounding the turbine of the turbocharger based on the pressure level stored at the accumulator. A fourth example of the method may optionally include one or more of the first to third examples, and further includes: initiating the first braking condition in response to the vehicle stopping and the pressure level stored in the accumulator being below a threshold pressure level without automatically stopping the engine.

[0080] A vehicle system includes: a diesel engine including a turbocharger and a hydraulic pump, the hydraulic pump being coupled to each of a shaft of the turbocharger and an accumulator adapted to store hydraulic pressure generated by rotation of the hydraulic pump; a hydraulic braking system coupled to each of the accumulator and a main hydraulic fluid source of the diesel engine; and a controller having computer-readable instructions for: providing hydraulic braking pressure from the accumulator to the hydraulic braking system in response to a vehicle stop in the vehicle system for a certain duration; and automatically stopping the diesel engine. In a first example of the vehicle system, the vehicle system further includes: wherein, after providing the hydraulic braking pressure from the accumulator and in response to a pressure in the accumulator exceeding a threshold pressure level, automatic engine stop is performed. A second example of the vehicle system optionally includes the first example and further includes: wherein the computer-readable instructions further include one or more instructions for supplying hydraulic braking pressure from the main hydraulic fluid source of the diesel engine to the hydraulic braking system in response to a pressure in the accumulator falling below a threshold pressure level and the diesel engine continuing to operate during braking.

[0081] In another description, the method includes: adjusting an exhaust valve located in a bypass passage near the turbine of a diesel engine's turbocharger, based on boost demand and pressure levels stored in an accumulator coupled to a hydraulic pump; and supplying pressure from the accumulator to the vehicle's hydraulic braking system during automatic engine start / stop while the vehicle equipped with the diesel engine is stopped.

[0082] Note that the example control and estimation programs included herein can be used with various engine and / or vehicle system configurations. The control methods and programs disclosed herein can be stored as executable instructions in non-transitory memory and can be executed by a control system including a controller in conjunction with various sensors, actuators, and other engine hardware. The specific programs described herein can represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, etc. Therefore, the various actions, operations, and / or functions described can be executed in the order shown, in parallel, or in some cases omitted. Similarly, the processing order is not required to realize the features and advantages of the exemplary embodiments of the invention described herein, but is provided for ease of illustration and description. Depending on the specific strategy used, one or more of the shown actions, operations, and / or functions can be repeatedly executed. Furthermore, the described actions, operations, and / or functions can be graphically represented by code encoded in non-transitory memory of a computer-readable storage medium within an engine control system, wherein the described actions are realized by combining instructions in a system including various engine hardware components with an electronic controller.

[0083] It should be recognized that the configurations and procedures disclosed herein are exemplary in nature, and these specific embodiments are not intended to be limiting, as many variations are possible. For example, the above-described technology can be applied to V-6, I-4, I-6, V-12, opposed 4-cylinder, and other engine types. The subject matter of this disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and constructions disclosed herein, as well as other features, functions, and / or properties.

[0084] The appended claims specifically point to certain combinations and sub-combinations that are considered novel and non-obvious. These claims may relate to a “one” element or a “first” element or an equivalent thereof. These claims should be understood to include combinations of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and / or characteristics may be claimed by amending existing claims or by filing new claims in this application or related applications. These claims, whether broader, narrower, identical, or different in scope from the original claims, are considered to be included within the subject matter of this disclosure.

Claims

1. A method for a vehicle, comprising: In response to the pressure in the accumulator coupled to the hydraulic pump being less than a first pressure threshold, the turbocharger is kept running to pressurize the accumulator; In response to the vehicle coming to a stop, and the pressure in the accumulator exceeding a second pressure threshold, the second pressure threshold being a hydraulic pressure level sufficient to automatically stop the vehicle's engine, Pressure is supplied from the accumulator to the vehicle's hydraulic braking system, and the hydraulic pump is coupled to the shaft of the turbocharger of the engine installed in the vehicle; and The engine is automatically shut off when the vehicle stops. During operation of the engine, the turbocharger shaft is capable of driving the hydraulic pump to increase the volume and / or pressure of the hydraulic fluid stored in the accumulator. The first pressure threshold is greater than the second pressure threshold.

2. The method according to claim 1, further comprising: During engine operation, when the vehicle is not stopped, pressure is supplied from the main engine source to the hydraulic braking system in response to a request to reduce the vehicle's speed.

3. The method of claim 1, wherein the automatic shutdown of the engine further responds to the vehicle stopping for a threshold duration.

4. The method according to claim 1, further comprising: In response to the pressure in the accumulator falling below the second pressure threshold, the engine is not shut off when the vehicle stops.

5. The method of claim 1, wherein supplying pressure from the accumulator to the hydraulic braking system comprises driving a valve via a controller to allow hydraulic pressure from the accumulator to be transmitted to the hydraulic braking system.

6. The method according to claim 1, further comprising: During engine operation, while the vehicle is in motion, the position of the exhaust valve located in the bypass passage surrounding the turbine of the turbocharger is adjusted based on the pressure level stored in the accumulator.

7. The method of claim 6, wherein adjusting the position of the exhaust valve comprises: The exhaust valve is opened in response to the pressure level stored in the accumulator being higher than the first pressure threshold.

8. The method of claim 6, wherein adjusting the position of the exhaust valve comprises: In response to the pressure level stored in the accumulator falling below the first pressure threshold and in response to the deceleration of the vehicle, the exhaust valve is closed.

9. The method according to claim 1, further comprising: In response to the pressure level stored in the accumulator reaching the first pressure threshold, the hydraulic pump is disconnected from the shaft of the turbocharger.

10. The method of claim 1, further comprising: During engine operation, when the vehicle is in motion, in response to pressing the accelerator pedal and the required boost level being higher than the threshold boost demand, the turbocharger is driven via the hydraulic pump using the hydraulic pressure stored in the accumulator.

11. The method according to claim 1, wherein the engine is a diesel engine.

12. A vehicle system comprising: A diesel engine comprising a turbocharger and a hydraulic pump, the hydraulic pump being coupled to each of a shaft of the turbocharger and an accumulator adapted to store hydraulic pressure generated by the rotation of the hydraulic pump; A hydraulic braking system coupled to each of the accumulator and the main hydraulic fluid source of the diesel engine; and The controller has computer-readable instructions for: In response to the pressure in the accumulator being less than a first pressure threshold, the turbocharger is kept running to pressurize the accumulator. In response to the vehicle system stopping for a certain duration and the pressure in the accumulator exceeding a second pressure threshold, hydraulic braking pressure is supplied from the accumulator to the hydraulic braking system, wherein the second pressure threshold is a hydraulic pressure level sufficient to automatically stop the diesel engine; and The diesel engine will automatically stop. During operation of the engine, the turbocharger shaft is capable of driving the hydraulic pump to increase the volume and / or pressure of the hydraulic fluid stored in the accumulator. The first pressure threshold is greater than the second pressure threshold.

13. The vehicle system of claim 12, wherein after the hydraulic braking pressure from the accumulator is provided and in response to a pressure in the accumulator exceeding a second pressure threshold, an automatic stop of the diesel engine is performed, and if, after the engine stops, the pressure in the accumulator is less than a third threshold, the diesel engine is restarted, wherein the third pressure threshold is the minimum hydraulic pressure in the accumulator capable of supplying sufficient braking pressure to the braking components.

14. The vehicle system of claim 12, wherein the computer-readable instructions further include one or more instructions for providing hydraulic braking pressure from the main hydraulic fluid source of the diesel engine to the hydraulic braking system in response to a pressure in the accumulator falling below the second pressure threshold and the diesel engine continuing to operate during braking conditions.

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