Combined braking method combined with engine thermal management

Abstract

The invention discloses a combined braking method combined with engine thermal management. The combined braking method comprises the steps that vehicle braking related data are obtained; calculating a braking power demand; comparing the supply-demand relationship between the braking power demand and the braking power in the engine cylinder; and determining a braking scheme according to the supply-demand relationship. According to the combined braking method combined with engine thermal management, on the basis of ensuring that the constant-speed downhill braking function of the vehicle is stably achieved, the cooperative working mode of engine in-cylinder braking and hydraulic slow braking is intelligently matched according to the braking power requirement, engine in-cylinder braking is fully utilized, the exhaust temperature is increased, and the service life of the vehicle is prolonged. And the intervention proportion of an engine heat management strategy is reduced, so that the fuel consumption of the vehicle is effectively reduced, and the braking performance and the fuel economy are both considered.

Description

Technical Field

[0001] This invention belongs to the field of vehicle braking technology and relates to a combined braking method that integrates engine thermal management. Background Technology

[0002] Diesel engines meeting China's National VI emission standards typically employ engine thermal management strategies to raise the after-treatment temperature and improve efficiency when the after-treatment temperature is low, in order to meet emission requirements. However, this results in some fuel economy losses. Commercial vehicles with hydraulic retarder brakes in constant-speed braking mode generally use both hydraulic retarder and engine braking to achieve constant-speed downhill driving. However, the strategy of using hydraulic retarder and engine braking in constant-speed braking mode does not consider the fuel consumption losses caused by engine thermal management.

[0003] In summary, existing technologies cannot reduce the proportion of engine thermal management to lower fuel consumption while ensuring braking power. Summary of the Invention

[0004] The purpose of this invention is to provide a combined braking method that integrates engine thermal management, which solves the problem in the prior art that diesel engines meeting China VI emission standards cannot reduce the proportion of engine thermal management to reduce fuel consumption while ensuring braking power.

[0005] The technical solution adopted in this invention is: a combined engine thermal management and braking method, comprising: Step 1: Obtain vehicle braking-related data; Step 2: Calculate the braking power requirement; Step 3: Compare the supply and demand relationship between braking power requirements and engine in-cylinder braking power; Step 4: Determine the braking scheme based on the supply and demand relationship.

[0006] The invention is further characterized by: Step one includes: After the vehicle activates constant speed braking mode, the VCU uses preset rolling resistance coefficient, air resistance coefficient, frontal area, and vehicle mass conversion factor to obtain vehicle braking-related data from the TCU.

[0007] Vehicle braking-related data includes vehicle driving-related data and vehicle speed-related data; Vehicle driving-related data includes the gradient of the current road and the total weight of the vehicle. Vehicle speed-related data includes the vehicle's real-time current speed and the speed requested by the driver through operation.

[0008] Step two includes: The VCU calculates the braking power required to reduce the vehicle speed from its current speed to the requested speed using a preset power calculation model based on vehicle braking-related data.

[0009] The formula for calculating braking power demand is as follows: p e3 =p e1 -p e2 , , Where, p e1 p represents the power required at the current vehicle speed. e2 p represents the power required for the target vehicle speed. e3 Indicates braking power requirement; p e Indicates the required power. G represents the vehicle's weight; f represents the rolling resistance coefficient; u represents the transmission efficiency; G represents the vehicle's weight; f represents the rolling resistance coefficient; u represents the vehicle's weight; f ... a Indicates vehicle speed; i represents gradient; C D δ represents the air drag coefficient; A represents the frontal area; δ represents the vehicle mass conversion factor; m represents the vehicle mass.

[0010] Step three includes: The engine sends the braking power data of partial cylinder braking and the maximum engine braking power data of all cylinder braking to the VCU. The VCU compares its calculated braking power requirement with the engine cylinder braking power. The VCU compares the braking power requirement with the engine's in-cylinder braking power, which is the maximum braking power that the engine itself can provide or the braking power when some cylinders are working, and then makes a judgment: if the braking power of some or all cylinders of the engine is less than the braking power requirement, it means that the in-cylinder braking alone cannot meet the constant speed requirement; if the braking power of some or all cylinders of the engine is greater than or equal to the braking power requirement, it means that the in-cylinder braking alone can meet or even exceed the constant speed requirement.

[0011] Step four includes: If the in-cylinder braking power is less than the braking power requirement, in-cylinder braking is activated: The VCU sends a command to the engine to determine the number of engine cylinders to be activated based on the difference between the braking power requirement and the in-cylinder braking power, in order to match part of the braking power requirement.

[0012] Step four includes: If the in-cylinder braking power is less than the braking power requirement, in-cylinder braking is activated: The VCU sends a command to the engine to determine the number of engine cylinders to be activated based on the difference between the braking power requirement and the in-cylinder braking power, in order to match part of the braking power requirement. If the braking power demand exceeds the engine braking maximum power, then the in-cylinder braking of all cylinders will be activated.

[0013] Step four includes: If the in-cylinder braking power is less than the braking power requirement, in-cylinder braking is activated: The VCU sends a command to the engine to determine the number of engine cylinders to be activated based on the difference between the braking power requirement and the in-cylinder braking power, in order to match part of the braking power requirement. If the braking power requirement is less than the maximum power of engine braking but greater than the braking power of partial cylinder braking, then the braking power of partial cylinder braking is used; for the remaining braking power gap not covered by in-cylinder braking, the VCU sends a command to the hydraulic retarder system to use hydraulic retarder braking, which forms a combined braking with in-cylinder braking to meet the total braking power requirement.

[0014] Step four includes: If the in-cylinder braking power of the engine is greater than or equal to the braking power requirement, the VCU directly sends a command to the hydraulic retarder system to call only the hydraulic retarder braking: based on the braking power requirement, the difference between the current vehicle speed and the target vehicle speed, the PID controller calls the hydraulic retarder to meet the vehicle speed control target.

[0015] The beneficial effects of this invention are: while ensuring the stable implementation of the vehicle's constant speed downhill braking function, by intelligently matching the coordinated working mode of engine in-cylinder braking and hydraulic slow braking according to the braking power demand, the in-cylinder braking is utilized to the maximum extent, reducing the intervention ratio of engine thermal management strategy, thereby effectively reducing the vehicle's fuel consumption and balancing braking performance and fuel economy. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of the combined engine thermal management and braking method of the present invention. Detailed Implementation

[0017] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0018] Combined with engine thermal management and braking methods, including: Step 1: Obtain vehicle braking-related data; After the vehicle engages constant speed braking mode, the VCU (Vehicle Control Unit) obtains vehicle braking-related data from the TCU (Transmission Control Unit). Vehicle braking-related data includes vehicle driving-related data and vehicle speed-related data; Vehicle driving-related data includes the gradient of the current road and the total weight of the vehicle. Vehicle speed-related data includes the vehicle's real-time current speed and the speed requested by the driver through operation; After the vehicle engages constant speed braking mode, the VCU uses preset rolling resistance coefficient, air resistance coefficient, frontal area, and vehicle mass conversion factor. Step 2: Calculate the braking power requirement; Based on vehicle braking-related data, the VCU calculates the braking power required to reduce the vehicle speed from its current speed to and maintain the requested speed using a preset power calculation model. The formula for calculating braking power requirement is as follows: p e3 =p e1 -p e2 , , Where, p e1 p represents the power required at the current vehicle speed. e2 p represents the power required for the target vehicle speed. e3 Indicates braking power requirement; p e Indicates the required power. G represents the vehicle's weight; f represents the rolling resistance coefficient; u represents the transmission efficiency; G represents the vehicle's weight; f represents the rolling resistance coefficient; u represents the vehicle's weight; f ... a Indicates vehicle speed; i represents gradient; C D The values ​​represent: drag coefficient (A), frontal area (δ), vehicle mass conversion factor (m), and vehicle mass (m). Step 3: Compare the supply and demand relationship between braking power requirements and engine in-cylinder braking power; The engine sends the braking power data of partial cylinder braking and the maximum engine braking power data of all cylinder braking to the VCU. The VCU compares its calculated braking power requirement with the engine cylinder braking power. The VCU compares the braking power requirement with the engine cylinder braking power, which is the maximum braking power that the engine itself can provide or the braking power when some cylinders are working, to obtain the judgment result. If the braking power of some or all cylinders of the engine is less than the braking power requirement, it means that the in-cylinder braking alone cannot meet the constant speed requirement; if the braking power of some or all cylinders of the engine is greater than or equal to the braking power requirement, it means that the in-cylinder braking alone can meet or even exceed the constant speed requirement. Step 4: Determine the braking scheme based on the supply and demand relationship; If the in-cylinder braking power is less than the braking power requirement, in-cylinder braking is activated: The VCU sends a command to the engine to determine the number of engine cylinders to be activated based on the difference between the braking power requirement and the in-cylinder braking power, in order to match part of the braking power requirement. If the braking power demand is greater than the maximum braking power of the engine, then the in-cylinder braking of all cylinders is activated; if the braking power demand is less than the maximum braking power of the engine but greater than the braking power of some cylinders, then the braking power of some cylinders is activated; for the remaining braking power gap not covered by the in-cylinder braking, the VCU sends a command to the hydraulic retarder system to activate the hydraulic retarder braking, which forms a combined braking with the in-cylinder braking to meet the total braking power demand. If the in-cylinder braking power of the engine is greater than or equal to the braking power requirement, the VCU directly sends a command to the hydraulic retarder system to call only the hydraulic retarder braking: based on the braking power requirement, the difference between the current vehicle speed and the target vehicle speed, the PID controller calls the hydraulic retarder to meet the vehicle speed control target.

[0019] This invention provides a braking strategy where, when using constant speed braking, the VCU (Vehicle Control Unit) calculates the braking power requirement based on gradient and vehicle weight data provided by the TCU (Transmission Control Unit), the current vehicle speed, and the driver's requested speed. The VCU then determines whether the engine's partial or complete in-cylinder braking power is less than the required braking power. If the engine's partial or complete in-cylinder braking power is less than the required braking power, in-cylinder braking is activated, and the VCU sends a command to the engine to determine the number of cylinders to activate; the remaining cylinders are activated via hydraulic buffer. If the engine's partial or complete in-cylinder braking power is greater than the required braking power, hydraulic buffer is activated directly, and a command is sent to the hydraulic buffer to activate the corresponding buffer ratio to control the vehicle to meet the constant speed requirement. This invention reduces the engine's thermal management ratio while achieving the same braking power, thus reducing fuel consumption. This invention is applicable to commercial vehicles equipped with AMT (Automated Manual Transmission) gearboxes and China VI diesel engines with thermal management.

[0020] This invention, through a refined braking control logic throughout the entire process, effectively resolves the contradiction between braking and fuel consumption in existing diesel-powered commercial vehicles meeting China VI emission standards, while ensuring stable braking function. First, this invention is based on precise data acquisition to ensure the accuracy of braking demand judgment, providing a prerequisite for subsequent efficient braking. After the vehicle engages constant speed braking mode, the VCU not only calls upon preset core parameters such as rolling resistance coefficient and air resistance coefficient, but also obtains key data such as current road slope and total vehicle weight in real time from the TCU. These data cover the road environment, vehicle itself, and driving needs that affect braking power, avoiding inaccurate braking power calculations due to missing data or estimation errors. This ensures that the subsequent braking scheme can accurately match the actual driving scenario. For example, under steep slopes and heavy loads, there will be no under-braking due to data errors, and under gentle slopes and light loads, there will be no over-braking, thus guaranteeing the reliability of the constant speed downhill braking function from the source.

[0021] Secondly, this invention achieves quantitative control of braking demand through a scientific braking power calculation model, providing a basis for allocating braking resources on demand. Based on the acquired full-dimensional data, the VCU calculates the braking power demand using a formula that includes variables such as rolling resistance, air resistance, vehicle weight, and mass conversion factor. It transforms the goal of reducing the current vehicle speed to and maintaining the requested speed into a specific power value. This quantitative calculation method avoids the drawbacks of empirical calls in traditional braking strategies. For example, it will not activate high-power in-cylinder braking when only low-power braking is needed, nor will it rely solely on hydraulic retarder to cause braking lag when high power is required. This ensures that the braking power supply meets safety requirements without generating redundant consumption, laying the foundation for balancing braking and fuel consumption in the future.

[0022] Furthermore, this invention achieves on-demand selection of braking methods through a refined comparison of braking power supply and demand, fully utilizing the engine's in-cylinder braking. The engine needs to transmit two types of data to the VCU: partial cylinder braking power and maximum braking power of all cylinders. The VCU will compare the calculated braking power demand with these two types of data separately, clarifying three scenarios: in-cylinder braking alone can meet the demand, in-cylinder braking needs to be combined with hydraulic buffer, and full-cylinder braking + hydraulic buffer is required. This detailed comparison logic changes the problem of existing constant-speed braking not considering engine thermal management: when the in-cylinder braking power is sufficient to meet the demand, it will be fully utilized to increase exhaust temperature, reducing the frequency and intensity of thermal management strategy intervention, and providing key support for fuel consumption optimization.

[0023] Finally, this invention achieves a dual balance between braking function and fuel economy through a dynamic braking scheme that combines in-cylinder braking with hydraulic retarder. When in-cylinder braking power is insufficient, it does not directly activate all cylinders for braking. Instead, it determines the number of cylinders to be used based on the power difference, and the remaining gap is filled by hydraulic retarder. For example, when the braking demand is greater than the braking power of some cylinders but less than the braking power of all cylinders, only partial cylinder braking plus hydraulic retarder is activated to ensure sufficient braking power. When the in-cylinder braking power is greater than the braking demand, hydraulic retarder braking is directly activated. The PID (Proportional-Integral-Derivative) controller precisely matches the vehicle speed target, and in-cylinder braking is not activated at all. This coordinated mode not only ensures the braking effect on constant-speed downhill slopes but also maximizes the use of the engine's in-cylinder braking, improving exhaust temperature. Ultimately, while achieving constant-speed braking function for commercial vehicles, it significantly reduces fuel consumption caused by engine thermal management intervention, achieving a balance between braking reliability and fuel economy.

[0024] Example 1 This embodiment proposes a combined braking method integrating engine thermal management, such as... Figure 1 As shown, it includes: Step 1: Obtain vehicle braking-related data; Step 2: Calculate the braking power requirement; Step 3: Compare the supply and demand relationship between braking power requirements and engine in-cylinder braking power; Step 4: Determine the braking scheme based on the supply and demand relationship.

[0025] Example 2 This embodiment proposes a combined braking method integrating engine thermal management, such as... Figure 1 As shown, it includes: Step 1: Obtain vehicle braking-related data; After the vehicle engages constant speed braking mode, the VCU uses preset rolling resistance coefficient, air resistance coefficient, frontal area, and vehicle mass conversion factor to obtain vehicle braking-related data from the TCU.

[0026] Vehicle braking-related data includes vehicle driving-related data and vehicle speed-related data; Vehicle driving-related data includes the gradient of the current road and the total weight of the vehicle. Vehicle speed-related data includes the vehicle's real-time current speed and the speed requested by the driver through operation.

[0027] Step 2: Calculate the braking power requirement; Step 3: Compare the supply and demand relationship between braking power requirements and engine in-cylinder braking power; Step 4: Determine the braking scheme based on the supply and demand relationship.

[0028] Example 3 This embodiment proposes a combined braking method integrating engine thermal management, such as... Figure 1 As shown, it includes: Step 1: Obtain vehicle braking-related data; Step 2: Calculate the braking power requirement; Based on vehicle braking-related data, the VCU calculates the braking power required to reduce the vehicle speed from its current speed to and maintain the requested speed using a preset power calculation model.

[0029] Step 3: Compare the supply and demand relationship between braking power requirements and engine in-cylinder braking power; Step 4: Determine the braking scheme based on the supply and demand relationship.

[0030] Example 4 This embodiment proposes a combined braking method integrating engine thermal management, such as... Figure 1 As shown, it includes: Step 1: Obtain vehicle braking-related data; Step 2: Calculate the braking power requirement; Step 3: Compare the supply and demand relationship between braking power requirements and engine in-cylinder braking power; The engine sends the braking power data of partial cylinder braking and the maximum engine braking power data of all cylinder braking to the VCU. The VCU compares its calculated braking power requirement with the engine cylinder braking power. The VCU compares the braking power requirement with the engine's in-cylinder braking power, which is the maximum braking power that the engine itself can provide or the braking power when some cylinders are working, and then makes a judgment: if the braking power of some or all cylinders of the engine is less than the braking power requirement, it means that the in-cylinder braking alone cannot meet the constant speed requirement; if the braking power of some or all cylinders of the engine is greater than or equal to the braking power requirement, it means that the in-cylinder braking alone can meet or even exceed the constant speed requirement.

[0031] Step 4: Determine the braking scheme based on the supply and demand relationship.

[0032] Example 5 This embodiment proposes a combined braking method integrating engine thermal management, such as... Figure 1 As shown, it includes: Step 1: Obtain vehicle braking-related data; Step 2: Calculate the braking power requirement; Step 3: Compare the supply and demand relationship between braking power requirements and engine in-cylinder braking power; Step 4: Determine the braking scheme based on the supply and demand relationship.

[0033] If the in-cylinder braking power is less than the braking power requirement, in-cylinder braking is activated: The VCU sends a command to the engine to determine the number of engine cylinders to be activated based on the difference between the braking power requirement and the in-cylinder braking power, in order to match part of the braking power requirement.

[0034] Example 6 This embodiment proposes a combined braking method integrating engine thermal management, such as... Figure 1 As shown, it includes: Step 1: Obtain vehicle braking-related data; Step 2: Calculate the braking power requirement; Step 3: Compare the supply and demand relationship between braking power requirements and engine in-cylinder braking power; Step 4: Determine the braking scheme based on the supply and demand relationship.

[0035] If the engine's in-cylinder braking power is less than the braking power requirement, in-cylinder braking is activated: The VCU sends a command to the engine to determine the number of engine cylinders to be activated based on the difference between the braking power requirement and the in-cylinder braking power, in order to match part of the braking power requirement; if the braking power requirement is greater than the engine's maximum braking power, then in-cylinder braking of all cylinders is activated.

[0036] Example 7 This embodiment proposes a combined braking method integrating engine thermal management, such as... Figure 1 As shown, it includes: Step 1: Obtain vehicle braking-related data; Step 2: Calculate the braking power requirement; Step 3: Compare the supply and demand relationship between braking power requirements and engine in-cylinder braking power; Step 4: Determine the braking scheme based on the supply and demand relationship.

[0037] If the in-cylinder braking power is less than the braking power requirement, in-cylinder braking is activated: The VCU sends a command to the engine to determine the number of engine cylinders to be activated based on the difference between the braking power requirement and the in-cylinder braking power, in order to match part of the braking power requirement. If the braking power requirement is less than the maximum power of engine braking but greater than the braking power of partial cylinder braking, then the braking power of partial cylinder braking is used; for the remaining braking power gap not covered by in-cylinder braking, the VCU sends a command to the hydraulic retarder system to use hydraulic retarder braking, which forms a combined braking with in-cylinder braking to meet the total braking power requirement.

[0038] Example 8 This embodiment proposes a combined braking method integrating engine thermal management, such as... Figure 1 As shown, it includes: Step 1: Obtain vehicle braking-related data; Step 2: Calculate the braking power requirement; Step 3: Compare the supply and demand relationship between braking power requirements and engine in-cylinder braking power; Step 4: Determine the braking scheme based on the supply and demand relationship.

[0039] If the in-cylinder braking power of the engine is greater than or equal to the braking power requirement, the VCU directly sends a command to the hydraulic retarder system to call only the hydraulic retarder braking: based on the braking power requirement, the difference between the current vehicle speed and the target vehicle speed, the PID controller calls the hydraulic retarder to meet the vehicle speed control target.

Claims

1. A combined engine thermal management and braking method, characterized in that, include: Step 1: Obtain vehicle braking-related data; Step 2: Calculate the braking power requirement; Step 3: Compare the supply and demand relationship between braking power requirements and engine in-cylinder braking power; Step 4: Determine the braking scheme based on the supply and demand relationship.

2. The combined engine thermal management and braking method according to claim 1, characterized in that, Step one includes: after the vehicle activates the constant speed braking mode, the VCU uses preset rolling resistance coefficient, air resistance coefficient, frontal area, and vehicle mass conversion factor to obtain vehicle braking-related data from the TCU.

3. The combined engine thermal management and braking method according to claim 2, characterized in that, The vehicle braking-related data includes vehicle driving-related data and vehicle speed-related data; The vehicle driving-related data includes the gradient of the current road and the total weight of the vehicle. The vehicle speed-related data includes the vehicle's real-time current speed and the requested speed set by the driver through operation.

4. The combined engine thermal management and braking method according to claim 1, characterized in that, Step two includes: The VCU calculates the braking power required to reduce the vehicle speed from its current speed to the requested speed and maintain it, based on vehicle braking-related data and a preset power calculation model.

5. The combined engine thermal management and braking method according to claim 1, characterized in that, The formula for calculating the braking power requirement is as follows: p e3 =p e1 -p e2 ， ， Where, p e1 p represents the power required at the current vehicle speed. e2 p represents the power required for the target vehicle speed. e3 Indicates braking power requirement; p e Indicates the required power. G represents the vehicle's weight; f represents the rolling resistance coefficient; u represents the transmission efficiency; G represents the vehicle's weight; f represents the rolling resistance coefficient; u represents the vehicle's weight; f ... a Indicates vehicle speed; i represents gradient; C D δ represents the air drag coefficient; A represents the frontal area; δ represents the vehicle mass conversion factor; m represents the vehicle mass.

6. The combined engine thermal management and braking method according to claim 1, characterized in that, Step three includes: The engine sends the braking power data of partial cylinder braking and the maximum engine braking power data of all cylinder braking to the VCU. The VCU compares its calculated braking power requirement with the engine cylinder braking power. The VCU compares the braking power requirement with the engine's in-cylinder braking power, which is the maximum braking power that the engine itself can provide or the braking power when some cylinders are working, and then makes a judgment: if the braking power of some or all cylinders of the engine is less than the braking power requirement, it means that the in-cylinder braking alone cannot meet the constant speed requirement; if the braking power of some or all cylinders of the engine is greater than or equal to the braking power requirement, it means that the in-cylinder braking alone can meet or even exceed the constant speed requirement.

7. The combined engine thermal management and braking method according to claim 1, characterized in that, Step four includes: If the in-cylinder braking power is less than the braking power requirement, in-cylinder braking is activated: The VCU sends a command to the engine to determine the number of engine cylinders to be activated based on the difference between the braking power requirement and the in-cylinder braking power, in order to match part of the braking power requirement.

8. The combined engine thermal management and braking method according to claim 1, characterized in that, Step four includes: If the in-cylinder braking power is less than the braking power requirement, in-cylinder braking is activated: The VCU sends a command to the engine to determine the number of engine cylinders to be activated based on the difference between the braking power requirement and the in-cylinder braking power, in order to match part of the braking power requirement. If the braking power demand exceeds the engine braking maximum power, then the in-cylinder braking of all cylinders will be activated.

9. The combined engine thermal management and braking method according to claim 1, characterized in that, Step four includes: If the in-cylinder braking power is less than the braking power requirement, in-cylinder braking is activated: The VCU sends a command to the engine to determine the number of engine cylinders to be activated based on the difference between the braking power requirement and the in-cylinder braking power, in order to match part of the braking power requirement. If the braking power requirement is less than the maximum power of engine braking but greater than the braking power of partial cylinder braking, then the braking power of partial cylinder braking is used; for the remaining braking power gap not covered by in-cylinder braking, the VCU sends a command to the hydraulic retarder system to use hydraulic retarder braking, which forms a combined braking with in-cylinder braking to meet the total braking power requirement.

10. The combined engine thermal management and braking method according to claim 1, characterized in that, Step four includes: If the in-cylinder braking power of the engine is greater than or equal to the braking power requirement, the VCU directly sends a command to the hydraulic retarder system to call only the hydraulic retarder braking: based on the braking power requirement, the difference between the current vehicle speed and the target vehicle speed, the PID controller calls the hydraulic retarder to meet the vehicle speed control target.

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