A method of hydraulic economy control for a purely hydraulically driven vehicle

Abstract

The application discloses a kind of pure hydraulic drive vehicle economy control method, comprising, according to vehicle actual driving speed and target speed whether vehicle is in uniform motion is judged, if vehicle is not in uniform motion at this time, then using economy basic control strategy, control vehicle acceleration to target speed;After vehicle speed is promoted to target speed and enters uniform motion stage, using efficiency compensation strategy, through motor displacement compensation, further improve the driving economy of uniform stage while guaranteeing target speed tracking.The application reduces the fuel consumption of vehicle driving process on the basis of realizing pure hydraulic drive vehicle target speed tracking, improves driving economy.

Description

Technical Field

[0001] This invention belongs to the field of vehicle transmission control, and particularly relates to an economical control method for purely hydraulically driven vehicles. Background Technology

[0002] Hydraulic drive technology for vehicles utilizes components such as hydraulic pumps and hydraulic motors to construct a transmission system, achieving continuously variable transmission. This results in better performance matching between the engine and the load, effectively improving overall energy utilization efficiency and showing broad application prospects in the field of off-road vehicles.

[0003] The purpose of fuel economy control is to enable a vehicle to operate with minimal fuel consumption. Under specific operating conditions, fuel consumption is primarily determined by the engine's operating point, pump efficiency, and motor efficiency. Generally, to ensure fuel economy, it's sufficient to control the engine at its lowest fuel consumption operating point. The engine operating point is mainly achieved by adjusting the throttle opening and the transmission ratio. In traditional vehicle transmission systems, the efficiency differences between various speed ratios are minimal. When transmission efficiency is disregarded, speed ratio adjustment does not significantly impact overall fuel consumption. Therefore, during operation, only the engine's fuel consumption rate needs to be considered, and the optimal fuel economy curve is typically used as the control target. Only the engine operating point needs to be considered throughout the entire driving process. However, in a purely hydraulic drive system, the transmission ratio is achieved by adjusting the pump / motor displacement. Changes in pump / motor displacement directly affect transmission efficiency, thus impacting overall fuel consumption. Therefore, fuel economy control must consider the influence of pump / motor displacement changes on system efficiency. Summary of the Invention

[0004] The purpose of the economic control method provided by this invention is to reduce fuel consumption and improve economy during vehicle operation by adjusting the speed ratio of the transmission system by adjusting the displacement of the pump motor, taking into account the influence of engine characteristics and pump motor efficiency, while achieving target speed tracking of a purely hydraulically driven vehicle.

[0005] To achieve the above objectives, the present invention provides the following solution: an economic control method for a purely hydraulically driven vehicle, comprising:

[0006] Based on the actual vehicle speed and the target speed, determine whether the vehicle is moving at a constant speed. If the vehicle is not moving at a constant speed, adopt the basic economic control strategy to control the vehicle to accelerate to the target speed.

[0007] After the vehicle speed increases to the target speed and enters the constant speed motion phase, an efficiency compensation strategy is adopted. By compensating for the motor displacement, the driving economy during the constant speed phase is further improved while ensuring the target speed is tracked.

[0008] Preferably, the process of using an economical basic control strategy to control the vehicle's acceleration to the target speed includes,

[0009] The driver accelerates the vehicle from a standstill by manipulating the accelerator pedal, and adjusts the pump / motor displacement to make the engine operate at the point of lowest fuel consumption.

[0010] Based on the engine's optimal operating curve and the structural characteristics of the hydraulic drive system, arbitrary control operations can be performed on the vehicle engine's operating state, unaffected by road load.

[0011] Preferably, the process of obtaining the engine's optimal operating curve includes,

[0012] Based on the analysis of historical test data of the engine, an engine characteristic diagram was drawn.

[0013] Based on the universal characteristic curve of the engine characteristic diagram, the minimum fuel consumption rate points corresponding to each power are connected to obtain the optimal operating curve of the engine.

[0014] Preferably, the efficiency compensation strategy is as follows: after the vehicle enters the constant speed driving stage, the influence of pump / motor efficiency is further considered, and the influence of pump / motor displacement change on system efficiency is compensated by adjusting the engine operating point and motor displacement, so as to realize the control of the engine-hydraulic drive system and further improve the economy of the vehicle during constant speed driving.

[0015] Preferably, the process of employing an efficiency compensation strategy to ensure target vehicle speed tracking through motor displacement compensation includes:

[0016] Determine the target engine torque during constant speed driving;

[0017] The process of determining the target engine torque during constant speed driving includes,

[0018] When the vehicle is traveling at a constant speed, the wheel torque and speed are obtained through longitudinal dynamics. Based on the wheel torque and speed, the engine torque and speed of the hydraulic drive system vehicle when traveling at a constant speed are obtained.

[0019] Based on the engine torque, the engine torque requirement is determined according to the pump / motor displacement, and the engine torque requirement is used as the target torque. The engine throttle opening is controlled through torque closed-loop control to achieve engine target torque tracking.

[0020] Preferably, the formulas for the wheel torque and rotational speed are as follows:

[0021]

[0022]

[0023] In the formula, G is the vehicle weight, f is the rolling resistance coefficient, and C D Where A is the drag coefficient, V is the vehicle's frontal area, and A is the wind resistance coefficient. x R is the vehicle speed, and r is the wheel radius;

[0024] The formulas for engine torque and speed are as follows:

[0025]

[0026] n e =n w i p i m i w iη n

[0027] In the formula, i p For the engine-pump reduction ratio, i m i is the reduction ratio from the motor to the busbar. w The main reduction ratio from the busbar to the wheels is η, where i is the pump / motor reduction ratio, and η is the pump / motor reduction ratio. T For mechanical efficiency, η n For volumetric efficiency;

[0028] The formula for the target torque of the engine is as follows:

[0029]

[0030] In the formula, ε T This is the torque correction factor.

[0031] Preferably, the process of employing an efficiency compensation strategy to ensure target vehicle speed tracking through motor displacement compensation includes:

[0032] Determine the motor displacement correction coefficient during constant speed driving;

[0033] The process of determining the motor displacement correction coefficient during constant speed driving includes,

[0034] Based on a comprehensive consideration of the target vehicle speed, engine operating point, and pump / motor system transmission efficiency, the pump / motor displacement with optimal economy is determined by iterating through the speed ratios, and then the motor displacement correction coefficient is determined.

[0035] Preferably, the process of determining the motor displacement correction coefficient includes,

[0036] Determine the speed ratio range of the straight-drive hydraulic circuit based on the pump / motor parameters, and then determine the engine target torque required for the vehicle to travel at a constant speed on the road by combining the vehicle's required power, speed ratio, and vehicle speed.

[0037] When the required engine torque meets the condition that the engine torque does not exceed the maximum torque, the motor output speed is then calculated, and the engine speed is obtained by combining the pump / motor system efficiency.

[0038] When the engine speed is greater than the idle speed but less than the maximum speed, the operating point fuel consumption is obtained by looking up the universal characteristic curve of the engine characteristic diagram based on the engine speed and torque, and the vehicle fuel consumption per 100 kilometers at this operating point is calculated.

[0039] Similarly, the fuel consumption corresponding to each speed ratio is calculated, and the speed ratio corresponding to the lowest fuel consumption is taken as the final target speed ratio, thereby determining the motor displacement correction coefficient.

[0040] Preferably, the determination of the motor displacement correction coefficient can be summarized as follows: under the conditions of satisfying the vehicle speed and engine target torque, find the optimal pump / motor speed ratio to minimize the fuel consumption of the vehicle during driving, which is then transformed into a problem of solving for the minimum objective function, the objective function being minQ. s =f(T) ed ,n e i), the constraints are:

[0041]

[0042] In the formula, T e_max Let n be the maximum torque of the engine at a certain speed. e_min ,n e_max i represents the minimum and maximum engine speeds. min i max These are the minimum and maximum speed ratios of the hydraulic drive system.

[0043] Preferably, the process of calculating the fuel consumption corresponding to each speed ratio, selecting the speed ratio corresponding to the lowest fuel consumption as the final target speed ratio, and then determining the motor displacement correction coefficient includes the following steps:

[0044] In the hydraulic drive system, the pump motor displacement is set to the maximum displacement, and the motor displacement is obtained through the target speed ratio, thereby determining the motor displacement correction coefficient.

[0045] The formula for the motor displacement correction factor is as follows:

[0046]

[0047] In the formula, V md To determine the motor displacement using the target speed ratio, V m This refers to the motor displacement at the end of the acceleration phase.

[0048] Compared with the prior art, the present invention has the following advantages and technical effects:

[0049] During the acceleration phase, this invention controls the pump motor displacement to ensure the engine operates at the most economical speed at various throttle openings, thereby reducing fuel consumption and improving fuel economy during the acceleration of a purely hydraulically driven vehicle. Once the vehicle accelerates to a constant speed, the invention further improves the fuel economy of the entire purely hydraulic drive system by taking into account the engine operating point and pump motor efficiency, through an efficiency compensation method. Attached Figure Description

[0050] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0051] Figure 1 This is a schematic diagram of the method flow according to an embodiment of the present invention;

[0052] Figure 2 This is a flowchart illustrating the determination of the motor displacement correction coefficient according to an embodiment of the present invention;

[0053] Figure 3 This is a simulation result diagram of a vehicle speed of 30km / h in an embodiment of the present invention;

[0054] Figure 4 This is a simulation result diagram of a vehicle speed of 40km / h in an embodiment of the present invention;

[0055] Figure 5 This is a simulation result of engine speed at 30km / h according to an embodiment of the present invention;

[0056] Figure 6 This is a simulation result of engine speed at 40km / h according to an embodiment of the present invention;

[0057] Figure 7 The figure shows the simulation results of fuel consumption at 30km / h in an embodiment of the present invention.

[0058] Figure 8 The figure shows the simulation results of fuel consumption at 40km / h in an embodiment of the present invention. Detailed Implementation

[0059] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0060] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0061] like Figure 1 As shown, the present invention provides an economic control method for a purely hydraulically driven vehicle, which consists of two parts: a basic economic control strategy and an efficiency compensation strategy. First, it determines whether the vehicle is moving at a constant speed based on its actual speed and the target speed. If the vehicle is not moving at a constant speed, the basic economic control strategy is adopted, the purpose of which is to control the vehicle to accelerate to the target speed. After the vehicle speed increases to the target speed and enters the constant speed phase, the efficiency compensation strategy is adopted. Through motor displacement compensation, while ensuring target speed tracking, the driving economy during the constant speed phase is further improved.

[0062] Furthermore, the basic economic control strategy includes: the driver accelerates the vehicle from a standstill by manipulating the accelerator pedal; to ensure economy during acceleration, the pump / motor displacement is adjusted so that the engine operates at its lowest fuel consumption point. Due to the structural characteristics of the hydraulic drive system, road loads are not directly applied or transmitted to the engine crankshaft via the hydraulic drive system; therefore, the engine's operating state (speed / torque) can be arbitrarily controllable and is unaffected by road loads. Therefore, the vehicle engine is controlled based on its optimal operating curve. Historical test data of the engine is analyzed, and an engine characteristic diagram is plotted. Connecting the minimum fuel consumption points corresponding to each power output on the universal characteristic curve yields the engine's optimal operating curve.

[0063] The aforementioned basic economic control strategy can achieve vehicle tracking of the ideal speed. However, this method does not consider the impact of pump / motor efficiency. To further improve the vehicle's economy during constant-speed driving, the impact of pump / motor efficiency is considered when controlling the engine-hydraulic drive system after the vehicle enters the constant-speed driving phase. The purpose of the economic efficiency compensation strategy is to compensate for the impact of pump / motor displacement changes on system efficiency by adjusting the engine operating point and motor displacement during the constant-speed driving phase, thereby further improving the vehicle's driving economy.

[0064] The key to the efficiency compensation strategy lies in determining the engine operating torque and motor displacement correction coefficient during constant speed driving. When the vehicle is traveling at a constant speed, the wheel torque and rotational speed are obtained through longitudinal dynamics:

[0065]

[0066]

[0067] In the formula, G is the vehicle weight, f is the rolling resistance coefficient, and C D Where A is the drag coefficient, V is the vehicle's frontal area, and A is the wind resistance coefficient. x R is the vehicle speed, and r is the wheel radius;

[0068] Furthermore, based on the wheel torque and speed, the engine torque and speed of the hydraulic drive system vehicle when traveling at a constant speed are obtained as follows:

[0069]

[0070] n e =n w i p i m i w iη n

[0071] In the formula, i p For the engine-pump reduction ratio, i m i is the reduction ratio from the motor to the busbar. w The main reduction ratio from the busbar to the wheels is η, where i is the pump / motor reduction ratio, and η is the pump / motor reduction ratio. T For mechanical efficiency, η n For volumetric efficiency;

[0072] Since the reduction ratios, except for those of the pump / motor, are constant, the engine speed and torque can be calculated once the pump / motor reduction ratio is determined. However, the pump / motor efficiency in the hydraulic drive system is significantly affected by displacement. The system efficiency and volumetric efficiency of the pump / motor circuit are highest when the displacement is close to the maximum displacement, and decrease as the displacement decreases. Therefore, the impact of motor efficiency on vehicle economy needs to be considered when setting the motor displacement ratio. Displacement changes have a relatively small impact on the mechanical efficiency of the hydraulic drive circuit. Therefore, after determining the load torque after the vehicle is traveling at a constant speed, the engine torque demand is determined based on the pump / motor displacement. Using this engine torque demand as the target torque, the engine throttle opening is controlled through a torque closed-loop control to achieve engine target torque tracking. The engine target torque after considering the influence of motor efficiency is:

[0073]

[0074] In the formula, ε T This is the torque correction factor.

[0075] After determining the target engine torque, it is necessary to determine the motor displacement correction factor ε. m However, changes in motor displacement have a significant impact on system volumetric efficiency. A correction factor that is too high or too low will affect vehicle speed, making it impossible to achieve uniform vehicle movement. Therefore, to ensure the rationality of the motor displacement correction factor, this embodiment, based on a comprehensive consideration of the target vehicle speed, engine operating point, and pump / motor system transmission efficiency, calculates the most economically efficient pump / motor displacement by iterating through the speed ratios, and then determines the motor displacement correction factor.

[0076] Determining the motor displacement correction factor can be reduced to the following problem: Under the conditions of satisfying vehicle speed and engine target torque, find the optimal pump / motor speed ratio to minimize fuel consumption during vehicle operation. This problem can be transformed into solving for the minimum objective function, which is minQ. s =f(T) ed ,n e i), the constraints are:

[0077]

[0078] In the formula, T e_max Let n be the maximum torque of the engine at a certain speed. e_min ,n e_max i represents the minimum and maximum engine speeds. min i max These are the minimum and maximum speed ratios of the hydraulic drive system.

[0079] The process for determining the motor displacement correction factor is as follows: Figure 2 As shown. First, the speed ratio range of the direct-drive hydraulic circuit is determined based on the pump / motor parameters. Then, the target engine torque required for the vehicle to travel at a constant speed on the road is determined by combining the vehicle's required power, speed ratio, and vehicle speed. When the required engine torque meets the condition that the engine torque does not exceed the maximum torque, the motor output speed is calculated, and the engine speed is calculated by combining the pump / motor system efficiency. When the calculated engine speed is greater than the idle speed but less than the maximum speed, the universal characteristic curve of the engine characteristic diagram is used to obtain the operating point fuel consumption based on the calculated engine speed and torque. The fuel consumption per 100 kilometers of the vehicle at this operating point is calculated. Similarly, the fuel consumption corresponding to each speed ratio is calculated, and the speed ratio corresponding to the lowest fuel consumption is taken as the final target speed ratio, thereby determining the motor displacement correction coefficient.

[0080] Because the pump / motor displacement relationship corresponding to a speed ratio in a pure hydraulic drive system is not unique and there are multiple combinations, that is, the mapping relationship between speed ratio and pump / motor displacement is not unique and the efficiency corresponding to different combinations is also different, in order to reduce and avoid solving such a complex mapping relationship problem, the pump and motor displacement in the hydraulic drive system is set to the maximum displacement, and the motor displacement is obtained through the target speed ratio, and then the motor displacement correction coefficient is determined.

[0081] The formula for the motor displacement correction factor is as follows:

[0082]

[0083] In the formula, V md To determine the motor displacement using the target speed ratio, V m This refers to the motor displacement at the end of the acceleration phase.

[0084] The motor displacement correction coefficients at different target vehicle speeds are obtained using the above method. After determining the motor displacement correction coefficients, the vehicle can be kept at a constant speed at the target vehicle speed based on the economic compensation strategy.

[0085] Implementation Case:

[0086] Taking constant speed driving conditions of 30km / h and 40km / h as examples, the results obtained by adopting the economic efficiency compensation strategy are as follows: Figures 3-8 As shown in the figure. Simulation results show that, under different operating conditions, the economic efficiency compensation strategy can maintain a constant vehicle speed during the constant-speed driving phase. Simulation results of engine speed and fuel consumption under different operating conditions show that the economic efficiency compensation strategy can further improve vehicle fuel economy by adjusting the engine operating point through motor displacement correction. Simulation results also show that the fuel consumption of the vehicle using the economic efficiency compensation strategy is further reduced after efficiency compensation under different operating conditions. A comparison of fuel consumption and vehicle speed results under different strategies is shown in Table 1. The fuel consumption per 100 kilometers without considering the influence of mechanical transmission efficiency is also shown in the table. The data in the table shows that the economic efficiency compensation method can further reduce vehicle fuel consumption and improve overall vehicle fuel economy.

[0087] Table 1

[0088]

[0089] This embodiment divides the fuel economy control of a purely hydraulically driven vehicle into two stages. During the acceleration stage, the optimal engine speed for fuel economy is targeted to reduce vehicle fuel consumption. During the constant speed stage, an efficiency compensation method is used to further improve the overall fuel economy of the vehicle.

[0090] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for economical control of a purely hydraulically driven vehicle, characterized in that, include: Based on the actual vehicle speed and the target speed, determine whether the vehicle is moving at a constant speed. If the vehicle is not moving at a constant speed, adopt the basic economic control strategy to control the vehicle to accelerate to the target speed. After the vehicle speed increases to the target speed and enters the constant speed motion stage, an efficiency compensation strategy is adopted. By compensating the motor displacement, the driving economy during the constant speed stage is further improved while ensuring the target speed is tracked. The process of employing an efficiency compensation strategy to ensure target vehicle speed tracking through motor displacement compensation includes the following steps: Determine the motor displacement correction coefficient during constant speed driving; The process of determining the motor displacement correction coefficient during constant speed driving includes, Based on a comprehensive consideration of the target vehicle speed, engine operating point, and pump / motor system transmission efficiency, the pump / motor displacement with optimal economy is determined by iterating through the speed ratios, and then the motor displacement correction coefficient is determined. The process of determining the motor displacement correction factor includes: Determine the speed ratio range of the straight-drive hydraulic circuit based on the pump / motor parameters, and then determine the engine target torque required for the vehicle to travel at a constant speed on the road by combining the vehicle's required power, speed ratio, and vehicle speed. When the required engine torque meets the condition that the engine torque does not exceed the maximum torque, the motor output speed is then calculated, and the engine speed is obtained by combining the pump / motor system efficiency. When the engine speed is greater than the idle speed but less than the maximum speed, the operating point fuel consumption is obtained by looking up the universal characteristic curve of the engine characteristic diagram based on the engine speed and torque, and the vehicle fuel consumption per 100 kilometers at this operating point is calculated. Similarly, the fuel consumption corresponding to each speed ratio is calculated, and the speed ratio corresponding to the lowest fuel consumption is taken as the final target speed ratio, thereby determining the motor displacement correction coefficient.

2. The economic control method for a purely hydraulically driven vehicle according to claim 1, characterized in that, The process of using an economical basic control strategy to control the vehicle's acceleration to the target speed includes, The driver accelerates the vehicle from a standstill by manipulating the accelerator pedal, and adjusts the pump / motor displacement to make the engine operate at the point of lowest fuel consumption. Based on the engine's optimal operating curve and the structural characteristics of the hydraulic drive system, arbitrary control operations can be performed on the vehicle engine's operating state, unaffected by road load.

3. The economic control method for a purely hydraulically driven vehicle according to claim 2, characterized in that, The process of obtaining the engine's optimal operating curve includes, Based on the analysis of historical test data of the engine, an engine characteristic diagram was drawn. Based on the universal characteristic curve of the engine characteristic diagram, the minimum fuel consumption rate points corresponding to each power are connected to obtain the optimal operating curve of the engine.

4. The economic control method for a purely hydraulically driven vehicle according to claim 1, characterized in that, The efficiency compensation strategy is as follows: after the vehicle enters the constant speed driving stage, the impact of pump / motor efficiency is further considered. The engine operating point and motor displacement are adjusted to compensate for the impact of pump / motor displacement changes on system efficiency, thereby realizing the control of the engine-hydraulic drive system and further improving the vehicle's economy during constant speed driving.

5. The method for controlling the economic efficiency of a purely hydraulically driven vehicle according to claim 1, characterized in that, The process of employing an efficiency compensation strategy to ensure target vehicle speed tracking through motor displacement compensation includes the following steps: Determine the target engine torque during constant speed driving; The process of determining the target engine torque during constant speed driving includes, When the vehicle is traveling at a constant speed, the wheel torque and speed are obtained through longitudinal dynamics. Based on the wheel torque and speed, the engine torque and speed of the hydraulic drive system vehicle when traveling at a constant speed are obtained. Based on the engine torque, the engine torque requirement is determined according to the pump / motor displacement, and the engine torque requirement is used as the target torque. The engine throttle opening is controlled through torque closed-loop control to achieve engine target torque tracking.

6. The method for controlling the economic efficiency of a purely hydraulically driven vehicle according to claim 5, characterized in that, The formulas for the wheel torque and rotational speed are as follows: In the formula, For vehicle weight, The rolling resistance coefficient, This is the drag coefficient. The vehicle's frontal area. For vehicle speed, The radius of the wheel; The formulas for engine torque and speed are as follows: In the formula, For the engine-pump reduction ratio, The reduction ratio from the motor to the busbar. To facilitate the main reduction ratio of the busbar to the wheels, This refers to the pump / motor reduction ratio. For mechanical efficiency, For volumetric efficiency; The formula for the target torque of the engine is as follows: In the formula, This is the torque correction factor.

7. The method for controlling the economic efficiency of a purely hydraulically driven vehicle according to claim 1, characterized in that, The determination of the motor displacement correction coefficient can be summarized as follows: under the conditions of satisfying vehicle speed and engine target torque, find the optimal pump / motor speed ratio to minimize fuel consumption during vehicle operation. This is transformed into a problem of minimizing the objective function, which is: The constraints are: In the formula, The maximum torque of the engine at a certain speed. These are the engine's minimum and maximum speeds. These are the minimum and maximum speed ratios of the hydraulic drive system.

8. The method for controlling the economic efficiency of a purely hydraulically driven vehicle according to claim 1, characterized in that, The process of calculating the fuel consumption at each speed ratio, selecting the speed ratio with the lowest fuel consumption as the final target speed ratio, and then determining the motor displacement correction factor includes... In the hydraulic drive system, the pump motor displacement is set to the maximum displacement, and the motor displacement is obtained through the target speed ratio, thereby determining the motor displacement correction coefficient. The formula for the motor displacement correction factor is as follows: In the formula, The motor displacement is obtained by using the target speed ratio. This refers to the motor displacement at the end of the acceleration phase.

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