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1 Overview
The travel drive system is an important part of construction machinery. Compared with the working system, the travel drive system not only needs to transmit more power, but also requires higher efficiency and longer life of the device. It also hopes to change the output shaft rotation direction and reverse transmission power in variable speed regulation, differential speed. Other aspects have good capabilities. Therefore, what kind of transmission method is adopted, how to better meet the needs of various construction machinery travel drives has always been a problem faced by the construction machinery industry. Especially in recent years, with the rapid development of China's transportation, energy and other infrastructure construction processes, the scale of construction and resource development continues to expand, while the construction machinery is greatly enhanced in the market demand, but also facing more harsh operating conditions. The challenges brought about by more complex conditions have further promoted the in-depth study of its travel drive system.
Here, we try to discuss the development and rules of hydraulic drive technology in the construction drive system of engineering machinery from the perspective of technical composition and performance characteristics.
2. Transmission method based on single technology
The construction machinery travel system initially used mechanical transmission and hydraulic mechanical transmission (except for full hydraulic excavators). Nowadays, the transmission mode of hydraulic and electric drive also appears in the driving drive device of engineering machinery, which fully demonstrates that the development of science and technology has greatly promoted this field.
2.1 Mechanical transmission
The purely mechanically-driven engine has a low average load factor, so generally only a step-variable shift can be performed and the layout is limited. However, due to its advantages in high steady-state transmission efficiency and low manufacturing cost, the general-purpose passenger car with a small speed regulation range and the agricultural tractor with strict economic requirements and constant working speed still occupy the dominant position.
2.2 Hydraulic transmission
The hydraulic transmission torque converter replaces the clutch in the mechanical transmission and has the stepless stepless speed regulation capability. Its outstanding advantage is that it has an output torque-speed characteristic close to the hyperbola, and the rear-mounted power shifting mechanical transmission can automatically match the load and prevent the power transmission from being overloaded. The torque converter has a large power density and low load stress, and the mass production cost is not high. It is widely used in large and medium-sized earthmoving machinery, lifting and transportation machinery, and high-speed vehicles such as automobiles and tanks. However, its characteristic matching and layout are limited, the torque range is small, and the dynamic braking capability is poor, which is not suitable for occasions requiring stable speed.
2.3 Hydraulic drive
Compared with mechanical transmission. The hydraulic drive makes it easier to control its motion parameters (flow) and power parameters (pressure), while the hydraulic drive has good low-speed load characteristics compared to hydraulic drives. Because of its high transmission efficiency, it can perform constant power output control, sufficient power utilization, simple system structure, stepless speed regulation of output speed, positive and negative operation, high speed rigidity, easy operation, etc. It has been widely used in machinery. Almost all construction machinery and equipment can see the trace of hydraulic technology, many of which have become the main transmission and control methods. The ultimate load regulation closed loop, the constant pressure of engine speed control, and the variable power system for constant power combination adjustment provide a broad development prospect for the application of hydraulic transmission to engineering machinery.
Compared with pure mechanical and hydraulic transmissions, the main advantages of hydraulic transmission are the convenience of adjustment and the flexibility of layout. The engine, drive wheel, working mechanism and other components can be selected according to the shape and working conditions of the construction machinery. They are arranged in reasonable parts, the engine works at any dispatching speed, the transmission system can exert a large traction force, and the transmission system can maintain high efficiency in a wide range of output speed, and can be easily obtained. A variety of optimized power transmission characteristics to suit the load conditions of various jobs. The traveling hydraulic drive with closed oil circuit used in the traveling machine with high speed can steplessly adjust the speed, make the vehicle start gently, change speed quickly and change the driving direction without impact. This performance is invaluable for vehicles that require frequent starting and shifting during frequent shifts and frequent shuttles. However, compared with the open circuit, the design, installation, commissioning and maintenance of the closed circuit have higher difficulty and technical requirements.
With the combination of electronic technology and hydraulic technology, various adjustments and controls of the hydraulic system can be easily realized. The introduction of computer control and the application of various sensing elements have greatly expanded the working range of hydraulic components. Through the sensor to monitor various state parameters of the engineering vehicle, the computer operation output control target command, so that the vehicle can be automatically controlled within the entire working range, and the fuel economy, power and work productivity of the machine reach the optimal value. Therefore, the use of hydraulic transmission can make engineering machinery easy to achieve intelligent, energy-saving and environmental protection, which has become the development trend of current and future engineering machinery.
2.4 Electric drive
The electric drive is driven by the internal combustion engine to generate electric energy to drive the motor to drive the moving part of the vehicle. The electric motor adjusts the speed and steering of the motor shaft through the electronic adjustment system. It has a wide range of speeds, input components (generators) and output components (motors). And the control device can be installed separately. Electric power transmission was first used in the field of diesel electric boats and diesel locomotives, and later extended to large-tonnage mining trucks and some large-scale construction machinery. In recent years, there have been small and medium-sized lifting and transportation such as forklifts and tractors for diesel electric power transmission. vehicle. However, for some reasons, such as technology and economy, power electric components suitable for mobile machinery are far less popular than those used for fixed equipment. Electric power transmission is only a "future technology" for most mobile machinery.
3. Developing composite drive technology
It can be seen from the previous analysis that the single-technology-based transmission method applied to the construction machinery travel drive system is simple in construction and reliable in transmission, and is suitable for certain specific occasions and fields. In most practical applications, these transmission technologies are often not isolated, and there is mutual penetration and integration between them. For example, hydraulic, hydraulic and electric transmissions contain more or less machinery. In the transmission section, electrical and hydraulic control systems are also provided in the new mechanical and hydraulic transmissions. In other words, using the targeted composite integration method, we can give full play to the advantages of each transmission mode, and foster strengths and avoid weaknesses, so as to obtain the best comprehensive benefits. It is worth noting that hydraulic transmissions with both adjustment and layout flexibility and high power density play an important role.
3.1 Combination of hydraulic and mechanical and hydraulic transmission
(1) Series mode
The series connection is the simplest and common compounding method. It is a high-efficiency zone where a mechanical transmission is arranged between the output end of the hydraulic motor or the hydraulic transmission and the transaxle to expand the speed regulation, and the stepless stepless shifting is realized. It has been widely used in loaders, combine harvesters and certain special vehicles. The development of the power shifting planetary transmission that can change the transmission ratio between the traveling forces is directly installed in the driving wheel, and the wheel-side hydraulic driving of the large speed ratio is realized, thereby eliminating the driving axle and facilitating layout.
(2) Parallel mode
It is commonly referred to as "hydraulic mechanical power split transmission", which can be understood as a transmission system that transmits power flow in parallel with hydraulic and mechanical devices, that is, using a multi-degree of freedom planetary differential to output the engine. The power is divided into two "power flows" of hydraulic and mechanical. With the controllability of the hydraulic power flow, the two power flows can be steplessly adjusted to the total output speed when recombining. In this way, the advantages of both the stepless speed regulation performance of the hydraulic transmission and the steady state efficiency of the mechanical transmission are combined to obtain a shifting speed with both infinitely variable speed performance and high efficiency and wide high efficiency zone. Device.
According to its structure, the composite transmission can be divided into two categories: the first type is an external split type that utilizes the planetary gear differential to split, and the common split transmission mechanism can be divided into an input split type and an output split type. The basic form; the second type is an internal split type that utilizes a differential displacement between the hydraulic pump or the motor rotor and the outer casing.
This composite hydraulic transmission has been developed by Komatsu Corporation of Japan and has been applied to construction machinery such as loaders and bulldozers. The agricultural tractors produced by the Fendt tractors in Germany equipped with the Vario-type continuously variable transmissions sold more than 30,000 units in 2003.
It can be seen that this new type of transmission has increasingly become a strong competitor for large and medium power hydraulic transmission and power shift transmission.
(3) Time-sharing mode
For the special vehicles with different speeds in the working speed and the non-working state, the traditional mechanical transmission is used for high-speed driving, and the additional hydraulic transmission device is used for low-speed operation, which can well meet the contradictory requirements of these two working conditions. Mechanical-hydraulic time-divisional driving has become commonplace in such vehicles, and this technology has also been applied to vehicles and implements that require "crawling speed" such as aircraft de-icing vehicles and field transplanters.
(4) Division method
The "wheel-side hydraulic drive" that mounts the hydraulic motor directly in the wheel is an auxiliary hydraulic drive that can solve the engineering machinery needs to improve the traction performance, but can not use the all-wheel drive mode, it is difficult to arrange the traditional mechanical transmission device. problem. The stepless speed regulation of the hydraulic transmission enables the coordinated synchronization between the drive wheels that are driven in different ways. In a sense, it can also be regarded as a power split transmission: the power of the power machine is distributed to several sets of drive wheels. After ground coupling, traction is generated to propel the vehicle. Currently, many construction machinery manufacturers use this technology for construction machinery with partial self-propelled drive capabilities, such as self-propelled graders and scrapers.
3.2 Combination of hydraulic and electric drive
Due to the development of modern technology, electronic technology has great advantages in signal processing capability and speed, and hydraulic and electric drive have their own advantages in the characteristics of their respective power components. Therefore, in addition to the now widely used "electronic nerve + hydraulic muscle" mode, there are many successful examples of the composite transmission of power flow, such as: variable frequency or DC speed motor and high efficiency, low pulsation A variable flow hydraulic oil source composed of a quantitative hydraulic pump, an electro-hydraulic actuator unit composed of an integrated electric pump-hydraulic cylinder or a low-speed high-torque hydraulic motor, and a drive system of a hybrid industrial vehicle.
3.3 Secondary adjustment hydrostatic transmission system
The secondary adjustment hydrostatic transmission technology realizes the mutual conversion between hydraulic energy and mechanical energy by adjusting the hydraulic components. In general, its implementation is based on a pressure-coupled system that uses a constant pressure coupling between the primary component (pump) and the secondary component (motor), relying on real-time adjustment of the motor displacement to balance the load torque. At present, the starting point of research on secondary regulation hydrostatic transmission technology is to recover energy and reuse energy in the transmission process, to rationally configure the overall structure of hydrostatic transmission from a macroscopic point of view and to improve the hydrostatic transmission system. Control characteristics.
In order to enable hydraulic motors and reciprocating hydraulic cylinders that do not have bidirectional stepless variable capacity to operate in the constant voltage network of the secondary regulation system, a "hydraulic transformer" using secondary regulation technology has emerged, which is similar to a power transformer. Used to match the user's different requirements for system pressure and flow to achieve power matching of the hydraulic system.
Compared with the traditional hydrostatic transmission system, the secondary adjustment hydrostatic transmission system has the advantages of easier control, working in four quadrants, recovering energy without changing the energy form, storing energy, and using hydraulic storage. The acceleration of the energy can greatly increase the acceleration power, and there is no pressure peak in the system. Since the primary component and the secondary component are separately installed, the oil source can be supplied to a plurality of hydraulic power components through one pumping station, thereby reducing the cooling cost and the manufacturing cost of the device. Reduced, system efficiency.
Compared with the electric drive, the secondary control hydrostatic drive has the advantages of fast closed-loop control, high power density, light weight and small installation space.
Due to the many advantages of the secondary regulator hydrostatic transmission system, it is widely used in many fields. It has been successfully applied in the fields of shipbuilding industry, steel industry, large test bench, vehicle transmission and so on. Mercedes-Benz has applied secondary regulation technology to driving drives in unmanned transport systems.
4 Conclusion
Since the 1990s, construction machinery has entered a new period of development, and the wide application of new technologies has led to the emergence of new structures and new products. With the penetration of microelectronics technology into engineering machinery, engineering machinery is increasingly moving toward intelligent and mechatronics, and the requirements for construction machinery travel drive devices are becoming more and more demanding. In recent years, the rapid development of hydraulic technology and the improvement of hydraulic components have made the application of hydraulic transmission in the engineering machinery transmission system leaps and bounds, and the advantages of hydraulic transmission have become increasingly prominent. It is believed that with the close integration of hydraulic technology and microelectronics technology, computer control technology and sensing technology, hydraulic transmission technology will play an increasingly important role in the development of engineering machinery travel drive system.
The travel drive system is an important part of construction machinery. Compared with the working system, the travel drive system not only needs to transmit more power, but also requires higher efficiency and longer life of the device. It also hopes to change the output shaft rotation direction and reverse transmission power in variable speed regulation, differential speed. Other aspects have good capabilities. Therefore, what kind of transmission method is adopted, how to better meet the needs of various construction machinery travel drives has always been a problem faced by the construction machinery industry. Especially in recent years, with the rapid development of China's transportation, energy and other infrastructure construction processes, the scale of construction and resource development continues to expand, while the construction machinery is greatly enhanced in the market demand, but also facing more harsh operating conditions. The challenges brought about by more complex conditions have further promoted the in-depth study of its travel drive system.
Here, we try to discuss the development and rules of hydraulic drive technology in the construction drive system of engineering machinery from the perspective of technical composition and performance characteristics.
2. Transmission method based on single technology
The construction machinery travel system initially used mechanical transmission and hydraulic mechanical transmission (except for full hydraulic excavators). Nowadays, the transmission mode of hydraulic and electric drive also appears in the driving drive device of engineering machinery, which fully demonstrates that the development of science and technology has greatly promoted this field.
2.1 Mechanical transmission
The purely mechanically-driven engine has a low average load factor, so generally only a step-variable shift can be performed and the layout is limited. However, due to its advantages in high steady-state transmission efficiency and low manufacturing cost, the general-purpose passenger car with a small speed regulation range and the agricultural tractor with strict economic requirements and constant working speed still occupy the dominant position.
2.2 Hydraulic transmission
The hydraulic transmission torque converter replaces the clutch in the mechanical transmission and has the stepless stepless speed regulation capability. Its outstanding advantage is that it has an output torque-speed characteristic close to the hyperbola, and the rear-mounted power shifting mechanical transmission can automatically match the load and prevent the power transmission from being overloaded. The torque converter has a large power density and low load stress, and the mass production cost is not high. It is widely used in large and medium-sized earthmoving machinery, lifting and transportation machinery, and high-speed vehicles such as automobiles and tanks. However, its characteristic matching and layout are limited, the torque range is small, and the dynamic braking capability is poor, which is not suitable for occasions requiring stable speed.
2.3 Hydraulic drive
Compared with mechanical transmission. The hydraulic drive makes it easier to control its motion parameters (flow) and power parameters (pressure), while the hydraulic drive has good low-speed load characteristics compared to hydraulic drives. Because of its high transmission efficiency, it can perform constant power output control, sufficient power utilization, simple system structure, stepless speed regulation of output speed, positive and negative operation, high speed rigidity, easy operation, etc. It has been widely used in machinery. Almost all construction machinery and equipment can see the trace of hydraulic technology, many of which have become the main transmission and control methods. The ultimate load regulation closed loop, the constant pressure of engine speed control, and the variable power system for constant power combination adjustment provide a broad development prospect for the application of hydraulic transmission to engineering machinery.
Compared with pure mechanical and hydraulic transmissions, the main advantages of hydraulic transmission are the convenience of adjustment and the flexibility of layout. The engine, drive wheel, working mechanism and other components can be selected according to the shape and working conditions of the construction machinery. They are arranged in reasonable parts, the engine works at any dispatching speed, the transmission system can exert a large traction force, and the transmission system can maintain high efficiency in a wide range of output speed, and can be easily obtained. A variety of optimized power transmission characteristics to suit the load conditions of various jobs. The traveling hydraulic drive with closed oil circuit used in the traveling machine with high speed can steplessly adjust the speed, make the vehicle start gently, change speed quickly and change the driving direction without impact. This performance is invaluable for vehicles that require frequent starting and shifting during frequent shifts and frequent shuttles. However, compared with the open circuit, the design, installation, commissioning and maintenance of the closed circuit have higher difficulty and technical requirements.
With the combination of electronic technology and hydraulic technology, various adjustments and controls of the hydraulic system can be easily realized. The introduction of computer control and the application of various sensing elements have greatly expanded the working range of hydraulic components. Through the sensor to monitor various state parameters of the engineering vehicle, the computer operation output control target command, so that the vehicle can be automatically controlled within the entire working range, and the fuel economy, power and work productivity of the machine reach the optimal value. Therefore, the use of hydraulic transmission can make engineering machinery easy to achieve intelligent, energy-saving and environmental protection, which has become the development trend of current and future engineering machinery.
2.4 Electric drive
The electric drive is driven by the internal combustion engine to generate electric energy to drive the motor to drive the moving part of the vehicle. The electric motor adjusts the speed and steering of the motor shaft through the electronic adjustment system. It has a wide range of speeds, input components (generators) and output components (motors). And the control device can be installed separately. Electric power transmission was first used in the field of diesel electric boats and diesel locomotives, and later extended to large-tonnage mining trucks and some large-scale construction machinery. In recent years, there have been small and medium-sized lifting and transportation such as forklifts and tractors for diesel electric power transmission. vehicle. However, for some reasons, such as technology and economy, power electric components suitable for mobile machinery are far less popular than those used for fixed equipment. Electric power transmission is only a "future technology" for most mobile machinery.
3. Developing composite drive technology
It can be seen from the previous analysis that the single-technology-based transmission method applied to the construction machinery travel drive system is simple in construction and reliable in transmission, and is suitable for certain specific occasions and fields. In most practical applications, these transmission technologies are often not isolated, and there is mutual penetration and integration between them. For example, hydraulic, hydraulic and electric transmissions contain more or less machinery. In the transmission section, electrical and hydraulic control systems are also provided in the new mechanical and hydraulic transmissions. In other words, using the targeted composite integration method, we can give full play to the advantages of each transmission mode, and foster strengths and avoid weaknesses, so as to obtain the best comprehensive benefits. It is worth noting that hydraulic transmissions with both adjustment and layout flexibility and high power density play an important role.
3.1 Combination of hydraulic and mechanical and hydraulic transmission
(1) Series mode
The series connection is the simplest and common compounding method. It is a high-efficiency zone where a mechanical transmission is arranged between the output end of the hydraulic motor or the hydraulic transmission and the transaxle to expand the speed regulation, and the stepless stepless shifting is realized. It has been widely used in loaders, combine harvesters and certain special vehicles. The development of the power shifting planetary transmission that can change the transmission ratio between the traveling forces is directly installed in the driving wheel, and the wheel-side hydraulic driving of the large speed ratio is realized, thereby eliminating the driving axle and facilitating layout.
(2) Parallel mode
It is commonly referred to as "hydraulic mechanical power split transmission", which can be understood as a transmission system that transmits power flow in parallel with hydraulic and mechanical devices, that is, using a multi-degree of freedom planetary differential to output the engine. The power is divided into two "power flows" of hydraulic and mechanical. With the controllability of the hydraulic power flow, the two power flows can be steplessly adjusted to the total output speed when recombining. In this way, the advantages of both the stepless speed regulation performance of the hydraulic transmission and the steady state efficiency of the mechanical transmission are combined to obtain a shifting speed with both infinitely variable speed performance and high efficiency and wide high efficiency zone. Device.
According to its structure, the composite transmission can be divided into two categories: the first type is an external split type that utilizes the planetary gear differential to split, and the common split transmission mechanism can be divided into an input split type and an output split type. The basic form; the second type is an internal split type that utilizes a differential displacement between the hydraulic pump or the motor rotor and the outer casing.
This composite hydraulic transmission has been developed by Komatsu Corporation of Japan and has been applied to construction machinery such as loaders and bulldozers. The agricultural tractors produced by the Fendt tractors in Germany equipped with the Vario-type continuously variable transmissions sold more than 30,000 units in 2003.
It can be seen that this new type of transmission has increasingly become a strong competitor for large and medium power hydraulic transmission and power shift transmission.
(3) Time-sharing mode
For the special vehicles with different speeds in the working speed and the non-working state, the traditional mechanical transmission is used for high-speed driving, and the additional hydraulic transmission device is used for low-speed operation, which can well meet the contradictory requirements of these two working conditions. Mechanical-hydraulic time-divisional driving has become commonplace in such vehicles, and this technology has also been applied to vehicles and implements that require "crawling speed" such as aircraft de-icing vehicles and field transplanters.
(4) Division method
The "wheel-side hydraulic drive" that mounts the hydraulic motor directly in the wheel is an auxiliary hydraulic drive that can solve the engineering machinery needs to improve the traction performance, but can not use the all-wheel drive mode, it is difficult to arrange the traditional mechanical transmission device. problem. The stepless speed regulation of the hydraulic transmission enables the coordinated synchronization between the drive wheels that are driven in different ways. In a sense, it can also be regarded as a power split transmission: the power of the power machine is distributed to several sets of drive wheels. After ground coupling, traction is generated to propel the vehicle. Currently, many construction machinery manufacturers use this technology for construction machinery with partial self-propelled drive capabilities, such as self-propelled graders and scrapers.
3.2 Combination of hydraulic and electric drive
Due to the development of modern technology, electronic technology has great advantages in signal processing capability and speed, and hydraulic and electric drive have their own advantages in the characteristics of their respective power components. Therefore, in addition to the now widely used "electronic nerve + hydraulic muscle" mode, there are many successful examples of the composite transmission of power flow, such as: variable frequency or DC speed motor and high efficiency, low pulsation A variable flow hydraulic oil source composed of a quantitative hydraulic pump, an electro-hydraulic actuator unit composed of an integrated electric pump-hydraulic cylinder or a low-speed high-torque hydraulic motor, and a drive system of a hybrid industrial vehicle.
3.3 Secondary adjustment hydrostatic transmission system
The secondary adjustment hydrostatic transmission technology realizes the mutual conversion between hydraulic energy and mechanical energy by adjusting the hydraulic components. In general, its implementation is based on a pressure-coupled system that uses a constant pressure coupling between the primary component (pump) and the secondary component (motor), relying on real-time adjustment of the motor displacement to balance the load torque. At present, the starting point of research on secondary regulation hydrostatic transmission technology is to recover energy and reuse energy in the transmission process, to rationally configure the overall structure of hydrostatic transmission from a macroscopic point of view and to improve the hydrostatic transmission system. Control characteristics.
In order to enable hydraulic motors and reciprocating hydraulic cylinders that do not have bidirectional stepless variable capacity to operate in the constant voltage network of the secondary regulation system, a "hydraulic transformer" using secondary regulation technology has emerged, which is similar to a power transformer. Used to match the user's different requirements for system pressure and flow to achieve power matching of the hydraulic system.
Compared with the traditional hydrostatic transmission system, the secondary adjustment hydrostatic transmission system has the advantages of easier control, working in four quadrants, recovering energy without changing the energy form, storing energy, and using hydraulic storage. The acceleration of the energy can greatly increase the acceleration power, and there is no pressure peak in the system. Since the primary component and the secondary component are separately installed, the oil source can be supplied to a plurality of hydraulic power components through one pumping station, thereby reducing the cooling cost and the manufacturing cost of the device. Reduced, system efficiency.
Compared with the electric drive, the secondary control hydrostatic drive has the advantages of fast closed-loop control, high power density, light weight and small installation space.
Due to the many advantages of the secondary regulator hydrostatic transmission system, it is widely used in many fields. It has been successfully applied in the fields of shipbuilding industry, steel industry, large test bench, vehicle transmission and so on. Mercedes-Benz has applied secondary regulation technology to driving drives in unmanned transport systems.
4 Conclusion
Since the 1990s, construction machinery has entered a new period of development, and the wide application of new technologies has led to the emergence of new structures and new products. With the penetration of microelectronics technology into engineering machinery, engineering machinery is increasingly moving toward intelligent and mechatronics, and the requirements for construction machinery travel drive devices are becoming more and more demanding. In recent years, the rapid development of hydraulic technology and the improvement of hydraulic components have made the application of hydraulic transmission in the engineering machinery transmission system leaps and bounds, and the advantages of hydraulic transmission have become increasingly prominent. It is believed that with the close integration of hydraulic technology and microelectronics technology, computer control technology and sensing technology, hydraulic transmission technology will play an increasingly important role in the development of engineering machinery travel drive system.
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