Road roller hydraulic auxiliary drive system, control method and road roller thereof

Abstract

The application discloses a road roller hydraulic auxiliary driving system, a control method and a road roller thereof, relates to the technical field of hydraulic transmission and control, and comprises a hydraulic pump, a first electromagnetic reversing valve and a second electromagnetic reversing valve. The hydraulic pump is sequentially connected with the first electromagnetic reversing valve, a rear wheel motor, the second electromagnetic reversing valve and the first electromagnetic reversing valve through oil paths to form a rear driving loop. The second electromagnetic reversing valve is further connected with the front wheel motor through an oil path to form a circulating loop, so that a double driving loop is formed in combination with the rear driving loop after the second electromagnetic reversing valve changes the working position. The hydraulic pump, the first electromagnetic reversing valve and the second electromagnetic reversing valve are all controlled by a controller. The switching among the rear driving mode, the double driving mode, the forward driving mode and the backward driving mode can be realized. The problem of the front and rear wheel slipping is solved. In the double driving mode, the speed difference between the front wheel and the rear wheel does not need to be judged, the pressure is stabilized by means of an overflow valve, the back-and-forth switching in the existing mode is avoided, and good system stability and driving comfort are achieved.

Description

Technical Field

[0001] This invention relates to the field of hydraulic transmission and control technology, and in particular to hydraulic auxiliary drive systems, control methods, and road rollers. Background Technology

[0002] In single-drum, fully hydraulically driven road rollers, the rear wheels are typically driven, while the front wheels vibrate, meaning it's a single-sided drive. However, single-sided drive has a drawback: on soft, uneven surfaces, the low friction of the steel wheel can easily cause it to slip and fail to rotate, limiting its passability. To address this issue, a fully driven road roller needs to be developed. This can be achieved using a single-pump dual-motor or dual-pump dual-motor system. The former uses a single hydraulic pump to simultaneously drive both the front and rear wheel motors, resulting in a simple control system, but when one wheel slips, the other also loses power. The latter adds another hydraulic pump, making the system more complex and significantly increasing costs.

[0003] Application number CN101392774A discloses a control method and control device for a hydraulic system of a single-pump dual-motor driven engineering vehicle. This method prevents slippage on one side by controlling the hydraulic system to switch between forced flow diversion and / or flow collection states and natural flow diversion and / or flow collection states. However, this solution has the following problems:

[0004] First, the hydraulic system uses two motors in parallel, but it cannot switch between single and dual drives. When the flow of one motor is turned off, the flow of the other motor doubles, and the speed also doubles, affecting the transmission ratio and vehicle speed.

[0005] Secondly, the method of using the speed difference between the two motors to determine whether there is slippage, and then automatically controlling the flow divider valve to switch to forced flow divider mode, has serious control lag. That is, when the speed difference occurs, a serious slippage has already occurred, which inevitably causes the system to switch back and forth between forced flow divider and free flow divider, thus affecting driving comfort.

[0006] Third, adding a flow divider valve before the two sets of motors in the hydraulic system not only increases the flow resistance and power loss of the hydraulic system, but also increases the complexity of the system. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a hydraulic auxiliary drive system, control method and road roller of the same, which can realize the switching of rear drive mode, dual drive mode, forward mode and reverse mode, greatly increasing the application scenarios, while the main structure is still a single pump dual motor structure, reducing the number of hydraulic pumps and saving production costs.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0009] In a first aspect, a hydraulic auxiliary drive system for a road roller includes a hydraulic pump, a first solenoid directional valve, and a second solenoid directional valve. The hydraulic pump is sequentially connected to the first solenoid directional valve, a rear wheel motor, the second solenoid directional valve, and the first solenoid directional valve via an oil circuit to form a rear drive circuit. The second solenoid directional valve also forms a circulation circuit with the front wheel motor via an oil circuit, so that after the second solenoid directional valve changes its working position, it combines with the rear drive circuit to form a dual drive circuit. The hydraulic pump, the first solenoid directional valve, and the second solenoid directional valve are all controlled by a controller.

[0010] As a further implementation, both the first electromagnetic directional valve and the second electromagnetic directional valve are two-position four-way directional valves.

[0011] As a further implementation, when both the first and second electromagnetic directional valves are in the first working position, the road roller is driven forward through the rear drive circuit.

[0012] As a further implementation, when the first electromagnetic directional valve is in the first working position and the second electromagnetic directional valve is in the second working position, the road roller is driven forward through the dual-drive circuit.

[0013] As a further implementation, when the first electromagnetic directional valve is in the second working position and the second electromagnetic directional valve is in the first working position, the road roller is driven to move backward through the rear drive circuit.

[0014] As a further implementation, when both the first and second electromagnetic directional valves are in the second working position, the road roller is driven to retreat through the dual-drive circuit.

[0015] As a further implementation, the oil circuit between the rear wheel motor and the first electromagnetic reversing valve is connected to the oil circuit between the front wheel motor and the second electromagnetic reversing valve through an oil circuit with a first overflow valve.

[0016] The oil circuit between the rear wheel motor and the second solenoid directional valve is connected to the oil circuit between the rear wheel motor and the first solenoid directional valve through an oil circuit with a second overflow valve.

[0017] A third relief valve is also connected in parallel on the circulation loop formed by the second electromagnetic reversing valve and the front wheel motor.

[0018] Secondly, a control method for a hydraulic auxiliary drive system of a road roller, used to control any of the above-described hydraulic auxiliary drive systems, includes the following steps:

[0019] Under normal road conditions, when the controller controls both the first and second solenoid directional valves to be in the first working position, the roller is driven forward through the rear drive circuit. If the road conditions are poor and there is a risk of steel wheel slippage, the controller can actively drive the second solenoid directional valve to the second working position, and the roller is driven forward through the dual drive circuit. The controller drives the first solenoid directional valve to switch between the first and second working positions, so as to realize the forward and reverse movement of the roller.

[0020] As a further implementation, in rear-drive mode, a first relief valve is used to balance the hydraulic difference between the rear-drive circuit and the circulation circuit.

[0021] Thirdly, a road roller employing a hydraulic auxiliary drive system as described in any of the above.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1. This invention can switch between rear-drive mode, dual-drive mode, forward mode and reverse mode, greatly increasing the application scenarios, while the main structure is still a single pump and dual motor structure, reducing the number of hydraulic pumps and saving production costs; and in dual-drive mode, the front wheel motor and the rear wheel motor are connected in series and the speed is synchronized, which solves the problem of front and rear wheel slippage, and there is no need for structures such as flow divider valves, which reduces flow resistance and improves transmission efficiency.

[0024] 2. This invention can switch to dual-mode in advance, eliminating the need to determine the speed difference between the front and rear wheels before taking action, thus solving the control lag problem in the prior art. Furthermore, with the addition of an overflow valve for pressure stabilization, it avoids the back-and-forth switching required in the existing modes, resulting in good system stability and driving comfort.

[0025] 3. Under the premise that the hydraulic pump displacement remains unchanged, the switching of dual drive mode will not affect the motor speed and the overall transmission ratio of the system, thus ensuring the stability of vehicle speed. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0027] Figure 1 This is a schematic diagram of the hydraulic auxiliary drive system for a road roller in an embodiment of the present invention.

[0028] The diagram exaggerates the spacing or dimensions between parts to show their positions; the diagram is for illustrative purposes only.

[0029] Among them: 1. Hydraulic pump, 2. Rear wheel motor, 3. Front wheel motor, 4. First solenoid directional valve, 5. Second solenoid directional valve, 6. First relief valve, 7. Second relief valve, 8. Third relief valve. Detailed Implementation

[0030] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0031] Hydraulic pump: Driven by an engine or other power source, it converts mechanical energy into hydraulic energy and is the power component of a hydraulic system. Its displacement is controllable.

[0032] Hydraulic motor: converts the liquid pressure energy provided by the hydraulic pump into the mechanical energy (speed and torque) of the shaft.

[0033] Relief valve: A pressure control valve that opens when the pressure at one or both ends exceeds a specified value. It serves to stabilize pressure, overflow, unload, and provide safety protection.

[0034] Solenoid directional valve: A valve controlled by electromagnetic induction that changes the direction of liquid flow. The solenoid directional valve involved in this system is a two-position four-way solenoid directional valve, meaning it has two working positions and four ports.

[0035] Displacement: The flow rate of liquid discharged per revolution of a pump or motor. It is an important parameter of motors and pumps and is adjustable.

[0036] Transmission ratio: The speed of the hydraulic motor divided by the speed of the hydraulic pump is a reflection of the transmission efficiency of the hydraulic system.

[0037] Example 1

[0038] In a typical embodiment of the present invention, reference is made to Figure 1 As shown, a hydraulic auxiliary drive system for a road roller adopts a single-pump dual-motor system, including a hydraulic pump 1, a rear wheel motor 2, and a front wheel motor 3. It also includes two solenoid directional valves, namely a first solenoid directional valve 4 and a second solenoid directional valve 5, forming a hydraulic auxiliary drive system. It can form a rear drive circuit to realize the rear drive mode, i.e., the single-sided drive mode; it can also form a dual drive circuit to realize the front wheel auxiliary drive mode, i.e., the dual-sided drive mode.

[0039] In this embodiment, both the first electromagnetic directional valve 4 and the second electromagnetic directional valve 5 are two-position four-way directional valves. The working position change of the electromagnetic directional valve is controlled by the controller. In addition, the controller also controls the displacement of the hydraulic pump 1 to achieve vehicle speed control.

[0040] like Figure 1As shown, in this state, both the first electromagnetic directional valve 4 and the second electromagnetic directional valve 5 are in the first working position. After the hydraulic pump 1 is connected to the first electromagnetic directional valve 4, the rear wheel motor 2, and the second electromagnetic directional valve 5 in sequence through the oil circuit, the oil circuit continues to pass through the first electromagnetic directional valve 4 and return to the hydraulic pump 1 to form the rear drive circuit.

[0041] The second electromagnetic directional valve 5 also forms a circulation loop with the front wheel motor 3 through the oil circuit, so that after the second electromagnetic directional valve 5 changes its working position, it can combine with the rear drive circuit to form a dual drive circuit. The hydraulic pump, the first electromagnetic directional valve, and the second electromagnetic directional valve are all controlled by the controller.

[0042] like Figure 1 As shown, when the first solenoid directional valve 4 and the second solenoid directional valve 5 are in their first operating positions, the first operating position of the first solenoid directional valve 4 has two passages, where the first passage is denoted as d4-d3 and the second passage is denoted as d1-d2. The first operating position of the second solenoid directional valve 5 also has two passages, where the first passage is denoted as e2-e1 and the other passage is e4-e3, but these belong to the circulation loop formed by the second solenoid directional valve 5 and the front wheel motor 3 through the oil circuit.

[0043] The outlet of hydraulic pump 1 is denoted as a2, and the inlet as a1. The two oil ports of the rear wheel motor 2 are denoted as b2 and b1, where b2-b1 indicates that the hydraulic oil drives the rear wheel motor 2 in the forward direction, and b1-b2 indicates that the hydraulic oil drives the rear wheel motor 2 in the reverse direction. Similarly, c1-c2 indicates that the front wheel motor 3 rotates in the forward direction, and c2-c1 indicates that the front wheel motor 3 rotates in the reverse direction.

[0044] When the road roller moves forward in rear-drive mode, passages e4-e3 in the rear-drive circuit do not participate in the operation. The oil circuit connected to outlet a2 of hydraulic pump 1 is connected to the first passage d4-d3 of the first solenoid directional valve 4 and continues to enter the rear wheel motor 2. After passing through b2-b1, it passes through passage e2-e1 of the second solenoid directional valve 5 and returns to the second passage d1-d2 of the first solenoid directional valve 4 through the oil circuit. The hydraulic oil coming out from d2 returns to a1.

[0045] The final hydraulic oil path of the rear drive circuit is: a2-d4-d3-b2-b1-e2-e1-d1-d2-a1. This hydraulic oil path process involves hydraulic pump 1 controlling the hydraulic oil to drive the rear wheel motor 2 to rotate forward, ultimately propelling the road roller forward.

[0046] When the road roller reverses in rear-drive mode, the rear wheel motor 2 needs to reverse. At this time, the controller controls the first solenoid directional valve 4 to change from the first working position to the second working position. Figure 1 The valve core in the first solenoid directional valve 4 needs to move to the left. The two passages of the second working position of the first solenoid directional valve 4 and the second solenoid directional valve 5 are in a cross state and are independent of each other.

[0047] The final hydraulic oil path of the rear drive circuit is: a2-d4-d1-e1-e2-b1-b2-d3-d2-a1. This hydraulic oil path process involves the hydraulic pump 1 controlling the hydraulic oil to drive the rear wheel motor 2 in reverse, ultimately causing the road roller to reverse.

[0048] It is understandable that the above describes the forward and backward processes achieved through the rear-drive circuit in the rear-drive mode of the road roller. The rear-drive mode is suitable for road rollers to operate under good road conditions, improving economic efficiency. In the rear-drive mode, no hydraulic oil passes through the circuits e4-e3-c1-c2, and the front wheel speed adapts to the rear wheel speed.

[0049] Therefore, when both the first solenoid directional valve 4 and the second solenoid directional valve 5 are in the first working position, the roller is driven forward through the rear drive circuit. When the first solenoid directional valve 4 is in the second working position and the second solenoid directional valve 5 is in the first working position, the roller is driven backward through the rear drive circuit.

[0050] When the first solenoid directional valve 4 is in the first working position and the second solenoid directional valve 5 is in the second working position, the road roller is driven forward through the dual-drive circuit. When both the first solenoid directional valve 4 and the second solenoid directional valve 5 are in the second working position, the road roller is driven backward through the dual-drive circuit. When the dual-drive circuit is working, it means that the front wheel motor 3 and the rear wheel motor 2 are working together.

[0051] In front-wheel auxiliary drive mode, also known as dual-wheel drive mode, both drive circuits are engaged. This mode is suitable for situations where the road roller is operating on poor road conditions with a risk of steel wheel slippage. The driver can manually activate the controller to change the working position of the second solenoid directional valve 5, thus achieving dual-wheel drive mode and preventing slippage risk in advance.

[0052] like Figure 1 As shown, when the dual-drive circuit is in operation, as the roller advances, the controller controls the valve core in the second solenoid directional valve 5 to move to the left, thus changing the second solenoid directional valve 5 from the first working position to the second working position. The hydraulic oil path is: a2-d4-d3-b2-b1-e2-e3-c1-c2-e4-e1-d1-d2-a1.

[0053] The system connects the rear wheel motor 2 and the front wheel motor 3 in series. The hydraulic pump drives the rear wheel motor 2 and the front wheel motor 3 to rotate simultaneously. The hydraulic oil eventually returns to the hydraulic pump 1, forming a dual-motor series circuit.

[0054] In this mode, because the front wheel motor 3 and the rear wheel motor 2 are connected in series, the hydraulic oil flow rate remains constant, the vehicle speed remains constant, and the rotational speeds of the front wheel motor 3 and the rear wheel motor 2 are synchronized, solving the problem of front and rear wheel slippage. Furthermore, it eliminates the need for structures such as flow dividers, reducing flow resistance and improving transmission efficiency. In dual-drive mode, there is no need to determine the speed difference between the front and rear wheels, solving the control lag problem present in existing technologies. With the addition of an overflow valve for pressure stabilization, it avoids the back-and-forth switching required in existing modes, resulting in excellent system stability and driving comfort.

[0055] In dual-drive mode, when the roller is reversing, based on the dual-drive forward movement, the controller controls the valve core in the first solenoid directional valve 4 to move to the left, thus changing the first solenoid directional valve 4 from the first working position to the second working position. The hydraulic oil path is: a2-d4-d1-e1-e4-c2-c1-e3-e2-b1-b2-d3-d2-a1.

[0056] It is understood that in this embodiment, the hydraulic auxiliary drive system uses a controller to control the first solenoid directional valve 4 to switch between forward and reverse modes of the road roller. This allows the controller to change the hydraulic flow direction of the motor while maintaining the same hydraulic flow direction in the hydraulic pump, thus enabling forward and reverse rotation of the motor. The controller also controls the second solenoid directional valve 5 to switch between rear-drive and dual-drive modes. Vehicle speed is controlled by the controller to adjust the displacement of the hydraulic pump 1.

[0057] This embodiment can switch between rear-drive mode, dual-drive mode, forward mode and reverse mode, which greatly increases the application scenarios, while the main structure is still a single pump and dual motor structure, reducing the number of hydraulic pumps and saving production costs.

[0058] Understandably, with the hydraulic pump displacement remaining unchanged, switching between dual-drive modes will not affect the motor speed and the overall system transmission ratio, thus ensuring vehicle speed stability.

[0059] like Figure 1 As shown, the oil circuit between the rear wheel motor 2 and the first solenoid directional valve 4 is connected to the oil circuit between the front wheel motor 3 and the second solenoid directional valve 5 through an oil circuit with a first relief valve 6; the oil circuit between the rear wheel motor 2 and the second solenoid directional valve 5 is connected to the oil circuit between the rear wheel motor 2 and the first solenoid directional valve 4 through an oil circuit with a second relief valve 7; a third relief valve 8 is also connected in parallel on the circulation loop formed by the second solenoid directional valve 5 and the front wheel motor 3.

[0060] In this embodiment, the first relief valve 6, the second relief valve 7, and the third relief valve 8 are configured to stabilize the pressure and protect the hydraulic system, thereby preventing pressure imbalance between the rear wheel motor circuit and the front wheel motor circuit. The second relief valve 7 is used to balance the rear wheel motor, the third relief valve 8 is used to balance the front wheel motor, and the first relief valve 6 is used to balance the hydraulic pressure difference between the rear drive circuit and the circulation circuit.

[0061] Specifically, the first relief valve 7 and the third relief valve 8 are configured to protect the hydraulic system in rear-wheel drive or dual-wheel drive modes when the rear wheel motor 2 and the front wheel motor 3 experience jamming, thereby stabilizing the pressure and speed of the rear wheel motor 2 and the front wheel motor 3. The first relief valve 6 is configured in rear-wheel drive mode, where the hydraulic systems of the rear wheel motor 2 and the front wheel motor 3 are relatively independent. By adding the first relief valve 6 between the two systems, excessive pressure difference between the two systems can prevent system imbalance, which could lead to excessively high or low pressure in one system.

[0062] In this embodiment, the first relief valve 6, the second relief valve 7, and the third relief valve 8 are all mechanical relief valves. They are not controlled by the controller and automatically open when the pressure difference is too large to stabilize and protect the hydraulic system.

[0063] It is understood that the hydraulic auxiliary drive system of this implementation is derived from road rollers, but it is not limited to road rollers; it is also applicable to all fully hydraulic mobile construction machinery.

[0064] Example 2

[0065] A control method for a hydraulic auxiliary drive system of a road roller, used to control the hydraulic auxiliary drive system of Embodiment 1, includes the following steps:

[0066] Under normal road conditions, when both the first solenoid directional valve 4 and the second solenoid directional valve 5 are in their first working positions, the roller is driven forward via the rear drive circuit. If the road conditions are poor and there is a risk of steel wheel slippage, the driver can initiate the operation by having the controller move the second solenoid directional valve 5 to its second working position, driving the roller forward via the dual drive circuit. The controller also drives the first solenoid directional valve 4 to switch between the first and second working positions, enabling the roller to move forward and backward. The controller controls the displacement of the hydraulic pump 1 to control the vehicle speed.

[0067] When both the first solenoid directional valve 4 and the second solenoid directional valve 5 are in the first working position, the road roller is driven forward through the rear drive circuit. When the first solenoid directional valve 4 is in the second working position and the second solenoid directional valve 5 is in the first working position, the road roller is driven backward through the rear drive circuit.

[0068] When the first solenoid directional valve 4 is in the first working position and the second solenoid directional valve 5 is in the second working position, the road roller is driven forward through the dual-drive circuit. When both the first solenoid directional valve 4 and the second solenoid directional valve 5 are in the second working position, the road roller is driven backward through the dual-drive circuit.

[0069] It can switch between rear-drive mode, dual-drive mode, forward mode and reverse mode, which greatly increases the application scenarios, while the main structure is still a single pump and dual motor structure, which reduces the number of hydraulic pumps and saves production costs.

[0070] In dual-drive mode, since the front wheel motor 3 and the rear wheel motor 2 are connected in series, the hydraulic oil flow rate and vehicle speed remain constant. The speeds of the front wheel motor 3 and the rear wheel motor 2 are synchronized, solving the problem of front and rear wheel slippage. Furthermore, it eliminates the need for structures such as flow dividers, reducing flow resistance and improving transmission efficiency. In dual-drive mode, there is no need to judge the speed difference between the front and rear wheels. With the aid of an overflow valve for pressure stabilization, the switching between modes in existing systems is avoided, resulting in good system stability and driving comfort. In rear-drive mode, the first overflow valve 6 balances the hydraulic pressure difference between the rear-drive circuit and the circulating circuit. The second overflow valve 7 and the third overflow valve 8 are used to protect the hydraulic system in rear-drive or dual-drive modes when the rear wheel motor 2 and the front wheel motor 3 experience jamming, stabilizing the pressure and speed of the rear wheel motor 2 and the front wheel motor 3.

[0071] Example 3

[0072] A road roller is provided, which is driven by the hydraulic auxiliary drive system in Embodiment 1 and the working process is controlled by the control method in Embodiment 2.

[0073] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A hydraulic auxiliary drive system for a road roller, characterized in that, The system includes a hydraulic pump, a first solenoid directional valve, and a second solenoid directional valve. The hydraulic pump is connected sequentially to the first solenoid directional valve, the rear wheel motor, the second solenoid directional valve, and the first solenoid directional valve via an oil circuit to form a rear drive circuit. The second solenoid directional valve also forms a circulation circuit with the front wheel motor via an oil circuit, so that after the second solenoid directional valve changes its working position, it combines with the rear drive circuit to form a dual drive circuit. The hydraulic pump, the first solenoid directional valve, and the second solenoid directional valve are all controlled by a controller. Both the first and second solenoid directional valves are two-position four-way directional valves. The oil circuit between the rear wheel motor and the first solenoid directional valve is connected to the oil circuit between the front wheel motor and the second solenoid directional valve via an oil circuit with a first relief valve. The oil circuit between the rear wheel motor and the second solenoid directional valve is connected to the oil circuit between the rear wheel motor and the first solenoid directional valve through an oil circuit with a second overflow valve. A third relief valve is also connected in parallel on the circulation loop formed by the second electromagnetic reversing valve and the front wheel motor.

2. The hydraulic auxiliary drive system for a road roller according to claim 1, characterized in that, When both the first and second electromagnetic directional valves are in the first working position, the road roller is driven forward through the rear drive circuit.

3. The hydraulic auxiliary drive system for a road roller according to claim 1, characterized in that, When the first electromagnetic directional valve is in the first working position and the second electromagnetic directional valve is in the second working position, the road roller is driven forward through the dual drive circuit.

4. The hydraulic auxiliary drive system for a road roller according to claim 1, characterized in that, When the first electromagnetic reversing valve is in the second working position and the second electromagnetic reversing valve is in the first working position, the road roller is driven to move backward through the rear drive circuit.

5. The hydraulic auxiliary drive system for a road roller according to claim 1, characterized in that, When both the first and second electromagnetic directional valves are in the second working position, the road roller is driven to retreat through the dual-drive circuit.

6. A control method for a hydraulic auxiliary drive system of a road roller, characterized in that, A method for controlling a hydraulic auxiliary drive system as described in any one of claims 1-5 includes the following steps: Under normal road conditions, when the controller controls both the first and second solenoid directional valves to be in the first working position, the roller is driven forward through the rear drive circuit. If the road conditions are poor and there is a risk of steel wheel slippage, the controller can actively drive the second solenoid directional valve to the second working position, and the roller is driven forward through the dual drive circuit. The controller drives the first solenoid directional valve to switch between the first and second working positions, so as to realize the forward and reverse movement of the roller.

7. The control method for a hydraulic auxiliary drive system of a road roller according to claim 6, characterized in that, In rear-drive mode, the hydraulic pressure difference between the rear-drive circuit and the circulation circuit is balanced by the first relief valve.

8. A road roller, characterized in that, Includes the hydraulic assisted drive system as described in any one of claims 1-7.

Images