Power device adaptive to various hydraulic systems, engineering machinery and test equipment

Abstract

The invention discloses a power device adaptive to a multi-type hydraulic system, engineering machinery and test equipment, and the power device adaptive to the multi-type hydraulic system comprises a working pump; the load-sensitive valve and the electric proportional displacement regulating valve are arranged in a displacement regulating control oil path of the working pump and are used for regulating the displacement of the working pump; and the mode switching valve is arranged in a load feedback oil path LS of the working pump and is used for switching the working pump to work in a load sensitive control mode or an electric proportional control mode. The requirements of various operation scenes for the hydraulic system can be met, and the operation cost of production enterprises and users is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of engineering machinery, and in particular relates to a power device, engineering machinery and testing equipment adapted to multiple types of hydraulic systems. Background Art

[0002] As an operating machine, a crane is essentially a profit-making tool for users. Operating costs have a decisive impact on profitability. Operating costs are mainly composed of fuel costs, maintenance costs, etc. Traditional cranes mostly use diesel engines as power sources. Due to the efficiency limitations of traditional fuel engines, fuel utilization is low. The typical operating conditions of cranes (mostly long-term construction at fixed sites, and long construction time at the same site) provide the possibility for cranes to use construction site power. Existing plug-in products are mostly developed based on models, and the electric power system is integrated with the whole machine, which cannot realize the application of a single power unit to drive multiple models.

[0003] Existing power units or power stations are matched according to the type of hydraulic system. Taking the commonly used hydraulic system of cranes as an example, there are three main types: quantitative pump throttling speed control system, load-sensitive pump hydraulic control throttling speed control system, and electric proportional pump + electric proportional valve pump control system. Many customers have cranes of different tonnages and need to match different power units according to the type of hydraulic system, which will greatly increase the customer's operating costs. Similarly, when crane manufacturers conduct on-board operation performance tests and debug the upper products of different models, they modify the chassis oil supply system to achieve multi-purpose use of a universal chassis. However, the modification is difficult and the modification cycle is long, and repeated modifications bring system reliability risks. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the present invention provides a power device, engineering machinery and testing equipment that are adaptable to multiple types of hydraulic systems, which can be compatible with the requirements of hydraulic systems in various operating scenarios and reduce the operating costs of manufacturers and users.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: In a first aspect, a power device adapted to multiple types of hydraulic systems is provided, including: a working pump; a load-sensitive valve and an electric proportional displacement regulating valve arranged in a displacement regulating control oil circuit of the working pump for regulating the displacement of the working pump; and a mode switching valve arranged in a load feedback oil circuit LS of the working pump for switching the working pump to operate in a load-sensitive control mode or an electric proportional control mode.

[0006] Furthermore, it also includes: a pressure cut-off valve arranged in the outlet circuit of the working pump for adjusting the maximum pressure of the system; and a power limiting valve arranged in the outlet circuit of the working pump for adjusting the maximum power of the system.

[0007] Further, the inlet of the mode switching valve is connected to the outlet of the working pump, outlet 1 of the mode switching valve is connected to control end 1 of the load sensitive valve, control end 2 of the load sensitive valve is connected to the load feedback oil circuit LS, and outlet 2 of the mode switching valve is connected to the inlet of the electric proportional displacement control valve; the outlet of the electric proportional displacement control valve is connected to inlet 2 of the power limiting valve, the outlet of the power limiting valve is connected to inlet 2 of the pressure cut-off valve, and the outlet of the pressure cut-off valve is connected to inlet 2 of the load sensitive valve; the outlet of the load sensitive valve is connected to one of the control ends of the working pump; inlet 1 of the load sensitive valve, inlet 1 of the pressure cut-off valve and inlet 1 of the power limiting valve are respectively connected to the outlet of the working pump.

[0008] Furthermore, when matching the load-sensitive pump system model, the mode switching valve shall not be energized, the electric proportional displacement control valve shall not be energized, the load feedback oil circuit LS acts on the control terminal 2 of the load-sensitive valve, and the working pump is used as a load-sensitive pump at this time; by adjusting the setting value of the power limiting valve to match different motor power requirements and the use restrictions of the distribution cabinet under plug-in operating conditions.

[0009] Furthermore, when matching the electronically controlled pump system model, the mode switching valve is in the energized state. At this time, the outlet pressure of the working pump enters the electric proportional displacement control valve through the mode switching valve. Since there is no load feedback oil circuit LS, the load sensing function of the load sensing valve fails. At this time, as soon as the control end of the electric proportional displacement control valve receives the PWM signal, the variable pump realizes the composite control of electric proportional displacement, pressure cut-off and constant power.

[0010] Furthermore, it also includes an auxiliary pump, which provides pilot pressure for the electronically controlled pump system through a parallel pressure reducing valve.

[0011] Further, the inlet 1 of the mode switching valve is connected to the outlet of the working pump, the inlet 2 of the mode switching valve is connected to the load feedback oil circuit LS, and the outlet of the mode switching valve is connected to the control end 2 of the load sensitive valve; the control end 1 of the load sensitive valve, the inlet 1 of the load sensitive valve, the control end 1 of the pressure cut-off valve, the inlet 1 of the pressure cut-off valve, the inlet 1 of the power limiting valve, and the inlet of the electric proportional displacement regulating valve are respectively connected to the outlet of the working pump; the outlet of the electric proportional displacement regulating valve is connected to the inlet 2 of the power limiting valve, the outlet of the power limiting valve is connected to the inlet 2 of the pressure cut-off valve, and the outlet of the pressure cut-off valve is connected to the inlet 2 of the load sensitive valve; the outlet of the load sensitive valve is connected to one of the control ends of the working pump; when the mode switching valve is not energized, the load feedback oil circuit LS enters the control end 2 of the load sensitive valve through the mode switching valve, and the outlet oil circuit of the working pump enters the control end 1 of the load sensitive valve, and the working pump is used as a load sensitive pump at this time; when the mode switching valve is energized, the outlet pressure of the working pump is introduced into both sides of the load sensitive valve, and at this time, under the action of the spring force, the load sensitive valve is always in the right position, and the load sensitive effect is shielded, and the working pump is used as an electric proportional pump.

[0012] Further, the inlet of the mode switching valve is connected to the outlet of the working pump, the control end 1 of the mode switching valve is connected to the load feedback oil circuit LS, the outlet 1 of the mode switching valve is connected to the control end 1 of the load sensitive valve, the outlet 2 of the mode switching valve is connected to the inlet of the electric proportional displacement control valve, the outlet of the electric proportional displacement control valve is connected to the inlet 2 of the power limiting valve, the outlet of the power limiting valve is connected to the inlet 2 of the pressure cut-off valve, the outlet of the pressure cut-off valve is connected to the inlet 2 of the load sensitive valve, and the outlet of the load sensitive valve is connected to one of the control ends of the working pump; the control end 2 of the load sensitive valve is connected to the load feedback oil circuit LS; the inlet 1 of the load sensitive valve, the control end of the pressure cut-off valve, the inlet 1 of the pressure cut-off valve, and the inlet 1 of the power limiting valve are respectively connected to the outlet of the working pump; when matching the load sensitive pump hydraulic system, the load feedback oil circuit LS is also used for the switching of the load sensitive valve and the mode switching valve, and the spring pressure of the mode switching valve is less than the pressure of the load feedback oil circuit LS.

[0013] In a second aspect, there is provided an engineering machine, wherein the engineering machine is equipped with a power device adapted to multiple types of hydraulic systems as described in the first aspect.

[0014] In a third aspect, there is provided an engineering machinery testing equipment, wherein the engineering machinery testing equipment is equipped with the power device adapted to multiple types of hydraulic systems as described in the first aspect.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: the present invention arranges a load-sensitive valve and an electric proportional displacement control valve for adjusting the displacement of the working pump in the displacement adjustment control oil circuit of the working pump; and arranges a mode switching valve for switching the working pump to operate in a load-sensitive control mode or an electric proportional control mode in the load feedback oil circuit LS of the working pump. This can accommodate the requirements of various operating scenarios for the hydraulic system and reduce the operating costs of manufacturers and users. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the principle of a power device adapted to multiple types of hydraulic systems provided in the first embodiment of the present invention; Figure 2 yes Figure 1 Schematic diagram of the working principle when matching the electronically controlled pump system model; Figure 3 It is a schematic diagram of the principle of a power device adapted to multiple types of hydraulic systems provided in the second embodiment of the present invention; Figure 4 It is a schematic diagram of the principle of a power device adapted to multiple types of hydraulic systems provided in the third embodiment of the present invention; In the figure: 1. working pump; 2. rotary pump; 3. auxiliary pump; 4. pressure reducing valve; 10. power unit adapted to various types of hydraulic systems; 11. load sensing valve; 12. pressure cut-off valve; 13. power limiting valve; 14. electric proportional displacement regulating valve; 15. mode switching valve; 20. main engine hydraulic system pump group; 30. center rotary joint. DETAILED DESCRIPTION

[0017] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0018] Embodiment 1 A power device adapted to multiple types of hydraulic systems comprises: a working pump 1; a load-sensitive valve 11 and an electric proportional displacement regulating valve 14 arranged in the displacement regulating control oil circuit of the working pump 1 for regulating the displacement of the working pump 1; a mode switching valve 15 arranged in the load feedback oil circuit LS of the working pump 1 for switching the working pump 1 to operate in a load-sensitive control mode or an electric proportional control mode; a pressure cut-off valve 12 arranged in the outlet circuit of the working pump for adjusting the maximum pressure of the system; and a power limiting valve 13 arranged in the outlet circuit of the working pump for adjusting the maximum power of the system.

[0019] like Figure 1 As shown, in the power device 10 adapted to multiple types of hydraulic systems, the working pump 1 adopts a plunger pump, and the outlet of the working pump 1 is connected to the oil port P1 in the center rotary joint 30. The outlet of the rotary pump 2 is connected to the oil port P2 in the center rotary joint 30. The outlet of the auxiliary pump 3 is connected to the oil port P3 in the center rotary joint 30. The oil ports P1, P2, P3, load feedback oil circuit LS, and return oil port T in the center rotary joint 30 are respectively connected to the main hydraulic system pump group 20.

[0020] The inlet of the mode switching valve 15 is connected to the outlet of the working pump 1, the outlet 1 of the mode switching valve 15 is connected to the control end 1 of the load sensing valve 11, the control end 2 of the load sensing valve 11 is connected to the load feedback oil circuit LS, and the outlet 2 of the mode switching valve 15 is connected to the inlet of the electric proportional displacement regulating valve 14; the outlet of the electric proportional displacement regulating valve 14 is connected to the inlet 2 of the power limiting valve 13, the outlet of the power limiting valve 13 is connected to the inlet 2 of the pressure cut-off valve 12, and the outlet of the pressure cut-off valve 12 is connected to the inlet 2 of the load sensing valve 11; the outlet of the load sensing valve 11 is connected to one of the control ends of the working pump 1; the inlet 1 of the load sensing valve 11, the inlet 1 of the pressure cut-off valve 12 and the inlet 1 of the power limiting valve 13 are respectively connected to the outlet of the working pump 1.

[0021] When matching the load-sensitive pump system model, the control end 1 (Y01) of the mode switching valve 15 must not be powered, the control end 1 (Y02) of the electric proportional displacement control valve 14 must not be powered, and the load feedback oil circuit LS acts on the right side (control end 2) of the load-sensitive valve 11. The working pump 1 is used as a load-sensitive pump at this time. By adjusting the setting value of the power limiting valve 13 to match the power requirements of different motors and the use restrictions of the power distribution cabinet under plug-in working conditions, the phenomenon of stalling during vehicle operation can be avoided. The priority of the three controls is pressure control, constant power control, and flow control.

[0022] When the electronically controlled pump system is matched, the mode switching valve 15 is in the energized state, such as Figure 2 As shown, at this time, the outlet pressure of the working pump 1 enters the electric proportional displacement control valve 14 through the mode switching valve 15. Since the system has no load feedback oil circuit LS, the load sensitive valve 11 is always in the right position at this time, and the load sensitive function of the load sensitive valve 11 fails. At this time, the control terminal 1 (Y02) of the electric proportional displacement control valve 14 receives the PWM signal, and the variable pump realizes the electric proportional displacement, pressure cut-off and constant power compound control. The auxiliary pump 3 provides the pilot pressure for the electric control pump system through the parallel pressure reducing valve 4.

[0023] The present invention realizes the switching between load-sensitive pump control and electric proportional pump control by controlling the mode switching valve 15, realizes the matching of power unit devices with different power / vehicle types with different tonnage by adjusting the power limiting valve 13, and the auxiliary pump 3 provides the pilot pressure for the initial displacement of the electric proportional pump control mode through the parallel pressure reducing valve 4, thereby realizing that the hydraulic system of the power unit cannot be compatible with the requirements of the hydraulic system of various operating scenarios.

[0024] The present invention breaks through the limitation that the existing variable pump system can only realize load-sensitive displacement adjustment / electric proportional valve-controlled displacement adjustment, and greatly improves the adaptability of the system. According to the characteristics of the hydraulic system of different models, the motor power and the power limit conditions of the distribution cabinet, the load-sensitive pump control / electric proportional pump control mode is switched by controlling the threshold value of the mode switching valve 15 and the power limiting valve 13. The control strategy is simple, the system integration is high, and one pump can be used for multiple purposes. By purchasing a power device that is compatible with multiple types of hydraulic systems, customers can match cranes of different hydraulic system types (covering cranes with a lifting capacity of 25t-300t), which greatly reduces the customer's operating costs.

[0025] The present invention can also be used in a test bench pump station / tool ​​test vehicle to implement performance testing of different types of main valves through mode switching, thereby reducing the number of pump station / tool ​​commissioning vehicles and further reducing the operating costs of manufacturing enterprises.

[0026] Embodiment 2 like Figure 3As shown, inlet 1 of the mode switching valve 15 is connected to the outlet of the working pump 1, inlet 2 of the mode switching valve 15 is connected to the load feedback oil circuit LS, and the outlet of the mode switching valve 15 is connected to control end 2 of the load sensing valve 11; control end 1 of the load sensing valve 11, inlet 1 of the load sensing valve 11, control end 1 of the pressure cut-off valve 12, inlet 1 of the pressure cut-off valve 12, inlet 1 of the power limiting valve 13, and inlet of the electric proportional displacement regulating valve 14 are respectively connected to the outlet of the working pump 1; the outlet of the electric proportional displacement regulating valve 14 is connected to inlet 2 of the power limiting valve 13, the outlet of the power limiting valve 13 is connected to inlet 2 of the pressure cut-off valve 12, and the outlet of the pressure cut-off valve 12 is connected to inlet 2 of the load sensing valve 11; the outlet of the load sensing valve 11 is connected to one of the control ends of the working pump 1.

[0027] On the basis of the first embodiment, the present embodiment changes the functional position of the mode switching valve 15. When the mode switching valve 15 is not energized, the load feedback oil circuit LS enters the right side (control end two) of the load sensitive valve 11 through the mode switching valve 15, and the outlet oil circuit of the working pump 1 enters the left side (control end one) of the load sensitive valve 11. At this time, the working pump 1 is used as a load sensitive pump. When the mode switching valve 15 is energized, the outlet pressure (P port pressure) of the working pump 1 is introduced into both sides of the load sensitive valve 11. At this time, under the action of the spring force, the load sensitive valve 11 is always in the right position, and the load sensitive effect is shielded. At this time, the working pump 1 is used as an electric proportional pump.

[0028] Embodiment 3 like Figure 4 As shown, the inlet of the mode switching valve 15 is connected to the outlet of the working pump 1, the control end 1 of the mode switching valve 15 is connected to the load feedback oil circuit LS, the outlet 1 of the mode switching valve 15 is connected to the control end 1 of the load sensitive valve 11, the outlet 2 of the mode switching valve 15 is connected to the inlet of the electric proportional displacement regulating valve 14, the outlet of the electric proportional displacement regulating valve 14 is connected to the inlet 2 of the power limiting valve 13, the outlet of the power limiting valve 13 is connected to the inlet 2 of the pressure cut-off valve 12, the outlet of the pressure cut-off valve 12 is connected to the inlet 2 of the load sensitive valve 11, and the outlet of the load sensitive valve 11 is connected to one of the control ends of the working pump 1; the control end 2 of the load sensitive valve 11 is connected to the load feedback oil circuit LS; the inlet 1 of the load sensitive valve 11, the control end of the pressure cut-off valve 12, the inlet 1 of the pressure cut-off valve 12, and the inlet 1 of the power limiting valve 13 are respectively connected to the outlet of the working pump 1.

[0029] When matched with a load-sensitive pump hydraulic system, the load feedback oil circuit LS can be used for two purposes, replacing the electromagnetic switching valve and playing the role of reversing, such as Figure 4 As shown, the load feedback oil circuit LS is used for switching the load sensing valve 11 and the mode switching valve 15. The cost of this embodiment is reduced, and to ensure the normal operation of the matching load feedback pump system, the spring pressure of the mode switching valve 15 is smaller than the pressure of the load feedback oil circuit LS.

[0030] The present invention only uses the variable mechanism of the A11V series pump as an example to explain the mode switching, but its implementation function is not limited to the A11V series plunger pump, and is not limited to the application in the power unit device, but also includes hydraulic test benches, test fixtures, etc.

[0031] Embodiment 4 Based on Embodiment 1 to Embodiment 3, this embodiment provides an engineering machine, wherein the engineering machine is equipped with a power device adapted to multiple types of hydraulic systems as described in any one of Embodiments 1 to Embodiment 3.

[0032] Embodiment 5 Based on Embodiment 1 to Embodiment 3, this embodiment provides an engineering machinery testing equipment, wherein the engineering machinery testing equipment is configured with a power device adapted to multiple types of hydraulic systems as described in any one of Embodiments 1 to Embodiment 3.

[0033] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A power device adapted to multiple types of hydraulic systems, characterized in that: include: Working pump (1); A load sensing valve (11) and an electric proportional displacement regulating valve (14) arranged in a displacement regulating control oil circuit of the working pump (1) for regulating the displacement of the working pump (1); A mode switching valve (15) is provided in a load feedback oil circuit LS of a working pump (1) and is used to switch the working pump (1) to operate in a load sensitive control mode or an electric proportional control mode.

2. The power device adapted to multiple types of hydraulic systems according to claim 1, characterized in that: Also includes: A pressure cut-off valve (12) provided in the outlet circuit of the working pump and used for adjusting the maximum pressure of the system; A power limiting valve (13) is provided in the outlet circuit of the working pump and is used to adjust the maximum power of the system.

3. The power device adapted to multiple types of hydraulic systems according to claim 2, characterized in that: The inlet of the mode switching valve (15) is connected to the outlet of the working pump (1), the outlet 1 of the mode switching valve (15) is connected to the control end 1 of the load sensing valve (11), the control end 2 of the load sensing valve (11) is connected to the load feedback oil circuit LS, the outlet 2 of the mode switching valve (15) is connected to the inlet of the electric proportional displacement control valve (14); the outlet of the electric proportional displacement control valve (14) is connected to the inlet 2 of the power limiting valve (13), the outlet of the power limiting valve (13) is connected to the inlet 2 of the pressure cut-off valve (12), the outlet of the pressure cut-off valve (12) is connected to the inlet 2 of the load sensing valve (11); the outlet of the load sensing valve (11) is connected to one of the control ends of the working pump (1); An inlet 1 of the load sensing valve (11), an inlet 1 of the pressure cut-off valve (12) and an inlet 1 of the power limiting valve (13) are respectively connected to an outlet of the working pump (1).

4. The power device adapted to multiple types of hydraulic systems according to claim 3, characterized in that: When matching a load-sensitive pump system model, the mode switching valve (15) shall not be energized, the electric proportional displacement control valve (14) shall not be energized, and the load feedback oil circuit LS acts on the control terminal 2 of the load-sensitive valve (11). The working pump (1) is then used as a load-sensitive pump. By adjusting the setting value of the power limiting valve (13), the power requirements of different motors and the use restrictions of the distribution cabinet under plug-in operation conditions can be matched.

5. The power device adapted to multiple types of hydraulic systems according to claim 3, characterized in that: When the electric control pump system is matched, the mode switching valve (15) is in the energized state. At this time, the outlet pressure of the working pump (1) enters the electric proportional displacement control valve (14) through the mode switching valve (15). Since there is no load feedback oil circuit LS, the load sensing function of the load sensing valve (11) is invalid. At this time, the control end of the electric proportional displacement control valve (14) receives the PWM signal, and the variable pump realizes the electric proportional displacement, pressure cut-off and constant power compound control.

6. The power device adapted to multiple types of hydraulic systems according to claim 5, characterized in that: It also includes an auxiliary pump (3), wherein the auxiliary pump (3) provides a pilot pressure for the electric control pump system via a parallel pressure reducing valve (4).

7. The power device adapted to multiple types of hydraulic systems according to claim 2, characterized in that: An inlet 1 of the mode switching valve (15) is connected to an outlet of the working pump (1), an inlet 2 of the mode switching valve (15) is connected to a load feedback oil circuit LS, and an outlet of the mode switching valve (15) is connected to a control terminal 2 of a load sensing valve (11); a control terminal 1 of the load sensing valve (11), an inlet 1 of the load sensing valve (11), a control terminal 1 of the pressure cut-off valve (12), an inlet 1 of the pressure cut-off valve (12), an inlet 1 of the power limiting valve (13), and an inlet of the electric proportional displacement regulating valve (14) are respectively connected to the outlet of the working pump (1); an outlet of the electric proportional displacement regulating valve (14) is connected to an inlet 2 of the power limiting valve (13), an outlet of the power limiting valve (13) is connected to an inlet 2 of the pressure cut-off valve (12), and an outlet of the pressure cut-off valve (12) is connected to an inlet 2 of the load sensing valve (11); an outlet of the load sensing valve (11) is connected to one of the control terminals of the working pump (1); When the mode switching valve (15) is de-energized, the load feedback oil circuit LS enters the control terminal 2 of the load sensing valve (11) through the mode switching valve (15), and the outlet oil circuit of the working pump (1) enters the control terminal 1 of the load sensing valve (11). At this time, the working pump (1) is used as a load sensing pump. When the mode switching valve (15) is energized, the outlet pressure of the working pump (1) is introduced to both sides of the load sensing valve (11). At this time, under the action of the spring force, the load sensing valve (11) is always in the right position, and the load sensing effect is shielded. At this time, the working pump (1) is used as an electric proportional pump.

8. The power device adapted to multiple types of hydraulic systems according to claim 2, characterized in that: The inlet of the mode switching valve (15) is connected to the outlet of the working pump (1), the control end 1 of the mode switching valve (15) is connected to the load feedback oil circuit LS, the outlet 1 of the mode switching valve (15) is connected to the control end 1 of the load sensing valve (11), the outlet 2 of the mode switching valve (15) is connected to the inlet of the electric proportional displacement control valve (14), the outlet of the electric proportional displacement control valve (14) is connected to the inlet 2 of the power limiting valve (13), the outlet of the power limiting valve (13) is connected to the inlet 2 of the pressure cut-off valve (12), the outlet of the pressure cut-off valve (12) is connected to the inlet 2 of the load sensing valve (11), and the outlet of the load sensing valve (11) is connected to one of the control ends of the working pump (1); the control end 2 of the load sensing valve (11) is connected to the load feedback oil circuit LS; the inlet 1 of the load sensing valve (11), the control end of the pressure cut-off valve (12), the inlet 1 of the pressure cut-off valve (12), and the inlet 1 of the power limiting valve (13) are respectively connected to the outlet of the working pump (1); When matched with a load sensing pump hydraulic system, the load feedback oil circuit LS is also used for switching of the load sensing valve (11) and the mode switching valve (15), and the spring pressure of the mode switching valve (15) is less than the pressure of the load feedback oil circuit LS.

9. An engineering machine, characterized in that: The engineering machinery is equipped with a power device adapted to multiple types of hydraulic systems as described in any one of claims 1 to 8.

10. An engineering machinery testing equipment, characterized in that: The engineering machinery testing equipment is equipped with a power device adapted to multiple types of hydraulic systems as described in any one of claims 1 to 8.

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