CN110281991A - Trolley - Google Patents

Abstract

The invention discloses a trolley, which has an unfolded state and a folded state, and comprises a bottom frame with wheels installed, side frames that are rotatably connected to the bottom frame are arranged on opposite sides of the bottom frame, and a transverse bar is arranged between the two side frames , the transverse bar and the side frames form a fence frame for accommodating children or goods, the transverse bar is a multi-fold bar structure with rotating joints, and each of the two ends of the transverse bar passes through at least two rotational degrees of freedom It is movably connected with the corresponding side frame, and when the trolley is folded, the horizontal bar is folded around the rotating joint, and at the same time, the two side frames are turned inward until the horizontal bar and the side frame lie flat and close to the bottom frame. The wheelbarrow of the present invention can reduce the longitudinal height of the wheelbarrow by folding the fence, and the operation is convenient. And the structure is simple and easy to realize.

Description

trolley

technical field

The invention relates to a trolley, in particular to a multifunctional trolley with small folding volume.

Background technique

Existing trolleys often have a single function and are only used for children to ride or to carry goods. In order to meet a variety of needs, some trolleys can also be used by children in addition to carrying goods, such as shopping carts in supermarkets. For example, CN103434554A discloses a multi-purpose shopping cart, which includes a car body and movable wheels arranged under the car body, a handle is fixedly arranged at the upper end of one side of the car body, and a fixed handle is arranged at the bottom of the other side of the car body. Seats, but shopping carts are often not foldable, and as a home it takes up a lot of space, making it inconvenient to store and carry.

CN207433596U A foldable multifunctional cart, comprising two square frames, two pairs of rotatably connected cross slanting bars between each side of the two square frames, in the same pair of crossing two slanting bars, one of them One root is connected to the square frame by rotation, and the other is slidingly matched with the square frame. When folding, the two square frames move closer together, and the angle between the crossed diagonal bars changes until they are close to coincident. function.

U.S. Patent No. 9,358,445 discloses a trolley that can carry goods and ride on children. It includes a chassis, a seat is provided on the chassis, a reversible backrest is provided on the seat, and a horizontal bar is provided on the back of the backrest. The backrest is in an upright state. The horizontal blocking rod is spliced and locked with the horizontal blocking rods on the adjacent two sides to form a substantially rectangular frame structure. Because each horizontal bar is a split structure, it is easy to pinch hands when forming a frame structure, and there is a potential safety hazard.

Contents of the invention

The invention provides a multifunctional trolley with convenient operation and good safety.

A trolley, which has an unfolded state and a folded state, and includes a chassis with wheels installed, side frames that are rotatably connected to the chassis are arranged on opposite sides of the bottom chassis, and a transverse bar is arranged between the two sides, and the transverse bar and the side frame to form a fence frame for accommodating children or goods, the horizontal bar is a multi-fold bar structure with rotating joints, and the two ends of the transverse bar are movable with the side frame through at least two rotational degrees of freedom connected, when the trolley is folded, the transverse bar is folded around the rotating joint, and at the same time the two side frames are turned inward until the transverse bar and the side frames lie flat and close to the bottom frame.

The rotational degree of freedom refers to the direction in which two objects rotate relative to each other, which is generally related to the direction in which the rotating shaft is set. If the rotating shafts of the two rotating joints are on the same straight line or parallel to each other, it means that the rotational degrees of freedom are the same, otherwise it is regarded as rotating The degrees of freedom are different. If the axes of rotation of two revolute joints are in a vertical relationship, it means that the degrees of freedom of rotation are perpendicular to each other.

To achieve folding, one of the two rotational degrees of freedom is the same as the rotational degree of freedom of the revolute joint, and the other is the same as the flipping degree of freedom of the side frame.

From the perspective of structural simplification, preferably, the transverse blocking rod is a two-fold rod structure, and a rotating joint is provided in the middle.

To minimize bulk, the swivel joints move inwards when the cart is folded.

In the folded state of the trolley, the two sections of the transverse bar are folded in half to maximize the height of the side frame.

In order to avoid automatic retraction of the transverse blocking rod, a locking mechanism is provided at the rotating joint.

The locking mechanism includes an upper joint cover, a lower joint cover and a ratchet between the two. The side walls of the inner chamber of the upper joint cover and the lower joint cover have limit grooves that match the ratchet teeth of the ratchet. The interior of the joint cover is provided with a return spring that abuts against the end face of the ratchet, and the side of the upper joint cover facing away from the lower joint cover is provided with a button that pushes the ratchet to disengage from the upper joint cover when unlocking.

The end of the transverse bar is movably connected with the side frame through a universal joint.

The end of the transverse bar is movably connected to the side frame through a corner connector, and the corner link is rotatably connected to the end of the transverse bar, and its degree of freedom of rotation is the same as that of the rotary joint. The corresponding side frames are rotatably connected, and the degree of freedom of rotation is the same as that of the side frames turning over.

The side frame includes a longitudinal bar and a vertical bar, the top end of the vertical bar is fixedly connected to the longitudinal bar, the bottom end is rotatably connected to the bottom frame, and the end of the longitudinal bar is connected to the end of the transverse bar. Department activity connection.

In order to allow children to ride, the underframe includes an annular frame, a seat is arranged in the annular frame, and a reversible backrest is arranged at the rear of the seat. In the folded state, the backrest lies flat and close to the seat.

A seat is provided at both ends of the annular frame, and an air-avoiding area is arranged between the two seats, and a footrest assembly lower than the seat is installed in the air-avoiding area.

The pedal assembly includes two support frames arranged below the underframe and rotatably connected to the ring frame, and a telescopic foot pedal rod arranged between the two support frames and rotatably connected to the support frames. In the folded state of the trolley, The support frame is turned inward, and the pedal rod is shortened and close to the bottom frame.

The inner side of the support frame has an extension section which is rotatably connected with the pedal rod. When the trolley is unfolded, the foot pedal rod and the extension section are at the same level.

The trolley includes two pedal assemblies arranged side by side, and a connecting rod that is plugged and fitted between two adjacent support frames.

The wheels include a front wheel and a rear wheel, and the front wheel and the rear wheel are installed under the chassis through the front wheel base and the rear wheel base respectively.

The front wheel seat has a connecting shaft that is plugged and fitted with the bottom frame. Two fixing seats are arranged on the back of the bottom frame. The lying state is close to the chassis.

The rear wheel seat is rotatably connected with the chassis, and in the folded state of the trolley, the rear wheel seat is turned inside, and the rear wheel lies close to the back of the chassis, and the rear wheel seat and the chassis are arranged There is a locking mechanism to keep the rear wheels unfolded and/or folded.

The locking mechanism includes:

Locking pins through the rear wheel base;

Two seat boards are arranged on the bottom frame to clamp the rear wheel base and are rotatably connected with the rear wheel base. The edge of the seat board has two ends that cooperate with the locking pins respectively corresponding to the folded state and the unfolded state the locking groove;

A spring that drives the locking pin against the edge of the seat pan.

The locking mechanism also includes:

A driving block that fixes the locking pin and abuts against the spring, and a driving rod arranged vertically to the moving direction of the driving block is arranged on the side of the driving block;

The pressing block that drives the locking pin to withdraw from the locking groove, the side of the pressing block has a waist-shaped hole that is inclined relative to the moving direction of the driving block and slidingly fits with the driving rod.

One end of the bottom frame is provided with a pull rod rotatably connected thereto, and in the folded state of the trolley, the pull rod turns over and approaches the bottom frame.

The transverse bar of the trolley of the present invention is movably connected to the side frame through at least two degrees of freedom. When the transverse bar is folded, the side frame is pulled to turn inward until the two lie flat and close to the bottom frame, thereby reducing the longitudinal height of the trolley. This operation can be completed in one step, and the structure is simple and easy to realize.

Description of drawings

Fig. 1 is a simplified structural schematic diagram of the trolley of the present invention.

Fig. 2 is a structural schematic diagram of the intermediate state of the trolley shown in Fig. 1 .

Fig. 3 is a structural schematic diagram of the folded state of the trolley shown in Fig. 1 .

Fig. 4 is a schematic structural view of the unfolded state of the trolley of the present invention.

Fig. 5 is a structural schematic diagram of the first folded state of the trolley shown in Fig. 4 .

Fig. 6 is a structural schematic diagram of the second folded state of the trolley shown in Fig. 4 .

Fig. 7 is a structural schematic diagram of the third folded state of the trolley shown in Fig. 4 .

Fig. 8 is a structural schematic diagram of the back of the trolley shown in Fig. 4 .

Fig. 9 is a structural schematic diagram of the fourth folded state of the trolley shown in Fig. 4 .

Fig. 10 is a structural schematic diagram of the fifth folded state of the trolley shown in Fig. 4 .

Fig. 11 is a schematic structural view of the sixth folded state of the trolley shown in Fig. 4 .

Fig. 12 is a structural schematic diagram of the transverse bar of the trolley.

Fig. 13 is a schematic diagram of the exploded structure of the transverse barrier shown in Fig. 12 .

Fig. 14 is a simplified structural schematic diagram of the transverse bar.

Fig. 15 is a simplified structural schematic diagram of another transverse barrier.

Fig. 16 is a schematic structural view of the pedal assembly of the trolley.

Fig. 17 is a schematic diagram of the exploded structure of the pedal assembly shown in Fig. 16 .

Fig. 18 is a structural schematic diagram of the pull rod assembly.

FIG. 19 is a schematic diagram of the exploded structure of the tie rod assembly shown in FIG. 18 .

Fig. 20 is a structural schematic diagram of the part where the rear wheel of the trolley is located.

Fig. 21 is a structural schematic diagram of the part where the rear wheel of the trolley is in the folded state.

Fig. 22 is a schematic diagram of the exploded structure of the part where the rear wheel of the trolley is located.

Detailed ways

As shown in Figures 1-6, a trolley has an unfolded state and a folded state, including an underframe 1, a side frame 2, and a transverse bar 3. A rear wheel 4 and a front wheel 5 are installed under the underframe 1. The bottom of the frame 2 is rotatably connected to the bottom frame 1, and two transverse barriers 3 are arranged between the two side frames 2, and the two ends are movably connected to the side frames 2 through at least two degrees of freedom, thereby forming a general structure for accommodating children or goods A rectangular fence.

The underframe 1 includes a substantially rectangular annular frame 10. In order to meet the needs of children riding, two seats 11 are arranged at both ends of the annular frame 10. The annular frame 10 and the seat 11 in this embodiment are split structures. Obviously, The ring frame 10 and the seat 11 can be integrally formed.

The rear portion of the seat 11 is provided with a backrest 7 which is rotatably connected thereto. As shown in FIGS. In the folded state of the handcart, the backrest 7 turns inwards and lies flat on the seat 11, and the top exceeds the seat 11.

An avoidance area 12 is also provided between the two seats 11, and a pedal assembly 8 is provided at the position of the avoidance area 12. The pedal assembly 8 sinks lower than the seat 11, and the foot pedal 82 is between the ring frame 10 and the ground. . Usually, a cloth cover or a net pocket (not shown in the figure) covering the footrest assembly 8 is also provided in the shelter area 12, thereby forming a relatively closed storage space.

In order to simplify the structure, as shown in Figures 4-5, the side frame 2 includes a longitudinal bar 21 and a vertical bar 22, the bottom of the vertical bar 22 is rotatably connected to the ring frame 10, and the top is fixedly connected to the longitudinal bar 21, And the end of longitudinal bar 21 is movably connected with the end of transverse bar 3, and the inboard of side frame 2 is generally also provided with cloth cover equally, when depositing goods, prevents goods from passing through the gap and falling. Of course, the side frame can also adopt a plate structure, which can save the cloth cover, but the cost is relatively high.

In order to achieve folding, as shown in Figures 12 and 13, the transverse bar 3 is a two-fold bar structure, which is composed of two hollow tube bodies 34, joints 33 and swivel joints 30, and the corner connector 32 has a joint with the joint 33. The opening groove 320 matched with the rotating part 330, when assembled, the rotating part 330 is inserted into the opening groove 320, and is used as a rivet or screw connection as a rotating shaft, and a decorative cover 321 for covering the rivet or screw is also provided on the outside of the corner connector 32.

The joint 33 is rotatably connected to the corner connector 32 , and the degree of freedom of rotation of both is the same as that of the swivel joint 30 . The end of the longitudinal bar 21 is also provided with a joint 23 , the joint 23 is rotationally connected with the corner connector 32 through the rotating shaft 24 , and the degree of freedom of rotation of the two is the same as that of the side frame 2 .

As shown in Figure 1-7, when the trolley is folded, the transverse bar 3 is folded in half around the rotating joint 30, and the side frame 2 is turned inward until the transverse bar 30 and the side frame lie flat and close to the bottom frame 1, so that the trolley can be reduced vertical height. Generally, when the swivel joint 30 is folded, it moves inwards, and if it moves outwards, the length of the trolley will be increased.

In another embodiment, the horizontal bar 3 is a three-fold bar structure. When folding, the middle section moves inward, and the two sections at both ends rotate and move closer to each other. If the middle section is short enough, the same folding effect can also be achieved. It can be seen that the horizontal bar can be a multi-stage folding bar structure, as long as it can be folded symmetrically.

In order to prevent the horizontal bar 9 from being folded automatically when the trolley is unfolded, a locking mechanism is provided at the rotating joint 30. The locking mechanism includes an upper joint cover 301, a lower joint cover 302 and a ratchet 303 between them, the upper joint cover 301 and the lower joint cover 301. The side wall of the inner cavity of the joint cover 302 has a limit groove 309 matched with the ratchet 304 of the ratchet, and the inside of the lower joint cover 302 is provided with a return spring 305 abutting against the end face of the ratchet 303. In order to limit the movement of the return spring 305, the bottom The joint cover 302 is provided with a limit post 310 inserted into the return spring 305 .

The side of the upper joint cover 301 facing away from the lower joint cover 302 is provided with a button 306 that pushes the ratchet 303 to disengage from the upper joint cover 301 when unlocking. The back of the button 306 is provided with a number of locking feet 307, and the locking feet 307 pass through the upper joint cover 301 The internal baffle plate 311 can prevent it from breaking away from the upper joint cover 301 . The back of the button 306 is also provided with a prop 308 passing through the baffle 311 , when the button 306 is pressed, the prop 308 can push the ratchet 303 .

In order to facilitate the ratchet 303 to break away from the upper joint cover 301 when folding, the upper end of the ratchet 304 is provided with a slope, and the bottom side of the limit groove of the corresponding upper joint cover 201 is provided with a matching slope (not shown). When 301 rotates relative to the lower joint cover 302 , the two slopes are in contact, and the ratchet 303 can be pushed away from the upper joint cover 301 .

There is a one-way rotation limiting mechanism between the upper joint cover 301 and the lower joint cover 302, and a one-way rotation limiting mechanism is also provided between the joint 33 and the corner connector 32, and the one-way rotation limiting mechanism refers to two There are protrusions on the rotating part. When the rotation is in place, the two protrusions will conflict, and the rotating joint cannot continue to rotate, but it can rotate in the opposite direction.

As shown in Figure 14, the corner connector 32 can be on the same straight line as the transverse bar 3, and of course it can be on the same line as the longitudinal bar 21. Figure 4 is just one of the preferred implementations. At the corner, the volume of the fold can be minimized while the storage space of the fence is maximized.

In another embodiment, as shown in Figure 15, the two ends of the transverse bar 3 are movably connected to the side frame through a universal joint 31, which can also achieve the same inventive effect. The position of the universal joint 31 is preferably set at the corner.

As shown in Figures 16 and 17, the pedal assembly 8 includes a telescopic pedal rod 82 and two symmetrically arranged support frames 81, the support frame 81 is L-shaped, the top end is rotatably connected with the fixed seat 84 on the ring frame 10, and the bottom The end has a horizontal extension section 810, and the horizontal extension section 810 is rotatably connected with the foot bar 81. In the unfolded state of the trolley, the horizontal extension section 810 is at the same height as the foot bar 81.

The pedal rod 82 has a three-section structure, including a fixed section 822 in the middle and movable sections 821 at both ends. One end of the movable section 821 extends into the fixed section 822 to slide and fit with it, and the other end is provided with a joint that is rotatably connected to the horizontal extension section 810 823. Obviously, the pedal rod 82 can also be a two-stage structure or other multi-stage telescopic structures.

In this embodiment, the trolley has two pedal assemblies 8 , each corresponding to a seat 11 , and the two pedal assemblies 8 are connected by a connecting rod 83 that is plugged and fitted with a support frame 81 .

When folding, push the two connecting rods 83, so that the support frame 81 turns inwards, and at the same time, the two movable sections 821 stretch into the fixed section 822, and the pedal rod 82 shortens and approaches the bottom frame 1 at the same time, as shown in Figures 10 and 11, the support The frame 81 is also turned over from the upright state to the flat state.

As shown in Figures 18 and 19, the front portion of the ring frame 10 is provided with a pull rod assembly 6, the pull rod assembly 6 includes a pull rod 61 and a connecting seat 66, the bottom of the pull rod 61 is provided with a rotating seat 62, and the rotating seat 62 is located at the bottom of the connecting seat 66. The two seat plates 660 are connected through a rotating shaft (not shown in the figure), and the rotating shaft can be selected from rivets or screws. In order to have a beautiful appearance, shells 67 are provided on both sides of the connecting seat 66 , which cooperate with the rotating seat 62 to cover the connecting seat 66 inside.

The swivel seat 62 is provided with a waist-shaped hole 620, the bottom of the pull rod 61 is inserted into the swivel seat 62, and its side is also provided with a waist-shaped hole. The locking pin 64 passes through the two waist-shaped holes, and both ends extend to the seat plate 660. The edge of the plate 660 has a plurality of locking grooves 661 that cooperate with the locking pins 64 . By making the locking pin 64 cooperate with different locking grooves 661, the inclination angle of the pull rod 61 can be adjusted, which is convenient to use.

The inside of the pull rod 61 is provided with a driving block 65 for fixing the locking pin 62. The driving block 65 is connected to the unlocking pull button 63 through a pull wire 651. A return spring 68 is worn on the pull wire 651. One end of the return spring 68 is against the driving block to drive the locking pin 64. When it is against the edge of the seat plate 660 and rotated to the position of the locking groove 661, it will be automatically locked. When unlocking is required, the unlocking pull button 63 is pulled, so that the driving block 65 compresses the return spring 68 and moves upward until the locking pin 64 breaks away from the locking groove 661, and the pull bar 61 can resume rotation.

As shown in Figures 20-22, the rear wheel 4 is installed under the underframe 1 through the rear wheel seat 9, and the back side of the underframe 1 is provided with a mounting seat 97 that cooperates with the rear wheel seat 9. The mounting seat 97 includes two clamps. Holding the seat plate 970 of the rear wheel base 9, the seat plate 970 is rotatably connected with the rear wheel base 97 by a rotating shaft. A locking mechanism is arranged between the rear wheel seat 9 and the mounting seat 97 .

The locking mechanism includes a locking pin 94 that runs through the rear wheel seat 9 and a return spring 96 that drives the locking pin 94 against the edge of the seat plate 970. The edge of the seat plate 970 has a locking groove 971 and a locking groove that cooperates with the locking pin 94. Groove 972.

The rear wheel base 9 is provided with a cavity 91 and a cover plate 910 that covers the cavity 91. The locking mechanism also includes a driving block 93 that is arranged in the cavity to fix the locking pin 94. The return spring 96 abuts against the driving block 93, The side of the drive block 93 is provided with a drive rod 95 perpendicular to its moving direction.

The rear wheel base 9 is also provided with a pressing block 92, which has a waist-shaped hole 98 which is inclined relative to the moving direction of the driving block 93, and the driving rod 95 is inserted into the waist-shaped hole 98 for sliding fit. Press and hold the pressing block 92 when unlocking, the waist-shaped hole 98 squeezes the driving rod 95, so that the driving block 93 moves down, compresses the return spring 96, and makes the locking pin 94 withdraw from the locking groove.

When the rear wheel seat 9 rotated relative to the mounting seat 97, due to the force of the return spring 96, the locking pin 94 was always against the edge of the seat plate 970, and when it fell into the locking groove, the locking mechanism locked, and the rear wheel 4 could not turn. There are locking grooves 971 and 972 on the seat plate, corresponding to the folded state and unfolded state of the rear wheel respectively. When the locking pin 94 falls into the locking groove 971, as shown in Figures 9, 10, 20 and 21, the rear wheel The wheels 4 lie flat and close to the chassis 1, and when the locking groove 94 falls into the locking groove 972, the rear wheels 4 stand upright and perpendicular to the chassis 1.

The front wheel 5 is installed under the underframe 1 through the front wheel seat 51, and the corner of the ring frame 10 is provided with a mounting seat 15 that is plugged and matched with the front wheel seat 51. The front wheel seat 51 has a connecting shaft 52 inserted into the mounting seat 15 (dotted line). A crossbar 13 is arranged on the back side of the chassis 1, and two fixing seats 14 are arranged on the crossbar, and the fixing seats 14 have insertion holes for the connecting shaft 52 to be plugged and matched. In the folded state of the trolley, as shown in FIGS. 8 and 9 , the two front wheels 5 are inserted and hung on the fixing seat 14 , and are close to the chassis 1 in a lying state.

The folding method of the front side of the trolley of the present invention is shown in Figure 4-7. In the unfolded state of the trolley, the side frame 2 is erected, the side frame 2 and the horizontal bar 3 form a fence, and the backrest 7 rests on the horizontal bar 3, which can be used by children. , in order to prevent the backrest 7 from turning over naturally, a locking mechanism can be set between the backrest 7 and the transverse bar 3 .

If it is necessary to load goods, as shown in FIG. 5 , the backrest 7 can be turned over and leaned against the seat 11 . If the fence has restrictions on the goods, as shown in Figure 6, the fence can be folded up. When folding, you only need to press the button 306 to unlock the swivel joint 30 and push it to move inward. The horizontal bar 3 revolves around the swivel joint 30 Fold, and drive the side frame 2 to turn inward at the same time, until both are in a flat state, leaning against the bottom frame 1, at this time, the trolley is deformed into a device similar to a flatbed.

If the trolley needs to be put away for storage, then pull the unlock button 63 to unlock the pull rod assembly 6, as shown in FIG.

The folding method of the back of the trolley of the present invention is shown in Figure 8-11, because the front wheel is detachable, when it needs to be folded, it is disassembled from the mounting seat 15, directly inserted and hung on the fixed seat 14, lying flat and close to the bottom frame 1. Press the pressing block 92 to unlock the locking mechanism, allowing the rear wheel 4 to turn over to a flat state and approach the chassis 1 . Finally, the support frame 81 is folded inward, and the pedal rod 82 is shortened to be close to the bottom frame 1 . Overall, the vertical height of the trolley is reduced, which is convenient for handling and storage.

Claims (21)

1. A trolley, which has an unfolded state and a folded state, and includes a chassis with wheels mounted on it. The opposite sides of the chassis are provided with side frames that are rotatably connected to the bottom frame. The barrier bar and the side frames form a fence frame for accommodating children or goods. The degree of freedom is movably connected with the corresponding side frame. When the trolley is folded, the horizontal bar is folded around the rotating joint, and at the same time, the two side frames are turned inward until the horizontal bar and the side frame lie flat and close to the bottom frame. 2. The trolley according to claim 1, wherein one of the two rotational degrees of freedom is the same as the rotational degree of freedom of the swivel joint, and the other is the same as the turning degree of freedom of the side frame. 3. The trolley according to claim 1, characterized in that, the transverse barrier is a two-fold structure, and a rotating joint is arranged in the middle. 4. The trolley of claim 3, wherein the pivot joints move inwardly when the trolley is folded. 5. The trolley according to claim 3 or 4, characterized in that, in the folded state of the trolley, the two sections of the transverse bar are folded in half. 6. The trolley according to claim 3, wherein a locking mechanism is provided at the rotating joint. 7. The trolley according to claim 6, wherein the locking mechanism comprises an upper joint cover, a lower joint cover and a ratchet between the two, and the inner cavity side walls of the upper joint cover and the lower joint cover have A limit groove matched with the ratchet teeth of the ratchet, a return spring that abuts against the end face of the ratchet is provided inside the lower joint cover, and the side of the upper joint cover facing away from the lower joint cover is provided with a push ratchet to disengage when unlocking The upper joint cover simultaneously compresses the button of the return spring. 8. The trolley according to claim 1, wherein the end of the transverse bar is movably connected to the side frame through a universal joint. 9. The trolley according to claim 1, characterized in that, the ends of the transverse bar are movably connected with the side frames through corner connectors, and the corner connectors are rotatably connected with the ends of the transverse bar, which The degree of freedom of rotation is the same as that of the rotary joint, and the degree of freedom of rotation is the same as that of the side frame. 10. The trolley according to claim 1, wherein the side frame comprises a longitudinal bar and a vertical bar, the top end of the vertical bar is fixedly connected to the longitudinal bar, and the bottom end is rotatably connected to the bottom frame , the end of the longitudinal bar is movably connected with the end of the transverse bar. 11. The trolley according to claim 1, wherein the underframe comprises an annular frame, a seat is arranged in the annular frame, and a reversible backrest is provided at the rear of the seat, and in the unfolded state of the trolley, the backrest Leaning on the transverse bar, in the folded state of the trolley, the backrest lies flat and close to the seat. 12. The trolley according to claim 11, wherein a seat is respectively provided at both ends of the annular frame, and an air-avoiding area is arranged between the two seats, and a seat lower than the seat is installed in the air-avoiding area. Pedal components. 13. The trolley according to claim 12, wherein the pedal assembly comprises two support frames arranged below the underframe and connected to the ring frame in rotation, and arranged between the two support frames and connected to the support frame Rotate the connected telescopic foot rod, in the folded state of the trolley, the support frame is turned inward, and the foot rod is shortened and close to the bottom frame. 14. The trolley according to claim 13, wherein the inside of the support frame has an extension section rotatably connected to the pedal rod, and when the trolley is unfolded, the pedal rod and the extension section are at the same level. 15. The trolley according to claim 13, characterized in that, the trolley comprises two pedal assemblies arranged side by side, and a connecting rod is provided between two adjacent support frames to fit them. 16. The trolley according to claim 1, wherein the wheels include front wheels and rear wheels, and the front wheels and rear wheels are installed under the chassis through front wheel seats and rear wheel seats respectively. 17. The trolley according to claim 16, wherein the front wheel seat has a connecting shaft that is plugged and fitted with the bottom frame, and two fixing seats are provided on the back of the bottom frame, and in the folded state of the trolley, the The front wheel is inserted on the fixed seat through the connecting shaft, and is close to the underframe in a flat state. 18. The trolley according to claim 16 or 17, wherein the rear wheel seat is rotatably connected to the chassis, and in the folded state of the trolley, the rear wheel seat turns inward, and the rear wheel lies close to the The back side of the underframe, a locking mechanism for keeping the rear wheels in an unfolded state and/or a folded state is arranged between the rear wheel base and the underframe. 19. The cart of claim 18, wherein the locking mechanism comprises: Locking pins through the rear wheel base; Two seat boards are arranged on the bottom frame to clamp the rear wheel base and are rotatably connected with the rear wheel base. The edge of the seat board has two ends that cooperate with the locking pins respectively corresponding to the folded state and the unfolded state the locking groove; A spring that drives the locking pin against the edge of the seat pan. 20. The cart of claim 19, wherein the locking mechanism further comprises: A driving block that fixes the locking pin and abuts against the spring, and a driving rod arranged vertically to the moving direction of the driving block is arranged on the side of the driving block; The pressing block that drives the locking pin to withdraw from the locking groove, the side of the pressing block has a waist-shaped hole that is inclined relative to the moving direction of the driving block and slidingly fits with the driving rod. 21. The trolley according to claim 1, wherein one end of the bottom frame is provided with a pull rod rotatably connected thereto, and in the folded state of the cart, the pull rod turns over and approaches the bottom frame.