Wheel loader

Abstract

To provide a wheel loader which can shorten a time until switching of a speed stage is completed after the switching is required, regardless of the size of a clutch chamber.SOLUTION: In a wheel loader 1 including a clutch 32C for a first speed corresponding to a first speed that is a speed stage selected when excavation operation is performed, and a first electromagnetic control valve 35 for controlling the clutch 32C for the first speed according to a signal output from a controller 4, the controller 4 outputs, to the first electromagnetic control valve 35, a start signal for starting first clutch switching preparation for bringing a first friction plate 325 and a first clutch plate 326 of the clutch 32C for the first speed into contact with each other when an attitude of a working device 2 is an attitude where a bottom face part 234 of a bucket 23 is grounded horizontally to a grounding surface of a vehicle body.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a wheel loader that performs excavation work using a working device.

Background Art

[0002] Generally, when performing excavation work, a wheel loader obtains the traction force required to push a bucket into an object to be excavated by controlling a clutch mechanism to switch the speed stage from second speed to first speed. Switching the speed stage takes a certain amount of time, so if the start of switching is delayed, the wheel loader may push the bucket into the object to be excavated before the switching is completed. In this case, the wheel loader will push the object to be excavated with a traction force of a magnitude that can be exerted in second speed, and since the traction force is smaller than the resistance force from the object to be excavated, the vehicle body will stop.

[0003] For example, in the wheel loader described in Patent Document 1, switching from second speed to first speed is started in accordance with a first clutch pressure characteristic, and when it is determined that excavation work conditions are satisfied before the switching is completed, the switching is controlled in accordance with a second clutch pressure characteristic that is steeper than the first clutch pressure characteristic.

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0005] However, in the case of large wheel loaders, where the clutch chamber is large and controlling the clutch mechanism itself requires a significant amount of time, even if the technology described in Patent Document 1 is applied and the switching is performed according to steep clutch pressure characteristics, the time required to control the clutch mechanism may prevent the switching from second gear to first gear from being completed before the bucket is pushed into the excavation target.

[0006] Therefore, the object of the present invention is to provide a wheel loader that can shorten the time from when a speed gear change is requested until the change is completed, regardless of the size of the clutch chamber. [Means for solving the problem]

[0007] To achieve the above objective, the present invention provides a wheel loader comprising: a vehicle body provided with a plurality of wheels; a work device having a lift arm rotatably mounted vertically to the vehicle body and a bucket rotatably mounted vertically to the lift arm; a power source mounted on the vehicle body; a transmission that can switch between a plurality of speed stages by controlling a plurality of clutches with a plurality of electromagnetic control valves, and transmits the output torque of the power source to the plurality of wheels by changing it; and a controller that controls each of the plurality of electromagnetic control valves, wherein the plurality of clutches includes a first clutch corresponding to a first speed which is a speed stage selected when performing an excavation operation, and the plurality of electromagnetic control valves include a first electromagnetic control valve that controls the first clutch according to a signal output from the controller, wherein the wheel loader has a posture detection means for detecting the posture of the work device, and the controller outputs a start signal to the first electromagnetic control valve to start preparing for first clutch switching, which brings the first friction plate and the first clutch plate of the first clutch into contact, when the posture of the work device detected by the posture detection means is such that the bottom surface of the bucket is horizontally grounded to the ground surface of the vehicle body. Then, after outputting the start signal to the first electromagnetic control valve, a main switching start signal is output to the first electromagnetic control valve to start the first clutch main switching, which engages the first friction plate and the first clutch plate. It is characterized by doing so. [Effects of the Invention]

[0008] According to the present invention, regardless of the size of the clutch chamber, the time from when a speed gear change is requested until the change is completed can be shortened. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments. [Brief explanation of the drawing]

[0009] [Figure 1] This is an external side view showing one example of the configuration of a wheel loader according to an embodiment of the present invention. [Figure 2A] This is an explanatory diagram illustrating the excavation operation of a wheel loader, showing the bucket being driven into the ground. [Figure 2B] This is an explanatory diagram illustrating the excavation work of a wheel loader, showing the bucket scooping up the load. [Figure 2C] This is an explanatory diagram illustrating the excavation operation of a wheel loader, showing the bucket, loaded with material, being lifted upwards. [Figure 3] This is an explanatory diagram describing the dosing operation of a wheel loader. [Figure 4] This is a system configuration diagram showing one example of a wheel loader drive system. [Figure 5] This graph shows the relationship between vehicle speed and traction force for each speed setting. [Figure 6] This diagram shows an example of some of the internal structure components of a clutch mechanism. [Figure 7] This is a functional block diagram showing the functions of the controller. [Figure 8] This flowchart shows the flow of processing performed by the controller. [Modes for carrying out the invention]

[0010] The configuration of a wheel loader according to an embodiment of the present invention will be described below with reference to Figures 1 to 8. In the following description, "front, back, left, and right" refers to the viewpoint of the operator riding on and operating the wheel loader, unless otherwise specified.

[0011] <Overall Configuration of Wheel Loader 1> First, the overall configuration of the wheel loader 1 will be described with reference to FIG. 1.

[0012] FIG. 1 is an external side view showing one configuration example of the wheel loader 1 according to an embodiment of the present invention.

[0013] The wheel loader 1 is an articulated work vehicle that is steered by the vehicle body bending in the middle near the center thereof. A front frame 1A that constitutes the front portion of the vehicle body and a rear frame 1B that constitutes the rear portion of the vehicle body are rotatably connected in the left-right direction by a center joint 10, and the front frame 1A bends in the left-right direction relative to the rear frame 1B in accordance with a steering operation.

[0014] Four wheels 11 are provided on the vehicle body: two of the wheels 11 serve as front wheels 11A and are provided on both left and right sides of the front frame 1A respectively, and the remaining two wheels 11 serve as rear wheels 11B and are provided on both left and right sides of the rear frame 1B respectively. Note that in FIG. 1, among the four wheels 11, only the left front wheel 11A and the left rear wheel 11B are shown.

[0015] A hydraulically driven working device 2 is attached to the front portion of the front frame 1A. Using this working device 2, the wheel loader 1 performs, for example, cargo handling work of excavating earth, sand, minerals, etc., and loading them onto a loading destination such as a dump truck or a hopper.

[0016] The working device 2 includes: a lift arm 21 having a base end portion attached to the front frame 1A; two lift arm cylinders 22 that drive the lift arm 21; a bucket 23 attached to a distal end portion of the lift arm 21; a bucket cylinder 24 that drives the bucket 23; and a bell crank 25 that is rotatably connected to the lift arm 21 and constitutes a link mechanism between the bucket 23 and the bucket cylinder 24.

[0017] The two lift arm cylinders 22 are arranged side by side in the left-right direction of the vehicle body. In FIG. 1, only the lift arm cylinder 22 arranged on the left side among the two lift arm cylinders 22 is shown by a broken line.

[0018] The lift arm 21 pivots vertically relative to the front frame 1A when hydraulic oil is supplied to each of the two lift arm cylinders 22 to extend and retract each rod 220. More specifically, the lift arm 21 pivots upward relative to the front frame 1A when each rod 220 of the two lift arm cylinders 22 extends, and pivots downward relative to the front frame 1A when each rod 220 retracts.

[0019] Further, a lift arm angle sensor 21A that detects the angle of the lift arm 21 relative to the vehicle body is attached to the lift arm 21. This lift arm angle sensor 21A is one aspect of a posture detection means for detecting the posture of the lift arm 21. The lift arm posture sensor is not necessarily required to be a sensor that detects an angle, and may be, for example, a sensor that detects the operation of the lift arm 21 or a sensor that detects the stroke amount of the lift arm cylinder 22.

[0020] The bucket 23 is a working tool for excavating earth, sand, minerals, etc., and leveling the ground. The bucket 23 includes: an opening 231 through which a load such as earth, sand, or minerals is charged and discharged; a pair of side surface portions 232 that face each other with an interval equal to the width of the opening 231 in the left-right direction (vehicle width direction); a back surface portion 233 that connects the pair of side surface portions 232 on the side facing the opening 231; a bottom surface portion 234 that extends from the back surface portion 233 toward the opening 231 on the ground contact surface side of the vehicle body; and a top surface portion 235 that extends from the back surface portion 233 toward the opening 231 on the side facing the bottom surface portion 234.

[0021] Thus, the bucket 23 is formed in a container shape that allows for loading cargo into the internal space enclosed by a pair of side sections 232, a rear section 233, a bottom section 234, and a top section 235. Note that in Figure 1, only the left-side section 232 of the pair of side sections 232 is shown.

[0022] Bucket 23 rotates vertically relative to the lift arm 21 as hydraulic fluid is supplied to the bucket cylinder 24, causing the rod 240 to extend and retract. More specifically, bucket 23 rotates upward relative to the lift arm 21 (tilt operation) when the rod 240 of the bucket cylinder 24 extends, and rotates downward relative to the lift arm 21 (dump operation) when the rod 240 retracts.

[0023] Furthermore, the wheel loader 1 can replace its bucket 23 with various attachments such as blades and plows, allowing it to perform various tasks such as snow removal in addition to excavation and dosing (soil pushing) using the bucket 23.

[0024] Furthermore, a bucket angle sensor 23A is attached to the bell crank 25 to detect the angle of the bucket 23 relative to the lift arm 21. This bucket angle sensor 23A is one form of attitude detection means for detecting the posture of the bucket 23. Note that the bucket attitude sensor does not necessarily have to be an angle detection sensor; for example, it may be a sensor that detects the operation of the bucket 23 or a sensor that detects the stroke amount of the bucket cylinder 24.

[0025] The rear frame 1B is provided with a driver's cab 12 where the operator sits, a machine room 13 that houses various equipment necessary for driving the wheel loader 1, and a counterweight 14 that maintains balance with the work device 2 to prevent the vehicle body from tilting. In the rear frame 1B, the driver's cab 12 is located at the front, the counterweight 14 is located at the rear, and the machine room 13 is located between the driver's cab 12 and the counterweight 14.

[0026] <Example of work performed by wheel loader 1> Next, as examples of work performed by wheel loader 1, excavation and dosing operations will be explained with reference to Figures 2A-C and 3.

[0027] Figures 2A to 2C are explanatory diagrams illustrating the excavation work of the wheel loader 1. Figure 2A shows the bucket 23 being driven into the ground 100, Figure 2B shows the bucket 23 scooping up the load, and Figure 2C shows the bucket 23, loaded with material, being lifted upwards.

[0028] During the excavation operation, the operator first tilts or dumps the bucket 23 and lowers the lift arm 21. This causes the wheel loader 1 to be in a position where the bottom surface 234 of the bucket 23 is horizontally in contact with the ground surface of the vehicle body.

[0029] Next, the operator moves the vehicle forward at a low speed towards the ground 100 (the object to be excavated), which consists of soil, minerals, etc., and plunges the bucket 23 into the ground 100, as shown in Figure 2A. At this time, the bucket 23 is subjected to a reaction force (resistance force) from the ground 100 due to the impact.

[0030] Next, the operator raises the lift arm 21 while tilting the bucket 23, as shown in Figures 2A and 2B, or raises the lift arm 21 first and then tilts the bucket 23. This allows the wheel loader 1 to scoop up loads such as soil and minerals from the ground 100.

[0031] Next, the operator raises the lift arm 21 further, as shown in Figure 2C. This causes the bucket 23, with the load loaded, to be lifted upwards.

[0032] Thus, the series of operations shown in Figures 2A to C represent the operation of the wheel loader 1 corresponding to the excavation work.

[0033] Figure 3 is an explanatory diagram illustrating the dosing operation of wheel loader 1.

[0034] In dosing operations, as in excavation operations, the operator first tilts or dumps the bucket 23 and lowers the lift arm 21. This brings the wheel loader 1 into a position where the bottom surface 234 of the bucket 23 is horizontally in contact with the ground surface of the vehicle body.

[0035] Next, the operator lowers the lift arm 21 further. This applies a downward force Fd to the bucket 23, pressing it against the ground, causing the bottom surface 234 of the bucket 23 to come into contact with the ground.

[0036] Next, as shown by the white arrows in Figure 3, the operator slowly moves the vehicle forward with the bottom surface 234 of the bucket 23 in contact with the ground surface. This allows the wheel loader 1 to level the ground surface using the bottom surface 234 of the bucket 23.

[0037] Thus, the operation shown in Figure 3 is the operation of the wheel loader 1 corresponding to the dosing operation.

[0038] <Drive system of wheel loader 1> Next, the drive system of the wheel loader 1 will be described with reference to Figures 4 and 5.

[0039] Figure 4 is a system configuration diagram showing one example of the drive system configuration of the wheel loader 1.

[0040] The wheel loader 1 has its movement controlled by a torque converter type drive system, and includes an engine 30 as the power source, a torque converter 31 (hereinafter referred to as "torque converter 31") connected to the output shaft of the engine 30, and a transmission 32 connected to the output shaft of the torque converter 31.

[0041] Each of these components, including the engine 30, torque converter 31, and transmission 32, is controlled according to command signals output from the controller 4.

[0042] The engine 30 is started when the operator moves the ignition switch to the start position. The rotational speed of the engine 30 increases in accordance with the amount the accelerator pedal 51 is pressed. For example, the rotational speed of the engine 30 is proportional to the amount the accelerator pedal 51 is pressed, and increases as the amount the accelerator pedal 51 is pressed increases.

[0043] The torque converter 31 is a fluid clutch consisting of an impeller, turbine, and stator. When the output torque of the engine 30 rotates the input shaft of the torque converter 31, the output shaft of the torque converter 31 rotates via the torque converter oil, which acts as the working fluid, and the output torque of the engine 30 is transmitted to the transmission 32.

[0044] The transmission 32 is mainly composed of a gear mechanism (not shown in the diagram) having multiple speed gears, and is a transmission that changes the output torque of the engine 30 by changing the rotation direction and gear ratio between the input shaft and the output shaft.

[0045] In this embodiment, the transmission 32 has four speed gears. However, the number of speed gears does not necessarily have to be four, and can be set appropriately according to the specifications of the wheel loader 1. The switching between the four speed gears is controlled by the clutch mechanism 320.

[0046] The output torque of the transmission 32 is transmitted to the four wheels 11 via the propeller shaft 15 and axle 16, thereby causing the wheel loader 1 to move. The travel speed of the wheel loader 1 is detected as the rotational speed of the propeller shaft 15 by a speed sensor 15A attached to the propeller shaft 15. In other words, the speed sensor 15A is one embodiment of a vehicle speed detection means for detecting the travel speed of the wheel loader 1.

[0047] The clutch mechanism 320 includes a forward clutch 32A and a reverse clutch 32B for switching between forward and reverse, and a clutch 32C for first gear, a clutch 32D for second gear, a clutch 32E for third gear, and a clutch 32F for fourth gear for switching between four speed stages.

[0048] As mentioned above, the transmission 32 according to this embodiment is designed to be switchable between four speed gears, and therefore the clutch mechanism 320 has six clutches 32A to 32F. In the following description, the forward clutch 32A, reverse clutch 32B, first-speed clutch 32C, second-speed clutch 32D, third-speed clutch 32E, and fourth-speed clutch 32F may be collectively referred to as "clutches 32A to 32F". The more specific structure and operation of the clutch mechanism 320 will be described later.

[0049] The forward and reverse movement of the wheel loader 1 is controlled by the operator operating the forward / reverse selector lever 52. When the forward / reverse selector lever 52 is switched to the forward position, the forward clutch 32A is engaged and the reverse clutch 32B is released. On the other hand, when the forward / reverse selector lever 52 is switched to the reverse position, the forward clutch 32A is released and the reverse clutch 32B is engaged. Also, when the forward / reverse selector lever 52 is switched to the neutral position, both the forward clutch 32A and the reverse clutch 32B are released.

[0050] The forward clutch 32A is controlled by the forward electromagnetic control valve 33, and the reverse clutch 32B is controlled by the reverse electromagnetic control valve 34. When the operator operates the forward / reverse selector lever 52, the forward / reverse selector lever 52 outputs a selector signal to the controller 4. The controller 4 controls the forward electromagnetic control valve 33 and the reverse electromagnetic control valve 34, respectively, based on the input selector signal.

[0051] In this embodiment, the controller 4 automatically switches (selects) the speed gears in the wheel loader 1 based on the wheel loader 1's travel speed and the posture of the work device 2. However, the switching of the four speed gears does not necessarily have to be done solely by the controller 4. For example, the operator may select one of the four speed gears by operating a shift switch 53 (see Figure 4), which acts as a speed gear selection device located in the driver's cab 12 (see Figure 1). In this case, the controller 4 selects one of the four speed gears based on the signal output from the shift switch 53.

[0052] Therefore, the speed gear switching in the wheel loader 1 may be done solely by automatic switching by the controller 4, or it may be done in combination with automatic switching by the controller 4 and manual switching by the shift switch 53.

[0053] When the transmission 32 is switched to first gear, the clutch 32C for first gear is engaged, and the clutches 32D for second gear, 32E for third gear, and 32F for fourth gear are disengaged.

[0054] When the transmission 32 is in second gear, the clutch 32D for second gear is engaged, and the clutches 32C for first gear, 32E for third gear, and 32F for fourth gear are disengaged.

[0055] When the transmission 32 is switched to third gear, the clutch 32E for third gear is engaged, and the clutches 32C for first gear, 32D for second gear, and 32F for fourth gear are disengaged.

[0056] When the transmission 32 is switched to 4th gear, the 4th gear clutch 32F is engaged, and the 1st gear clutch 32C, 2nd gear clutch 32D, and 3rd gear clutch 32E are disengaged.

[0057] The clutch for first gear 32C is controlled by the first electromagnetic control valve 35, the clutch for second gear 32D is controlled by the second electromagnetic control valve 36, the clutch for third gear 32E is controlled by the third electromagnetic control valve 37, and the clutch for fourth gear 32F is controlled by the fourth electromagnetic control valve 38.

[0058] When the controller 4 selects one of the four speed stages, it outputs a control signal to the first to fourth electromagnetic control valves 35 to 38 so that the clutch for the selected speed stage engages and the clutches for the other speed stages disengage.

[0059] Here, Figure 5 is a graph showing the relationship between vehicle speed and traction force for each speed setting.

[0060] First gear is the lowest speed gear of the transmission 32. This first gear is selected when the vehicle's travel speed can be kept to a minimum, but a large towing force is required, such as during excavation or uphill work. Therefore, first gear corresponds to the first gear, which is the speed gear selected when performing excavation operations, and the clutch 32C for first gear corresponds to the first clutch that corresponds to first gear.

[0061] Second gear is set one step higher than first gear, which is the lowest speed gear in transmission 32, and corresponds to second gear, which has less traction than first gear. Second gear is selected when a good balance between vehicle speed and traction is required, for example, during dump approach operations. The clutch 32D for second gear corresponds to the second clutch for second gear.

[0062] Third gear is set one step higher than second gear, and fourth gear is set one step higher than third gear and is the highest speed gear of the transmission 32. These third and fourth gears are selected when, for example, when transporting a load to a distant location, the towing force only needs to be kept to a minimum, while the vehicle's speed should be as high as possible.

[0063] Furthermore, as shown in Figure 4, the wheel loader 1 is equipped with a load handling drive system for driving the work device 2, in addition to the vehicle body's driving drive system.

[0064] The cargo handling drive system comprises a hydraulic pump 61 that supplies hydraulic fluid to each of the two lift arm cylinders 22 and the bucket cylinder 24, a directional control valve unit 62 provided between the hydraulic pump 61 and the two lift arm cylinders 22 and the bucket cylinder 24, and a hydraulic fluid tank 63 for storing the hydraulic fluid.

[0065] The hydraulic pump 61 is driven by the engine 30 and draws in and discharges hydraulic fluid from the hydraulic fluid tank 63. In this embodiment, the hydraulic pump 61 is a variable displacement type hydraulic pump, but it is not limited to this, and a fixed displacement type hydraulic pump may also be used.

[0066] The directional control valve unit 62, although not shown in Figure 4, consists of two hydraulic directional control valves, a first directional control valve and a second directional control valve, which are driven by pilot pressure.

[0067] The first directional control valve is positioned between the hydraulic pump 61 and the two lift arm cylinders 22 and controls the flow (flow rate and direction) of the hydraulic fluid discharged from the hydraulic pump 61 and supplied to the two lift arm cylinders 22. The first directional control valve is controlled based on the operation (specifically, the direction of operation and the amount of operation) of the lift arm operating lever 54 located in the operator's cab 12 (see Figure 1).

[0068] The amount of movement of the lift arm operating lever 54 is detected by a lift arm operating amount sensor 54A, which detects the pilot pressure generated by the operation of the lift arm operating lever 54. This lift arm operating amount sensor 54A is one embodiment of a lift arm operating sensor that detects whether or not the lift arm operating lever 54 is being operated.

[0069] The lift arm operation sensor does not necessarily have to be a sensor that directly detects the amount of operation of the lift arm operation lever 54, such as the lift arm operation amount sensor 54A. For example, it may be a sensor that detects the amount of operation of the lift arm operation lever 54 from the posture of the lift arm 21, such as the lift arm angle sensor 21A mentioned above. In other words, the lift arm angle sensor 21A is also one form of operation detection means that detects whether or not the lift arm operation lever 54 is being operated.

[0070] Furthermore, a pressure sensor 22A is attached to the lift arm cylinder 22 (either of the two is acceptable) to detect the internal pressure (cylinder pressure). The pressure value detected by the pressure sensor 22A is input to the controller 4. This pressure sensor 22A is one embodiment of a force detection means that detects the force acting on the bucket 23 from the outside. This is based on the fact that when an external force acts on the bucket 23, the cylinder pressure of the lift arm cylinder 22 increases, that is, there is a correlation between the cylinder pressure of the lift arm cylinder 22 and the force acting on the bucket 23 from the outside.

[0071] The second directional control valve is positioned between the hydraulic pump 61 and the bucket cylinder 24 and controls the flow (flow rate and direction) of the hydraulic fluid discharged from the hydraulic pump 61 and supplied to the bucket cylinder 24. The second directional control valve is controlled based on the operation (operating direction and amount) of the bucket operating lever 55 located in the operator's cab 12 (see Figure 1).

[0072] The amount of movement of the bucket operating lever 55 is detected by a bucket operating amount sensor 55A, which detects the pilot pressure generated by the operation of the bucket operating lever 55. This bucket operating amount sensor 55A is one embodiment of a bucket operating sensor that detects whether or not the bucket operating lever 55 is being operated.

[0073] Furthermore, the bucket operation sensor, like the lift arm operation sensor, does not necessarily have to be a sensor that directly detects the amount of operation of the bucket operation lever 55, such as the bucket operation amount sensor 55A. For example, it may be a sensor that detects the amount of operation of the bucket operation lever 55 from the posture of the bucket 23, such as the bucket angle sensor 23A mentioned above. In other words, the bucket angle sensor 23A is also one form of operation detection means that detects whether or not the bucket operation lever 55 is being operated.

[0074] The lift arm operating lever 54 and the bucket operating lever 55 are one form of operating means for operating the work device 2, and the lift arm operating sensor and the bucket operating sensor are one form of operation detection means for detecting whether or not the operating means are being operated.

[0075] Furthermore, the operating means for the work device 2 does not necessarily have to be a lever-type device; it may be a dial-type or pedal-type operating device, and there are no particular restrictions on the form of the operating means. Also, in this embodiment, the lift arm operating lever 54 and the bucket operating lever 55 may be composed of two separate levers, or they may be composed of a single lever capable of operating both the lift arm 21 and the bucket 23.

[0076] <Structure and operation of clutch mechanism 320> Next, the specific structure and operation of the clutch mechanism 320 of the transmission 32 will be explained with reference to Figure 6.

[0077] Figure 6 shows an example of a part of the internal structure of the clutch mechanism 320. Note that Figure 6 shows the structure of the 1st gear clutch 32C and the 2nd gear clutch 32D as examples, and the structures of the forward clutch 32A and the reverse clutch 32B, as well as the 3rd gear clutch 32E and the 4th gear clutch 32F, are all the same as the structure of the 1st gear clutch 32C and the 2nd gear clutch 32D, so they are not shown.

[0078] The clutch mechanism 320 includes an input shaft 321 to which rotational torque output from the torque converter 31 is input, six clutches 32A to 32F provided on the outer circumference of the input shaft 321, a clutch housing 322 fixed to the input shaft 321 and housing the six clutches 32A to 32F inside, six gears 323 connected to the outer circumference of the input shaft 321 via bearings 323A, six clutch pistons 324 provided on the outer circumference of the input shaft 321 and driven along the axial direction of the input shaft 321, and six return springs 325 that bias the six clutch pistons 324 on the outer circumference of the input shaft 321.

[0079] The six gears 323, six bearings 323A, six clutch pistons 324, and six return springs 325 are all arranged within the clutch housing 322 to correspond to the six clutches 32A to 32F.

[0080] Each of the six clutches 32A to 32F consists of multiple friction plates 326 fitted to a gear 323 and multiple clutch plates 327 fitted to a clutch housing 322, arranged alternately facing each other along the axial direction of the input shaft 321. In other words, each of the six clutches 32A to 32F is fitted both internally to the gear 323 and externally to the clutch housing 322.

[0081] In this embodiment, as shown in Figure 6, each of the six clutches 32A to 32F has four friction plates 326 and five clutch plates 327, but is not limited to this, and the number of each plate 326, 327 will vary depending on the specifications of the wheel loader 1, that is, the performance required of the transmission 32 mounted on the wheel loader 1.

[0082] Each friction plate 326 rotates with the gear 323 around the input shaft 321, and each clutch plate 327 rotates with the clutch housing 322 around the input shaft 321. Therefore, when the friction plates 326 and clutch plates 327 are separated from each other, multiple friction plates 326 and multiple clutch plates 327 rotate independently and separately.

[0083] This state, in which adjacent friction plates 326 and clutch plates 327 are disengaged and the engagement between multiple friction plates 326 and multiple clutch plates 327 is released, corresponds to the "released state" of each clutch 32A to 32F.

[0084] On the other hand, when the clutch piston 324 is driven by hydraulic pressure against the spring force (biasing force) of the return spring 325 toward the side where each clutch 32A to 32F is located (in the direction of the arrows shown in Figure 6), each friction plate 326 and each clutch plate 327 are pressed in the axial direction of the input shaft 321, and the frictional force generated between each friction plate 326 and each clutch plate 327 fixes them together.

[0085] As a result, multiple friction plates 326 and multiple clutch plates 327 rotate together around the input shaft 321 as the central axis, and the rotational torque input to the input shaft 321 is transmitted to the gear 323 via the multiple friction plates 326 and multiple clutch plates 327. The rotational torque transmitted to the gear 323 is then transmitted to the propeller shaft 15.

[0086] This state, in which each friction plate 326 and each clutch plate 327 are pressed by the clutch piston 324, and multiple friction plates 326 and multiple clutch plates 327 are engaged, corresponds to the "engaged state" of each clutch 32A to 32F.

[0087] Furthermore, when hydraulic pressure is released from the clutch piston 324, the clutch piston 324 returns to its original position due to the spring force of the return spring 325 (driven in the opposite direction to the arrows shown in Figure 6), causing each friction plate 326 and each clutch plate 327 to separate from each other (= clutch release / cutoff), and the rotational torque input to the input shaft 321 is no longer transmitted to the gear 323.

[0088] Here, the drive control of the clutch piston 324 in the forward clutch 32A and the reverse clutch 32B, i.e., the hydraulic control of the clutch piston 324, is performed by the forward electromagnetic control valve 33 and the reverse electromagnetic control valve 34, respectively. Similarly, the drive control of the clutch piston 324 in the first to fourth speed clutches 32C to 32F is performed by the first to fourth electromagnetic control valves 35 to 38, respectively.

[0089] In the wheel loader 1, switching between forward and reverse movement and switching between speed stages is performed by engaging multiple friction plates 326 and multiple clutch plates 327 after going through a preparation stage P1, which is a preparatory processing stage, and a main switching stage P2, which is the main processing stage.

[0090] The switching preparation P1 is sometimes called "initial filling (initial filling process)," in which the clutch piston 324 lightly presses the multiple friction plates 326 and multiple clutch plates 327 in the axial direction of the input shaft 321, thereby bringing the separated friction plates 326 and clutch plates 327 into contact with each other.

[0091] At this switching preparation stage P1, it is sufficient that no gap is formed between adjacent friction plates 326 and clutch plates 327, and the force that the clutch piston 324 applies to the multiple friction plates 326 and multiple clutch plates 327 should be a weak force, just enough to cause each friction plate 326 and each clutch plate 327 to touch.

[0092] This switching P2 engages each friction plate 326 and each clutch plate 327 by having the clutch piston 324 strongly press the multiple friction plates 326 and multiple clutch plates 327, which are in contact with each other, in the axial direction of the input shaft 321.

[0093] In this switching stage P2, the force that the clutch piston 324 applies to the multiple friction plates 326 and the multiple clutch plates 327 needs to be large enough that each friction plate 326 and each clutch plate 327 is fixed to each other by friction.

[0094] For example, when the wheel loader 1 switches the transmission 32's speed gear from 2nd gear to 1st gear in order to perform excavation work, the clutch mechanism 320 performs a preparation P1 (preparation for first clutch switching) for the 1st gear clutch 32C, followed by the main switching P2 (main first clutch switching) of the 1st gear clutch 32C and the release (cutoff) Q of the 2nd gear clutch 32D.

[0095] Thus, switching speeds in the wheel loader 1 requires two processes: preparation for switching P1 and the actual switching P2, which takes a certain amount of time. If these two processes are not performed quickly, especially when attempting excavation work, the bucket 23 may enter the ground 100 before the switch from 2nd gear to 1st gear is completed, potentially causing the vehicle to stop due to the resistance force from the excavated material. Therefore, the wheel loader 1 improves the speed of switching from 2nd gear to 1st gear through control by the controller 4.

[0096] <Controller 4 Configuration> Next, the configuration of controller 4 will be explained with reference to Figure 7.

[0097] Figure 7 is a functional block diagram showing the functions of controller 4.

[0098] Controller 4 is configured with a CPU, RAM, ROM, HDD, input interface, and output interface all connected to each other via a bus. Various operating devices and various sensors, such as a lift arm angle sensor 21A, a bucket angle sensor 23A, a pressure sensor 22A, and a speed sensor 15A, are connected to the input interface, while, for example, a first electromagnetic control valve 35 and a second electromagnetic control valve 36 are connected to the output interface.

[0099] In this hardware configuration, the CPU reads the control program (software) stored on a recording medium such as ROM, HDD, or optical disc, expands it into RAM, and executes the expanded control program. Through this process, the control program and hardware work together to realize the functions of the controller 4.

[0100] In this embodiment, the controller 4 is described as a computer composed of a combination of software and hardware. However, it is not limited to this configuration. For example, an integrated circuit that implements the functions of the control program executed on the wheel loader 1 may be used as an example of another computer configuration.

[0101] As shown in Figure 7, the controller 4 includes a data acquisition unit 41, a posture determination unit 42, an operation intention determination unit 43, a signal output unit 44, an excavation determination unit 45, a time measurement unit 46, an elapsed time determination unit 47, and a storage unit 48.

[0102] The data acquisition unit 41 acquires data on the angle α of the lift arm 21 relative to the vehicle body (front frame 1A) detected by the lift arm angle sensor 21A (hereinafter simply referred to as "lift arm angle α"), the angle β of the bucket 23 relative to the lift arm 21 detected by the bucket angle sensor 23A (hereinafter simply referred to as "bucket angle β"), the pressure P of the lift arm cylinder 22 detected by the pressure sensor 22A (hereinafter simply referred to as "lift arm cylinder pressure P"), and the vehicle's travel speed V detected by the speed sensor 15A (hereinafter simply referred to as "vehicle speed V").

[0103] The posture determination unit 42 determines, based on the lift arm angle α and bucket angle β acquired by the data acquisition unit 41, whether the posture of the work device 2 is such that the bottom surface 234 of the bucket 23 is horizontally in contact with the ground surface of the vehicle body (the state shown in Figures 1, 2A, and 3, respectively).

[0104] Specifically, the attitude determination unit 42 determines whether the lift arm angle α acquired by the data acquisition unit 41 is less than or equal to the lift arm angle threshold αth, and whether the absolute value |β| of the bucket angle β acquired by the data acquisition unit 41 is less than or equal to the bucket angle threshold βth.

[0105] Here, the "lift arm angle threshold αth" is a threshold set based on the lift arm angle when the lift arm 21 is lowered to its lowest position. The "bucket angle threshold βth" is a threshold set based on the bucket angle when the bottom surface 234 of the bucket 23 is horizontally in contact with the ground surface of the vehicle body.

[0106] In this embodiment, the bucket angle β is defined as follows: the reference angle (=0°) is when the bottom surface 234 of the bucket 23 is perfectly horizontal with respect to the ground contact surface of the vehicle body; a positive value is used when the bucket 23 moves in the tilt direction from the reference angle; and a negative value is used when the bucket 23 moves in the dump direction from the reference angle.

[0107] Therefore, since the bucket angle β acquired by the data acquisition unit 41 can be either a positive or negative value, the attitude determination unit 42 takes the absolute value of the bucket angle β acquired by the data acquisition unit 41 and then compares it with the bucket angle threshold βth (β→|β|).

[0108] The operation intention determination unit 43 determines whether or not the lift arm 21 has been lowered after the posture determination unit 42 has determined the posture of the work device 2. Specifically, after the determination by the posture determination unit 42, the operation intention determination unit 43 determines whether or not the lift arm angle α is smaller than the lift arm angle threshold αth after the data acquisition unit 41 has acquired the lift arm angle α. In other words, the operation intention determination unit 43 determines whether the operator intends to perform excavation work or dosing work.

[0109] This is because, even if the posture determination unit 42 determines that the posture of the work device 2 is such that the bottom surface 234 of the bucket 23 is horizontally grounded to the ground surface of the vehicle body, the wheel loader 1 is not necessarily performing excavation work, but may also be performing dosing work. Therefore, this is to clarify which type of work the wheel loader 1 is performing. When the wheel loader 1 is performing dosing work, as mentioned above, the operator further lowers the lift arm 21, so the distinction between excavation work and dosing work is made by whether or not the lift arm 21 is lowered.

[0110] The signal output unit 44 outputs a switching preparation start signal to the first electromagnetic control valve 35 to start preparing to switch the first-speed clutch 32C when the operation intention determination unit 43 determines that the lift arm 21 has not been lowered. In other words, "when the operation intention determination unit 43 determines that the lift arm 21 has not been lowered" means that the operator does not intend to perform dosing work and is presumed to be planning to perform excavation work.

[0111] Furthermore, when the drilling determination unit 45 determines that drilling has started, the signal output unit 44 outputs a main switching start signal to the first electromagnetic control valve 35 to start the main switching of the first-speed clutch 32C (the first clutch main switching which engages the first friction plate 326 and the first clutch plate 327), and outputs a release signal to the second electromagnetic control valve 36 to release the engagement of the second-speed clutch 32D (the engagement of the second friction plate 326 and the second clutch plate 327 of the second clutch).

[0112] Furthermore, if the drilling determination unit 45 determines that the drilling operation has not started, and the elapsed time determination unit 47 determines that a predetermined time Tth has elapsed, the signal output unit 44 outputs a switching preparation release signal to the first electromagnetic control valve 35 to release the switching preparation.

[0113] After the signal output unit 44 outputs a switching preparation start signal to the first electromagnetic control valve 35, the excavation determination unit 45 determines whether or not the wheel loader 1 will start excavating based on the lift arm cylinder pressure P and vehicle speed V acquired by the data acquisition unit 41.

[0114] Specifically, the excavation determination unit 45 determines whether the lift arm cylinder pressure P acquired by the data acquisition unit 41 is equal to or greater than a predetermined pressure threshold Pth, and whether the vehicle speed V acquired by the data acquisition unit 41 is equal to or less than a predetermined vehicle speed Vth.

[0115] Here, the "predetermined pressure threshold Pth" is a pressure threshold set based on the reaction force from the ground 100 (object to be excavated) acting on the bucket 23 at the start of the excavation operation. Also, the "predetermined vehicle speed Vth" is a speed threshold set based on the vehicle speed corresponding to the start of the excavation operation. In other words, the excavation determination unit 45 determines whether or not the wheel loader 1 will start the excavation work.

[0116] When the signal output unit 44 outputs a switching preparation start signal to the first electromagnetic control valve 35, the time measurement unit 46 starts measuring time T.

[0117] The elapsed time determination unit 47 determines whether the time T (measured time T) measured by the time measurement unit 46 has elapsed a predetermined elapsed time Tth. This "predetermined elapsed time Tth" can be set arbitrarily and is, for example, about 10 seconds. The predetermined elapsed time Tth is set to a time that can suppress wear between each friction plate 326 and each clutch plate 327 that are in contact with each other in the first gear clutch 32C when the switching preparation has started.

[0118] The memory unit 48 is a memory that stores the lift arm angle threshold αth, the bucket angle threshold βth, a predetermined pressure threshold Pth, a predetermined vehicle speed Vth, and a predetermined elapsed time Tth, respectively.

[0119] <Processing within Controller 4> Next, we will explain the specific processing flow executed within Controller 4, referring to Figure 8.

[0120] Figure 8 is a flowchart showing the processing flow executed by controller 4.

[0121] First, the data acquisition unit 41 acquires the lift arm angle α detected by the lift arm angle sensor 21A and the bucket angle β detected by the bucket angle sensor 23A (step S401).

[0122] Next, the attitude determination unit 42 determines whether the lift arm angle α obtained in step S401 is less than or equal to the lift arm angle threshold αth, and whether the absolute value |β| of the bucket angle β obtained in step S401 is less than or equal to the bucket angle threshold βth (step S402).

[0123] If, in step S402, it is determined that the lift arm angle α is less than or equal to the lift arm angle threshold αth, and the absolute value of the bucket angle β, |β|, is less than or equal to the bucket angle threshold βth (α ≤ αth and |β| ≤ βth) (step S402 / YES), then the operation intention determination unit 43 subsequently determines whether or not there is a lowering operation of the lift arm 21, that is, whether or not the data acquisition unit 41 has acquired a lift arm angle α corresponding to a lift arm lowering operation (step S403).

[0124] On the other hand, if it is determined in step S402 that the lift arm angle α is greater than the lift arm angle threshold αth, or that the absolute value of the bucket angle β|| is greater than the bucket angle threshold βth (α>αth or |β|>βth) (step S402 / NO), the process returns to step S401 and is repeated.

[0125] If it is determined in step S403 that there is no lowering operation of the lift arm 21 (step S403 / YES), the signal output unit 44 outputs a switching preparation start signal to the first electromagnetic control valve 35 (step S404).

[0126] In step S404, when a switching preparation start signal is output to the first electromagnetic control valve 35, the time measurement unit 46 starts measuring time T (step S405). Subsequently, the data acquisition unit 41 acquires the lift arm cylinder pressure P detected by the pressure sensor 22A and the vehicle speed V detected by the speed sensor 15A (step S406).

[0127] Next, the excavation determination unit 45 determines whether the lift arm cylinder pressure P obtained in step 606 is equal to or greater than a predetermined pressure threshold Pth, and whether the vehicle speed V obtained in step S406 is equal to or less than a predetermined vehicle speed Vth, that is, whether the wheel loader 1 has started excavation (step S407).

[0128] If it is determined in step S407 that the lift arm cylinder pressure P is equal to or higher than the predetermined pressure threshold Pth and the vehicle speed V is equal to or lower than the predetermined vehicle speed Vth (P≧Pth and V≦Vth), that is, if it is determined that the wheel loader 1 has started an excavation operation (step S408), the signal output unit 44 outputs the main switching start signal to the first electromagnetic control valve 35, and outputs the release signal to the second electromagnetic control valve 36 (step S408), and the processing in the controller 4 ends.

[0129] On the other hand, if it is determined in step S407 that the lift arm cylinder pressure P is lower than the predetermined pressure threshold Pth, or the vehicle speed V is higher than the predetermined vehicle speed Vth (P<Pth or V>Vth), that is, if it is determined that the wheel loader 1 has not started an excavation operation (step S407 / NO), the elapsed time determination unit 47 determines whether or not the measurement time T measured by the time measurement unit 46 is equal to or longer than the predetermined elapsed time Tth (step S409).

[0130] If it is determined in step S409 that the measurement time T is equal to or longer than the predetermined elapsed time Tth (T≧Tth) (step S409 / YES), the signal output unit 44 outputs a switching preparation cancellation signal to the first electromagnetic control valve 35 (step S410), and the processing in the controller 4 ends.

[0131] Note that if it is determined in step S409 that the measurement time T has not elapsed the predetermined elapsed time Tth (T<Tth) (step S409 / NO), the process returns to step S406.

[0132] As described above, the controller 4 outputs the switching preparation start signal to the first electromagnetic control valve 35 at the stage when the wheel loader 1 is in the preparation posture before starting excavation work (the posture in which the bottom surface portion 234 of the bucket 23 is in contact with the ground contact surface of the vehicle body horizontally).

[0133] As a result, the clutch mechanism 320 can complete preparation for switching from 2nd gear to 1st gear before the wheel loader 1 starts excavation (before the bucket 23 enters the ground 100), and perform the actual switching simultaneously with the start of excavation. Therefore, it is possible to quickly switch from 2nd gear to 1st gear in accordance with the operation of the work device 2 and then begin excavation work.

[0134] Furthermore, this control by controller 4 makes it possible to shorten the time from when a shift from second gear to first gear is requested until the shift is completed, regardless of the specifications of the clutch mechanism 320, specifically the size of the clutch chambers (housing spaces) of the first-gear clutch 32C and the second-gear clutch 32D.

[0135] Furthermore, in this embodiment, the controller 4 outputs a switching preparation start signal to the first electromagnetic control valve 35 only after it has determined that the working device 2 is in a position where the bottom surface 234 of the bucket 23 is in contact with the ground surface of the vehicle body horizontally, and that no further lowering operation of the lift arm 21 has been performed.

[0136] As a result, when dosing work is performed, the control related to switching from 2nd gear to 1st gear by controller 4 does not activate. Thus, the control related to switching from 2nd gear to 1st gear by controller 4 only activates when excavation work is performed, and does not activate when other work or operations are performed, so that work efficiency is not impaired when other work is performed.

[0137] Furthermore, in this embodiment, if the wheel loader 1 does not start excavation operation within a predetermined time (predetermined elapsed time Tth) after the controller 4 has output a switching preparation start signal to the first electromagnetic control valve 35, the controller 4 outputs a switching preparation release signal to the first electromagnetic control valve 35.

[0138] As a result, in the clutch mechanism 320, the switching preparation in the first-gear clutch 32C is released, and the friction plates 326 and clutch plates 327 that were in contact are separated in the axial direction of the input shaft 321, thus preventing excessive wear on the plates 326 and 327.

[0139] Embodiments of the present invention have been described above. It should be noted that the present invention is not limited to the embodiments described above, and various modifications are included. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the described configurations. Furthermore, it is possible to replace some of the configurations of this embodiment with those of other embodiments, and it is also possible to add configurations from other embodiments to the configuration of this embodiment. Moreover, it is possible to add, delete, or replace some of the configurations of this embodiment with those of other embodiments.

[0140] For example, in the above embodiment, if the controller 4 determines in step S403 that no further lowering operation of the lift arm 21 has been performed (step S403 / YES), it proceeds to step S404 and outputs a switching preparation start signal to the first electromagnetic control valve 35. However, it is not limited to this, and in step S402, if it determines that the posture of the work device 2 is such that the bottom surface 234 of the bucket 23 is horizontally grounded to the ground surface of the vehicle body (step S402 / YES), it may proceed to step S404.

[0141] Furthermore, although the wheel loader 1 in the above embodiment was equipped with a torque converter type drive system, it is not limited to this, and other drive systems such as an HST type may also be used.

[0142] Furthermore, in the above embodiment, a lift arm angle sensor 21A and a bucket angle sensor 23A were used as posture detection means for detecting the posture of the work device 2, and a speed sensor 15A was used as a vehicle speed detection means for detecting the travel speed of the wheel loader 1. However, the "detection means" do not necessarily have to be sensors. For example, the controller 4 may calculate the posture of the work device 2 and the travel speed of the wheel loader 1 based on images acquired by a camera mounted on the vehicle body. [Explanation of Symbols]

[0143] 1: Wheel loader 1A: Front frame (body) 1B: Rear frame (body) 2: Working equipment 4: Controller 11,11A: Front wheel (wheel) 11,11B: Rear wheel (wheel) 15A: Speed ​​sensor (vehicle speed detection means) 21: Lift Arm 21A: Lift arm angle sensor (attitude detection means) 22A: Pressure sensor (force detection means) 23: Bucket 23A: Bucket angle sensor (attitude detection means) 30: Engine (power source) 32: Transmission 32A~32F: Clutch 33-38: Solenoid control valve 54: Lift arm operating lever (operating means) 55: Bucket operating lever (operating mechanism) 234: Bottom part 325: Friction Plate 326: Clutch Plate Tth: Predetermined elapsed time (predetermined time)

Claims

1. A vehicle body equipped with multiple wheels, A work device having a lift arm mounted to the vehicle body so as to be rotatable in the vertical direction and a bucket mounted to the lift arm so as to be rotatable in the vertical direction, The power source mounted on the aforementioned vehicle body, A transmission that can switch between multiple speed stages by controlling multiple clutches with multiple electromagnetic control valves, and transmits the output torque of the power source to the multiple wheels by changing it, The system includes a controller that controls each of the aforementioned plurality of electromagnetic control valves, The aforementioned multiple clutches are It includes a first clutch corresponding to the first speed, which is the speed stage selected when performing an excavation operation, The plurality of electromagnetic control valves are, Includes a first electric control valve that controls the first clutch according to a signal output from the controller. In a wheel loader, The device has a posture detection means for detecting the posture of the work device, The aforementioned controller, When the posture of the work device detected by the posture detection means is such that the bottom surface of the bucket is horizontally grounded to the ground surface of the vehicle body, a start signal is output to the first electromagnetic control valve to initiate preparation for first clutch switching, which involves bringing the first friction plate and the first clutch plate of the first clutch into contact. After outputting the start signal to the first electromagnetic control valve, a main switching start signal is output to the first electromagnetic control valve to initiate the first clutch main switching, which engages the first friction plate and the first clutch plate. A wheel loader characterized by the following features.

2. In the wheel loader according to claim 1, A vehicle speed detection means for detecting the vehicle's travel speed, The system further includes force detection means for detecting an external force acting on the bucket, The aforementioned multiple clutches are It includes a second clutch corresponding to the second gear, which is a speed gear with less traction force than the first gear, The plurality of electromagnetic control valves are, Includes a second electromagnetic control valve that controls the second clutch according to a signal output from the controller, The aforementioned controller, After outputting the start signal to the first electromagnetic control valve, if the vehicle speed detected by the vehicle speed detection means becomes less than or equal to a predetermined travel speed corresponding to the start of the excavation operation, and the value detected by the applied force detection means becomes greater than or equal to a predetermined threshold corresponding to the reaction force from the excavation target applied to the bucket at the start of the excavation operation, the main switching start signal is output to the first electromagnetic control valve, and a release signal is output to the second electromagnetic control valve to release the engagement between the second friction plate and the second clutch plate of the second clutch. A wheel loader characterized by the following features.

3. In the wheel loader according to claim 1, The device further includes operating means for operating the aforementioned work device, The aforementioned controller, Furthermore, if the lift arm is not further lowered by the operating means, the start signal is output to the first electromagnetic control valve. A wheel loader characterized by the following features.

4. In the wheel loader according to claim 2, The aforementioned controller, If the vehicle speed detected by the vehicle speed detection means is greater than the predetermined travel speed, or if the value detected by the force detection means is less than the predetermined threshold, and a predetermined time has elapsed since the start signal was output to the first electromagnetic control valve, a release signal to release the first clutch switching preparation is output to the first electromagnetic control valve. A wheel loader characterized by the following features.

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