JPH08239026A - Method for controlling braking force - Google Patents

Abstract

PURPOSE: To provide a braking force control method capable of realizing constant speed traveling by setting a braking force to an optimal value according to a movable load without forcing a driver to perform burdensome switching operations during traveling. CONSTITUTION: A movable load detecting sensor 10 for detecting the movable load of a vehicle is provided and by means of a brake device control unit 8 for controlling the operations of auxiliary brake devices 3 and 4 for producing braking forces, the operations of the auxiliary brake devices 3 and 4 are controlled based on the detecting signal of the movable load detecting sensor 10 so as to obtain larger braking forces when the movable load is large.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a braking force control method for controlling a braking force by a braking device to realize constant speed traveling. More specifically, the present invention relates to a loading weight without a driver's hand during traveling. The present invention relates to a new braking force control method capable of obtaining a braking force according to the above and reducing driver's fatigue.

[0002]

2. Description of the Related Art For example, when a vehicle travels down a slope, the vehicle is subjected to acceleration due to the slope of the slope. Will increase. However, the friction brake device has a problem that when it is continuously operated for a long time, the braking performance is significantly deteriorated due to a fade phenomenon due to a temperature rise. Therefore, in recent years, in large vehicles such as trucks and buses, for example, those equipped with a retarder have become popular. This retarder reduces the number of times the brakes are used to prevent overheating of the brake drum, etc., and keeps the main brake device in a good condition in case of an emergency, improving safety and extending the life of the lining. Have

This retarder includes one using a fluid and one using an eddy current. In particular, since the braking force exerted by changing the pressure of the working liquid can be changed in the fluid retarder, the pressure of the working liquid supplied to the fluid retarder together with the fluid retarder can be adjusted in multiple stages. There has also been proposed a braking force control device equipped with a control device and switching the braking force by a fluid retarder according to the slope of a slope or the like.

Further, in addition to the retarder as the auxiliary braking device, an exhaust brake is additionally provided to provide a plurality of auxiliary braking devices, and the slope of the slope is steep and a large braking force is required. In such a case, a braking force control device that can use these plural types of auxiliary braking devices together is also being researched and developed.

In the case of the conventional braking force control device equipped with a plurality of types of auxiliary braking devices, when the braking is started by the auxiliary braking device, the rate of change (acceleration) of the running speed of the vehicle is considered. Estimate the required braking force, and if the required braking force is small, for example, activate only the retarder, and if a larger braking force is required, apply both the retarder and the exhaust brake. A braking force control method has been studied in which the auxiliary braking device to be used in combination is gradually increased as the required braking force increases, such as actuation.

[0006]

However, the braking force required for constant speed traveling on a downhill fluctuates depending not only on the traveling speed and the slope of the slope, but also on the load weight of the luggage. In particular, in a large vehicle such as a truck or a bus, a large amount of loading is possible and the influence of the loading weight is great, and it is impossible to perform optimum braking without considering the loading weight.

Therefore, conventionally, in a braking force control device equipped with a plurality of types of auxiliary braking devices as described above,
When a braking device selection switch for selecting an auxiliary braking device to be operated is provided and the braking force control device is operated, the driver operates the braking device selection switch in advance according to the loaded weight and the like. Has studied a structure that realizes braking in consideration of the loaded weight.

However, the operation of the braking device selection switch usually has to be carried out while the vehicle is running, which results in the driver being required to perform frequent switch operations while the vehicle is running, resulting in increased fatigue of the driver. It was feared that it would cause inconvenience.

Therefore, an object of the present invention is to solve the above-mentioned problems, and the braking force to be applied is set to an optimum value according to the loaded weight without forcing the driver to perform a troublesome switch operation during traveling. It is an object of the present invention to provide a braking force control method capable of realizing high speed traveling and reducing driver fatigue.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a plurality of auxiliary braking devices which can change the magnitude of the braking force of a vehicle in combination, and at least detect a loading state on the vehicle to generate a predetermined signal. A signal generating means for generating and a braking device control unit for controlling the operation of the braking device based on an output signal from the signal generating means are provided, and the signal generating means for setting the braking force corresponding to the loaded weight. A braking force control method is characterized in that the use combination of the plurality of auxiliary braking devices is controlled based on the output signal of the means.

Further, in the above braking force control method,
As one of the auxiliary braking devices, a fluid type retarder capable of changing a braking force generated by the working fluid pressure is used, and the working fluid pressure supplied to the fluid type retarder according to an output signal of the signal generating means. The above object can also be achieved by a braking force control method in which the braking force of the fluid retarder is controlled by adjusting

Furthermore, in the above braking force control method, the control range of the braking force according to the loaded weight is set by the signal of the deceleration selection switch capable of selecting the magnitude of the braking force. The power control method can also achieve the above object.

[0013]

The present invention is equipped with, for example, a loaded weight detection sensor for detecting the loaded weight of a vehicle, and the braking device control unit for controlling the operation of the braking device for generating a braking force is used when the loaded weight is large. Is configured to control the operation of the braking device based on the detection signal of the loaded weight detection sensor so that a larger braking force can be obtained, which forces the driver to perform a troublesome switch operation while the vehicle is traveling. Instead, the braking force to be applied can be set to an optimum value according to the loaded weight to realize constant speed traveling, and the driver's fatigue can be reduced.

Further, by using a plurality of auxiliary braking devices as the braking device or by using a fluid retarder as an auxiliary braking device which is a constituent element, finer and proper braking can be exerted. become.

Further, by setting the control range of the braking force by operating the deceleration selection switch capable of selecting the magnitude of the braking force according to the loaded weight, the range in which the braking force is automatically obtained can be set. The driver can select it according to the situation.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a braking force control device for realizing constant speed running by the braking force control method according to the present invention. The braking force control device 1 of the present embodiment realizes constant speed running by exerting the braking force of the auxiliary braking device equipped on the vehicle when the vehicle goes down a slope. An exhaust brake device 3 and a fluid retarder 4 that function as an auxiliary braking device that applies a braking force to a rotating shaft 2 such as a propeller shaft that rotates together with the wheels W.
And a signal transmission means 9 for detecting the running state of the vehicle and a driver's instruction, and a braking device control unit for controlling the operating states of the above-mentioned auxiliary braking devices 3, 4 based on the output signals of the signal transmission means 9. It is a configuration equipped with 8 and.

The rotating shaft 2 described above is connected to the output shaft of the engine 11 via a transmission. The exhaust brake device 3 uses the exhaust gas pressure discharged to the exhaust pipe 13 of the engine 11 as a braking force, and is used as a first auxiliary braking device in this embodiment.

The fluid type retarder 4 rotates the rotor 17 in the working liquid (usually the working oil which is also used as the cooling oil) filled in the container 15 to obtain the braking torque by the friction loss of the working liquid. . In this example,
The fluid retarder 4 is connected to the rotary shaft 2 via a clutch unit 20 controlled by a braking device control unit 8. In the clutch unit 20, the rotor 17 is connected to the rotary shaft 2 or the rotor 17 is disconnected from the rotary shaft 2 by the pneumatic cylinder device 22 driven by the pneumatic pressure supplied from the clutch control device 21. The operation is switched.

The operation of the fluid retarder 4 will be described in more detail. The clutch unit 20 includes a clutch plate 24 that rotates integrally with the rotating shaft 2 in the working liquid and a pressure plate 25 that rotates integrally with the rotor 17. The wet multi-plate clutches arranged alternately are supplied with predetermined pressure air from the clutch control device 21 to the pressure chambers 26 of the pneumatic cylinder device 22 and are clutched by the piston 27 rotatably fitted to the rotary shaft 2. Plates 24 and 2
5 The two are pressed into close contact with each other. This makes the rotor 1
7 is connected to the rotary shaft 2 and the braking function is exerted. Then, the pressure control chamber 2 is controlled by the clutch control device 21.
When the pressure air in 6 is released, the clutch plates 24,
25 is in a separated state, and the rotor 17 is in a braking release state in which it is separated from the rotating shaft 2.

The clutch control device 21 includes a pressure reducing valve 30 and
The configuration includes a direction switching valve 31. Pressure reducing valve 30
Reduces the pressure air of the pressure air source 29 (air tank) to generate pressure air to be supplied to the pressure chamber 26 of the pneumatic cylinder device 22. Further, the direction switching valve 31 is a two-position switching valve whose position is switched by a control signal from the braking device control unit 8, and a pressure supply position for supplying the pressure air provided by the pressure reducing valve 30 to the pressure chamber 26, and a pressure supply position. The position can be switched to a pressure discharge position for releasing the pressure in the chamber 26 (in FIG. 1, the state is switched to the pressure discharge position).

The above-mentioned hydraulic retarder 4 is constructed so that the braking force can be adjusted by switching the hydraulic pressure, and is used as the second auxiliary braking device in this embodiment. As means for switching the hydraulic pressure of the fluid retarder 4, a pressure control device 3 for switching the output air pressure based on a control signal from the braking device control unit 8 is used.
3 and a cooler unit 34 that circulates the working liquid in the fluid retarder 4. The cooler unit 34 uses the output air pressure of the pressure control device 33 as the pressure of the working liquid circulating in the cooler unit 34. An air-liquid conversion device 35 for converting is built in.

The pressure control device 33 shown here includes a first pressure reducing valve 37 for reducing the pressure of the relatively high pressure air from the pressure air source 29 to supply it as low pressure air, and the output of the first pressure reducing valve 37. Second pressure reducing valve 3 for further reducing the pressure of the compressed air
8, a third pressure reducing valve 39 for further reducing the pressure air output from the second pressure reducing valve 37, and these three pressure reducing valves 3
Two of the direction switching valves 42 and 43 for selecting one of the pressure air output from 7, 38 and 39 and supplying the desired pressure air to the air-liquid conversion device 35 are provided. There is.

The direction switching valves 42 and 43 shown here
Is a two-position switching valve whose position is switched by a control signal from the braking device control unit 8.
That is, the direction switching valve 42 allows the pressure air output from the pressure reducing valve 38 to pass through the pressure air passage 44 to the direction switching valve 4.
It is possible to switch the position between a first pressure supply position where the pressure reducing air is output to the pressure reducing valve 39 and a second pressure supply position where the pressure air output from the pressure reducing valve 39 is output to the direction switching valve 43 via the pressure air passage 44. . The direction switching valve 43 is the pressure air output from the first pressure reducing valve 37 or the direction switching valve 4
The position can be switched so that either one of the pressure air output to the pressure air passage 44 by 2 can be selected and supplied to the air chamber 35a of the air-liquid conversion device 35 via the pressure air passage 45. There is. The clutch control device 21 and the pressure control device 33 are equipped as a valve unit in an integrated state in one unit.

The cooler unit 34 is a fluid type retarder 4.
The heated working liquid in the container 15 is guided from the working liquid outlet 46 formed in the container 15 to a cooler (radiator) 48 for working liquid via a pipe line 47 to cool the working liquid. The cooled working liquid is then pumped by the pump 49 through the conduit 50 and the working liquid inlet 51 provided in the container 15 to the container 1
Returned to within 5. A working liquid chamber 35b of the air-liquid conversion device 35 is always in communication with the working liquid circulation path of the cooler unit 34.

The air-liquid conversion device 35 has a working fluid chamber 35b for storing a working fluid and an air chamber 35a defined by a rubber film 35c which is an airtight and easily deformable film. The pressure of the working liquid on the side of the working fluid chamber 35b is adjusted by the air pressure supplied to the air chamber 35a.

The sensors / switches 9 are a set switch 5 for instructing the start of control processing of the braking force, a speed sensor 6 for detecting the traveling speed of the vehicle, and a brake operating means such as a brake pedal or a brake lever. A brake sensor 7 that detects the operating state of the brake (that is, whether it is an on state or an off state) from the operation of
A loaded weight detection sensor 10 for detecting a loaded weight of a vehicle,
From the operation of the accelerator pedal to the operating state of the accelerator (that is,
An accelerator sensor 14 for detecting whether it is in an on state or an off state, a retarder output selection switch 61 for allowing a driver to previously specify a braking force generated by the fluid retarder 4, and the braking Deceleration selection for the driver to select and specify the magnitude of deceleration in consideration of the loaded weight before traveling so that the braking force obtained by the control of the device control unit 8 becomes an optimum value according to the loaded weight of the vehicle. The switch 62 and an exhaust brake manual switch 63 for selectively operating only the exhaust brake device 3 according to the driver's preference or the like.

The set switch 5 is, for example, a push button switch or the like, and is arranged around the steering wheel, which is easy for the driver to operate, or on the front panel or the like. In the case of this embodiment, the speed sensor 6 detects the rotation speed of the wheels as the traveling speed of the vehicle.

In the case of this embodiment, the loaded weight detection sensor 10 detects the loaded weight from the displacement between the bed 12 and the axle 16 of the vehicle, which changes according to the loaded weight, as shown in FIG. is there.

Both the retarder output selection switch 61 and the exhaust brake manual switch 63 allow the driver to determine whether or not the braking device control unit is to perform a braking force adjustment process for adjusting the braking force according to the loaded weight. The retarder output selection switch 61 functions as an operation mode selection switch for instructing selection, and the retarder output selection switch 61 operates as a mode 0 in which the fluid retarder 4 is not operated and a braking force by the fluid retarder 4 to the loaded weight detection sensor 10. Mode 1 in which the control is performed in accordance with the detection signal of No. 1 and the braking force of the fluid retarder 4 is made small regardless of the detection signal of the loaded weight detection sensor 10 (that is, the air pressure output from the third pressure reducing valve 39 is converted to air-liquid conversion). Act on device 35) Mode 2
And mode 3 in which the braking force of the fluid retarder 4 is increased (that is, the air pressure output from the first pressure reducing valve 37 acts on the air-liquid conversion device 35) regardless of the detection signal of the loaded weight detection sensor 10. It is selectable.

In order for the driver to obtain the braking force according to the loaded weight, the deceleration selection switch 62 should have the braking force control device 1 exert a large braking force in consideration of the loaded weight before traveling. The operation mode is mode 0 for avoiding the control processing of the braking force according to the detection signal of the loaded weight detection sensor 10, and the braking force is decreased according to the detection signal of the loaded weight detection sensor 10. To generate in mode 1
It is possible to select a mode 2 in which the braking force is generated in a large amount according to the detection signal of the loaded weight detection sensor 10.

The exhaust brake manual switch 63 is a switch for operating only the exhaust brake device 3 without operating the fluid retarder 4.

The braking device control unit 8 includes the sensor
The operations of the exhaust brake device 3 and the fluid retarder 4 are controlled based on the output signal of the stitches 9 in the procedure shown in FIG.

That is, the braking device control unit 8 starts the process when the set switch 5 is turned on, and first checks that the brake and the accelerator are not in operation (steps 101 and 102). And when the brake and accelerator are not in operation,
It is determined whether or not the exhaust brake manual switch 63 is off, and when the exhaust brake manual switch 63 is on, braking is performed by operating only the exhaust brake device 3 (steps 103 and 104). ).

When it is judged in step 103 that the exhaust brake manual switch 63 is off, it is judged which mode the operation mode of the retarder output selection switch 61 is set to, and it is set. The operations of the exhaust brake device 3 and the fluid retarder 4 are controlled according to the mode being set (step 105).

In this step 105, if the operation mode is set to mode 0, the control process is performed in step 1.
01, the operation of the pressure control device 33 is controlled so that the air pressure output from the third pressure reducing valve 39 is supplied to the air-liquid conversion device 35 when the operation mode is set to the mode 2. The braking force generated by the fluid retarder 4 is reduced (step 106). The operation mode is mode 3
When set to 1, the operation of the pressure control device 33 is controlled so that the air pressure output from the first pressure reducing valve 37 is supplied to the air-liquid conversion device 35, and the braking force generated by the hydraulic retarder 4 is controlled. Is increased (step 107). When the operation mode of the retarder output selection switch 61 is the mode 2 or the mode 3, the exhaust brake device 3 is not operated.

If it is determined in step 105 that the operation mode of the retarder output selection switch 61 is mode 1, the operation mode of the deceleration selection switch 62 is checked (step 108). This step 10
8, when the operation mode of the deceleration selection switch 62 is the mode 0, the process is returned to the step 101, and the mode 1
In the case of, it moves to the next step 110, and in the case of mode 2, it moves to another step 120.

Step 110 and step 120
In the step of determining the required braking force according to the loaded weight detected by the loaded weight detection sensor 10, the required braking force according to the loaded amount is set to three values: large, medium and small.
Sort into stages. Then, the exhaust brake device 3 and the fluid retarder 4 are operated according to the separated stage (steps 111 to 113, steps 121 to 12).
3).

When the operation mode of the deceleration selection switch 62 is mode 1 (when the driver sets a small braking force), when the loaded weight is small depending on whether the loaded weight is large, medium or small, Only the exhaust brake device 3 is activated, and when the loaded weight is medium, the exhaust brake device 3 is activated, and at the same time, the hydraulic retarder 4 is activated by setting the operating liquid pressure to a small value. In this case, the exhaust brake device 3 is actuated and at the same time the actuating fluid pressure is set to medium and the fluid retarder 4 is actuated (step 111).
~ 113).

On the other hand, the operation mode of the deceleration selection switch 62 is the mode 2 (when the driver sets a large braking force).
In the case of, when the loaded weight is small, the exhaust brake device 3 is activated at the same time as the loaded weight is small, and at the same time, the hydraulic fluid pressure is set to a small value to activate the hydraulic retarder 4 to load the loaded weight. When the load is medium, the exhaust brake device 3 is operated, and at the same time, the working liquid pressure is set to the middle to operate the fluid retarder 4, and when the loaded weight is large, the exhaust brake device 3 is operated. At the same time, the working liquid pressure is set to a large value to operate the fluid retarder 4 (steps 121 to 123).

Then, each exhaust brake device 3, which is in operation,
In the fluid retarder 4, the accelerator is turned on, or the exhaust brake manual switch 63 is turned on (o).
n) or the retarder output selection switch 6
When the operation mode of No. 1 is switched to a mode other than the mode 1, the braking operation is canceled and the process returns to step 101 (steps 130 to 133). Retarder output selection switch 6
When the operation mode of 1 is the mode 1, the exhaust brake device 3 and the fluid retarder 4 in operation are left as they are,
Return to step 108.

According to the above braking control, the loaded weight detection sensor 10 for detecting the loaded weight of the vehicle is provided,
The braking device control unit 8 that controls the operation of each of the auxiliary braking devices 3 and 4 that generate the braking force detects the loaded weight detection sensor 10 so that a larger braking force is obtained when the loaded weight is large. Each auxiliary braking device 3, based on the signal
By controlling the operation of No. 4, the braking force to be applied is set to an optimum value according to the loaded weight and constant speed traveling is realized without forcing the driver to perform a troublesome switch operation while the vehicle is traveling. Therefore, the driver's fatigue can be reduced.

By providing two auxiliary braking devices 3 and 4 and using a fluid type retarder capable of switching braking force in three steps as the auxiliary braking device 4, the braking force control device 1 has 4 It becomes possible to finely control the braking force in stages, and it becomes possible to exert finer and proper braking.

Further, the control range of the braking force can be appropriately set by operating the deceleration selection switch 62 capable of selecting the magnitude of the braking force according to the loaded weight, and the range where the braking force is automatically obtained can be set. Since the driver can make a selection according to the situation, it becomes possible to more flexibly use the braking device in response to the driver.

In the case of the above-described embodiment, the hydraulic retarder 4 equipped as an auxiliary braking device is connected to the rotating shaft 2 rotating with the traveling wheels via the clutch unit 20 controlled by the braking device control unit 8. With such a configuration, the effect of braking torque on the rotary shaft 2 can be eliminated when unnecessary, and deterioration of fuel consumption can be prevented.

Furthermore, as a means for switching the hydraulic fluid pressure of the fluid retarder 4, a pressure control device 33 for switching the output air pressure based on a control signal from the braking device control unit 8 and the hydraulic fluid are circulated to the fluid retarder 4. By providing the cooler unit 34 for controlling and the air-liquid converter 35 for converting the output air pressure of the pressure controller 33 into the pressure of the working liquid circulating in the cooler unit 34, for example, engine characteristics and vehicle Regardless of individual vehicle specifications such as weight and running performance, the pressure control device 33 can be used as a general-purpose specification and can be conveniently used for various vehicles.

In the above embodiment, the fluid retarder is used as one of the auxiliary braking devices, but a braking device other than the fluid retarder (for example, an eddy current retarder) may be used as appropriate. . Further, the fluid type retarder used in the above-mentioned embodiment is adapted to obtain the braking force in three stages having different sizes by switching the pressure of the working liquid in three stages and using the pressure. It may be configured to be switchable in two stages, or in multiple stages of four stages or more, or may be configured to be able to adjust steplessly. Further, in the above-described embodiment, the present invention has a configuration in which the exhaust brake device and the fluid retarder are provided as the auxiliary braking devices, but the number of the auxiliary braking devices is further increased to obtain a finer braking force. Needless to say, a configuration that enables setting can be used.

Further, in the above-described embodiment, two types of auxiliary braking devices, that is, the exhaust braking device 3 and the fluid retarder 4 are provided as the braking devices, and these auxiliary braking devices 3 and 3 are provided.
Although the operation of No. 4 is controlled based on the detection signal of the loaded weight detection sensor 10, the control device that controls the operation based on the detection signal of the loaded weight detection sensor 10 is not limited to the above auxiliary braking device. However, it is conceivable to add other auxiliary braking devices and main brakes to the control target. Further, the above-described embodiment has been shown as a braking force control method for realizing constant speed traveling on a downhill, but the braking process according to the present invention is applied to the braking force control for constant speed traveling on a flat ground. It is also possible to do so.

[0048]

As described above, according to the braking force control method of the present invention, the braking force is controlled via the braking device control unit on the basis of the output signal from the load weight detection sensor for detecting the load weight of the vehicle. The operation of the generated braking device can be controlled so that a larger braking force can be obtained, for example, when the loaded weight is large, so that it can be applied without forcing the driver to perform a troublesome switch operation while the vehicle is traveling. The braking force can be set to an optimum value according to the loaded weight to realize constant speed traveling, and the fatigue of the driver can be reduced. Further, by configuring the braking device with a plurality of auxiliary braking devices, or by using a fluid retarder as an auxiliary braking device that is a constituent element, it becomes possible to work finer and more appropriate braking. Also, by setting the control range of the braking force by operating the deceleration selection switch that can select the magnitude of the braking force according to the loaded weight, the driver can automatically determine the range in which the braking force can be obtained. The braking device can be selected according to the situation, and the braking device can be used more flexibly in response to the driver.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a braking force control device according to the present invention.

FIG. 2 is a flowchart showing a part of a braking force control method executed by a braking force control device according to an embodiment of the present invention.

[Explanation of symbols]

 1 Braking Force Control Device 2 Rotating Shaft 3 Exhaust Brake Device 4 Fluid Retarder 5 Set Switch 6 Speed Sensor 7 Brake Sensor 8 Braking Device Control Unit 9 Sensors / Stitches 10 Loaded Weight Detection Sensor 11 Engine 13 Exhaust Pipe 14 Accelerator Sensor 15 Container 17 rotor 20 clutch unit 21 clutch control device 22 pneumatic cylinder device 24 clutch plate 25 pressure plate 26 pressure chamber 27 piston 29 pressure air source 30 pressure reducing valve 31 direction switching valve 33 pressure control device 34 cooler unit 35 air-liquid conversion device 37 first Pressure reducing valve 38 Second pressure reducing valve 42 Direction switching valve 44 Pressure air passage 49 Pump 61 Retarder output selection switch 62 Deceleration selection switch 63 Exhaust brake manual switch

Claims (3)

[Claims] 1. A plurality of auxiliary braking devices capable of varying a magnitude of a braking force of a vehicle by combining, a signal generating means for detecting at least a loading state on the vehicle and generating a predetermined signal, and the signal generating means. A braking device control unit that controls the operation of the braking device based on an output signal from the plurality of the plurality of units, based on the output signal of the signal generating unit to set the braking force corresponding to the loaded weight. A braking force control method comprising controlling a combination of use of an auxiliary braking device. 2. The braking force control method according to claim 1, wherein, as one of the auxiliary braking devices, a fluid retarder capable of changing a braking force generated by a working liquid pressure is used, and the signal generating means is used. The braking force control method is characterized in that the braking force of the fluid retarder is controlled by adjusting the working liquid pressure supplied to the fluid retarder according to the output signal of the fluid retarder. 3. The braking force control method according to claim 1, wherein a control range of the braking force according to the loaded weight is set by a signal from a deceleration selection switch capable of selecting the magnitude of the braking force. A braking force control method characterized by setting.