Forklift active braking control method and system based on power shift transmission

1 . A forklift active braking control method based on power shift transmission, wherein the power shift transmission comprises a forward gear clutch controlled by a forward gear proportional solenoid valve and a reverse gear clutch controlled by a reverse gear proportional solenoid valve, comprising the following steps:

step 1: obtaining forklift state parameters, and determining a current state of a forklift according to the forklift state parameters, wherein if the current state of the forklift is an active braking state, performing step 2;

step 2: obtaining forklift speed-duty ratio relationship, inputting a current speed signal of the forklift, and according to the forklift speed-duty ratio relationship, obtaining duty ratio parameters that cause a braking deceleration of the forklift to be within a preset range and can produce a maximum braking force at the current speed, and outputting proportional solenoid valve control parameters of the forward gear proportional solenoid valve or the reverse gear proportional solenoid valve of the power shift transmission according to the obtained duty ratio parameters;

step 3: using the proportional solenoid valve control parameters generated in step 2 to control the forward gear proportional solenoid valve or the reverse gear proportional solenoid valve of the power shift transmission to take action, to engage the reverse gear clutch when the forklift is in a forward gear, or to engage the forward gear clutch when the forklift is in a reverse gear, thereby controlling a forklift power system to output a driving force opposite to a current movement direction of the forklift to drive the forklift to actively brake; and

step 4: exiting active braking of the forklift when a forklift speed is detected to be zero.

2 . The forklift active braking control method based on power shift transmission according to claim 1 , wherein the forklift state parameters comprise brake pedal state, accelerator pedal switch state, forklift speed, and forklift gear position.

3 . The forklift active braking control method based on power shift transmission according to claim 2 , wherein the forklift state comprises active braking state, combined braking state, emergency braking state, and normal driving state, wherein the combined braking state is a transmission active braking and a combined braking of the forklift braking system.

4 . The forklift active braking control method based on power shift transmission according to claim 3 , wherein the forklift state determination in step 1 comprises the following steps:

step 1.1: if the accelerator pedal switch is in an on state, entering the normal driving state without any braking;

step 1.2: if the accelerator pedal switch is in an off state, θ=0, entering clutch active braking state, wherein in the active braking state, only the transmission performs active braking through gear shifting;

step 1.3: if the accelerator pedal switch is in the off state, θ≠0, entering the combined braking state;

step 1.4: if the accelerator pedal switch is in the off state and Δt 2 is less than a set threshold, entering the emergency braking state, wherein the power shift transmission performs emergency braking;

wherein θ is a pressed angle of the brake pedal;

Δt 2 is an emergency braking time of the brake pedal, Δt 2 is a time when θ 1 changes to θ max , θ 1 and θ max respectively represent an angular position of the brake pedal at a previous moment and an angular position when the brake pedal is pressed to a fully depressed position.

5 . The forklift active braking control method based on power shift transmission according to claim 1 , wherein the forklift speed-duty ratio relationship in step 2 is obtained by the following method:

step 2.1: setting a normal range of the forklift speed as v 1 ~v y , and dividing a forklift speed range evenly into y−1 segments with a total of y points, respectively, as v 1 , v 2 , v 3 . . . v y-2 , v y-1 , v y ; a value of the duty ratio is b %, and a unit change difference of adjusting the duty ratio is 1%, an experimental value of the duty ratio is determined as (b−m 1 ) % for the m 1 -th time; a forklift speed-duty ratio graph curve determines a number of experimental tests as y×m 1 ; initializing b %=90%, when the duty ratio experiment starts;

step 2.2: adjusting the forklift speed to v 1 , assigning duty ratio value to b %, observing whether the braking deceleration a is within a preset range;

if it is not in the preset range, assigning (b−1) to b, and repeating step 2.2;

if it is observed that the braking deceleration is within the preset range, determining a maximum duty ratio at which the active braking of the power shift transmission can produce a maximum braking force without braking shock at the forklift speed of v 1 as the current value b 1 %;

step 2.3: remaining other conditions unchanged, adjusting the forklift speed to v 2 , v 3 . . . v y-2 , v y-1 , v y , respectively, and repeating step 2.3 to obtain the maximum duty ratios b 2 %, b 3 % . . . b y-2 %, b y-1 %, b y %, respectively, at which the active braking of the power shift transmission can produce the maximum braking force without braking shock at the forklift speed of v 2 , v 3 . . . v y-2 , v y-1 , v y ;

step 2.4: after obtaining the maximum duty ratios at which the active braking of the power shift transmission can produce the maximum braking force without braking shock at y different forklift speeds, respectively, determining y straight line segments using y−1 sets of data (v 1 , b 1 ), (v 2 , b 2 ); (v 2 , b 2 ), (v 3 , b 3 ) . . . (v y-2 , b y-2 ), (v y-1 , b y-1 ); (v y-1 , b y-1 ), (v y , b y ), and obtaining a forklift speed-duty ratio relationship curve by connecting the y straight line segments.

6 . The forklift active braking control method based on power shift transmission according to claim 1 , wherein a forklift gear position signal is detected; and

if the forklift is in a forward gear, the forward gear clutch is controlled to disconnect, and then the reverse gear clutch is controlled to engage, whereby the forklift transmission system is dragged in a reverse direction to slow down the forklift;

if the forklift is in the reverse gear, the reverse gear clutch is controlled to disconnect, and then the forward gear clutch is controlled to engage, whereby the forklift transmission system is dragged in the reverse direction to slow down the forklift.

7 . The forklift active braking control method based on power shift transmission according to claim 3 , wherein the control method of the power shift transmission in the combined braking state is the same as the control method of the power shift transmission in the active braking state.

8 . The forklift active braking control method based on power shift transmission according to claim 3 , wherein when the forklift is in an emergency braking state, a solenoid valve duty ratio of the power shift transmission should immediately respond to 100%, and the forward gear clutch or the reverse gear clutch should be engaged and locked.

9 . A control system using the forklift active braking control method based on power shift transmission according to claim 1 , the control system comprises:

a vehicle speed sensor, a brake pedal signal sensor, an accelerator pedal switch signal sensor, a vehicle gear signal sensor, a power shift transmission and a processor;

wherein the power shift transmission comprises a forward gear proportional solenoid valve, a reverse gear proportional solenoid valve, a forward gear clutch, and a reverse gear clutch;

wherein an input end of the processor is respectively connected to the vehicle speed sensor, the brake pedal signal sensor, the accelerator pedal switch signal sensor and the vehicle gear signal sensor, and an output end of the processor is respectively connected to the power shift transmission and a vehicle braking system.

10 . The control system according to claim 9 , wherein the vehicle speed sensor is installed at a forklift wheel and is used to collect vehicle speed information;

wherein the brake pedal signal sensor is installed on the brake pedal and is used to collect a driver's operation signal on the brake pedal;

wherein the accelerator pedal switch signal sensor is installed on the accelerator pedal and is used to collect a driver's operation signal on the accelerator pedal;

wherein the vehicle gear signal sensor is installed on a gear operating handle and is used to collect signals that the forklift is currently in forward gear, reverse gear or neutral gear.