compressed gas and the weight of the hammer body, which has larger strike energy.
Hydraulic system has high strike frequency through the fast alternation of electromagnetic reversing valve, oil supply and drainage of hydraulic cylinder and
nitrogen chamber of hydraulic cylinder. The closed structure can also meet the
special requirements of underwater pile driving and inclined pile driving. The
stroke of the hammer head can be adjusted arbitrarily according to the soil condition
and the strength of the pile, and the strike energy of the hammer can be adjusted.
Hydraulic–pneumatic composite hammer components require higher precision and
higher price.
12.3.2 Mathematical Model
12.3.2.1 Hammer Body Rising Stage
As shown in Fig. 12.12, during the rising stage of the hammer body, the hydraulic
pump and high-pressure accumulator simultaneously supply oil to the lower
chamber of the hydraulic cylinder through the electromagnetic directional valve,
and the hammer body is lifted. Ignoring the compressibility of hydraulic oil,
pipeline expansion and leakage, the flow continuity equation of hammer body in
rising stage is as follows:
Q d ¼ Q ha þ Q p
ð12:24Þ
The flow Rate of hydraulic cylinder is
Q d ¼ A d v u
ð12:25Þ
where
v u Rising speed of hammer body;
Q p Output flow of hydraulic pump, Q p ¼ nq;
n Motor speed;
q Pump displacement.
From Eqs. (12.24) and (12.25), the flow equation of high-pressure accumulator
is obtained as follows.
Q ha ¼ A d v u À Q p
ð12:26Þ
It is assumed that the pre-charging pressure and volume of high-pressure
accumulator are p ha0 and V ha0 respectively. When the hydraulic hammer is in the
highest working position, the gas pressure of the high-pressure accumulator is the
lowest and the volume is the largest, which are p ha1 and V ha1 , respectively. When
290
12 Pneumatic–Hydraulic Pile Driving Hammer
Hydraulic system has high strike frequency through the fast alternation of electromagnetic reversing valve, oil supply and drainage of hydraulic cylinder and
nitrogen chamber of hydraulic cylinder. The closed structure can also meet the
special requirements of underwater pile driving and inclined pile driving. The
stroke of the hammer head can be adjusted arbitrarily according to the soil condition
and the strength of the pile, and the strike energy of the hammer can be adjusted.
Hydraulic–pneumatic composite hammer components require higher precision and
higher price.
12.3.2 Mathematical Model
12.3.2.1 Hammer Body Rising Stage
As shown in Fig. 12.12, during the rising stage of the hammer body, the hydraulic
pump and high-pressure accumulator simultaneously supply oil to the lower
chamber of the hydraulic cylinder through the electromagnetic directional valve,
and the hammer body is lifted. Ignoring the compressibility of hydraulic oil,
pipeline expansion and leakage, the flow continuity equation of hammer body in
rising stage is as follows:
Q d ¼ Q ha þ Q p
ð12:24Þ
The flow Rate of hydraulic cylinder is
Q d ¼ A d v u
ð12:25Þ
where
v u Rising speed of hammer body;
Q p Output flow of hydraulic pump, Q p ¼ nq;
n Motor speed;
q Pump displacement.
From Eqs. (12.24) and (12.25), the flow equation of high-pressure accumulator
is obtained as follows.
Q ha ¼ A d v u À Q p
ð12:26Þ
It is assumed that the pre-charging pressure and volume of high-pressure
accumulator are p ha0 and V ha0 respectively. When the hydraulic hammer is in the
highest working position, the gas pressure of the high-pressure accumulator is the
lowest and the volume is the largest, which are p ha1 and V ha1 , respectively. When
290
12 Pneumatic–Hydraulic Pile Driving Hammer