Power plants – Pressure fluid source and motor – Having a mechanical clutch or brake device in the power train
Reexamination Certificate
1998-05-01
2001-06-26
Lopez, F. Daniel (Department: 3622)
Power plants
Pressure fluid source and motor
Having a mechanical clutch or brake device in the power train
C060S442000, C180S338000
Reexamination Certificate
active
06250077
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a hydraulic continuously variable transmission, which can be used on a vehicle. This hydraulic transmission comprises a hydraulic variable pump and a hydraulic variable motor, and the pump being driven by the engine of the vehicle delivers the hydraulic oil to actuate the motor, which will drive the wheels.
BACKGROUND OF THE INVENTION
Such hydraulic transmissions have been well-known and put into use in automobiles and other vehicles. For example, Japanese Laid-Open Patent Publication No. H6(1994)-42635 discloses an automotive mowing tractor which comprises a hydraulic swash plate pump for variable delivery and a hydraulic motor with fixed displacement. In this tractor, the pump, which is driven by the engine, delivers the hydraulic pressure to the motor, which rotates the wheels. Furthermore, this tractor is provided with a seesaw pedal, which is stepped and operated by the driver with a foot. When this pedal is stepped forward, the swash plate is swiveled to a “forward drive direction”, and the vehicle is driven forward. Likewise, when this pedal is stepped rearward, the swash plate is swiveled to a “rearward drive direction”, and the vehicle is driven backward.
This pedal is designed to automatically return to a neutral position when it is not stepped, i.e., when it is released. With the pedal at the neutral position, the angle of skew of the swash plate is zero, and the pump discharges no oil. In this condition, the rotation of the motor is locked because the pump does not allow any oil to flow. This locking is so complete that any attempt to rotate the motor, which must force the oil to flow through the pump, is futile. Thus, without operating the brake, the driver can prevent the wheels from rotating by maintaining the skew angle of the swash plate of the pump at zero and locking the rotation of the motor.
If the vehicle is on a slope, for example, and the swash plate of the pump is operated to make the skew angle of the pump to zero in order to lock the rotation of the motor, then the motor is subjected to a torque which is transmitted through the wheels of the vehicle because of the component force resulting from the weight of the vehicle that acts to move the vehicle in the downward direction parallel to the slope. In this condition, as long as there is no leak in the hydraulic circuit, which includes the pump and the motor, the rotation of the motor is kept being locked. However, if any leak occurs, then the motor will rotate slowly at the speed which corresponds to the rate of the oil leak. In this leaky condition, even if the driver tries to stop the vehicle by setting the skew angle of the swash plate to zero, the vehicle moves slowly down the slope.
This problem is not very serious if the direction of unintended slow move of the vehicle is forward, and such creeping is often observed in automobiles which are equipped with an automatic gear shift. However, if the direction of this unintended move is rearward, then the problem is serious. For example, if the vehicle moves back slowly when the driver stops the vehicle on an up-hill slope with the shift lever set at the D range (a forward drive), then it is a dangerous condition.
SUMMARY OF THE INVENTION
The present invention is to solve the above mentioned problems. It is an object of the present invention to make sure of the operation of hydraulic lock in the standstill of a vehicle on a slope, the vehicle being equipped with a hydraulic continuously variable transmission.
It is another object of the present invention to prevent a vehicle which is stopped on a slope in hydraulic lock from moving downward slowly against the direction set with the shift lever (prevention of relapse phenomenon).
It is yet another object of the present invention to make sure the standstill of a vehicle in hydraulic lock and at the same time to improve the fuel efficiency of the engine of the vehicle.
It is still another object of the present invention to improve the fuel efficiency of the engine of a vehicle which is stationary in braking operation and to realize the vehicle's smooth start when the brake pedal is released.
In order to achieve these objects, the present invention embodies a hydraulic continuously variable transmission comprising a hydraulic variable pump, which is driven by the engine, and a hydraulic variable motor, which is driven by oil discharged from the hydraulic variable pump to drive the drive wheels. This transmission further comprises shift position detecting means, which detects a shift position that is set with the shift lever operated by the driver; vehicle stop detecting means, which detects whether the vehicle is in halt or not; pump capacity controlling means, which controls discharge capacity of the hydraulic variable pump; and motor capacity controlling means, which controls discharge capacity of the hydraulic variable motor. In this transmission, when the vehicle stop detecting means detects that the vehicle is in halt and the shift position detecting means detects that the shift position is in a drive position, the pump capacity controlling means controls the discharge capacity of the hydraulic variable pump to a first pump capacity in correspondence with the shift position, which is detected by the shift position detecting means, and the motor capacity controlling means controls the discharge capacity of the hydraulic variable motor to a predetermined motor capacity (>0).
With this construction, when the vehicle is stopped with the shift position set for a forward or rearward drive, the capacity of the hydraulic motor is set at a predetermined capacity (e.g., the maximum capacity), and the capacity of the hydraulic pump is set at the first pump capacity. As a result, for example, a little amount of hydraulic oil which corresponds with the set capacity is supplied to the motor that is idling while the vehicle is in halt. Therefore, this amount of oil, which is supplied to the motor, is set to such amount as to supplement the amount of oil leaking in the transmission when the vehicle is stopped on an allowable slope (without any braking operation) with the hydraulic motor receiving a driving torque. In this way, the hydraulic motor is locked, and the vehicle is retained stationary on the slope.
In this case, a problem is that the vehicle may move in the direction opposite to the direction set with the shift position. For example, the vehicle may move backward even though the shift position is set for a forward drive. However, the capacity of the pump is controlled to prevent such relapse movement.
Furthermore, if the vehicle stop detecting means detects that the vehicle is in halt, the shift position detecting means detects that the shift position is in a forward or rearward drive position, and the brake operation detecting means detects the operation of the brake; then it is preferable that the pump capacity controlling means control the discharge capacity of the hydraulic variable pump to a second pump capacity, which is smaller than the first pump capacity. When the brake of the vehicle is operated, there is no relapse movement, so the skew angle of the pump swash plate can be set to zero. However, the skew angle of the swash plate is set to create the second pump capacity, which is smaller than the first pump capacity, so that the vehicle can start smoothly from the halt when the brake is released. Thereby, the engine drive is decreased while the brake is being operated, thus improving the fuel efficiency as well as realizing the vehicles smooth switching to the start-up control.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed d
Iino Takashi
Morimoto Shigeru
Okuda Akihito
Honda Giken Kogyo Kabushiki Kaisha
Lopez F. Daniel
Lyon & Lyon LLP
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