Smooth gear change during inching

Abstract

A method of shifting a transmission in which a clutch, located in the torque flow, in a first gear and in a second gear is controlled in such manner that, in the first gear, the clutch slips and transmits a first torque and, in the second gear, the clutch slips and transmits a second torque. The second torque is chosen such that an output torque of the transmission remains the same when shifting from the first gear to the second gear.

Claims

1. A method of shifting a transmission, the method comprising: controlling a clutch, which is located in a torque flow, in a first gear and in a second gear in such a manner that: in the first gear, the clutch slips and transmits a first torque, in the second gear, the clutch slips and transmits a second torque; and when shifting from the first gear to the second gear, selecting the second torque as the torque to be transmitted by the transmission and varying an inching pressure of the clutch such that a drive torque, outputted by the transmission, remains constant during a shift from the first gear to the second gear.

2. A control unit for a transmission, wherein the control unit is designed to control a clutch which is located in a torque flow in a first gear and in a second gear, in such a manner that: in the first gear, the clutch slips and transmits a first torque, in the second gear, the clutch slips and transmits a second torque; and when shifting from the first gear to the second gear, selecting the second torque as the torque to be transmitted by the transmission and varying an inching pressure of the clutch such that a drive torque, outputted by the transmission, remains constant during a shift from the first gear to the second gear.

3. A computer program product, designed to enable a control unit to carry out a method including controlling a clutch, which is located in torque flow, in a first gear and in a second gear in such a manner that in the first gear, the clutch slips and transmits a first torque, and in the second gear, the clutch slips and transmits a second torque; and when shifting from the first gear to the second gear, selecting the second torque as the torque to be transmitted by the transmission and varying an inching pressure of the clutch such that a drive torque, outputted by the transmission, remains constant during a shift from the first gear to the second gear.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A method according to the prior art is illustrated in FIG. 1. FIG. 2 shows an example embodiment of the method according to the invention. In detail, the figures show:

(2) FIG. 1: Variations of the traction force and inching pressure as a function of a brake pedal path, according to the prior art; and

(3) FIG. 2: Corresponding variations according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) A brake pedal path 101 is plotted along the abscissa of the diagrams shown in FIGS. 1 and 2. A traction force 103 or 203, respectively, and an inching pressure 105 or 205, respectively, are plotted on the ordinates. The traction force 103 or 203 correspond to a drive torque applied to the driven wheels of a vehicle. As a result of the drive torque, a force acts upon the vehicle in the travel direction or opposite to that direction. The force is called the traction force.

(5) The inching pressure is a modulation pressure applied to a clutch located in a torque flow from the engine of the vehicle to the driven wheels. As a function of the inching pressure, the contact pressure of the clutch disks and consequently the slip and the torque transmitted by the clutch vary.

(6) If the brake pedal path 101 exceeds a shifting threshold 107, the transmission shifts to another gear. If the inching pressure 105 is constant as in FIG. 1, the shifting process results in a sudden increase of the traction force 103.

(7) The example embodiment of the method according to the invention shown in FIG. 2 provides that the inching pressure 205 is reduced as soon as the brake pedal path 101 exceeds the shifting threshold 107. The modulation of the inching pressure 205 takes place in such manner that the traction force 203 remains constant on either side of the shifting threshold 107.

INDEXES

(8) 101 Brake pedal path 103 Traction force 105 Inching pressure 107 Shifting threshold 203 Traction force 205 Inching pressure.