Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
I assume you are using PWM to switch a fixed voltage to the motor. The torque is mostly a function of the current through the motor. So what is the current when the voltage is fixed? Well, when the motor is held stopped then the current is just the voltage divided by the motor resistance. In that case the torque would be linearly proportional to the PWM duty cycle. But as soon as the motor starts turning it develops a back EMF that opposes the applied voltage, thus reducing the current. So the torque will be reduced the faster the motor turns.
But you asked about controlling the torque and the speed together. This is not possible unless you can control the load. Usually the load is what it is and is not under your control. But a given torque together with a given load will produce a given speed. Speed and torque cannot be controlled independently in that case.